procaris is a genus of shrimp in the family procarididae .

it contains the following species : procaris ascensionis chace & manning , 1972 procaris chacei hart & manning , 1986 procaris hawaiana holthuis , 1973 procaris mexicana von sternberg & schotte , 2004 procaris noelensis bruce & davie , 2006

procaris

phylum arthropoda subphylum crustacea class eumalacostraca order decapoda family procarididae procaris sp . kensley , 1988
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u . s . fish and wildlife service . 2003 . candidate assessment and listing priority assignment form - procaris hawaiana . u . s . fish and wildlife service , pacific islands office . 6 pp .
bruce , a . j . ; davie , p . j . f . ( 2006 ) . a new anchialine shrimp of the genus procaris from christmas island : the first occurrence of the procarididae in the indian ocean ( crustacea : decapoda : caridea ) . zootaxa . 1238 : 223 - 252 . [ details ] available for editors [ request ]
two of the known pools containing procaris hawaiana lie within a state natural area reserve . the rarity of this shrimp contributed to the current protection received by the maui anchialine pools ( holthuis 1973 ) . no conservation agreements between federal , state , or private landowners have been drafted or initiated and , aside from placement of some pools / pool systems within reserves , virtually no conservation activities have been conducted .
ty - jour ti - a new anchialine shrimp of the genus procaris ( crustacea : decapoda : procarididae ) from the yucatan peninsula t2 - proceedings of the biological society of washington . vl - 117 ur - urltoken pb - biological society of washington cy - washington , py - 2004 sp - 514 ep - 522 sn - 0006 - 324x au - sternberg , richard v au - schotte , marilyn er -
@ article { bhlpart49127 , title = { a new anchialine shrimp of the genus procaris ( crustacea : decapoda : procarididae ) from the yucatan peninsula } , journal = { proceedings of the biological society of washington . } , volume = { 117 } , copyright = { in copyright . digitized with the permission of the rights holder . } , url = urltoken publisher = { washington , biological society of washington } , author = { sternberg , richard v and schotte , marilyn } , year = { 2004 } , pages = { 514 - - 522 } , }
main threat = alien species . greatest potential threat is cited as the introduction of non - native fish into the pools ( u . s . fish and wildlife service 1998 ; 2003 ) . anchialine pools have been used to discard or hold bait - fish and / or aquarium fish . these fish either directly consume the native shrimp or , as with introduced tilapia ( oreochromis mossambica ) , out - compete the native herbivorous species of shrimp which typically serve as the prey - base for the rarer , predatory species of shrimp . habitat modification is also a threat ; up to 90 % of the anchialine pools on the island of hawaii have been either destroyed or altered . on the island of hawaii , dr . r . brock ( pers . comm . , 1998 ) estimates that up to 90 percent of the anchialine pools have been destroyed or altered by human activities . although the two known maui pools , which are contain procaris hawaiana , occur within a protected state reserve , habitat modifications by early hawaiians and later inhabitants have occurred in the area .
chace , f . a . jr . & r . b . manning , 1972 . two new caridean shrimps , one representing a new family , from marine pools on ascension island ( crustacea : decapoda : natantia ) . — smithsonian contributions to zoology 131 : 1 - 18 . [ details ]
de grave , s . & c . h . j . m . fransen . ( 2011 ) . carideorum catalogus : the recent species of the dendrobranchiate , stenopodidean , procarididean and caridean shrimps ( crustacea : decapoda ) . zool . med . leiden . 85 ( 9 ) : 30 . ix . 2011 : 195 - 589 figs 1 - 59 . ( look up in imis ) [ details ] available for editors [ request ]
bouchet , p . ; fontaine , b . ( 2009 ) . list of new marine species described between 2002 - 2006 . census of marine life . [ details ]
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phyllobranchiate gills ; maxillipeds and pereiopods with strong exopods ; none of pereiopods chelate or subchelate ; rostrum small and unarmed ( kensley , 1988 ) .
are quite similar , showing few differentiating characters ( hart & manning , 1986 ) .
abele and felgenhauer ( 1985 ) have studied the ecology of the ascension species . they report that smaller individuals spend most of their time in crevices , while larger individuals are observed swimming in open water . examination of gut contents reveals that they feed on both plant matter and crustaceans including amphipods and atyid shrimp .
( felgenhauer et al . , 1988 ) . although more than 1 , 000 specimens of
were observed in the field , no ovigerous females were seen . a single female maintained in the laboratory bore approximately 60 bright orange eggs on the endopods of pleopods . the large size of these eggs ( 0 . 83 - 0 . 93 mm ) suggests the existence of a zoeal larval stage ( felgenhauer et al . , 1988 ) .
hart and manning ( 1986 : 416 ) note that the similarities between species and their highly anomalous distribution in marine caves indicate an extremely slow rate of evolution . they suggest that ,
, or its predecessors , may , at one time , have been widely distributed throughout the oceans , surviving today only in cryptic habitats removed from some of the environmental pressures necessitating change .
felgenhauer , b . e . , l . g . abele and w . kim . 1988 . reproductive morphology of the anchialine shrimp
hart , c . w . and r . b . manning . 1986 . two new shrimps ( procaridae and agostocarididae , new family ) from marine caves of the western north atlantic .
kensley , b . 1988 . new species and records of cave shrimps from the yucatan peninsula ( decapoda : agostocarididae and hippolytidae ) .
schram , f . r . 1986 . crustacea . oxford university press , oxford , xii + 606 pp .
this shrimp was discovered in february 1972 by j . a . maciolek in anchialine lava pools at cape kinau , maui and also in anchialine pools at lua o palehemo , south point on the big island of hawaii . only three populations of this rare shrimp are known .
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u . s . fish and wildlife service ( usfws ) . 1989a . endangered and threatened wildlife and plants ; animal notice of review . federal register , department of the interior 54 ( 4 ) : 554 - 579 .
apparently endemic to the hawaiian islands where it has only been recorded from three anchialine pools .
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known from the hawaiian islands of hawaii ( 1 site ) and maui ( 2 sites ) ( holthuis , 1973 ; maciolek 1983 ; u . s . fish and wildlife service 1998 ; 2003 ) . current range considered to be relictual of an early global distribution .
known from two sites on maui and one site on hawaii ( usfws , 1998 ) .
known from one site on hawaii and two sites on maui ( holthuis , 1973 ; u . s . fish and wildlife service 1998 ; 2003 ) .
it was estimated to occur in the thousands at the hawaii site ( kensely and williams 1986 ) . due to their rarity within these locations since the previous estimate , population estimates have not been attempted .
it was estimated to occur in the thousands at the hawaii site ( kensely and williams 1986 ) .
in hawaii , there are estimated to be over 650 anchialine pools , with an estimated 90 % of these occurring on hawaii . approximately 90 % of the pools on that island have been destroyed or otherwise impacted by development or other human uses ( richard brock , university of hawaii , personal communication , 1998 in usfws , 1998 ) .
in the state of hawaii , there are estimated to be over 650 anchialine pools , with an estimated 90 % of these occurring on the island of hawaii . unfortunately , approximately 90 percent of the pools on that island have been destroyed or otherwise impacted by development or other human uses ( usfws , 2003 ) .
