bluuebunny/crossref_metadata_2025 huggingface dataset:
White blood cell counts in house sparrows (Passer domesticus) before and after moult and after testosterone treatment
Authors: Nava María Paz , Veiga José Pablo , Puerta Marisa
Published: April 2011

In this study two experiments were run in parallel. To evaluate the possible influence of moult and age on differential white blood cell (WBC) counts, we captured juvenile and adult house sparrows (Passer domesticus) and housed them in outdoor aviaries. Blood was collected twice, before and after moult. Numbers of basophils, lymphocytes, and monocytes were higher in juveniles than in adults, whereas numbers of eosinophilic cells were similar in the two age groups. Moult induced an increase in basophils and monocytes in both juveniles and adults. This indicates that moult and age impose different immunological challenges on house sparrows. To evaluate the effect of testosterone on differential WBC counts, some house sparrows in aviaries received testosterone during the moult period. Testosterone administration reduced, though not significantly, the number of all WBC types in juveniles, and therefore appeared to have an nonspecific effect. However, the number of lymphocytes increased only in adults, which suggests a specific effect on this cell type in this age group.
Winter habitat selection by a montane forest bird assemblage: the effects of solar radiation
Authors: Huertas Daniel L , Díaz José A
Published: April 2011

A relationship between sunlight and bird abundance in cold climates may seem intuitive and perhaps obvious. However, there is, surprisingly, little or no evidence to support it. We investigated the effects of solar radiation on the winter abundance of insectivorous birds inhabiting a Mediterranean montane forest with a high frequency of cold, cloudless days. We censused birds by ear in 20 different forest tracts in which we simultaneously quantified a number of variables related to the availability of solar radiation, vegetation structure, arthropod abundance, and altitude. All variables related to solar radiation were reduced to a single principal component that attained high scores for south-facing transects, where many tree trunks received direct sunlight for a long period daily. The abundance of all bird species was positively related to the scores of transects on this component after the effects of vegetation structure, altitude, and prey availability were controlled for. Solar radiation was the main predictor of overall abundance and species richness of bird assemblages. Body mass and diet (insectivorous vs. mixed) explained 94.6% of interspecific variation in the strength of the relationship between solar radiation and bird abundance. We hypothesize that selecting forest sectors with a higher availability of sunlit patches allows birds to improve their winter survival by reducing the metabolic costs of thermoregulation, decreasing movement rates, and (or) increasing the time spent motionless in safe locations.
The neuroendocrine system of annelids
Authors: Salzet Michel
Published: April 2011

In vertebrates the neuroendocrine system is based on chemical signaling between neural and endocrine structures. Final outcomes may be realized via chemical messengers traveling through circulatory conduits to their specific target sites. This process may rely, in part, on neurosecretion of the signaling molecules. The complexity of this system can be readily visualized when one considers the way in which interactions among classical neurotransmitters, cytokines, growth factors, and neuroendocrine hormones, in combination with autocrine and paracrine communication, can regulate cells and tissues. Apart from the neuroendocrine system there is also neuroimmune communication, consisting of reciprocal signaling between neuroendocrine and immune cells, which use the same molecules to coordinate their activity. Thus, our concept of the neuroendocrine system is constantly growing, despite its complexity, but it may be simply summarized as allowing bidirectional communication between neural and endocrine structures over distances greater than that achieved by synaptic communication. In the light of this, I demonstrate in this review that annelids, which are considered "simple" animals, also possess a neuroendocrine system.
Ectoparasites, nestling growth, parental feeding rates, and begging intensity of tree swallows
Authors: Thomas Krista , Shutler Dave
Published: April 2011

Many studies fail to show relationships between ectoparasite loads and nestling growth rates. One explanation is that parent birds increase feeding rates to compensate for nestling energetic losses to ectoparasites. Nestling begging behaviours could signal need to parents. Accordingly, we tested whether higher flea and blow fly loads in tree swallow (Tachycineta bicolor) nests were associated with smaller nestlings, higher parental feeding rates, and increased nestling begging intensity. The study area was the Gaspereau Valley of Nova Scotia, Canada. When nestlings were 10 days old, parental feeding rates and nestling begging intensity were measured with tape recorders. At 13 days of age, nestlings were weighed and measured. Within 2 days of fledging, nest material was removed from nest boxes and enumerated for adult fleas and blow fly pupae. After including brood size and date of first egg as covariates in general linear models, no significant relationships were found between ectoparasite loads and nestling size, parental feeding rate, or nestling begging intensity. Our results suggest that nestling tree swallows were able to buffer the effects of naturally occurring ectoparasite loads without significant help from their parents. Low levels of virulence may have resulted from relatively benign weather during the study, low numbers of ectoparasites, selection on ectoparasites to avoid killing their hosts, and host defences.
Effects of sterilization on territory fidelity and maintenance, pair bonds, and survival rates of free-ranging coyotes
Authors: Bromley Cassity , Gese Eric M
Published: April 2011

