Biology Letters最新文献

Land conversion is a widespread form of environmental change that can alter infection dynamics in wildlife by modifying host immune defence. Such effects may be compounded by seasonal variation in resources and reproduction and differ among members of a host community, yet the combined effects of habitat, season and species identity on wildlife immunity remain poorly understood. We tested within- and across-species effects of land conversion and seasonality on immunity in Neotropical bats by quantifying haematological markers of physiological stress and inflammation. We sampled seven species across a large forest preserve and smaller nearby forest fragment in northern Belize during the dry and wet seasons. Using phylogenetic generalized linear mixed models, we tested overall effects of habitat and season and quantified per-species impacts. Total leukocyte counts and neutrophil-to-lymphocyte ratios showed no overall habitat or seasonal effects but displayed strong species-specific responses to these predictors. In contrast, the systemic inflammation response index was higher across species in the dry season and in the smaller fragment, suggesting poor health in unfavourable conditions. Species-specific effects did not align with diet guilds, indicating potential roles for finer-scale ecological traits. Our results highlight the complex, species-dependent effects of environmental change on wildlife immunity.

Publishing non-significant findings is essential for the progress of science. However, many of us forget that 'absence of evidence is not evidence of absence' and believe that a statistically non-significant result is evidence of no effect. Regrettably, and despite the null hypothesis being simple, elegant and often underpinned by evidenced or reasoned convictions, conventional p-value analysis can only argue against the null hypothesis, never in favour of it. Here, I provide a quick-and-easy guide to simple yet powerful statistical options available to biologists for investigating the absence of a meaningful effect, namely equivalence tests, confidence intervals and credible intervals; or the absence of any effect, namely likelihood ratios and Bayes factors. These approaches, supported by accessible software, allow biologists to draw direct conclusions about the null hypothesis.

Ground sloths were terrestrial megafauna that inhabited the Western Hemisphere. While they are inferred to have been browsers and grazers based on craniodental morphology, it is plausible that they performed a wide range of ecological functions, including seed dispersal, bioturbation and nutrient cycling. Understanding ground sloth ecology is challenging due to their enamel-free dentition, which poses limitations to palaeodietary methods, like stable isotope analysis, due to the increased probability of diagenesis in more porous tissues. Here, we conduct dental microwear texture analysis on Paramylodon harlani and Nothrotheriops shastensis specimens from the La Brea Tar Pits in southern California to compare these species to each other, to co-occurring megafauna and to modern analogues to clarify ground sloth dietary ecology. DMTA of P. harlani (i.e. low anisotropy and high complexity) and N. shastensis (i.e. low anisotropy and low complexity) suggests that P. harlani consumed significantly harder foods (e.g. tubers, roots, seeds, fruit pits) than N. shastensis. Findings underscore that these species were not functional replicates of each other or of co-occurring browsers and grazers (e.g. camels and bison). Considering the high degree of dietary overlap in extant folivorous sloths, the extinction of giant ground sloths represents a true loss of ecological function.

The Late Pleistocene was a time of global megafaunal extinctions that were particularly severe in North America. The continent lost many mammal taxa, but the validity of several remains ambiguous, including a high proportion of Cervidae taxa. Torontoceros hypogaeus is represented by a single specimen (ROMM75974) discovered in 1976 during excavation work for the Toronto subway in Canada. The species was described based on its unique antler morphology, but the variable nature of that trait and the species near absence in the fossil record leads to uncertainty concerning its systematic relationships. We used ancient DNA to clarify the taxonomic relationship and evolutionary history of T. hypogaeus. We performed mitochondrial and whole genome analyses with related cervids and showed that ROMM75974 has a close affinity, but relatively high divergence from Odocoileus sister species. While some ambiguity remains, ROMM75974 could represent a distinct Odocoileus species to be included in the list of extinct North American taxa. This unique population was likely adapted to open landscape, which was rapidly replaced with dense woodland in this region at the end of the Pleistocene, highlighting the role of climate change in the extinction of megafauna biodiversity at the end of the ice age.

Human activity has profoundly shaped the landscape of resources available to animals. While certain species, such as scavengers, are particularly adapted to exploit resources that fluctuate significantly over space and time, their responses to sudden human-induced changes in resources remain poorly understood. The COVID-19 lockdown offered a natural experiment to study these dynamics, as reduced human mobility abruptly decreased roadkill availability for scavengers. Here, we examined how reductions in roadkill affected the foraging behaviour of an avian facultative scavenger, the red kite (Milvus milvus). We hypothesized that with fewer carcasses available, red kites would decrease their use of roads for scavenging. GPS tracking data from 199 non-breeding individuals confirmed that red kites switched from actively selecting roads before the lockdown (2017-2019) to avoiding them during lockdown (2020), with the trend reversing again afterwards (2021-2023). Selection for areas with higher probability of anthropogenic feeding increased during lockdown and remained elevated afterwards. Our findings highlight that abrupt changes in human activity can drive rapid behavioural shifts in a generalist forager, with certain effects lasting for years after the change.

