Journal of Zoology最新文献

Gliding has evolved independently as an isolated adaptive event within many vertebrate taxa. Yet, the underlying selection forces that led to these innovative adaptations remain ambiguous, especially in species that preclude direct observation. Our study utilized accelerometry and machine learning algorithms to compare the behavioural repertoires of two sympatric species, the Mahogany glider (Petaurus gracilis) and brushtail possum (Trichosaurus vulpecula), as to explore previously proposed selection pressures such as energy expenditure (VeBA), canopy use and ground avoidance measured by activity budgets. We found that mahogany gliders on average expend more activity-related energy than brushtail possums but at different stages throughout the day. Canopy use was observed to be greater amongst mahogany gliders than brushtail possums, and we observed frequent ground use in brushtail possums yet none in mahogany gliders. The study found strong evidence to support ground avoidance as a potential driver for gliding evolution. The implications of these findings are important when considering the lack of knowledge surrounding evolved gliding behaviours in marsupials. Furthermore, the use of accelerometers and machine learning algorithms in behavioural studies has proven to be a robust and informative method and should be incorporated into future studies to understand the evolution of gliding behaviour.

The coexistence of multiple discrete color phenotypes (i.e. color polymorphism) has been studied in many diurnal species where environmental light allows most visual systems to chromatically discriminate color morphs. However, there is a large gap in our understanding of the discrimination thresholds and the function color polymorphisms play at night. We collected spectral data from the throats of red- and yellow-morph males in a polymorphic population of the nocturnal amphibian Salamandra salamandra gallaica. We estimated the discriminability between morphs and their conspicuousness at night by fitting visual models of conspecifics and predators. We also collected morphological, behavioral and physiological data and assessed the abundance and activity patterns of each morph to explore their potential function. Visual models indicated that both conspecifics and predators can visually discriminate salamander color morphs under night-light conditions. Assuming the potential role of yellow and red color patches as visual signals, putatively related to social signaling, we could suspect that these colors represent different adaptive optima. Red-morph individuals had shorter bodies and lower body condition, but both morphs showed similar space use. In addition, both color morphs exhibited similar metabolic physiology, suggesting that the observed similarity in these traits may be better explained by the shared environmental conditions, rather than color. Finally, differences in the conspicuousness of red and yellow morphs could result in differential predation pressure.

Sperm production represents a costly reproductive investment by males. High reproductive competition within the female reproductive tract may select for higher sperm counts or quality resulting in selection for larger testes size. In species where females mate multiply or have more offspring per litter (litter size), or more litters per year (litter rate), male reproductive competition may select for larger relative testes size (i.e., scaled by body mass). Given that different mating systems vary in the alternative forms of reproductive investment available to males, sperm production levels may vary with social system. Here, we examined the relationship between testes size and mating systems, litter size, and litter rate while considering male lifespan and investment in paternal care in 224 terrestrial mammalian species in 15 orders. Relative testes size was larger in species where females mated with multiple males. Furthermore, in species with multiple mating females, species with higher litter rates had larger testes compared to species with fewer litters per year. In contrast, in monogamous species, species that had multiple litters per year had smaller relative testes sizes compared to species with fewer litters per year. Neither longevity nor paternal care influenced testes size. Our results elucidate the effect of female reproductive strategies on relative testes size is nuanced and varies between mating systems. Our findings suggest that the interplay between male reproductive investment and female reproductive investment may be different within similar social mating systems.

