bluuebunny/crossref_metadata_2025 huggingface dataset:
Pollock and the decline of Steller sea lions: testing the junk-food hypothesis
Authors: Rosen David AS , Trites Andrew W
Published: April 2011

The decline of Steller sea lions (Eumetopias jubatus) in the Gulf of Alaska and the Aleutian Islands may be the result of them eating too much pollock (a gadid fish) instead of a more balanced and diverse diet containing fattier fishes, such as herring or sandlance. We sought to test this junk-food hypothesis by feeding six captive Steller sea lions (ages 0.9-4.5 years) only pollock or herring. All sea lions gained mass while eating herring. However, eating only pollock for short periods (11-23 d) caused the study animals to lose an average of 6.5% of their initial body mass (0.6 kg/d) over an average feeding trial of 16 d (initial mass averaged 125 kg). The animals were allowed to eat as much pollock as they wanted but did not increase their food intake to compensate for the low energy they were receiving. The sea lions showed progressive metabolic depression while losing body mass on a pollock-only diet. The loss of body mass while eating pollock was due to the lower gross energy content of pollock versus herring, the higher cost of digesting pollock, and the increased energy loss from digesting the larger quantity of fish needed to compensate for the lower energy content of pollock. Thus, our sea lions would have had to eat 35-80% more pollock than herring to maintain similar net energy intakes. Results from our captive-feeding studies are consistent with the junk-food hypothesis and have serious implications for Steller sea lions that have been eating primarily pollock in the Gulf of Alaska and the Aleutian Islands.
Selective foraging in the white sucker (Catostomus commersoni)
Authors: Saint-Jacques Nathalie , Harvey Harold H , Jackson Donald A
Published: April 2011

The white sucker (Catostomus commersoni) is a widespread and often abundant North American species. This benthivore can play an important role in the ecology of both fish and benthic communities in lakes and streams. However, the feeding behaviour and ecology of the white sucker have received limited study beyond a description of gut contents from small samples of fish. In this study, the diet of white suckers was determined in relation to season and depth distribution of the fish, as well as to the abundance and type of zoobenthos sampled at the site of fish capture. Suckers fed predominantly on either zoobenthos or zooplankton, with some seasonal variation. They specialized on particular prey and also on the largest individuals within their "speciality," thus exhibiting both resource partitioning and size-selective predation. These findings demonstrate that white suckers can be extremely flexible in their use of resources as opposed to being simple generalist feeders. This attribute, plus their tolerance of a range of environmental conditions, partly explains the abundance of white suckers and their wide distribution in temperate lakes and streams.
Nematode parasite species richness and the evolution of spleen size in birds
Authors: Morand Serge , Poulin Robert
Published: April 2011

Some of the interspecific variation in spleen sizes among bird species can be explained by interspecific variation in the proportion of birds infected by parasitic nematodes. Because prevalences of parasitic infections vary considerably in space and time within a host species, other variables may provide better measures of the selective pressure exerted by parasites on their hosts. For instance, the number of parasite species (species richness) exploiting a host population or species provides a more reliable index of the pressure exerted by parasites across generations. Among bird species, relative spleen size correlated positively with the species richness of nematode parasites exploiting a host species. This relationship was found after correcting for avian body mass (g), avian phylogeny, and sampling effort. A possible trade-off between investment in resistance against parasites and investment in reproduction was highlighted by a negative relationship between relative spleen size and relative testis mass. Parasitic nematodes could influence the trade-off, increasingly favoring investment in resistance as their species richness increases. The results of this comparative analysis and of previous ones suggest a causative role for parasitic nematodes in the evolution of avian spleen size.
Microsculpture and phylogenetic significance of the spermatheca of black flies (Diptera: Simuliidae)
Authors: Evans Christopher L , Adler Peter H
Published: April 2011

The highly varied spermatheca of black flies provided an under-studied character system for phylogenetic reconstruction of the Simuliidae. Scanning electron microscopy of the spermatheca of 17 simuliid species elucidated folds and spicules on the inner surface; callosities, anastomosing ridges, and minute tubercles on the outer surface; and an intricately fluted spermathecal duct. The spermatheca of Parasimulium crosskeyi, the most plesiomorphic taxon, had a slightly wrinkled inner surface and an outer surface with acutely raised polygonal ridges. Species hypothesized to be among the basal lineages of the simuliids (e.g., Helodon susanae and Prosimulium magnum) had an irregularly folded inner spermathecal surface, but their relationships were not well resolved on the basis of information about the spermatheca. More evolutionarily derived species, including a number of species in the genus Simulium, had short or filiform spicules on the inner surface of the spermatheca. Although the use of a single character system, the spermatheca, did not fully resolve relationships among Simuliidae, its utility as a rich source of phylogenetic information was demonstrated.
Long-term effects of anthropogenic habitat disturbance on a lizard assemblage inhabiting coastal dunes in Argentina
Authors: Vega Laura E , Bellagamba Patricio J , Fitzgerald Lee A
Published: April 2011

