Biology Letters最新文献

Islands have long represented natural laboratories for studying many aspects of ecology and evolutionary biology, from speciation to community assembly. One aspect that has been well documented is the correlation between island size and taxonomic diversity, likely due to decreased complexity and population size on small islands. This same logic can apply to genetic diversity, which should predictably decrease with effective population size. The island size-diversity correlation has received support over the years but often focuses on single metrics of genetic diversity. Here, we use Zosterops white-eyes in the Solomon Islands to study the correlation between island size and various metrics related to genetic diversity, including runs of homozygosity and fixation of transposable elements. We find that almost all these metrics strongly correlate with island size, and in turn with each other. We infer that island size is independently correlated with these different variables, demonstrating that population size impacts genomic metrics of diversity in a variety of ways across temporal and hierarchical scales.

In most human societies, grandparents often provide substantial care and support for their grandchildren, including as babies. Given that previous studies have shown that ageing is accompanied by a gradual decline in our ability to identify other people's emotions, does age also reduce our skill at understanding a baby's cries? Here, we show that older people with experience of caring for babies remain able to correctly decode the information conveyed by babies' cries. The results of our psychoacoustic experiments underline that older people were at least as good as younger adults at identifying whether a baby is crying in pain or rather as a result of simple discomfort. These results are consistent with the notion that humans are cooperative breeders where older generations can effectively help younger ones with alloparental care. Favouring intergenerational solidarity is likely to simultaneously benefit the quality of life of young parents and older, knowledgeable carers.

Most mammals, including humans, exhibit even or slightly male-biased birth sex ratios (BSRs) and female-biased adult sex ratios (ASRs) much later in life due to higher male mortality rates. The group-living primates of Madagascar are unusual in this respect because they lack female-biased ASRs, but it is unknown whether this is the result of skewed BSRs or sex-specific disappearance patterns. Using long-term demographic data from wild red-fronted lemurs (Eulemur rufifrons), we analysed their sex ratio dynamics across the lifespan. We assessed BSR via prenatal sex determination using maternal faecal oestrogen metabolite measurements during late pregnancy, confirming a visually determined equal sex ratio three months after birth, and indicating no early sex-specific mortality. Demographic analyses additionally disclosed higher female disappearance within the first 8 years of age, likely associated with reproductive effort early in life. Thereby, adult male survival had the greatest positive effect on the ASR. Our study offers a rare perspective on the dynamics of age- and sex-specific disappearance in a wild primate population, whose sex-reversed patterns may also contribute to a more general understanding of the mechanisms generating sex-biased mortality.

Dispersal is a ubiquitous process occurring in any ecosystem, with a critical role in the regional coexistence of species that cannot coexist locally. However, previous studies have typically focused on a specific scenario where dispersal is isotropic, leaving the consequence of anisotropic, directionally skewed dispersal largely unexplored, despite its prevalence in natural ecosystems. In this study, we used simulations to study whether the anisotropy of dispersal promotes or hinders species coexistence in a metacommunity. We found that dispersal anisotropy plays a decisive role in species coexistence-with coexistence promoted when dispersal is more directed orthogonally to an environmental gradient, while it is less likely when dispersal is primarily parallel with the gradient. This occurred because dispersal directed orthogonally to the background environmental gradient transports individuals produced in 'good' habitats to other good habitats, creating conditions that favour several spatial coexistence mechanisms, such as spatial storage effects and fitness-density covariance. We conclude that the effect of anisotropic dispersal could be diverse, and therefore, it is necessary to consider the anisotropy and the distribution of environments for a better understanding of species coexistence in a metacommunity.

Telomeres, the protective ends of chromosomes, progressively shorten due to incomplete mitotic replication and oxidative stress. In some organisms, transient telomere elongation may occur, for example, when individuals have an energy surplus to counter stress-induced life events or when elongating telomeres is a last chance to increase fitness. Mammalian hibernators are good models to test telomere dynamics, as they cycle between prolonged bouts of metabolic depression (torpor) punctuated by short surges to euthermia (arousals). We studied captive fat-tailed dwarf lemurs (Cheirogaleus medius), strepsirrhine primate hibernators, that were food-deprived (n = 8) or fed daily (n = 7) during hibernation (4.5 months). We compared telomere lengths, assayed via qPCR from oral swabs, at five strategic time points that span a full year. Food-deprived subjects underwent multi-day torpor/arousal cycles, lost considerable body mass and elongated telomeres during hibernation but shortened them upon emergence. In contrast, food-provisioned subjects ate daily, lost body mass more slowly, underwent shallower and shorter torpor bouts and experienced little change in telomere lengths during the same periods. Our results highlight a complex relationship between telomere dynamics, energy balance and torpor expression. Further investigation is warranted to elucidate the regulation of protective mechanisms in these primate hibernators.

