Journal of Zoology最新文献

Hyper-allometry, whereby an anatomical unit increases in size at a faster rate than other structures of the same organism, is considered to be an important feature of many sexually selected structures, with large ‘high-quality’ animals carrying a feature that is proportionally larger than smaller, ‘low-quality’ animals. When these structures are bilaterally symmetrical, it has been suggested that the degree of fluctuating asymmetry (deviation from perfect symmetry) acts as an indicator of the quality of the bearer. Bovids are useful models for testing sexual selection hypotheses due to their large horns and variety of reproductive systems. Here we use male and female specimens of the southern African blue wildebeest (Connochaetes taurinus) to assess the levels of allometry and fluctuating asymmetry in morphological features of the horns and skull. Males were found to be significantly larger than females for overall horn size, horn length and horn circumference and the horns were found to be isometric in both sexes. Directional asymmetry was found for horn length and horn circumference with the right being longer than the left side. These findings suggest that in C. taurinus the horns follow predicted patterns of variation for sexually selected traits, but that here fluctuating asymmetry may not be as important in sexual selection as previously suggested. Additionally, females did not differ greatly from males in variation and asymmetry and allometry, indicating their horns could be under sexual selection as a result of male choice, or that like males, they also engage in intraspecific combat as well.

Proximity to the seashore is a critical structuring factor of coastal wetlands due to its influence on varying sources of nutrients (marine and terrestrial) and on the spatial gradient of salinity (higher salinity closer to the seashore). The spatial gradient of salinity may impact organisms because most organisms need to maintain an osmotic balance. Osmoregulation is energetically costly, and exposure to salinity should induce a trade-off in energetic allocation between osmoregulation and other competing functions such as growth rates and movement patterns. In this study, we used a capture–mark–recapture design during 3 consecutive years to investigate how distance to the sea influences growth rates and foraging movements (outside reproduction) in the western spadefoot toad (Pelobates cultripes), a typical coastal amphibian, in three populations from the French Atlantic coast. Growth rates were lower in larger individuals and in individuals living closer to the seashore. Distances travelled between captures were very limited (~20 m). Between years, these distances were larger for individuals located on the beach rather than inland, but were not influenced by body size or sex. Exposure to salinity and associated costs of osmoregulation may explain lower growth rates closer to the shoreline. The mechanisms underlying the effects of location on distances between captures remain to be identified, but may be related to foraging for abundant prey items on the wrack line. Our study confirms the remarkable terrestrial site fidelity in P. cultripes, which might be detrimental to coastal populations if localized perturbations affect coastal environments.

Host–parasite systems, including social parasites that exploit resources of the host colonies, are fascinating objects for evolutionary biologists mainly due to the dynamic and often rapid host–parasite coevolution. Host-switching events are believed to induce rapid speciation of parasitic species. The socially parasitic ant lineage Myrmoxenus, which corresponds to the monophyletic Temnothorax corsicus group, counts in total a dozen species. Most Myrmoxenus species utilize a single host species, but a few others, like Myrmoxenus ravouxi (André, 1896) and M. gordiagini Ruzsky, 1902, are known to use multiple host taxa. Myrmoxenus zaleskyi (Sadil, 1953) was described as a putative congener of M. ravouxi based on its distinct host selection. In this paper, we investigate the diversity of the widely distributed European lineages M. ravouxi and M. zaleskyi from multiple and complementary perspectives to understand whether the host preference exhibited by these two forms implies speciation. We integrated evidence from molecular genetics using mitochondrial CO I/CO II genes, including the tLeu-region, and multivariate analyses of morphometric data collected from workers and female sexuals (gynes). Although there is substantial regional host species specificity, results suggest that host switching did not result in phylogenetic or morphological divergence and that the central European M. zaleskyi can be considered the junior synonym of M. ravouxi. As the lineage Myrmoxenus has been the subject of considerable evolutionary research, these results are essential to achieve a more accurate picture of host–parasite systems in the future and further strengthen the justification of an integrative approach in studying similarly complex systems. We advise against describing new parasitic species based on host preference unless coupled with marked heritable phenotypic adaptations.