We studied abundance and habitat use in two species of Liolaemus (Squamata: Tropiduridae) at a coastal dune site in eastern Argentina before and 7 years after a road was built at the site. Before disturbance, lizards exhibited similar abundances and a wide segregation in microhabitat use. Liolaemus multimaculatus used flat dunes scarcely covered by Spartina ciliata, while Liolaemus gracilis used the grass Panicum racemosum as cover. After disturbance, the mean number of L. multimaculatus detected by month was significantly less than that observed in the predisturbance period, owing to a drastic reduction in S. ciliata microhabitat patches. The mean number of L. gracilis was similar to that seen during the first period. These differences were clearly linked to habitat loss at the site. We concluded that human impact on the habitat structure of foredunes induced changes in the structure of the lizard assemblage, including shifts in the relative abundance of species and the proportional use of their preferred microhabitats.
Effects of weather and snow on habitat selection by American martens (Martes americana)
Authors: Wilbert Connie J , Buskirk Steven W , Gerow Kenneth G
Published: April 2011

To better understand how a species known to thermoregulate behaviorally switches among microsites and habitats in response to weather and snow, we studied influences of weather and snow conditions on resting by the American marten, Martes americana. Vertical location of resting sites varied with air temperature and snowfall during the previous 24 h. Subnivean resting was most likely when air temperature was low and when recent snowfall had been heavy, and tended to be in stands dominated by spruce-fir. Supranivean resting tended to occur when weather was warmer and when recent snowfall had been light, and tended to occur in stands dominated by lodgepole pine (Pinus contorta), the predominant conifer in the study area. Fidelity of martens to resting sites varied with season; martens reused sites more in winter than in spring, hypothetically a result of trading-off increased energy savings accrued from using a few especially efficient sites against longer distances traveled to reach them. Such travel may not be rewarded in warm weather. Stand characteristics associated with resting in cold snowy winter periods are typical of low disturbance frequencies, including old-growth conditions in the Rocky Mountains.
The evolution of adult body size in black-bellied salamanders (Desmognathusquadramaculatuscomplex)
Authors: Camp Carlos D , Marshall Jeremy L , Austin, Jr. Richard M
Published: April 2011

We investigated the possible role of environmental variables in determining body size within a complex of salamander species (Desmognathus quadramaculatus). We analyzed data generated from life-history studies on populations from throughout the range of this species complex. We incorporated an alternative-hypothesis framework (sensu Platt) to determine the better predictor of adult body size, age at maturity, or size at metamorphosis. We found that almost 90% of the variation in adult body size was explained by size at metamorphosis, which was determined by a combination of rate of larval growth and length of the larval period. Environmental temperature and moisture level were positively correlated with larval growth rate and length of the larval period, respectively. We propose a simple model of body-size evolution that incorporates both adaptive and plastic components. We suggest that the length of the larval period may adaptively respond to moisture-level predictability. In addition, we suggest that the response of the larval growth rate to temperature may be plastic. Because the selection pressure due to drying-induced mortality is pervasive among species of amphibians, it may have played a role in shaping body-size radiation in desmognathines as well as the ecological structure of Appalachian streamside communities.
Physiological effects of capturing Kemp's ridley sea turtles, Lepidochelys kempii, in entanglement nets
Authors: Hoopes Lisa A , Landry Jr. André M , Stabenau Erich K
Published: April 2011

Blood samples were collected from 58 wild Kemp's ridley sea turtles (Lepidochelys kempii) to examine the physiological effects of capture in entanglement nets. Captured turtles were placed in holding tanks or in-water cages to examine whether the postcapture holding protocol influenced the time course of recovery of blood homeostasis. Lactate concentrations at capture were 4.5 ± 0.3 and 3.5 ± 0.3 mmol/L (mean ± SE) for L. kempii assigned to the in-water-cage and holding-tank treatments, respectively. Turtles held in holding tanks for 1 h exhibited a significant increase in lactate concentration over capture levels, whereas lactate concentrations in the cage-held animals did not change. Lactate concentrations declined to less than 1.0 mmol/L by 6 and 10 h post capture for turtles in the in-water-cage and holding-tank treatments, respectively. Plasma norepinephrine (NE) and epinephrine (E) concentrations at capture were substantially elevated above base-line levels reported in the literature for comparably sized loggerhead sea turtles (Caretta caretta). Turtles in holding tanks exhibited greater reductions in NE and E at 1 h post capture than did their counterparts in the in-water cages. Although plasma Na+ and Cl- concentrations were not affected by entanglement netting, K+ concentration was elevated in tank-held L. kempii at 1 h post capture. Taken together, these data indicate that entanglement netting causes significant physiological disturbance in sea turtles and that recovery of blood homeostasis is influenced by the postcapture holding protocol.
Na+-dependent transport of pyruvate in erythrocytes of the Pacific hagfish (Eptatretus stouti)
Authors: Tiihonen Kirsti , Yao Sylvia YM , Nikinmaa Mikko , Young James D
Published: April 2011

