Journal of Zoology最新文献

Predator–prey interactions are ubiquitous and under strong selection because of the consequences experienced by both predator and prey if they lose the interaction. Biomechanics and behavior play important roles in the outcome of these interactions, but many studies focus on the prey, restrict the range of behaviors considered, and the role of prey boldness in the outcome is not understood. We used high-speed video to test for effects of multiple measures of performance and kinematics of both the predator and prey, and boldness of prey on the outcome of interactions between Pike Cichlids (Crenicichla sp.) and Guppies (Poecilia reticulata). We found high variation in the behaviors employed during the predator–prey interactions, including in suction versus raptorial feeding, strike accuracy, and guppy responsiveness. We also found that predators moving relatively slower and prey moving relatively faster were more successful at consuming the prey and evading the predator, respectively. Prey that reacted farther from the predator was more likely to escape predation, but boldness of the prey did not affect the interaction. Our work suggests that a high level of variation in predator–prey interactions is widespread, even when strike and escape behaviors are stereotyped. We also showed that what both the predator and the prey do during an interaction are important in determining the outcome.

Although the nutritional demands of animals are known to differ between immature and mature stages and between neonates from different clutches in various organisms, little evidence has been accumulated to examine this possibility in crustacean zooplankters. To this end, we examined the five digestive enzyme activities related to assimilations of carbohydrates, lipids, amino acids and phosphorus in the neonates, immature and mature individuals of panarctic Daphnia pulex. We found that all the enzyme activities were higher at lower food levels, indicating that the activities increased with decreasing supplies of the nutritional substances relative to the demands. As expected, these enzyme activities changed ontogenetically. Beta-glucosidase activities increased with age, especially at a high food level, while the opposite pattern was found for lipase activities. A decreasing trend with age was also found in the activities of arginine and alanine amino-peptidase and alkaline phosphatase at a low food level. These results suggest that juvenile individuals require more lipids, amino acids and phosphorus relative to the requirements of adult individuals, while the opposite pattern was true for carbohydrates. We also measured the enzyme activities of the neonates born from the 1^st and 2^nd clutches of the maternal individuals. The results showed that most digestive enzyme activities differed significantly between the neonates from the first and second clutches depending on the food levels. The present study confirmed that the nutritional demands differ not only between mature and immature individuals in Daphnia pulex and suggests that the mature individuals invest nutrients and energy reserves differently to neonates of the different clutches depending on their nutritional conditions.

The size of both predators and prey can profoundly affect the foraging ecology of animals. This is especially true for snakes which consume prey whole. Although their gape imposes an anatomical limit on prey size, different snake species have a wide variety of prey types, prey sizes, and dietary breadth. To test whether a dietary specialist that only consumes bird eggs (Dasypeltis gansi) differed from a generalist that occasionally eats eggs (Pantherophis obsoletus), I quantified and compared the scaling relationships between overall size, cranial dimensions, and maximal gape and the orientation and mobility of relevant bones. Compared to P. obsoletus with a given overall size, D. gansi had maximal gape areas approximately 3–4 times greater and a significantly larger relative contribution to gape by the intermandibular (IM) soft tissues (50% vs. 19%). The greater distensibility of the IM soft tissues also allowed much greater lateral displacement of the distal end of the lower jaw in D. gansi versus P. obsoletus, but at maximal gape, the bones of these species had unexpectedly similar orientations in lateral view. The large gape of D. gansi was attained despite having a significantly shorter head than P obsoletus for a given snout–vent length. As a result of their large gape and more slender build, the predicted values of relative prey masses (RPM) for D. gansi at maximal gape vastly exceeded those of P. obsoletus for a given prey type. Although eggs are much stouter than rats, values of RPM at maximal gape for D. gansi eating eggs greatly exceeded those for P. obsoletus eating rats. Perhaps, Dasypeltis has the greatest size-corrected gape and potential values of RPM (for a given prey shape) of any snake taxon as these values of D. gansi exceed those from all previously studied species with similar data.

