Evolutionary Ecology

Understanding when species diversification and phenotypic evolution are coupled remains a central challenge in macroevolution. Such coupling may depend on the traits considered, phenotypic integration, or the geographic context in which diversification occurs. Here, we investigate these relationships in Ithomiini, a diverse Neotropical butterfly tribe whose diversification is strongly associated with the Andes-Amazonia system. We quantified forewing and hindwing size and shape for 1,618 individuals representing 291 species using geometric morphometrics, and combined these data with phylogenetic comparative methods, diversification-rate estimates, and spatial analyses of species distributions. Evolutionary rate shifts were largely trait- and wing-specific, indicating limited coupling between forewing and hindwing evolution. Across the phylogeny, wing size evolution and extant wing size were not associated with species diversification, nor was hindwing shape evolution. By contrast, forewing shape evolutionary rates showed a positive association with diversification. Spatial analyses revealed that this coupling was geographically concentrated in the Andes, where high diversification rates coincided with elevated forewing size and shape diversity and increased forewing evolutionary rates. Hindwing diversity, by contrast, more closely tracked phylogenetic diversity and showed weaker or opposing relationships with diversification. Our results show that diversification and phenotypic evolution in Ithomiini are neither generally coupled nor fully independent, but linked in trait-specific and geographically structured ways. More broadly, they highlight the need to decompose complex phenotypes and integrate spatial context when testing macroevolutionary coupling.

Sperm competition can occur when sperm from two or more males compete for fertilization of a batch of eggs. While it has been extensively studied in internal fertilizers, it remains poorly under-stood in external fertilizers. To investigate how sperm competition affects fertilization under sperm limitation, we conducted controlled experiments on two sea urchin species: Paracentrotus lividus and Dendraster excentricus. Eggs from a single female were exposed to sperm from three individ-ual males separately (non-competitive treatment) or to a pooled sample from three males (competi-tive treatment). We measured fertilization success as proportion of eggs fertilized after two hours and assessed sperm motility as percentage of motile sperm and curvilinear velocity. For P. lividus , we estimated the sperm concentrations where fertilization success was 50% of maximum observed fertilization success (F50), and the fertilization efficiency of the sperm (Fe), i.e. the likelihood that a sperm - egg encounter results in a fertilizing contact, using the fertilization kinetics model of Styan (1998). For D. excentricus, fertilization success was measured at a sperm concentration expected to produce 50% fertilization success. Sperm competition reduced fertilization success and increased F50 compared to non-competitive treatments, suggesting antagonistic effects that may compromise fertilization under sperm-limited conditions in external fertilizers.

Species interactions shape ecological dynamics, but adaptation to one interaction can trade off with others. Experiments that measure such evolved fitness changes across multiple interactions remain rare. We used experimental evolution to test whether recent selection under one ecological interaction changes fitness under other interactions in a fly-parasitoid system. We evolved a genetically diverse Drosophila melanogaster population for 15-17 generations under three regimes: benign conditions (control), high intraspecific competition, and infection by the parasitoid wasp Leptopilina boulardi. We then measured fly fitness (egg-to-adult survival and subsequent reproduction) under benign conditions, high intraspecific competition, and infection by three other parasitoid species and an additional conspecific L. boulardi strain. Selection history strongly influenced fitness across interactions. Populations maintained under high larval density showed reduced survival under infection by L. boulardi and L. victoriae, indicating a trade-off between past selection for competition and defence against some parasitoids. Populations evolved under parasitoid infection by L. boulardi showed increased resistance to a conspecific strain but reduced fitness when infected by another species, L. heterotoma. Our results show that rapid evolution in response to a single interaction can reshape multiple ecological interactions through fitness trade-offs, highlighting how recent evolutionary history may influence community dynamics and invasion susceptibility.

