bluuebunny/crossref_metadata_2025 huggingface dataset:
Howling by coyotes ( Canis latrans): variation among social classes, seasons, and pack sizes
Authors: Gese Eric M , Ruff Robert L
Published: April 2011

From January 1991 to June 1993 we observed 54 coyotes (Canis latrans) for 2507 h in Yellowstone National Park,Wyoming, during which we observed 517 howling events. Among coyotes of different types of social organization (residentversus transient), members of resident packs initiated or participated in howling events, while transient individuals were neverobserved howling (n = 51 h of observation). For members of resident packs, alpha coyotes spent more time howling and had ahigher rate of howling events than beta coyotes and pups; beta coyotes and pups howled similarly. The percentage of time andthe rate of howling events typically peaked in the dispersal and breeding seasons, with the lowest rate of howling during puprearing. Social rank and season did not influence the length of howling events. Pack size did not affect howling rates amongindividuals in a pack or the alpha pair. With respect to space-use patterns, coyotes in resident packs howled more frequentlythan expected along the periphery of the territory than in the core area. We concluded that, like wolves (Canis lupus), allcoyotes in the resident pack did not contribute equally to howling duties; alpha coyotes howled more than all coyotes. Howlingby coyotes appears to serve a territorial spacing function that is mainly performed by the alpha pair of the resident pack.
Diet and feeding behaviour of the sea cucumber Cucumaria frondosa in the St. Lawrence estuary, eastern Canada
Authors: Hamel Jean-Francois , Mercier Annie
Published: April 2011

Combined laboratory and field experiments showed that sea cucumbers (Cucumaria frondosa) from the St. Lawrence estuary in eastern Canada have well-defined feeding cycles with marked seasonal and tidal variations. Typical feeding behaviour involved extension of the tentacles, which were then successively introduced into the oral cavity. Field observations and analysis of intestinal contents and indices demonstrated that C. frondosa fed mainly during spring and summer. Their diet comprised an abundance of phytoplanktonic cells (Coscinodiscus centralis, Chaetoceros debilis, Skeletonema costatum, and Thalassiosira gravida), with occasional ingestion of small crustaceans and a variety of eggs and larvae. Food types found in the digestive tract were closely related to the periodic abundance of plankton species in the water. Fewer individuals were observed feeding during fall and winter; they mostly ingested nonliving particles and the intestinal indices were low. In field populations, feeding rates were highest during ebb and rising tides, whereas under laboratory conditions without tidal variation, individuals showed no distinct feeding periods. However, individuals maintained under laboratory conditions and periodically provided with phytoplanktonic cells demonstrated a strong ability to detect the food in the water and react accordingly by extending their tentacles and beginning to feed. The results of the study suggest that food availability, rather than physical parameters such as temperature or current, best explains the cyclic feeding behaviour of C.\x11frondosa at seasonal and tidal scales.
Cell types in regenerating claws of the snapping shrimp, Alpheus heterochelis
Authors: Read A T , Govind C K
Published: April 2011

Cell types in the regenerating claws of adult snapping shrimps, Alpheus heterochelis, are described, based onelectron microscopy. Following autotomy of a limb, the coxal stump is secured by a membrane lined by a layer of proliferatingepithelial cells. Numerous fibroblasts with long cytoplasmic processes form small fluid-filled compartments that provide astructural framework and are inundated with mostly hemocytes and blood vessels. Agranular hemocytes are uncommoncompared with granular ones, which have prominent pseudopodia, vacuoles, and lysosomes, features that suggest a phagocyticfunction. The cytoplasmic network formed by fibroblasts persists in the regenerating blastema and papilla, together withgranular hemocytes and blastemal cells. Close structural associations were observed amongst all four cell types. Regionalproliferation of epithelial cells subdivides the distal tip of the papilla into the presumptive propus and dactyl and marks thebeginning of segmentation, which proceeds in a distal to proximal direction. This is accompanied by the appearance of firstafferent innervation, also proceeding in a distal to proximal direction, and multinucleate myoblasts identified by fragments ofmyofibrils, then efferent innervation and well-organized muscle. Prominent intercellular contacts between hemocytes and othercell types within the papilla may serve for adhesion as well as for communication. The early and prevalent appearance ofhemocytes in the regenerating limb bud, as well as their pluripotent nature in other regenerating tissues, implicates them as theorigin of blastemal cells.
Food intake and spontaneous swimming activity in Arctic char (Salvelinus alpinus): role of brain serotonergic activity and social interactions
Authors: Øverli Øyvind , Winberg Svante , Damsård Børge , Jobling Malcolm
Published: April 2011

