Biology Letters最新文献

Antarctic krill (Euphausia superba) are a key species in the marine Antarctic ecosystem. Food boluses, a by-product of feeding where Antarctic krill form a compact food mass within their feeding basket, were formed and rejected under laboratory conditions. We explored the conditions leading to bolus formation by examining feeding behaviour of Antarctic krill in response to different phytoplankton types and concentrations. Two scenarios were observed that increased the likelihood of bolus formation: (i) when food concentrations exceed the krill's filtering capacity and (ii) when particles are caught in the feeding basket. We measured the frequency of rejection of boluses, along with their composition, carbon and nitrogen contents, and sinking rates. For cell concentrations approximately 10⁸ cells l^-1, the frequency of rejection ranged from 2.6 to 17.0 boluses per hour. The carbon and nitrogen contents averaged 24.1 µg C mm^-3 and 2.3 µg N mm^-3, and sinking rates averaged 367 m d^-1. Our findings suggest this behaviour may also occur in situ and could contribute to organic carbon export, with bolus sinking rates comparable to or exceeding those of Antarctic krill faecal pellets. If confirmed in the field, this behaviour may also occur in other krill species with similar feeding behaviours.

Pigmentation in mammalian hair follicles is governed in part by interactions between agouti signalling protein (ASIP) and the melanocortin 1 receptor (MC1R). The most common coat colours in mammals result from alternating bands of dark eumelanin and light phaeomelanin within individual hair shafts. However, coats dominated by a single melanin have arisen several times. Here, we examine the genetic basis of two instances in marsupials: a melanistic morph of the eastern quoll (Dasyurus viverrinus) found at high frequency in the wild, and a rare case of fixed xanthism in the marsupial moles. In eastern quolls, we identify a deletion encompassing the ASIP start codon which was found to be homozygous only in the melanistic animals examined. This mutation appears to be convergent with that recently discovered in its dark-coated relative, the Tasmanian devil (Sarcophilus harrisii). Conversely, we show that a non-sense mutation which severely truncates MC1R in the southern marsupial mole (Notoryctes typhlops) is a candidate driver of its pale-yellow coat. Together with other recent findings, our results suggest that loss-of-function mutations have occurred repeatedly within the marsupials, representing a mechanism underpinning coat colour variation.

The 'Chicago Rat Hole' is a remarkable full body impression ostensibly created by a brown rat (Rattus norvegicus) crossing fresh concrete in Chicago's Roscoe Village that became a viral sensation. While the public attributed the mark to a brown rat, no formal analysis had been conducted to confirm its identity. Using clear anatomical landmarks, we compared measurements from the 'Chicago Rat Hole' to eight sympatric rodent species using univariate and multivariate analyses. Univariate tests showed no significant differences in snout-to-tail length, head width, tail-base width or third digit length between the imprint and members of the genus Sciurus (i.e. tree squirrels). Discriminant function analysis indicated a 98.67% likelihood that the 'Chicago Rat Hole' was a squirrel, with classifications split between the eastern grey squirrel (50.67%) and the fox squirrel (48.00%). Given local population densities, an eastern grey squirrel likely represents the most parsimonious species-level match. This investigation underscores the challenges of attributing a trace to the tracemaker. While we acknowledge the playful spirit of this investigation, our broader aim is to highlight that scientific inquiry begins with curiosity and observation: qualities that are not exclusive to professional scientists, but accessible to anyone with an interest in understanding the natural world.

Sex-determining genes remain largely uncharacterized outside classical models in vertebrates and insects, leaving a gap in our understanding of their evolutionary emergence. The terrestrial isopod Armadillidium vulgare provides an excellent model for investigating this question, as it presents multiple genetic sex determinants. Some lineages possess a masculinizing dominant allele at a locus called the 'M gene', which is analogous to an XY system. This allele is hypothesized to have been selected due to the deficit of males caused by a non-Mendelian feminizing factor previously described. The existence of the M gene was inferred from crosses carried out in the 1990s, but its molecular nature remains unresolved. Here, we conducted a genome-wide single-nucleotide polymorphisms analysis combining pooled sequencing of male and female progenies with sequencing of individual parents across two families. Bayesian estimation of haplotype frequencies in progenies pinpointed a candidate genomic region of approximately two megabases. Notably, this region contains the gene encoding the androgenic gland hormone, a protein involved in male sexual differentiation. Our findings lay the groundwork for functional investigations of the M gene, offering novel insights into the dynamics of sex determination in terrestrial isopods and into the turnover of sex chromosomes in response to sex-ratio distortion.

Predator physiology is often overlooked in predator-prey interactions, despite its potential to significantly influence hunting dynamics and social cooperation among predators. We address this gap by investigating how physiological alignment relates to group dynamics and hunting performance in a unique interspecies mutualism: artisanal net-casting fishers who target fish with assistance from wild dolphins. We monitored 24 fishers using high-resolution chest-belt sensors, recording continuous electrocardiograms (ECG) and GPS positions. We then calculated interpersonal heart rate variability (HRV) synchrony in low (LF) and high frequency (HF) bands while tracking changes in foraging and social contexts. In both LF and HF HRV domains, positive social factors increased HRV synchrony among fishers, especially those with established cooperative bonds, whereas distance between fishers decreased HRV synchrony. External factors-the presence and activity of dolphins-had no measurable impact on HRV synchrony. We also found a negative association between group-level hunting success and HRV synchrony in the LF domain, which is influenced by both sympathetic and parasympathetic activity. By demonstrating the role of physiological synchrony during collective hunting in humans-driven by social factors and with direct implications for hunting outcomes-our study advances the current understanding of the eco-physiological dynamics of social predators in predator-prey systems.

