bluuebunny/crossref_metadata_2025 huggingface dataset:
Chromosomal Toxin-Antitoxin Systems May Act as Antiaddiction Modules
Authors: Saavedra De Bast Manuel , Mine Natacha , Van Melderen Laurence
Published: April 2008

Toxin-antitoxin (TA) systems are widespread among bacterial chromosomes and mobile genetic elements. Although in plasmids TA systems have a clear role in their vertical inheritance by selectively killing plasmid-free daughter cells (postsegregational killing or addiction phenomenon), the physiological role of chromosomally encoded ones remains under debate. The assumption that chromosomally encoded TA systems are part of stress response networks and/or programmed cell death machinery has been called into question recently by the observation that none of the five canonical chromosomally encoded TA systems in the
Escherichia coli
chromosome seem to confer any selective advantage under stressful conditions (V. Tsilibaris, G. Maenhaut-Michel, N. Mine, and L. Van Melderen, J. Bacteriol. 189:6101-6108, 2007). Their prevalence in bacterial chromosomes indicates that they might have been acquired through horizontal gene transfer. Once integrated in chromosomes, they might in turn interfere with their homologues encoded by mobile genetic elements. In this work, we show that the chromosomally encoded
Erwinia chrysanthemi ccd
(
c
ontrol of
c
ell
d
eath) (

ccd
Ech

) system indeed protects the cell against postsegregational killing mediated by its F-plasmid
ccd
(
ccd
F
) homologue. Moreover, competition experiments have shown that this system confers a fitness advantage under postsegregational conditions mediated by the
ccd
F
system. We propose that

ccd
Ech

acts as an antiaddiction module and, more generally, that the integration of TA systems in bacterial chromosomes could drive the evolution of plasmid-encoded ones and select toxins that are no longer recognized by the antiaddiction module.
Glucomannan-Mediated Attachment ofRhizobium leguminosarumto Pea Root Hairs Is Required for Competitive Nodule Infection
Authors: Williams Alan , Wilkinson Adam , Krehenbrink Martin , Russo Daniela M. , Zorreguieta Angeles , Downie J. Allan
Published: April 2008

TheRhizobium leguminosarumbiovar viciae genome contains several genes predicted to determine surface polysaccharides. Mutants predicted to affect the initial steps of polysaccharide synthesis were identified and characterized. In addition to the known cellulose (cel) and acidic exopolysaccharide (EPS) (pss) genes, we mutated three other loci; one of these loci (gmsA) determines glucomannan synthesis and one (gelA) determines a gel-forming polysaccharide, but the role of the other locus (anexoY-like gene) was not identified. Mutants were tested for attachment and biofilm formation in vitro and on root hairs; the mutant lacking the EPS was defective for both of these characteristics, but mutation ofgelAor theexoY-like gene had no effect on either type of attachment. The cellulose (celA) mutant attached and formed normal biofilms in vitro, but it did not form a biofilm on root hairs, although attachment did occur. The cellulose-dependent biofilm on root hairs appears not to be critical for nodulation, because thecelAmutant competed with the wild-type for nodule infection. The glucomannan (gmsA) mutant attached and formed normal biofilms in vitro, but it was defective for attachment and biofilm formation on root hairs. Although this mutant formed nodules on peas, it was very strongly outcompeted by the wild type in mixed inoculations, showing that glucomannan is critical for competitive nodulation. The polysaccharide synthesis genes aroundgmsAare highly conserved among other rhizobia and agrobacteria but are absent from closely related bacteria (such asBrucellaspp.) that are not normally plant associated, suggesting that these genes may play a wide role in bacterium-plant interactions.
Variants within theCOL5A1gene are associated with Achilles tendinopathy in two populations
Authors: September A V , Cook J , Handley C J , van der Merwe L , Schwellnus M P , Collins M
Published: April 2008

Objectives:

ACOL5A1gene variant was shown to be associated with chronic Achilles tendinopathy in a South African population. The aim of this case–control genetic association study was to investigate theBstUI andDpnII restriction fragment length polymorphisms (RFLP) in a second population from Australia and to identify a predisposing haplotype for Achilles tendinopathy in both populations.

Methods:

85 Australian and 93 South African patients with tendinopathy, as well as 210 Australian and 132 white South African control subjects were genotyped for theBstUI (rs12722) andDpnII (rs13946) RFLP, as well as markersrs10858286,rs3196378,rs11103544,rs4504708 andrs3128575.

Results:

TheBstUI RFLP (p<0.001) and markerrs3196378 (p = 0.016) were associated with chronic Achilles tendinopathy in Australian subjects. Individuals within both populations with a CC genotype for theBstUI RFLP had a significantly decreased risk of developing tendinopathy versus any other genotypes (Australian odds ratio 0.42, 95% CI 0.20 to 0.86, p = 0.017). The TC inferred haplotype (rs12722,rs3196378) was found to be overrepresented (global p = 0.008) in the South African tendinopathy group compared with all other haplotypes.