We investigated the mechanisms of pyruvate transport in the erythrocytes of an ancient marine agnathan, the Pacific hagfish (Eptatretus stouti), and a sedentary euryhaline teleost, the starry flounder (Platichthys stellatus). Uptake of [14C]pyruvate (50 µM, 10°C) by flounder erythrocytes was slow (t1/2(half-life) ~ 30 min), nonconcentrative, and mediated by the band 3 Cl-/HCO-3exchanger in combination with a process similar to the H+/monocarboxylate symporter present in freshwater teleosts and mammalian erythrocytes. In contrast, pyruvate uptake by hagfish erythrocytes (50 µM, 10°C) was rapid (t1/2~ 1.5 min) and, in 10 min, reached an intracellular concentration more than 20-fold higher than that present in the extracellular medium. Pyruvate accounted for almost 90% of the accumulated intracellular radioactivity, the remaining label being incorporated into tricarboxylic acid cycle intermediates and glutamate. Influx of pyruvate was saturable (apparent Km= 12 mM) and inhibited by p-chloromercuriphenylsulphonate (PCMBS) (Ki= 71 µM) and 4,4'-diisothiocyanatostilbene-2,2'-disulphonate (DIDS) (Ki= 0.49 mM). Transport was inhibited poorly by α-cyano-4-hydroxycinnamate (CIN) (Ki> 4 mM) and was not coupled to the movement of protons. Instead, the influx of pyruvate was Na+dependent. A sigmoidal relationship between pyruvate transport and extracellular Na+concentration was observed, suggesting a Na+:pyruvate coupling ratio greater than 1:1. In contrast with previously described Na+-dependent monocarboxylate transport activities in mammalian renal and intestinal epithelia, the hagfish erythrocyte system did not transport lactate.
Are virgin male lepidopterans more successful in mate acquisition than previously mated individuals? A study of the European corn borer, Ostrinia nubilalis (Lepidoptera: Pyralidae)
Authors: Schlaepfer Martin A , McNeil Jeremy N
Published: April 2011

Male phenotypic quality may significantly influence female reproductive success. Depletion of sperm and accessory-gland secretions with successive matings represents a reduction in male phenotypic quality and is known to decrease female reproductive output in several lepidopteran species, including the European corn borer (ECB), Ostrinia nubilalis. We therefore tested the hypothesis that female ECBs, given the simultaneous choice of an experienced male and a virgin male, preferentially mate with the virgin. However, contrary to prediction, females mated significantly more often with experienced males. Experienced males were significantly lighter than their virgin counterparts, the result of producing three spermatophores that were transferred during previous matings. However, differences in body mass or wing-loading did not appear to play an important role, for within either the experienced or virgin classes, heavier males obtained more matings than lighter ones. Why would females prefer to mate with sexually experienced males? Females may not be exercising any precopulatory choice, and the greater mating success of previously mated males may be related to previous experience. Behavioral observations, however, suggest that female choice occurred. In the process of selecting experienced males, the number of consecutive matings was correlated with low fluctuating asymmetry of the forewing (R-L). This suggests that males who acquired 3 consecutive matings were of above-average quality and were actively selected by females.
Social organization of mammal-eating killer whales: group stability and dispersal patterns
Authors: Baird Robin W , Whitehead Hal
Published: April 2011

The social organization of mammal-eating "transient" killer whales (Orcinus orca) was studied off southern Vancouver Island from 1985 through 1996. Strong and long-term associations exist between individual transients, so sets of individuals with consistently high association levels, termed pods, can be delineated. Pods consist of individuals of mixed ages and sexes, and typically contain an adult female and one or two offspring (averaging 2.4 individuals). The mother-offspring bond remains strong into adulthood for some male (and less often for female) offspring. Other males disperse from their maternal pod and appear to become "roving" males, spending some of their time alone, and occasionally associating with groups that contain potentially reproductive females. These males appear to have no strong or long-term relationships with any individuals, and adult male - adult male associations occur significantly less often than expected by chance. Females that disperse from their natal pod appear to be gregarious (having high average association rates) but socially mobile (having low maximum association rates). Differences in social organization from the sympatric fish-eating "resident" killer whales (where no dispersal of either sex occurs) likely relate to differences in foraging ecology. Transient killer whales maximize per capita energy intake by foraging in groups of three individuals, whereas no such relationship has been documented for resident killer whales.
Activity-related constraints on overwintering young-of-the-year striped bass (Morone saxatilis)
Authors: Hurst Thomas P , Conover David O
Published: April 2011