The Hawaiian honeycreepers simultaneously represent one of the most spectacular avian adaptive radiations and are one of the most endangered avian groups. This clade's few geographically widespread species can serve as a model to understand population-level processes shaping differentiation and characterizing decline. One such species is the likely extinct 'ō'ū (Psittirostra psittacea), a parrot-like beaked honeycreeper with a frugivorous feeding ecology. We compiled morphological and hybridization-captured ancient DNA datasets for the 'ō'ū from museum specimens from across the Hawaiian archipelago. We find (i) genomic differentiation among 'ō'ū from Kaua'i, Lāna'i, and the remaining Hawaiian Islands and (ii) a larger phenotype on Kaua'i and smaller Maui Nui morphological phenotypes. While the differentiated population on Kaua'i is likely a result of Kaua'i's geographical isolation, the divergent population on Lāna'i is harder to explain by biogeography alone. Thus, we investigated whether the unexpected divergence of Lāna'i 'ō'ū could be attributed to inter-species admixture with the geographically overlapping, now extinct 'parrot-billed' Lāna'i hookbill (Dysmorodrepanis munroi) or a critically endangered Maui endemic, the kiwikiu (Pseudonestor xanthophrys). We detect significant admixture between the Lāna'i 'ō'ū population and the Lāna'i hookbill, possibly explaining the observed population structure and associating interspecific breeding with populations on the precipice of extinction.

Frequent and intense heatwaves are causing heat-related avian mass mortality events to become more common, but the role of elevated humidity as a contributing factor remains unclear. Here, we quantified the effect of humidity on risks of lethal hyperthermia for blue waxbills (Uraeginthus angolensis), the species most common among the victims of South Africa's first documented heat-related mass mortality event involving wild bird populations. We quantified waxbills' body temperature (T_b), metabolic heat production and evaporative heat loss at air temperatures (T_air) approaching and surpassing normothermic T_b in dry (1.1 ± 0.9 g m^-3) and humid (21.3 ± 0.4 g m^-3) air. The humid treatment was associated with significant declines in evaporative cooling capacity, and maximum T_air tolerated by waxbills was approximately 2°C lower (45.7°C) compared to the dry air treatment (47.9°C). A model of end-Century exposure for the waxbills reveals that elevated humidity could increase the risks of lethal hyperthermia by threefold to sevenfold in some parts of southern Africa.

A central question in understanding acoustic communication systems is how auditory processing develops relative to vocal differentiation. While the development of auditory processing of conspecific vocalizations has been studied in songbirds and mammals, it remains unexplored in fish. The Lusitanian toadfish (Halobatrachus didactylus) is an highly soniferous fish that exhibits sound production early in ontogeny, representing an ideal model to investigate the development of the vertebrate auditory-vocal system. Based on the auditory evoked potential (AEP) recording technique, we evaluated differences in auditory representation of boatwhistles (reproductive, agonistic and juvenile calls) and territorial grunts between different-sized toadfish groups-small juveniles (1.4-1.8 cm standard length), large juveniles (6.7-10.6 cm) and adults (up to 36 cm). Significant ontogenetic improvements were found in representing temporal patterns of boatwhistles (response latency and duration) and grunts (latency, pulse period and duration), as well as in detecting boatwhistle amplitude modulation. These acoustic parameters can potentially function as social cues for individual quality, motivation and mate choice. We present the first evidence of ontogenetic refinement in resolving fine features of conspecific calls in a fish species, suggesting this may be a conserved mechanism enhancing social communication across vocal vertebrates.

Problem-solving is an integral part of most animals' lives. There are generally four types of solutions animals may use: innate, learned previously, learned de novo or insightful. Identifying the types of solutions animals use can be difficult, especially with the trend of having increasingly difficult requirements to test hypotheses in this field. These requirements often amount to proving a negative, which may be impossible. Therefore, here we develop a novel framework for testing hypotheses that can help distinguish the types of solutions animals may use that does not require proving a negative. This framework is based on distinct patterns of qualitative and quantitative variation between and within individuals. Because this framework does not require knowledge of animal's prior history nor that the problem be evolutionarily novel, it can be used with a variety of animals, experimental designs and settings. We suggest this framework could serve as a valuable tool in expanding how we study animal problem-solving, especially in the types of animals studied. Studying problem-solving in a wide variety of animals would allow us to form a better understanding of the problem-solving abilities different brain sizes and structures confer and, more broadly, the evolution of those abilities.

Caenorhabditis elegans has evolved from its dioecious ancestors to adopt an androdioecious reproductive strategy. In this process, ancestral female C. elegans acquired genetic modifications that enabled self-sperm generation, self-sperm activation and a reduced reliance on sexual reproduction. However, how males have adapted during this transition from dioecy to androdioecy is less explored. Using Caenorhabditis species, we demonstrated that androdioecious hermaphrodites exhibit attenuated sex pheromone potency, while androdioecious males show heightened olfactory habituation and diminished mate exploration capabilities. The behaviour of androdioecious males can be reverted to resemble that of dioecious males by replacing the SRD-1 receptor with its dioecious orthologues. This intrinsic characteristic is contingent upon the C-terminal cytoplasmic domain of the receptor. We propose a theoretical framework where C. elegans males have accumulated genetic variations in their pheromone receptor, leading to altered chemosensory perception of the opposite sex, which confers a selective advantage favouring hermaphroditism. Our study provides insights into overlooked male traits, shaped by changes in chemosensory signalling. The findings underscore the capacity of chemosensory variations to influence how organisms perceive critical ecological factors, eventually facilitating the emergence and stabilization of hermaphroditism.