Predation on sheep by coyotes (Canis latrans) is a longstanding problem for sheep producers. Current research suggests that surgical sterilization of coyotes could prove to be an effective method of reducing their depredation rates on domestic sheep by modifying their predatory behavior. However, for sterilization to be a viable management tool, the territorial and affiliative behaviors of pack members would need to remain in place. We tested whether surgically sterilized coyotes maintained pair bonds and territories in the same manner as intact coyotes. We also examined if territory fidelity and survival rates differed between sterile and intact coyotes. From June 1997 to April 2000, 10 males and 9 females were sham-operated and radio-collared, while 20 males and 6 females were surgically sterilized and radio-collared. We monitored members of 5 sterile and 4 intact packs during 1998, 6 sterile and 7 intact packs during 1999, and 4 sterile and 6 intact packs through the 2000 breeding season. Behaviorally, sterile packs appeared to be no different than intact packs. A half-weight association index showed that social dyads within sterile coyote packs were located together as frequently as dyads within intact packs. Simultaneous radiolocations of members of sterile packs showed that members of sterile packs were significantly closer to each other than would be expected from random locations. There was no difference in size or degree of overlap between territories of sterile and sham-operated coyote packs. Sterile coyotes had a higher annual survival rate than reproductive animals in 2 of the 3 years, and there was no difference in the level of territory fidelity. We concluded that surgical sterilization did not modify the territorial or affiliative behaviors of free-ranging coyotes, and therefore sterile coyotes could be used as a management tool to exclude other potential sheep-killing coyotes.
Larval and life-cycle patterns in echinoderms
Authors: McEdward Larry R , Miner Benjamin G
Published: April 2011

We review the literature on larval development of 182 asteroids, 20 crinoids, 177 echinoids, 69 holothuroids, and 67 ophiuroids. For each class, we describe the various larval types, common features of a larval body plan, developmental patterns in terms of life-cycle character states and sequences of larval stages, phylogenetic distribution of these traits, and infer evolutionary transitions that account for the documented diversity. Asteroids, echinoids, holothuroids, and ophiuroids, but not crinoids, have feeding larvae. All five classes have evolved nonfeeding larvae. Direct development has been documented in asteroids, echinoids, and ophiuroids. Facultative planktotrophy has been documented only in echinoids. It is surprising that benthic, free-living, feeding larvae have not been reported in echinoderms. From this review, we conclude that it is the ecological and functional demands on larvae which impose limits on developmental evolution and determine the associations of larval types and life-cycle character states that give rise to the developmental patterns that we observe in echinoderms. Two factors seriously limit analyses of larval and life-cycle evolution in echinoderms. First is the limited understanding of developmental diversity and second is the lack of good phylogenies.
Changes in trophic abundance of soil arthropods along a grass-shrub-forest gradient
Authors: Ferguson Steven H
Published: April 2011

Ecological theory suggests that along productivity gradients, abundances of organisms within trophic levels will increase in a stepwise pattern from producers to consumers. To test this theory I investigated changes in abundance of soil arthropods at three trophic levels: microphytophages, represented by Collembola, predacious mites (Acari) that feed on Collembola, and three groups of macroarthropods (spiders, ants, and centipedes) that were observed to feed on mites. Changes in abundance were monitored along a gradient in vegetation structure from grass to shrub to forest in the Canadian prairies. I controlled for temporal variation in abundance among years and surveys within a year. As predicted, (i) numbers of Collembola did not change with increases in productivity; (ii) mite numbers were greatest in the shrublands; and (iii) numbers of macroarthropod predators increased from grassland to shrubland, and there was a nonsignificant increase in numbers of spiders and centipedes in forest habitat. Contrary to predictions, macroarthropod numbers were not significantly greater in forest habitat, and ant numbers actually declined. Possible explanations for the lack of increase in macroarthropod predator abundance in the forest habitat with the greatest productivity include decreased ground-level humidity and greater abundance of macroarthropod predators and parasites in forest environments.
The reproductive performance of female red foxes, Vulpes vulpes, in central-western New South Wales during and after a drought
Authors: McIlroy John , Saunders Glen , Hinds Lyn A
Published: April 2011