The link between skull shape and dietary ecology in birds at macroevolutionary scales has recently been called into question by analyses of 3D shape that reveal that cranial anatomy is mainly influenced by other factors such as allometry. It is still unknown whether this form-function disconnect also exists at smaller evolutionary scales, for example within specialized ecological guilds. Vultures are a diverse guild of 23 extant species in two families (Accipitridae and Cathartidae) that exhibit evolutionary convergence as a result of highly specialized feeding ecology. Vultures are the only known obligate scavengers among vertebrates and are usually grouped together under this single dietary category, but within this specialized diet there are three distinct, species-specific feeding strategies termed ripper, gulper, and scrapper. We use three-dimensional geometric morphometrics to quantify the relative contributions of feeding ecology, allometry, and phylogeny on vulture skull shape, along with several non-vulture raptors of similar size, range and ecology. Families show clear separation in shape, but phylogenetic signal is comparatively weak (K_mult = 0.33). Taking into account the influence of phylogeny, skull shape is not significantly correlated with either skull size or feeding type, but there are examples of strong, significant convergence and parallel shape evolution across feeding groups. Furthermore, skull shape performs strongly in predicting feeding ecology in a phylogenetic discriminant function analysis. These findings highlight the importance of detailed assessment of feeding behavior in studies of ecomorphology, rather than broader dietary categories alone, and reveal that ecology can be readily inferred from form given appropriate information.

Studies of diurnal primates have long considered the nocturnal period to be a time spent merely sleeping and not effectively utilized for foraging or social behaviours. However, digestive activity should continue during the night. To explore the adaptive significance of the primate rumination-like behaviour, that is, regurgitation and re-mastication (R/R), observed in the proboscis monkey Nasalis larvatus (but only infrequently during the day), we tested the hypothesis that they frequently awaken and ‘ruminate’ at night through detailed nocturnal observations. We analysed infrared video recordings of nocturnal behaviours of 179 individuals over 35 nights, totalling over 251 h, of free-ranging proboscis monkeys in the lower Kinabatangan region of Sabah, Malaysian Borneo. The results showed that, as we expected, proboscis monkeys were frequently awake at night; they only slept about one third of the time observed at night (27.4 ± 24.6%), with juveniles sleeping the most and subadults sleeping the least. However, contrary to our expectations, R/R did not appear to occur more frequently than during daytime observations and accounted for a minor proportion of the total activity budget during the night. Whether frequent waking up during the night represents an adaptive strategy in relation to predation avoidance, or is a consequence of disturbance (e.g. due to moving branches or mosquitoes), requires further study, ideally in comparison with protected ex situ conditions. Our findings suggest that without detailed observations, primate sleeping times may easily be overestimated due to a high proportion of time spent awake but resting.

Maternal condition is influenced by multiple variables that individuals experience at seasonal and local levels, and thus condition-dependent sex allocation is likely also multifactorial. Here, we test the Trivers-Willard Hypothesis (TWH) using a multivariable approach on a dataset of thoroughbred mare breeding records. There is no sex ratio variation when examined at univariable level, mirroring the usual approach to test condition-dependent sex allocation. Conversely, the multivariate model shows multiple variables interact to influence the likelihood of producing a male. Mare and management variables that represent better body condition is associated with an increase in likelihood of a male offspring. The magnitude and direction of sex ratio skew correspond closely with predicted mare energy balance, consistent with TWH predictions. Our findings therefore support the TWH and show that, while sex allocation is multifactorial, maternal energy status emerges as the dominant driver. The additive and agonistic interactions of different variables demonstrate that a multifactorial approach should be a key consideration in sex allocation studies.

The morphological differentiation between coastal and offshore ecotypes of bottlenose dolphins (genus Tursiops) has been researched since the 1960s, particularly in T. truncatus (Montagu, 1821), although most morphological studies have focused on localized populations. Therefore, it is unclear how patterns observed in these individual populations integrate within the global morphological variation. Here we carry out a meta-analysis of global morphological variation between coastal and offshore ecotypes from 532 museum specimens, using both linear measurements (LM; 282 specimens), and shape data using geometric morphometrics (GM; 290 specimens). Together these analyses show consistent differentiation in skull morphology between coastal and offshore ecotypes, and provide a detailed description of variation patterns within each ecotype. These patterns show high individual morphological variation in the coastal ecotype between locations, while the offshore ecotype appears morphologically more uniform across the areas sampled. Overall, most skull shape variation can be described by features noticeable dorsally in the structures of the rostrum, whereas more limited change was found in ventral traits. Our results suggest that individual coastal populations may vary according to local environmental conditions, while those corresponding to the offshore ecotype appear to share similar morphological characteristics that might increase fitness in offshore habitats.