We investigated the relationship between social interactions, brain serotonergic activity, and two behavioural patterns in juvenile Arctic char (Salvelinus alpinus): feeding and spontaneous swimming activity. Dominant and subordinate individuals were observed during rearing in pairs, followed by rearing in isolation. Throughout the experiment, levels of both food intake and swimming activity remained high in dominant fish. When they were in pairs, food intake was completely inhibited in subordinate fish; thus, dominant fish were able to monopolise food. At the same time, brain serotonergic activity, as indexed by the ratio of 5-hydroxyindoleacetic acid (5-HIAA) to serotonin (5-hydroxytryptamine, 5-HT) was elevated in the hypothalamus and brain stem of subordinate fish compared with dominants. During subsequent rearing in isolation, food intake, but not spontaneous locomotor activity, gradually increased in previously subordinate fish, while serotonergic activity fell to near that of dominants. Thus, appetite inhibition in subordinate fish can be reversed by rearing in isolation, an effect that may be related to the reversal of a stress-induced activation of brain serotonergic neurones accompanying social subordination. Reduced swimming activity is either a long-lasting response to social subordination or reflects permanently different behavioural strategies of subordinate and dominant individuals.
Effect of mating on female phonotactic response in Gryllus integer (Orthoptera: Gryllidae)
Authors: Lickman Kelly , Murray Anne-Marie , Cade William H
Published: April 2011

Little work has examined the importance of the variation in mating preferences shown by individual females in a population. In acoustical insects, female response in terms of orientation and movement towards the male calling song is one aspect of female mating preferences. In this study, the effects of mating status on female phonotactic responses in the field cricket, Gryllus integer, were investigated. All test subjects were 10-14 days old and varied in their pretrial mating history. Mated females had copulated 24 h prior to testing. Virgin females, however, had visual, olfactory, and acoustical exposure to males during the pretrial matings of the mated females. Phonotactic responses were measured using a noncompensating treadmill called the kugel. Females were presented with simulated conspecific calling songs differing in trill length in either choice or no-choice protocols. Virgin females exhibited greater overall movement than mated females as well as increased directional movement in multi-stimulus presentations but not in single-stimulus presentations. Neither virgin nor mated females differentiated between the two songs differing in trill length. The data demonstrate that female G. integer phonotaxis is influenced, in part, by both mating status and the availability of mates.
Estimates of age and growth in a population of green sea turtles (Chelonia mydas) from the Indian River lagoon system, Florida: a skeletochronological analysis
Authors: Zug George R , Glor Richard E
Published: April 2011

The Indian River lagoon system harbors a dynamic population of juvenile green sea turtles (Chelonia mydas). This foraging or developmental population occupies the lagoon year-round and periodically experiences cold-stunning events that kill a portion of the population. A sample of 59 C. mydas (28-74 cm straight carapace length) from the December 1989 cold-stunning event was aged by skeletochronology, yielding age estimates of 3-14 years. Mean growth-rate estimates range from 30 to 52 mm/year for most age and size classes, with means for the 6- to 11-year age classes (44-49 mm/year) not significantly different but greater than those of the youngest and oldest classes (3-5 and 12 years old, respectively) (32-38 mm/year). Because of the lack of adults and near-adults in the sample, growth models (e.g., Gompertz) do not yield biologically realistic asymptotes, hence they do not provide accurate estimates of age at sexual maturity. The age estimates suggest that the western Atlantic C. mydas change from a pelagic to a neritic life predominantly as 5- to 6-year-olds and, in central Florida, juveniles may live in a developmental habitat for 6 or more years.
The trophi of Bdelloidea (Rotifera): a comparative study across the class
Authors: Melone G , Ricci C , Segers H
Published: April 2011

The fine morphology of the trophi of bdelloid rotifers was investigated using scanning electron microscopy to provide a detailed description of the structure and to assess its variability within the class. Twelve genera of the four families of Bdelloidea were considered. All trophi studied fit the ramate type typical of bdelloids, and comprise three paired elements: rami, unci (with three groups of teeth: a proximal group of minor teeth, a median group of major teeth with a pore, and a distal group of minor teeth), and manubria. The morphology of the trophi in Adinetida and Philodinida is fairly homogeneous. The trophi of Philodinavida differ in position, orientation, and structure: the proximal group of minor uncus teeth is reduced and the ramus apophysis is more developed. In contrast to the trophi of Flosculariacea, small differences in the number of uncus teeth appear to be taxonomically irrelevant in Bdelloidea. The following features of the trophi are recognized as synapomorphies for the Bdelloidea: absence of the fulcrum; formation of major uncus teeth by fusion of elements; and deposition of calcium as a means of stiffening the manubria. The existence of these synapomorphies suggests that the ramate type of trophi in Bdelloidea does not represent the primitive type in Rotifera.
Variation in offspring sex ratios in the northern water snake (Nerodia sipedon)
Authors: Weatherhead Patrick J , Brown Gregory P , Prosser Melanie R , Kissner Kelley J
Published: April 2011