( 250 - 1000 square km ( about 100 - 400 square miles ) ) known from the hawaiian islands of hawaii ( 1 site ) and maui ( 2 sites ) ( holthuis , 1973 ; maciolek 1983 ; u . s . fish and wildlife service 1998 ; 2003 ) . current range considered to be relictual of an early global distribution .
has pink to light - red pigmentation that is darkest along the midline with the dorsal thorax being white to yellow . black pigments are associated with the eyss . conspicuous chelapeds ( claws ) are lacking . locomotion is accomplished by swimming with the swimmerets ( pareopods and uropods ) and occurs just above the substate to mid - water ( usfws , 1998 ; 2003 ) .
found in anchialine pools with salinities generally ranging from 19 - 25 ppt . anchialine pools are tidally influenced saline pools that occur along the coast but are not openly connected to the ocean . this includes water in natural depressions , fissures , quarries , and craters . the site on hawaii is an anchialine pool that is connected to deeper waters leading to a submerged lava tube ( kensley and williams 1986 ) .
use the generic guidelines for the application of occurrence ranks ( 2008 ) . the key for ranking species occurrences using the generic approach provides a step - wise process for implementing this method .
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holthuis , l . b . 1973 . caridean shrimps found in land - locked saltwater pools at four indo - west pacific localities ( sinai peninsula , funafuti atoll , maui and hawaii islands ) , with the description of one new genus and four new species . zoollogische verhandelingen 128 : 3 - 55 .
kensley , b . and d . williams . 1986 . new shrimps ( families procarididae and atyidae ) from a submerged lave tube on hawaii . journal of crustacean biology 6 ( 3 ) : 417 - 437 .
maciolek , j . a . 1983 . distribution and biology of indo - pacific insular hypogeal shrimps . bulletin of marine science 33 : 606 - 618 .
maciolek , j . a . 1986 . environmental features and biota of anchialine pools on cape kinau , maui , hawaii . stygologia 2 ( 1 / 2 ) : 119 - 129 .
u . s . fish and wildlife service ( usfws ) . 1998 . category and listing priority forms .
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this procarid shrimp has a thin , fragile integument ( hard outer covering of the body ) . the carapace and short , triangular rostrum are unarmed , and the eyestalks split into two blunt lobes . all five pairs of walking limbs ( pereiopods ) are similar , each with large , bristle - like structures ( 2 ) .
recorded only from green bay cave in hamilton parish , bermuda ( 2 ) .
classified as critically endangered ( cr ) on the iucn red list 2006 ( 1 ) .
this information is awaiting authentication by a species expert , and will be updated as soon as possible . if you are able to help please contact : arkive @ urltoken
anchialine coastal bodies of standing waters that have no surface connections to the ocean but display both tidal fluctuations and salinity ranges characteristic of fresh and brackish waters , indicating the presence of subsurface connections to the watertable and ocean . carapace the hard shell covering the upper surface of part of the body of a crustacean . rostrum central , forward - projecting and occasionally long spine between the eyes of crustaceans .
dr . thomas m . iliffe department of marine biology texas a & m ; university at galveston 5007 ave . u galveston tx 77551 united states of america iliffe @ urltoken http : / / www . urltoken
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mclaughlin et al . 2005 . common and scientific names of aquatic invertebrates from the united states and canada : crustaceans . american fisheries society special publication 31
disclaimer : itis taxonomy is based on the latest scientific consensus available , and is provided as a general reference source for interested parties . however , it is not a legal authority for statutory or regulatory purposes . while every effort has been made to provide the most reliable and up - to - date information available , ultimate legal requirements with respect to species are contained in provisions of treaties to which the united states is a party , wildlife statutes , regulations , and any applicable notices that have been published in the federal register . for further information on u . s . legal requirements with respect to protected taxa , please contact the u . s . fish and wildlife service .


the cumberland snubnose darter ( etheostoma atripinne ) is a small , perciform fish found it the middle cumberland river drainage in tennessee , kentucky , virginia , north carolina , georgia , and alabama .

it is absent in reaches above the big south fork , rare in north carolina , and absent in western tributaries of the tennessee river .

while research on the ecology of e. atripinne is not extensive , what is known is they are usually found in small to medium freshwater streams in gravel riffle areas where their eggs can attach to the substrate and be left unguarded .

e. atripinne can be found within a wide range of depths in its environment , leading its being classified as benthopelagic .

while its global status is secure , the american fisheries society labels it with a status of “ special concern ” .

cumberland snubnose darter

etheostoma atripinne ( d . s . jordan , 1877 ) ( cumberland snubnose darter )
the snubnose darter ( etheostoma simoterum ) is a species of darter endemic to the southeastern united states .
cumberland snubnose darters spawning in small creek in wilson county tennessee . april 24 , 2014 . canon powershot 710is version .
etheostoma susanae ( d . s . jordan & swain , 1883 ) ( cumberland darter )
, and the other greenside darter species were nested in a clade containing most of the snubnose darter species . in addition ,
locus was the most congruent with regard to the subgeneric taxonomy of greenside and snubnose darters . greenside darters , snubnose darters , and
were nested as successive sister lineages at the base of the snubnose–greenside darter clade . the sister lineage of
the snubnose darter has two recognized subspecies , including the cumberland snubnose darter . e . s . atripinne , and the tennessee snubnose darter , e . s . simoterum . intergradation between the two subspecies occurs in the lower tennessee river unit . the mean length of snubnose darters is 45 millimetres ( 1 . 8 in ) , the reported average clutch size is 152 , and the maximum age is less than two years . the snubnose darter inhabits riffles and rock - bottomed pools in streams with low turbidity . as of 2000 , the snubnose darter was listed as currently stable , meaning it is widespread and not in need of any immediate conservation action .
etnier , d . a . 1980 . etheostoma acuticeps bailey , sharphead darter ; e . atripinne ( jordan ) , cumberland snubnose darter ; e . duryi henshall , blackside snubnose darter ; e . luteovinctum gilbert and swain , redband darter ; e . maculatum kirtland , spotted darter ; e . rufilineatum ( cope ) , redline darter ; e . simoterum ( cope ) , tennessee snubnose darter ; and percina tanasi etnier , snail darter ; pp . 622 , 625 , 642 , 663 , 664 , 687 , 693 , 743 , in : d . s . lee et al . , atlas of north american freshwater fishes . nc state mus . nat . hist . , raleigh , 864 p .
the snubnose darter is native to the tennessee and cumberland river drainages of tennessee , virginia , kentucky , north carolina , georgia and alabama . warren et al . described the distribution of the freshwater fish native to the southern united states by drainage basin . the historical range of the tennessee snubnose darter ( e . s . simoterum ) includes the upper and lower tennessee river drainage units , and it has been introduced into both the licking big sandy creek river and the kanawha - new - guyandotte - little kanawha river . the historical range of the cumberland snubnose darter ( e . s . atripinne ) includes the lower tennessee river and cumberland river drainages . intergradation between the two subspecies occurs in the lower tennessee river unit .