Conclusion:

TheBstUI RFLP is associated with chronic Achilles tendinopathy in a second population and a region within theCOL5A13′ untranslated region may predispose individuals to an increased risk of developing chronic Achilles tendinopathy.
Evaluation of strength and set behavior of mortar containing shotcrete set accelerators
Authors: Kim Jincheol , Ryu Jonghyun , Hooton R. D.
Published: April 2008

The influence of rapid-set accelerating admixtures on the setting behavior and early-age strength of a cement matrix was investigated to evaluate the appropriateness of the specification and test methods for shotcrete set accelerators. The results verified two different rapid setting behaviors according to the types of accelerator. The aluminate-base and the calcium aluminate cement-base accelerators facilitate hydration by formation of a calcium aluminate solid solution, whereas the alkali-free set accelerating agents present rapid setting time by the formation of ettringite. It was also found that the Vicat test was more desirable than the Gillmore test as the standard for setting time evaluation. Additionally, the cement mortar mixed with the aluminate-base and the calcium aluminate cement-base accelerators exhibited very fast development of early-age compressive strength. However, most of the set accelerators, except for alkali-free accelerators, failed to satisfy the specification because of greater than 40% compressive strength loss at 28 d.
Neural-network-based cycle length design for real-time traffic control
Authors: Kim Jin-Tae , Lee Jeongyoon , Chang Myungsoon
Published: April 2008

Adaptive traffic control systems (ATCS) are designed to calculate traffic signal timings in real time to accommodate current traffic demand changes. A conventional off-line computer-based design procedure that uses iterative evaluations to select alternatives may not be appropriate for ATCS due to its unstable searching time. Search-free analytical procedures that directly find solutions have been noted for ATCS for this reason. This paper demonstrates (i) the shortcomings of an analytical cycle-length design model, specifically COSMOS, in its ability to generate satisfactory solutions at various saturation levels and (ii) an artificial neural network (ANN) based model that can overcome these shortcomings. The ANN-based model consistently yielded cycle lengths that ensure a proper operational target volume to capacity (v/c) ratio, whereas the use of the analytical model resulted in unstable target v/c ratios that might promote congestion.
A comparison of body condition and reproduction of caribou on two predator-free arctic islands
Authors: Ouellet Jean-Pierre , Heard Douglas C. , Boutin Stan , Mulders Robert
Published: April 2008

To examine the relationships between body condition, pregnancy, and population dynamics in predator-free caribou (Rangifer tarandus groenlandicus), 147 females of the rapidly increasing Southampton Island herd were collected during the spring (n = 100) and autumn (n = 47) from 1988 through 1991 to assess their reproductive status and body condition (i.e., fat and muscle reserves). Caribou had been hunted to extinction on Southampton Island by 1953. Forty-eight animals were transferred from Coats Island to Southampton Island in 1967. During this study, caribou population density on Southampton Island was low and range quality high in both summer and winter. Results were compared with previously published data from the winter food limited Coats Island herd. On Southampton Island, 1-year-old or older caribou showed no annual or seasonal variation in body condition, and the pregnancy rate was exceptionally high (97%; n = 93). All 21 yearling females and 69 of 72 older females were pregnant. Southampton Island caribou were lighter and had less fat in autumn than Coats Island caribou, but Southampton Island caribou were both heavier and fatter in spring. This result suggests that the autumn "set point" in body composition (the maximum amount of body reserves animals attempt to acquire by autumn) may not be fixed as is usually assumed but may vary in response to winter feeding conditions. Pregnancy in yearlings does not preclude pregnancy when the animals are 2 years old. The ability to maintain large body reserves into the late stages of pregnancy could explain this finding. Finally, comparisons with other studies suggest that body condition and pregnancy rate, particularly for yearlings, are at least partly density dependent in predator-free caribou populations.
Dopaminergic modulation of spontaneous activity in the brain of the crayfishCherax destructor(Decapoda, Crustacea)
Authors: Johansson Kjell U. I. , Schmidt Manfred
Published: April 2008

The role of dopamine in the crayfish (Cherax destructor) brain was studied in an isolated head preparation by means of extracellular recordings from unidentified neurons located in the circumoesophageal connectives. Perfusion of dopamine and the dopamine receptor agonist (±)-2-amino-6,7-dihydroxy-1,2,3,4-tetrahydronaphthalene hydrobromide into the brain induced excitatory as well as inhibitory modulation of spontaneous activity. The physiological effects of both drugs were reversible and showed concentration dependency in the concentration range 10−7to 10−3 M. Two vertebrate-derived dopamine receptor antagonists, chlorpromazine and fluphenazine, reversibly blocked the action of dopamine (10−5 M). The threshold for antagonistic blockade by chlorpromazine and fluphenazine occurred at a relatively low concentration (10−7 M) and was concentration dependent. These data collectively suggest that dopamine plays a physiological role in the crayfish brain, stimulating putative dopamine receptor(s) to alter neuronal activity.
Drift diving in female northern elephant seals: implications for food processing
Authors: Crocker Daniel E. , Boeuf Burney J. Le , Costa Daniel P.
Published: April 2008