The importance of activity to overwintering fishes has received little attention. Activity imposes two constraints: maximum swimming speed limits habitats that can be occupied for short periods of time, while the metabolic cost of swimming limits the habitats that are suitable for long-term residence. We measured the energetic consequences of activity and maximum swimming speeds of young-of-the-year striped bass (Morone saxatilis), a species that overwinters in tidal estuaries. The energetic cost of swimming was determined from energy changes in unfed fish forced to swim at various speeds, while energy changes in fed fish provided a measure of their ability to offset swimming costs through feeding. In high-velocity treatments, mortality was size-dependent and appeared to be related to fatigue rather than to depletion of energy reserves. The energetic cost of swimming increased with swimming velocity, but fish increased food consumption and thereby met their metabolic needs. In a second experiment the thermal dependence of swimming capacity in winter-acclimated striped bass was measured. Swimming speeds increased with temperature, from 2.7 body lengths (BL)/s at 2°C to 4.8 BL/s at 8 and 11°C, but were considerably below observed flow velocities in the Hudson River, suggesting a need for behavioral or physical refuge from tidal currents. These results indicate the flexibility of energy budgets of overwintering fishes, allowing energetic stress to be minimized by reducing activity or elevating food-consumption rates when sufficient prey are available.
Neuronal growth and target recognition: lessons from the leech
Authors: Baker Michael W , Macagno Eduardo R
Published: April 2011

The nervous system of the leech has been the subject of numerous studies since its "rediscovery" in the 1960s as a unique system for the study of the properties of glial cells. Subsequently, anatomical, physiological, and embryological studies of identified neurons have yielded a wealth of information about the differentiation of neuronal structure and function. In recent years, cellular approaches to the development of identified central and peripheral neurons have been complemented by molecular studies that promise to reveal the mechanisms by which neurons form their complex arbors and innervate specific targets.
Epithelial transport and osmoregulation in annelids
Authors: Clauss Wolfgang G
Published: April 2011

Epithelial transport related to osmoregulation has so far not been extensively investigated in annelids. Compared with the large body of information about ion transport across crustacean or insect epithelia, only a few studies have been done with isolated preparations of annelids, using the body wall of marine polychaetes or Hirudinea. Nephridial function and general body homeostasis have received more attention, and have probably been best investigated in Hirudinea. With recent advances in the molecular physiology of epithelial transport systems in vertebrates, the cloning of various transporters and ion channels, and the considerable number of osmoregulatory peptides that have now been found and analyzed from annelids, it should now be possible, and is timely, to conduct functional studies on individual selected epithelial preparations or isolated cells from annelids. Such studies may be important for establishing useful models with somewhat less complexity than mammalian systems. For example, annelids lack aldosterone, an important osmoregulatory hormone, which is a key factor in the regulation of sodium reabsorption in vertebrates. Therefore, not only would such studies contribute to annelid physiology, but they would be important in a broader sense for understanding osmoregulation and its evolution. They should also facilitate the discovery and investigation of new specific regulatory pathways.
Regular Articles / Articles RéguliersRibeiroia ondatrae (Trematoda: Digenea) infection induces severe limb malformations in western toads (Bufo boreas)
Authors: Johnson Pieter TJ , Lunde Kevin B , Haight Ryan W , Bowerman Jay , Blaustein Andrew R
Published: April 2011

Widespread reports of malformed amphibians in North America have prompted investigations into the cause(s) and implications of the phenomenon. Recently, a trematode parasite (Ribeiroia ondatrae) was identified as the probable cause o
Concentrations of electrolytes, hormones, and other constituents in fresh postmortem blood and urine of fin whales (Balaenoptera physalus)
Authors: Kjeld M
Published: April 2011

Concentrations of various blood and urine constituents were measured on postmortem samples from 286 fin whales (Balaenoptera physalus) caught off Iceland during the summers of 19811989. Measurements were carried out on both serum and urine from 21 whales so that results could be compared. The mean serum urea concentration in fin whales was similar to that in odontocetes but 5 times higher than in domesticated terrestrial mammals. Serum triglyceride concentrations were twice as high as in fasting man and showed no diurnal peaks. Serum cortisol concentrations were about 2 times lower than in domestic mammals and showed neither diurnal variation nor a significant correlation with chase time (time from sighting until killing). Serum aldosterone concentrations were similar to those in bottlenose dolphins and, as expected, showed a negative correlation with urinary Na+concentration. Blood thyroxine levels correlated significantly (p < 0.003) with chase time. Mean urinary potassium concentrations were 6 times higher than average seawater levels, while sodium and chloride levels were about 23 times higher than in humans but never as high as those in seawater. Urinary magnesium levels were 45 times higher than in domestic animals but less than half those in seawater. Average urine osmolality was higher than in seawater.
Mortality in relation to season, age, sex, and reproduction in Columbian ground squirrels (Spermophilus columbianus)
Authors: Neuhaus P , Pelletier N
Published: April 2011

