Evolutionary Ecology

The evolution of visual traits in closely-related species living in sympatry is highly influenced by their ecological interactions: while sexual selection tends to promote the divergence of visual cues involved in mate choice, natural selection via predation may promote the convergence of dissuasive signals between prey species, especially in unpalatable or evasive prey. Here, we investigate the impact of sympatry on the evolution of the blue structural colouration in the wings of two closely-related Morpho butterfly species across several localities throughout Central and South America. Dorsal iridescence might affect mate choice and species recognition, which should promote its local divergence among species. However, the bright flashes and dynamic colour patterns produced by iridescence during flight might also increase survival by confusing predators and favouring escape. Such an effect might in turn lead to convergence in wing iridescence between evasive species occurring in sympatry, a phenomenon dubbed evasive mimicry. To test the effect of these putative antagonistic selective forces on visual cues evolution, we quantified the variation of the structural blue colour displayed at 13 different combinations of illumination/observation angles, on the wings of two closely-related Morpho species. We contrasted 10 sympatric and 11 allopatric locations and specifically compared the phenotypic distances between individuals from different species. Phenotypic distances between heterospecific pairs of individuals were significantly smaller in sympatry, consistent with the hypothesis of a local convergence of iridescence due to evasive mimicry. Interestingly, sexual dimorphism was found between males and females, suggesting that the trade-off between natural and sexual selection on the evolution of iridescence might differ between sexes. Our results suggest that local predation pressures may promote repeated evolutionary convergence of structural colouration between evasive prey species living in sympatry.

Islands serve as natural laboratories for exploring evolutionary processes, often fostering unique species through their isolation and distinct ecological conditions. These environments present opportunities to study how a range of selective pressures shape biodiversity. Bird plumage colouration is one trait that has shown to consistently change in island populations, and predation has been hypothesized to influence these differences. While animals often face a trade-off between signalling to conspecifics and avoiding detection by predators, the role of predation in shaping conspicuousness remains underexplored experimentally. In this study, we asked how predation pressure differs between insular and mainland habitats, and whether predation risk covaries with conspicuousness of male and female birds across environments. In a field experiment, we investigated predation rates using 3D-printed models painted to represent both sexes of 12 bird species from three archipelagos (Madeira, Azores, and Canary Islands) and their closest mainland relatives. These models were deployed in the species natural environments to measure hit rates (a proxy for predation risk), accounting for factors that influence prey detectability, such as colour of the models, background contrast, and vegetation. We found that models on the islands experienced less hits compared to those on the mainland, while sexual dichromatic models were more likely to be dislodged on the mainland. In addition, for mainland sites, increased chromatic contrast correlated with a higher probability of dislodgment, suggesting that more conspicuous models were more likely to be hit. These results highlight that while predation constrains conspicuousness, other ecological and evolutionary factors likely drive the reduced plumage colouration observed in island birds. Our research offers experimental insights into how predation interacts with conspicuous traits in shaping plumage colouration in birds.

Climate change is pushing species northward, where they will encounter novel abiotic conditions, such as novel daily light cycles and seasonal lengths, to which they will have to adapt. Despite the diversification of these adaptations being well described, the direct fitness consequences of the natural variation is rarely estimated in the field. To test the fitness effects of local adaptations to daylength and season length, we studied diapause induction and growth rate in the range expanding butterfly Lasiommata megera (wall brown). Using a common garden field-experiment (conducted near the northern range margin) where we manipulated the start of the last generation in the year that typically enter diapause, we compared populations from the southern-Swedish core range with populations from the northern-Swedish margin. Our results show differences between populations in diapause response and growth rate. In line with adaptive predictions caterpillars from the northern populations entered diapause earlier in the season compared to the southern populations. However, this difference was only present in larvae produced by the earliest individuals in the last adult generation. Consequently, the early laid eggs of the southern populations were more likely to produce an additional generation that turned out to be highly maladaptive. Additionally, caterpillars of northern origin grew faster compared to caterpillars from the southern populations, even though we found no clear evidence of prewinter larval mass affecting winter survival. The wall brown butterfly showed local evolution of seasonal timing traits, but just at a specific time of the season. This highlights the importance of local adaptations in northern-Swedish populations, during the early stages of the last annual generation. Despite that the additional generation is presently maladaptive, our fitness estimates suggests that a warmer climate is likely to favour the production of an additional generation.

