Evolution Letters

In most species, unmated individuals run the risk of dying with zero fitness. This strong selection on virgin females to mate may also explain why females subsequently remate, despite fitness costs; all that is required is a genetic correlation between virgin and non-virgin mating propensity. Despite being the null model for the evolution and maintenance of polyandry, this hypothesis has received no empirical test. We performed separate quantitative genetic and artificial selection experiments to test the presence of this cross-context genetic correlation in the cow-pea weevil, Callosobruchus maculatus. A quantitative genetic experiment did not find evidence of the hypothesised genetic correlation. However, after 13 generations of artificial selection on virgin mating latency, we found strong evidence for evolutionary divergence in remating latency. Females from lines selected for longer virgin mating latency took approximately twice as long to remate and, were less polyandrous if their virgin mating latency was longer. There was no evidence that females could mate indiscriminately and then trade-up, rather, trading up could only occur if virgin discrimination was present. Selection against virgin death will thus constrain both the evolution of non-virgin discrimination and trading up, increasing rates of polyandry. These findings reveal a genetic correlation between virgin and non-virgin latency to mate suggesting that polyandry may be maintained because of the need to breed.

Organisms have evolved a remarkable diversity of reproductive strategies in response to environmental variations and selective pressures. Although most vertebrates do reproduce biparentally, rare alternative modes such as selfing (self-fertilization) and different forms of parthenogenesis exist, but remain poorly characterized. Here, we investigated an unusual reproductive event in the normally biparental cichlid fish Cyphotilapia frontosa, in which a female produced offspring in the absence of a male. Using whole-genome sequencing data, we analyzed whether reproduction occurred via selfing or parthenogenesis by comparing patterns of heterozygosity with those from a wild, genetically diverse C. frontosa family collected in Lake Tanganyika and a closely related inbred Ctenochromis benthicola family. The uniparental family exhibited reduced genetic diversity, elevated relatedness, and genome-wide patterns of homozygosity distinct from those expected under parthenogenesis or inbreeding, but consistent with self-fertilization. Our study provides rare genomic evidence of selfing in a vertebrate and suggests that such alternative reproductive modes may be overlooked rather than truly absent. These findings contribute to a broader understanding of how alternative reproductive strategies evolve in vertebrate lineages. SignificanceThe overwhelming majority of vertebrates reproduce sexually, requiring a male and a female to produce genetically distinct offspring. Yet, rare alternative modes involving only a single parent such as asexual parthenogenesis ("virgin birth") or self-fertilization challenge this paradigm. Among these, selfing is exceptionally uncommon and poorly studied in vertebrates. Here, we unveiled - based on genomic analyses - the reproductive strategy of a member of the extraordinarily diverse cichlid fish radiation in Lake Tanganyika that reproduced in captivity in the absence of a male. By comparing patterns of genome-wide heterozygosity with both wild and inbred reference families, we identified a rare case of selfing. This finding adds to the limited records of selfing in vertebrates and expands current understanding of reproductive diversity, highlighting the power of whole-genome sequencing to distinguish among alternative reproductive mechanisms.

The evolution of alternative male reproductive strategies represents an intriguing evolutionary phenomenon. Divergent strategies are persistently at risk of local extinction or invasion, depending on the suites of traits expressed within and between morphs; hence, understanding the correlational selection that aligns reproductive strategies with behaviour, morphology and physiology is key to understanding the origin and maintenance of genetic polymorphisms. In the polychromatic painted dragon, Ctenophorus pictus, yellow, orange and red morphs are well characterised, but the blue morph has been historically absent from studied populations. Here we document the local distribution, morphology and male-contest interactions in a population where blue males are relatively common. We find that blue males express head colouration after a reaching a threshold body size, and that small blue males can reside in close proximity to other males; patterns consistent with a novel size-dependent conditional tactic within the suite of genetic strategies seen in this species. Condition-dependent, positively allometric throat bibs were non-randomly distributed among male morphs, implicating variation in correlational selection and the genetic architecture of the polymorphism. We were unable to definitively assign a morph that was superior in male competition but found that within morphs, male size was the determinant of competitive success, whilst between morphs it was not. Furthermore, contests between morphs were resolved with less aggression than contests within morphs, supporting the idea that badges resolve conflict, and that the invasion of new colour morphs may be facilitated by negative frequency dependent benefits to novel colour variants. These findings highlight the divergent phenotypic, genetic and selective environments that lead to the diversity of colour morphs.

