Current Zoology最新文献

Dietary specialists consume specific prey items, and they are often morphologically and behaviorally specialized to feed efficiently on those prey animals. Among specialist snakes, consumption of terrestrial arthropods is relatively rare. Because most terrestrial arthropods possess hardened sclerites and appendages, it is possible that snakes that feed on arthropods would show specialized prey-handling behavior. In this study, we describe prey-handling behavior of a snake feeding on terrestrial arthropods, which hitherto has not been well documented. We focused on Rhabdophis chiwen, which mainly feeds on earthworms, but also consumes lampyrine firefly larvae, sequestering cardiotonic steroids from them in its defensive organs, called nucho-dorsal glands. When feeding on earthworms, snakes showed size-dependent selection of swallowing direction, but this tendency was not observed when feeding on firefly larvae. Manipulation of firefly larvae did not seem to be efficient, probably because they possess sclerites and appendages such as legs that impede smooth handling. Although fireflies are an essential food for R. chiwen as a toxin source, our results showed that the snake is not adept at handling firefly larvae compared to earthworms, implying that dietary specialization does not necessarily accompany behavioral specialization. We discuss possible reasons for this inconsistency.

Sleeping site selection is essential for understanding primate behavioral ecology and survival. Identifying where species sleep helps determine priority areas and critical resources for targeted conservation efforts. However, observing sleeping sites at night is challenging, especially for species sensitive to human disturbance. Thermal infrared imaging (TIR) with drones is increasingly used for detecting and counting primates, yet it has not been utilized to investigate ecological strategies. This study investigates the sleeping site selection of the Critically Endangered black-shanked douc langur (Pygathrix nigripes) in Cát Tiên National Park, Vietnam. Our aim is to assess the feasibility of using a TIR drone to test sleeping site selection strategies in non-nesting primates, specifically examining hypotheses related to predation avoidance and food proximity. Between January and April 2023, we conducted 120 drone flights along 22 transects (~1-km long) and identified 114 sleeping sites via thermal imaging. We established 116 forest structure plots along 29 transects in non-selected sites and 65 plots within douc langur sleeping sites. Our observations reveal that douc langurs selected tall and large trees that may provide protection against predators. Additionally, they selected sleeping sites with increased access to food, such as Afzelia xylocarpa, which serves as a preferred food source during the dry season. These results highlight the effective use of TIR drones for studying douc langur sleeping site selection with minimal disturbance. Besides offering valuable insights into habitat selection and behavioral ecology for conservation, TIR drones hold great promise for the noninvasive and long-term monitoring of large-bodied arboreal species.

Aposematism is an antipredator strategy in which conspicuous coloration acts as a warning of chemical defenses to potential predators. Evidence suggests that aposematism largely functions under positive frequency-dependent selection, which is thought to maintain uniformity of aposematic signals. Many studies of aposematic organisms have found evidence that color signals and defenses are positively correlated, indicating a quantitatively honest aposematic signal. Dendrobatid poison frogs represent a well-studied group of aposematic organisms that in addition to exhibiting a diversity of color signals also display unique defensive behaviors. Few studies have examined if both behavior and coloration act as quantitative honest signals of alkaloid defenses in poison frogs. We aimed to determine if coloration and behavior are quantitatively honest signals in the green and black poison frog (Dendrobates auratus) among 6 populations from Costa Rica. We (1) evaluated antipredator displays by using behavioral assays in the field, (2) assessed frog conspicuousness and pattern using digital images, and (3) quantified alkaloid profiles from frog skin secretions. We found that Pacific populations are less conspicuous in coloration, had greater quantities of alkaloids, and more frequently performed body-raising defensive behaviors when compared with Caribbean populations. Our results do not support the hypothesis that aposematic traits in D. auratus are quantitatively honest. Rather, our results suggest that phenotypic differences among populations may represent different phenotypic optima for advertising unprofitability to predators based on local environmental conditions, leading to the diversification of aposematic signals in this species.

Accurate estimations of animal population size are pivotal for implementing management strategies properly. Recapture technique based on sounds as a specimen identification mark has barely been used for marine mammals. However, inferring abundance estimates from acoustic methods could enhance the accuracy and precision of population size assessments. Here, we tested the possibility of using signature whistles as individual marks for estimating the size of common bottlenose dolphin (Tursiops truncatus) populations. Data were continuously collected for 326 days in 2015-2016, by using a fixed acoustic device located in the Sicily Strait (Italy). The SIGID method was applied to identify Signature Whistles Types (SWTs) over 7,000 h of recordings. Eighty SWTs were detected as long as their stereotyped fundamental frequency contours were repeated in bouts of at least 6 renditions. The mean SWTs monthly recording rate resulted in 0.19 (Standard deviation = 0.16), with 20 SWTs recorded over 5 or more different encounters (until a maximum of 30 encounters). The Jolly-Seber model (with POPAN formulation) was run in Mark software to estimate the population size. The estimated population size resulted in 171 bottlenose dolphins (95% confidence interval = 137-215). Even if the detection and identification of signature whistles required crucial precautions, and animals could be detected differently from visual techniques, the population size estimate obtained was comparable with previous results based on physical marks data. These outcomes demonstrated that signature whistles can be considered a strongly effective tool for integrating traditional mark-recapture techniques with finely estimated dolphins' population abundances.