Rain-harvesting behaviour represents an adaptation for water collection that has evolved in some species of iguanian reptiles inhabiting arid environments. To date, such behaviour has been observed only in members of the families Agamidae and Phrynosomatidae. A common set of integumentary features characterizes these rain-harvesting species, including scale surface microstructures (SSMs), capillary channels and hinge joints. The influence of variations in these features on rain-harvesting has been a subject of discussion for many decades. Nevertheless, a comprehensive comparative study of similarities and differences between harvesting and non-harvesting species on a broader scale remains lacking. In this study, we classify scale surface microstructures into three categories: large hexagons (SSM1), smaller nested hexagons (SSM2) and hinge pits (SSM2H). As the first two SSM types are widespread, they do not appear to be directly linked to the adaptation for rain-harvesting. Conversely, the presence or absence of hinge pits distinguishes harvesters from non-harvesters. Additionally, channel hierarchy, width and structure determine the effectiveness of the rain-harvesting architecture. Only Moloch horridus exhibits distinct integumentary features in comparison to other agamids and rain-harvesting species. Ancestral character state reconstruction suggests that rain-harvesting behaviour was likely absent in the ancestor of Iguanians, even though overlapping scales and SSM1 were present. Our findings illustrate that rain-harvesting species have independently converged upon similar structural solutions to address their water acquisition challenges, building upon shared pre-existing features.

Functional requirements for different diets have a strong selective pressure leading to convergent adaptations across different groups of mammals. As body size has an influence on many biomechanical and physiological characteristics, it is logical that dietary adaptations often have a strong link to body size resulting in observed ‘size guilds’ in many diverse phylogenetic lineages. However, non-allometric variation in skull shape may provide an alternative pathway for species to adapt to diets or prey handling by breaking the mould away from the line of least evolutionary resistance, increased body size. We investigated the relationships between cranial shape and body size in the evolutionary context of the shift from insectivory to hypercarnivory in a monophyletic group of 16 dasyurine marsupial species. Analysis of 35 Procrustes-corrected 3D skull landmarks revealed that overall, there was a correlation between mean skull shape and size that correlated with diet. However, the dominant shape variation (almost 80% irrespective of phylogeny, and more than 90% when constrained by phylogeny) was not size-related. This non-allometric pattern of skull shape reveals adaptation for different feeding strategies that is independent of absolute size. This highlights the potential for specific ‘thresholds’ in size and shape to exist that have the potential to mark shifts from one dietary niche to the next, that might be applied to the evolution of carnivorous taxa from other lineages.

Bolitoglossa ramosi is a terrestrial plethodontid salamander particularly active during cloudy nights with high relative humidity in the environment. In this work, we tested the hypotheses that: (1) the hydration state of B. ramosi directly affects its locomotor performance; (2) dehydrated salamanders spend less time to find a water source than hydrated salamanders and (3) dehydrated salamanders find a water source in fewer attempts than hydrated individuals. To evaluate these hypotheses, salamanders at different levels of body hydration were used for an experiment of maximum locomotor performance, and a behavioral assessment test for searching a water source that was randomly located in one of the eight arms of a labyrinth. We found that salamanders hydrated at 95% had a greater locomotor performance (speed) than those hydrated at 85% and 75%. On the other hand, salamanders hydrated at 75% found the water source faster than those hydrated at 95%, although there was not a significant difference between these two groups of salamanders tested in the number of arms visited to find the water source. According to our results, we propose that dehydration in salamanders could be a causal factor for the inactivity of these animals during low levels of environmental humidity, and can also motivate a faster response to find a water source. In addition, we postulate that B. ramosi seems to use a random searching behavior to locate a water source as both hydrated and dehydrated salamanders find it after several attempts.