We investigated the timing of and age at mortality in Columbian ground squirrels (Spermophilus columbianus) in relation to sex and reproductive status. Life-history data were collected from 1994 to 1999 in the foothills of the Rocky Mountains, Alberta, Canada. We predicted increased mortality for males during mating and for females during lactation. Further, we expected reproductively successful females to have higher mortality than females that did not reproduce successfully. Finally we assumed that at some age reproductive success of females would decrease and mortality increase because of old age. For both sexes, survival over winter was high (ca. 90%) for adults. While there was a significant increase in mortality of adult males during the mating season, females did not have higher mortality during lactation than during the rest of the active season. Reproductive status influenced mortality in females: non-reproducing females had a higher chance of surviving than reproducing females. Females that weaned young were more likely to die after the weaning period than females that lost their litter during lactation. There was a positive correlation between maternal survival and survival of offspring to yearling age. Our results showed evidence of trade-offs between reproduction and survival of male and female Columbian ground squirrels.
Population variation in the metabolic response of deer mice to infection with Capillaria hepatica (Nematoda)
Authors: Meagher Shawn , O'Connor Timothy P
Published: April 2011

The effects of parasites on their hosts can vary among host populations, but few studies have examined geographic variation in host-parasite interactions. We examined the effects of Capillaria hepatica (Nematoda) infection on deer mice (Peromyscus maniculatus gracilis) from two different populations. Specifically, we measured the basal metabolic rate (BMR), cold-stress maximum oxygen consumption (MRpeak), metabolic scope (MRpeak/BMR), and thermogenic endurance of infected and uninfected mice from one population with, and a second population without, a history with C. hepatica. Infection had no effect on BMR, but did have effects on cold-stress measures. A previous study documented a significant relationship between survival and MRpeak in wild deer mice; hence, the effects of infection on the parameters that we measured could influence fitness. Only mice that had no historical association with C. hepatica displayed negative consequences of infection, which suggests that the historical host population has evolved mechanisms to cope with infection. Models of the evolution of virulence should include evolutionary responses of both hosts and parasites, particularly when systems involve macroparasites that have long generation times.
Food selection by the white-footed mouse (Peromyscus leucopus) on the basis of energy and protein contents
Authors: Lewis Chad E , Clark Tim W , Derting Terry L
Published: April 2011

We studied the combined effects of energy and protein contents on food selection by the white-footed mouse, Peromyscus leucopus. Our objective was to determine how variation in levels of a food component affected the overall attractiveness of a food to the mice and whether trade-offs are made in selecting dietary protein compared with energy. We conducted food-selection tests in the laboratory and field using foods containing different combinations of energy and protein levels. In the laboratory, P. leucopus were offered a choice between a high-energy and a low-energy food with the protein level held constant and between a high-protein and a low-protein food with the energy level held constant. The field study was set up to offer an encounter with all four combinations of energy and protein simultaneously. We also tested for preferred levels of protein using pairwise food-selection tests in the laboratory. In the laboratory and field tests, P. leucopus selected high-energy foods that were low in protein, but avoided all foods with a high protein content. When given pairwise choices among foods containing 5, 15, 25, or 35% protein, P. leucopus consistently preferred the food with 15% protein. Peromyscus leucopus quickly detected differences in protein and energy levels in foods, selecting specific foods according to metabolic profitability and nutrient needs.
Distribution of Carnus hemapterus in a starling colony
Authors: Liker András , Márkus Márta , Vozár Ágnes , Zemankovics Eszter , Rózsa Lajos
Published: April 2011

The distribution of the haematophagous fly Carnus hemapterus among starling (Sturnus vulgaris) broods was investigated in a nest-box colony. Prevalence of infection was 94% among broods and 69% among individual nestlings, while median abundance was 54 flies per brood (range 0284 flies; n = 33) and 8 flies per individual nestling (range 0117 flies; n = 140). Parasites exhibited an aggregated distribution among starling broods. Carnus hemapterus populations changed significantly during the development of nestlings: fly abundance increased rapidly after nestlings hatched, peaked 58 days after hatching, and decreased thereafter. The proportion of winged flies (assumed to be the transmissive form) and the proportion of male flies decreased with increasing nestling mass. Measures of within-colony spatial position of nests were not related to mean brood abundance, proportion of winged flies, or sex ratio of the flies. Parasite abundance did not correlate with mortality rate or growth rate of nestlings. In conclusion, nestling developmental stage was the only significant predictor of variation in C. hemapterus populations in this starling colony.
Spatial and temporal interactions between female American black bears in mixed forests of eastern Canada
Authors: Samson Claude , Huot Jean
Published: April 2011