the snubnose darter is listed as
currently stable
, which is defined as
a species or subspecies whose distribution is widespread and stable or a species or subspecies that may have declined in portions of its range but is not in need of immediate conservation management actions
. based on certain lifecycle parameters , the american fisheries society lists the snubnose darter as highly resilient with low vulnerability .
north america : found only in cumberland and tennessee river drainages in virginia , north carolina , kentucky , tennessee , georgia and alabama , usa .
heins , d . c . 2001 . variation in clutch size and ovum size of the snubnose darter , etheostoma simoterum ( cope ) , from two populations in tennessee . american midland naturalist . 145 : 74 - 79 .
large darters are susceptible to internal parasitism by flukes and nematodes . external parasites such as black spot disease caused by metacercariae flukes and piscicolid leeches also affect snubnose darters .
blanton , r . e . , and r . e . jenkins . 2008 . three new darter species of the etheostoma percnurum species complex ( percidae , subgenus catonotus ) from the tennessee and cumberland river drainages . zootaxa . 1963 : 1 - 24 .
etheostoma artesiae ( o . p . hay , 1881 ) ( redspot darter )
etheostoma asprigene ( s . a . forbes , 1878 ) ( mud darter )
etheostoma bellator suttkus & r . m . bailey , 1993 ( warrior darter )
etheostoma boschungi wall & j . d . williams , 1974 ( slackwater darter )
etheostoma chlorosoma ( o . p . hay , 1881 ) ( bluntnose darter )
etheostoma chuckwachatte mayden & r . m . wood , 1993 ( lipstick darter )
etheostoma collettei birdsong & l . w . knapp , 1969 ( creole darter )
etheostoma colorosum suttkus & r . m . bailey , 1993 ( coastal darter )
etheostoma flavum etnier & r . m . bailey , 1989 ( saffron darter )
etheostoma lachneri suttkus & r . m . bailey , 1994 ( tombigbee darter )
etheostoma marmorpinnum blanton & r . e . jenkins , 2008 ( marbled darter )
etheostoma phytophilum bart & m . s . taylor , 1999 ( rush darter )
etheostoma proeliare ( o . p . hay , 1881 ) ( cypress darter )
etheostoma ramseyi suttkus & r . m . bailey , 1994 ( alabama darter )
etheostoma stigmaeum ( d . s . jordan , 1877 ) ( speckled darter )
etheostoma swaini ( d . s . jordan , 1884 ) ( gulf darter )
etheostoma virgatum ( d . s . jordan , 1880 ) ( striped darter )
etheostoma wapiti etnier & j . d . williams , 1989 ( boulder darter )
( watercress darter ) to be an endangered species . fed regist 35 : 16047
harrington r . c . , near t . j . forthcoming . phylogenetic and coalescent strategies of species delimitation in snubnose darters ( percidae : etheostoma ) . syst . biol .
etnier , d . a . , and r . m . bailey . 1989 . etheostoma ( ulocentra ) flavum , a new darter from the tennessee and cumberland river drainages . occ . pap . mus . zool . univ . mich . 717 : 1 - 24 .
although the term
darter
is shared by several other genera . many can produce
etheostoma erythrozonum switzer & r . m . wood , 2009 ( meramec saddled darter )
range includes tributaries of the cumberland river system in the nashville basin , from near the mouth of the roaring river to mansker creek ( northeastern nashville ) , tennessee ( page and burr 2011 ) .
snubnose darters inhabit flowing bedrock or gravel - bottomed pools with moderate current in small to medium streams . they have been observed spawning in streams with water temperature ranging from 11 to 18 °c . etheostoma simoterum prefers a habitat with no vegetation or light algae . snubnose darters are rarely found in water with high turbidity or where the substrate has been silted , and human activities such as dam building or destruction of riparian buffers may lead to increased siltation , thereby threatening darter populations .
etheostoma collis ( c . l . hubbs & cannon , 1935 ) ( carolina darter )
etheostoma edwini ( c . l . hubbs & cannon , 1935 ) ( brown darter )
etheostoma inscriptum ( d . s . jordan & brayton , 1878 ) ( turquoise darter )
etheostoma lepidum ( s . f . baird & girard , 1853 ) ( greenthroat darter )
etheostoma osburni ( c . l . hubbs & trautman , 1932 ) ( candy darter )
etheostoma perlongum ( c . l . hubbs & raney , 1946 ) ( waccamaw darter )
etheostoma sagitta ( d . s . jordan & swain , 1883 ) ( arrow darter )
etheostoma saludae ( c . l . hubbs & cannon , 1935 ) ( saluda darter )
etheostoma sellare ( radcliffe & w . w . welsh , 1913 ) ( maryland darter )
etheostoma serrifer ( c . l . hubbs & cannon , 1935 ) ( sawcheek darter )
etheostoma thalassinum ( d . s . jordan & brayton , 1878 ) ( seagreen darter )
etheostoma zonifer ( c . l . hubbs & cannon , 1935 ) ( backwater darter )
, a new darter from a limestone spring in alabama . tulane stud zool 12 : 101–108
comiskey , c . e . and d . a . etnier . 1972 . fishes of the big south fork of the cumberland river . j . tenn . acad . sci . 47 : 140 - 145 .
powers , s . l . , r . l . mayden , and d . a . etnier . 2004 . conservation genetics of the ashy darter , etheostoma cinereum ( percidae : subgenus allohistium ) , in the cumberland and tennessee rivers of the southeastern united states . copeia . 3 : 632 - 637 .
near , t . j . , e . d . france , r . c . harrington , b . p . keck ( 2016 ) . systematics and taxonomy of the snubnose darter , etheostoma simoterum ( cope ) . bulletin of the peabody museum of natural history 57 ( 2 ) : 127 - 145 .
( percidae ) , and their potential utility for other darter species . mol ecol notes 6 : 230–232
harrington , r . c . , t . j . near ( 2012 ) . phylogenetic and coalescent strategies of species delimitation in snubnose darters ( percidae : etheostoma ) . systematic biology . 61 ( 1 ) : 63 - 69 .
eisenhour , d . j . 1995 . systematics of etheostoma camurum and e . chlorobranchium ( osteichthyes , percidae ) in the tennessee and cumberland river drainages with analysis of hybridization in the nolichucky river system . copeia . 2 : 368 - 379 .
keck , b . p . and t . j . near . 2010 . a young clade repeating an old pattern : diversity in nothonotus darters ( teleostei : percidae ) endemic to the cumberland river . molecular ecology . 19 : 5030 - 5042 .
the combined mtdna and nuclear gene phylogeny was similar to the mtdna cytb gene , particularly with respect to the paraphyly of catonotus and the snubnose darters ( fig . 3a ) . removal of mtdna sequences with a heterospecific origin from the alignment resulted in the monophyly of both oligocephalus and psychromaster ( fig . 3b , c ) . etheostoma baileyi and e . histrio formed a significantly supported clade that was sister to a clade containing e . cinereum , all other greenside darters , and all other snubnose darter species ( fig . 3c ) . etheostoma zonale and e . lynceum were resolved with significant bayesian posterior support as the sister lineage of a clade that contained all greenside darter species ( sans e . histrio ) .