We tested predictions from the hypothesis that northern elephant seals, Mirounga angustirostris, drift during the bottom segment of some dives (called C dives) using oxygen saved from reduced locomotion to process food. Sixteen free-ranging dive records were obtained with microcomputer dive recorders attached to 13 adult females from Año Nuevo, California, during biannual foraging trips when they were in early or late stages of gestation; swim speed was recorded throughout one dive record. Body composition was measured before and after trips to sea. C dives with a bout length of 2 – 10 dives and a mean duration similar to those of other dive types made up 6.3 ± 1.9% of the dives recorded. Swim speed was near or below the recorder stall speed (0.22 m/s) during the second, drift segment of these dives. The rate of vertical depth change while drifting varied little within bouts, was initially significantly correlated with the ratio of fat to lean body mass at departure, and changed systematically as the seals fed while at sea. Females in early gestation, with initial mean body fat of 24%, drifted down at a mean rate of 0.31 ± 0.04 m/s; females in late gestation, with mean body fat approaching 36%, drifted up at an average rate of 0.17 ± 0.05 m/s. The frequency, duration, and temporal pattern of drift dives were correlated with foraging behavior, supporting the hypothesis that drifting while diving is associated with the metabolic cost of processing food. This study provides indirect support for the hypothesis that elephant seals suspend active swimming on certain dives, during which a greater proportion of oxygen stores is allocated to the processing of food, without interrupting the seals' normal pattern of continuous diving and allowing them to remain within their aerobic dive limit.
Temperature and family effects on muscle cellularity at hatch and first feeding in Atlantic salmon (Salmo salarL.)
Authors: Johnston Ian A. , McLay H. Anne
Published: April 2008

Muscle cellularity was investigated in alevins from five families of Atlantic salmon (Salmo salar L.) reared at variable ambient temperatures averaging 4.3 °C and in water heated to ca. 8 °C. At hatch, fish reared at 8 °C had fewer muscle fibres and myonuclei per myotome and lower mean fibre cross-sectional areas than fish reared at ambient temperature. The total cross-sectional area of white muscle was 40% less in the group reared at 8 °C than in the group reared at ambient temperature. Muscle cellularity and response to temperature varied among families and there was evidence of interactions with temperature and developmental stage. The number of red and white muscle fibres approximately doubled between hatch and first feeding. At hatch, red muscle fibres stained with an antibody to fast myosin light chains, but expression was gradually switched off as development proceeded. Following hatch, alevins reared at 8 °C were more effective in translating yolk into muscle than those reared at ambient temperature, so towards the end of yolk resorption there were no significant differences in fibre number or cross-sectional area.
Effects of environmental history, sibship, and age on predator-avoidance responses of tadpoles
Authors: Bridges Christine M. , Gutzke William H. N.
Published: April 2008

Gray treefrog (Hyla chrysoscelis) tadpoles exhibit predator-avoidance behaviors, such as increased refugium use, in the presence of predators. We presented tadpoles with waterborne chemical cues from predators and with epidermal extracts of conspecifics. We also examined whether responses of tadpoles are affected by the presence of a predator in the environment in which they were reared, by their developmental stage, or by genetic (family) effects. Predator cues significantly increased the tadpoles' use of a refugium. Although there was no effect due to age alone, there was a significant interaction between predator cues and age, indicating that tadpoles may exhibit predator avoidance at most vulnerable sizes. The degree of expression of this behavior is also dependent upon the environmental history of the organism (i.e., rearing condition), indicating that this response can interact with environmental conditions (i.e., composition of the predator community). Additionally, we found no differences among full-sib families, suggesting that predator avoidance in this species may be influenced more by the environment than by genes.
Redescription of Filaroides (Parafilaroides) gymnurus (Railliet, 1899) (Nematoda: Metastrongyloidea), with comments on other species in pinnipeds
Authors: Gosselin Jean-François , Measures Lena N.
Published: April 2008

The species Filaroides (Parafilaroides) gymnurus (Railliet, 1899) Anderson, 1978 is redescribed, based on examination of mature fifth-stage specimens from wild infected ringed seals (Phoca hispida), harp seals (Phoca groenlandica), harbour seals (Phoca vitulina), and grey seals (Halichoerus grypus) collected in eastern and arctic Canadian waters. Mature specimens of Filaroides (Parafilaroides) hispidus Kennedy, 1986 from ringed seals and grey seals were also examined. Comparison of these worms with museum specimens and the literature led to a review of species in the subgenus Parafilaroides (Dougherty, 1946) Anderson, 1978. Filaroides (Parafilaroides) gymnurus (Railliet, 1899) Anderson, 1978, F. (P.) decorus (Dougherty and Herman, 1947) Anderson, 1978, F. (P.) hydrurgae (Mawson, 1953) Kennedy, 1986, and F. (P.) hispidus Kennedy, 1986 are recognized as valid species. Filaroides (Parafilaroides) arcticus (Delyamure and Alekseev, 1966) Kennedy, 1986 and F. (P.) krascheninnikovi (Yurakhno and Skrjabin, 1971) Kennedy, 1986 are synonymized with F. (P.) gymnurus (Railliet, 1899) Anderson, 1978. Filaroides (Parafilaroides) caspicus (Kurochkin and Zablotsky, 1958) Kennedy, 1986 is considered a species inquirenda.
Seasonal movements of lake sturgeon in Lake of the Woods and the Rainy River, Ontario
Authors: Rusak J. A. , Mosindy T.
Published: April 2008

