Biological Journal of the Linnean Society

The diversity of body shapes is one of the most prominent features of phenotypic variation in mammals. Yet, mammalian body shapes are poorly quantified and the underlying components contributing to its diversity as well as its relationship to other components of the skeleton are rarely tested. Here, we use lagomorphs (hares, rabbits and pikas) as a model system to (1) investigate which components of the skeleton contributed the most to body shape diversity, (2) examine the relationships between body shape and relative limb lengths, and (3) test how body size, ecotype, burrowing behavior, and locomotor mode influenced variation in lagomorph body shape and appendicular morphology. We quantified the body shape and functional proxies of the appendicular skeleton in 40 lagomorph species from osteological specimens held at museum collections. Using phylogenetic comparative methods, we found the relative length of the ribs and elongation or shortening of the thoracic and lumbar regions contributed the most to body shape evolution across lagomorphs. Second, we found that only leporids (hares and rabbits) exhibited a significant relationship between limb length and body shape, where more elongate species exhibit relatively shorter forelimbs and hindlimbs. Lastly, we found that models incorporating body size were the best predictors of lagomorph body shape and the majority of the appendicular traits, whereas models incorporating burrowing behavior and locomotor mode were largely poor fits. Broadly, these results indicate that larger lagomorphs tend to exhibit more robust body shapes with longer, more gracile forelimbs, whereas smaller lagomorphs tend to exhibit more elongate body shapes with shorter, more robust forelimbs. Overall, this work contributes to the growing understanding of mammalian body shape evolution and demonstrates the importance of not omitting body size in ecomorphological analyses.

Silk glands have been found in two groups of amphipods: the Corophiida and the Ampeliscidae. The silk glands in Ampeliscidae, however, have yet to be examined in detail. Here we report, for the first time, the morphology and distribution of pereopodal glands in the Ampeliscidae, in non-thread producing Synopiidae, and in the Paragammaropsidae. In the Ampeliscidae we found two gland types distributed throughout all pereopods which have the ability to create threads. Pereopods three and four have additional silk extrusion morphology at the tip of the dactylus in which silk is transformed into semi-cylindrical threads used for building domiciles. Synopiid outgroup species have one of the gland types but lack silk extrusion morphology. Using ancestral state reconstruction analysis, we find that glands in the Synopiidae are likely ancestral and hypothesize that silk glands in Ampeliscidae are derived from these ancestral glands. Silk-spinning pereopods in the Paragammaropsidae had similarities with both Corophiida and Ampeliscidae but had distinctions. Ampeliscidae silk-spinning systems bear surprising resemblance to the Corophiida which presents one to reconsider the taxonomic placement of Ampeliscidae and the origins of silk-spinning in amphipods. This is the first comprehensive study on the glandular systems of Ampeliscidae, Synopiidae, and Paragammaropsidae using advanced microscopy, providing pertinent morphological data to the study of arthropod silk gland evolution and complex traits.

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

Non-avian reptiles have been assumed to be non-social for many years, yet recent studies show diverse social behaviours in squamates, crocodilians, and turtles. Here, we investigate social structure within feeding aggregations of three freshwater turtle species caught in baited traps in a coastal marsh over 12 years. In 488 instances in which traps contained turtles, 45% contained multiple individuals, and these aggregations were strongly positively assorted by species. midland painted turtles (Chrysemys picta) and Blandings turtles (Emydoidea blandingii) were captured with conspecifics more often than expected in a non-social null model. Snapping turtles (Chelydra serpentina), the largest species in this study, were caught with conspecifics at rates consistent with the non-social null model, and were avoided by heterospecifics. This suggests that species differences play a role in how feeding aggregations are structured, with painted and Blandings turtles driving positive species assortment while avoiding snapping turtles around food sources. We did not detect significant intraspecific sex assortment in any of the three species, nor did turtle body size strongly affect the probability of aggregating with conspecifics at the perceived food source in the traps. Our study illustrates how long-term monitoring data can be used to investigate social structure in wild populations, an approach that may be valuable for species of conservation concern. Significance StatementReptile sociality has been historically overlooked, but recent work has revealed intriguing social behaviours in non-avian reptiles. We investigated associations among three species of freshwater turtle, captured in baited traps over 12 years of trapping. Turtles in these feeding aggregations grouped with their own species more often than expected by chance. This result was driven by the two smaller-bodied species (midland painted turtle and Blandings turtle), which were more likely to be caught with conspecifics than with other species. In contrast, the largest species (snapping turtle) showed no evidence of attraction to other snapping turtles, and midland painted turtles and Blandings turtles showed avoidance of the larger snapping turtles. Our analyses illustrate how long-term monitoring data can be used to uncover previously unrecognized social behaviour in turtles and other species in which behaviour is difficult to observe directly.