The connection between female host plant preference and offspring performance is important for understanding how relationships between plants and phytophagous insects have evolved. According to the preference-performance hypothesis, female insects should evolve to oviposit on host plants on which offspring performance is the highest. Here, we examined the preference-performance hypothesis in the northern brown argus (Aricia artaxerxes) butterfly in the province of Uppland, Sweden, by comparing female host plant preference and larval growth between the host plant species wood cranesbill (Geranium sylvaticum) and bloody cranesbill (G. sanguineum). We also investigated if host plant preference in A. artaxerxes was related to the geographic distribution of A. artaxerxes and its host plants in the province Uppland. We found that the A. artaxerxes females, contrary to the preference-performance hypothesis, preferred ovipositing on G. sylvaticum, even though larvae feeding on G. sylvaticum were slightly smaller than those feeding on G. sanguineum. Since G. sylvaticum is more abundant and probably more utilized than G. sanguineum in Uppland, an explanation for this negative preference-performance connection may be that there are advantages associated with utilizing a more common host plant species, even though larvae feeding on this plant show reduced growth rates. Overall, the results show that factors other than offspring performance, such as geographic distribution, may influence female host plant preference in A. artaxerxes.

Sexual size dimorphism (SSD), the difference in body size between males and females, typically conforms to Renschs rule across species: SSD increases with body size when males are larger but decreases when females are larger. Although this macroevolutionary pattern has been extensively documented, intraspecific analyses remain rare, yet they are essential for understanding the proximate mechanisms underlying the origin and maintenance of sexual dimorphism. In particular, it remains unclear whether within-species variation in SSD is driven primarily by sex-specific differences in growth rate or in development time. Here, we addressed this question by examining SSD scaling in inbred lines of Drosophila melanogaster from the well-established Drosophila melanogaster Genetic Reference Panel (DGRP) reared under two thermal environments (25 {degrees}C and 28 {degrees}C). Females were consistently larger than males, resulting in pronounced female-biased SSD across different lines of this model insect. Moreover, SSD increased with overall body size, representing a reversal of Renschs rule at the intraspecific level. This scaling pattern was largely explained by higher female growth rates rather than sexual differences in development time. Elevated temperature reduced SSD by decreasing female growth rate while slightly enhancing that of males. Together, our results demonstrate that Renschs rule does not universally apply at intraspecific level and underscore the critical role of growth rate and environmental sensitivity in shaping SSD at the intraspecific level.

Biotic interactions can drive evolutionary diversification, but the underlying mechanisms differ depending on the type of interaction. For instance, Ehrlich and Ravens escape-and-radiate coevolution provides a pathway of diversification in antagonistic interactions, whereas in mutualistic networks, coevolution is hypothesized to result in trait convergence rather than diversification. The combined effect of mutualism and antagonism on diversification remains unclear, even though organisms naturally engage in multiple types of interactions simultaneously. Using an eco-evolutionary simulation model, we investigate diversification in tripartite ecological networks such as plant-pollinator-herbivore networks. We find that diversification patterns vary according to the way mutualism and antagonism are connected on the trait level. If the two interactions are governed by uncorrelated plant traits, we observe little diversification in the mutualistic and substantial diversification in the antagonistic subnetwork. By contrast, if the same plant trait mediates both mutualism and antagonism (an example of ecological pleiotropy), diversification rates in all guilds become interdependent. In this case, even the mutualistic guild diversifies considerably when antagonism is strong, while strong mutualism restricts diversification also in the antagonistic guild. Our study underlines that the inclusion of multiple interaction types is necessary to advance our understanding of evolutionary dynamics in ecological networks.

