Journal of Zoology最新文献

Hummingbirds use their extreme maneuverability to defend territories and win competitions. In theory, a bird can tap into its muscular power reserves to perform complex maneuvers, with the size of the power reserves dictating the maximum maneuvering performance. To test the link between power reserves and maximum maneuvering performance, we used load-lifting trials to measure the power reserves of Anna's hummingbirds (Calypte anna). Based on these estimates, we calculated the theoretical maximum arcing turn performance. Finally, we used thousands of arcing turns measured with an automated tracking system to evaluate whether maximum turning ability aligned with the theoretical predictions. The maximum turning performance of the hummingbirds closely matched the maximum predicted by their power reserves, even though individual performance maximums were not correlated with individual power reserves. Therefore, our evidence that power reserves underlie maximum performance is mixed: it is in the aggregated turns across all individuals that the large-scale patterns of maximal performance begin to emerge. Because they limited turning performance, power reserves also created a trade-off between radius and velocity. As large free-flight datasets continue to be explored, it is likely that we will continue to find associations between burst power and maximal maneuvering performance.

Our study explores the dynamics of introgressive hybridization between two sympatric crocodilian species, Caiman latirostris and Caiman yacare, shedding light on the ongoing genetic exchange. Hybrid individuals exhibit a notable absence of distinct boundaries between parental and hybrid forms, potentially influenced by factors like limited dispersal potential or unexplored extrinsic variables. Despite sympatric coexistence, the species occupy distinct ecological niches, limiting hybridization. Climatic factors, particularly during autumn and winter, may further impact migration and energy allocation, contributing to the observed introgression pattern. Significantly, the prevalence of individuals with hybrid index values indicates introgressive hybridization between C. yacare and C. latirostris populations, supported by ecological niche models that found wide areas with potential for hybridization across much of their distribution. The range of hybrid index values suggests gene flow and the transfer of adaptive traits through hybridization. The divergence between C. yacare and C. latirostris, approximately 26 million years ago, aligns with geological and climatic changes during the Oligocene. Furthermore, our findings support a directional radiation pattern in C. latirostris populations from south to north, influenced by climatic changes and ecological niche shifts. This study revealed the dynamics of introgressive hybridization between C. yacare and C. latirostris, emphasizing the complex interplay of ecological, temporal, and environmental factors in shaping genetic patterns and evolutionary history.

Iridescence refers to the optical property of surfaces for which the reflected wavelengths depend on viewing geometry. Although iridescence underlies some of the most striking animal colours, the sensory stimulation elicited by iridescent spectral shifts in relevant observers has seldom been explored. Wall lizards (genus Podarcis), with remarkable intraspecific colour variation and possible iridescence, offer a unique opportunity to investigate how these traits interact to shape overall colour appearance. Here, we set out to study iridescence in Podarcis liolepis in two localities in which lizards differ in dorsal coloration: the València Botanical Garden (EB) and La Murta Natural Park (LM). To determine the presence of angle-dependent reflectance, we measured dorsal coloration at three different configurations (0°, 60° and 90° angles between incident light and observer location) in 87 lizards of either sex and used visual modelling to determine their detectability when viewed by conspecifics, raptors and humans. Our results show that P. liolepis dorsal coloration varies chromatically with sex and locality and also shows iridescence (i.e. reflectance peaks at shorter wavelengths with increasing viewing angle). Lizards from EB are brown dorsally, whereas most lizards from LM, especially males, show a green dorsal background coloration, reflectance peaking at shorter wavelengths in lizards from LM compared to lizards from EB. Angle-dependent shifts in peak location are smaller in LM males than in other groups, yet iridescence appears more pronounced (i.e. larger chromatic distances between viewing angles) in LM than in EB due to greater overlap between the involved waveband and receiver cone sensitivities. Additionally, P. liolepis dorsal iridescence may be more noticeable to humans and raptors than to lizards. Our findings suggest that intraspecific colour variation influences iridescence detectability across observers, underscoring the need for objective colour quantification and visual modelling to assess the ecological consequences of animal coloration.