We used data from 88 litters of northern water snakes (Nerodia sipedon) to test predictions about how mothers would adaptively vary the sex ratios of their offspring. Larger mothers produced significantly more daughters (r2 = 0.04, P = 0.05), and mothers producing larger offspring produced significantly more daughters (r2 = 0.06, P = 0.02). Because neonate size did not vary with maternal size, these sex-ratio patterns were independent of each other. These patterns were more pronounced for wild females than for females maintained in captivity while gravid, but rearing conditions did not have a significant effect on sex ratio. Also, because sex ratios were similar between captive and free-living females despite captive females giving birth 16 days earlier, on average, and because sex ratios did not vary with birth date within the two groups of females, gestation appeared not to affect sex ratio. If females vary sex ratios adaptively, only the relationship between sex ratio and neonate size was consistent with our predictions. Limited evidence from other snake species also indicates variation in neonatal sex ratios that is nonrandom but not necessarily adaptive. A better understanding of these patterns will require information on the factors that affect the fitness of male and female neonates differently. An unexpected sex-ratio pattern that we found was that 14 of 19 stillborn young were male. We speculate that this pattern could be a result of male embryonic sensitivity to temperature. Thus, the need for gravid females to maintain a high body temperature so that their young are born with enough time to find hibernation sites may conflict with the need for embryos to develop at a safe temperature.
Neither large nor small: intermediate-sized food items for the cubs of the Patagonian gray fox (Pseudoalopex griseus)
Authors: Zapata Sonia C , Travaini Alejandro , Delibes Miguel
Published: April 2011

According to central place foraging theory, adult Patagonian gray foxes (Pseudoalopex griseus) behaving efficiently should consume on the spot those food items too large to be carried and those too small to warrant being carried to the den. Consequently, fox cubs should be provisioned with intermediate-sized items. We tested this prediction by analyzing 96 fecal samples from adult foxes and 82 fecal samples from cubs belonging to three different dens collected near Junín de los Andes in the province of Neuquén, Argentina, from November 1994 to January 1995. As predicted, adult foxes consumed carrion of large ungulates (large items) and arthropods and berries (small items) significantly more often than cubs did. Cubs ate more intermediate-sized vertebrates, from lizards and birds to rodents and hares. Medium-sized armadillos, which are difficult to handle and transport, were consumed only by adults. Cubs ate some insects, which were probably captured by the cubs themselves near the den.
Dispersal of juvenile collared lemmings (Dicrostonyx groenlandicus) in a high-density population
Authors: Blackburn Gwylim S , Wilson Deborah J , Krebs Charles J
Published: April 2011

We tested whether dispersal of juvenile lemmings occurs at high population densities and whether predation risk affects movements of juveniles. The study was conducted in July and August 1996 on the Kent Peninsula, Northwest Territories, during a peak in the lemming cycle. We fitted 43 juvenile collared lemmings (Dicrostonyx groenlandicus) of the summer generations on a control plot and a predator-exclosure plot with radio transmitters and examined their home ranges and movement patterns. We tested the following hypotheses: (i) extensive juvenile dispersal will occur at high population densities, (ii) male juveniles will move greater distances than females, and (iii) juveniles will move greater distances in the absence of predators. We rejected all these hypotheses. All juvenile collared lemmings remained in the vicinity of their original home ranges. Home-range sizes of all juveniles were similar, the mean size being 100 m2. Mean and maximum distances moved were similar among all juveniles. However, juveniles moved less frequently on the control plot than on the exclosure plot. Juvenile collared lemmings do not disperse at high densities. The lack of dispersal may have been the result of avoidance of confrontations with other lemmings, and may also have been related to delayed breeding, since most juveniles and subadults did not mature in late summer. Differential predation risk or predation mortality may have had no effect on the distances moved by juveniles or may have been masked by strong density effects on both plots.
The importance of meat, particularly salmon, to body size, population productivity, and conservation of North American brown bears
Authors: Hilderbrand G V , Schwartz C C , Robbins C T , Jacoby M E , Hanley T A , Arthur S M , Servheen C
Published: April 2011

We hypothesized that the relative availability of meat, indicated by contribution to the diet, would be positively related to body size and population productivity of North American brown, or grizzly, bears (Ursus arctos). Dietary contributions of plant matter and meat derived from both terrestrial and marine sources were quantified by stable-isotope analysis (δ13C and δ15N) of hair samples from 13 brown bear populations. Estimates of adult female body mass, mean litter size, and population density were obtained from two field studies of ours and from other published reports. The populations ranged from largely vegetarian to largely carnivorous, and food resources ranged from mostly terrestrial to mostly marine (salmon, Oncorhynchus spp.). The proportion of meat in the diet was significantly correlated with mean adult female body mass (r = 0.87, P < 0.01), mean litter size (r = 0.72, P < 0.01), and mean population density (r = 0.91, P < 0.01). Salmon was the most important source of meat for the largest, most carnivorous bears and most productive populations. We conclude that availability of meat, particularly salmon, greatly influences habitat quality for brown bears at both the individual level and the population level.
Repeatability of parental effort in male and female Pied Flycatchers as measured with doubly labeled water
Authors: Potti J , Moreno J , Merino S
Published: April 2011

