Journal of Zoology最新文献

The responsiveness of the hypothalamic–pituitary-adrenocortical axis to stressors is crucial for wild animals to survive and adapt to environmental changes without compromising individual welfare. We analysed the influence of prior weather conditions, seasonality, the influx of ecotourism, and nutrition on stress levels in a wild population of red deer in a Mediterranean hunting reserve in the Pre-Pyrenees, Spain. We used faecal cortisol metabolites as a proxy for physiological and psychological stress, and faecal triiodothyronine metabolites as an indicator of nutritional stress. Faecal analyses were chosen because it is a non-invasive technique that does not alter an individual's behaviour, and it is easy to conduct in a wild population, something which presents added challenges due to the lack of a controlled environment. Our results indicate that prior weather conditions, rather than just seasonality, best explained the variations in these hormones within seasons and among years. On the contrary, the results showed that high levels of the cortisol hormone did not necessarily correspond to low levels of the triiodothyronine hormone. This could be a sign of acute nutritional stress in this population. Finally, we did not find an effect of the ecotourism influx on cortisol levels, suggesting that this deer population tolerates the presence of tourists.

It has been suggested that the American black bear (Ursus americanus) may be responsible for a significant number of purported sightings of an alleged unknown species of hominid in North America. Previous analyses have identified a correlation between ‘sasquatch’ or ‘bigfoot’ sightings and black bear populations in the Pacific Northwest using ecological niche models and simple models of expected animal sightings. The present study expands the analysis to the entire US and Canada by modelling sasquatch sightings and bear populations in each state/province while adjusting for human population and forest area in a generalized linear model. Sasquatch sightings were statistically significantly associated with bear populations such that, on the average, every $��1000�$ bear increase in the bear population is associated with a $��4�\%�$ ($��95�\%�$ CI: $��1�$–$��7�\%�$) increase in sasquatch sightings. Thus, as black bear populations increase, sasquatch sightings are expected to increase. On average, across all states and provinces in 2006, after controlling for human population and forest area, there were approximately $��5000�$ bears per sasquatch sighting. Based on statistical considerations, it is likely that many supposed sasquatch are really misidentified known forms. If bigfoot is there, it could be a bear.

Laboratory experiments suggest that reversible changes in the heart ventricle phenotype of fish accompany acclimation to temperature change to maintain cardiac function, but related work in fish living in natural conditions is scant. We investigated seasonal variation in heart ventricular mass and collagen content in pumpkinseed sunfish (Lepomis gibbosus) living in outdoor ponds where they experienced high seasonality conditions. Additionally, we compared populations adapted to high and low seasonality to evaluate potential divergence in seasonal heart plasticity. Heart ventricular mass decreased in the summer compared to colder seasons only in populations adapted to high seasonality. The absence of seasonal variation in ventricular mass in sunfish adapted to low seasonality was not due to changes in foraging activity, suggesting a loss of ventricle size plasticity due to either costs of plasticity or relaxed selection. Seasonal variation in ventricle collagen content also occurred, with the highest collagen content in summer regardless of population adaptation to high or low seasonality. Only the proportion of thick collagen fibres changed across seasons. We conclude that natural seasonal cues induce plastic responses in some functional heart traits and propose that these responses can rapidly diverge among populations under different seasonal regimes.

In free-living species, the comparison of eggshell microstructure focus mainly on species representing extremely different reproductive strategies or with phylogenetically divergent taxa. The purpose of this study was to compare the microstructure of the mammillary layer in two bird orders (Galliformes and Anseriformes) representing phylogenetically close precocials, and to relate eggshell microstructure to female body weight and egg characteristics. The results showed significant differences between the studied orders. The mammillary layer in Galliformes had more knobs, and consequently, the percent coverage with them was higher than in Anseriformes. The size of individual knobs did not differ significantly between the orders. The obtained results are consistent with the reports that the ossification at the time of hatching is more advanced in Galliformes, so representatives of this order must resorb more calcium from the eggshell. Egg parameters and female body weight were correlated significantly negatively only with the number of knobs per mm² for Anseriformes and, to a lesser extent, for Galliformes, but not with the coverage per cent of knobs or the size of individual knobs. Only for the three largest species, which lay proportionally larger eggs than the other species studied, the number of knobs per mm² was significantly lower, but no difference was found in the per cent coverage of knobs. Our results showed that order was a stronger predictor of microstructure than species. Different ossification patterns of the embryonic skeletal system described in these two orders could be the explanation for the observed differences in eggshell microstructure; however, more research is needed.