Defended prey are often thought to rely on conspicuous warning signals to distinguish themselves from undefended prey, facilitating predator learning and avoidance. Yet many chemically defended organisms are inconspicuous and difficult to distinguish from palatable prey, raising a fundamental question: how do predators avoid defended prey when prey themselves provide little or no reliable signals of defense? We tested whether host plants can function as indirect indicators of prey defense using Carolina wrens (Thryothorus ludovicianus), chemically defended Eumaeus atala larvae, undefended Galleria mellonella larvae, and two distinct plant species. Defended and undefended prey were experimentally made to appear visually identical, forcing predators to rely on host-plant associations as the only available source of information. Wrens rapidly altered both search behavior and attack decisions according to plant identity. Mechanistic attack models incorporating predator discrimination between defended and undefended prey were strongly favored when plants were present, with defended prey experiencing substantially lower attack risk than undefended prey. When plants were removed, support for discrimination weakened and attacks on both prey types increased. Spatial autocorrelation of host plants further shaped predator behavior, with strongly clustered plants hosting defended prey receiving disproportionately fewer visits. Together, these results suggest host plants can function as ecologically meaningful cues of prey defense, influencing both predator search patterns and attack decisions. More broadly, our findings suggest warning systems may extend beyond prey phenotype alone, and that ecological context (including host-plant identity and spatial structure) may contribute to the evolution and maintenance of aposematism.

A longstanding question in evolution is if similar morphologies shared by distantly related organisms facing similar environmental pressures belie similar functions. The carnivorous pitcher form has evolved in three distinct plant lineages and encompasses a suite of convergent morphological traits, providing a natural experiment to test hypothesized links between morphology and function. Multiple pitcher plant species possess fenestrations (i.e., small windows) that let light pass through the pitcher leaf. While research on one species, Nepenthes aristolochioides, demonstrates that fenestrations manipulate light to create false exits and increase prey capture, whether this convergent morphology serves this convergent function in other pitcher species remains unresolved. We explored the function of fenestrations in two additional species of pitcher plants, Nepenthes klossii and Cephalotus follicularis, where the morphology and function of fenestration were previously unexplored. We inspected micromorphology of pitcher structure, conducted an insect bioassay with live plants to test for links between morphology and function, and quantified traits associated with light manipulation from herbarium specimens. Both species exhibited fenestration and related pitcher morphology similar to N. aristolochioides. Yet our experiments did not reveal a significant effect of light passing through fenestrations on fly capture for these two species. Key differences between these species and the previously investigated species may be the presence of wax crystals and the absence of viscoelastic fluid. While future studies may uncover weak to moderate light manipulation function not detected in our study, our data do not support convergent function in these distantly related, morphologically similar species.

Evolution has given rise to the diversity of life on Earth, but it can also cause species extinctions. While major extinction events are usually associated with external drivers, in this study, we show mechanistically how evolution can trigger abrupt extinction avalanches in ecological networks without any environmental change. In particular, we investigate an eco-evolutionary simulation model of a tripartite mutualistic-antagonistic network, such as a plant-pollinator-herbivore network, with additional intraguild competition. The prevalence of self-organised extinction avalanches depends on a subtle balance of the different interaction types, where antagonism and similarity-based competition are needed for initial diversification while mutualism and trait-independent competition foster evolutionarily driven extinction events. Extinction avalanches are triggered by a mutualist evolving to interact with plants that are not subject to sufficient antagonistic control. Subsequently, the mutualist, its plant partners and their main antagonist potentially outcompete the rest of the community. Our findings point out that evolutionary murder may claim many victims simultaneously and highlight the need to take different interaction types into account to gain a comprehensive understanding of the links between evolution and biodiversity in ecological communities.

Animal behaviour is both innately constrained and shaped by learning. This mosaic organization has evolved in response to species-specific ecological demands and may differ between sensory modalities. Flower-visiting animals are a particularly useful system for investigating the relationship between sensory ecology and learning because they rely on multiple floral cues, particularly odour and colour, to locate food sources. However, it remains largely unexplored whether specialization on floral resources entails divergence in learning abilities across sensory modalities. Drosophila elegans is a flower-feeding species that depends heavily on floral resources throughout its life; adults spend much of their time on flowers and larvae develop on fallen flower leaves. Here, we compared odour-reward and colour-reward associative learning between the flower-feeding D. elegans and the fruit-feeding D. melanogaster. We found that, under conditions of equilibrated motivation, odour- and colour-preference, and using the same sugar reward, D. elegans exhibited poorer odour-reward learning performance but better colour-reward learning performance than D. melanogaster. These results suggest that the modality-specific eligibility of sensory information to enter into associations, known as the 'Garcia-effect' in experimental psychology, can evolve oppositely between species. This highlights the relationship between ecological specialization and mnemonic processing, and shows that biological 'intelligence' is not general.

