Journal of Zoology最新文献

Although the widespread effects of climate change impact almost all ecosystems, we lack a detailed understanding of how wildlife that thrive in human-dominated environments are able to adjust their life history to modifications in land use of their natural habitat. In particular, spatial variation in environmental conditions is predicted to influence body development during the crucial early life phase, with marked impacts on individual performance and population dynamics for long-lived species. Large herbivores have increased substantially in number and distribution over the last half century across Europe. The synanthropic roe deer (Capreolus capreolus) has been particularly successful, gradually colonizing agricultural landscapes. However, little is known about how habitat heterogeneity in this heavily human-impacted environment impacts demographic performance. Specifically, we predicted that fawns born in predominantly cultivated local habitats would achieve faster early development due to the food subsidies obtained from agricultural crops by their mothers. Contrary to our expectations, fawns in semi-natural forest were around 10% heavier at birth than those born in more mixed (by 0.163 ± 0.058 kg) and open (by 0.169 ± 0.006 kg) agricultural habitats. However, the body mass of all fawns subsequently increased at a similar average rate (0.148 ± 0.058 kg/day) over the first 20 days of life, irrespective of their habitat. This habitat-dependent variation in early life mass appeared to be driven by reproductive phenology, as (1) early-born fawns were heavier than late-born fawns, and (2) mothers living in forest gave birth around 10 days earlier than those living in the mixed and open sectors. Semi-natural habitats might thus be the more suitable for fawn early development, despite the availability and abundance of energetically rich food resources for lactating mothers in open and mixed habitats.

The baculum is a morphologically highly diverse genital bone found in most male eutherian mammals. Its exact function is still debated, but its role during mating and/or copulation might be linked to, among others, support during intromission or sexual selection. Less is known about how the shape of the baculum develops throughout ontogeny. Differences between juveniles and adults could reveal morphological changes related to sexual maturity and, in turn, provide evidence for a functional role in sexual reproduction. In this paper, we investigated the postnatal development of baculum shape in the harbour seal (Phoca vitulina) by using μCT scans of 298 specimens, ranging from juveniles to 28 years of age. We applied a 3D geometric morphometrics approach to analyse how the shape and centroid size of the baculum change throughout ontogeny. We found that in the first 3 years of life, barely any changes happen to size, but before reaching sexual maturity, both shape and size change immensely within a short period of time. After becoming fully grown around the age of seven, we did not find any further major changes in these attributes. The postnatal development of the baculum appears to be linked to changes in hormone levels, which would explain the rapid changes during puberty. The largest shape variation is characterized by an increase in bone curvature from juveniles to adults, while the baculum appears to be most robust (in terms of relative thickness) during puberty, which is difficult to explain. Still, the relatively small shape variation after reaching sexual maturity indicates that the shape of the baculum is functionally constrained in the context of sexual reproduction.

The presence of parasites can significantly influence animal behavior. Specifically, grooming behavior may have evolved in part as a response to the physical and psychological challenges induced by parasitism. Grooming behaviors, which can be individual or social, help remove parasites, maintain hygiene, and offer stress relief. These interactions underscore the adaptive coping strategies of animals for environmental challenges, highlighting the role of parasites in shaping animal behavior and survival. A continual rise in human cases of vector-borne disease demands a more detailed understanding of how ticks interact with their host species that usually serve as pathogen reservoirs. White-footed mice (Peromyscus leucopus) are one of the most frequently studied hosts of blacklegged ticks (Ixodes scapularis); however, interactions between white-footed mice and ticks are not easily observed. This study aimed to quantify activity patterns in white-footed mice and to assess their behavioral responses to parasitism by blacklegged ticks within a controlled setting using Ethovision® software. White-footed mice were infested with nymphal blacklegged ticks or evaluated without tick infestation over 4 days. The mean number of ticks on the mice after the infestation period was 19.6 ± 5.9, and the mean number of ticks that attached and fed through the duration of the trial on the infested mice out of these was 8.6 ± 4.4. Grooming frequency was not significantly affected by tick parasitism, regardless of the number of attached ticks. While this study was the first to quantify behavior in lab-reared white-footed mice in response to blacklegged tick parasitism, further work is needed to determine how wild-caught white-footed mouse behavior might differ.