The reproductive condition of 295 female red foxes, Vulpes vulpes, collected during and shortly after a severe drought in central-western New South Wales, Australia, was assessed to assist research on the potential use of immunocontraception. The ovulation and conception rates per vixen for the 222 foxes that ovulated were 4.62 ± 1.50 and 3.58 ± 2.18 (mean ± SD), respectively. The resorption rate and mean litter size per vixen for the 188 foxes that were pregnant were 0.47 ± 0.92 and 3.75 ± 1.91, respectively. Details of the parameters are provided for each age-class. The proportion of the overall population that was pregnant was 0.847. Conception rates and litter sizes peaked in fifth- and sixth-year vixens, but vixens over 8 years of age produced as many cubs as first-year breeders did. Vixens collected during 1996, when rainfall was above average, contained significantly more corpora lutea than vixens collected during the drought years 1994 and 1995. There were no significant differences in other reproductive parameters (i.e., conception and resorption rates, litter size, and proportion of the population that was pregnant) between the 3 collection years. Mating occurred within a 3- to 7-week period from mid-June to the end of July and births from early August to late September. From a practical point of view, vixens will need to be targeted with immunocontraceptive baits in autumn.
Dietary differences between phenotypes with symmetrical and asymmetrical pelvis in the stickleback Gasterosteus aculeatus
Authors: Reimchen T E , Nosil P
Published: April 2011

Differential parasitism among phenotypes within populations can result from intrinsic factors such as immunocompetence or extrinsic factors such as ecological overlap with pathogens. In a recent study of a population of sticklebacks (Gasterosteus aculeatus) from Boulton Lake, British Columbia, relative cestode infections were related to pelvic-girdle symmetry. Adult sticklebacks with an asymmetrical pelvis had a higher incidence of infections than fish with a symmetrical pelvis, yet the pattern was reversed among yearlings. In the current study we test whether this unexpected result for yearlings, which is inconsistent with general theory coupling asymmetry with reduced immuno competence, might be due to ecological factors rather than to differences in immunocompetence. We analyze the diet of 9089 uninfected sticklebacks collected during a 15-year study and show that male and female yearling sticklebacks with an asymmetrical pelvis are more benthic than symmetrical phenotypes. This could reduce the probability of exposure to pelagic copepods, the primary hosts of the cestode Schistocephalus solidus, and thereby lead to lower infection rates relative to pelagic fish. This finding would account for the unusual reversal in relative parasitism in this population and raises the possibility of finding further diet-induced causes of differential parasitism in studies of asymmetry.
Consistency and flexibility in the scrounging behaviour of zebra finches
Authors: Beauchamp G
Published: April 2011

When foraging in groups, individuals can use the "producer" tactic to locate food patches and the "scrounger" tactic to exploit the food discoveries of companions. Most producerscrounger models assume that birds are flexible in using tactics in response to changing conditions and that foragers are phenotypically identical. Individual differences and flexibility in tactic use were investigated in zebra finches (Taenopygia guttata) foraging in two flocks of different composition. Birds varied widely in their use of tactics, and individual differences proved consistent both within and between flocks. Significant adjustments in tactic use occurred from one flock to the other. Results suggest that tactic use in zebra finches foraging in small flocks is characterized by consistency and flexibility. Individual differences in tactic use demonstrate the need to examine further the consequences of phenotypic variation in producerscrounger models.
Functional and numerical responses of predators to cyclic lemming abundance: effects on loss of goose nests
Authors: Wilson Deborah J , Bromley Robert G
Published: April 2011

The alternative-prey hypothesis predicts that predation on goose eggs will be most severe the year following a lemming peak. We tested this by investigating how predators of goose eggs responded to lemming abundance on the Kent Peninsula, Nunavut, Canada, where nest success of white-fronted geese (Anser albifrons frontalis) and Canada geese (Branta canadensis hutchinsii) fluctuates widely. The main predators of both goose eggs and lemmings are arctic foxes (Alopex lagopus), glaucous gulls (Larus hyperboreus), and parasitic jaegers (Stercorarius parasiticus). Foxes responded functionally to lemming density: in prime goose-nesting areas they spent less time foraging during the peak lemming year than during the increase, and were seen foraging in prime nesting areas less often during the peak than during the decline. However, numbers of fox sightings in the study area during the nesting period did not differ significantly among years. The total response (functional × numerical) of gulls was lowest at the lemming peak and highest during the increase. The total response of parasitic jaegers did not vary significantly among years. Hence, we predicted that the number of nests lost to all predators combined should be lowest at the peak and possibly highest during the increase. During the 3 years of this study, loss of Canada goose nests was lowest at the peak but highest during the decline, and annual losses of white-fronted goose nests varied little. In cycles prior to this study, nest loss was high in declines but not particularly low during peaks. Several factors may alter the functional and numerical responses of predators, obscuring the simple pattern of nest loss predicted by the alternative-prey hypothesis.
Range shift and winter foraging ecology of a population of Arctic tundra caribou
Authors: Ferguson Michael AD , Gauthier Line , Messier François
Published: April 2011