1. Group foraging reduces the risks associated with foraging: larger groups dilute individual predation risk, allow group members to share the costs of vigilance, and provide a social structure for exchanging information about predators. The benefits of shared social information over simple safety in numbers should depend on the relationships among group members. Consequently, group composition should affect the selection of risky and safe habitats in social species. 2. We asked whether relationships among elk (Cervus canadensis) group members moving together influence their selection of risky habitats more than grouping alone. We tested three hypotheses. The familiarity hypothesis predicts that elk with close social ties are most likely to select risky habitats together. The inclusive fitness hypothesis predicts that the closest genetic relatives are most likely to select risky habitats together. The dilution hypothesis predicts that familiarity and genetic relationships do not influence habitat selection, with all group foraging benefits derived from proximity to others. 3. We used integrated Step Selection Analysis to test whether the identity of the closest group members influenced habitat selection. We tested whether the relationship of the nearest elk--either genetic or social--incentivized selection of risky habitat more than proximity to the nearest elk. 4. Group foraging clearly reduced risk, with elk more likely to select risky habitat when near others. Elk were also more likely to select risky habitats when near closer relatives, albeit with considerable variation among individuals. However, familiarity had a large and consistent effect: elk were far more likely to select risky habitats when near socially familiar group members. 5. Our results suggest that information shared within foraging groups, especially between socially familiar individuals, may lower the risks associated with habitat selection. Similarly, the benefits of reliable social information for reducing risk likely incentivizes the formation of stronger social ties within foraging groups. This positive feedback between social familiarity and habitat selection could thereby increase access to profitable habitats that are otherwise too risky, cementing what we term the social information landscape as a key driver of movement and habitat selection.

The toxicity of chemical defences is well studied, but the potential contribution of compound structure to predator deterrence remains largely unexplored. Whether predation acts more strongly on toxicity or unpalatability remains largely untested, partly because few systems allow toxin structure to vary independently of quantity. Heliconius sara larvae provide such a system: those reared on Passiflora auriculata sequester cyclopentenyl cyanogenic glucosides (CGs), while those reared on P. biflora biosynthesise comparable quantities of aliphatic CGs. Using two invertebrate predators, Camponotus floridanus ants and Hierodula membranacea mantids, we tested whether this structural difference affects palatability independent of toxicity. Mantids rejected larvae with cyclopentenyl CGs more often than larvae with aliphatic CGs, despite no detectable difference in total CG content. This pattern was mirrored in extract-based assays with ants, independently of cyanide release: extracts with cyclopentenyl CGs remained deterrent, while extracts with aliphatic CGs did not differ in deterrence from water. Live larvae, by contrast, elicited similar responses from ants regardless of CG structure. These results show that variation in toxin structure can strongly affect palatability, with some compounds conferring greater protection than others. This demonstrates the importance of chemical structural diversity in the evolution of chemical defences.

Urbanisation imposes novel environmental conditions that can shape phenotypic traits including plumage, yet, its effects on characteristics beyond colouration remain poorly understood. Feather microstructure plays an important role in thermoregulation, protection from solar radiation and waterproofing, and its expression is sensitive to environmental conditions. Here, we quantified feather barbule density, a key component of feather microstructure, in great tits (Parus major) from five urban-rural paired populations across Europe to assess its association with urbanisation, temperature and elevation. We found no significant effects of the urban environment or temperature. However, feather microstructure significantly varied between the studied areas and was positively associated with elevation and ultraviolet B (UV-B) radiation, suggesting a potential adaptive response to variation in solar radiation.

Global warming will impact natural selection on plant traits and their plasticity by influencing phenotypes, biotic interactions, and fitness. Because warming affects biotic interactions, community composition may influence how warming affects selection on plants, but this is little studied. We grew full-sibling pairs of Brassica rapa plants in an ambient and hot temperature environment and exposed them to visitation by a pollinator (Bombus terrestris), a pollinating herbivore (Pieris rapae), or their combination. We recorded plant phenotypes, insect visitation, herbivory, and plant fitness. We used these to calculated phenotypic selection on plant traits and their plasticity, including additive and nonadditive effects. Elevated temperature changed selection on traits related to pollinator attraction, such as flower number, nectar production, and floral scent emission. We found both positive and negative selection on temperature-mediated trait plasticity depending on the biotic treatment. Elevated temperature changed patterns of additive and non-additive selection on a variety of traits including flower morphology and scent. This study shows that elevated temperatures can reshape patterns of phenotypic selection, including nonadditive effects, and plastic trait expression. Effects of elevated temperature on phenotypic selection depended on the biotic interactors, highlighting the importance of community context for the effects of warming on natural selection.