etheostoma fonticola ( d . s . jordan & c . h . gilbert , 1886 ) ( fountain darter )
etheostoma radiosum ( c . l . hubbs & j . d . black , 1941 ) ( orangebelly darter )
howell wm , black a ( 1976 ) status of the watercress darter . southeast fishes counc proc 1 : 1–4
e . baileyi is restricted to the cumberland plateau , including only the upper cumberland river drainages in eastern kentucky and northeastern tennessee . rivers where emerald darters can be found include the red river , jacks creek , indian creek in kentucky , and clear creek , elk creek , poor creek , and other small water systems . though populations have fluctuated through the years , the emerald darter’s geographic range has stayed the same , and in some areas they can even be found in abundance . [ 4 ] populations may have experienced declines in the past due to strip - mining and siltation in the gravel substrates in which it spawns . [ 5 ]
etheostoma euzonum ( c . l . hubbs & j . d . black , 1940 ) ( arkansas saddled darter )
etheostoma tetrazonum ( c . l . hubbs & j . d . black , 1940 ) ( missouri saddled darter )
porter , b . a . , t . m . cavender , and p . a . fuerst . 2002a . molecular phylogeny of the snubnose darters , subgenus ulocentra ( genus etheostoma , family percidae ) . molecular phylogenetics and evolution . 22 : 364 - 374 .
a new darter from the southern bend of the tennessee river system in alabama and tennessee . proc . biol . soc . wash
etheostoma lawrencei , a new species of darter in the e . spectabile species complex ( percidae : subgenus oligocephalus ) , from kentucky and tennessee
etheostoma ditrema , a new darter of the subgenus oligocephalus ( percidae ) from springs of the alabama river basin in alabama and georgia . tulane stud
cumberland and tennessee drainages in virginia , north carolina , kentucky , tennessee , georgia , and alabama ( page and burr 1991 ) . however , menhinick ( 1991 ) did not list in north carolina . the inclusion of north carolina is probably based on cope ( 1870 ) who listed the species in the state without comment .
the crown clade etheostoma dates to the earliest oligocene , whereas the crown ages of other major darter clades ( percina , carnipellucida , and nothonotus ) originated in the late oligocene and miocene ( table 3 ) . these age estimates demonstrate that the majority of reconstructed speciation events in the darter phylogeny date to the miocene and pliocene , indicating that most extant darter species and ecological communities of darter species have an origin within the last 15 myr . the dense species sampling in the darter chronograms will provide an informative basis for the investigation of long - standing hypotheses regarding the role of paleoclimate and paleogeography on the evolution and diversification of the species - rich north american freshwater fish fauna ( e . g . , wiley and mayden 1985 ; mayden 1988 ; near and keck 2005 ) .
the posterior molecular evolutionary rates estimated for each of the three genes using the centrarchid - only alignments were used as priors for the molecular evolutionary rates in the analyses of the darter and non - darter percid alignments . the mean and standard deviation of the molecular evolutionary rate for each of the three genes were determined from the posterior distribution resulting from the fossil - calibrated ucln analyses of the centrarchid gene alignments . the mean and standard deviation of the centrarchid molecular evolutionary rates were subsequently used to construct a normal prior on the molecular evolutionary rate in the ucln analyses of divergence times using the darter and non - darter percid alignments .
simons , a . m . 1991 . phylogenetic relationships of the crystal darter , crystallaria asprella ( teleostei : percidae ) . copeia 1991 : 927 - 936 .
starnes , w . c . , and d . a . etnier . 1986 . drainage evolution and fish biogeography of the tennessee and cumberland river drainages , chapter 10 , p . 325 - 361 , in : zoogeography of north american freshwater fishes , c . h . hocutt and e . o . wiley , eds . wiley interscience , new york , 866 p .
etnier , d . a . , and w . c . starnes . 1978 . wildlife profile , snail darter ( percina tanasi ) . tennessee wildlife . 1 : 24 - 25 .
clayton , j . 1984 . population differences and life history of emerald darter , etheostoma baileyi ( pisces , percidae ) . university of kentucky , lexington : m . s . thesis .
snubnose darters reach sexual maturity at one year of age and only survive for one breeding season , which occurs in april to early may . the darter breeds in bedrock pools and crevices with low siltation . the testes of breeding males gradually begin to increase in size in january and reach their peak in april . males also begin to develop bright breeding colors in january , and by april , all males are deep green to blue - green with red dorsal fins and red spots along their bodies . breeding females do not change color , but they may be slightly brighter in tone . mature eggs are transparent , contain oil droplets , and are an average of 1 . 2 mm in diameter . one study showed the number of mature eggs per female ranges from 110 to 240 by april . males court females by displaying erect fins and bright breeding colors . a female responds to this display by leading the male to an appropriate site for egg deposition , such as a large stone or , more rarely , a gravel bed . the pair vibrates together , and after one or two eggs are released and fertilized by the male , the pair may move to another acceptable site to repeat the spawning act . however , snubnose darters are often promiscuous and may move on to find other mates , instead . no parental care , such as egg guarding , occurs after spawning . snubnose darters survive to a maximum age of 18 months .
divergence times in darters were estimated using two calibration strategies that were derived from the centrarchid fossil calibrations . the first method used gene alignments that included all sampled darter species , 2 non - darter percid species , and 33 of the sampled species of centrarchidae . the centrarchid fossil calibrations were used to estimate divergence times in relaxed - clock analyses of these large data matrices . the second approach used rates of molecular evolution estimated from the relaxed - clock analyses of centrarchidae for each of the three genes . the bayesian posterior distribution of estimated nucleotide substitution rates from the centrarchid relaxed - clock analyses was then used as a prior in relaxed - clock analyses of gene alignments that contained only the sampled darter and non - darter percid species ( e . g . , saarma et al . 2007 ) .
kozal , l . c . , j . w . simmons , j . m . mollish , d . j . macguigan , e benavides , b . p . keck , t . j . near ( 2017 ) . phylogenetic and morphological diversity of the etheostoma zonistium species complex with the description of a new species endemic to the cumberland plateau of alabama . bulletin of the peabody museum of natural history 58 ( 2 ) : 263 - 286 .
blanton , r . e . , and g . a . schuster . 2008 . taxonomic status of etheostoma brevispinum , the carolina fantail darter ( percidae : catonotus ) . copeia . 4 : 844 - 857 .
fluker bl , kuhajda br , duncan rs , salter el , schulman m ( 2009 ) impacts of a small dam removal on the endangered watercress darter . proc annu conf southeast assoc fish wildl agencies 63 : 188–195
baker , j . a . , and d . c . heins . 1994 . effects of drying temperature on weight estimates for oocytes and eggs in the darter etheostoma lynceum . copeia . 3 : 821 - 823 .