Polychromatism refers to the presence of two or more color patterns within a species. Several species exhibit polychromatic patterns, including some elasmobranchs such as the Xingu Freshwater Stingray (Potamotrygon leopoldi), a threatened, endemic freshwater stingray species that is exploited in the international aquarium trade. Analysis of polychromatic patterns can provide insight into evolutionary mechanisms and be a useful tool for monitoring international trade. In this context, the present study analyzed intraspecific color variation in P. leopoldi. A total of 241 individuals collected in two areas along the Xingu River in Brazil were used for the study. Four dorsal color patterns of P. leopoldi were described. Size differences between color classes were statistically significant, suggesting that these color variations are associated with ontogenetic color changes. In addition, two color morphs specific to each locality were identified and described. Moreover, the occurrence of polychromatic forms in a Potamotrygoninae species may contribute to the understanding of diversification in this group, since some mechanisms of speciation are associated with polychromatism. Analysis of color variation in P. leopoldi is expected to help improve trade monitoring, especially given the existence of look-alike species.

Landscape transformation by humans through habitat degradation, agriculture intensification and urbanization results in the loss of natural feeding areas. However, populations of certain species have adapted to these changes and benefit from some anthropogenic food sources as well as an absence of predators and milder environmental conditions in urban landscapes. Although breeding near landfills secures food availability and saves energy and time spent on foraging activities, the poor food quality and risks associated with these facilities imply some fitness costs. Our study shows the effects of landfills on nest-site selection and breeding success in white storks (Ciconia ciconia). Birds breeding near landfills occupy more urban areas where many structures are available to nest, while breeding pairs 20–30 km from landfills select nest sites with high-quality food sources in the vicinity such as pastures, meadows and agro-forestry areas. Furthermore, we demonstrate that habitat quality in the surrounding area is more relevant than landfills for breeding outcomes, but both of these are crucial for brood size. The number of fledglings was higher at a medium distance to the landfill than at 20–30 km from the landfill, but not near the landfill (0–10 km). This suggests that the best strategy includes food from landfills as a complementary or alternative food source. Future studies should further investigate if these shifts in habitat preference are permanent, and the potential impact of habitat degradation and landfill closures at a population level, for this species.

To understand fitness consequences of performance, one must determine how underlying physiological traits result in and constrain performance. Biochemical and mechanistic investment in a performance trait may cause decreased performance elsewhere: a performance tradeoff, indicating performance specialization in a population. (Co)variation exists within individuals, and among individuals, populations, and species. Conflicting patterns of among-individual and within-individual covariation may eliminate, or mask, the relationship at the phenotypic level. Multivariate mixed-effects models (MMMs) model within-individual and among-individual variation separately. We used MMMs to test for relationships between physiological and performance traits associated with locomotion in the prairie lizard Sceloporus consobrinus, and tested for tradeoffs at multiple hierarchical levels. We then compared these results to the conventional Pearson correlations. We found a significant among-individual tradeoff between endurance and climbing speed. Positive covariation within individuals masked the tradeoff at the phenotypic level. Sprint speed positively covaried with climbing speed. Excluding anaerobic scope, which was associated with endurance, no measured physiological traits were predictive of locomotor performance. These data indicate that performance specialization exists among prairie lizards and contribute to a growing body of literature that have successfully used MMMs to uncover performance tradeoffs which may have been masked using conventional methods.

In some species, permanent curtailment of reproduction part-way through the lifespan of adult females is a feature of their evolved life history. The existence of such a post-reproductive life stage is apparently rare; reasonably robust evidence for this is confined to only six species (humans, Asian elephants and four whales). That it occurs at all appears to contradict our view of natural selection operating to maximize fitness and special circumstances must exist to explain its occurrence. We evaluate the main hypotheses posited to explain the evolution of this life stage, why it occurs in a restricted group of animals, and why only in females. We bring together literature from multiple biological disciplines and levels of enquiry, ranging through evolutionary ecology, developmental biology, physiology, neuroscience, molecular biology, and human medicine. We conclude that while time-limited fertility is not in itself adaptive, the duration of subsequent survival is likely to be linked to inclusive fitness benefits. We present a new hypothesis which posits that the duration of female fertility in certain long-lived, highly encephalised species, with no post-natal oogenesis, is limited by the need for intense screening of oocyte mitochondria. This is required to support endothermy coupled with the very high energy requirement for the development and maintenance of the exceptionally large brain size required for complex social living. This limits the number and shelf-life of oocytes, creating an antagonistically pleotropic effect that is beneficial to the production of high performing offspring but carries the later life cost of time-limited female fertility. But the end of the fertile period is no time to die. Inclusive fitness benefits arising from protracted parental care of offspring, overlapping generations, and kin group structures means that continued survival of post-reproductive females is favoured by selection. We suggest further lines of research to test these ideas.