Few studies have examined in detail the spacing patterns of American black bears (Ursus americanus), especially populations protected from hunting. We radio-tracked bears between 1990 and 1992 in La Mauricie National Park in southern Quebec to study their social interactions. We measured the zone of overlap between home-range core areas and evaluated the spatial and temporal use of the overlap zones for 12 adult females radio-tracked during 1992. The proportion of overlap between the core areas used by 22 pairs of females was variable but low (14.2 ± 17.6% (mean ± SD)). This proportion did not differ (p > 0.05) from that obtained from a random distribution of home ranges (17.1 ± 17.1%). For 12 (55%) of 22 pairs with overlapping core areas, at least one of the females was significantly attracted by the overlap zone, whereas one of the females of another pair significantly avoided it. Significant simultaneous use of the overlap zone was observed for 7 pairs and significant temporal avoidance of the overlap zone was noted for 1 pair. The overlap zone contained a significantly higher proportion of food-producing cover types (maplebeech and early-successional stands) than the overall study area. Our results indicate that although most females did not share a large proportion of their core area with their neighbours, the overlap zone was used intensively for foraging by more than one bear, often simultaneously. Some aggressive behaviours were noted when bears were seen foraging simultaneously in the same area. We discuss the influence of spatial and temporal interactions on the regulation of this unhunted population.
The implications of bite performance for diet in two species of lacertid lizards
Authors: Herrel A , Damme R Van , Vanhooydonck B , Vree F De
Published: April 2011

One of the performance features that is generally considered crucial to increasing the potential prey spectrum of lizards is bite capacity. In this study we tested whether bite forces may serve as a basis for diet selection in two syntopically occurring lacertid lizards. We did so by measuring bite forces in vivo for a large sample of lizards of the species Podarcis muralis and Lacerta vivipara. To assess the ecological relevance of the bite forces, we tested the hardness of a number of natural prey items of both species. The results of our study support the predictions of biomechanical models of biting in lizards and indicate that both larger animals and larger headed ones bite harder. Surprisingly, head shape is an excellent predictor of bite performance in the species studied. Moreover, it is demonstrated that bite capacity is a potentially important ecological variable that could be used as a factor in explaining patterns of food-resource use, ontogenetic dietary shifts, and sexual dimorphism in diet.
Behaviour and growth of southern leopard frog (Rana sphenocephala) tadpoles: effects of food and predation risk
Authors: Babbitt K J
Published: April 2011

I examined the effects of a nonlethal predator, larvae of the odonate Anax junius, and food-resource level on behaviour and growth of larval southern leopard frogs (Rana sphenocephala) to test whether the strength of effects of a nonlethal predator was influenced by background resource level. I crossed two levels of food resources, growth-limiting and non-growth-limiting, with the presence or absence of A. junius. Tadpoles responded to predators by altering spatial distribution and activity. When predators were present, tadpoles on both food treatments had similar low levels of activity, but tadpoles on the nonlimiting food treatment showed a much larger reduction in activity than tadpoles on the growth-limiting treatment. Tadpoles on both food treatments delayed metamorphosis when exposed to predators. Growth and size at metamorphosis were affected significantly by food treatment but not by predator treatment. However, the direction of response to predators differed. Tadpoles on the growth-limiting treatment were larger at metamorphosis and grew faster when exposed to predators; the opposite was true for tadpoles on the non-growth-limited food treatment. This raises the interesting possibility that for some species experiencing low resource availability, predators may induce a behaviourally mediated positive effect on growth.
Infant ultrasonic vocalizations and parental responses in two species of voles (Microtus)
Authors: Rabon Jr. David R , Sawrey D Kim , Webster Wm. David
Published: April 2011

When separated from conspecifics, the young of many rodent species produce ultrasonic vocalizations (USVs) that may facilitate parental approach. Ultrasounds were recorded from infants (014 days post partum) of two closely related species that exhibit different social systems, the montane vole (Microtus montanus) and the prairie vole (Microtus ochrogaster). Infant prairie voles emitted a greater number of USVs when isolated from conspecifics than did infant montane voles. Infant prairie voles also emitted a greater number of USVs in the presence of a parent than did infant montane voles. For both species, parental responses to individual infants were most rapid when pups were at those ages when they emitted the greatest numbers of USVs. Prairie vole parents approached pups most rapidly on days 68, whereas montane vole parents approached pups most rapidly on days 1214. There were no differences between sires and dams of either species in their latencies to approach and contact pups. In general, however, infants of both species were retrieved more rapidly by dams than by sires. We suggest that differences in ultrasound production among vole species may correlate with differences in their species-specific social systems. It appears that the number of USVs produced by pups may vary with the amount of parent-pup contact typical of each species.
Hydrostatic-pressure and temperature effects on the molecular order of erythrocyte membranes from deep-, shallow-, and non-diving mammals
Authors: Williams E E , Stewart B S , Beuchat C A , Somero G N , Hazel J R
Published: April 2011