Some researchers have suggested that over periods of several decades, Arctic tundra caribou (Rangifer tarandus) may be regulated by density-dependent forage depletion. Winter range shifts could potentially delay such regulation when a population is at or near long-term maximum abundance. In the 1980s, Inuit correctly predicted the mass emigration of caribou from a traditional winter range on Foxe Peninsula (FP) on southern Baffin Island, Nunavut, Canada. Most FP caribou subsequently emigrated to a new winter range on Meta Incognita Peninsula (MIP). To determine if MIP provided emigrating caribou with better foraging habitats, we compared winter forage resources and snow cover at caribou foraging sites, and food selection by caribou on FP and MIP in April 1992. Caribou that remained on FP dug feeding craters in shallower, softer snow than those on MIP did. Biomass of most fruticose lichens was greater within foraging sites on MIP than on FP. Biomass of shrubs, other than Cassiope tetragona and Dryas integrifolia, was also greater on MIP than on FP. Dryas integrifolia was the only plant class that had higher biomass on FP than on MIP. Cladina spp. / Cladonia spp., Sphaerophorus fragilis, and Cetraria nivalis occurred less frequently in the rumens of FP caribou. Proportions of fruticose lichens in rumens of caribou on both peninsulas were similar to those on other overgrazed and High Arctic tundra winter ranges. Caribou on FP showed a higher preference for the shrub C. tetragona. Biomasses of plants sensitive to long-term feeding or trampling by caribou (i.e., the five most common fruticose lichens, other shrubs, and plant debris) were consistently lower on FP, which is congruous with Inuit reports that long-term cumulative overgrazing had reduced the supply of important forage plants on FP sites that were accessible to caribou in winter. FP caribou that emigrated to MIP gained access to more abundant, higher quality forage resources than those that remained on FP. Because most FP caribou had emigrated, this South Baffin subpopulation escaped, at least temporarily, the regulating effects of historical cumulative overgrazing.
Closure violation in DNA-based mark-recapture estimation of grizzly bear populations
Authors: Boulanger John , McLellan Bruce
Published: April 2011

We use methods in the program MARK to explore the effects of closure violation when DNA-based markrecapture methods are used to estimate grizzly bear (Ursus arctos) populations. Our approach involves the use of Pradel models in MARK to explore the relationship between recruitment, apparent survival rates, recapture rates, and distance between mean bear-capture locations and the edge of the sampling grid. If the population is demographically closed, it can be assumed that apparent survival estimates the fidelity of bears to the grid area and recruitment estimates rates of addition of bears to the grid area. A core bear population is defined from the Pradel analysis and is used to approximate the grid-based population size. The Huggins closed-population model in MARK is used to provide robust superpopulation estimates by explicitly modeling the relationship between capture probability and distance of bear-capture location from the grid edge. Data from a grizzly bear DNA-based markrecapture inventory conducted in British Columbia is used to illustrate this method. The results of the Pradel analysis suggest that bears with mean capture locations within 10 km of the grid edge exhibit reduced fidelity rates and higher addition rates. Using the population of bears captured more than 10 km from the grid edge, a core-extrapolated estimate is derived, which is substantially lower than naïve CAPTURE superpopulation estimates. The Huggins model superpopulation estimate displays superior precision compared with CAPTURE model estimates. Our results illustrate the danger of naïve interpretation of closed-model estimates. This method allows further inferences to be made concerning the spatial causes of closure violation, and the degree of bias caused by closure violation to be explored.
Prenatal investment in the subantarctic fur seal, Arctocephalus tropicalis
Authors: Georges Jean-Yves , Guinet Christophe
Published: April 2011

We investigated prenatal investment in a large sexually dimorphic mammal, the subantarctic fur seal, Arctocephalus tropicalis, on Amsterdam Island in the Indian Ocean. Pups' sex ratio and body mass, body length, and body condition at birth were studied in relation to timing of birth and maternal characteristics (body length and body condition) during three consecutive breeding seasons. Pups' sex ratio did not differ from unity throughout the pupping period. The sex of the pup was related to neither maternal body length (i.e., maternal age) nor maternal body condition when mating occurred or at parturition (1 year later), which suggests that the sex ratio was not biased toward one sex during gestation. Newborn male pups were heavier and longer than female pups in all years. Longer mothers tended to arrive later in the season regardless of their body condition, and gave birth to heavier pups whatever the sex of the pup. Mothers in good condition gave birth to heavier male pups than mothers in poor condition, but no significant differences were found for female pups, suggesting that the costs of carrying male foetuses is higher than that of carrying female foetuses. Differences in allocation of maternal resources between male and female pups may be due to sex-related differences in body composition, since male pups were heavier than female pups for a given body length at birth. Thus, male and female foetuses may use maternal resources differently, with males growing in length whereas females appear to grow in body mass. The mothers we monitored over 2 consecutive years gave birth to pups that were similar in quality (in terms of birth mass) over years regardless of the sex of the previous pup and the mother's body length, suggesting that individual reproductive value is independent of maternal age. Furthermore, maternal body condition was not affected by the sex of the foetus, suggesting that there is no differential reproductive cost in carrying a male or a female foetus. Interannual differences in pup body size at birth suggest that environmental conditions such as prey availability during the last stages of gestation, and consequent maternal body condition, are important components of maternal investment in fur seals.
Incubation behaviour of greater snow geese in relation to weather conditions
Authors: Poussart Catherine , Gauthier Gilles , Larochelle Jacques
Published: April 2011

