Journal of Zoology最新文献

The expansion of human activities into natural environments constantly exposes wild animals to novel and potentially dangerous conditions, forcing them to modify their behaviour to cope with these challenges. Here we analysed the behavioural responses of a threatened South American seabird to novel stimuli in controlled experimental situations. In particular, we assessed responses to novel objects, considering intrinsic characteristics of the individuals (i.e., sex and age), and their relationship with the propensity to try novel food. We tested 40 Olrog's gull (Larus atlanticus) for neophobia in the presence of different novel objects placed near their familiar food while isolated in outdoor aviaries. We also conducted a novel food test to analyse individuals' propensity to approach and eat novel food. We found that individuals took longer to consume food in the presence of novel objects compared to the familiar situation. The neophobic responses varied with the object type, but not with either sex or age. The propensity to try novel food did not vary with sex and age, and was not related to their neophobic response towards novel objects. In threatened species like the Olrog's gull, the differences in neophobic responses of individuals within a population may provide insight about the behavioural flexibility required to cope with environmental challenges, especially when individuals are exposed to unfamiliar stimuli, such as objects or food. This flexibility may be critical to quickly adapt to environmental changes, which are becoming more frequent with the increasing urbanization of natural environments.

Shifts in phenological events (reproduction, migration, etc.) appear to be a common response to a changing climate by many taxa. Phenological shifts may elicit stronger responses in organisms with complex life histories as effects could compound across life stages. To better understand growth and survival consequences in the early-breeding wood frog (Rana sylvatica), we examined larval response to hatching phenology (early and late [+14 days]) and increased pond temperatures (ambient and warm [+4.3°C above ambient]) on tadpole growth and development. We expected that tadpoles would respond to delayed hatching via accelerated growth and development. However, we hypothesized that increased temperatures would be antagonistic to a compensatory acceleration of tadpole growth and development and result in slower tadpole growth, later metamorphosis, and smaller size at metamorphosis. Contrary to our expectations, tadpole responses to delayed hatching were not temperature-dependent. While temperature and hatch timing had significant effects on all focal response variables, their effects were independent and additive. Larvae were able to compensate for the 2-week delay in hatch timing through accelerated growth and developmental rates. In fact, delayed tadpoles appeared to overcompensate, metamorphosing several days earlier than their early-hatching counterparts. Finally, although accelerated growth rates in delayed treatments could help compensate for a later start, they were ultimately insufficient to equalize size at metamorphosis. Our results portray the complexity in growth and developmental rate responses due to variation in reproductive timing and temperature. They also highlight a clear need to understand the putative fitness costs of compensatory responses across life stages.

In this study, we examine the dimensions of the nasal horns of woolly rhinoceroses and describe the longest rhino horn known to date, which was recently discovered in the permafrost of Yakutia. The extinct woolly rhinoceros is an iconic representative of the Late Pleistocene mammoth fauna of Eurasia, characterized by two huge keratinous horns. The nasal horn is considerably longer than the frontal one; it is laterally flattened and has a saber-like shape, which is unparalleled among modern-day rhinoceroses. The nasal horns of adult woolly rhinoceroses range in length along the anterior curvature from 68.5 to 134 cm (101.7 cm on average). Their mass varies between 2.5 and 11.4 kg (6 kg on average). Both of these values exceed those of all extant rhinoceroses. The record-breaking nasal horn discovered in Yakutia last year reaches 164.7 cm along the anterior curvature and weighs ~9 kg. The relatively small size of the skull in this specimen indicates that it probably belonged to a rhinoceros female. This suggests that Coelodonta antiquitatis may have had the longest horns in females, similar to modern-day African rhinoceroses. The number of periodic transverse bands (each of which consists of two, darker and lighter, keratin zones) along the length of the horn suggests that the discovered horn belonged to the oldest known woolly rhinoceros with an individual age of ≥40 years. Thus, this discovery not only provides insights into the morphological features of woolly rhinoceroses but also offers valuable information about their palaeoecology and sexual dimorphism.

Sleeping underwater is challenging for lung-breathing animals because of their inability to breathe and rapid heat loss caused by high thermal conductivity. However, cetaceans can sleep/rest underwater despite these constraints. It has been hypothesized that sleep behaviour is related to the balance between heat loss and thermogenesis, relative to body size. We verified this hypothesis through inter-and intraspecific comparisons using observational data on the sleeping/resting behaviour of 10 captive cetacean species. Our results quantitatively demonstrated that as body size decreased, the amount of behavioural sleep while being stationary (stationary sleep) reduced and the amount of behavioural sleep while swimming (swim sleep) increased. Conversely, the opposite occurred when body size increased. To further assess this correlation, the influence of ambient temperature on the choice of sleeping behaviour was investigated through intraspecific comparisons using nine captive bottlenose dolphins (Tursiops truncatus). At lower ambient temperatures, dolphins exhibited more swim sleep than stationary sleep. This suggests a potential sleep strategy that adjusts behaviour based on body size and ambient temperature, possibly owing to differences in heat loss. Our findings provide valuable insights into the thermal challenges cetaceans encounter during sleeping/resting underwater and how behavioural thermoregulation helps them overcome these challenges.

