Biology Letters最新文献

The cliff swallow (Petrochelidon pyrrhonota) is a colonial bird that nests in groups of different sizes. Adult cliff swallows have a prominent white forehead patch that we hypothesize functions as a signal of nest occupancy to mitigate costly nest intrusions, especially in crowded nesting colonies. To test this hypothesis, we measured variation in forehead patch area and brightness relative to sex, colony size and date of collection for 241 preserved specimens collected over 43 years. Additionally, we experimentally tested signal function by darkening the foreheads of nesting birds and observing intraspecific interactions. Consistent with a signalling role, we found that females had larger patches than males, patch area increased with colony size, and nests of birds with darkened forehead patches attracted significantly more visits from transient cliff swallows than did nests with no darkened owners. These results suggest that variation in social environment, both in space and time, as well as intersexual differences in incubation behaviour shape the evolution of this conspicuous plumage patch.

The exaggerated evolution hypothesis proposes that intrasexual competition accelerates the evolution of contest-related traits. This hypothesis is supported by a simulation model and empirical data from beetles and mammals using horns or antlers as true weapons. However, it has never been tested for threat devices, which are expected to be under directional selection. Using a clade of neotropical harvestmen where males employ their fourth leg pair as a threat device, we test whether intrasexual competition accelerates the evolutionary rates of these legs. We used a time-calibrated molecular phylogeny and morphometric data to estimate evolutionary rates of each leg pair in males and females of 23 species. We found that the fourth legs in males evolved at rates 5.5-44 times higher than the other legs and 6.5 times higher than the homologous legs in females. In conclusion, threat devices also show accelerated evolutionary rates, supporting the exaggerated evolution hypothesis.

†Otodus megalodon, the largest known macropredatory shark, was globally distributed from the Miocene to Pliocene, yet most ecological and palaeobiological inferences rely heavily on American collections. This geographical bias limits understanding of its population structure and life-history strategies elsewhere. Two explanations have been proposed for its body-size patterns: a Bergmann-type cline, with larger individuals at higher, cooler latitudes and a related hypothesis of Mediterranean dwarfism; and the influence of localized nursery areas that generate assemblages dominated by small juveniles, as documented in several American sites and the Reverté quarries in the western Mediterranean. Here, we present the first extensive dataset outside the Americas designed to test these alternatives across two adjacent basins. Body-size estimates show no significant difference between Atlantic and non-Reverté Mediterranean populations, whereas the Reverté assemblage is smaller. This pattern contradicts basin-wide Mediterranean dwarfism and does not support a Bergmann-type size-latitude relationship. Instead, it strongly indicates a localized nursery at Reverté. More broadly, the results align with an emerging view of widespread nursery habitats in †O. megalodon, comparable to those of extant sharks. By filling a key regional gap, the Iberian record provides tests of competing hypotheses and refines understanding of †O. megalodon population structure and life history.

Recognizing one's own eggs is crucial for birds, especially for hosts of brood parasites that must identify and reject different-looking parasitic eggs. While birds seem to possess a 'template image' of their eggs, whether it is innate or refined over time remains unclear. We addressed this question by experimentally inserting either artificial mimetic eggs (ME) or non-mimetic eggs (NME) into the nests of barn swallows (Hirundo rustica) during the pre-laying stage. We harnessed the potential of our individually marked population to perform a unique comparison between naive first-time breeders and experienced females, as well as females with 'old' (from a previous season) and 'recent' (from the previous breeding attempt within the same season) experience, allowing us to investigate the role of memory. We found that neither naive nor experienced females ejected NME more often than ME, suggesting that the template image does not play a primary role in egg recognition. Instead, awareness of own egg-laying might be the crucial mechanism at play, facilitating nest sanitation behaviour. Lastly, we provide the first evidence that this mechanism improves with recent breeding experience.

Mitochondrial plasticity enables ectothermic animals to maintain performance under changing thermal conditions, but whether this ability declines through adulthood is unknown. We explored changes in mitochondrial plasticity in the three-spined stickleback (Gasterosteus aculeatus), a temperate fish that in many populations has a single breeding season over which it produces multiple clutches and then dies. Wild-caught fish were exposed to one of three thermal regimes: remaining at 12°C, switching to constant warm (21°C) or diel cycling (12-21°C) for three weeks at either the beginning or end of the season. We quantified both phosphorylating and non-ATP-producing (OXPHOS and LEAK) respiration in isolated muscle mitochondria and oxidative control efficiency (OxCE). Early in the breeding season, young fish responded to elevated temperatures by adjusting both their capacity for ATP production and non-ATP-production respiration, but this mitochondrial plasticity declined over the season. OxCE was unaffected by time of season or temperature treatment. Changing body condition was unrelated to mitochondrial function. Our findings indicate that mitochondrial plasticity declines across adult life, potentially limiting thermal resilience in older individuals, the first time this has been reported in an ectotherm. This highlights the need to account for age-related physiological changes in capacity when predicting species' responses to environmental change.