Lake sturgeon (Acipenser fulvescens) inhabiting the southern portion of Lake of the Woods and the Rainy River, a north-temperate watershed straddling the Canada – United States border, were studied to test hypotheses concerning seasonal movement patterns, including spawning migrations, and habitat use. We implanted radio transmitters into 26 fish and monitored seasonal movements during 3 consecutive years. Data indicated the existence of two discrete populations of sturgeon in this watershed, differentiated by seasonal habitat use, movement patterns and rates, and timing of spawning. The "lake" population, a designation suggested by a consistent preference for lentic winter habitat, appeared to spawn and initiate extensive spring and summer movements later than the "river" population, which consistently inhabited the river during the winter months. Overall, movement rates were significantly greater in the spring and summer months than at other times of the year and decreased with water temperature. General preferences exhibited by lake sturgeon for certain habitat types at different times of the year appeared to be linked to foraging behaviour. The results suggest that population differentiation may be prevalent for this species inhabiting large lake–river systems, given some diversity in habitat structure and spawning cues. In management efforts, this potential should be taken into consideration and reflected.
The contribution of insulation changes to the energy cost of avian molt
Authors: Schieltz Paul C. , Murphy Mary E.
Published: April 2008

To evaluate the contribution of changes in plumage insulation to the energy cost of molt, we measured oxygen consumption by wintering White-crowned Sparrows (Zonotrichia leucophrys gambelii) before and after plucking 12, 24, or 36% of their plumage, and when they were replacing these feathers. Measurements were made at 20 and 25 °C, two temperatures bracketing the lower critical temperature (ca. 23 °C) of wintering Z. l. gambelii, and at 10 °C, well below the birds' lower critical temperature. For comparison, oxygen consumption by naturally molting birds was measured at 25 °C during summer. In these sparrows, feather loss resulted in increased oxygen consumption only at 10 °C and when feather loss was moderate (24% plumage; 10% increase) to intensive (36% plumage; 24% increase). Regrowth of 24 and 36% of plumage resulted in increased oxygen consumption at 20 °C (10 and 8.5%, respectively) and 10 °C (16 and 28%, respectively). Oxygen consumption by birds was unaffected by loss or regrowth of 12% of the plumage regardless of temperature, and at 25 °C, oxygen consumption was unaffected by the intensity of plumage replacement (0–36%). Comparison of oxygen consumption at 25 °C between naturally molting summer birds and treated winter birds revealed that the energy cost of molt and the apparent energy inefficiency of molt result neither from added thermoregulatory costs nor from the costs of feather synthesis per se, but seemingly from metabolic changes entrained by molt.
Exposure of Spectacled Eiders and other diving ducks to lead in western Alaska
Authors: Flint Paul L. , Petersen Margaret R. , Grand J. Barry
Published: April 2008

Lead poisoning, resulting from ingestion of spent shot, has been identified as a cause of mortality in Spectacled Eiders (Somateria fischeri) on the Yukon–Kuskokwim Delta, Alaska. We examined lead-exposure rates of adult and juvenile Spectacled Eiders and other diving ducks, using atomic absorption spectrophotometry of blood samples. Additionally, we X-rayed birds in the field to identify ingested shot. We detected shot in the gizzards of 11.6% of Spectacled Eiders X-rayed. During the period from arrival through incubation, 13.0% of adult females and 6.6% of adult males had elevated blood lead levels when captured. During the brood-rearing period, 35.8% of adult females and 12.2% of ducklings were exposed to lead when captured. There was an increase in the probability of exposure of adult females with date sampled. We predict that 50% of the successfully breeding hens were likely exposed to lead, and 25–37% of the Spectacled Eider breeding population was exposed to lead. The long-term effects of sublethal doses on Spectacled Eiders are unknown; however, exposure of nesting females and young birds to lead may result in reduced over-winter survival and (or) reduced fecundity.
Thermosensibilité des lignées germinales de Trichogramma brassicae Bezdenko (Hymenoptera). Conséquences sur l'efficacité du parasitoïde
Authors: Chihrane J. , Laugé G.
Published: April 2008

Trichogramma brassicae, a parasitoid used in the biological control of the European corn borer, Ostrinia nubilalis, becomes less effective if certain thermal conditions prevail at the time of its release. A laboratory study demonstrated that the generation liberated in the field had reduced fecundity and that the proportion of females was lower in the following generation. These results prompted us to examine the germ lines of the parasitoid. Exposure to a temperature of 35 °C at the white nymph stage does not affect ovarian function, but exposure to 44 °C does: the number of mature ovocytes at emergence is lower than that observed in controls; certain ovaries are abnormal or remain juvenile. At the time of emergence, the seminal vesicles of male controls contain large numbers of typical sperm and a few atypical sperm, the latter becoming more numerous in males exposed to 35 °C. After exposure to 44 °C, vesicles contain only a few sperm or are completely empty. Since T. brassicae is an arrhenotokous parthenogenetic species (unfertilized eggs become males), these observations explain the reduced number of females in the second generation.[Journal translation]
Length–biomass and energy relationships of terrestrial gastropods in northern forest ecosystems
Authors: Hawkins J. W. , Lankester M. W. , Lautenschlager R. A. , Bell F. W.
Published: April 2008

Length–biomass models are a convenient and time-efficient method of estimating the biomass of invertebrates. Our purpose was to develop such a model for terrestrial gastropods that adequately predicted gastropod dry tissue biomass (Y) on the basis of animal length (X). The power equation Y = 0.172X1.688(r2 = 0.85) proved to be the best model for this purpose. Gastropod dry tissue biomass was 6.52 ± 1.58 mg (mean ± SE) and, based on gastropod densities ranging from 2 to 38/m2reported in the literature, snails and slugs active on the surface of the forest floor accounted for 2.5 and 6% of the total animal biomass and energy, respectively, of boreal forest ecosystems. However, because densities of gastropods in both the litter and underlying soil can reach 1607/m2, our results suggest that published values for total animal biomass (4.9 g/m2) and caloric energy (104 cal/m2) in boreal forest ecosystems are underestimated.
Effects of murre nest site characteristics and wind conditions on predation by glaucous gulls
Authors: Gilchrist H. Grant , Gaston Anthony J.
Published: April 2008