The phenotypic alterations brought by domestication have been hypothesized to be driven by selection for tameness. To explore this, we selected red junglefowl (RJF) for high (HF) and low (LF) fear of humans for 14 generations. We previously found that domesticated chickens performed more play-like behaviours during early ontogeny, and therefore, in this study, we explored potential effects of tameness. Groups of three to four chicks were randomly created from each selection line, and each group was moved to an enriched play arena twice per week, from day 6 until day 53 post-hatch. The frequency of 14 different play-like behaviours, categorized as locomotor, social and object play-like behaviour were recorded for 30 min at every observation instance. Every group of three or four birds constituted the independent statistical replicates and measures were averaged within the groups. The frequency of total play-like behaviour as well as object, and locomotor play-like behaviour was significantly higher in LF, while social play-like behaviour was significantly more common in HF. This largely mirrors previous observations of differences between domesticated and ancestral chickens. Hence, our results support the important role of tameness for the evolution of domesticated behaviour.

As a defining feature of the clade, feathers are key to understanding bird biology. Discoveries of spectacular dinosaur and pterosaur fossils preserving feathers and feather-like integumentary appendages demonstrate trends of increasing complexity in gross morphology and microstructure through avemetatarsalian evolution, and the acquisition of complex flight feathers before the origin of birds. Moreover, this material shows some early feathers differed from modern feathers morphologically, ultrastructurally, biochemically and developmentally, revealing integumentary evolutionary pathways absent in modern taxa. These advances have changed conventional understanding of dinosaurs and impacted conceptions of both birds and feathers. However, it remains unknown if 'true' feathers originated at the base of Avemetatarsalia or within Theropoda. The former scenario implies multiple feather losses, the evolutionary and developmental mechanisms of which require investigation; the latter suggests pterosaurs and ornithischians independently evolved filamentous integumentary appendages, which might have shared genetic regulatory networks with theropod feathers. Answering these questions requires additional data on avemetatarsalian integument, particularly for sauropodomorphs, early diverging theropods and dinosaur outgroups, and more information on those taxa with known integumentary features. An integrative approach combining morphological, developmental, biochemical and taphonomic data, including extinct and extant taxa, is essential for a clearer understanding of feather origin and evolution.

Trade-offs occur when an organism has to allocate limited resources to multiple biological processes. How organisms allocate their resources and whether one trait gets priority over another is poorly understood. Prior work has shown that reproductive investment reduces the capacity of Drosophila melanogaster to mount an effective immune response against subsequent bacterial infection. However, it has not been tested whether the observed trade-off was unidirectional with reproductive fitness given primacy over immunity, or whether it might also occur in the reciprocal direction with an active prior immune response reducing reproductive output. In this work, we delivered bacterial infection to female D. melanogaster prior to mating and tested whether reproductive capacity became reduced. We found that infected females produced the same number of eggs as uninfected females, but the eggs from infected females exhibited lower survivorship to adulthood. Additionally, we found that mating destabilizes chronic bacterial infections, stimulating additional host death and increasing variance in pathogen burden. Together, our results suggest the cost of reproduction and infection in Drosophila females is reciprocal, regardless of the order in which they occur.

Foraging opportunities can be unpredictable. When foragers face a choice between resources that vary in predictability, foraging decisions not only depend on the profitability of food but also on their physiological state. This risk-sensitive foraging approach, in which animals take greater foraging risks when starving, remains relatively untested in reptiles compared with other taxa. We tested the risk-sensitive foraging theory in the tropical lizard, Psammophilus dorsalis, by manipulating energy budgets (satiated versus 48 h starved) and measuring foraging preferences for options that differed in rewards: constant (two mealworms) versus variable (zero or four mealworms). We found that satiated lizards were risk averse to variability in reward amounts and chose the constant food option more frequently than the variable option. In contrast, starved lizards were risk-prone and chose the variable reward option more often than the constant one. At the end of foraging trials, these strategies resulted in both starved and satiated groups achieving similar net resource gains. As new support for risk-sensitive foraging in a tropical reptile species, these results provide insight into how resource uncertainty influences foraging strategies. For lizards in the tropics, which have high-energy requirements year-round, risk-sensitive foraging could be an effective strategy in stochastic environments.

Many animal species have been shown to discriminate between individual humans in captive settings and may use a variety of cues to do so. Empirical evidence remains scarce for animals in the wild, however, particularly in aquatic contexts. For the first time, we investigated discrimination of individual humans by fish in the wild. We first trained two species of fish, saddled sea bream Oblada melanura and black sea bream Spondyliosoma cantharus, to follow a human diver to obtain a food reward. We then investigated whether they could discriminate between two human divers and follow the correct one in an operant-conditioning paradigm. We show that both species were able to quickly learn to discriminate between the two divers when they wore different diving gear. However, they showed no preference when both divers wore identical gear, suggesting that discrimination is based predominantly on visual cues from the dive gear. We discuss the implications of these results for ethical considerations and research practices.