Metabolic rate governs the pace of life through the allocation and expenditure of energy, yet metabolic rate data are unavailable for most species. External morphological traits, such as gill slits, have been used to infer respiratory physiology and metabolism in sharks, yet, whether that pattern is generalizable across rays is unknown. In rays (Batoidea), spiracle length seems adaptive to oxygen uptake capacity, environmental oxygen availability, and activity level. Thus, we evaluate the allometry of external respiratory morphology (spiracles and gill slits) in rays using 550 museum specimens representing 88 species. We test whether spiracle length and gill slit height grow isometrically with body size (total length or disc width) within and across species. Overall, we find spiracles and gill slits are morphologically diverse, varying widely in shape within and between families. Spiracle length and gill slit height scale isometrically and are a consistent proportion of body size, despite such high morphological variability. While that proportion is consistent through ontogeny, each species proportion differs (e.g. gill slit height ranges from 0.93% of total length in Spotted Legskate to 2.93% in Pacific Electric Ray). Of the three swimming styles, pectoral oscillating species (Mobulid and Eagle Rays) may have steeper scaling of spiracle length with gill slit height - consistent with greater respiratory capacity in species with more active lifestyles. Our findings are consistent with literature hypothesizing external respiratory morphology (spiracles and gill slits) is tightly related to metabolic rate and activity level, and demonstrate the value of natural history collections in ecological research. Importantly, the isometry of both respiratory traits means that a single measure of any individual, irrespective of size, will be representative of the species thus providing a basis for expanding our understanding of metabolic morphology, enabling future work on life history, extinction risk, and ecological function.

Multifunctional anatomical structures must accommodate potentially competing performance demands, leading to functional tradeoffs. The mammal rostrum (snout) is involved in multiple functions, including feeding, respiratory conditioning, olfaction, and, in most bats, echolocation. Therefore, it serves as an ideal system to investigate whether and how functional tradeoffs promote or constrain morphological diversification. While the external morphology of the rostrum has been linked with mechanical demands of feeding in bats, the factors and processes influencing its internal morphology, including the turbinals in the nasal cavity, remain comparatively unexplored. Here we investigate how internal rostral morphology reflects specialization and tradeoffs among respiratory air conditioning, echolocation, and olfaction by quantifying turbinal morphological diversity in a phylogenetically and ecologically diverse sample of bat species. We find that echolocation mode predominantly influences both the ethmoturbinal complex (ETc) and maxilloturbinal (MT) systems, with nasal-emitting bats having reduced and less complex turbinals compared to oral and non-laryngeally echolocating bat species. MT complexity and surface area are not associated with bioclimatic variables representing thermal variability and aridity. However, the ETc exhibits higher complexity in plantivorous bats than faunivorous bats, suggesting higher olfactory reliance. While MT morphological disparity was predominantly explained by echolocation mode, ETc morphological disparity was associated with both echolocation mode and diet, suggesting potentially opposing demands favoring turbinal reduction for sound transmission and elaboration for olfaction. Among nasal emitters, which must accommodate both demands within the nasal cavity, ETc complexity exhibited higher relative disparity compared to MT complexity. These patterns suggest that competing functional demands may promote or maintain morphological diversity, possibly through ecological specialization and/or many-to-one mapping between morphology and performance.