The seasonal forms of the temperate butterfly Araschnia levana (Nymphalidae: Nymphalinae) differ in morphology (weight, wing area, and wing loading) and colouration. Spring individuals are predominantly orange with higher weight per wing area, (i.e. wing loading) while summer individuals are black with a white stripe and have lower wing loading. However, it remains unclear if and how these seasonal differences affect heating and cooling dynamics. We compared thermal responses of seasonal forms, focusing on the roles of morphology and colouration. Further, we assessed whether live butterflies heat and cool differently from dead individuals to detect the presence of active thermoregulation. Morphology and colouration influenced the thermal dynamics of the thorax and wings as expected from heat-transfer principles, but we found no evidence of active thermoregulation on the thorax. Based on aligned temperature curves, seasonal forms showed similar thermal dynamics. This similarity was driven by morphology and colouration, with larger wing area accelerating thermal change and higher body weight (or wing loading) reducing it, thereby masking underlying form-specific patterns. After accounting for significant morphological differences between forms, the thorax of spring individuals heated and cooled faster than that of summer ones. This trend suggests form-specific optimisation of thermal performance, likely as a response to temperate climates. Thermal responses differ between forms in ways not directly explained by the polyphenism itself, potentially reflecting a broader trait of multivoltine ectotherms to cope with seasonal temperature changes.

Reproductive Character Displacement (RCD) often occurs when species with mating-related polymorphism come into secondary contact, leading to divergence in reproductive traits. Ischnura elegans and Ischnura graellsii have formed two independent hybrid zones in Spain where reinforcement has strengthened a mechanical barrier, and RCD has shaped mating-related structures, although reinforcement is asymmetric only in gynochrome females. This study examines the link between asymmetric reinforcement and asymmetric RCD. Using geometric morphometrics, we analyze prothorax shape and size in both female morphs and males, and male caudal appendages, to assess morphological divergence, determine whether gynochrome females show stronger divergence, and test for morphological covariation between male traits involved in the tandem position. Our results reveal consistent patterns of size and shape variation across species and zones: in I. elegans, androchromes are larger and resemble males in size, with clear shape differentiation between female morphs that diminishes in hybrid zones. In contrast, I. graellsii shows less consistent size differences between males and morphs, and weaker shape differentiation. Our results confirm RCD in prothorax shape in I. elegans females from both hybrid zones, but reveal that RCD in prothorax size is asymmetric, occurring only in gynochrome females from the NC hybrid zone. We also detected RCD in the prothorax shape of I. elegans males from the NC hybrid zone, extending previous evidence of RCD in male caudal appendages, while morphological covariation between male cerci and the prothorax was limited to size in I. elegans. Together, these findings illustrate how hybridization may generate morph-specific patterns of reproductive divergence.

The evolution of body shape reflects the interplay between functional constraints and habitat structure. In fishes, cave environments are well known for promoting regressive traits such as eye and pigment loss, yet their influence on overall body form remains poorly understood. Here, we examine patterns of body shape variation in cave- and surface-dwelling trichomycterid catfishes from northeastern Colombia to assess whether consistent associations exist between habitat type and morphology. Using geometric morphometric analyses, we quantified differences in body shape among species inhabiting subterranean and surface environments. Our results reveal significant habitat-associated differentiation in body shape along the main axes of morphological variation. Cave-dwelling species exhibit more elongated and fusiform body shapes, whereas surface-dwelling species tend to show deeper and more robust morphologies. In a functional context, these contrasting body patterns suggest associations with differing locomotor demands imposed by subterranean versus surface habitats. Although we do not explicitly test convergence or performance, the recurrence of similar body shapes among species from different clades occupying comparable habitats is consistent with repeated morphological responses to shared ecological constraints. Research HighligthsO_LIMultivariate shape analyses reveal significant habitat-associated variation in trichomycterid fishes. Recurrent morphological patterns suggest repeated responses potentially mediated by habitat constraints. C_LIO_LIBody shape differs consistently between cave- and surface-dwelling trichomycterids. Cave species exhibit more elongated and fusiform forms, whereas surface species display deeper body configurations. C_LI

Given the accumulation of evidence that evolution can affect ecological dynamics, especially under global change scenarios, a key question is how such ecoevolutionary dynamics may change the coexistence of species and biodiversity in general. In the present article, we propose a graphical approach allowing to simultaneously discuss ecological coexistence and phenotype evolution. Our graphical approach allows tackling the two aspects in the same parameter space, allowing direct links between ecological and evolutionary perspectives. While evolution is often thought positive for the resilience of ecological systems, we first highlight it does not usually allow for better coexistence for the system as a whole. Even when focusing on the fate of the species that is evolving, evolution often leads to greater vulnerability. The graphical approach we propose is flexible and can be applied to all interaction types and covers variations in trade-off structures. Using this flexibility, we highlight how evolutionary effects can be positive or negative for coexistence, depending on these two components. Finally, we illustrate how the approach can be applied, using empirical examples derived from the literature. We thereby highlight the critical ingredients needed to inform the graphical approach, its potential use for proposing testable scenarios, but also clarify its limits.