Adaptations of nocturnal insects' visual systems to dim light environments include increased photon capture and sensitivity. Yet this risks saturation, which is countered by screening pigments limiting the photons reaching the photoreceptors. Male glow-worms must detect the females' green bioluminescence at night to mate. In addition to screening pigments, males possess a differentially pigmented pronotal shield beneath which they can retract their compound eyes. The possible role of the pronotal shield in behavioural regulation of the light reaching their eyes has not, to our knowledge, been investigated. Here, we characterize the spectral filter properties of the pronotal shield and combine this with behavioural assays of males' response to light exposure. We show that the pronotal shield acts as a differential filter transmitting longer wavelengths of light to the compound eyes beneath while blocking shorter wavelengths. Male glow-worms in the dark or in the presence of green light extend their head but rapidly retract it beneath the pronotal shield when exposed to white or UV light, thereby shielding their compound eyes. Thus, our findings suggest the pronotal shield acts as a behaviourally implemented extraretinal optical filter for the compound eye.

Parental care is a diverse phenotype present in many lineages that is both an important social adaptation and a precursor to other elaborate social systems. Transcriptomics has been widely used to determine the origins of care but has been less often deployed to understand the mechanisms that parenting species use to respond to the costs imposed by care. Here, we perform RNA-sequencing to understand the behavioural and physiological consequences of maternal care in the terrestrial isopod Armadillidium nasatum, a species that broods and provisions both eggs and hatched offspring (mancae) in a marsupium. We sequenced heads of individuals prior to reproduction, during egg-brooding, during mancae-brooding and post-reproduction. As predicted, we found modest but clear gene expression differences between the non-parenting and parenting stages, with few differences differentiating mothers brooding eggs versus mancae. However, we were surprised to find that the bulk of gene expression differences represented downregulation of cell-cycle genes during both parenting stages. This indicates that A. nasatum mothers enter a period of cell-cycle arrest resembling diapause, which may facilitate the diversion of resources towards the developing brood. This finding broadens our understanding of the diverse developmental pathways organisms have used in the evolution of social phenotypes.

Many organisms across ecosystems track odour plumes to locate mates and food. For flying insects, the task of localizing an odour source is particularly challenging due to the complicated dynamics associated with wind flow and odour plume dispersion through spatially complex environments. Although wind tunnel experiments have been instrumental in answering many questions related to olfactory search, such experiments cannot replicate the complexity of natural wind conditions. Thus, our knowledge of how real-world wind characteristics influence insects' success and strategies to locate odour sources remains an open area of investigation. Here, we tested whether certain wind conditions were more favourable for foraging insects by comparing yellowjacket arrival times and corresponding wind conditions across three distinct natural environments. Our results indicate that Vespula pensylvanica are capable of locating odour sources across the full range of observed wind conditions, without any clear preferences. This suggests that insects have adapted strategies to perform odour localization tasks across the full spectrum of natural wind that they may encounter. Our field-based approach provides insights into key considerations for future wind tunnel experiments that seek to better resolve insect plume tracking in understudied flow regimes.

Anaesthesia in fish is commonly assessed through visual inspection, yet behavioural indicators of consciousness are not always reliable. Complementary measurements of brain activity can enhance accuracy and generate evidence-based welfare guidelines. Here, we anaesthetized rainbow trout with five common anaesthetic agents and assessed presence or absence of visual evoked responses (VERs) on the electroencephalogram as a neurophysiological indicator of unconsciousness combined with the behavioural indicators of consciousness balance and mobility to determine the duration of induction-to and recovery-from narcosis. As expected, both induction and recovery times varied depending on anaesthetic compound and dose. Tricaine methanesulfonate stood out as the compound with the most rapid induction and recovery. Notably, we observed significant discrepancies between neurophysiological and behavioural indicators of consciousness. For example, metomidate induced immobility at relatively low concentrations, whereas much higher doses were required to achieve unconsciousness. Across compounds, trout typically regained motor function well before VERs. This may suggest biological prioritization of mobility during recovery from unconsciousness, or potential visual impairment caused by the anaesthetic agents. These mismatches have important implications for the interpretation of behavioural responses under anaesthesia and should be carefully considered in both research and applied settings.

Historical sites preserved within cities often serve as refuges for local biodiversity. However, these sites are surrounded by buildings and roads, creating sharp contrasts in habitat suitability between them and the surrounding urban matrix. Under such conditions, reduced dispersal potential may be favoured if remaining within the site enhances fitness. We tested this hypothesis in the self-incompatible dandelion, Taraxacum platycarpum (Asteraceae). We compared the morphological traits affecting seed-dispersal potential between populations inhabiting historical sites (castles and shrines) in a major metropolitan area and those inhabiting open sites in rural areas. Pappus volume, which is positively associated with dispersal potential, was significantly smaller in historical-site than in open-site populations. In contrast, achene volume, which is less directly related to dispersal potential, did not differ between site types. Moreover, populations in historical sites tended to exhibit a lower genetic diversity than those in open sites did. These results suggest that seed dispersal traits in dandelions have diminished in urban historical sites, potentially leading to reduced genetic diversity as an evolutionary consequence. Together, our findings illustrate how extreme habitat isolation within cities can shape dispersal evolution and emphasize the importance of incorporating evolutionary processes into the conservation of plant populations in these environments.