Biology Letters最新文献

Cosmetic colourations of animals have been mainly studied in scenarios of sexual selection, while there has been no assessment of the partial contribution of cosmetics to the final colouration of begging-related traits. In birds, the uropygial gland is functional soon after hatching, and we experimentally investigated the effects of uropygial secretion on mouth-flange colouration in spotless starling (Sturnus unicolor) nestlings. Nestlings' flange colouration was measured with a spectrophotometer before and after being either cleaned of, or painted with, its own uropygial secretion. After cleaning, flanges were brighter, more UV and less yellow-red coloured (chroma). Instead, painting the mouth flanges of nestlings with their own uropygial secretion did not modify any of the considered colour components. Our findings therefore show that the uropygial secretion of nestlings alters their beak colouration and open the possibility for future research to investigate the role of uropygial secretion in reinforcing the signalling role of begging-related traits involved in parent-offspring communication.

Many animals maintain long-term monogamous partnerships, but the extent to which partners associate varies substantially and has implications for the scope of cooperation between pair members. Zebra finches (Taeniopygia castanosis) are monogamously paired for life and maintain continuous partnerships, raising questions as to if and how they maintain pair cohesion despite being non-territorial and having only short-range acoustic signals. While zebra finches are the best-studied songbird in captivity, their social and spatial behaviour in the wild is poorly understood. Determining pair cohesion in songbirds to date has almost exclusively been studied at specific locations where pairs would be expected to meet, such as nesting or feeding sites, without quantifying broader movements. Here, we used solar-powered automated tracking to simultaneously monitor the movements of radio-tagged zebra finch pairs during periods of breeding activity. We reveal extremely high spatial cohesion with pairs using nearly identical home ranges and maintaining close spatial proximity across large areas. This characterization of extremely high spatio-temporal coordination of zebra finch pairs provides important insights into the operation and benefits of monogamous relationships in highly mobile taxa, such as birds.

The accident that occurred at the Chornobyl nuclear power plant (Ukraine, 1986) contaminated a large extension of territory after the deposition of radioactive material. It is still under debate whether the chronic exposure to the radiation levels currently present in the area has long-term effects on organisms, such as decreases in longevity. Here, we investigate whether current levels of radiation in Chornobyl negatively impact the age of the Eastern tree frog Hyla orientalis. We also explore whether radiation induces changes in an ageing marker, telomere length or the stress hormone corticosterone. We found no effect of total individual absorbed radiation (including both external and internal exposure) on frog age (n = 197 individuals sampled in 3 consecutive years). We also did not find any relationship between individual absorbed radiation and telomere length, nor between individual absorbed radiation and corticosterone levels. Our results suggest that radiation levels currently experienced by Chornobyl tree frogs may not be high enough to cause severe chronic damage to semi-aquatic vertebrates such as this species. This is the first study addressing age and stress hormones in Chornobyl wildlife, and thus future research will confirm if these results can be extended to other taxa.

Overfishing is one of the greatest threats to fish populations. Size-selective harvesting favours faster juvenile growth, younger maturation, small adult body size and low reproductive output. Such changes might be slow to recover and ultimately threaten population fitness and survival. To study the recovery potential of exploited experimental populations, we compared life-history traits in three differently size-selected experimental lines (large-selected, small-selected and random-selected) after five generations of harvesting and 10 subsequent generations of recovery (i.e. cessation of harvesting). We show that after a recovery period twice as long as the harvesting period, the differences in adult body size among the selection lines have eroded. While there was still a significant body size difference among the selection lines, this did not translate to differences in reproductive success. Although size-selective harvesting causes phenotypic changes in exploited fish populations, we show that such changes are reversible if the recovery period is long enough.

The question of whether males or females are the more variable sex is long-standing, and yet to be fully answered. We investigate the relationships between body mass and variation across species using a phylogenetically informed analysis of the body mass of 337 species representing six mammalian orders. Within each order, we found that the larger sex is typically the more variable sex, whether male or female, and the variation-size relationship is arguably often close to unity. Thus, size may be the main or even sole driver of variability in at least some orders. Deviations from the expected 1 : 1 relationship emerged, however, in regressions of male : female mass variance against male : female mean mass, for Chiroptera and Rodentia, which both presented hyperallometric relationships suggesting that drivers over and above size influence differences in variation between the sexes. In Chiroptera, most species have larger females. The y-intercept value for Artiodactyla and Primates were significantly greater than 0 suggesting greater male variation in species where the sexes are of commensurable size. Historic belief of exclusively greater male variability may have resulted from a focus on species with intense male-male competition and, thus, larger male body sizes. Our results suggest that it is often size, not sex per se, that influences within-sex variability, although additional sex-specific factors might be present in at least some orders.