In androdioecious species like Caenorhabditis elegans, where the primary mode of reproduction is self-fertilization, the evolutionary role of males has long puzzled biologists. One proposed benefit of males is the potential to escape inbreeding depression. We tested this by enforcing seven generations of inbreeding across nine C. elegans strains differing in baseline male frequency and measuring competitive relative fitness before and after inbreeding. We then relaxed inbreeding for four generations to assess recovery. We predicted that strains with higher male frequency, and greater opportunity for outcrossing, would exhibit faster recovery once inbreeding was relaxed. Strains varied substantially in their responses with most showing significant fitness declines and partial recovery but neither the magnitude of inbreeding depression nor the extent of recovery correlated with male frequency. These results show that male frequency is a poor predictor of inbreeding responses and does not reliably reflect realized outcrossing or its fitness consequences.

Avoiding fertilization with genetically incompatible partners, whether too similar or too divergent, is a central challenge for sexually reproducing organisms. Selection can favor mechanisms acting before and after mating, with postmating processes potentially compensating for constraints on premating choice. In the postmating context, female reproductive fluid (FRF) can modulate sperm performance and bias fertilization outcomes, but its contribution to reproductive isolation remains unclear. We tested whether FRF mediates discrimination against heterospecific and related sperm in two naturally hybridizing sister species of swordtails, Xiphophorus birchmanni and X. malinche, that diverge in premating behavior towards heterospecifics. Effects of FRF differed sharply between species. In X. malinche, FRF enhanced the velocity of conspecific sperm relative to heterospecifics, consistent with postmating discrimination against hybridization. In contrast, FRF in X. birchmanni did not favor conspecific sperm. Evidence for inbreeding avoidance was weaker, and we found no indication of a trade-off between discrimination against genetically similar and dissimilar sperm. These results show that female reproductive fluid can serve as a rapidly evolving axis of reproductive isolation through postmating female choice.

Matching habitat choice provides a mechanism for individuals to maximise their expected fitness by selecting an environment that better fits their phenotype. Many animals choose their local environment by evaluating levels of perceived predation risk against possible resource gain. To test if predation risk is a major driver of habitat choice, we quantify scototaxis, or preference for dark versus light backgrounds, in juvenile guppies. As light backgrounds increase visibility to predators, this aspect of habitat choice captures variation in boldness in small fishes. By rearing and testing 586 fish descended from ten natural populations from Trinidad under common garden conditions, we first quantify (broad sense) heritable variation, i.e. evolutionary potential, within populations. Next, we test for evolutionary divergence among populations in mean preference, and if present, whether ancestral predation regime is a mediator of divergence. Finally, we ask whether families and/or populations differ in the amount of behavioural variation they contain. Habitat choice varied among families (12% of total variance), consistent with heritable variation (0.2). We also found mean preference varies among populations (11% of total variance explained). Evolutionary divergence among-populations is partly explained by ancestral predation regime, with populations from low-predation sites showing a stronger average preference for dark backgrounds than high-predation populations from the same river. Additionally, we find that within-population behavioural variation is greater in high-predation populations. We conclude that guppy populations contain heritable variation that could facilitate adaptive evolution if scototaxis is subject to natural selection. Furthermore, while genetic drift may also contribute to evolutionary divergence among-populations, observed patterns are qualitatively consistent with local adaption to predation regime. Our results suggests that high predation sites favour bolder habitat choice on average, but also that local predation regime shape the evolutionary dynamics of variation, perhaps by maintaining shy-bold variation among-individuals or by favouring individuals with less-predicable behaviour.