howell , w . m . , and h . t . boschung . 1966 . a natural hybrid darter etheostoma whipplii artesiae x etheostoma stigmaeum ( pisces : percidae ) . american midland naturalist . 76 : 510 - 514 .
page , l . m . , and t . j . near . 2007 . a new darter from the upper tennessee river drainage related to percina macrocephala ( percidae : etheostomatinae ) . copeia . 3 : 605 - 613 .
heins , d . c . , and j . a . baker . 1993 . clutch production in the darter etheostoma lynceum and its implications for life - history study . journal of fish biology . 42 : 819 - 829 .
carlson , r . l . , p . c . wainwright . 2010 . the ecological morphology of darter fishes ( percidae : etheostomatinae ) . the linnean society of london , biological journal of the linnean society . 100 : 30–45 .
grandmaison , d , j . mayasich , and d . etnier . 2004 . eastern sand darter status assessment . nrri tech . rept . nrri / tr - 2003 / 40 , us fish & wildlife srvice , 39 p + appendices .
grandmaison , d , j . mayasich , and d . etnier . 2003 . crystal darter status assessment report . nrri tech . rept . nrri / tr - 2003 / 19 , us fish & wildlife srvice , 37 p + appendices .
layman , s . r . , and r . l . mayden . 2009 . a new species of the darter subgenus doration ( percidae : etheostoma ) from the caney fork river system , tennessee . copeia . 1 : 157 - 170 .
mayasich , j . m . , d . grandmaison , and d . etnier . 2004 . spotted darter status assessment . nrri tech . rept . nrri / tr - 2003 / 02 , us fish & wildlife service , 25 p + appendices .
the emerald darter is not currently listed as a state or federal threatened species , though they are experiencing population declines in tennessee . though emerald darters have experienced population fragmentation , their range has not undergone declines . threats to populations include limited range , as well as strip - mining , which results in heavy siltation of the gravel substrates on which they depend for reproduction . [ 8 ] damming of tennessee’s main waterways has fragmented the emerald darter’s habitat . kentucky’s populations are not considered threatened . [ 9 ]
the phylogenetic classification presented in figure 4 and the appendix communicates our best understanding of darter relationships and includes major alterations to the previous non - phylogenetic taxonomies for the clade . for example , there were 19 or 21 polytypic subgenera present in the most recently proposed darter classifications ( bailey and etnier 1988 ; page 2000 ) . our phylogenetic analyses indicate that 10 of these subgenera are not monophyletic ( table 1 ) . substantial nonmonophyly of darter subgenera was also intimated in the previously published morphological and molecular phylogenetic analyses ( e . g . , near 2002 ; mayden et al . 2006 ; ayache and near 2009 ) , but the extent of the failure of these taxonomies to reflect monophyletic lineages was not apparent until comparison with the comprehensive phylogenetic analyses presented in this investigation .
suttkus , r . d . , h . d . bart , and d . a . etnier . 2009 ( accepted ) . etheostoma thompsoni , a new darter , subgenus oligocephalus , from southeastern texas and southwestern louisiana . tulane stud . zool . bot .
layman s . r . , r . l . mayden ( 2012 ) . morphological diversity and phylogenetics of the darter subgenus doration ( percidae : etheostoma ) , with descriptions of five new species . bull . alabma mus . nat . hist . 30 : 1 - 83 .
shepard , t . e . , and b . m . burr . 1984 . systematics , status , and life - history aspects of the ashy darter , etheostoma cinereum ( pisces , percidae ) . proceedings of the biological society of washington . 97 : 693 - 715 .
keck , b . p . , t . j . near ( 2013 ) . a new species of nothonotus darter ( teleostei : percidae ) from the caney fork in tennessee , usa . bulletin of the peabody museum of natural history 54 ( 1 ) : 3 - 21 .
near , t . j . , b . p . keck ( 2013 ) . free from motochondrial dna : nuclear genes and the inference of species trees among closely related darter lineages ( teleostei : percidae : etheostomatinae ) . molecular phylogenetics and evolution 66 ( 3 ) : 868 - 876 .
suttkus , r . d . , h . l . , bart jr . and d . a . etnier , 2012 . a new darter of the subgenus oligocephalus , genus etheostoma , from southeastern texas and southwestern louisiana . tulane stud . zool . bot . 32 : 6 - 30 .
piller , k . r . , h . l . bart , and d . l . hurley . 2008 . phylogeography of the greenside darter complex , etheostoma blennioides ( teleostomi : percidae ) : a wide - ranging polytypic taxon . molecular phylogenetics and evolution . 46 : 974 - 985 .
bauer , b . h . , d . a . etnier , and n . m . burkhead . 1995 . etheostoma ( ulocentra ) scotti ( osteichthyes : percidae ) , a new darter from the etowah river system in georgia . bulletin alabama museum of natural history . 17 : 1 - 16 .
porter , b . a . , a . c . fiumera , and j . c . avise . 2002b . egg mimicry and allopaternal care : two mate - attracting tactics by which nesting striped darter ( etheostoma virgatum ) males enhance reproductive success . behavioral ecology and sociobiology . 51 : 350 - 359 .
etnier , d . a . , and j . d . williams . 1989 . etheostoma ( nothonotus ) wapiti ( osteichthyes , percidae ) , a new darter from the southern bend of the tennessee river system in alabama and tennessee . proceedings of the biological society of washington . 102 : 987 - 1000 .
an excellent group in which to investigate the history of mtdna introgression and divergence time estimation in species - rich lineages is the darter clade , which contains approximately 250 species endemic to eastern north america that comprises more than 20 % of the entire hyperdiverse north american freshwater fish fauna ( table 1 ; lundberg et al . 2000 ) . darters are classified as etheostomatinae , which is a subclade of percidae . in addition to etheostomatinae , two other major freshwater clades with holarctic distributions , percinae and luciopercinae , comprise percidae . however , neither percinae nor luciopercinae contains more than 10 species ( collette and banarescu 1977 ; song et al . 1998 ) . darter species differ substantially from those in the two other lineages of percidae by having a smaller body size , males of many darter species develop elaborate nuptial colors , and the majority of species lack a functional swim bladder ( page 1983 ; page and swofford 1984 ; etnier and starnes 1993 ) .
a composite phylogeny based primarily on the analyses of the concatenated data sets was used to phylogenetically define 45 clade names for darters ( fig . 4 and appendix ) . the proposed phylogenetic classification in figure 4 represents the most current knowledge of the evolutionary relationships among darter species while also preserving previously used names when appropriate . most of the names in the phylogenetic classification are converted clade names from ranked genus and subgenus names , and four of these converted clade names— austroperca , astatichthys , pileoma , and richiella —were treated as invalid synonyms in the most recent darter classifications . a total of 16 new clade names are proposed in the phylogenetic definitions ( fig . 4 and appendix ) . some of the well - supported nodes in the darter phylogeny are not named primarily as a result of incongruence between the mtdna and nuclear gene trees ( e . g . , relationships within hadropterus ) or our desire to avoid the possibility of having to redefine clade names subsequent to future phylogenetic analyses .