Predation, a major cause of natural selection, is classically thought to target the weak and sick. However, predators can target animals with condition-dependent sexual traits, and therefore, high-quality individuals can also be the focus of predation. Thus, it is not always clear which individuals are the foci of predators or how this affects trait evolution. Here, we tested for evolutionary effects of sex-specific predation on male and female longevity using replicate populations of the broad-horned flour beetle Gnatocerus cornutus. We found that male-limited predation resulted in the evolution of reduced male and increased female longevity, while female-limited predation had no effects on the longevity of either sex. We also document the costs of reproduction. Coupled with other findings, our results suggest that predation impacts high-quality males and, because of negative intersexual genetic correlations, this increases female longevity.

Vehicle headlights create pulsed artificial light at night (pALAN) that is unpredictable, intense and extends into previously dark areas. Nocturnal insects often have remarkable low-light vision, but their slow pupillary light responses may leave them vulnerable to pALAN, which has important ecological consequences. To test this, we exposed nocturnal moths-important pollinators and prey-to four pALAN treatments. These comprised 'cool' and 'warm' lights, either emitted from phosphor-coated light-emitting diodes (LEDs) or RGB (red-green-blue) LEDs, matched in colour (CCT) and intensity to human vision. We assessed the initial behavioural response, likely crucial to the survival of an organism, of 428 wild-caught moths comprising 64 species. We found that exposure to a cool phosphor-coated LED light pulse increased instances of erratic flight and flight-to-light that are likely detrimental as they increase the risks of impact with a vehicle, predation or excess energy expenditure. Our findings suggest that pALAN can cause a wide range of behavioural responses in nocturnal moths, but that the most harmful effects could be minimized by reversing the current shift towards high CCT (cool) phosphor-coated LED car headlights. Lower CCT or RGB alternatives are likely to provide benefits for road safety while reducing ecological harm.

Although evolutionary transitions of individuality have been extensively theorized, little attention has been paid to the origin of levels of organization within organisms. How and why do specialized cells become organized into specialized tissues or organs? What spurs a transition in organizational level in cases where the function is already present in constituent cell types? We propose a hypothesis for this kind of evolutionary transition based on two features of cellular metabolism: metabolic constraints on functional performance and the capacity for metabolic complementation between parenchymal and supporting cells. These features suggest a scenario whereby pre-existing specialized cell types are integrated into tissues when changes to the internal or external environment favour offloading metabolic burdens from a primary specialized cell type onto supporting cells. We illustrate this process of 'supra-functionalization' using the nervous system and pancreas.

Despite well-documented disparities disadvantaging women (e.g. discrepancies between men and women in salaries and leadership roles), we argue that there are contexts in which disparities disadvantage men. We review the literature suggesting harm to women is perceived as more severe and unacceptable than identical harm to men, a bias potentially rooted in evolutionary, base rate, stereotype-based and cultural shift explanations. We explore how these biases manifest in protective responses toward women and harsher judgements toward men, particularly in contexts of victimization and perpetration. Our review aims to complement the existing literature on gender biases by presenting a balanced view that acknowledges men and women face unique challenges. By understanding these biases, we hope to foster a more equitable discourse on gender and harm, encouraging empathy and validation of suffering irrespective of gender. This holistic approach aims to de-escalate gender-based conflicts and promote effective interventions for both men and women.

Weight, though it cannot be seen directly, pervades nearly every aspect of an animal's life. However, the extent to which non-human animals reason about the property of weight remains poorly understood. Recent evidence highlights birds as a promising group for testing this ability: for example, New Caledonian crows can infer the weight of objects after observing their movements in a breeze. Here, we tested for similar weight inference abilities in kea (Nestor notabilis), a parrot species known for its sophisticated problem-solving skills. Subjects were trained to exchange objects of a target weight (light or heavy) for a food reward. They were then allowed to observe pairs of novel objects (one light and one heavy) hung in front of an electric fan in both an experimental condition (fan on, light object moving) and a control condition (fan off, both objects motionless). The birds were subsequently presented with test trials in which they could use the information from the demonstration to select an object of their target weight. We found that, unlike New Caledonian crows, kea did not perform significantly better on trials in which they observed the objects' movements and discussed our findings within the context of the kea's highly explorative nature.