The most studied symbiosis between land vertebrates and algae, is the one between Ambystoma maculatum and Oophila amblystomatis, where the latter colonizes the amphibian''s eggs. Although clear benefit given by algal growth for the salamander embryo has been observed, mutualism is not widely accepted. Mutualistic hypotheses posit benefits from the host to the algae which include protection, N- and C-sources, but no experimental evidence has been obtained. In fact, recent studies suggest that the algae are stressed during this relationship and propose fermentation rather than photosynthesis as main driver for algal growth. In this work, we analyzed embryonic host developmental rate, algal and embryo growth and photosynthetic function of eggs housed at different light intensities. We provide evidence that photosynthetic growth is the main driver for Oophila and that higher algal growth yields faster developmental rate and embryo size. Also, we provide strong evidence that rates of photosynthetic electron transport (and the concomitant O2 evolution) must be higher than those of consumption by the embryo for this symbiosis to be mutualistic. Since photosynthetic rate is dependent on light, this work illustrates the importance of light intensity in this symbiotic relationship.

The mechanisms by which organisms extract relevant information from complex sensory signals and use it for decision-making constitute a fundamental issue in biological and cognitive sciences. In social animal societies, individual decision-making is profoundly shaped by information provided by conspecifics. Collective patch-foraging experiments in the laboratory provide a controlled setting in which social information use can be quantified. Here, we consider a go/no-go task in which groups choose between two patches differing in food reward probability. We use agent-based simulations, underpinned by an augmented collective drift-diffusion model, to investigate alternative mechanisms for representing and integrating social information. We consider two representations, continuous (counting representation) and discrete (pulsatile representation), and two integration mechanisms, biasing the decision threshold (threshold modulation) and modifying the accumulated belief (belief modulation), yielding four distinct social models, in addition to a non-interacting model. We first characterize the collective dynamics generated by these models across cognitive parameters and experimental conditions. The temporal dynamics of group accuracy provide informative signatures of the underlying mechanisms. We then assess model selection and parameter identifiability using Bayesian inference and Wasserstein distance minimization, applied to group-accuracy and departure-time distributions. Bayesian inference using distributions of group accuracy provides the most reliable identification across the conditions considered. Importantly, model selection and parameter identifiability are associated with different aspects of collective behavior: model selection is closely linked to the presence of oscillations in the temporal dynamics, whereas parameter identifiability is more closely related to the global accuracy value. Thus, the information available for distinguishing the underlying cognitive mechanisms is not necessarily the same as that required to recover their parameters. Our results further show that identification depends not only on model structure but also on the experimental conditions. Overall, this study provides practical guidelines for identifying socio-cognitive mechanisms in collective foraging experiments.

Foraging decisions often depend on net energy intake, but the need for specific micronutrients means that foods are not always comparable based on energy content. Although sodium is essential for many physiological functions, many organisms face challenges obtaining it, especially those relying on a plant-based diet. Flowering plants often lure pollinators by manipulating nectar carbohydrate content, but nectar sodium might also influence pollinator choice. We experimentally tested how sodium addition and nectar carbohydrate concentration interact to affect bumble bee foraging decisions by allowing bees to forage on artificial flowers containing either low- or high-sucrose nectar, with or without sodium. We also explored whether sugar and sodium content in floral nectar trade-off across plant species. Bees preferred sodium-enriched nectar and preference nearly doubled when sucrose concentration was low. Furthermore, bees switched more often from flowers without sodium to those with sodium when sucrose concentration was low. Given increased fidelity for artificial flowers with nectar sodium, sodium may enhance plant fitness by increasing conspecific pollen receipt. Yet despite behavioral evidence that sodium enhances the perceived quality of low-sucrose nectar for bees, we found no evidence for a nectar sugar-sodium trade-off across plant species. We discuss implications for plant-pollinator interactions and flower evolution.

Colony defence is critical for the survival of wild honeybees but presents a challenge for local populations and beekeepers. Apis mellifera scutellata is an important pollinator in its native range, a large area of Southern and Eastern Africa 1, but is reputed for its explosive temperament. Here, we present data demonstrating that this behaviour is only exhibited by a small fraction of colonies, while others are relatively docile. This sheds new light on this subspecies and on its likely evolutionary trajectory. We further characterize the different elements of this defensive response and compare them to that of A. m. carnica and A. m. mellifera. We show that each subspecies invests differently in the two steps of the behavioural sequence (alert and attack). Furthermore, our results suggest that the task of attacking is carried out by specialized workers in carnica, but not in the other subspecies tested, highlighting subtle differences in colony organization across subspecies. Finally, we discovered that defenders from A. m. scutellata and scutellata-hybrid colonies can locate a target that was stung up to 2 h and 3 h earlier, respectively, whereas European bees could only do so for 30 min. This long-term marking could confer an advantage against returning predators with few weak points, such as honey badgers and humans wearing protective clothing. Overall, we offer a fresh perspective on this controversial but important subspecies of honeybees, with implications for both future studies and daily management.