Intensity of parental care is one of the critical factors affecting offspring growth and final size and thus is a key variable in life-history evolution. In the study population of Pied Flycatchers (Ficedula hypoleuca), it was previously shown that maternal daily energy expenditure was an important source of variance in offspring size and likelihood of infection by blood parasites. Thus, energy expenditure may be considered a parental-performance effect, and variation among females in the intensity of parental care they provide might itself be influenced by genetic differences, affording the opportunity for evolutionary change. To address whether parental work load is a consistent trait and thus may retain additive genetic variance, the same individuals were scored for mass-independent daily energy expenditure (DEE) across two consecutive breeding seasons, while feeding nestlings close to fledging. While DEE of females was significantly repeatable between years, this was not the case for males. DEE may retain additive genetic variance in females, although its expression may be obscured in males by their less constrained activity budgets and lower confidence of paternity.
Variations in prevalence and intensity of blow fly infestations in an insular Mediterranean population of blue tits
Authors: Hurtrez-Boussès Sylvie , Garine-Wichatitsky Michel de , Perret Philippe , Blondel Jacques , Renaud François
Published: April 2011

A Corsican population of blue tits (Parus caeruleus) suffers extremely high levels of infestation by two species of blow flies (genus Protocalliphora) that have been suspected to influence the life-history traits of their hosts. By quantifying the abundance of the blow fly larvae infesting each brood of this population during 2 consecutive years, we showed that the distribution of these parasites did not differ from a Poisson distribution. The intensity of blow fly parasitism (mean parasite load per infested nest) was independent of the time of breeding and the available space in the nest of their bird hosts. Moreover, the total blow fly load per nest increased significantly with the number of chicks, whereas the parasite load per chick was not linearly related to brood size.
Maturation génitale des varans du nil mâles (Varanus niloticus) dans trois populations du Sahel
Authors: de Buffrénil Vivian , Castanet Jacques , Rimblot Frédérique
Published: April 2011

Genital maturation of male monitor lizards, a subject poorly documented up to now in spite of the heavy exploitation of these animals, was studied on a sample of 211 Nile monitors (Varanus niloticus) from Chad (Lake Chad), Mali (central delta of the Niger), and Nigeria (Hadejia-N'Guru wetlands). Snout-vent lengths (LC) in the sample ranged from 15.6 to 85.5 cm. After a morphometric study of the monitors, their testes were sampled, weighed at ±0.01 g and fixed for histology. The age of each specimen was estimated by skeletochronology. The testes of monitors less than 36 cm LC (Malian specimens) or 40 cm LC (Chadian and Nigerian individuals) do not contain mature spermatozoa, whereas the testes of larger specimens do. Most Malian monitors aged 18 months (1.5 years) have mature spermatozoa. Conversely, in Chadian and Nigerian individuals, mature gametes appear only in specimens aged 30 months (2.5 years). These data indicate that genital maturity in the Nile monitor is reached at 36-40 cm LC and 1.5-2.5 years according to the populations. The growth in mass of the testes, compared with LC, is an accurate indicator of body size at sexual maturity, and confirms the precocity of Malian specimens. Conversely, testis growth is poorly related to age. These results are discussed with reference to the possible accommodation of Nile monitor populations to heavy exploitation by means of precocious recruitment of the male breeding stock.
Female preference and male nuptial colouration in the freshwater fish Gobiomorphus breviceps: geographic variation among populations
Authors: Hamilton William J , Poulin Robert
Published: April 2011

Geographic variation in the strength or direction of sexual selection acting on different populations has been documented before but has not been the subject of intense study. We examine covariation among sexually selected traits and environmental factors for five stream populations of a small New Zealand freshwater fish, the upland bully, Gobiomorphus breviceps (Eleotridae). Levels of infection by a trematode parasite and some aspects of female behaviour and male colouration varied significantly among populations. Among individual fish we found that female mate choice behaviours and male colouration did not correlate similarly with other traits, or with parasite load, in the different populations studied. We also determined whether average population values correlated among the different stream populations. Whereas environmental factors such as water clarity and substrate colouration appeared to be unimportant, average parasite load correlated with some components of male colouration, and female preferences appeared to be correlated with male colouration. These results illustrate both the variability among populations that prevents results obtained from one population from being generalized to the entire species, and the plasticity of sexually selected traits in relation to local conditions.
The growth pattern of the African tortoise Geochelone pardalis and other chelonians
Authors: Hailey Adrian , Coulson Ian M
Published: April 2011

Growth rings were measured in dead African leopard tortoises, Geochelone pardalis, collected in the seasonal tropics of Zimbabwe over an 11-year period. A series of Ford-Walford plots using growth measured from annuli showed that growth fitted a logistic by mass curve best, logistic by length and Gompertz curves less well, and a Bertalanffy curve least well. The Bertalanffy curve, often fitted to growth of chelonians, is characterised by particularly high growth rates of juveniles compared with larger individuals. It is suggested that this growth pattern is likely to be found in species showing a marked decrease in diet quality with size. This hypothesis is supported by a review of growth patterns in chelonians: Bertalanffy curves are associated with an omnivorous (and thus potentially variable) diet and other growth patterns with an obligate carnivorous or herbivorous diet. Geochelone pardalis in Zimbabwe showed significant sexual size dimorphism, the mean asymptotic mass of females being 1.7 times that of males, unlike populations with larger body sizes to the north and south. Annual survival estimated from age-frequency distributions was significantly higher in males (0.80) than in females (0.72), the difference being sufficient to account for the male-biased sex ratio of live animals.
Density-dependence in habitat utilisation by wood mice in a Sitka spruce successional mosaic: the roles of immigration, emigration, and variation among local demographic parameters
Authors: Fernandez Fernando AS , Dunstone Nigel , Evans Peter R
Published: April 2011