Understanding the genetic diversity-area relationship (GAR) is essential for comprehending how species adapt to environmental changes, as genetic diversity is an indicator of a species' adaptive potential. Variation in environmental adaptation capacity exists among species and animal taxa with different distribution areas, highlighting the importance of understanding the GAR. To obtain a more comprehensive understanding of the GAR in terrestrial vertebrates, we assessed both haplotype diversity-area and nucleotide diversity-area relationships using 25,453 cytochrome c oxidase subunit I (COI) sequences from 142 amphibian species, 574 bird species, and 342 mammal species. We found that both measures of genetic diversity increased with species range size across major animal groups. Nevertheless, the GAR did not differ among animal groups, while haplotype diversity performed better than nucleotide diversity in profiling the GAR, as indicated by higher R ² values. The difference in the modeling fit may stem from the distinct biological and mathematical significance of nucleotide diversity and haplotype diversity. These results suggest that the GAR follows similar rules among different animal taxa. Furthermore, haplotype diversity may serve as a more reliable indicator for assessing the potential effects of area size changes on animal populations and provide better guidance for conserving genetic diversity.

Eyespots have been shown to perform an anti-predator function by intimidating predators. However, whether predators are deterred by the eyespots' mimicking eyes of higher-order predators, or by the conspicuousness of the spots, is still being debated. The anti-predator mechanism of eyespots, which involves the predator's visual perception and cognition, urges to be examined. To explore the "eye mimicry hypothesis" and "conspicuous signal hypothesis," we designed prey with deceptive eyespots eliciting 2-dimensional (2D) or 3-dimensional (3D) visual illusions for domestic chicks (as predators). For 2D visual illusion, we provided prey with occluded eyespots for chicks. Chicks can "complete" the occluded eyespots into a full 2D concentric circle by the amodal completion mechanism, that is, one of visual illusion. For 3D visual illusion, we created the crescent-shaped sparkles on the eyespots to simulate a visually 3D eye. Our result indicated that (1) 2D: chicks hesitated more when facing preys with occluded eyespots than facing preys with broken eyespots and (2) 3D: compared to prey with no-sparkle eyespots, chicks spent more time approaching prey with sparkle eyespots and were more likely to approach them tangentially. Thus, the visual illusion perceived by chicks would impact the anti-predation effectiveness of eyespots. Eyespots that more closely resemble the real eyes, especially those with 3-dimensionality, provided more effective protection. Our study supported the eye mimicry hypothesis from the perspective of visual illusion.

Dispersal is an important life history trait with significant consequences for spatially structured populations, as the exchange of individuals between habitat patches is crucial for maintaining metapopulation connectivity. In this study, we used a long-term data set (2005-2023) to describe dispersal patterns in a patchy population of the Western Yellow Wagtail Motacilla flava within a large (approximately 1,300 km²) study area in the boreal zone of European Russia. We quantified dispersal distances for birds that dispersed outside their natal or breeding habitat patches and applied a multistate capture-recapture approach to estimate natal and breeding dispersal probabilities. Of 395 adult wagtails and 1,610 nestlings ringed, 3% of birds ringed as adults and 3% of birds ringed as nestlings were resighted outside their natal or breeding patches. The probability of natal dispersal (0.29 ± 0.05) was significantly higher than the probability of breeding dispersal (0.05 ± 0.01). The median natal dispersal distances (2.8 km for males, 3.9 km for females) were the same as the median breeding dispersal distances (2.7 km for males, 3.9 km for females). We did not find a significant effect of the fledging date on either the natal dispersal distance or the natal dispersal probability. Similarly, we did not find a significant effect of the previous reproductive success on either the breeding dispersal distance or the breeding dispersal probability. Our results indicate that strong breeding site fidelity and short-distance natal dispersal are the dominant dispersal strategies in a patchy population of the western yellow wagtail.

Although mollusks represent Earth's second most diverse invertebrate group, their natural history and ecology are still scarcely known. The compilation of non-traditional data, such as those from citizen science, represents an alternative to fill these gaps, particularly on striking land snail species such as Macrocyclis peruvianus. Based on long-term citizen science, we aimed to update and describe some basic ecological aspects, such as the distribution and protected area types used by M. peruvianus. We performed pairwise comparisons to test potential changes in occurrence and occupancy among administrative regions, forest types, and protected area types using chi-squared tests. The citizen scientists were also asked to provide the number of M. peruvianus individuals observed and the tree species that dominated their habitat. Thus, we tested if the number of land snails found by citizen scientists could be related to forest and protected area types using a generalized linear mixed model. We expanded the northern distributional limit, with Nothofagus, evergreen, and mixed forests far the most frequented by M. peruvianus. Parallelly, the occurrence of M. peruvianus in official protected areas (65.73%) was significantly higher than in privately owned areas. Moreover, we did not find associations between forest and protected area types with the number of M. peruvianus recorded. Although citizen science is a helpful method for obtaining novel information regarding the ecology of neglected species such as M. peruvianus, it also introduces spatial and occurrence biases explained by the access and attractiveness of the officially protected areas compared to privately owned patches of native forest.