Backgrounds and Aims: Partitioning of biomass to various organs is fundamental to growth and survival strategies of plant species, with broad-scale ecological implications from competition to carbon flux of ecosystems. Although partitioning patterns have been studied extensively in embryophytes, little is known about the variation and evolutionary drivers of biomass partitioning strategies in marine plants, such as seaweeds, that form marine forests analogous to those on land. Methods: We measured developmental variation in standing organ biomass for 18 species of kelp and used a previously published dataset on land plants to draw comparisons between kelps and embryophytes, with respect to developmental allometry, interspecific allometry and the relationship between the two measures. Key results: We report that kelps exhibit large variation in partitioning patterns, with some species differing by more than an order of magnitude in holdfast and stipe investment when controlling for size. The range of biomass partitioning patterns exhibited by kelps includes values not found among embryophytes, highlighting differences in selective pressures on land and in the ocean. However, as previously demonstrated, empirical values of interspecific scaling curves closely match those of land plants. This suggests that despite fundamentally different physical constraints, evolutionary scaling has converged on nearly identical interspecific exponents. We further demonstrate that allometric covariation exists between support organs (stipe and holdfast), highlighting the importance of physical forces in driving functional diversification of marine plants and supporting the notion that covariation of traits is a hallmark of botanical structure and function. Conclusions: The results of our study illuminate the variation and evolutionary patterns of biomass partitioning in marine primary producers. Moreover, these results highlight that universal evolutionary scaling relationships can emerge from fundamentally divergent developmental and biomechanical pathways.

Shifts in predation and human harvest often coincide with changes in life history trait distributions in prey populations. These changes may arise via evolution or plasticity, and extrinsic environmental effects may affect such traits. This complexity prompts questions about how trait distributions are shaped by multiple factors' interactions. We hypothesized that food availability and climate affect both the magnitude, and mechanism (evolution vs. plasticity), by which traits change in response to harvest's intensity and size selectivity. We tested these hypotheses using individual-based bioenergetic population models allowing both plasticity and evolution. We exposed genetically diverse fish populations to gradients of productivity and stochasticity in food availability, crossed with gradients of selective or nonselective fishing mortality. Food availability shaped traits both plastically and evolutionarily, and modulated how harvesting influenced those responses. Food effects can suppress harvest impacts altogether, or obscure evolution's effects on phenotypes. However, when climatic factors shape food-driven changes by affecting both fish and their prey, either synergistic or antagonistic interactions can emerge between food variation and harvest in determining phenotype distributions. Our research suggests that understanding consumer-resource dynamics, and climatic processes shaping them, is essential to interpreting how harvest can shape traits relevant to population viability and fisheries sustainability.

Precocious reproduction, prior to the acquisition of the final adult morphology, occurs in a variety of animals and represents a distinct life-history strategy with important consequences for growth and survival. Larval reproduction is far rarer and usually restricted to groups that go through metamorphosis. In ctenophores, Carl Chun described dissogeny more than 130 years ago, a distinctive life-history pattern involving larval and adult reproductive periods separated by gonadal regression. Yet, the potential plasticity of larval reproduction in ctenophores remains unresolved. Here, we developed a method to follow and quantify reproductive output in Mnemiopsis leidyi larvae and tested environmental factors that may regulate precocious reproduction. We found that conspecific density strongly influences its onset: low-density, well-fed animals can bypass reproduction at the cydippid stage and develop rapidly into the lobed form, whereas higher density promotes precocious reproduction. Food availability and associated growth rate also contribute but cannot alone explain the observed differences. Once reproduction is established, however, high conspecific density suppresses reproductive output, an effect reproduced by exposure to seawater incubated with high M. leidyi densities, consistent with water-borne chemical communication. Salinity and light conditions further modulate spawning. Together, our results reveal substantial environmental plasticity in precocious reproduction in M. leidyi, reconcile long-standing contradictory observations of ctenophore development, and highlight how environmental cues can reshape reproductive life-history transitions.