Social interactions are ubiquitous in nature and have the potential to affect trait evolution, particularly in group-living animals such as cooperative breeders. Interactions among conspecific individuals can affect the amount of additive genetic variation for a trait when the phenotype of an individual is also affected by the genotype of its social partner(s) via indirect genetic effects. Thus, quantifying both direct and indirect genetic effects of social partners is critical for understanding and predicting evolutionary trajectories. While much is known about maternal indirect genetic effects, empirical estimates of indirect genetic effects from other social partners remain limited, particularly in wild populations. Here, we use animal models to assess the contribution of indirect genetic effects from all social partners in a family group (mothers, fathers, and helpers) on juvenile morphometric traits across ontogeny in the cooperatively-breeding Florida scrub-jay (Aphelocoma coerulescens). We found indirect genetic effects of helpers and fathers on nestling weight, but no indirect genetic effect of mothers. Across ontogeny, we found increasing additive genetic variation in both weight and tarsus length. Our study provides a comprehensive assessment of within-group indirect genetic effects in a cooperative breeder and highlights the importance of considering indirect genetic effects beyond maternal effects.

Parasites can alter host populations in fundamentally different ways depending on whether exposure results in infection. Yet, most epidemiological and evolutionary inference focuses on established infections, leaving the fitness consequences of parasite exposure comparatively understudied. This gap is consequential because hosts are frequently exposed to diverse parasite genotypes, and these encounters can impose substantial fitness costs even when infection does not occur. Theory predicts that hosts may mitigate these costs when interacting with commonly encountered parasite genotypes, such that exposure to sympatric parasites incurs lower fitness consequences than exposure to novel, allopatric parasites. Here, we examine the fitness consequences of exposure and infection in the first intermediate host of the trophically transmitted tapeworm Schistocephalus solidus, a cyclopoid copepod that serves as the first host in a three-host life cycle. Using sympatric (Vancouver Island, Canada) and allopatric (Norway) host-parasite combinations, we found a striking reciprocal asymmetry. Sympatric parasites were significantly more infective, yet exposure to sympatric parasites imposed weaker fitness costs when infection did not establish. In contrast, allopatric parasites were less infective, but exposed females produced fewer eggs and had lower hatching success than both controls and females exposed to sympatric parasites, indicating substantial genotype-dependent costs of exposure. Moreover, we found that infection was highly virulent across all genotypes: a single parasite caused near-complete reproductive suppression and reduced host survival across all host-parasite pairings, confirming S. solidus as a castrating parasite in copepods. Together, these results demonstrate that exposure, not just infection, acts as a critical ecological filter with potentially large and underappreciated consequences for host population dynamics and parasite transmission.

Most species are geographically structured, leaving characteristic signatures in neutral regions of the genome. These signatures can be distorted when neutral regions are linked to deleterious mutations. In such regions, purifying selection can reduce genetic diversity through Background Selection (BGS) or, for recessive mutations, increase diversity through Associative Overdominance (AOD). While the effect of BGS and AOD are well characterized in panmictic populations, their effects remain largely unexplored in structured populations. Here, we investigated an Isolation with Migration model using forward simulations across a range of migration, selection, dominance, and recombination parameters. We first used a genotype-based approach to quantify the effects of deleterious mutations on standard summary statistics ({pi}, dxy, FST, DAFi). We then showed that an Ancestral Recombination Graph-based (ARG) approach, tracking tree sequences from a sample of one diploid per deme, recovers the same patterns while directly relating genetic variation to the underlying coalescent processes. When recombination is sufficiently low, we found a BGS-driven regime for weakly codominant mutations, characterized by lower diversity and increased genetic differentiation (FST). For recessive mutations, we first identified an AOD-driven regime, characterized by increased diversity and lower FST values followed by a transition to a subsequent BGS-driven regime. Genealogies were similarly impacted by deleterious mutations: BGS shrunk coalescent times and produced a shift towards lineage sorting topologies, while AOD stretched coalescent times and produced a shift toward incomplete lineage-sorting topologies. These patterns were weakened by gene flow, with FST and topologies remaining close to expected under neutrality, while diversity and coalescence times remained robust to demography. Our results provide clear evidence of BGS, AOD, and of their transition in a structured model with gene flow. Importantly, these processes leave distinct and interpretable signatures on gene trees, highlighting the potential of ARG-based approaches for inferring linked selection and dominance in structured populations. Author summaryCharacterizing how demography and selection jointly shape genomic variation is a central question in population genetics. As deleterious mutations reduce fitness, they are continuously removed from populations by purifying selection. Through linkage, this affects nearby regions of the genome, leaving signatures of selection on linked neutral genetic diversity. While these effects are well understood in random mating populations, much less is known in structured populations. Specifically, the occurrence of Background Selection (BGS), which reduces diversity, and Associative Overdominance (AOD), which increases diversity, remains underexplored. Here, we used simulations to investigate how deleterious mutations shape genomic variation in a structured two-population isolation with migration model. By combining standard population genetic analyses with a genealogical approach based on Ancestral Recombination Graphs (ARGs), we showed that BGS and AOD leave distinct and interpretable signatures on common summary statistics and the underlying genealogies. We identified clear signatures of BGS and AOD when recombination was low and revealed a transition from AOD to BGS for recessive mutations, as the strength of selection increased. Our results highlight the importance of jointly considering demography and linked selection when interpreting genomic data and demonstrate the potential of ARGs to jointly infer demography, selection, and dominance from genomic data.