Accurate aging is a useful tool in wildlife management, providing critical information for population dynamics research, age-specific limiting factors, and conservation efforts. Many methods used to age mammalian carnivores are either invasive, expensive, or inconvenient to use in the field. In felids, the gum-line recession has been found to accurately estimate the age of female mountain lions and tigers. In contrast, expert-based aging techniques used on cheetahs (Acinonyx jubatus) can only categorize adults into broad age classes. We assessed whether the gum-line recession of the upper canine teeth provides reliable information for aging cheetahs by using measurements on cheetahs of known age (n = 37) in sex-specific linear models. We found a significant positive relationship between gum-line recession and known age for both female (n = 21) and male cheetahs (n = 16), and we contribute herein sex-specific regression models that can be used to age the animals based on the gum-line measurements collected during handling. In addition, we compared expert-derived age categories assigned to cheetahs of unknown age (n = 23) to the ages estimated by the gum-line recession models. Expert-based aging produced similar results to gum-line recession for some individuals, but the ages of other individuals were underestimated by biologists, particularly for older cheetahs. Our data show that gum-line recession measurements provide biologists with a reliable, minimally invasive, and convenient technique to age cheetahs in the field, and we encourage validation of this technique in other field-intensive projects involving felid capture.

Isolation and extreme environmental conditions have significantly impacted terrestrial invertebrate biodiversity in Antarctica, with glacial cycles further limiting animal diversity to a small number of species. Among these, springtails are relatively abundant, though their taxonomic diversity remains low. Antarctic glaciers may serve as major dispersal barriers, leading to high levels of genetic divergence among isolated populations. In Victoria Land (continental Antarctica), the Tucker Glacier has been proposed as an example of such a barrier; however, different species or taxa may respond differently to the same geographical features. In this study, we tested whether geographic distance, major glacier tongues, and seawater channels influence the distribution of Kaylathalia klovstadi (Collembola; Isotomidae) in Northern Victoria Land. We conducted mitochondrial DNA haplotype analysis on fragments of cytochrome c oxidase subunit 1 (cox1) and ATP synthase 6 (atp6) in 62 individuals from six K. klovstadi populations. Our analysis provides new insights into the genetic diversity and distribution patterns of K. klovstadi by incorporating additional sampling sites, specimens, and molecular markers. We challenge previous views regarding the role of the Tucker Glacier as a significant physical barrier to springtail dispersal in Northern Victoria Land. Our findings suggest that the impact of physical barriers on the genetic diversity of Antarctic Collembola, including the species studied here, requires a more careful evaluation.

Cooperation and group living have been suggested to facilitate survival in varying environments and under challenging conditions. However, group living may also be associated with costs, particularly in species where individuals within groups may compete for limited resources. The costs and benefits of cooperative group living on cooperatively breeding mammals in varying environments remain unclear. Here, we use data collected from wild, cooperatively breeding Natal mole-rats (Cryptomys hottentotus natalensis) inhabiting a seasonally varying environment to assess whether body condition changes between seasons and whether these changes are contingent upon group size. We demonstrate that the body condition of reproductive females improved with increasing helper number during both the benign summer and the harsher winter seasons. However, the body condition of other group members showed little dependency on group size or season. Only when including one extremely large group did the body condition of non-breeders weakly, albeit significantly, change depending on group size and seasonality. These results suggest that larger group sizes may yield some benefits for non-breeding group members during winter and may invoke some costs during summer. Group living in Natal mole-rats is likely promoted by a combination of collective foraging, thermoregulatory benefits, and potentially some indirect fitness benefits through improved body condition of the breeding female.

Characterizing the dietary niche partitioning of sympatric mesocarnivores is fundamental for understanding their mechanisms of coexistence and ecosystem function. By utilizing scat DNA and DNA metabarcoding, our study revealed a detailed picture of the trophic interaction between two mesocarnivores in a cool temperate forest ecosystem in Northeast China. Both red foxes (Vulpes vulpes) and leopard cats (Prionailurus bengalensis) consumed a diverse range of prey (52 prey taxa from 11 orders) dominated by Rodentia (56.5–64.9%). Bipartite trophic network analysis suggested that both predators are generalists and have a high degree of niche overlap (Pianka's index = 0.77). However, diet patterns differed between the predators. Both predators consumed more diverse prey during the snow-free period than during the snow-covered period, which resulted in lower niche overlap between the predators (Pianka's index = 0.43). Another important source of diet niche partitioning was the proportion of large prey consumed, with red foxes consuming more ungulates than leopard cats do throughout the year in regions with two apex carnivores, tigers (Panthera tigris) and leopards (P. pardus). The presence of apex carnivores provides more stable carrion resources, which facilitates dietary niche partitioning and the coexistence of mesocarnivores. Our study provides important clues about the strategies of dietary niche partitioning between sympatric mesocarnivores, which is critical for understanding coexistence within carnivore communities.