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.

Sentinel behaviour occurs when individuals use raised positions to scan for predators while the rest of the group forages. Here, we investigated whether a colonial cooperatively breeding species that forages in large groups, the sociable weaver, Philetairus socius, displays sentinel behaviour. This behaviour has been reported in species with similar ecology, behaviour and foraging habits, (e.g. ground foraging in open habitats where aerial predators are common) and, hence, we expected that it could occur in sociable weavers. On the other hand, sentinel behaviour appears to be less common in species that live in very large groups. We used an experimental set-up consisting of an artificial feeding station and perches to assess occurrence of sentinel related behaviours: (i) perching events > 30s on an elevated position, (ii) head-movements and (iii) alarm calling. Birds were seldom observed perching while others fed, and those that did, perched for periods that were too short to be considered as sentinel behaviour (less than 5s on average). Our results suggest that this behaviour is uncommon or even absent in sociable weavers. We discuss whether other factors such as foraging in very large groups, or interspecific foraging associations might make sentinel behaviour less important in this species.

Incilius marmoreus inhabits an extensive range along the Pacific Coast of Mexico and a smaller allopatric region in the State of Veracruz, exhibiting an unusual distribution among herpetofauna. Gunther (1901) classified the Pacific coastal toads Bufo argillaceus and B. lateralis as conspecific with Incilius [Bufo] marmoreus, which has its type locality in Veracruz. Here, we adopt a multidisciplinary approach to reevaluate the phylogeography and taxonomy of I. marmoreus by gathering and analyzing morphological data and conducting phylogenetic and population genetic analyses from genome-wide SNP data. Our results uphold the current taxonomy by concurring with Gunther (1901). Our phylogenetic and population genetic analyses suggest that I. marmoreus from Veracruz are closely related to those from Oaxaca whilst coalescent analyses recovered a north-south split along the Pacific Coast estimated to have occurred [~]0.86 Mya followed by a shallow east-west split in the southern lineage that separates the Pacific coastal populations and the allopatric population in Veracruz [~]0.33 Mya. This species displays marked morphological and genetic diversity throughout its range, but this variation appears to be consistent with gene flow across contiguous populations rather than the existence of independent evolutionary lineages. The processes leading to the geographic isolation of the population on the coast of Veracruz remain uncertain, but we hypothesize that climatic and vegetation changes in the Late Pleistocene may have played a role.

AO_SCPLOWBSTRACTC_SCPLOWEnvironmental heterogeneity across freshwater systems often promotes phenotypic variation, yet disentangling environmentally induced variation from heritable differentiation remains a central goal in evolutionary ecology. We investigated the geographic distribution and morphological differentiation, and heritability of shell traits among populations of the freshwater lymnaeid snail Pectinidens diaphanus in Patagonia. Extensive field surveys across 196 freshwater sites revealed that the species occupies a broad range of lentic and lotic habitats and constitutes the only lymnaeid inhabiting southern Patagonia. While reproductive anatomical structures were conserved across populations, shell shape differed markedly among populations from contrasting habitat types, with population identity explaining nearly 50% of total shape variation. Populations from hydrologically unstable habitats (ponds and streams) exhibited more elongated shells and relatively smaller apertures, a pattern consistent with functional responses to hydroperiod variability and desiccation risk. To assess the heritability of this differentiation, we conducted a common-garden experiment across two generations. Shell shape differences between permanent- (lagoon) and temporary- (pond) habitat-derived populations persisted into the G2 generation reared under standardized laboratory conditions, indicating that the observed variation is not solely a response to local environmental conditions but includes a heritable component. Together, our findings demonstrate that P. diaphanus constitutes the sole lymnaeid across southern Patagonia, occupying a broader range than previously documented, and that populations show heritable shell differentiation potentially associated with contrasting freshwater habitats. By integrating large-scale biogeographic surveys with morphometric and experimental approaches, this study provides new insight into how habitat variation may contribute to ecological and evolutionary differentiation in freshwater gastropods.