Rapid environmental change is exposing organisms to conditions that do not match those under which they evolved, making it increasingly important to understand how genetic variation shapes phenotypic responses to environmental stress. Since most phenotypic traits arise from interactions between genetic variation and the environments experienced throughout an organisms lifetime, understanding the genetic architecture of these interactions is central to predicting how populations will respond to novel environments. While genotype-by-environment interactions (GxE) are well studied in quantitative genetics, identifying specific loci that contribute to environmentally dependent trait expression remains rare. Salmonids already exhibit a wide portfolio of plastic life-history strategies, reflecting adaptation to highly heterogeneous environments, yet it remains unclear whether known major-effect loci involved in life-history regulation also contribute to variation in plastic responses to environmental change. One such major-effect locus is the transcription factor six6, which has been repeatedly associated with variation in age at maturity across multiple populations of rainbow trout (Oncorhynchus mykiss). Since maturation timing is closely linked to growth trajectories and patterns of energetic allocation during early development, allelic variation at this locus may also influence growth responses to warming conditions. Here, we test this hypothesis using a common-garden experiment in which 6 months old juvenile rainbow trout were reared under current and warming (+2{degrees}C) temperature regimes. By quantifying genotype-specific reaction norms across environments, we show that six6 genotype contributes to environmentally dependent variation in growth and body composition, with individuals heterozygous for the six6 locus showing a distinct and steeper response to warming relative to homozygotes. These findings provide evidence that a major life-history gene shapes plastic responses to thermal stress in juvenile rainbow trout, with novel implications for how standing genetic variation at in large-effect loci may influence population-level responses to climate warming.

Immunoglobulin genes are a central component of jawed-vertebrate adaptive immunity. A previous study showed that the blunt-snouted clingfish Gouania willdenowi lacks immunoglobulin genes and T-cell receptor gamma/delta loci, while retaining T-cell receptor alpha/beta genes, MHC genes, and RAG1 /RAG2. Here I extend that observation to the family Gobiesocidae using all seven chromosome-level Gobiesocidae genome assemblies currently available. Manual tblastn and synteny-guided searches found no convincing immunoglobulin heavy-chain or light-chain loci in G. willdenowi, Gouania pigra, Gobiesox punctulatus, Apletodon dentatus, Lepadogaster candolii, Lepadogaster purpurea, or Diplecogaster bimaculata. Thus, the absence of antibody genes is best interpreted as a root-level character of clingfishes. The latest seven-species screen of 40 additional immune-associated genes shifts the broader interpretation in the same direction: the B-cell/adaptive core genes CD79A, CD79B, CIITA, TNFRSF13B, and TNFSF13B lack strong tblastn support in all sampled Gobiesocidae, and 37 of the 40 tested targets show an all-zero binary pattern at the presence threshold. Only IL21R.1, TYROBP, and TNFRSF11A show strong hits in one or more species. I therefore interpret the principal immune-gene erosion as occurring at or near the Gobiesocidae root rather than as a recent Gouania-specific process, while keeping weak, paralog-sensitive, and patchy loci provisional. RAG2 comparisons show a shared Gobiesocidae PHD-domain C-to-S replacement in the zinc-binding motif, with apparently intact RAG2 coding sequence. A family-wide TRG/TRD screen did not recover TRGV V segments or accepted TRDC constant-region exons, but it did detect TRGC-like constant exons in several genomes. These TRGC-like sequences are probably not canonical TRG constant exons without further validation, so I treat the gamma/delta system as eroded or rearranged rather than as a complete root-level loss equivalent to the Ig loss. The RAG2 variant provides a plausible molecular context for antigen-receptor remodeling, but it is not evidence that RAG genes are pseudogenized, because TCR alpha/beta, MHC genes, and RAG1 /RAG2 are retained. Gobiesocidae are therefore best described as a vertebrate family with ancestral loss of canonical immunoglobulin genes and associated root-level erosion of B-cell and immune-related genes, not as a lineage lacking adaptive immunity in its entirety. HighlightsO_LISeven chromosome-level Gobiesocidae genomes lack convincing canonical IgH and IgL loci. C_LIO_LIThe strongest non-Ig losses map to the B-cell/adaptive core: CD79A, CD79B, CIITA, TNFRSF13B, and TNFSF13B. C_LIO_LITCR alpha/beta, MHC genes, and RAG1 /RAG2 are retained, so Gobiesocidae should not be described as lacking adaptive immunity in full. C_LIO_LIA shared Gobiesocidae RAG2 PHD-domain C-to-S variant provides candidate molecular context for antigen-receptor remodeling. C_LI