, approximately 10 % of the specimens included in this study were obtained from several other natural history museums including university of alabama ichthyology collection ( uaic ) , the north carolina state museum ( ncsm ) , tulane university ( tu ) , and the university of kansas natural history museum ( ku ) . the non - darter percid species
the phylogenetic resolution given by the three genes sampled in this study provided an excellent opportunity to revise the classification of darters in a phylogenetic context . the classification presented in figure 4 and the appendix represents the first attempt to provide a comprehensive taxonomy for darters that is based on the results of explicit phylogenetic analysis of comparative data . all previous delimitations of ranked taxonomic groups were based on morphological diagnoses that did not attempt to assess monophyly of the proposed groups ( e . g . , bailey and gosline 1955 ; page 1974 ; 1981 ) . the rich history of darter taxonomy is reflected in the scores of group names that have been introduced over the past two centuries ( collette and knapp 1966 ; collette 1967 ) . previous attempts to codify darter taxonomy have delimited groups of darter species using the available group names as ranked genera and subgenera ( e . g . , jordan and evermann 1896 , p . 1015–1105 ; bailey et al . 1954 ; page 1974 , page 1981 , page 2000 ; bailey and etnier 1988 ) .
a previous phylogenetic analysis of darters using cytb gene sequences was reluctant to recognize the darter clade nothonotus as distinct from etheostoma ( mayden et al . 2006 ) , as was proposed in a previous study ( near and keck 2005 ) , on the grounds that all darter lineages exclusive of percina could form a clade named etheostoma . our phylogenetic analyses resolve percina as the sister lineage of all other darters but consistently result in trees that place nothonotus outside of a monophyletic etheostoma and distinct from carnipellucida ( figs . 2 and 3 ) . although our phylogenies are consistent with the clade - naming scenario presented in mayden et al . ( 2006 ) , we believe that the scenario has limited utility because it fails to communicate the wealth of knowledge now available about the phylogenetic relationships among carnipellucida , nothonotus , and etheostoma ( fig . 4 ) .
phylogenetic classification of darters communicated using a composite phylogeny of darters based on the phylogenies inferred from mitochondrial and nuclear gene dna sequences . the 45 darter clade names that are defined phylogenetically ( see appendix ) are listed and marked with an unfilled circle . filled circles mark clades that were well supported in the phylogenetic analyses but not named in this study . clade names commonly associated with the rank of genus are marked with an asterisk . 4
phylogenies inferred using bayesian inference from each gene resulted in a large number of significantly supported interspecific nodes , but not all genes contributed equally to our understanding of the darter phylogeny ( fig . 2 ) . despite resolving a large fraction of the nodes in the phylogeny , the s 7 intron 1 gene tree contained relationships that were not congruent with those in the gene trees estimated from cytb and rag1 . the incongruence of the s 7 gene tree is illustrated by the incongruence among phylogenetic relationships of etheostoma and nothonotus that subtend some of the oldest nodes in the darter phylogeny ( fig . 2 ) . relative to rag1 , the s 7 gene tree had fewer nodes with significant posterior support in the 10 - to 20ma age and the 20ma root node age intervals ( fig . 5 ) . the proportion of 10–20 ma age nodes supported with significant posteriors in the s 7 gene tree was similar to that observed in the mitochondrial cytb gene tree . in contrast , 10 % more nodes in this age interval were supported in the rag1 gene tree . in addition , we had difficulty aligning the darter s 7 intron dna sequences with those of non - percid teleosts ( e . g . , centrarchidae ) , limiting our ability to include the external age information necessary to time - calibrate the s 7 gene tree .
using external calibrations to estimate divergence times for clades lacking a fossil record can be complicated by the presence of substantial differences in molecular evolutionary rates ; however , our analyses did not appear to be confounded by appreciable rate heterogeneity between darters and centrarchidae . the posterior mean rate estimate for cytb and rag1 did not change substantially between beast runs that contained only centrarchid species ( table 2 ) and the runs that included all sampled centrarchid and darter species .
gene alignments , two sets of beast ucln analyses were run , each with a different calibration strategy . analyses for both genes under both calibration strategies produced similar posterior age estimates for all the major darter clades ( table 3 ) . the mean posterior age estimates for the mrca of all darters , the etheostomatinae , ranged between 30 . 7 and 38 . 4 ma ; however , the 95 % hpd for each of the five estimates exhibited broad overlap (
ulocentra jordan ( p . 223 1878 ) [ t . j . near & b . p . keck ] , converted clade name . comments on name . —applied as a monotypic genus containing e . atripinne ( jordan and brayton 1878 , p . 223 ) and subsequently expanded to include all “snubnose darters” that are classified here as ulocentra and adonia ( bailey and gosline 1955 ; bailey and etnier 1988 ) . definition ( node - based ) . —the least inclusive clade containing e . atripinne ( jordan ) and etheostoma barrenense burr & page . reference phylogeny . — figure 3c . composition . —includes the species designated in the definition and etheostoma planasaxatile powers & mayden , etheostoma rafinesquei burr & page , and e . simoterum ( cope ) . synapomorphies . —species of ulocentra are diagnosed from other species of simoperca by the presence of a very narrow frenum and a lack of teeth on the vomer ( bailey and etnier 1988 ) . type species . — e . atripinne ( jordan ) .
reliance on a ranked classification of darters that emphasizes subgenera without assessing the monophyly of these groups has long been an impediment to comparative studies of darters . for example , bart and page ( 1992 ) analyzed a rich database of information on the size at maturity , fecundity , and egg size in 64 darter species to examine the effects of body size and phylogeny on variation in life history traits ( e . g . , stearns 1984 ; dunham and miles 1985 ) . species data were pooled into clustered groups of genera , groups of subgenera , and subgenera for the analysis of covariance . however , 8 of the 15 polytypic subgenera sampled in the study of bart and page ( 1992 ) are not monophyletic in our phylogenetic analyses . thus , the variance in life history variables explained by the taxonomic nesting in bart and page ( 1992 ) was calculated incorrectly , and as a result , the data need reevaluation in the context of our revised understanding of darter phylogeny .
we recommend that ammocrypta , crystallaria , etheostoma , nothonotus , and percina continue to be used as the primary clade names with species epithets . the other clade names highlight phylogenetically related groups of species and will find validity in discussions of character diversity , biogeography , and ecological differences . in addition , the phylogenetic classification and the clade names will provide a comparative basis with which to investigate the ecology and evolutionary biology of darters in a way that was not possible with the previous darter classifications because the classifications did not consistently delimit monophyletic groups of species .
we were able to reconstruct the phylogenetic relationships of nearly all extant darter species , while avoiding inference pathologies stemming from incomplete taxon sampling ( e . g . , heath et al . 2008 ) . complete taxon sampling , however , does not resolve issues relating to character sampling ; more characters are generally required to resolve phylogenies that contain a moderate to high number of terminal taxa ( e . g . , bremer et al . 1999 ) . because the darter radiation was expected to contain a mixture of lineages with a fairly recent time since common ancestry and lineages with a much older common ancestor , we aimed to assess if a modest data set of mitochondrial and nuclearencoded gene sequences could result in well - resolved and congruent phylogenetic hypotheses for the clade . the analyses of the two sampled nuclear genes result in an appreciable degree of phylogenetic resolution among closely related species . however , our analyses do substantiate commonly held conceptions in molecular systematics that faster evolving genes provide phylogenetic resolution and clade support for younger nodes in the tree , whereas slower evolving genes are able to provide support for deeper nodes in the phylogeny ( fig . 5 ) .