Little is known about the cellular mechanisms involved in the tolerance of deep-diving marine mammals to hydrostatic pressures that cause serious pathologies when experienced by other mammals. We compared fatty-acid composition, cholesterol content, and the effects of pressure on the molecular order of erythrocyte membranes from deep-, shallow-, and non-diving mammals to determine how these properties may be related to diving performance. Erythrocytes were collected from two deep-diving phocid pinnipeds (northern elephant seal (Mirounga angustirostris) and harbor seal (Phoca vitulina)), a relatively shallow-diving otariid pinniped (northern fur seal (Callorhinus ursinus)), and several nondiving terrestrial mammals (dog (Canis familiaris), horse (Equus caballus), and cow (Bos taurus)). Fatty-acid composition clearly distinguished the phocids from the other species. The monoene content of erythrocyte membranes was substantially lower (3 vs.»20%), whereas the lipid unsaturation indices, the ratio of α- to γ-linolenic acids, and the proportions of long-chain polyunsaturated fatty acids were substantially higher in the phocids. The cell-membrane cholesterol content was also significantly lower in erythrocytes from the deep-diving phocids (cholesterol:phospholipid ratios 0.20.3) than from most other mammals (1.0). Membranes from the phocids were more ordered than those from the shallow- and non-divers, and were also more sensitive to changes in pressure and temperature. The physiological significance of these differences in cell-membrane structure, which affect the order and sensitivity of cell membranes to hydrostatic pressure, is unknown, but they may be important adaptations that allow repeated and prolonged exposure to great hydrostatic pressure.
Natal dispersal of grizzly bears
Authors: McLellan Bruce N , Hovey Frederick W
Published: April 2011

We studied natal dispersal of grizzly bears (Ursus arctos), a solitary nonterritorial carnivore with a promiscuous mating system, between 1979 and 1998. Dispersal distances for 2-year-olds did not differ between males and females, but by 3 years of age, males had dispersed farther than females, and farther still by 4 years of age. Dispersal of both sexes was a gradual process, occurring over 14 years. From the locations of death, or last annual ranges, it was estimated that 18 males dispersed 29.9 ± 3.5 km (mean ± SE) and 12 females dispersed 9.8 ± 1.6 km. Eleven of these males dispersed the equivalent of at least the diameter of 1 adult male home range, whereas only 3 of the females dispersed at least the diameter of 1 adult female home range. The longest dispersals recorded were 67 km for a male and 20 km for a female. Because the social system consists of numerous overlapping home ranges of both sexes, long dispersal distances may not be required to avoid inbreeding or competition with relatives. Simple models suggest that 61% of the ranges of brother and sister pairs would not overlap, but the home range of every daughter would overlap her father's range. The home range of an estimated 19 ± 4 (mean ± SD) adult males, however, would overlap at least a portion of each female's range, thereby reducing the chance of a female mating with her brother or father. Understanding the dispersal behaviour of grizzly bears is essential for developing conservation strategies. Our results suggest that meta-population reserve designs must provide corridors wide enough for male grizzly bears to live in with little risk of being killed.
Growth rates of vibrissae of harbor seals (Phoca vitulina) and Steller sea lions (Eumetopias jubatus)
Authors: Hirons Amy C , Schell Donald M , St. Aubin David J
Published: April 2011

Growth rates of vibrissae (whiskers), which act as a temporal record of feeding in harbor seals (Phoca vitulina) and Steller sea lions (Eumetopias jubatus), were estimated using13C- and15N-labeled glycine followed by stable-isotope analysis. The labeled glycine was incorporated into keratin and served as a temporal marker for growth-rate calculation. One captive harbor seal received two doses 147 days apart, while a second seal received one dose; vibrissae were analyzed after 86 and 154 days. The peak positions indicated that growth began in the fall, continued into spring, but ceased in June, with active growth rates of 0.33 mm/day. Two adult captive Steller sea lions each received two labeled doses during a 308-day period. After 427 days vibrissae in both sea lions showed two peaks corresponding to the markers; growth rates were calculated as 0.050.07 mm/day. Growth rates in captive juvenile and wild adult Steller sea lions, 0.100.17 mm/day, supported the assumption that major isotopic oscillations in vibrissae of wild sea lions were annual. The multiyear records imply that Steller sea lions retain their vibrissae; harbor seal vibrissae, in contrast, have periods of rapid growth and appear to be shed, at least in part, annually.
Implications of climate change for parasitism of animals in the aquatic environment
Authors: Marcogliese David J
Published: April 2011

Climate change can occur over evolutionary and ecological time scales as a result of natural and anthropogenic causes. Considerable attention has been focused in recent years on the biological consequences of global warming. However, aside from studies on those deleterious parasites that cause disease in man, little effort has been dedicated to understanding the potential changes in the parasite fauna of animal populations, especially those in aquatic systems. Predictions using General Circulation Models, among others, are examined in terms of their consequences for parasite populations in freshwater and marine ecosystems, concentrating on the temperate and boreal regions of eastern North America. Biological effects due to global warming are not predictable simply in terms of temperature response. It is also essential to explore the effects on aquatic parasites of alterations in host distribution, water levels, eutrophication, stratification, ice cover, acidification, oceanic currents, ultraviolet-light penetration, weather extremes, and human interference. Evaluation of the potential response of parasites of aquatic organisms to climate change illustrates the complexity of hostparasite systems and the difficulty of making accurate predictions for biological systems. Parasites in aquatic systems will respond directly to changes in temperature but also indirectly to changes in other abiotic parameters that are mediated indirectly through changes in the distribution and abundance of their hosts. Local extirpations and introductions may be expected as a result. In the long term, climatic change may influence selection of different life-history traits, affecting parasite transmission and, potentially, virulence.
Maternal effects on offspring growth rate and weaning mass in harbour seals
Authors: Bowen W Don , Ellis Sara L , Iverson Sara J , Boness Daryl J
Published: April 2011