Based on allometric considerations, goose species with larger body masses should spend more time on their nest during incubation than smaller ones. We documented hourly and daily variations in incubation behaviour of large goose species nesting in the Arctic, the greater snow goose (Chen caerulescens atlantica), and examined the effect of weather conditions on recess frequency and duration. Incubation behaviour was inferred from variations in temperature recorded by adding artificial eggs to clutches. Mean nest attentiveness during the incubation period was 91.4%, indicating that it can be relatively low even for a large goose. Females took 56 recesses/day, which lasted for an average of 22.7 min each. Variability in incubation behaviour over time was greater within females than among females. Recesses were more frequent, and of longer duration, in the afternoon than at night. Females were also less attentive to their nest as incubation progressed, a consequence of both an increase in recess frequency and duration, except in the days before hatching, when nest attentiveness rose abruptly. The relatively low nest attendance of incubating greater snow geese may be a consequence of the opportunity to feed close to the nest during recesses. Weather parameters influenced movements away from the nests in 11 of the 12 females monitored. Females took more recesses when wind velocity was low and, to a lesser extent, when air temperature and solar radiation were high, but the response was quite variable among females. Although females seem to adjust their behaviour in order to limit egg cooling, variations in risk of predation according to time of day may also influence incubation patterns.
The recovery, distribution, and population dynamics of wolves on the Scandinavian peninsula, 1978-1998
Authors: Wabakken Petter , Sand Håkan , Liberg Olof , Bjärvall Anders
Published: April 2011

In 1966 the gray wolf (Canis lupus) was regarded as functionally extinct in Norway and Sweden (the Scandinavian peninsula). In 1978 the first confirmed reproduction on the peninsula in 14 years was recorded. During 20 successive winters, from 19781979 to 19971998, the status, distribution, and dynamics of the wolf population were monitored by snow-tracking as a cooperative SwedishNorwegian project. After the 1978 reproduction in northern Sweden, all new pairs and packs were located in south-central parts of the Scandinavian peninsula. Between 1983 and 1990 wolves reproduced each year except 1986, but in only one territory. There was no population growth during this period and the population never exceeded 10 animals. In 1991 reproduction was recorded in two territories. After that there were multiple reproductions each year and the population started growing. In 1998 there were 5072 wolves and six reproducing packs on the peninsula. Between 1991 and 1998 the annual growth rate was 1.29 ± 0.035 (mean ± SD). A minimum of 25 litters were born during the study period. The early-winter size of packs reproducing for the first time was 6.2 ± 1.4 wolves (n = 9), and this decreased with time during the study. The size of packs that had reproduced more than once was 6.4 ± 1.8 wolves (n = 12), and this increased with time over the study period. All but 1 of 30 reported wolf deaths were human-caused. The annual mortality rate was 0.13 ± 0.11, and this decreased with time during the study period. The minimum dispersal distance was 323 ± 212 km for males and 123 ± 67 km for females. Of 10 new wolf territories where breeding occurred, only 1 bordered other, existing territories. The distance from newly established wolf pairs to the nearest existing packs was 119 ± 73 km. Simulation of population growth based on known reproductions and mortalities showed a close similarity to the results from population censuses up to the mid-1990s. To what extent this population is genetically isolated is at present unclear.
REGULAR ARTICLES / ARTICLES RÉGULIERSMovement of the cirri during the creeping of Euplotes crassus (Ciliata, Hypotrichida)
Authors: Erra F , Iervasi A , Ricci N , Banchetti R
Published: April 2011

The beating cycle of several cirri (frontal cirri 1/0, 3/I, 3/II, 3/III; transverse cirri; one caudal cirrus) of the ciliate Euplotes crassus was studied and described thoroughly in specimens that were actually creeping along the substrate. The beating cycle of the frontal cirri was measured both spatially and temporally, and it was found that (i) the single beating cycle was formed by an active propulsion phase (about 70% of the single step), followed by a recovery phase that so far has never been described and is where the cirri are transferred forwards passively (about 30% of the step); (ii) whenever the euplotes stops, it assumes its "zero position," repositioning all of its frontal cirri to their respective "standard positions"; and (iii) at the beginning of a new creeping phase the frontal cirri were reactivated in a well-defined order. The transverse cirri were kept still during forward creeping, while their angular position was changed with respect to the substrate during the stops and backward movements of the ciliate. The first left caudal cirrus beats constantly and its operating cycle appeared to be independent of the creeping or immobile state of the organism. The findings are discussed from the functional point of view and in the context of available literature on the internal beating potentialities of the different cirri.
The effects of woodland fragmentation and human activity on roe deer distribution in agricultural landscapes
Authors: Hewison A JM , Vincent J P , Joachim J , Angibault J M , Cargnelutti B , Cibien C
Published: April 2011