Many animals reap significant benefits from migration, yet they face high mortality rates during the journey. As the mortality during migration typically operates more strongly on smaller migratory individuals (migrants), small pre-migrants among migratory animals tend to grow better than larger ones prior to migration, enabling them to attain a larger body size. A common growth strategy for smaller pre-migrants is extending their growth period compared to larger ones. Although this tactic has been documented in previous studies, the landscape-scale habitat utilization that allowed smaller pre-migrants to stay longer prior to migration remains largely unknown. Here, we focused on two distinct riverscape habitats (nursery habitat and transitional habitat) and investigated where smaller pre-migrants of masu salmon (Oncorhynchus masou) stayed longer than larger ones prior to oceanic migration. We conducted an individual monitoring survey on their habitat utilization in two distinct migration years. We found that in 1 year, smaller pre-migrants stayed longer in the transitional habitat compared to the nursery habitat, whereas in the other year, they stayed longer in the nursery habitat compared to the transitional habitat. This suggests that smaller pre-migrants can adjust their duration of stay in each riverscape habitat. Our findings highlight the importance of conserving the entire pre-migration habitat to enhance the resilience of migratory animals in the face of rapid environmental changes.

Different defensive strategies are used by tadpoles to avoid or escape from predators, and it is possible that differences in the microhabitat of prey and predators influence the defensive strategies used by tadpoles. Therefore, we experimentally tested whether the presence of a nektonic fish predator (Oreochromis niloticus) reduces the time of displacement, increases the latency to start foraging, and reduces the amount of food consumed by nektonic (Scinax fuscovarius) and benthic (Physalaemus nattereri) tadpoles. Contrary to our expectations, the presence of the predator did not affect the behavior of the nektonic tadpoles. Conversely, however, benthic tadpoles reduced their displacement time in the presence of the predator. It is possible that, due to the ability of nektonic predators to occupy the entire water column, they may trigger defensive behaviors in benthic prey, while the silvery coloring of nektonic tadpoles would reduce their detectability by aquatic predators. Thus, nektonic tadpoles were less reactive toward the presence of predators, despite sharing the same microspatial niche, whereas benthic tadpoles seem to be more reactive toward predators, despite the fact that they do not share their microspatial niche.

In coevolved native ungulate assemblages, the mechanisms underlying competition remain unclear because, to date, little direct evidence of competition exists. In high-elevation areas in Japan, the number of native Japanese serows (Capricornis crispus) has been decreasing as the number of native sika deer (Cervus nippon) increases. Here, we assessed the effects of deer on vegetation, vigilance and foraging behavior, physiological stress, and relative abundance and ratio of young individuals of serows throughout the warm season across two study sites with different deer densities and similar landscapes in high-elevation areas of Mount Asama, Central Japan. The abundance and diversity of palatable forage for serows (i.e., herbaceous forbs) were significantly lower in areas with abundant deer, suggesting that deer abundance reduced the vegetation quality for serows. Serow vigilance rate was significantly greater in areas with abundant deer, suggesting that the increased probability of encountering deer or of intraspecific aggression increased vigilance. Serow bite rate was significantly lower and their step rate was greater in areas with abundant deer, suggesting that lower availability of herbaceous forbs and higher vigilance reduced serow foraging efficiency. Levels of serow fecal cortisol metabolites were significantly greater in areas with abundant deer, suggesting that deer abundance and decreased foraging efficiency increased physiological stress of serows. The relative abundance and ratio of young individuals of serow populations were significantly lower in areas with abundant deer, suggesting that deer abundance negatively affected the serow population through both exploitative and interference competition. This is a rare case to show direct evidence and mechanisms of interspecific competition in native ungulate assemblages. Human alteration of ecosystem processes, such as the elimination of top predators and decreased human hunting pressure on deer, may determine changes in ecological relationships between serow and deer.

Melanism is a common trait in vertebrates. While in endotherms, melanism has been primarily associated with the protection against oxidative stress caused by incoming UV radiation, in ectotherms, it is far less understood. Bogert's rule, the most widely supported biogeographical framework explaining the occurrence of melanism in reptiles, states that melanistic individuals should be favoured thanks to faster heating rates. It has led to the formulation of the Thermal Melanism Hypothesis to explain the evolution and maintenance of melanism in ectotherms. Although some support for this hypothesis exists, it is not broadly accepted, and the importance of the thermal advantage as an evolutionary driver of melanism in ectotherms needs to be specifically addressed. Melanism is common in squamate reptiles, where it occurs at various extents depending on the considered taxonomic level. Such variability opens the use of a phylogenetic comparative approach to test whether climatic conditions, by pivoting thermal advantage, could drive the evolution of melanism in reptiles. By focusing on the snake family Elapidae, we firstly reconstructed the evolutionary history of melanism and, subsequently, tested whether climate affects the frequency of melanism. Ancestral state reconstruction estimated that the ability to express melanism is the ancestral condition of elapid snakes. Furthermore, we found statistically significant effects of both average diurnal temperature and precipitation on the probability of a species to be melanistic, so that melanism is more frequent in colder and wetter climates. Melanism in Elapidae seems to be highly correlated with colder temperatures, so that it is most likely favoured compared with normal colourations to boost thermoregulation under less favourable conditions. Although broad-scale conclusions still must be drawn for squamates, with this research, we provide additional support for the TMH in ectotherms as a key adaptive interpretation of this phenotypic trait in wild populations.