While for decades behavioural ecologists have studied the costs and benefits of group living, solitary living has received little attention. Instead, it was assumed to be the default stage from which sociality evolved. Mammals underwent around 200 million years of social evolution, with a few species evolving communal or cooperative breeding in harsh environments. Other mammal species are successful with solitary living in exactly the same and many other environments, indicating that solitary living is beneficial under many environmental conditions. Comparative studies on mammals indicate that solitary living might not be the ancestral but a derived state. Solitary living in mammals is less common than previously believed, occurring in 22% of the studied species. Here, we review costs and benefits of solitary living in mammals. We found very few studies that considered solitary living and show important future avenues of research based on the factors that are important for the evolution of group living. We also emphasize that a solitary form of social organization does not imply an unsocial lifestyle: solitary mammals typically have non-random but individualized social interactions with their neighbours, indicating important social structure.

Phenotypic plasticity, which encompasses the diversification of both irreversible and reversible traits, has long been considered an adaptive response by animals to varying environmental conditions. However, the process by which irreversible and reversible traits are coordinated to form an adaptive response to the changing environment has yet to be clarified. Here, we investigated the variation in body size of two urban insect species in the context of habitat fragmentation. These species were the Chinese cricket Gryllus chinensis and the stove grasshopper Diestrammena japonica, which are sympatric in urban housing estates. Results indicated that both species changed in body size in patches of urban environment. However, their body size shifts showed opposite tendencies and were influenced by distinct selective forces: Chinese crickets increased their body size with the patch history and predation risk, whereas stove grasshoppers decreased their body size with the degree of fragmentation of the patches. Territorial and competitive Chinese crickets rarely experience resource scarcity during urban environment fragmentation. Thus, a larger body size was preferred in response to intraspecific competition among Chinese crickets. By contrast, stove grasshoppers are group-living and scramble for resources as competitors, requiring a large territory to secure adequate food for supporting a group of individuals. Consequently, stove grasshoppers frequently experienced resource scarcity in the patchy habitat, favoring small body size to reduce individual requirements throughout the life cycle. Our findings indicate that the body size shift of sympatric insects may be subjected to distinct selective forces in fragmented habitats, depending primarily on their reversible traits.

Genetic exchanges between species provide valuable opportunities to dissect the relative importance of neutral and selective processes driving introgression events and to test their functional relevance. In the northern half of the Iberian Peninsula, the Iberian hare, Lepus granatensis, presents extensive patterns of mitochondrial DNA (mtDNA) introgression from the mountain hare, L. timidus, a species that disappeared from the region after the Last Glacial Maximum. Here, we test whether mtDNA introgression affects reproductive success and body condition of Iberian hare individuals. For that end, hares (n = 149) were sampled from populations along the mtDNA introgression gradient during the 2013–2014 and 2014–2015 hunting seasons. Reproductive performance indicators, including pregnancy status and testicular weight, were recorded, while body condition was measured as kidney fat (our response variables). Predictors included individual traits (sex and age), sampling period (month and hunting season), mtDNA introgression, occurrence or burden of different endoparasites and environmental factors. Our results showed that mtDNA introgression was negatively associated with pregnancy in females and body condition in males, while a positive association was found with body condition in females. These results suggest that carrying the mountain hare mtDNA has physiological effects in Iberian hares, but that the allospecific mtDNA type may not always be beneficial for the individual. This study shows that the patterns of mtDNA introgression seen in the Iberian hare today may result from a complex balance between deleterious and beneficial individual effects.

Chlamyphorus truncatus is the smallest known armadillo, weighing about 100 grams and measuring less than 15 cm from head to tail. It is endemic to central Argentina and the species is named after its unique carapace. This armadillo has almost completely subterranean habits and, unlike all other subterranean mammals, C. truncatus has a carapace composed of osteoderms and cornified scales. Furthermore, the skin and carapace show unique characteristics compared even with other armadillos. Owing to the reduced development of its eyes, it is important to analyse the skin morphology of this species, as well as specialized sensory organs like vibrissae. The aim of this contribution is to describe the histomorphology of the integumentary system of C. truncatus. For this, histological sections of the skin with and without osteoderms were made, and routine histological and immunohistochemical techniques were performed. Furthermore, microCTs were performed on osteoderms to describe their micromorphology. Our results show that the integumentary system presents unique characteristics compared to other armadillos, such as the peculiar skin under the dorsal shield and the flexibility of almost all of its carapace. Furthermore, the modification of the arrangement of hairs in the first pelvic buckler osteoderms may suggest biomechanical adaptations, such as an improvement in the displacement through the tunnels of sandy soils. The skin without osteoderms presents convergent characteristics with that of other subterranean mammals. Furthermore, the vibrissae conserve the structure of the armadillos (the cavernous sinuses extend throughout the follicle-sinus complex) with a thinning and shortening of the hairs, which are probably linked to passive monitoring of the surrounding environment. Evidently, the adaptations of subterranean mammals to their environment imply structural and functional changes, which are both regressive and progressive in nature.

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.