Acoustic signaling is key to individual and species recognition, playing a major role in sexual and social communication. Since reproductive isolation is often maintained through pre-mating mechanisms, song can be an early isolating trait leading to assortative mating, promoting reproductive divergence, and potentially contributing to speciation. However, whether song differences alone are sufficient to prevent interbreeding or if other traits also contribute, remains a matter of debate. Playback experiments provide a more direct way to test the role of song as a reproductive barrier. Here, we use playback experiments to test the hypothesis that song acts as a pre-mating barrier in two recently diverged populations of an island passerine, the Canary Islands Chaffinch (Fringilla canariensis palmae), which inhabit ecologically distinct laurel and pine forests within the island of La Palma. Assuming that male song has diverged in the two habitats, we tested if territorial males from a given habitat responded differently to songs from intruding males from their own habitat or from the other habitat type, using a closely related mainland species as a control. We found that probability of response was weaker to songs of the closely related species and to the different-habitat birds than to songs of the same-habitat birds, but differences for the latter were weak. The intensity of response followed the same pattern. Overall, song divergence between laurel and pine forest chaffinches does not appear strong enough to cause clear behavioural discrimination against individuals from the alternative habitat. Other factors such as morphological and ecological divergence associated with adaptation to local resources might better explain population differentiation. However, testing female responses will be essential to determine whether songs convey lineage-specific information that may elicit assortative mating.

Historically, venom potencies have been assessed using measures of lethality, such as the median lethal dose (LD50). However, venoms may be selected primarily for their ability to rapidly incapacitate rather than cause mortality, meaning LD50 may not capture the efficacy of venoms in an ecological and evolutionary context. To capture this context, recent studies have adapted measures that assess venoms ability to rapidly incapacitate, such as the median effective dose (ED50). However, while ED50 values are expected to provide a more proximate assessment of ecological variation in venom potency, it is unknown whether historically available LD50 values are still useful proxies of ecologically relevant potency or whether they capture independent axes of venom variation. Here, we test the relationship between LD50 and ED50 in spider venoms by experimentally estimating LD50 and ED50 for 12 species and collating additional potency data for 40 species retrieved from the literature. We observed an isometric relationship between LD50 and ED50 in both analyses, showing these potency measures are both strongly coupled, with an increase in paralysis efficiency associated with a similar increase in lethality. Our results suggest that the functional aspects of venom potency, paralysis and lethality, are intrinsically linked, and due to this strong mechanistic coupling, historically available LD50 values may be used to compare general venom potencies in spiders, provided that they are based on the same prey model.

Escape behaviour directly influences survival, yet individuals often vary substantially in escape performance. Laboratory studies have documented trade-offs between anti-predator responses and life-history traits, but it remains unclear whether such trade-offs occur under natural predation risk. We studied a natural population of the field cricket Gryllus campestris. Mortality risk and behavioural performance are known to change with age in this species. We aimed to determine whether individuals expressing a higher escape response pay a cost in terms of a faster increase in mortality risk with age or a shorter lifespan. We quantified escape speed in response to a vibrational predation cue. We found no clear evidence for a trade-off between escape performance and lifespan or age-specific mortality risk. The relationship between escape speed and the among-individual effect of age differed between sexes: older males showed faster escape speeds compared with younger males, whereas younger females were faster than older females. This pattern is consistent with sex-specific selective disappearance. Individual baseline mortality risk varied with sex and escape speed, but age-dependent mortality did not. It suggests that such trade-offs in the wild may be context- or condition-dependent rather than reflecting a universal life-history trade-off.