The phenotypic plasticity of the digestive system is important to cope with the variations in food quality for wild small mammals, in particular for the lactating females because they must increase food intake to meet the highest energy requirements of offspring. This study aimed to investigate the energy budget and reproductive performance of striped hamsters (Cricetulus barabensis) fed on a high-fiber or high-fat diet across lactation. Body mass, food intake, resting metabolic rate (RMR), milk energy output (MEO), and litter size and mass were measured at peak lactation. The body composition, digestive enzymes activity, as well as the hypothalamus-driven gene expression relating to orexigenic or anorexigenic neuropeptides was determined at weaning. The food intake at peak lactation was not significantly changed in the females fed on a high-fiber diet, while it was decreased in those fed on a high-fat diet compared with the females fed a control diet. The females fed a high-fiber diet did not change RMR, but decreased MEO, and had smaller litters with lower masses. The females fed a high-fiber diet had a larger stomach, small and large intestine, and caecum, in parallel with increases in maltase and aminopeptidase activity, but these females did not show significant changes in amylase, lipase, lactase, or chymotrypsin compared with the females fed a control diet. The mRNA expression of AgRP was increased, and POMC was decreased in the hamsters fed a high-fiber diet compared with control ones. The high-fat group did not vary from the control group in almost all of the parameters. These findings suggest that the adaptive modulations in the digestive enzyme activity may be maximized at peak lactation, creating a hard limitation for SusEI in response to a high-fiber diet, which may be independent of either orexigenic or anorexigenic neuropeptides.

Morphological traits of animals have evolved to solve ecological requirements, the optimization of locomotion in each environment being one of the most frequent selective forces shaping morphology. Amphisbaenians are strictly fossorial reptiles that have evolved various snout shapes for burrowing head-first underground, yet the evolutionary and ecological origins of these different morphologies are little known. Here, we used a geometric morphometric approach to investigate head shape intrapopulational variation in the round-snouted checkerboard worm lizard (Trogonophis wiegmanni). We took 2D photographs of live animals in a North African island population. At each capture site, we also measured microhabitat characteristics and soil compaction, and took soil samples to analyze soil physical structure. While we detected no signal of sexual dimorphism in head shape and overall head disparity was low, we found significant relationships between the head shape of T. wiegmanni and some characteristics of vegetation and soil. Relatively more tapered snouts and narrower heads occurred in sites with taller bushes and soils containing higher amounts of clay (i.e. harder substrates that are more difficult to excavate). We hypothesise that differences in head shape due to microhabitat and soil variation might be considered a scenario under which different amphisbaenian head morphologies initially evolved.

Mate guarding is a common behavioral adaptation in males to ensure mating or to hinder current partners from remating with rival males. In the decorated cricket, Gryllodes sigillatus, males transfer a spermatophore to females at mating, comprising a sperm-containing ampulla enveloped in a large gelatinous mass, the spermatophylax, that serves as a nuptial food gift for the female. Males guard the female while she feeds on the nuptial gift and while sperm are evacuated from the ampulla into her reproductive tract. Mate guarding behavior functions to prevent competitors from mating with the female but may also represent a behavioral counter-adaptation to the propensity of females to cease nuptial feeding and to terminate sperm transfer prematurely. Using an experimental evolution approach, we tested the prediction that males would guard females more vigorously in response to an experimentally intensified sexual conflict. We recorded the intensity of male mate guarding from replicate lines reared for 25 generations at either an elevated or a reduced intensity of sexual conflict by imposing male- and female-biased adult sex ratios each generation, respectively. We observed the evolution of higher intensity mate guarding behavior in one of the four male-biased selection lines, but in none of the female-biased lines; previous work has revealed that the males in this specific line also produce less manipulative food gifts, suggesting the existence of alternative mating strategies. Additionally, we found a positive correlation between the behavioral investment in mate guarding and the duration of the sperm transfer from the ampulla. As such, this provides a possible mechanism through which more intense mate guarding could increase male fitness.