Glaucous gulls, Larus hyperboreus, are the primary predator of thick-billed murre, Uria lomvia, eggs at arctic breeding colonies. This study used eggs placed experimentally on murre nesting ledges to test the effects on glaucous gull foraging success of (i) murre nesting density; (ii) murre group defence; (iii) nesting ledge width; (iv) timing of murre laying; and (v) wind speed. Defensive responses by murres increased egg survival times, and gull foraging success was reduced by high murre nesting density. The timing of murre egg laying and ledge width also influenced the effectiveness of murre defence within the colony. Eggs placed following the peak of murre egg laying survived longer than eggs placed on the same nest sites prior to the peak. Murres without eggs early in the season often abandoned the group when attacked, leaving experimental eggs and brooding murres vulnerable to gulls. Gulls had difficulty reaching exposed eggs on narrow ledges when foraging on foot. At wind speeds greater than 15 km/h, however, egg survival was independent of ledge width because wind increased the maneuverability of gulls in flight and enabled them to reach narrow ledges. Murre defence at high nesting densities was also less effective on narrow ledges. Apparently, murres had difficulty rotating on their nest sites to face attacking gulls without dislodging their eggs. We conclude that moderate wind speeds enhanced the ability of gulls to reach narrow ledges and avoid contact with defending murres while stealing eggs. Consequently, the vulnerability of murre nest sites depended on wind conditions at the colony.
Communal nesting in prairie voles (Microtus ochrogaster): formation, composition, and persistence of communal groups
Authors: Getz Lowell L. , McGuire Betty
Published: April 2008

We describe factors related to the formation, composition, and persistence of communal groups in the prairie vole (Microtus ochrogaster). Communal groups formed by the addition of philopatric offspring and unrelated adults to male – female pair and single-female breeding units. Although unrelated adults did not join a group until at least two philopatric offspring 30 days of age were present, there was no relationship between the presence of reproductively active philopatric offspring of the opposite sex and joining of unrelated adults. Most adults that joined a group were reproductive when they joined. Reproductive activation of philopatric offspring was not related to the joining of unrelated adults. During the breeding period all communal groups included 1 or more reproductive adults of each sex; in at least 75% of the groups, 2 or more adults of each sex were reproductive. There was no relationship between low temperature, snow cover, or population density and formation of communal groups. Dissolution of communal groups was not related to reproductive activation of residents.
Intraspecific variation in mitochondrial DNA of muskoxen, based on control-region sequences
Authors: Groves Pamela
Published: April 2008

The muskox (Ovibos moschatus) is thought to have experienced significant genetic bottlenecks. Despite these bottlenecks, two subspecies of muskox, O. m. wardi and O. m. moschatus, have been commonly accepted, based on morphological differences and geographic separation. The reintroduction of muskoxen to Alaska from Greenland has created a situation in which the proposed subspecies might meet and interbreed as the Alaskan (O. m. wardi) and mainland Canadian (O. m. moschatus) populations expand their ranges. To attempt to define subspecific differences and investigate the appropriateness of potential interbreeding of Alaskan and Canadian mainland muskoxen, control-region sequences of mitochondrial DNA were compared among 37 muskoxen. Extremely little variation was found among all the muskoxen sampled. These results do not allow definition of muskox subspecies and suggest that the different populations may already have mixed. The low levels of variability further support historical and archaeological evidence of repeated bottlenecks throughout the history of the species.
Temporal drop-off pattern of juvenile Ixodes pacificus (Acari: Ixodidae)
Authors: Vredevoe L. K. , Kimsey R. B. , Richter P. J.
Published: April 2008

We determined the temporal drop-off pattern of juvenile western black-legged ticks, Ixodes pacificus Cooley and Kohls, by recording the time of day that replete ticks dropped off common laboratory-reared and field-caught rodents. The majority of subadult ticks dropped during daylight hours. Larvae that attached to nocturnally active murid or diurnal sciurid rodents left their hosts during slightly different periods of the day. Larvae primarily departed from murids between 14:00 and 18:00 and from sciurids between 10:00 and 14:00. Drop-off of nymphs from rodents was significantly greater between 14:00 and 18:00 than between 18:00 and 06:00, although nymphs tended to leave BALB/c white mice earlier in the day. Because subadult ticks leave diurnally or nocturnally active hosts at the same time of day, drop-off appears to be independent of the temporal patterns of host activity. Diurnal drop-off will result in engorged ticks remaining in the nests of nocturnal hosts but dropping to the ground from diurnal hosts. Thus, we propose that temporal patterns of host activity mediate the spatial distribution of I. pacificus.
Ecological relationships between two sympatric congeneric species, Common Murres and Thick-billed Murres,Uria aalgeandU.lomvia, breeding in the Barents Sea
Authors: Barrett R. T. , Asheim M. , Bakken V.
Published: April 2008