Bird wings vary in size and morphology in terms of both size and number of feathers and the underlying skeletal anatomy. The number of primary remiges does not seem to vary much between bird species but, by contrast, the number of secondary remiges is reported to range between 6 and 40 depending on bird size. Given that the primaries are attached to the manus, and the secondaries are attached to the ulna, it was predicted that as bone lengths increased with increasing size of the bird, then feather count would increase. Data were collected for 268 species from 25 different orders, and phylogenetically controlled analysis explored the allometry between feather count and bone size. The number of primaries was typically 10 or 11 and did not vary with manus size. By contrast, the number of secondaries increased with ulna length, but only in some orders. For example, in Gruiformes, the number of secondary feathers increased concomitantly with ulna length but despite a two orders of magnitude range in body mass, almost all species in the Passeriformes had nine secondary remiges. It is unclear why, for instance, species with an ulna length of 70 mm can have between 9 and 24 secondaries depending on their order. This variation in secondary feather number can be added to variation in relative wing bone lengths, flight feather lengths, flight feather mechanical properties, and flight feather vane densities as another potential mechanism of adaptation to flight requirements. The apparent constraint of wingspan is scaling as approximately body mass^1/3. Further research is needed to explore whether changes in secondary feather number relative to ulna length are accompanied by changes in feather vane width or the overlap of adjacent feathers and how this relates to wing aerodynamics.

Climate warming combined with intensive human activities are modifying ecosystems globally, and the Arctic biota is shifting substantially faster than the global average, allowing many new species to expand their range poleward. One such species, is the American beaver (Castor canadensis), a highly specialized rodent capable of greatly modifying ecosystems by altering forest composition through selective foraging and by flooding the landscape through dam and channel building. As rodent cranial morphology is highly related to its functional requirements for foraging and feeding, the beaver provides an opportunity to evaluate the phenotypic response of species to changing environmental conditions. Here, we test the hypothesis that beaver skull morphology is optimized for its local environmental and habitat conditions across Canadian ecosystems. We found that temperature, precipitations, biomass, and local average tree hardness significantly affect the morphology of key masticatory functional traits of the skull, but not its size. Our results suggest that the beaver's phenotype is locally adapted to environmental conditions as a result of its selective foraging behavior. This work provides insight into the adaptive potential of newly established beaver populations in the sub-Arctic to inform management strategies for this keystone species. More generally, our work emphasizes the need to consider traits other than body size in research seeking to better understand the response of species to current global change.

Variation in thermal conditions during embryogenesis can have far-reaching impact throughout ontogeny and may give rise to behavioural variation. Many animals, such as salmonids, exhibit behavioural trade-offs related to foraging and predator avoidance. How embryonic temperature affects these behaviours has remained unexplored. Not only abiotic conditions during embryogenesis but also biotic factors such as predator conditioning may affect fish behaviour, especially anti-predator responses. We examined how elevated temperatures and predator odours throughout embryogenesis affect the behaviour of 28–37 mm young-of-the-year brown trout (Salmo trutta) in encounters with predators, namely Atlantic salmon (Salmo salar; 20 cm) and burbot (Lota lota; 40 cm). Juvenile brown trout were more active and aggressive if they were incubated in warmer water as eggs than if they were incubated in colder water, and trout remained inactive longer when encountering predators if they were cold incubated. Brown trout were less active and aggressive when an Atlantic salmon was present than when a burbot or no predator was present. Behavioural responses did not differ between trout that had been subjected to water with versus without predator odours during embryogenesis, possibly because brown trout were not subjected to conspecific alarm cues during egg incubation. This study shows that thermal conditions during embryogenesis can influence fish behaviour early in life and thus contribute to behavioural variation, with potential effects on life history. Considering the rapid warming of northern regions, elevated embryonic temperatures may contribute substantially to variation in salmonid behaviour in the near future.