Density dependence in habitat utilisation by a population of wood mice (Apodemus sylvaticus L.) was investigated within a habitat mosaic produced by the felling of mature Sitka spruce (Picea sitchensis Bong. Carrière). A capture-mark-recapture study was carried out from May 1990 to June 1992, with trapping in five 0.81-ha grids marked in mature forest and clear-fellings of different ages. Intergrid movements were frequent (15.3% of all recaptures). A significant linear negative relationship was found between overall population sizes and degree of heterogeneity in habitat utilisation, although the former explained only about one-quarter of the variation in the latter (r2= 0.233). Wood mice were more evenly distributed among grids when numbers in the area were high, indicating density-dependence in their habitat utilisation. Demography was studied at subpopulation (grid) level to determine whether the observed pattern was due to movements among grids or to intergrid variation in the balance between recruitment and losses. Partial regression coefficients in a multiple regression showed that emigration/immigration had a lesser role in explaining the pattern, although the former was significant in explaining part of subpopulation decreases and the latter was significant in explaining part of their increases. Differences in the balance between recruitment and loss rates among local subpopulations accounted for most of the observed density-dependent changes in habitat utilisation. These results do not support the view that such changes are mostly due to active choices made by individuals moving among habitats.
Energy expenditure in European roe deer fawns during the suckling period and its relationship with maternal reproductive cost
Authors: Mauget Christiane , Mauget Robert , Sempéré Antoine
Published: April 2011

We measured energy expenditure by means of indirect calorimetry in European roe deer (Capreolus capreolus) fawns at frequent intervals from birth to 45 days of age. Mean resting metabolic rate (RMR) and body mass (BM) did not differ significantly between males (N = 9) and females (N = 14). RMR significantly increased with the fawn age following the equation RMR (kJ·d-1) = 956 + 31.4 age (days). Growth in BM was linear: BM (kg) = 1.565 + 0.135 age (days). Mass-specific RMR decreased from a peak value of ca. 500 kJ·kg-1·d-1in the first week to 290.4 ± 10.0 kJ·kg-1·d-1in the sixth week. Concomitant metabolic trials performed with 14 lactating females and their 19 fawns indicated that metabolic weaning began in the third week, when the fawn's energy expenditure became markedly higher than could be compensated for by the mother's milk. Comparison of the energy expenditure of singletons and twins showed that female roe deer are energetically well adapted to nurse two fawns.
Retrograde movement of urine into the gut of salt water acclimated Mallards (Anas platyrhynchos)
Authors: Hughes M R , Bennett D C , Sullivan T M , Hwang H
Published: April 2011

The influence of sex and salt-water intake on retrograde movement of urine into the hindgut was examined in captive adult wild Mallards (Anas platyrhynchos). Ducks were given intravenous injections of tritiated polyethylene glycol (3H-PEG) and killed 3 h later. The fluid content of each gut segment and its concentrations of3H-PEG, sodium, and potassium were determined. Retrograde movement of urine into each gut segment was estimated from the quantity of3H-PEG recovered there. In both ducks that drank tap water and those that drank saline, about 20% of the urine was moved into the hindgut, two-thirds of this into the ceca. Males deposited more urine in the ceca and reabsorbed more water from this urine than did females (P < 0.01). We conclude that retrograde movement of urine into the hindgut was unaffected by the salinity of drinking water and was greater in males than in females. Reabsorption of urinary sodium and water in the hindgut, particularly the ceca, may play an important role in osmoregulation in birds with salt glands.
Reproductive products in the adult snow crab (Chionoecetes opilio). II. Multiple types of sperm cells and of spermatophores in the spermathecae of mated females
Authors: Sainte-Marie Guy , Sainte-Marie Bernard
Published: April 2011

Contents of the spermathecae of mated adult snow crabs (Chionoecetes opilio) were examined by light microscopy. The contents could consist of water and three basic types of amorphous matter and of spermatophores. Water was present in the form of large patches or smaller spheres. Of the two major types of amorphous matter, one reacted positively and one negatively to periodic acid - Schiff's reagent (PAS), and one was only, and one predominantly, of male origin. The minor type of amorphous matter was orange and of female origin and could include dark cellular debris. Spermatophores enclosed either immature spermatids, mature spermatids, hitherto unreported spermatozoa, or cell forms intermediate between these three types. Peripheral mature spermatids and spermatozoa had a polarized orientation and were attached to the spermatophore wall. Overall, amorphous matter and spermatophores were topographically segregated by type within a spermatheca, and spermatophores enclosing immature spermatids occurred mostly in PAS-negative amorphous matter. Spermatid differentiation can unfold in the female reproductive tract as well as in the vas deferens, while the transformation of spermatids into spermatozoa was observed only in the female. The diversity of sperm cell types and the ordered placement of semen constituents within the spermatheca suggest that sperm are partitioned for short- or long-term use.
Co-existence of zebra mussels and freshwater unionids: population dynamics of Leptodea fragilis in a coastal wetland infested with zebra mussels
Authors: Nichols S Jerrine , Amberg Jon
Published: April 2011

