Biology Letters最新文献

Sex differences in thermal tolerance may significantly impact population responses to climate change, yet most studies examining geographic variation in thermal tolerance focus on a single sex. Here, we investigate how males and females might vary in their capacity to tolerate the heat along a latitudinal cline using the Australian water flea, Daphnia carinata. We measured heat knockdown times in males and females using clones of Daphnia from six populations spanning eastern Australia, raised under two acclimation temperatures (20°C and 25°C). Females consistently showed higher thermal tolerances than males, with greater capacity for thermal acclimation. Critically, we discovered that latitudinal clines in thermal tolerance were sex-specific: females showed a much steeper decline in heat tolerance with increasing latitude compared with males. As a result, sexual dimorphism in thermal tolerance was more than twice as large in northern populations compared with southern populations. These results suggest that sex-specific selection, potentially driven by differential habitat use or the female-biased demography of cyclical parthenogenesis, may be driving divergent thermal adaptation between the sexes. Our findings highlight the importance of considering both sexes when predicting population vulnerability to climate change, as sex-averaged estimates may misrepresent the heat tolerance of populations along environmental gradients.

Populations in managed care are valuable resources that complement in situ conservation efforts, but adaptation to captive conditions and other domestication effects present concerns for conservation. Many populations of fish adapted to sulfide springs are highly endemic and imperiled, potentially benefiting from ex situ conservation efforts. However, it is challenging to maintain natural conditions in the laboratory as hydrogen sulfide (H2S) is highly toxic and coincides with severe hypoxia. Here, we tested whether long-term standardized rearing of sulfide spring fishes leads to the loss of H2S and hypoxia tolerances. We compared the tolerances of Poecilia mexicana (Poeciliidae) from sulfidic and non-sulfidic habitats that were reared in the laboratory for 18 years and wild-caught fish from the same sites. Both H2S and hypoxia tolerances were maintained in laboratory-reared fish from the sulfidic habitat. Additionally, fish from a non-sulfidic cave site, evolutionarily derived from a sulfidic population, exhibited higher H2S and hypoxia tolerances than fish from the non-sulfidic surface site. While domestication can lead to the loss of adaptations to extreme environmental conditions, our research indicates this is not a concern in laboratory stocks of P. mexicana, which retained tolerance of H2S and hypoxia despite not experiencing these stressors for approximately 40 generations.

Failures of the lysosome-autophagy system are a hallmark of ageing and many disease states. As a consequence, interventions that enhance lysosome function are of keen interest in the context of drug development. Throughout the biomedical literature, evolutionary biologists have found cases in which challenges faced by humans in clinical settings have been resolved by non-model organisms adapting to wild environments. Here, we used a primary cell culture approach to survey lysosomal characteristics in species of the genus Mus. We found that fibroblasts from M. spretus, a wild Mediterranean mouse, exhibited elevated lysosomal mass and enzyme activity along with reduced activity of β-galactosidase, a classical marker of cellular senescence, compared with those from M. musculus, a related species adapted to human-associated environments. We propose that classic laboratory models of lysosome function and senescence may reflect characters that diverge from the phenotypes of wild mice. The M. spretus phenotype may ultimately serve as a blueprint for interventions that ameliorate lysosomal dysfunction under conditions of stress and disease.

Heatwaves negatively impact behaviour with associated cognitive impairment in humans. A growing body of literature also reports negative effects of heatwaves on cognition in other animals. A larger brain is known to generate enhanced cognitive abilities that may buffer against environmental changes and thereby potentially increase fitness in large-brained individuals. How a larger brain buffers against adverse effects on cognitive abilities induced by thermal stress, such as that experienced during heatwaves, remains unknown. We examined detour problem solving and working memory during an experimental heatwave in guppies artificially selected on brain size with matching differences in neuron number. Overall, detour problem-solving was impaired among guppies during the heatwave, while working memory was unaffected. Large-brained guppies outperformed small-brained guppies in detour problem-solving and working memory in both the heatwave and control temperature treatments. During the heatwave, large-brained guppies exhibited cognitive performance levels comparable to those of small-brained guppies under normal temperature conditions in the detour task. Our study thus suggests that small-brained individuals might have lower fitness also during heatwaves if increased temperature impair cognitive abilities required for survival and reproduction. Furthermore, our results open up the possibility that cognition-driven brain size evolution may have been influenced by abiotic factors.