There are some disputed hypotheses for the recurrent observations of insular gigantism and dwarfism, like the island rule: small organisms would become larger on islands, while large organisms would become smaller. But, why is the latter? In addition, not all the observations fit this rule. Here I propose a causal model. Following the Island Biogeography Theory (IBT), insular aspects influence the census N. Observations suggest that variation in N is associated with variation in effective population size (Ne). The body size of insular colonisers might change, following Damuths law, as Ne can decrease at a differential rate from the island area A, resulting in a distinctive effective density [Formula]. Interestingly, a prediction of the drift-barrier hypothesis is that Ne is affecting mutation rates. Consequently, body mass, genome size and {micro} may be predicted to some extent by island area, as they are influenced by De and Ne. Falsification of the latter hypothesis is feasible by determining changes in genomic features of insular species. We now have the opportunity to interrogate the extensive data available. Here I ask: (i) How is decreasing island area predicting average body sizes? (ii) To which levels does this prediction apply (species, cells, genomes)? (iii) How well does the model fare on predicting {micro} over paradigmatic case studies? The resolution of these questions may provide a more reliable diagnosis of the evolutionary causes for somatic size variation. Significance statementNaturalists have long reported that insular species tend to become unusually large or small compared to their mainland relatives. Despite the familiarity of this "island rule", there is still no broad mechanistic explanation for why these changes occur so consistently across different groups of organisms. This work proposes that an important neutral factor can be the change in effective density of isolated populations. By combining the expectations of Damuths law, the IBT model, and the nearly-neutral theory it offers unified predictions on how sudden constraints in island area can influence not only the evolution of body size, but also the direction of changes in genome size and evolutionary rates.

Dormancy is a widespread adaptive strategy that allows organisms to survive in temporally varying habitats by suspending development and reproduction. Although environmental variability is expected to shape dormancy strategies, it remains unclear how differences in environmental variability and predictability influence both the production of dormant embryos and the termination of dormancy. We addressed these questions by comparing D. pulex and D. obtusa, two closely related species that inhabit environments differing in variability and predictability. We hypothesized that D. obtusa, which inhabits ephemeral environments, would exhibit a greater propensity for sexual reproduction and dormancy and would require stronger cues to break dormancy than D. pulex, which occurs in more permanent, predictable habitats. Consistent with our hypothesis, D. obtusa lineages produced significantly more males and ephippia than D. pulex when reared under identical laboratory conditions, indicating greater investment in sexual reproduction and dormancy. Contrary to our hypothesis, we found no difference in responsiveness to cues between the two species. Across species, embryos broke dormancy and hatched most readily after experiencing changes in cold and light, even if not experienced at the same time. In contrast, desiccation reduced the propensity to break dormancy. Together, these results indicate that species occupying more ephemeral environments invest more heavily in the production of dormant offspring, but that the environmental cues regulating dormancy termination appear broadly similar between species. This pattern suggests that while investment in dormancy may evolve in response to environmental variability, the mechanisms controlling dormancy termination are more conserved.