recent phylogenetic analyses of darter subclades have revealed instances of mtdna introgression that range from a few sampled individuals exhibiting heterospecific mtdna genomes to species with complete mtdna genome replacement by heterospecific haplotypes ( bossu and near 2009 ; heckman et al . 2009 ; keck and near 2010 ) . in comparing the phylogenies inferred from mtdna with those inferred from the nuclear genes , we noted a number of topological differences that are likely the result of mtdna introgression . the frequency of mtdna introgression was noted , and mtdna haplotypes that were identified as resulting from introgression were scored as missing data in the bayesian phylogenetic analyses of combined mtdna and nuclear gene data sets .
as the architecture of the deepest parts of the tree of life become articulated through analyses of ever larger genomic - scale data sets , the challenges of resolving relationships among the most closely related branches and twigs remain . the history of investigating phylogenetic relationships among closely related animal species using molecular data is dominated by the use of mtdna . zoological systematists had been reluctant to explore the use of single - copy nuclear proteincoding genes for closely related lineages because mtdna sequences consistently provided substantial phylogenetic resolution . our investigation of darter phylogenetics based on the near - complete species sampling of a species - rich clade results in several important conclusions : 1 ) the sampling of a modest data set of nuclear genes results in appreciable phylogenetic resolution among closely related species ; 2 ) mtdna introgression in darters is extensive and complicated by the presence of at least three distinct phylogenetic patterns ; 3 ) resolved phylogenetic hypotheses for darters allow the construction of an informative phylogeny - based classification ; and 4 ) strategies of external calibration result in consistent relaxed - clock age estimates for clades across different genes and calibration methods . the results of our analyses provide critical insights in the pattern and timing of darter diversification , but perhaps more importantly , these analyses offer a prospectus for the use of nuclear gene sequence data to resolve the most closely related portions of the animal tree of life .
in order to determine whether genes that exhibited differing rates of nucleotide substitution provided resolved and significantly supported nodes at different time depths in the phylogeny , the posterior probability clade support values were plotted against the estimated age of the node . only interspecific nodes in the gene trees were scored . the posterior probabilities of clade support were extracted from the mrbayes posterior tree files by adding all compatible groups to the standard 50 % majorityrule consensus trees using the “allcompat” option in the mrbayes “sumt” command . only nodes that were present in both the beast and the mrbayes sets of posterior trees were recorded . there was substantial congruence among the tree topologies inferred from the mrbayes and beast analyses ; however , there were a few differences that involved the youngest clades in the darter phylogeny .
there has been a dramatic increase in the number of recognized darter species since the listing of 129 species in page ' s monographic treatment of the clade ; the increase to 248 species represents nearly a doubling of the number of recognized species over the past 25 years ( table 1 ) . this increase in the recognized species diversity of darters is the result of the discovery of previously unknown or unrecognized species ( e . g . , page et al . 2003 ; page and near 2007 ; layman and mayden 2009 ; switzer and wood 2009 ) , resurrecting species from synonymy ( e . g . , etnier and starnes 1986 ; near 2008 ) , and recognition of species formerly ranked as subspecies ( e . g . , etnier and williams 1989 ; piller et al . 2001 ; robins and page 2007 ) .
phylogeny of darters inferred from a partitioned bayesian analysis of a combined data set consisting of the mitochondrial cytochrome b gene ( cytb ) , the nuclear s 7 ribosomal protein intron 1 gene ( s 7 ) , and the nuclear recombination activating gene 1 exon 3 ( rag1 ) . the sequences for cytochrome b for species with heterospecific mitochondrial genomes were removed prior to the analysis . filled black circles identify clades supported with a bayesian posterior of 1 . 00 , and unfilled circles identify clades with bayesian posterior support that ranges between 0 . 95 and 0 . 99 . the shaded portion of the phylogeny at the top of the figure indicates placement of clades in the darter phylogeny . asterisks connect disconnected branches in the phylogeny . the phylogeny is presented in three parts , labeled ( a ) , ( b ) , and ( c ) .
there were three instances of deep introgression observed in the darter phylogeny , two of which involved the clades oligocephalus and psychromaster ( fig . 1 and table 4 ) . when comparing the phylogeny of these lineages inferred from the two nuclear genes with the cytb gene tree , two separate introgression events were detected . there was an mtdna transfer event from a lineage related to the extant species of psychromaster into the common ancestral lineage of vexillapinna , boleichthys , austroperca , and astatichthys . a second deep introgression event involved the transfer of mtdna originating from an oligocephalus lineage into the common ancestor of e . punctulatum , e . autumnale , and e . mihileze . in both cases , there has been species diversification in these lineages subsequent to the transfer and fixation of the heterospecific mtdna ; however , the phylogenetic affinities of these lineages in the mtdna gene tree are dramatically obscured by the deep introgression .
the other two species with heterospecific mtdna labeled as examples of indeterminate mtdna introgression may also be considered to harbor mitochondrial fossils ( table 4 ) . for example , the phylogenetic relationships of e . cinereum have long intrigued darter systematists ( bailey and gosline 1955 ; page and whitt 1973b ; page 1977 ; bailey and etnier 1988 ; dimmick and page 1992 ) , and the phylogenetic analyses of mtdna sequences have resulted in the placement of this species distantly related to other etheostoma lineages and more closely related to carnipellucida , percina , or nothonotus ( song et al . 1998 ; sloss et al . 2004 ; mayden et al . 2006 ; lang and mayden 2007 ) . our analyses of the two sampled nuclear genes place e . cinereum in the etheostoma subclade simoperca , a result consistent with the previous analyses of nuclear gene dna sequences and allozymes ( wood and mayden 1997 ; lang and mayden 2007 ; bossu and near 2009 ) .
our phylogenetic analyses of cytb and the two sampled nuclear genes indicate that 31 species , comprising more than 12 % of all darter species ( tables 1 and 4 ) , exhibit some degree of mitochondrial introgression , which ranges from complete replacement to an appreciable frequency of sampled individuals with heterospecific mtdna genomes . as in the previous investigations of boleosoma and nothonotus , we found no introgression of the two examined autosomal ( nuclear ) loci in any of the species exhibiting mtdna introgression ( heckman et al . 2009 ; keck and near 2010 ) . three different patterns of mtdna transfer were observed in our phylogenetic trees . among the 13 detected mtdna introgression events in darters , 8 involved proximal mtdna transfer ( table 4 ) . this pattern is detected by reference to a phylogeny that shows the phylogenetic nesting of haplotypes sampled from the recipient lineage in the donor lineage clade . these introgressed haplotypes may be fixed in the recipient lineage or show variation in the degree of introgression among geographic populations , and the introgressed haplotypes in the recipient lineage may be identical or very similar to those observed in the donor lineage ( fig . 1 ) .
