Leukocyte counts are widely used as integrative biomarkers of immune function and physiological condition across ecological and biomedical sciences. However, their reliability can be compromised by s...

Abstract. Some cognitive abilities are suggested to be the result of a complex social life, allowing individuals to achieve higher fitness through advanced

The activation of the immune system in response to a pathogen infection can impose significant costs on growth and oxidative stress. Developing individuals are particularly vulnerable to this challeng...

AbstractThe resource-tracking/facultative brood reduction hypothesis suggests that, under food stress, many altricial birds sacrifice the youngest brood members to enhance the growth and survival of their siblings. Studies examining staggered hatching and food shortage have generally supported this idea, although staggered hatching may serve additional purposes. However, the direct beneficiaries of this selective mortality remain unclear, as most research has overlooked parents and post-fledging outcomes. A life history perspective has rarely been applied to brood reduction. Using a 34-year individual-based dataset on blue-footed booby (Sula nebouxii) reproduction, we investigated whether siblicidal reduction of food-stressed two-chick broods benefits mothers, fathers, or surviving offspring. Results revealed that mothers of reduced broods were ~16% more likely to survive to the next breeding season than mothers of intact broods, indicating a significant maternal benefit. And cessation of sibling competition allowed surviving chicks to achieve fledging body condition, breeding probability, longevity, and lifetime reproductive success comparable to chicks from intact broods. Thus, sacrificing the subordinate chick ensures adequate—not privileged—growth of the surviving sibling and enhances maternal survival, while apparently providing no survival benefit to fathers. However, experimental confirmation is required to validate these findings and further explore the underlying mechanisms.

AbstractThe resource-tracking/facultative brood reduction hypothesis suggests that, under food stress, many altricial birds sacrifice the youngest brood members to enhance the growth and survival of their siblings. Studies examining staggered hatching and food shortage have generally supported this idea, although staggered hatching may serve additional purposes. However, the direct beneficiaries of this selective mortality remain unclear, as most research has overlooked parents and post-fledging outcomes. A life history perspective has rarely been applied to brood reduction. Using a 34-year individual-based dataset on blue-footed booby (Sula nebouxii) reproduction, we investigated whether siblicidal reduction of food-stressed two-chick broods benefits mothers, fathers, or surviving offspring. Results revealed that mothers of reduced broods were ~16% more likely to survive to the next breeding season than mothers of intact broods, indicating a significant maternal benefit. And cessation of sibling competition allowed surviving chicks to achieve fledging body condition, breeding probability, longevity, and lifetime reproductive success comparable to chicks from intact broods. Thus, sacrificing the subordinate chick ensures adequate—not privileged—growth of the surviving sibling and enhances maternal survival, while apparently providing no survival benefit to fathers. However, experimental confirmation is required to validate these findings and further explore the underlying mechanisms.

AbstractThe strength of interspecific and intraspecific competition depends on resource availability, competitor abundance, and specialization. Most studies are conducted with single species pairs, constraining our understanding of what drives competition in multispecies communities. We investigated the effect of floral density, competitor abundance, flowering period, and trait specialization (proboscis length) on the potential for interspecific and intraspecific competition between seven common bumblebee species in the Hengduan Mountains of southwest China. We estimated the potential for interspecific and intraspecific competition using resource partitioning indices in plant-bumblebee networks (Müller’s index) over five consecutive years, quantifying changes in floral densities and bumblebee abundance throughout the season. The potential for interspecific competition increased with bumblebee abundance, particularly when floral density was low later in the season. On the other hand, the potential for intraspecific competition increased with abundance of focal bumblebee species and for specialized long-tongued bumblebees, especially when floral density was low. This suggests that resource scarcity regulates species coexistence by limiting abundant species dominance via interspecific competition and intraspecific competition. Our results indicate the importance of intraspecific competition and specialization in maintaining diversity in multispecies communities.