Factors varying along elevational gradients impose strong aerodynamic and physiological constraints on powered flight, yet the internal anatomical correlates of flight performance in animals under such conditions remain poorly understood. In hummingbirds, sustained hovering requires extreme muscular power output, making the pectoralis muscle a key interface between environmental constraint and performance. We tested whether elevation is associated with variation in pectoralis microanatomy across three hummingbird assemblages spanning a [~]1500 m gradient in the Colombian Andes. Using tissue morphometry of trichrome-stained transverse sections of the pectoralis, we measured interstitial collagen fraction as a proxy for extracellular matrix investment and quantified fiber cross-sectional area, packing density, and size heterogeneity. Collagen investment varied across elevational bands, peaking at mid elevation ([~]1750 m) and declining toward high elevation ([~]2600 m). In contrast, muscle fibers were smaller and more densely packed at higher elevations. Variation among species was small relative to differences among elevational assemblages. Formal model comparisons provided limited support for non-linear responses to elevation, indicating that patterns across traits are better explained by interacting constraints than by a single monotonic response to factors varying along elevational gradients. These results show that hummingbird flight muscle microanatomy varies with elevation in a trait-specific manner, with the strongest evidence in fiber geometry. More broadly, our findings highlight that multiple components of muscle microarchitecture, including the extracellular matrix, vary in a context-dependent manner across elevational gradients in an extreme volant system.

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.

Species delimitation is a fundamental challenge in systematic biology, particularly for geographically variable taxa with hierarchical population structure and gene flow. Migration-aware coalescent models provide a powerful framework for investigating lineage divergence and accurately defining species boundaries. In this study, we combine statistical evaluations of gene flow with phylogenetic and population structure analyses to delimit species of fence lizards within the Sceloporus undulatus complex, a group characterized by extensive population subdivision, mitochondrial DNA introgression, and nuclear gene flow. We find that the undulatus complex exhibits uneven variation in genetic, morphological, and bioclimatic traits, resulting in variable distinctiveness among groups. In some cases, species boundaries are recognized by clear genetic discontinuities without gene flow. In others, shallow divergence, paraphyly, and gene flow produce leaky boundaries and fuzzy species limits. Mitochondrial introgression is extensive and concentrated at species boundaries, whereas nuclear gene flow occurs between only a few species and at much lower levels than within species. Neither within-species populations or species are substantially diverged across morphology or bioclimatic space, highlighting the limited utility of these traits for diagnosing species in this group. By integrating estimates of gene flow with phylogenetic and population structure analyses, this study provides a robust and biologically meaningful revised taxonomic framework for the undulatus complex that identifies independently evolving lineages as species.

Predation is a driving force in the ecology and evolution of prey, and primates exhibit diverse anti-predator strategies for minimizing risk. Because these behaviors can be costly, individuals must balance costs and benefits when responding to perceived threats. The cognitive capacity and behavioral plasticity of baboons make them an ideal taxon for studying the context-dependent variation in anti-predator strategies. Here, we used an autonomous, motion-activated playback experiment to study the behavioral responses of chacma baboons (Papio ursinus griseipes) to simulated predator encounters in Gorongosa National Park, Mozambique. We compared responses in 2021, when predator densities were relatively low, to responses in 2024, after predation increased due to lion (Panthera leo) population recovery and African wild dog (Lycaon pictus) reintroduction. We compared flight and vigilance responses to vocalizations of these common predators with responses to leopard (Panthera pardus), historically a key predator; spotted hyena (Crocuta crocuta), a rare predator; and cheetah (Acinonyx jubatus), absent historically and currently. We also assessed how responses varied with habitat, age-sex class, presence of offspring, and group size. Across 916 predator playbacks, baboons fled in 19% and displayed vigilance in 71% of trials. When predator density was higher, baboons displayed weakened antipredator responses, consistent with the risk allocation hypothesis. Baboons were more likely to flee in response to lion and wild dog cues. Juveniles fled more frequently than other demographic classes, while adult females with offspring were more vigilant. Overall, responses were highly heterogeneous, reflecting the substantial intraspecific variation and behavioral flexibility characteristic of baboons.