Vertebrate carcasses are a valuable resource for a wide range of organisms, although their consumption rates can vary greatly by the type of carcasses. Studies have indicated that mammalian carnivores rarely consume carnivore carcasses, particularly in the early stages of decay, and thus these carcasses may potentially serve as a reproductive resource for necrophagous arthropods such as blowflies. However, it is unknown whether delays in consumption by carnivores are sufficient for necrophagous arthropods to complete their life cycle in the carcasses. This study addressed this question by monitoring 69 raccoon carcasses using camera traps in Yakumo, southern Hokkaido, Japan, during the summer seasons of 2016–2019. The decay stages of the carcasses were categorized by carefully observing the videos captured by the camera traps, and the timing of maggot dispersion was estimated. The first visitation and first consumption of vertebrate scavengers were also modelled, and the proportion of carcasses visited or consumed by vertebrate scavengers prior to maggot dispersion was determined each year. The proportion of carcasses visited by vertebrate scavengers before maggot dispersal ranged between c. 50% in 2017 and c. 30% in other years. However, only c. 20% of carcasses in each year were consumed before maggot dispersal, and consumption was only partial. The first species to scavenge at carcasses were red foxes and raccoon dogs, with the exception of two carcasses that were first scavenged by large-billed crows. These results suggest that while delayed visitation of carcasses may partly explain delayed consumption, active avoidance of phylogenetically related species may increase the chances of successful maggot dispersal. Our approach of using careful video observations and statistical modelling may apply to a wide range of habitats and could improve our understanding of the ecological consequences of the taboo against cannibalism.

The benefits of sociality are not equitably shared among members of a social group. The position individuals occupy in social networks is key to maximizing their fitness and contribution to group cohesion, as well as stability in the network structure. Individuals' position in a social network is highly influenced by intra-group competition and affiliation; therefore, it should be assessed by examining various spatial-social variables. In this study, we examined the relationship between proximity, grooming and agonistic networks, controlling for genetic relatedness, and the effects of sociodemographic factors on the strength centrality (SC) of these social networks. We combined drone technology and social network analysis to test several hypotheses on 16 feral horse (Equus ferus caballus) groups during three consecutive breeding seasons. Our results show a clear relationship between spatial and social behaviours, suggesting that proximity and grooming are intimately connected in promoting social bonding, and agonism may be a consequence of close proximity between conspecifics. Sociodemographic factors shaped the three network centralities differently. Females and higher-ranking individuals are more central in spatial networks, whereas younger ones may benefit from higher centrality in affiliative networks. Newly integrated individuals tend to be peripheral on spatial networks and engage more in agonistic behaviours; corroborating that integration into a new group is a costly process for females, ultimately leading to a decreased foaling rate. Individuals in multi-male groups showed higher SC in proximity, but not in agonistic networks, suggesting that a second male may play a role in decreasing overall intra-group competition. Our results provide a step forward in understanding the costs and benefits of network centrality in non-matrilineal societies and mechanisms leading to social cohesion, namely in populations under the constant threat of predation and human pressures.

The Sahara Desert is one of the major ecological barriers of the Palearctic-Africa bird migration system. We analysed the behaviour of GPS-tagged booted eagles (Aquila pennata) breeding in Spain and wintering in Tropical Africa, focusing on the Sahara crossing. We searched for anomalous track segments recorded during the desert crossing, finding that non-directional and/or slow movements occur in 35% of the migratory journeys and last up to 31 days (average: 5.9). The analyses show that this behaviour is not triggered by adverse weather conditions, and is shown especially by females during spring. The length of the stopping periods affects the arrival date to the breeding grounds only in males, which means that females buffer the potential delay with an earlier migration start, suggesting that this behaviour is followed deliberately. These wandering movements occur in hyper-arid areas without vegetation cover. A similar behaviour has not been previously recorded in any other trans-Saharan raptor and is probably related to the ability of booted eagles to take advantage of food resources unexploited by other predators, such as migratory songbirds stopping in the desert during the day, and migratory locusts. If confirmed by further research involving higher resolution tracking and field observations, our findings may show a new way of combining foraging and migration, without a well-defined directed trajectory, nor stopping in a restricted spot, but instead wandering over wide areas.