Journal of Zoology最新文献

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.

For animals exhibiting range residency, the home range is a useful framework to quantify space use. Some reptiles can live decades in the wild and experience extreme environmental variation that influences patterns of habitat use. Individuals may modify their use of space over time, reducing the utility of single-year home range estimates. Very high frequency (VHF) telemetry data were collected for Gila monsters (Heloderma suspectum) at three Mojave Desert sites in Clark County, Nevada, and home range utilization distributions were calculated using an autocorrelated kernel density estimator. Home range size was consistent within individuals and populations, and home range size did not vary across years at any site. To measure home range fidelity (year-to-year reuse), we calculated Bhattacharyya's coefficient (BC) for each combination of years in which an individual was tracked and averaged estimates across individuals and populations. The average BC score was 0.86 (scale from 0 to 1; 0 = no overlap and 1 = complete overlap) and did not vary among populations. We modeled home range area accumulation to estimate the minimum sample size needed for asymptotic stability and found home range accumulation to be dynamic and variable within and across years and individuals. Analysis of the frequency of movement by individuals, average distance traveled per movement, and cumulative distance traveled per active season revealed that movement patterns vary considerably by year. Heterogeneity of space use among populations and individuals suggests that individual and local environmental variation, rather than annual variation in resource availability, may drive home range size and movement patterns of Gila monsters in southern Nevada. Annual variability in movement patterns did not translate to variability in home range size or location, and the species exhibits extremely high philopatry, using the same areas for periods of at least 3–5 years.

Although the spotted hyaena (Crocuta crocuta) has been widely considered to be resilient to human disturbance, the species is now thought to be undergoing widespread population declines. Nevertheless, only a handful of population density estimates are available for the species, despite the importance of this information for informing conservation management. This is a consequence of both a lack of surveys and logistical challenges associated with processing spotted hyaena data. In this study, we collaborated with a cohort of students to process camera trap data from the Ruaha-Rungwa landscape initially collected to estimate lion (Panthera leo) and leopard (Panthera pardus) population density. By doing so, we provide the first spatially explicit population density estimates for spotted hyaena in Tanzania, via spatially explicit capture-recapture (SECR) modelling. We also examine the relationship between population densities of spotted hyaena, lion and leopard at each site. Spotted hyaena densities varied from 3.55 ± 0.72 adults and sub-adults per 100 km² in a miombo (Brachystegia-Julbernardia) woodland area of Ruaha National Park, to 10.80 ± 1.08 per 100 km² in a prey-rich open woodland savannah habitat in Ruaha National Park, with intermediate densities recorded in Rungwa Game Reserve and MBOMIPA Wildlife Management Area. Our results suggest that spotted hyaena density is influenced by prey availability and protection, and the species may be less resilient to human pressures than widely thought. Spotted hyaena densities were generally positively correlated with densities of lion and leopard, suggesting that prey availability and anthropogenic disturbance had a greater impact than interspecific effects in shaping large carnivore densities in this system. Overall, our study provides some of the first insights into an under-studied species in an under-researched part of its range, while shedding light into the impact of anthropogenic versus interspecific effects in shaping population status of spotted hyaena in human-impacted African systems.