Dental morphology and wear patterns provide insight into the dietary adaptations and ecological niches of living and extinct herbivores. Traditional classification statistics such as Linear Discriminant Analysis (LDA) are limited by assumptions of linearity, normality, and homoscedasticity. This study quantifies mesowear, the shape of molar cusps resulting from occlusal wear, and evaluates the performance of non-linear machine learning models in predicting herbivore diets based on geometric morphometric (GMM) data from adult mandibular second molars (M2) in bovids. We applied Generalized Procrustes Analysis and Principal Component Analysis (PCA) to digitized occlusal shape coordinates from 132 M2 specimens across 64 species. Using the resulting principal component scores, we compared the classification accuracy of LDA with three non-linear models: Random Forest, K-Nearest Neighbors, and Gradient Boosting. While LDA achieved a cross-validated accuracy of just 31%, all non-linear models achieved 99% cross-validation accuracy and 90% test accuracy, demonstrating substantially improved performance. Misclassification analyses revealed that non-linear models more effectively captured complex shape differences, particularly among species with overlapping wear patterns. Our findings support the integration of machine learning with geometric morphometrics to quantify mesowear and improve dietary classification, providing a framework for robust paleoecological inference.

Escape responses are a critical behavioural mechanism influencing survival during predation events. In most species of teleosts and several other lower vertebrates, these responses are triggered by Mauthner cells (M-cells), which generate faster escapes (characterised by higher turning rates and shorter response latencies) than non-M-cell triggered responses. Most adult elasmobranchs lack M-cells and consequently exhibit slower escape response timing than teleosts. Spotted Ratfish (Hydrolagus colliei) are a notable exception in that adults possess M-cells, yet their escape response performance has not been explored. Here, we quantify the kinematics and timing of ratfish escape responses elicited by a mechano-acoustic stimulus. We show that ratfish exhibit higher turning rates and shorter response latencies than other adult chondrichthyans, though their response latencies are also significantly longer than those of teleosts. These findings suggest that retention of M-cells confers enhanced escape performance in ratfish, with important implications for their vulnerability to predator attacks. Summary statementThis study reveals that adult Spotted Ratfish (Hydrolagus colliei) show fast escape response with a performance that is intermediate between teleosts and previously studied elasmobranchs.

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.

Predator-prey interactions are key drivers of behavioural and life-history evolution, yet their mechanisms remain difficult to study in natural contexts. The nematode Pristionchus pacificus is a model predator, but most studies exploring its behaviours use Caenorhabditis elegans as prey, a species that it likely only rarely encountered in nature. Here, we examine predation within nematode communities associated with beetle carcasses, the native necromenic habitat of P. pacificus. We identify Oscheius myriophilus as a cohabiting species, likely representing natural prey. Using predatory assays, automated tracking, and machine-learning-based behavioural analysis, we show that P. pacificus actively kills and consumes O. myriophilus. Strikingly, predation rates are lower than those observed for C. elegans, suggesting partial resistance or reciprocal adaptation in O. myriophilus. Consistent with this, O. myriophilus exhibits a mixed reproductive strategy, with early oviposition followed by ovoviviparity and matricide. As later developmental stages are more resistant to predation, internal hatching may protect offspring while providing maternal resources for development. These findings establish these nematodes as a tractable model for investigating predator-prey interactions and their evolutionary consequences, highlighting how behavioural strategies and life-history traits can co-evolve in natural communities.

Multimodal communication plays a central role in animal behavior, particularly when individuals must integrate information from different sensory channels to make rapid decisions. In aquatic environments, chemical and visual cues differ markedly in their spatial and temporal properties, such that chemical signals may be constrained by limited spatial resolution and temporal instability, potentially requiring visual information to reliably guide social decisions. In decapod crustaceans, both cue types are known to mediate reproduction, yet their relative contribution to mate-location behavior remains unclear. Here, we tested how visual and chemical cues from males influence mate-location behavior in females of the prawn Macrobrachium rosenbergii. Females were placed in a central arena and exposed to four stimulus configurations combining visual cues (a life-size photograph of a male or a control background) and chemical cues (water from an aquarium with or without a male). Attraction was quantified as the time spent in each half of the arena. Females showed no directional preference when exposed to chemical cues alone or when visual and chemical cues were spatially incongruent. In contrast, females spent significantly more time near male-associated stimuli only when visual and chemical cues were spatially congruent. These results indicate that mate-location behavior in this species depends on multimodal integration with a strong contextual dependence on visual information, which appears to gate the effectiveness of chemical cues. Spatially congruent multimodal signals are therefore necessary to guide orientation during mate search, suggesting that disruption of visual or chemical information in aquaculture systems may impair mating efficiency.