We studied maternal effects on offspring traits during lactation in harbour seals (Phoca vitulina) on Sable Island, Nova Scotia, from 1988 to 1996. Duration of lactation was correlated with rate of pup mass gain (r = %#150;0.34, n = 116) and weaning mass (r = 0.29, n = 154). Pups that grew faster had shorter nursing periods, whereas those that attained higher weaning masses nursed for a greater number of days. Pup sex did not affect patterns of maternal effects. The pups of young females (4%#150;6 years old) gained mass at a constant but lower rate (0.56 kg/d) than the pups of older females through midlactation (0.74%#150;0.78 kg/d; n = 75). In older females, rates of pup mass gain decelerated between mid and late lactation. Although maternal age did not directly affect weaning mass of pups, path analysis showed that maternal age acted on weaning mass through intermediary traits. Lighter females gave birth to smaller and slower growing pups, but invested relatively more than heavier females (n = 153). Effects of maternal postpartum mass on weaning mass (n = 100) were weaker in harbour seals than in phocids that fast during lactation, but apparently stronger than in otariids that forage during lactation, suggesting that the strength of maternal effects is influenced by lactation strategy.
Sexual dimorphism in body composition of small mammals
Authors: Schulte-Hostedde A I , Millar J S , Hickling G J
Published: April 2011

Differences in reproductive roles between the sexes may lead to sexual dimorphism in body composition. Body size and composition of three species of small mammals (bushy-tailed wood rats (Neotoma cinerea Ord), deer mice (Peromyscus maniculatus Wagner), and red-backed voles (Clethrionomys gapperi Vigors)) were analyzed to test the predictions that (i) males will have more muscle mass than females and (ii) females will have more fat than males. Results supported the first prediction but not the second. For all three species, males had more lean dry mass relative to body size than females, but females did not have relatively more fat than males. Muscle mass of males may aid in mate-searching and mate-guarding activities, but fat content may not differ between the sexes because female small mammals depend on increased ingestion rates, rather than fat stores, to support reproduction.
REGULAR ARTICLES / ARTICLES RÉGULIERSFactors affecting the distribution and transmission ofElaphostrongylus rangiferi(Protostrongylidae) in caribou (Rangifer tarandus caribou) of Newfoundland, Canada
Authors: Ball Mark C , Lankester Murray W , Mahoney Shane P
Published: April 2011

Elaphostrongylus rangiferi was introduced to caribou (Rangifer tarandus caribou) of Newfoundland by infected reindeer (R. t. tarandus) from Norway and has caused at least two epizootics of cerebrospinal elaphostrongylosis (CSE), a debilitating neurologic disease. In an attempt to understand the conditions necessary for such outbreaks, we examined the effects of herd density and climatic factors on parasite abundance. The abundance of E. rangiferi was represented by counts of first-stage larvae in feces collected from young caribou (calves and yearlings) in 7 distinct caribou herds in Newfoundland. Abundance of E. rangiferi was highest in February and in the Avalon (632 ± 14 (mean ± SE)) and St. Anthony (526 ± 145) herds, the 2 herds in which CSE was most frequently reported. Mean abundance in February samples from young animals correlated positively with mean annual minimum temperature (rS= 0.829, df = 6, P = 0.04) and the number of days per year above 0°C (rS= 0.812, df = 6, P = 0.05) and negatively with mean summer temperatures (rS= 0.830, df = 6, P = 0.04). Results suggest that abundance of E. rangiferi and the likelihood of cases of CSE are increased by moderate summer temperatures suitable for the activity and infection of gastropod intermediate hosts and by mild winters with little snow that extend the transmission period. Abundance of larvae was not correlated with herd density. Animals in all 7 herds also had the muscle worm Parelaphostrongylus andersoni, a related nematode with similar dorsal-spined larvae. In 2 additional herds (Cape Shore and Bay de Verde), P. andersoni occurred alone and larvae were passed only by young caribou. In herds with dual infections, numbers of P. andersoni larvae were depressed, declined more quickly in young animals, and were considered to be present in only low numbers in February samples used for E. rangiferi analysis. Upon initial infection, young caribou develop a resistance to E. rangiferi that prevents or reduces reinfection later in life. This was demonstrated by examining the brains of caribou for recently acquired worms, which must develop there for up to 90 days before continuing their tissue migration into the skeletal muscles. Recent infections were detected in only calves and yearlings in all herds with E. rangiferi except the Avalon herd, where developing worms were also found on the brains of older caribou. The infection of older animals in the Avalon herd may reflect a lower immunocompetence of a naive herd that has only recently been exposed to E. rangiferi.