In 1996, thousands of live Leptodea fragilis were collected from a marsh located in the western basin of Lake Erie that was infested with zebra mussels (Dreissena polymorpha). Despite the presence of zebra mussels at this site for a number of years, this L. fragilis population showed no signs of competition-induced changes in population dynamics. Biofouling was limited: fewer than 1% of the L. fragilis showed evidence of recent or past zebra mussel colonization. Successful recruitment occurred yearly, with multiple year classes collected that ranged in age from 1 to 12 years. However, age and shell length were not well correlated. Seventy-one percent of the individuals collected were 51-80 mm long, but ranged in age from 2 to 4.5 years. Three different patterns of growth or shell deposition were found. Some individuals grew rapidly, reaching 105 mm in 3.5 years, while others grew only 4.5 mm over the same time period. A few grew poorly during some years but very rapidly in others. Individuals with a shell length of 41 mm or more were sexually mature and females were more common than males. The strong recruitment and steady growth of this population showed no change between the years before and after the zebra mussel invasion, indicating that this marsh is functioning as a natural refugium from potential problems caused by zebra mussels.
Multiple visits of individual humpback whales (Megaptera novaeangliae) between the Hawaiian and Japanese winter grounds
Authors: Salden Dan R , Herman Louis M , Yamaguchi Manami , Sato Fumihiko
Published: April 2011

We document through photographic identifications three humpback whale (Megaptera novaeangliae) winter ground interchanges between Hawai'i and Japan. Two of these whales, identified as male by their behavioral roles, made multiple interchanges across years; i.e., they were initially seen in Hawai'i, were later observed in Japan, and subsequently, returned to Hawai'i. The third whale was seen in only 2 different years, once in Japan and then in Hawai'i. Prior to this report, there has been only one published report of a Hawai'i-Japan interchange and only eight between Hawai'i and Mexico. None of these involved multiple interchanges. The current findings demonstrate that individual whales may be highly flexible in their annual choice of widely separated winter destinations and suggest that these wanderers may be mainly males. The occurrence of wanderers provides a mechanism for increasing genetic variability in the breeding populations and also suggests a mechanism for noted song similarities across different North Pacific winter grounds.
Age and growth estimates of bowhead whales (Balaena mysticetus) via aspartic acid racemization
Authors: George John C , Bada Jeffrey , Zeh Judith , Scott Laura , Brown Stephen E , O'Hara Todd , Suydam Robert
Published: April 2011

A total of 48 eye globes were collected and analyzed to estimate ages of bowhead whales using the aspartic acid racemization technique. In this technique, age is estimated based on intrinsic changes in the D and L enantiomeric isomeric forms of aspartic acid in the eye lens nucleus. Age estimates were successful for 42 animals. Racemization rate (kAsp) for aspartic acid was based on data from earlier studies of humans and fin whales; the estimate used was 1.18 10-3/year. The D/L ratio at birth ((D/L)0) was estimated using animals less than or equal to 2 years of age (n = 8), since variability in the D/L measurements is large enough that differences among ages in this range are unmeasurable. The (D/L)0estimate was 0.0285. Variance of the age estimates was obtained using the delta method. Based on these data, growth appears faster for females than males, and age at sexual maturity (age at length 12-13 m for males and 13-13.5 m for females) occurs at around 25 years of age. Growth slows markedly for both sexes at roughly 40-50 years of age. Four individuals (all males) exceed 100 years of age. Standard error increased with estimated age, but the age estimates had lower coefficients of variation for older animals. Recoveries of traditional whale-hunting tools from five recently harvested whales also suggest life-spans in excess of 100 years of age in some cases.
Egg burial depth by sockeye salmon (Oncorhynchus nerka): implications for survival of embryos and natural selection on female body size
Authors: Steen Ryan P , Quinn Thomas P
Published: April 2011