The Allee effect is a phenomenon where individual fitness is reduced in small populations, for example because of mate-finding difficulties or increased predation. Allee effects matter in conservation biology because they can drive small populations to extinction. The severity of Allee effects can depend on traits such as mate-search rate and defense against predators. Many natural populations exhibit considerable intraspecific trait variation (ITV) in such traits, but most studies so far assume these traits to be constant. Thus the impact of ITV on populations with Allee effect is largely unknown. Here we create two individual-based stochastic models that simulate a small population experiencing either a mate-finding Allee effect or a predator-driven Allee effect. We analyze how ITV, trait inheritance, and mutation affect the proportion of surviving populations. Under the mate-finding Allee effect, higher ITV hindered population survival and increased Allee thresholds. This can be explained by Jensens inequality and the negative curvature of the mate-finding function. Under the predator-driven Allee effect, ITV effects were weak, but higher mutation standard deviations were beneficial, likely because they provided more substrate for selection to act on. We thus recommend to take into account ITV when dealing with threatened populations with an Allee effect.

The relationship between morphology and ecology is mediated by behavior. We explore this relationship by assessing the link between trophic ecology and the use of prey-specific feeding behaviors in a cichlid fish system. Cichlid diversification features repeated transitions between free-moving prey and attached benthic prey, requiring predators to evolve prey-specific approaches to feeding. Using 2000 Hz video, we characterized feeding behavior on an experimental attached benthic prey in seven species of Mesoamerican heroine cichlid spanning three independent transitions to specialized piscivory and two to specialized benthic-feeding ecology. We investigated the effect of feeding ecology on the behavior and kinematics of benthic grazing, a derived, specialized mode of cichlid feeding. Surprisingly, all species readily fed on benthic prey, regardless of their feeding ecology. Nearly all non-benthic species used the same benthic-feeding behaviors as ecological benthic-feeders. Our findings demonstrate an unexpected level of behavioral versatility among cichlid species in exploiting functionally demanding prey outside their typical diets. We propose that this repertoire of latent feeding behaviors supports trophic versatility and facilitates niche diversification. We also show that two benthic-feeding lineages of Neotropical cichlids evolved distinct approaches to benthic feeding, exhibiting the highest and lowest total feeding-strike kinesis, respectively. Together, our findings highlight the importance of behavior in linking morphology and ecology and motivate further study into the diversity and evolutionary context of benthic feeding across the Cichlidae. SUMMARY STATEMENTWe demonstrate that prey-specific feeding behaviors and strike kinematics vary with trophic ecology in heroine cichlids and discuss the potential role of latent feeding behaviors in trophic diversification.

Fishing deeply alters marine food webs structure and can drive the evolution of species traits, whether the species are directly targeted or not. Yet, studies rarely account for fisheries-induced evolution, and consequences are generally interpreted at the single-species level. Theory however predicts that eco-evolutionary dynamics within food webs can either promote biodiversity maintenance or accelerate its decline. In this study, we investigate how evolution affects the robustness of trophic networks under fishing pressure. Modifying evolution speed and the allocation of fishing effort across 458 structurally distinct allometric networks enables us to show that evolution most often enhances robustness. Network evolutionary response however becomes more variable (and possibly negative) as evolutionary rates increase and when fishing preferentially targets predators. By contrast, fishing strategies that concentrate effort on lower trophic levels, or distribute it more evenly, promote network persistence through evolutionary rescue while substantially reducing the risk of evolutionary collapse. Moreover, our results appear to be sensitive to the main forces governing ecological dynamics within the network such as competition or predation intensity. Finally, the consequences of network evolution differ across trophic levels. Evolution often drives the collapse of higher trophic levels while simultaneously promoting evolutionary rescue and enhancing diversity at lower levels through increased diversification, thereby generating a trade-off between vertical diversity (number of trophic levels) and total diversity. This highlights the importance of accounting for evolutionary dynamics and food web functioning in fisheries management, and suggests that reducing predator mortality may help prevent network evolutionary collapse.