Landscape structure and human activity influence the distribution and abundance of species. Landscape modifications have resulted in loss of habitat, increased isolation between remnant patches, and increased disturbance. We compare distributions and group sizes of roe deer across four open agricultural landscapes of differing structure. The roe deer, essentially a woodland species, exhibits behavioural plasticity, recently colonising the agricultural plain. Our results suggest that the switch between forest and field behaviour may involve a threshold of landscape geometry concerning woodland connectivity. Where woodland fragments are numerous and widely dispersed, roe deer retain strong links to woodland structures, probably for cover and social reasons. Where remaining woodland is clumped, with little edge, roe deer adopt an open field habit, remaining at a distance from woodland. Average winter group size increased with distance from woodland, resulting in large herds typical of field roe deer populations at the more open sites. In addition, roe deer avoided areas associated with human activity, probably because of associated disturbance, particularly where woodland cover was lacking. Finally, average group size was lower in areas where the level of human activity was high. The behavioural plasticity of this species means that landscape change may not be limiting. Therefore, to predict the effects of landscape modification, models need to incorporate variation in the animallandscape relationship due to behavioural plasticity.
Interspecific variation in sexual dimorphism in brain size in Nearctic ground squirrels (Spermophilus spp.)
Authors: Iwaniuk Andrew N
Published: April 2011

A possible relationship between sexual dimorphism in brain size and mating system was investigated in five ground squirrel species: Spermophilus lateralis, S. tridecemlineatus, S. richardsonii, S. columbianus, and S. parryii. Relative brain size was measured by determining the endocranial volume of 247 ground squirrel skulls and regressing these values against two measurements of body size: mass and length. Analyses of covariation in the brain size / body size relationship within the five species revealed that sexual brain-size dimorphism occurs in three of the five species: S. lateralis, S. richardsonii, and S. tridecemlineatus. Application of a reduced major axis regression model indicated, however, that only S. lateralis and S. richardsonii exhibit significant sexual brain-size dimorphism. These findings suggest that the degree of sexual brain-size dimorphism is not directly correlated with variation in mating systems. Spatial abilities may play a role in the evolution of sexual brain-size dimorphism in ground squirrels, but the spatial requirements of mating systems appear to be insufficient. The possibility of sex differences in cognition, resource competition, and other variables as contributory factors to the evolution of sexual brain-size dimorphism is offered, but detailed knowledge of sex differences in the behaviour of ground squirrels is required to provide a definitive answer.
Threat-sensitive predator avoidance by slimy sculpins: understanding the importance of visual versus chemical information
Authors: Chivers Douglas P , Mirza Reehan S , Bryer Pamela J , Kiesecker Joseph M
Published: April 2011

The supposition that prey animals assess and behave flexibly in response to different degrees of predation threat is known as the threat-sensitive predator avoidance hypothesis. We completed a series of field and laboratory experiments to examine whether slimy sculpins (Cottus cognatus) exhibit threat-sensitive predator avoidance when exposed to sympatric predatory brook trout (Salvelinus fontinalis). In a field experiment we caged small and large trout in similar habitats and found that sculpins avoided areas containing trout that were large enough to pose a threat to them, but did not avoid areas containing trout that were small and hence not a threat. In a series of laboratory experiments we found that sculpins showed threat-sensitive predator avoidance when they could assess the predator visually. However, when only chemical cues from the predator were presented, sculpins responded to the predator regardless of its size. Chemical cues seem to function to warn the sculpin that the predator is in the vicinity, but visual cues are needed in order to accurately assess the risk posed by the predator.
Threat display in birds
Authors: Hurd Peter L , Enquist Magnus
Published: April 2011

The study of threat displays has long been an area in which theory and empirical work have each spurred the other forward. Communication is currently the focus of great interest and effort on the part of modellers. A great deal that classical ethologists have accurately described about threat displays still lacks adequate explanation. Here we review the empirical literature on the use of threat displays by birds competing for small valued resources, both to refocus theoretical attention upon the key characteristics of threat and to assess the degree to which current theory explains these characteristics. We aim to demonstrate that threat displays communicate information about aggressive motivation, but are not handicaps. Handicap models predict a single graded display, while the vast majority of studies report repertoires of about four to six discrete threats for any given species. These displays vary with motivational and strategic considerations, and may be demonstrated to rank consistently on a scale of willingness to escalate, thus providing information about aggressive motivation. We conclude by identifying those features of avian threat displays that have not been adequately explained, in the hope that this reexamination of empirical data will help focus theoretical attention on these issues.
REGULAR ARTICLES / ARTICLES RÉGULIERSSize-related predation reduces intramorph competition in paedomorphic Alpine newts
Authors: Denoël Mathieu , Joly Pierre
Published: April 2011