We studied the relationship between female sockeye salmon (Oncorhynchus nerka) body size and egg burial depth in a small Alaskan stream to better understand the ways in which stream-bed scour or digging by other females might destroy embryos. Two different measurements of egg burial depth were taken: depth from the original stream-bed surface to the top of the egg pocket and depth from the disturbed substrate directly above the egg pocket to the top of the egg pocket. The former may represent the depth to which stream-bed scouring would have to go to reach the eggs, but the latter represents the depth to which a second female would have to dig to disturb the egg pocket. Larger females buried their eggs deeper, relative to the original substrate level, than smaller females. This suggests that streams with frequent scour events would select for larger females. However, mean depth from the disturbed substrate level was significantly shallower than mean depth from the original stream-bed level, suggesting that even the smallest females could dig deep enough to disturb the egg pockets of the largest females. Finally, the egg burial depth - fish size relationship that we observed was compared with published data on other salmonid species, revealing considerable variation but a clear positive relationship between female size and burial depth. Because embryonic survival is affected by scour and nest disturbance, and because changes in fish body size, density, and flow regime can affect the vulnerability of embryos to such mortality, we recommend further, standardized measurements of the relationship between egg burial depth and female body size.
Prey-size selection by brown trout (Salmo trutta L.) in a stream in northern Spain
Authors: Rincón Pedro A , Lobón-Cerviá Javier
Published: April 2011

Brown trout in the River Negro in northern Spain preferentially ate larger aquatic prey items (found throughout the water column). A model based on size-dependent prey encounters was able to account for this trend and to generate accurate predictions of the consumption of aquatic prey of different sizes. In contrast, the same model failed to predict the size composition of terrestrial prey (restricted to the upper layers of the water column) eaten bv the trout. Trout ignored the larger (more profitable) terrestrial prey, and the consumption of prey of a given size class was more dependent on their relative abundance than on their size. However, the smallest prey were rejected. We suggest that trout were switching, i.e., overexploiting the most abundant prey, because of perceptual limitations mediated by large differences in relative abundance of the different size classes of terrestrial prey. The size-frequency distributions of the available terrestrial prey were always greatly dominated (75-90%) by the two smallest size classes (1-2 and 2-3 mm long), prey over 4 mm long being extremely scarce, while size distributions of aquatic prey were less skewed. Overall, active choice guided by energetic optimization criteria appeared to be of limited importance in determining the size composition of prey eaten by this population of brown trout Our results also indicate that the operating mechanisms of prey-size selection are probably not independent of the characteristics of the size-frequency distribution of the available prey.
Nitrogenous waste excretion by the larvae of a phylogenetically ancient vertebrate: the sea lamprey (Petromyzon marinus)
Authors: Wilkie M P , Wang Y. , Walsh P J , Youson J H
Published: April 2011

Larval sea lampreys (Petromyzon marinus) (ammocoetes) excreted significant quantities of urea, which composed 15-20% of the total nitrogenous waste excreted. Compared with teleosts of similar size, ammonia and urea excretion rates (JAmmand JUrea, respectively) in ammocoetes were relatively low, reflecting the low metabolic rate of these burrow-dwelling suspension feeders. Analyses of liver enzymes indicated that ammocoetes had all the enzymes necessary to produce urea via uricolysis, but not those of the ornithine-urea cycle (OUC). Further, exposure to 2 mmol·L-1total ammonia for 5 d was accompanied by a 3-fold elevation of JUrea, but did not lead to greater OUC activity. Internal ammonia levels increased markedly, however, exceeding 2000 µmol·L-1in plasma and 5000 µmol·L-1in muscle after the 5-d exposure period. This high resistance to internal ammonia accumulation was related to the very high glutamine synthetase activities measured in ammocoete brains. The excretion and production of urea by ammocoetes demonstrates for the first time that agnathans are capable of producing physiologically relevant amounts of urea. Given the ancient origins and conserved evolution of lampreys, these observations also suggest that at least some of the early jawless vertebrates were able to produce and excrete urea.
Behavioural oxy-regulation by cold-submerged frogs in heterogeneous oxygen environments
Authors: Tattersall Glenn J , Boutilier Robert G
Published: April 2011

Amphibians overwintering in ice-covered aquatic environments encounter levels of hypoxia that present significant challenges to the maintenance of aerobic metabolism. Earlier laboratory experiments showed that cold-submerged frogs will seek out lower temperatures when confronted with severe hypoxia. This so-called behavioural hypothermia response effectively reduces the aerobic metabolic rate and thereby minimises the lactic acidosis associated with oxygen lack. The results of these previous experiments suggest that frogs overwintering in hypoxic environments have the capacity to exploit thermal gradients under the ice to forestall the onset of anaerobiosis. What is not yet known is whether overwintering frogs can detect and therefore react to the large isothermal oxygen gradients that also exist under the ice. To determine the behavioural response of frogs to dissolved oxygen, the movements of submerged animals were followed for 6 h in an aquatic chamber that presented a linear horizontal oxygen gradient (14-130 mmHg) at two constant temperatures (1.5 and 7°C). At both temperatures, frogs spent significantly less time in regions of the tank that were hypoxic than they did in the same regions when no oxygen gradient was present. Submerged frogs also showed an overall preference for oxygen levels above their critical oxygen partial pressures for the aerobic metabolic rate (41 mmHg at 1.5°C and 76 mmHg at 7°C). Thus, cold-submerged frogs not only respond to oxygen gradients, but they do so in a fashion that favours oxygen uptake and aerobic metabolism. This "behavioural oxy-regulation," although slow-acting, would appear to be adequate for frogs responding to the progressively developing oxygen and temperature gradients in their natural overwintering environments.
Male mate guarding increases females' predation risk? A case study on tandem oviposition in the damselflyCoenagrion puella(Insecta: Odonata)
Authors: Zeiss Christoph , Martens Andreas , Rolff Jens
Published: April 2011