Concurrent studies of the breeding ecology of Common Murres and Thick-billed Murres, Uria aalge and U. lomvia, on Hornøya, a colony in northern Norway, showed significant differences between the species in the timing of egg laying but no consistent differences in food choice, feeding frequency and rhythm, dive depth, or chick growth. Both species fed their chicks on capelin, Mallotus villosus, sand lance Ammodytes sp., and herring Clupea harengus. However, on Bear Island in the Barents Sea, the diet differed significantly, with Common Murre chicks being fed nearly exclusively capelin while Thick-billed Murre chicks received capelin, squid Gonatus fabricii, Arctic cod, Boreogadus saida, sculpins (Cottidae), shannies Lumpenus sp., and eelpouts (Zoarcidae). The lack of dietary segregation on Hornøya was in strong contrast with the results of earlier studies of sympatrically breeding murres and was probaby due to a near superabundance of food around the colony.
Effects of temperature and predator:prey ratio on feeding rate in larvae of Atherix lantha Webb (Diptera: Athericidae)
Authors: Hunter Fiona F. , Sadonoja Tami M.
Published: April 2008

Predator:prey experiments were conducted in the laboratory using snipe fly (Atherix lantha Webb) larvae as predators and hydropsychid caddisflies (Cheumatopsyche spp.) as prey. The effects on feeding rate of two different temperature regimes (20 and 10 °C) and five different predator:prey ratios (3:1, 2:1, 1:1, 1:2, 1:3) were tested. The number of caddisflies consumed per A. lantha larva per day was significantly greater at 20 °C than at 10 °C for the 2:1, 1:1, and 1:2 ratios (2×, 7×, and 2× greater, respectively). There were no significant differences between the 20 and 10 °C treatments at either the 3:1 or 1:3 ratio.
Fetal sex ratio in relation to maternal mass and age in reindeer
Authors: Reimers Eigil , Lenvik Dag
Published: April 2008

Theory suggests that a male in good condition at the end of the period of parental investment will outproduce a sister in similar condition, while she will outproduce him if both are in poor condition. Accordingly, natural selection should favor parental ability to adjust the sex ratio of offspring produced according to parental ability to invest. As maternal condition declines from good to poor, the fetal sex ratio should decline from a high proportion of males to a high proportion of females. Data from 1525 domestic reindeer (Rangifer tarandus) in six different herds slaughtered during December and January in 1976 through 1979 do not support a relationship between the sex of the fetus and either the condition of the mother or her age.
The ontogenetic development of body segments and sexual dimorphism in brown trout (Salmo trutta L.)
Authors: Reyes-Gavilán F. G. , Ojanguren A. F. , Braña F.
Published: April 2008

Nonmigratory brown trout (Salmo trutta L.) from northern Spain showed no between-sex differences in total length or mass and only moderate, but significant, dimorphism in some morphometric traits. The main dimorphic features were the sizes of the abdomen (larger in females) and head (larger in males, including the upper jaw), relative to each other and also to the post-anal length, the latter being considered a control for body size. Least-squares linear regressions of head length on abdomen length were homogeneous in both the slopes and the intercepts for immature fish of both sexes, but mature males exhibited significantly steeper slopes than mature females. Within each sex the slopes for immature and mature fish were homogeneous, and mature fish of both sexes had higher intercepts than immature ones. Therefore, immature individuals were monomorphic and mature individuals of both sexes diverged from the juvenile pattern, each in a particular fashion: males acquired a greater relative head length (particularly a longer jaw) and females a greater relative abdomen length. Sexual selection for larger head size relative to body size in males and fecundity selection for larger abdomen size relative to body size in females are hypothesized to be important in the evolution of sexual dimorphism in brown trout.
Sexual dimorphism and evidence for intrasexual selection from quill impalements, injuries, and mate guarding in porcupines (Erethizon dorsatum)
Authors: Sweitzer Richard Alan , Berger Joel
Published: April 2008

Sexual selection is a commonly cited explanation for sexual size dimorphism. We examined patterns of sexual dimorphism in North American porcupines (Erethizon dorsatum) and used data on quill impalements, injuries, and guarding behavior to examine the intrasexual component of sexual selection among male porcupines. Results indicated that porcupines were sexually dimorphic for foot-pad length, body length, and body mass because males grew more rapidly and for longer periods than females. Quill impalements, injuries, and guarding episodes were restricted predominantly to older, larger males, intimating that only the largest porcupines were reproductively active. Regression analyses suggested that size was more important than age in predicting reproductive activity among males. Also, relatively few quill impalements and guarding episodes among younger, smaller animals suggest that there is a threshold size below which male porcupines do not attempt to compete for mate access. Although our data do not directly link larger body size in males with relatively high reproductive success, they suggest that sexual dimorphism in this species is at least partly the result of the intrasexual component of sexual selection. It is also possible that females select males on the basis of quill morphology or some other indicator of male quality. Thus, our understanding of sexual dimorphism in porcupines would benefit from additional research investigating the extent to which body size and patterns of quill number or size are advantageous to male porcupines in garnering mating opportunities and enhancing fitness.
Developmental stability in perch (Perca fluviatilis) in acidic aluminium-rich lakes
Authors: Østbye Kjartan , Øxnevad Sigurd A. , Vøllestad Leif Asbjørn
Published: April 2008