Adaptation to high-altitude environments has long been a significant topic in biology. The plateau brown frog (Rana kukunoris) occurs at high altitudes, while the Chinese brown frog (Rana chensinensis) inhabits low altitudes. These closely related species provide an ideal model for studying high-altitude adaptation. Here, we present a de novo genome assembly of R. chensinensis (totaling 4.23 Gb, with a contig N50 of 2.34 Mb), along with genome resequencing data from 87 individuals sampled across China. Our results indicate that unique and expanded gene families in R. kukunoris are significantly enriched in immune regulation and oxygen-related activities. Several immune-related genes were identified to experience positive selection or rapid evolution in R. kukunoris, suggesting the potential significance of immune regulation in high-altitude adaptation. Additionally, genomic scans suggest that two genes, EPAS1 and ARNT2, which belong to the hypoxia-inducible factor (HIF) family, are under strong positive natural selection. Our study provides further insights into high-altitude adaptation and offers genomic resources for future research.

Gulls are opportunistic birds that take advantage of anthropogenic food subsidies, often leading to conflicts with human populations. In Argentina, the Kelp Gull (Larus dominicanus) is distributed along the Atlantic coast and in some freshwater environments. We evaluated the trophic ecology of a population nesting in Nahuel Huapi Lake, with access to anthropogenic food subsidies. We used complementary methodologies (pellets, stomach contents, stable isotopes) to determine their diet during the incubation and chick-rearing periods in 2019 and 2020, in two colonies (~261 and 314 nests) located close to urban areas. Pellets showed a relatively high percentage of anthropogenic food resources (>40%) and terrestrial arthropod remains (>40%) in all breeding stages and years, except during incubation in 2019, when >70% of rodent remains were recorded. Stomach contents also showed a high percentage of garbage in both years (40–80% incubating adults, 30–40% chicks) and of terrestrial arthropods (30–60%). Isotopic niche width differed between years, and the isotopic composition (δ¹³C and δ¹⁵N) of adult and chick red blood cells showed a significant proportion of terrestrial resource (natural and anthropogenic items combined) consumption in all stages and years and a lower proportion of garbage in 2019. This study shows the generalist and opportunistic habits of Kelp Gulls at the Nahuel Huapi Lake colonies, evidenced by the wide variety of food consumed and the ability to take advantage of the food that becomes available in the natural environment (e.g., rodent outbreak throughout 2019). This study of the trophic ecology of the Kelp Gulls in the Nahuel Huapi Lake provides essential baseline information for future assessments of the gulls' demographic behaviour and their role within the urban-lake-terrestrial ecosystem. Further studies to understand the use of resources during the non-breeding season are recommended.

Understanding morphological traits and environmental preferences within a population is essential to comprehend the relationship of species with their environment and to develop useful conservation strategies. This is especially important for secretive species such as arboreal snakes. Our study assessed how morphological variation in sex and age classes influenced environmental preferences in the Blunt-headed tree snake Imantodes cenchoa in Los Tuxtlas, Veracruz, Mexico. We used data from 249 individuals, consisting of 143 adults, 47 juveniles, and 59 hatchlings. We found significant linear relationships of snout-vent length and body mass with elevation and humidity. Environmental preferences did not differ between sexes, but elevation, humidity and temperature are differently selected by age classes. The greater tolerance of adults to environmental conditions allowed them to expand their habitat to places where they can find more food and shelter. In contrast, less tolerant hatchlings and juveniles benefited from vegetated, humid locations at lower elevation sites where food and shelter remain available during a longer period of the year. Our findings are relevant for the management and conservation of this species, listed as “with special protection” by Mexican Law, since environmental preferences are very restricted in hatchlings, a vital stage for the maintenance of the population. Efforts preserving lower sites, in constant threat by cattle breeders in the area, will preserve both sexes and all three age categories.

Sociality plays a major role in an array of factors critical to the ecology of many species, including sexual selection, migration, habitat selection, predation risk, and parasite infection. Group size is a fundamental metric used to assess sociality in many species. While barren-ground caribou (Rangifer tarandus) are highly social, there is little quantitative documentation of the patterns in their year-round group sizes. I report the daily and monthly average group sizes of the Nelchina Caribou Herd in east-central Alaska. Group sizes were small not only in winter and late summer but also during calving. Group sizes increased post-calving and reached their maximum during the peak of insect harassment in July. The largest single group observed was >30% of the entire herd. July was the only month where the average group size was more than 1% of the size of the herd. Group sizes were relatively large during migration but larger during fall migration than spring, which may reflect the importance of sociality during the rut and/or the dispersed nature of barren-ground caribou during winter.