Evolutionary theory assumes that facultative paedomorphosis in newts and salamanders is adaptive in allowing either a younger age at maturity or resource partitioning between the heterochronic morphs. In newt populations that only take the metamorphic ontogenetic pathway, juveniles are terrestrial and avoid food competition with larvae and breeding adults. In contrast, in populations where paedomorphosis occurs, branchiate newts of all sizes coexist in the aquatic habitats, posing the question of whether intramorph competition exists and its relationship with the evolution of paedomorphosis. We studied size-related predation in such a size-structured community of branchiate Alpine newts (Triturus alpestris) inhabiting a deep alpine lake. Although gape limitation may explain such size-related predation, individuals also exhibited selectivity according to prey size. Amongst small prey that were within the capture range of all newt size classes, smaller newts preyed on smaller items than did larger ones. We assume that such decisions favour the coexistence of different-sized individuals. It is suspected that such size-selective predation on items which are avoided by water-living metamorphs allows the maintenance of facultative paedomorphosis, in favouring resource partitioning between morphs.
Reproductive trade-offs in the elapid snakes Austrelaps superbus and Austrelaps ramsayi
Authors: Rohr Detlef H
Published: April 2011

Reproductive traits and the trade-offs among these traits were examined in two venomous terrestrial elapid snakes, the Australian lowland copperhead, Austrelaps superbus, and the Australian highland copperhead, Austrelaps ramsayi. Sampling was difficult, so gravid females had to be held in captivity for up to several months prior to parturition. Analyses showed that captivity affected the time of parturition and maternal body condition, but it had no apparent effect on offspring traits. The results were corroborated by conducting partial follicular ablations in gravid A. superbus with fully yolked follicles. While these females gave birth earlier than unmanipulated females, offspring size was highly correlated with follicular size at the time of ablation and fell within the size range observed in the other females. This suggests that offspring size is fixed by the time follicles are fully yolked. Among unmanipulated females, reproductive traits were similar in A. superbus and A. ramsayi, but relationships among the traits differed. In the A. superbus sample, the trade-off between litter size and offspring size only became apparent after partial correlations, presumably because spring foraging obscured this relationship. In the A. ramsayi sample, however, the trade-off between litter size and offspring size was very pronounced. At this locality, there was no evidence of spring foraging, and snakes had fully developed follicles before or soon after they emerged from hibernation. This reduces the temporal separation between the times when litter size and offspring size are fixed and may allow greater control over the distribution of resources to offspring as a function of litter size.
Foraging patterns of juvenile walleye (Stizostedion vitreum) in a system consisting of a single predator and two prey species: testing model predictions
Authors: Czesny S , Dabrowski K , Frankiewicz P
Published: April 2011

We tested the hypothesis that the presence of a large number of energetically inferior prey (Daphnia pulex) in the environment with energetically superior prey (larval carp, Cyprinus carpio) interferes with foraging efficiency of juvenile walleye (Stizostedion vitreum). We monitored functional responses of juvenile walleye feeding on larval carp alone or in combination with D. pulex. When walleye were offered larval carp at increasing densities (10, 20, 50, and 100 individuals/30-L aquarium), they responded in accordance with a type-II functional response in 10-min trials. Walleye captured the maximum number of larval carp when offered a carp density of 20 individuals/aquarium without the daphnids. Further increase in density of larval carp had no effect on walleye foraging rate. The presence of D. pulex (900 individuals/aquarium) suppressed the efficiency of foraging walleye. The predator consistently captured fewer larval carp in all treatments when they were offered together with the daphnids even though walleye continued to select the more profitable larval carp. The negative effect of daphnids on the feeding rate is an example of environmental constraints interfering with optimal foraging models. In this study, walleye appeared to experience a confusion effect caused by the large number of inferior prey. Consequently, the predator could not gain as much energy per unit time when confronted with two prey types as it was when foraging on larval carp alone.
Site selection and repeatability in Brown-Headed Cowbird (Molothrus ater) parasitism of Eastern Phoebe (Sayornis phoebe) nests
Authors: Hauber Mark E
Published: April 2011

The reproductive success of obligate brood parasitic birds depends on their ability to seek out heterospecific nests. Some nests are more suitable for parasitism than others and, for example, parasitic females may benefit from laying eggs preferentially and repeatedly at safer sites. Observations on patterns of Brown-headed Cowbird (Molothrus ater) parasitism on Eastern Phoebes (Sayornis phoebe) across 2 years suggested that parasitism occurred at above chance levels during the first rather than the second nesting attempts and at nests located under eaves rather than bridges. Previously parasitized nests were more likely to be parasitized again in the subsequent breeding season. Sites under eaves and bridges did not differ in whether Brown-headed Cowbirds could be detected in the proximity of the nest. However, nests from first nesting attempts and nests under eaves were less likely to be lost as a result of structural failure of the Eastern Phoebe's mud nest. These data suggest that site discrimination by Brown-headed Cowbirds leads to adaptive patterns of parasitism among available Eastern Phoebe nests.
Sulfate absorption inAplysiacalifornicagut: intracellular regulation by cyclic guanosine monophosphate
Authors: Gerencser George A , Levin Randy , Robbins Frank
Published: April 2011