Fluctuating asymmetry is defined as random deviation from perfect bilateral symmetry resulting from environmental or genetic disturbances (termed developmental noise) during early embryonic development. Developmental instability is defined as the inability of an organism to follow the a priori defined growth trajectory that results in perfect bilateral symmetry, owing to insufficient buffering of the disruptive effects of developmental noise during development. Fluctuating asymmetry has been proposed for use as a measure of developmental instability. In this study we tested whether fluctuating asymmetry can be an early indication of acidification stress. Samples were taken from 10 perch (Perca fluviatilis) populations exposed to varying pH levels and aluminium concentrations. We scored 13 bilateral meristic and morphometric characters to assess fluctuating asymmetry. The level of fluctuating asymmetry in the mandibular pores and one index summarizing three of the meristic characters were significantly correlated with the acidification level. When the lakes were split into two groups, "acidified" and "control," each consisting of five lakes, the same pattern emerged. The variance of fluctuating asymmetry estimates was larger in the acidified lakes than in the control lakes. These findings imply that perch in acidic environments experience developmental perturbations during early embryogenesis, resulting in deviating bilateral morphology. The variation in fluctuating asymmetry among lakes was at the same level as previously found among age groups within one acidified lake. Based on these findings, the use of fluctuating asymmetry as a management tool to evaluate the viability of fish populations in acidified waters is of limited value unless a more comprehensive approach is used.
Decrease in litter size in the shrew Crocidura suaveolens (Mammalia, Insectivora) from Corsica (France): Evolutionary response to insularity?
Authors: Fons Roger , Poitevin Françoise , Catalan Josette , Croset Henri
Published: April 2008

Populations of the lesser white-toothed shrew, Crocidura suaveolens (Pallas, 1811), from Corsica show an increase in adult body size associated with a decrease in litter size. The average number of embryos in wild Corsican females is smaller (mean 2.6, n = 62) than in mainland females (mean 4.6, n = 173). A breeding experiment was run for 4 years, yielding three generations. Under standard breeding conditions, the differences between island and mainland populations were maintained and were significant (median litter size was 2 for Corsica and 5 for the mainland). These differences in life-history traits were therefore proved experimentally to be genetically determined. Hypotheses concerning the mechanisms responsible for these differences are discussed.
Ascites, premature emergence, increased gonadal cell apoptosis, and cytochrome P4501A induction in pink salmon larvae continuously exposed to oil-contaminated gravel during development
Authors: Marty Gary D. , Hinton David E. , Short Jeffrey W. , Heintz Ronald A. , Rice Stanley D. , Dambach Donna M. , Willits Neil H. , Stegeman John J.
Published: April 2008

Development of pink salmon (Oncorhynchus gorbuscha) incubating in gravel contaminated with weathered Prudhoe Bay crude oil was retarded at concentrations as low as 55.2 μg oil/g gravel. Larvae exposed to various levels of oil contamination were sampled 4 weeks before emergence, at emergence, and 13 days after emergence for histopathology (quantitative and semiquantitative) and cytochrome P4501A (CYP1A) induction (using immunohistochemical staining). A subset of postemergent fish was not fed. Hydrocarbon analysis by gas chromatography and mass spectroscopy revealed that tissue uptake of polynuclear aromatic hydrocarbons (PAH) was mediated by oil's dissolution in water, with significant biological effects when the peak total PAH concentration in water was as low as 4.4 μg/L. Oil-related effects included induction of CYP1A, development of ascites, and increased mortality. Several oil-related changes were indicative of premature emergence. Compared with control fish, for example, exposed fish of the same age and emerging on the same day had greater amounts of yolk and hepatocellular glycogen, increased apoptosis of gonadal cells and midventral skin cells, and less food in the gastrointestinal tract. Histological features were similar within groups of larvae sampled 4 weeks before and 13 days after emergence, and oil-induced changes were not affected by feeding during the first 13 days after emergence. Increased gonadal cell apoptosis may be related to later reproductive impairment documented in field studies of pink salmon up to 4 years after the Exxon Valdez oil spill.
Hatching success and larval survival of the frogsHyla regillaandRana auroraunder ambient and artificially enhanced solar ultraviolet radiation
Authors: Ovaska Kristiina , Davis Theodore M. , Flamarique Iñigo Novales
Published: April 2008

The aquatic stages of amphibians may be sensitive to increased levels of solar ultraviolet B radiation (UV-B, 280–320 nm) that have been observed at higher latitudes over the past several decades, but the effects on most species are unknown. We exposed eggs and larvae of Hyla regilla and Rana aurora to three experimental treatments: (1) solar UV < 450 nm blocked (control), (2) ambient solar UV, and (3) solar UV-B enhanced 15 and 30% above ambient levels at midday to simulate conditions predicted for the next decades at midlatitudes. The rearing containers were covered with acrylic filters to provide the desired radiation regimes. Hatching success of H. regilla did not differ among the treatments and was 87.7, 71.8, and 87.1% in April 1995 and 94.0, 85.1, and 97.4% in May 1995 for the control, ambient, and enhanced UV-B treatments, respectively. In contrast, hatching success of R. aurora in the enhanced UV-B treatment (56.0%) was lower than in the ambient UV (89.8%) and control (81.0%) treatments. Larval survival over the first 2 months of development was reduced to 18.4% for H. regilla and 2.6% for R. aurora in the enhanced UV-B treatment compared with the ambient UV and control treatments. We conclude that ambient UV levels at the study site did not affect the embryonic or early larval survival of either of the species tested under the experimental conditions, but both species are potentially vulnerable to increases in solar UV-B.
Lung-liquid production in vitro by lungs from fetal guinea pigs: effects of amiloride on responses to aldosterone
Authors: Perks A. M. , Stockbrocks M. , Chuang D. C. , Muhll I. Vonder , Kindler P. W.
Published: April 2008