Allopatric isolation under contrasting environments can drive rapid phenotypic divergence, even over contemporary timescales. Rapid changes in morphology or physiology can allow organisms to adapt to biotic and abiotic characteristics of their habitats. While studying metabolism, growth and resources needs may allow to understand adaptation to several selective pressures, these traits are rarely jointly considered. We investigated morphological, growth, and metabolic divergence in two allopatric populations of Arctic charr (Salvelinus alpinus) sharing a common evolutionary origin but inhabiting contrasting environments. We combined field observations, common garden and quantitative genetic approaches to disentangle contributions of genetic divergence and plasticity to phenotypic variability. Wild adults differed in body shape and growth trajectories, potentially reflecting plasticity related to resource availability and temperature variations. Under common garden conditions, juveniles displayed inter-population differences in routine metabolic rate, its allometric scaling with body mass. These patterns suggest divergent selection on physiological traits. Despite low neutral genetic differentiation, phenotypic divergence unfolded in fewer than 100 years, suggesting that plasticity and selection can promote rapid multi-trait changes. These findings highlight that considering changes in physiological, growth and morphological traits can reveal the adaptive potential of small, isolated populations facing rapid environmental change.

Conspecific sperm precedence via cryptic female choice is a post-ejaculatory selection process that reduces hybridization, and can be pronounced in sympatric species. In their native Europe, Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) exert conspecific sperm precedence under heterospecific sperm competition, which is at least partially enabled by female reproductive fluid. We examined post-ejaculatory selection of both species in Newfoundland, Canada, where Atlantic salmon evolved in absence of brown trout, but now experience hybridization threats due to anthropogenic introductions. Using split-ejaculate and split-clutch in-vitro fertilizations we evaluated whether allopatric evolution has relaxed this selection in Atlantic salmon, and found that they had no ability to bias paternity towards conspecific males, whereas naturalized brown trout retained a strong ability to do so. Female reproductive fluid influenced this, as when fluid associated with a species eggs was swapped, hybridization increased. In the artificial situation of no female reproductive fluid during sperm competition, paternity changed dramatically, but sperm swimming performance did not predict it. Our findings contribute to understanding the evolution of cryptic female choice and how the mechanisms of reproductive isolation can be reinforced through sympatry, while also highlighting a new potential conservation concern for North American Atlantic salmon.

Sexual selection is a major evolutionary force, yet its demographic consequences remain unclear. While experimental studies often report positive effects of sexual selection on traits linked to population performance, comparative studies often find null or negative associations with population persistence. One explanation for this discrepancy is that the demographic consequences of sexual selection depend on ecological context, particularly variation in mortality and fecundity. Here, we used six decades of abundance data and test whether sexual selection predicts population trends across 738 bird species from Europe and North America. We quantify sexual selection using complementary proxies capturing different components of sexual selection: mating system, sexual dichromatism, sexual size dimorphism and relative testes mass. We further assess whether the effect of sexual selection in population trends is mediated by mortality and fecundity. Across all proxies, we found no evidence that sexual selection is associated with population trends. This result is consistent across continents and robust to variation in mortality and fecundity. Our findings suggest that, despite its central role in shaping phenotypic evolution, sexual selection does not translate into consistent effects on long-term population trends at macroecological scales. More broadly, these results highlight a potential disconnect between evolutionary processes and population dynamics.

Background and AimsGroundwater-dependent ecosystems support disproportionate biodiversity in arid regions, yet the population genetics of spring-specialist plants remains poorly understood. Here, we present the first species-wide genetic dataset for crimson monkeyflower ( Mimulus verbenaceus, Phrymaceae), a spring-specialist plant distributed in seeps, springs, and associated riparian areas across desert regions of North America. MethodsUsing genome-wide reduced representation sequencing data consisting of 10,760 SNPs from 175 individuals across 17 populations, we characterized the patterns of genetic diversity using FST and Neis D. Population structure was assessed using ADMIXTURE and PCA. We examined the contributions of climate to range-wide genetic variation in crimson monkeyflower using redundancy analysis. Key ResultsPatterns of genetic differentiation were more consistent with those of spring-specialist animal taxa than those of upland plants or generalist riparian plants. We found strong population structure at both broad regional scales and at fine local scales. While riparian connectivity influenced local patterns of diversity, adaptation to local climatic variation was more influential at regional scales, with temperature, relative humidity, and a monsoon-driven climate gradient structuring genetic differentiation. ConclusionsOur findings highlight the distinctive influence of isolated perennial groundwater sources, as well as adaptation to climate, in shaping genetic variation in this spring-specialist plant. These findings suggest that spring-specialist plants deserve special consideration in ecological theory, management, and conservation.