Millions of animals are killed by vehicles on roads yearly, left mostly to rot, but these unfortunate mortalities may have a benefit to society that is not widely appreciated: they represent a valuable source of animals for study that does not require and could even replace the use of live wildlife. Here, we provide the first literature review to uncover validated uses for roadkill and, in doing so, encourage uptake of this valuable resource. We located 312 studies using roadkill whose aim included purposes other than enumerating or mitigating roadkill. We identified 26 broad-use and 91 specific-use categories of roadkill carcasses. Most common uses included assessing species presence or distribution, assessing parasite, disease or pathogen presence, assessing roadkill as an index of species abundance, describing species diet and lodging specimens in museums. The studies included at least 650 species; mammals dominated the studies, followed sequentially by reptiles, birds, amphibians and invertebrates. We discuss how we might better take advantage of this source of animals for study and highlight limitations and cautions in their use. Given the proven and diverse uses demonstrated in our review, we encourage the scientific community to now (re-)consider roadkill as an ethical alternative to live animal sampling.

Nests are extended phenotypes capable of providing brood protection against predators, and because they are motionless structures, camouflage is expected to emerge. Birds from different families construct a tail of hung materials underneath their nests, which has been hypothesized to be a type of disruptive camouflage, i.e. an appendage that gives a nest a false shape for hindering detection by predators. Predictions of this hypothesis are that for predators that are visually oriented, nests without a tail are easier to detect, yet this hypothesis never received support likely because predator species and other variables were not considered. Here, we compared predation between nests of blue manakins for which tails were maintained or experimentally removed. To avoid the effects of parental movements in predator's attraction, we used real inactive nests with Plasticine eggs. We also controlled for nest site variables and excluded nests depredated by olfactory animals by monitoring nests with infrared camera traps. Predation was 10 times higher in nests without a tail, and tail absence was the only significant variable explaining nest predation. Furthermore, all of the recorded predators were visually oriented. This is the first work confirming the antipredatory adaptive function of avian nest tails, and corroborated the disruptive camouflage hypothesis.

Many emerging viruses of public health concern originate in animals and have the potential to transmit to humans or cause spillover. Orthoebolavirus zairense (EBOV) is one example, circulating in wildlife in Central and West Africa, with high mortality in humans and animals. Previous studies have linked Ebola outbreaks to transitions in rainfall seasonality, proximity to deforestation and areas with high human population density. However, a universal driver or mechanism has not been described and spillovers remain unpredictable. To assess potential environmental determinants of EBOV spillovers, we analysed time series of vegetation health, rainfall, temperature, forest loss and human population size surrounding Central African spillover locations from 1990 to 2022. We evaluated whether environmental conditions before spillover were atypical for each location by quantifying the similarities in environmental time series between spillover years and non-spillover years. Contrary to past work, we found no single environmental trigger that universally prompts spillover. While some outbreaks were preceded by atypical environmental conditions, others occurred when conditions were strongly similar to non-spillover years. We also modelled the relationship between anthropogenic factors and the occurrence of spillover and found no association. We find EBOV spillovers occur following various environmental conditions and no consistent anthropogenic associations.

The global decline in wild populations and the growing demand for bioresources have spurred efforts to enhance wildlife populations through captive breeding programmes. However, the success of these initiatives remains limited. Using data from a long-term captive breeding programme conducted by a national salmon hatchery in Japan, I examined the influence of an individual's origin on mortality in captivity. My results showed that wild individuals had higher mortality rates in captivity than captive-bred individuals. These findings suggest that efforts to enhance wildlife populations through captive breeding can result in the loss of wild individuals with high fitness in the wild and the ability to enhance their offspring's fitness in the wild, underscoring the need for approaches that lower the mortality of wild individuals in captivity.

Social signals about current environmental risks can shape development in young animals. Distress calls made by young chickens (Gallus gallus domesticus) may also encode affective state, with high arousal, potentially 'anxiety-like' state characterized by continuous calling, and learned helplessness or potentially 'depression-like' state by a more intermittent pattern. During early life (age 4-7 days), we played chicks artificial stimuli mimicking these two call patterns. Growth effects suggest caller affective state can modulate this social signal: chicks exposed to bouts of 'Continuous' calls grew faster and were heavier by late commercial life (day 43) than Controls. In contrast, chicks exposed to 'Intermittent' calling showed slow, then compensatory, growth. A third experimental treatment with similar 'noisiness' to distress calls did not influence growth. Responses to a late-life social isolation trial suggested lasting impacts on stressor perception or resilience. Comb temperature elevation during isolation, indicating acute stress, was greatest in the Continuous group. Call rate decline during isolation, potentially indicating a tendency towards learned helplessness, was steep in all three experimental treatments; hence, noise-related disturbance from vocalizations may also shape development. Distress calls are consequently an important consideration in farms, where young are raised at high density and one individual is heard by many.