Lungs from near-term fetal guinea pigs (62 ± 2 days of gestation) were supported in vitro for 3 h; lung-liquid production was monitored by a dye-dilution method based on Blue Dextran 2000. Untreated preparations produced fluid at 1.26 ± 0.14 mL∙kg−1body mass∙h−1, with no significant change over the ensuing hours (ANOVA, regression analysis; n = 16). Experimental preparations received aldosterone at plasma concentrations reported to be present at birth. Aldosterone produced rapid, significant reductions in fluid production, and occasionally reabsorptions, which persisted beyond treatment. Reductions during treatment were as follows: 10−8 M aldosterone, 90.8 ± 4.9% (P < 0.001; n = 4); 2 × 10−9 M aldosterone, 64.1 ± 16.6% (P < 0.05–0.001; n = 6), and 7 × 10−10 M aldosterone, 48.6 ± 11.7% (P < 0.005–0.001; n = 6). The linear log dose response curve (r = 0.99) showed a theoretical threshold at 3.4 × 10−11 M aldosterone. Responses to 7 × 10−10 M aldosterone were abolished by 10−6 M amiloride. At the highest concentration of aldosterone (10−8 M), 10−6 M amiloride significantly reduced responses, and the changes were no longer significant by ANOVA. At both high and low aldosterone concentrations, responses with amiloride were significantly lower than those without amiloride (ANOVA, P < 0.03–0.04). Amiloride controls and untreated preparations showed no significant changes in fluid production. It is concluded that aldosterone at plasma concentrations present at birth can cause reductions in lung-liquid production or reabsorption through effects on amiloride-sensitive Na+channels, and that the responses are remarkably rapid.
Evidence of a heritable component to body shape in the northern redbelly dace (Phoxinus eos)
Authors: Toline C. Anna , Baker Allan J.
Published: April 2008

Hypotheses about the role of selection on body-shape evolution assume a heritable component to this phenotypic character. To examine the influence of environmental induction on body shape, offspring form two morphologically differentiated populations of northern redbelly dace (Phoxinus eos) were reared in a common laboratory environment. Additionally, shape changes were monitored over 3 consecutive years in six populations. Offspring reared in a common environment retained the body shape of individuals from their natal pond, and shape changes among fish in different ponds were maintained in natural populations over years. These results strongly suggest a heritable component to body shape in P. eos. These results complement earlier work examining foraging tactics as a potential selection pressure on body shape and support the conclusion that body-shape differences among fish in different ponds are being maintained by selection for foraging ability.
A taxonomic reevaluation of North AmericanDaphnia(Crustacea: Cladocera). III. TheD.catawbacomplex
Authors: Hebert Paul D. N. , Finston Terrie L.
Published: April 2008

Despite the importance of Daphnia in freshwater zooplankton assemblages, species boundaries in the genus are unclear. This study verifies the taxonomic validity of D. catawba by establishing its genetic divergence from other species of Daphnia that occur in eastern North America. In addition, it reveals the presence of a second, closely allied species, D. minnehaha, which had previously been placed in synonomy with D. pulex. Daphnia catawba and D. minnehaha share a preference for acidic habitats and are restricted to the deciduous and boreal forest regions of the eastern portion of the continent, where D. catawba is restricted to lakes, while D. minnehaha occurs in ponds. Both species reproduce by cyclic parthenogenesis and, based on the extent of their allozyme differentiation, last had a common ancestor more than 7 million years ago. Populations of D. minnehaha fall into two genetic clades; those from the Great Lakes watershed are morphologically divergent and have much lower levels of genotypic diversity than those from eastern Canada and the New England states.
Early gonadal development and sexual differentiation in muskellunge (Esox masquinongy)
Authors: Lin Feng , Dabrowski Konrad , Timmermans Lucy P. M.
Published: April 2008

Primordial germ cells (PGCs) were first identified in muskellunge (Esox masquinongy) of 14 mm total length (TL) 3 weeks post fertilization. At 32 mm TL, gonad strings were complete and formed a typical gonad shape in cross section. Blood vessels were first found in the gonads with Crossmon staining at 46 mm TL. Some of the PGCs underwent mitotic division at this stage. The ovarian sac started to develop in a fish of 82 mm TL, while the germ cells were still considered to be undifferentiated. In a fish of 138 mm TL, female gonads could be clearly identified from the ovarian sac and groups of oogonia, whereas in another type of gonad, the morphology of undifferentiated gonads was maintained. Germ cells became numerous in both sexes at 211 mm TL. Female gonads contained lobes with germ cells, including oogonia, early-prophase oocytes, and large oocytes. Spermatogonia and cells undergoing mitosis were observed in the testis. Ovaries in a fish of 250 mm TL were at the early stage of perinucleolus (early diplotene). Our observations indicate that in muskellunge (i) the PGCs remained in a resting state for up to 8 weeks post fertilization, (ii) gametogenesis occurred earlier in females than in males, (iii) the gonads developed from an undifferentiated stage directly into an ovary or testis, and (iv) the somatic elements in the gonads differentiated prior to the germ cells.