To estimate whether male mate guarding alters the predation risk for females, we conducted experiments in field cages with the damselfly Coenagrion puella. We experimentally compared the risk for females ovipositing solitarily versus in tandem with the male. The backswimmer Notonecta glauca was used as a predator. Owing to the oviposition behaviour of the damselflies, N. glauca only preys on females, therefore it was possible to determine whether the presence of males decreases or increases females' predation risk. Females in tandem were more frequently touched and grasped by N. glauca than solitary females. In most tandem pairs, the female showed the first reaction to the attack and the male responded subsequently. After an attack, most solitary females left the oviposition site but most tandem females stayed. Once grasped by the predator, more solitary females were killed.
Sexual dimorphism and allometry in the giant water strider Gigantometra gigas
Authors: Tseng Michelle , Rowe Locke
Published: April 2011

This study describes sexual dimorphism in size (total body length and lengths of leg components) and in the allometric relationships between leg-component lengths and total body length in the giant water strider Gigantometra gigas (Heteroptera: Gerridae). Gigantometra gigas is the largest known gerrid, and has been previously described as monomorphic for body size. We compare our results with analogous data collected on Gerris buenoi, a species of more moderate size, where females are larger than males. Based on 94 specimens of G. gigas, we conclude that males are larger than females in all measured traits. This dimorphism was most spectacular in the leg components, which are 10-50% longer in males than in females. Males are generally more variable in size than females, and this is especially so for leg components. Allometric analysis suggests that total leg lengths (particularly middle and rear) increase at a much greater rate with body size in males than in females, therefore there is sexual dimorphism in allometries on the scale of that in the traits themselves. The relationship between middle and hind leg lengths is strong in both sexes, and appears to differ very little between the sexes or between G. gigas, and Ge. buenoi. These data suggest a constraint on this relationship, perhaps because of the biomechanics of locomotion. We propose that sexual selection acting on middle leg lengths in males explains both the increase and variance in middle leg length, and that hind leg length follows by correlated response.
Diet and growth of glaucous gulls at a large Arctic goose colony
Authors: Samelius Gustaf , Alisauskas Ray T
Published: April 2011

We examined the diet and growth of glaucous gull (Larus hyperboreus) chicks at Karrak Lake goose colony in 1994 and were especially interested in how these factors were affected by geese leaving the colony after goose hatch. Insects and bird prey each occurred in about 80% of regurgitated pellets during the first week after hatch of gulls. Thereafter, the frequency of insects in pellets diminished to <20%, whereas the frequency of bird parts and eggshells increased to about 100 and 80%, respectively, and remained high in gull diets during the 6 weeks of this study. We observed no effect of laying order on the size of gull eggs, nor any effects of chick sequence on growth or survival of chicks, suggesting that food was abundant during egg-laying and possibly early in chick rearing. Overall, both the growth rate and final size of chicks varied among nests, and chicks from small broods grew larger than chicks from large broods. Egg size and hatch date had no effect on growth. We suspect that brood size emerged as an important effect on growth, because food abundance declined as gull chicks grew older and brood competition came in to play.
15N signatures do not reflect body condition in Arctic ground squirrels
Authors: Ben-David M , McColl C J , Boonstra R , Karels T J
Published: April 2011

Studies using stable-isotope analysis documented an enrichment in δ15N values in nutritionally stressed animals. Investigators suggested that changes in δ15N values measured in urine, hair, and blood may be a good indicator of lean-tissue losses. During our investigations into the effects of population density on body condition and reproduction of female Arctic ground squirrels (Spermophilus parryii plesius) near Kluane Lake, Yukon, Canada, we examined the relations between body condition and δ15N values. Data obtained from 20 livetrapped female ground squirrels suggested that reproductive females from a population with moderate density and low food availability experienced a reduction in body condition, as indicated by mass loss and changes in blood urea nitrogen (BUN) and glucose concentrations. In contrast, those from a population that failed to reproduce successfully and had high density and low food availability experienced no nutritional stress. Similarly, those females from a high-density population with high food availability (i.e., supplemented food) that reproduced successfully suffered no noticeable nutritional stress. In contrast to our prediction, δ15N values did not show a decline with increasing body mass, and animals in poor and excellent body condition had similar δ15N values. In addition, female ground squirrels from the same group with access to similar types of food (natural or supplemented) and with similar body masses, BUN, and blood glucose concentrations showed a difference of up to 1.8 in δ15N values. Thus, our results suggest that the ecological process (i.e., diet selection) may have obscured the physiological one (i.e., recycling of nitrogen). Therefore, we recommend that field ecologists studying animal diets using stable-isotope analysis use alternative techniques when attempting to evaluate the body condition of their subjects.