Luminal membranes of foregut epithelia of Aplysia californica contain a sodiumsulfate symporter. Cyclic guanosine monophosphate stimulated the absorptive activity of the sodiumsulfate symporter, whereas cyclic adenosine monophosphate had no effect on the sodiumsulfate symporter. It appears that guanylate cyclase plays a role in the overall regulation of sulfate homeostasis by the A. californica gut.
The shape of eggs in different-sized clutches of the house wren (Troglodytes aedon)
Authors: Johnson L Scott , Leyhe Jennifer E , Werner Caryn
Published: April 2011

The substantial inter- and intra-specific variation that occurs in the shape of birds' eggs remains largely unexplained. Several researchers have hypothesized that selection will favour a shape that results in the most compact fit of eggs under the incubating parent. Mathematical modeling has suggested that optimal egg shape depends on the number of eggs laid. We tested predictions of one previously published model by comparing the shape of eggs in clutches of 4, 5, 6, 7, and 8 eggs in a Wyoming, U.S.A., population of the house wren (Troglodytes aedon), a small, cavity-nesting songbird whose eggs vary considerably in shape. Contrary to predictions of the model, the typical shapes of eggs from different-sized clutches were very similar. Moreover, slight differences in shape detected were not in directions predicted by the model. There may be less selection on house wrens to adjust egg shape to clutch size because they lay eggs that are small relative to female body size, because eggs are placed in a deep spherical cup that conforms to the shape of the female's abdomen and because nests are to some degree insulated, being located in tree cavities. Full evaluation of the model will require comparisons of egg shape and clutch size in a large set of species that differ in natural-history characteristics such as egg size, nest shape, and nest placement.
On the origin and systematics of the northern African wood mouse (Apodemus sylvaticus) populations: a comparative study of mtDNA restriction patterns
Authors: Libois R M , Michaux J R , Ramalhinho M G , Maurois C , Sarà M
Published: April 2011

Conflicting hypotheses have been formulated regarding the origin of wood mouse (Apodemus sylvaticus) populations in northern Africa. In this study, the mtDNA restriction patterns of mice (n = 28) collected in Tunisia and Morocco are compared with those of representatives from southern Europe (n = 102). The neighbour-joining tree confirms the existence of the three lineages previously found in the Mediterranean area: western, TyrrhenianBalkan, and Sicilian. The western group is isolated from the two others, with bootstrap values of 89 and 95%. Northern African patterns are included in the western group. Their variability is low, the same pattern being shared by five Tunisian and all Moroccan animals (n = 18), caught either in the north of the country (Cap Spartel) or in the south (Marrakech). This implies that northern African wood mouse populations have a southwestern European origin and that their presence in the region is probably recent, which corresponds to both paleontological data and the hypothesis of anthropogenic introduction.
Investigating opposing patterns of character displacement in release and advertisement vocalizations ofBufo fowleriandBufo americanus(Anura; Bufonidae)
Authors: Leary Christopher J
Published: April 2011

Anuran release vocalizations function to prevent prolonged amplexus between males, whereas advertisement vocalizations potentially act as a premating isolation mechanism. To facilitate rapid release during heterospecific amplexus, selection should favor convergent character displacement in release vocalizations. Conversely, to promote isolation between sympatric congeners, selection should favor divergent character displacement in advertisement vocalizations. I examined properties of release and advertisement vocalizations of Bufo fowleri and Bufo americanus that are important in mate recognition (periodicity and dominant frequency) to determine if the two calls exhibit opposing patterns of character displacement. Release vocalizations showed no pattern of displacement. The periodicity of sympatric advertisement vocalizations differed from that of allopatric vocalizations for B. americanus but not for B. fowleri. However, the results were not consistent with the pattern expected for divergent character displacement because the two species differed in this parameter in allopatry. These results are compared with published reports of char acter displacement in the B. americanus species-group in the context of a possible mosaic hybrid zone for these species.
Effectiveness of predator odors as gray squirrel repellents
Authors: Rosell Frank
Published: April 2011

The ability of gray squirrels (Sciurus carolinensis) to discriminate between different predator odors and the use of predator odors to deter gray squirrels from foraging on plants have not been previously investigated. To test the hypothesis that predator scent decreases foraging, I investigated the effect of such scent on consumption of butternuts (Juglans cinerea) in the field. Results showed that (i) red fox (Vulpes vulpes) scent was significantly more effective than either a control or human scent; (ii) raccoon (Procyon lotor) scent was significantly more effective than white-tailed deer (Odocoileus virginianus) scent (but only after 79 h); (iii) red fox scent was not significantly more effective than raccoon scent; and (iv) human scent was not significantly more effective than the control. The utility of predator odors in controlling damage by gray squirrels should be explored.