Understanding the trade-off between resource acquisition and risk avoidance is crucial in behavioral ecology. Differences in parental investment and reproductive success between males and females can result in intersexual variations in the trade-off between resource acquisition and risk-taking. Roads, a major cause of habitat fragmentation, pose significant mortality risks to animals. We investigated the sex and seasonal differences in road-crossing behavior and home ranges of Asian black bears (Ursus thibetanus), as an example of risk-taking behavior of mammals in a fragmented landscape, in the Ashio-Nikko Mountains, Japan, from 2005 to 2023. Using GPS relocation data, we analyzed the frequency of road crossings and home range sizes and applied integrated step selection analysis to assess road-crossing avoidance in relation to sex, season, road type, and time of day. Bears generally avoided crossing roads, indicating that roads act as movement barriers. During the mating season, males crossed all types of roads and had larger home ranges, whereas females did not cross main and minor roads. During the hyperphagia season, both sexes crossed all road types and had larger home ranges compared to the mating season. Our findings suggest that sex- and season-specific risk-taking behavior of bears relates to mate and food acquisition: males take more risks to search for mates during the mating season compared to females. Bears crossed gated minor roads most frequently, followed by minor roads and main roads, with crossings occurring more often at night than during the day across all road types. These results suggest bears perceive and respond differently to risks of roads, which are linked to the level of human activity.

Recent years have seen the emergence of spatially explicit capture-recapture (SECR) modeling as the recommended tool to monitor lion populations. In this study, we apply this method to camera trap data collected within Tanzania's Selous–Nyerere landscape, which is considered one of the species' few remaining strongholds in Africa. We estimated lion population density through SECR modeling of camera trap data from seven sites within Nyerere National Park (NP) and Selous Game Reserve (GR), the largest protected areas in the complex, to examine variation in lion population density. Our findings reveal lion population densities ranging from 0.33 (95% CIs: 0.12–0.91) lions over 1 year of age per 100 km² in the dry eastern Miguruwe sector of Selous GR to 6.27 (95% CIs: 4.18–9.39) individuals over 1 year per 100 km² in the prey-rich lakes area of the Matambwe sector of Nyerere NP. Dry season lion density in the system appears to be primarily driven by prey availability, which is itself principally determined by the productivity of miombo woodlands. However, evidence of human impacts and lower than expected densities at some sites suggest that anthropogenic pressure may be affecting Selous–Nyerere's lion population, particularly in areas close to boundaries. We show that camera trap-based monitoring combined with SECR can be a valuable tool to monitor lion populations in remote areas, particularly as it allows for simultaneous monitoring of other large carnivores, provides insights into wider mammal communities, aids the identification of threats, and can form the basis of sustainable offtake quotas. Our findings also demonstrate the importance of direct monitoring to understand how carnivore populations are faring and inform evidence-based conservation management.

The seasonal use of caves by bats can be attributed to physiologically demanding activities like mating and reproduction in spring and torpor in winter. Cave use, however, varies within and across species and can depend on the physical and microclimatic conditions of the caves. Understanding the current patterns and predictors of cave use is therefore crucial to develop a reference for assessing the response of bats to future changes in climatic conditions. We quantified the diversity and abundance of bats in 41 caves that varied in structure and temperature across a seasonal (mid-winter, late-winter and early-spring) and an elevational (400–2700 m above sea level) gradient in the central Himalayas. Richness and abundance of bat species exhibited seasonal variation, with more species and individuals present in caves during early-spring (n = 15) compared to mid-winter (n = 9). Species richness declined linearly with elevation in mid-winter but remained relatively similar until 900 msl and then declined in late-winter and early-spring. Species such as Hipposideros armiger (20.14 ± 1.60°C in spring and 17.97 ± 0.88°C in mid-winter), Rhinolophus affinis (19.98 ± 1.76°C in spring and 16.18 ± 3.09°C in mid-winter) and Rhinolophus cf. pusillus (19.55 ± 1.64°C in spring and 15.43 ± 2.87°C in mid-winter) preferred warmer microclimates within caves during early-spring compared to mid-winter. The season- and species-specific cave use that we report here suggests that even minor fluctuations in cave temperatures could potentially alter the composition of bat communities inside caves. Prioritization assessment based on a bat cave vulnerability index indicates that different caves must be protected based on their specific usage patterns and the abundance of species they support at various times. Overall, we highlight the importance of studying cave-dwelling bats in climate-vulnerable areas such as the Himalayas where species richness is high to help understand and predict the responses of animals to climate change.