Repeatedly, intervention studies report that participants undertaking a new exercise regimen lose weight initially, but then their weight loss quickly plateaus. A careful look at the literature shows that plateauing happens even when participants' food intake does not increase and their exercise intensity is maintained. So how can we explain this, given that if the body is consistently in energy debt, surely weight loss must result. I argue that energy expenditure compensation-reductions in energy expended on some biological processes to counteract increases in energy expended on activity levels-is an under-recognized compensatory response to heightened exercise. We observe energy expenditure compensation 'in the field', for example, people in pre-industrialized nations expend a lot of energy each day on physical activity but nonetheless have a daily energy expenditure commensurate with that of relatively sedentary Westerners. But most researchers and practitioners have not connected the aforementioned laboratory and field observations-that is, if our activity levels are consistently heightened for long enough, our bodies adaptively compensate in terms of overall energy expenditure, such that if we undertake an exercise regimen, in the long run we only lose a fraction of the weight we aspire to. We need to raise awareness about energy expenditure compensation, how it can limit weight loss and how in light of this knowledge we might better prescribe 'weight loss regimens' to encourage additional weight reduction in those who aspire to it.

Co-variation with functionally integrated sensory structures contributes to the size evolution of brain regions. In this study, we investigated co-variation between sizes of the optic tectum and eye of Asiatic toads (Bufo gargarizans) along altitudinal gradients. The relative sizes of both the optic tectum and eye decrease significantly along with increases in altitude. Furthermore, optic tectum size is positively correlated with eye size among populations (p < 0.05, R² = 0.290), but not among individuals within each population, where natural selection occurs. The eye and optic tectum are likely subjected to parallel and independent local adaptation along altitudinal gradients that produce the correlative pattern; however, the pattern does not support functional integration and selection on their correlation. Eye size change may not have a significant impact on optic tectum evolution. Our study highlights the importance of cross-scale comparative analysis for inferring evolutionary processes.

Functional specialization of the brain hemispheres has been observed across the animal kingdom, with the left hemisphere being associated with positive emotions while the right hemisphere is associated with negative emotions. In vertebrates, contralateral eye use is indicative of which brain hemisphere is being used for processing and so may therefore reveal affective state. Using a within-subjects design, we investigated whether lateralized eye use could be used as a non-invasive welfare indicator in captive-bred lizards (Pogona vitticeps) housed in standard or enriched enclosures for four weeks. Eye use was recorded during basking, a key maintenance behaviour. We found that when lizards were housed in standard enclosures (an environment associated with reduced welfare) they exhibited significantly greater use of their left eye (right brain hemisphere) compared to when they were housed in enriched enclosures (an environment associated with improved welfare). These findings suggest that the negative affective state induced by housing conditions is reflected in lateralized eye use, making this a promising, non-invasive tool for assessing animal welfare that is likely to be of value across vertebrate species.

In this article, we consider the extent to which wildlife tourism in China has become a nodal point where human-animal interactions have been consistently shaped and reshaped by the multiple layers of naturecultural complexity. We do this by investigating Chinese visitors' evaluation of animal welfare as they apply to red and giant pandas at the Chengdu Research Base of Giant Panda Breeding (Panda Base). A survey of Chinese visitors indicated generally positive perceptions of the welfare conditions of pandas at Panda Base. Visitors largely viewed the institution as providing excellent care to pandas, reflecting a high degree of public trust in the organization. While red pandas were perceived to experience slightly better welfare conditions, visitor concern and attention focussed more heavily on giant pandas-possibly due to their iconic status. This study investigates how species status and environmental visibility influence Chinese visitors' perceptions of animal welfare at a major wildlife tourism site. It highlights how iconic animals such as the giant panda are often assumed to receive excellent care, while lesser-known species like the red panda invite more diverse interpretations-thus revealing a potential symbolic bias in public welfare judgements. These findings suggest a symbolic bias in welfare judgements, shaped not only by observable enclosure features but also by the animals' cultural significance in the native culture.

Leafcutter farming systems are ant-fungus mutualisms whose ecological success hinges on differentiation of fungal hyphae into swollen cells called gongylidia that ants consume. While gongylidium cells are unique signatures of coevolved crop domestication, their cell biology is poorly understood. Each gongylidium cell contains a large vacuole that is thought to protectively store plant degradation enzymes that ants ingest and vector unharmed in faecal droplets back to the fungus. We hypothesized that enzyme storage requires gongylidium vacuoles to have distinct levels of pH and reactive oxygen species (ROS) compared to the vacuoles of undifferentiated hyphae that likely degrade cellular waste. We used live-cell fluorescence microscopy of fungal isolates with targeted probes to first show that both cell types had vacuoles with lower pH than the surrounding cytosol. In contrast, while hyphal vacuoles stored ROS, gongylidium vacuoles excluded these potentially harmful molecules. These findings suggest derived cellular adaptations in a mutualistic fungus where gongylidia protect ant-vectored enzymes through specialized subcellular ROS compartmentalization.