divergence times were estimated using an uncorrelated lognormal ( ucln ) model of molecular evolutionary rate heterogeneity implemented in the computer program beast v . 1 . 53 ( drummond et al . 2006 ; drummond and rambaut 2007 ) . data sets used in the mrbayes analyses were pruned to contain only one specimen per sampled species in the ucln analyses . the optimal molecular evolutionary models were identified using aic , partitioning schemes were assessed using bayes factor comparisons , and the ucln model was implemented in beast to estimate the posterior density of divergence times . a birthdeath speciation prior was used for the branching rates in the phylogeny . five sets of relaxed - clock analyses were performed . divergence times were estimated using the centrarchid fossil calibrations and alignments of darters and centrarchids for each of the proteincoding cytb and rag1 genes . the centrarchid fossil calibrations were not used to estimate divergence times in darters for the s 7 intron 1 locus because substantial divergence between darters and centrarchids makes alignment of this locus problematic . the posterior densities of centrarchid molecular evolutionary rates estimated from alignments that contained only centrarchid species were used as priors in the analyses of darter alignments from each of the three genes ( cytb , s 7 , and rag1 ) .
scores of colleagues either directly contributed specimens for this study or facilitated our fieldwork . in particular , we thank h . l . bart , b . h . bauer , a . c . bentley , g . r dinkins , b . j . freeman , m . c . freeman , g . hogue , r . e . johansen , r . l . mayden , l . m . page , k . r . piller , b . a . porter , s . l . powers , m . e . raley , r . h . robins , a . m . simons , w . c starnes , e . o . wiley , and r . m . wood . our views on darter phylogeny were shaped through discussions with h . l . bart , b . h . bauer , m . j . donoghue , a . dornburg , b . r moore , t . c . mendelson , l . m . page , k . r . piller , and r . m . strange . b . j . kendrick provided assistance in the laboratory . g . watkins - cowell and j . p . joice provided assistance with museum collections . we thank k . de queiroz and r . e . glor for valuable comments on earlier versions of our manuscript .
there are considerable challenges to estimating divergence times using molecular data because of the near - ubiquitous presence of among - lineage molecular evolutionary rate heterogeneity and the need for external age calibration information ( sanderson 1998 ) . unfortunately , the fossil record for darters is poor and offers no information to provide minimal age constraints for nodes in molecular phylogenies ( ossian 1973 ; smith 1981 ; cavender 1986 , cavender 1998 ) . although the fossil record for non - darter percids ( e . g . , perca and sander ) extends to the early miocene , the morphological features preserved in these fossils do not permit the phylogenetic placement of the taxa relative to extant percid species ( svetovidov and dorofeeva 1963 ; cziczer et al . 2009 ; murray et al . 2009 ) . previous analyses of molecular divergence times in darters have used external fossil calibrations from the percoid clade centrarchidae ( near and benard 2004 ; near and keck 2005 ; carlson et al . 2009 ; hollingsworth and near 2009 ) . centrarchid fishes are classified in the same taxonomic order as darters ( nelson 2006 ) and have a rich fossil record that has been used to calibrate molecular phylogenies . there is also a substantial set of comparative molecular data sets available for this clade ( near et al . 2003 , near et al . 2004 , near , bolnick , et al . 2005 ) .
emerald darters spawn in late april and early may . though actual spawning has not been observed , attempts by males to mate include swimming from side to side over the female’s back . further , males have been observed in the wild trying to mount unresponsive females from behind or from the side . emerald darter larvae usually measure 4 . 5 to 6 . 0 mm in length and emerge from the egg with yolk sacs still attached . water temperature has a direct correlation with juvenile development , with warmer water temperatures resulting in a faster development and smaller sizes . warmer temperatures can have even more detrimental effects on populations . warmer temperatures in the later weeks of the breeding season can cause females to reabsorb their eggs and become unreceptive . spawning occurs in the center of riffles . larger males place themselves in pools near the middle of these turbulent areas so they will have a higher probability of encountering more females , which tend to use these areas . emerald darters prefer gravel substrates that lack silt . eggs and sperm are released simultaneously through mutual vibration and are attached by the female directly onto the gravel substrate . [ 7 ] emerald darters generally average 36 offspring per year . most captured emerald darters have been aged at up to three years old . in the red river drainage , 53 % of the population survived its second year , while only 7 . 7 % survived the third . third - year individuals were predominantly male .
the classification of darters has historically been characterized by the recognition of genera and subgenera that were assumed to represent monophyletic groups of species ( page 1981 , page 1983 ; bailey and etnier 1988 ; etnier and starnes 1993 ; boschung and mayden 2004 ) . because we are able to present well - resolved and strongly supported phylogenies based on mtdna and nuclear genes that are , with a few exceptions , generally in agreement with one another , we developed a phylogeny - based classification of darters that follows the principles of phylogenetic nomenclature described in the phylocode ( de queiroz and gauthier 1990 , de queiroz and gauthier 1992 , de queiroz and gauthier 1994 ; cantino and de queiroz 2009 ) . we attempted to preserve the nomenclatural history of group names by retaining preexisting names for clades when they exist ( e . g . , collette and knapp 1966 ) and by providing new names for clades that have never had formal names applied . we based our decision to name a clade on both its diagnosability and the need to communicate the clade in comparative and taxonomic studies ( e . g . , cantino et al . 2007 ) . thus , not all well - supported clades in the darter phylogenies were named . in addition , the clade names were given phylogenetic definitions that can only be applied in the context of a given phylogeny , and clades were identified by reference to a branch or a node in the phylogeny ( de queiroz and gauthier 1990 , de queiroz and gauthier 1992 ) .
comparison of posterior node ages estimated using external centrarchid fossil calibrations and those estimated using external rate calibrations reveals slight differences in the posterior age estimates between the two strategies . although there were no significant differences in the posterior node heights estimated by the two calibration strategies , fossil - calibrated ages were on average younger for the cytb chronogram and older for the rag1 chronogram relative to those estimated using external rate calibrations ( table 3 ) . this slight difference in node ages between the fossil and rate calibration analyses may be due to a difference in the width of the prior distribution of the rate calibrations , which are modeled on the posterior distributions of rate estimates from the centrarchid - only beast analyses ( table 2 ) . the prior distribution of the mean rate of the cytb gene was much wider than that of the rag1 gene . in the rate calibration analysis , the sampling of rates within this prior distribution may be limited relative to the sampling of rates in the fossil - calibrated analysis for rag1 . for the cytb rate calibration analysis , the converse may be true : a wide posterior on rates implies a wider sampling of rate variation relative to the rates sampled in the fossil calibration analysis . the assessment of posterior ages resulting from fossil - based versus rate calibration should therefore ideally consider the density of fossil calibration and the disparity in the credible intervals of the individual genes in the analysis . however , our analyses of darter divergence times using external centrarchid calibrations demonstrate promising consistency in posterior ages estimated using fossil and rate calibrations .