Behaviour is a key yet often overlooked component of animal camouflage and how it evolves alongside colour and morphology remains poorly understood. The repeated evolution of stick-like postures in spiders offers a useful framework for investigating the importance of behaviour for concealment, since matching the environment should rely on specific body forms and postures, not just colouration. We hypothesised that when spiders behaviourally align their body with the background orientation it should influence the shape, posture and colouration that best enhances camouflage. To test this, we used a genetic algorithm and human observers to evolve digital spiders to be harder to find. We evaluated how selection under three behavioural orientation treatments (aligned, random, and evolvable orientation) influenced spider capture time, background match (lightness and colour), posture, and body (cephalothorax and abdomen) dimensions. We found that spiders that behaviourally aligned with the background took substantially longer to find through evolving a better background match, and a more elongated posture and body shape than randomly orientated spiders. Our spiders mirrored the shape and posture adopted by numerous clades, illustrating how behavioural camouflage represents a key concealment strategy in structurally complex habitats, part of an interacting suite of traits that encompass successful concealment.

The fitness of immigrants and their descendants determines the effectiveness of gene flow. Genetic incompatibilities or outbreeding depression can limit the spread of novel alleles, while highly fit immigrant lineages can hasten introgression. These fitness effects of gene flow can also differ between generations as immigrant and resident haplotypes recombine. Understanding the genetic factors that shape immigrant fitness over multiple generations is increasingly important as habitat fragmentation threatens populations by reducing genetic variation and leading to increased levels of inbreeding. Few studies have measured the multigenerational fitness of immigrant lineages, especially within populations that had histories of high gene flow. We used 33 years of life history and pedigree data on a population of Florida scrub-jays (Aphelocoma coerulescens) with historically high immigration to quantify the fitness of immigrants and their descendants. We compared the fitness of immigrants and residents as well as their resulting descendants (F1, F2, etc.) to determine the composite genetic effects responsible for fitness differences. We found evidence of additive benefits of immigrant ancestry and heterosis driven by non-additive effects that persists for multiple generations. These results are promising for conservation efforts aiming to increase connectivity and illustrate the complex dynamics that determine the rates of introgression in natural populations.

Arthropods exhibit an exceptional diversity of life histories, where developmental modes involve moulting stage progressions with changes ranging from the bare minimal to the dramatically transformative. While this variability drives many research questions aiming to understand evolutionary and developmental underpinnings of life history differences, it can complicate comparative analyses across taxa. However, this can be approached by applying a framework that defines metamorphosis as a post-embryonic stage progression characterised by substantial changes in morphology and adaptive landscape. Employing this framework with a phylogenomic dataset spanning 26 orders and encompassing four independently arising metamorphic lineages, we explore gene repertoire evolutionary dynamics potentially associated with metamorphosis in Pancrustacea. The approach contrasts gene family evolutionary dynamics inferred to have occurred in the last common ancestors of the metamorphic Insecta, Copepoda, Eucarida, and Thecostraca, with those of their sister lineages, as well as of descendent and ancestral nodes. The results reveal that the metamorphosis ancestors are characterised by an elevated number of gene family births and expansions. Expanded gene families share a set of commonly enriched biological processes across all metamorphosis ancestors, suggesting functional convergence by independent evolution of distinct gene families involved in embryonic and post-embryonic development and nervous system differentiation. Evolutionary modelling further highlights a subset of these families exhibiting signatures of adaptive, lineage-specific gene family size increases associated with metamorphic development. These families include genes implicated in neural and sensory development, segmentation, and moulting. These findings support a model of the evolution of pancrustacean metamorphosis where distinct gene families from a common functional toolkit expand and are co-opted into facilitating transitions to multi-phasic life cycles. This reframes the role of moulting in arthropod diversification to be recognised as an important reservoir of genetic change that can potentiate truly remarkable life history transitions.