The ability of animals to innovate - solve novel problems - can shape their ecology and evolution. Here we investigate how individual traits and environmental complexity relate to successful solving of a novel problem. We presented foraging bumble bees (Bombus impatiens) with artificial flowers of not-previously-encountered shapes and recorded the bees latency to access nectar. We measured individual foraging traits across multiple trips with simple flowers that did not require innovation, and bees were foraging either in a simple or complex environment (cluttered flight arena). Bees in complex environments took longer to find and were less likely to land on novel flowers, indicating that environmental complexity may take up cognitive resources and make search more difficult. However, we did not find an effect of environmental treatment on the ability or time to access reward in novel flowers once bees had landed on them. In contrast, behavioral traits significantly predicted how quickly bees solved novel flowers. In particular, overall foraging tempo as well as routine formation, i.e. how much bees followed a fixed route on known flowers, predicted innovation - faster bees innovated faster, and bees with more repetitive foraging sequences were slower to solve the novel tasks. Overall, while the degree of evolutionary novelty in tasks or solutions is always hard to evaluate, our findings demonstrate that environment and individual traits may affect innovation in different ways. Individuals in simple environments may be more likely to detect, and individuals that are generally faster and have a lower tendency to develop fixed routines may be more likely to solve, novel tasks.

Conspicuous coloration in animals is generally thought to evolve and be maintained through inter- or intraspecific interactions such as mate choice, but this might not always be the case. The sight-line hypothesis proposes that conspicuous light-dark contrast in front of the eyes (hereafter, eyeline) evolves and is maintained due to viability selection, enhancing an individual visual acuity and thus evolutionarily associated with a particular foraging behavior that requires accurate aiming. However, empirical evidence that supports the sight-line hypothesis is virtually absent, with no studies demonstrating the key prediction that the direction of eyelines matters. Here, I tested the sight-line hypothesis using macroevolutionary analyses in terns and allies, which are a suitable study system, because they have variation in facial color patterns, including presence/absence and, if any, various angles of eyelines. They also have a large variation in foraging behavior, including picking, plunge diving, and skimming. As predicted by the sight-line hypothesis, tern lineages that require accurate aiming at foraging (e.g., plunge diving) are more likely to have eyelines. In addition, the evolutionary transition to the state with eyelines and these foraging behaviors was more likely to occur than the reverse transition. Furthermore, as expected by the fact that the direction of travel is upwardly deviated from the direction of the bills during skimming, the eyeline angle from bills was evolutionarily positively associated with the occurrence of skimming behavior. To my knowledge, the current study is the first to demonstrate that the direction of the eyeline matters, thereby strongly supporting the sight-line hypothesis.

Body mass is a key organismal characteristic that impacts many physiological and ecological processes and often a strong determinant of fitness. Recent studies have documented temporal phenotypic changes in this trait in many populations, but identifying the mechanisms underpinning these changes can be difficult. Here, we use 47 years of data to analyse how adult and nestling body mass have changed over time in a great tit Parus major population in Wytham Woods (UK). Further, we link those changes to three environmental variables previously recognised as drivers of body mass: temperature, intra- and inter-specific competition and temporal mismatch with a key prey during breeding, winter moth Operophtera brumata caterpillars. Temporal analyses of adult body mass revealed contrasting dynamics at the between- and within-cohort levels, mirroring Simpsons Paradox. At the population level we report a marked decrease in body mass in adults between 1978 and 2024 (-0.042 Haldanes), and show that this results from phenotypic plasticity, driven by a negative between-cohort trend likely reflecting carry-over effects of the early environment. Within cohorts, however, trends were consistently positive likely reflecting an age-dependent mass increase. The change in adults was paralleled by a change in nestling body mass (-0.036 Haldanes). Nestling mass was negatively associated with estimated intensity of intraspecific competition, as well as inter-specific competition from blue tits Cyanistes caeruleus, as quantified by local population density. These effects carried over to adulthood, as shown by a negative association between adult mass and the population density experienced at early life. Temperature during development and mismatch with the caterpillar food supply, despite being associated with adult and nestling mass, did not explain the observed declines in mass, largely because these have not changed over time. Overall, our results illustrate the potential for effects mediated early in development to carry-over into long-term phenotypic change at later life history stages, and emphasise the value of considering multiple effects as drivers of phenotypic change in natural populations.