Environmental factors, such as temperature, precipitation, and elevation, explain most of the variation in species richness at the global scale. Nevertheless, richness patterns may have different drivers across taxa and regions. To date, a comprehensive global examination of how various factors such as climate or topography drive patterns of species richness across all terrestrial vertebrates, using the same methods and predictors, has been lacking. Recent advances in species-distribution data allowed us to model and examine the richness pattern of all terrestrial tetrapods comprehensively. We tested the relationship between environmental and biogeographical variables and richness of amphibians (5983 species), birds (9630), mammals (5004), reptiles (8939), and tetrapods as a whole, globally, and across biogeographical realms. We studied the effects of climatic, ecological, and biogeographic drivers using generalized additive models. Richness patterns and their environmental associations varied among taxa and realms. Overall precipitation was the predominant richness predictor. However, temperature was more important in realms where both cold and warm conditions exist. In the Indomalayan realm, elevational range was very important. Richness patterns of mammals, birds, and amphibians were strongly related to precipitation whereas reptile richness was mostly associated with temperature. Our results support the universal importance of precipitation but also suggest that future global-scaled research should incorporate other relevant variables other than climate, such as elevational range, to gain a better understanding of the richness–environment relationship. By doing so, we can further advance our knowledge of the complex relationships between biodiversity and the environment.

Broad geographical distributions that include marked climatic variation may expose populations to distinct selective pressures. Local adaptation to differences in developmental conditions may lead to divergence in embryonic and hatchling traits for populations of oviparous reptiles. Among-population differences in hatchling size and the duration of development are often observed in lizards with wide and climatically diverse distributions. Variation in hatchling phenotypes can arise from variation in maternal allocation, developmental plasticity or selection acting on embryonic traits. We studied variation in hatchlings of the Australian water dragon (Intellagama lesueurii), comparing traits related to growth and patterns of developmental plasticity. We recorded marked differences in hatchling sizes among populations from different climate types, which did not result from differences in maternal investment or from a plastic response to incubation temperatures. Embryos from southern, temperate populations exhibited shorter incubation times when incubated at cold temperatures but utilized less yolk during development and hatched smaller, with more residual yolk, regardless of incubation treatment. We suggest that these findings represent the first example of among-population variation in patterns of embryonic resource allocation and a novel mechanism mediating offspring size in reptiles. We further suggest that variation in embryonic resource allocation in I. lesueurii, together with evolutionary changes in reaction norms for developmental rate, evolved as adaptations to seasonal length and conditions associated with a tropical-temperate gradient.

Understanding animals' selection of microhabitats is important in both ecology and biodiversity conservation. However, there is no generally accepted methodology for the characterization of microhabitats, especially for vegetation structure. We studied microhabitat selection of three Vipera snakes by comparing grassland vegetation structure between viper occurrence points and random points in three grassland ecosystems: V. graeca in mountain meadows of Albania, V. renardi in loess steppes of Ukraine and V. ursinii in sand grasslands in Hungary. We quantified vegetation structure in an objective manner by automated processing of images taken of the vegetation against a vegetation profile board under standardized conditions. We developed an R script for automatic calculation of four vegetation structure variables derived from raster data obtained in the images: leaf area (LA), height of closed vegetation (HCV), maximum height of vegetation (MHV) and foliage height diversity (FHD). Generalized linear mixed models revealed that snake occurrence was positively related to HCV in V. graeca, to LA in V. renardi and to LA and MHV in V. ursinii, and negatively to HCV in V. ursinii. Our results demonstrate that vegetation structure variables derived from automated image processing significantly relate to viper microhabitat selection. Our method minimizes the risk of subjectivity in measuring vegetation structure, enables the aggregation of adjacent pixel data and is suitable for comparison of or extrapolation across different vegetation types or ecosystems.