AbstractHeatwaves, increasingly common and intense due to climate change, are increasing mortality rates and disrupting vital functions. Recent research has begun exploring their impact on cognition. Since cognition underlies key fitness-related behaviours, such as foraging, predator avoidance, and mate choice, understanding the cognitive costs of heatwaves is crucial. Here, we investigate whether heatwaves impact cognition using male guppies (Poecilia reticulata) as a vertebrate model. We focussed on males due to their behavioural consistency in cognitive tests and because they were previously observed to alter sexual behaviour after a heatwave. Males were exposed to a 5-day experimental heatwave (32°C) or control treatment (26°C). The chosen temperatures are ecologically relevant for the species, fall within their natural habitat’s thermal range, and reflect extreme climatic events that are projected to become even more frequent and severe under future climate scenarios. Following treatment, all fish were tested at 26°C for spatial memory and learning, mate choice, inhibitory control, and anti-predator responses. We also conducted histopathological evaluations of brain tissue to investigate potential central nervous system lesions. The results show that heatwave exposure declined maze solving efficiency, affected mate choice-related cognitive capacities, and led to suboptimal anti-predatory responses. No effects were observed on inhibitory control or habituation. Importantly, heatwave exposure induced morphological alterations in the central nervous system, potentially explaining the observed changes in cognitive performance. Our study provides a comprehensive evaluation of heatwave impacts on cognitive function, highlighting the need of investigating their subtle yet significant effects to fully understand how heatwaves influence fitness beyond survival.

AbstractIncreasing developmental temperatures are well-known to impact fertility, yet their effects on pre-copulatory behaviors, despite having clear fitness consequences, are often overlooked. In many species, male nuptial gift presentation during courtship plays an important role in sex-specific mate choice, fitness and subsequent co-evolutionary dynamics. However, developmental temperature effects on nuptial gift behaviors and their implications for population fitness remain unknown. Heat-induced changes to male behavior may signal fertility, diving female discrimination, particularly in monandrous systems where exclusively pairing with an infertile male threatens population growth. Additionally, as nuptial gift production is costly, the differential allocation hypothesis suggests males should adjust gift investment based on female fitness. Here, we investigated how elevated developmental temperature affects nuptial gift behavior, mating likelihood and reproductive output in the monandrous species Drosophila subobscura. Individuals developed at either a control or stressful temperature, and fully factorial no-choice mating tests were used to identify sex-specific effects of heat stress. Heat-stressed males were largely infertile, less likely to mate, present a gift, or have a gift accepted, suggesting nuptial gifts may signal male fertility and influence female mate choice. Heat-stressed females were also less likely to mate or receive a gift, and were presented with fewer gifts from heat-stressed males. As heat-stressed females required more gifts to match the reproductive output of controls, selection may drive male mate choice through strategic resource allocation. These findings highlight how climate change may significantly impact sex-specific mate choice, with important implications for selection on pre-copulatory courtship traits and population dynamics.

AbstractIn birds, many components of visual communication (i.e. plumage and non-plumage ornaments) play an important role in signaling of individual quality. It is widely acknowledged that ornament expression may be modulated by environmental conditions, however, it remains relatively poorly explored whether and how urbanization affects the expression of non-plumage ornamentation in urban dwelling-individuals. Here, we investigated the effect of urbanization on the expression of bare-part (non-plumage) putative ornament (i.e., the frontal shield size) across eight populations of a common reed-nesting waterbird, the Eurasian coot Fulica atra. Most importantly, we found robust support for the positive effect of urbanization on shield size and its condition-dependent character in coots. Also, long-term monitoring of a single urban population revealed relationships between the ornament expression and nest site selection patterns, as coots with larger shields were bold enough to colonize more anthropogenically transformed urban sites with stronger human disturbance and better accessibility to anthropogenic food. At the same time, we found no support for associations between the shield size and either nest defense behavior or reproductive performance in coots, likely reflecting stochasticity of anthropogenic selective pressures. To our knowledge, this study provides the first evidence for the enhanced expression of an unpigmented non-plumage putative ornament in urban-dwelling birds. Our results show that the effects of urbanization on non-plumage components of quality signaling in birds may be complex and multifaceted, and reinforces a need for further investigation focusing on different types of ornamentation across divergent avian species.