Injuries are common in animals and represent a major threat to individual survival. They can result from inter- or intraspecific conflict, predation, or pugnacious prey. Despite their potential ecological and evolutionary importance, injury patterns remain poorly documented in animal populations. To test whether a species feeding ecology or habitat can predict injury patterns, we quantified injury rates and affected body regions among native ant species collected from different habitats in Bavaria, Germany. Specimens were sampled using pitfall traps, which proved to be an efficient method for injury assessment. Injury rates varied substantially among species and genera, ranging from 0% to 38%. Predatory ant species exhibited higher frequencies of leg injuries, whereas omnivorous species were more frequently injured at the antennae. The distribution of injuries likely reflects both foraging ecology and species-specific wound care behaviors, with a high frequency of trochanter injuries potentially indicating prior amputation events to cope with infected leg injuries, as observed in Lasius alienus. Our findings demonstrate that injury propensity and distribution are shaped by feeding habits and behavioral adaptations, providing comparative evidence that the costs and management of injuries vary systematically among ant species. Our study thus highlights injuries as a measurable axis of selection that may have contributed to the emergence of wound care and other forms of social immunity in ants.

Many demographic models assume that only females matter for population dynamics. However, theory and evidence of sexual conflict suggest that males can affect female fitness through mating competition between and within the sexes, yet it is unclear how such effects may influence population dynamics. We used experimental population demography to understand how sexual conflict affects offspring recruitment in Drosophila melanogaster, a model species for studying the evolution of sexual conflict. By manipulating sex ratio and male/female density independently in a response surface design we found that increasing male density, and thereby the intensity of sexual conflict, led to fewer offspring per female, but that effect was nearly half the strength of female density dependence. Consistent with this, our best fitting birth function showed female dominance of births with sex-specific density dependence, indicating that males have a demographic effect even if females have demographic dominance. Our results confirm that females have a larger influence than males on offspring recruitment, however, more importantly our result increases our understanding about the demographic effects males have through sexual conflict.

Finding resources for the colony is one of the most difficult and risky tasks for a social insect worker. A worker on a foraging trip can face a number of challenges, including interference from other individuals, her own errors, and environmental disturbances. Collectively, colonies may use a variety of strategies to minimize the impact of such perturbations on the foraging process. Here, we investigated how individual Solenopsis xyloni ant workers react to perturbation of an established pheromone trail. We trained foragers from colonies in the field to either a low or high concentration sucrose solution in a feeder on a T-maze setup, then replaced a section of floor covering, removing a section of the pheromone trail previously laid. We found that while ants made correct choices on the T-maze when the trail was intact, their choices did not differ from chance when the trail was absent, indicating strong reliance on a pheromone trail (and not, for example, memory) to return to the resource. Moreover, when the trail was absent, we found that a majority of ants abandoned the resource, and that even the ants that were able to reach the resource did not repair the perturbed trail. However, with a high-quality resource, more ants persisted in attempting to reach it (instead of abandoning). We interpret these responses in the framework of robustness mechanisms discussed in systems biology. Our study thus links individual and collective responses to perturbations, and provides an empirical example of how information use interacts with system robustness. Statements and declarationsThe authors have no competing interests to declare that are relevant to the content of this article.

Sarita Lake, British Columbia houses a distinctive population of threespine stickleback (Gastrosteus aculeatus L.) with a phenotype characterized by unusually large individuals relative to nearby conspecifics. We tested the hypothesis that members of this population are not isometrically larger but rather exhibit variation in allometric trajectories that reflect changes in developmental timing impacting the developmental-genetic architecture of the phenotype. We used 3D geometric morphometrics to characterize the size and shape of skulls, pectoral girdles and pelvic girdles from a sample of individuals from nearby freshwater and marine populations and compare them to a sample from Sarita Lake. We showed that individuals from the Sarita Lake population are larger in each body region compared to most other populations examined. Further, these individuals have dorsally expanded skulls and relatively robust pelvic armour. We also showed that the relationship between size and shape is differently structured among body regions and is heavily influenced by non-uniform sexually-mediated variation across populations sampled. Our results reflect complex underlying developmental trajectories, and we suggest that the large phenotype observed may be driven by fecundity selection on female size in combination with a limnetic trophic niche and relatively increased predation pressure in Sarita Lake.