Evolutionary Biology

Data on the shape of a group of organisms can be conceptualized as forming a point cloud in the multivariate space of measurement. This is literally true for traditional linear measures, while in a geometric morphometric context the cloud resides in Kendalls shape space, tangent to the true shape space. Regardless of the method of construction, the topology of this point cloud, or phenotypic (hyper)ellipse, is a beguiling target for evolutionary analysis. Reordination of the axes will not change the geometry of this phenotypic ellipse, and the notion that its geometry carries a meaningful biological signal is an old idea; but the character of this signal is often elusive. This paper explores the application of the most commonly used parameter designed to summarize differences in phenotypic ellipse geometry (relative eigenvalue variance, or Vrel), and demonstrates that it is incapable of differentiating between several plausible ways in which phenotypic ellipse geometry might differ among species, because it confounds three separate parameters necessary to describe the ellipse. Two example data sets are analyzed to illustrate variability in phenotypic ellipse geometry and draw conclusions about observed differences. The first case compares wolves to domestic dogs, and replicates previous findings of much greater variance yet tighter integration in dogs. This calls into question the simple model of a single peak in the fitness landscape of dogs. The second example comprises geometric morphometric landmarks from the jaws of a clade of sigmodontine rodents, and allows comparison of ellipse geometry in a phylogenetically controlled setting with qualitative ecological categories. Three parameters are found to vary in concert along a grade of most to least ecologically specialized: the phenotypic variance, the effective rank (dimensionality), and the degree of covariance (Vrel and related metrics). Use of all three of these quantities to characterize the geometry of the phenotypic ellipse is advocated, as all are necessary to characterize how variance is distributed in the ellipse in different taxa. The phenotypic ellipse geometries illustrated here appear to reflect something of the geometry of the adaptive peak upon which each taxon sits; or that they represent (aspects of) the mapping function of adaptive peak to phenotypic ellipse, in ways first predicted by Simpson in the twentieth century.

Dense semilandmarks describe 3D surfaces with hundreds to thousands of points, and sliding them by bending energy or Procrustes distance is a near-universal default. Three questions remain open: does dense sampling add shape beyond fixed landmarks, how many points are needed, and does sliding help or harm? Real specimens cannot answer them: the true correspondence is unknown. We tested two workflows, ALPACA (single-template registration) and DeCAL (landmark-anchored correspondence), on 496 mouse skulls at 250-1,000 points, with and without sliding, scored by surface reconstruction. We repeated it on 500 synthetic skulls with exact correspondence, measuring each point's distance to its true homologue. Dense semilandmarks lowered error for almost every specimen; the fixed landmarks added little but supplied anchoring the semilandmarks could not, and the anchored method was more accurate. The benefit saturated near 250 points for ALPACA but kept improving to 1,000 for DeCAL. Procrustes-distance sliding harmed every configuration; bending-energy sliding helped only a poor, landmark-free correspondence, vanishing once anatomical anchors spanned the form. Match the sliding decision to the correspondence in hand: relax a poor one, leave a good one alone, never slide toward the mean. Known-correspondence specimens offer a general test of landmarking and sliding against ground truth.

Morphological measurements underpin a wide range of ecological and evolutionary research, yet the manual landmarking workflows on which most morphometric studies depend remain a persistent bottleneck that limits both the pace and scale of biological research. Machine learning offers compelling solutions, but most automated landmarking tools require substantial computational expertise, creating a gap between technical capability and practical adoption by biologists. Here, we present LizardMorph, an integrated machine learning pipeline and web-based interface for semi-automated anatomical landmark detection on biological images. LizardMorph couples a fine-tuned ML-Morph shape predictor with an accessible, browser-based interface that enables researchers to upload images, review automated landmark predictions, interactively correct outliers through point-and-click editing, and export results in standard morphometric formats--all without programming expertise or local software installation. Using dorsal X-ray radiographs of Anolis lizards with 34 anatomical landmarks as a proof-of-concept, we show that the ML-Morph model achieves high predictive accuracy, with landmarks on well-defined skeletal structures predicted with 100% accuracy within a 1 mm tolerance threshold. A controlled user study comparing LizardMorph against traditional manual landmarking (TpsDig2) demonstrated significant efficiency gains: experienced annotators completed LizardMorph landmark verification 37.5% faster than manual annotation. Extrapolated to batch processing 1,000 lizards, LizardMorph saves experienced researchers approximately 6.5 hours of manual processing time. Critically, LizardMorph implements a human-in-the-loop design in which automated predictions serve as editable starting points, preserving researcher oversight and enabling correction of the occasional large-error outliers that would be unacceptable in fully automated workflows. LizardMorph is freely available as an open-source tool and provides a replicable framework for developing ML-assisted annotation tools that can democratize access to high-quality morphometric analysis across diverse biological research communities.

Perceptual experiments show that listeners recognize female speakers with lower accuracy than male speakers. Automatic speaker recognition systems may also show performance bias against female speakers even when training data sets are gender balanced. The underlying reasons for this discrepancy are unclear. Here, we apply geometric morphometrics to quantify sex-related morphological vocal tract disparity -- the extent of shape variation -- across both resting and articulatory configurations. We find that male speakers exhibit greater disparity in both resting and articulatory configurations. This morphological idiosyncrasy may in turn generate more discriminable acoustic signatures and offer a biological explanation for higher recognition accuracies for male voices by humans and machines. Our results suggest that innate variation in vocal tract morphology may contribute to performance bias in voice technology and voice perception by human listeners.

Reconstructing ancestral morphologies on a phylogenetic tree is a central task in evolutionary morphometrics. Established reconstruction methods, including multivariate Brownian-motion approaches, rely on linear assumptions and do not directly model the correlations between landmarks within a shape, which can oversimplify the reconstructed morphology. The DICAROS method (Diffeomorphic Independent Contrasts for Ancestral Reconstruction of Shapes; Severinsen et al., 2026) instead fuses sibling shapes along branches with large-deformation diffeomorphic (LDDMM) landmark dynamics that model these correlations, so that ancestors remain on the shape manifold. DICAROS was shown to outperform ordinary least-squares, Brownian-motion, and penalized-likelihood reconstruction, particularly on non-symmetric trees. The dicaros package repackages that pipeline as a documented, pip-installable tool that runs on arbitrary landmark datasets from a single command. It handles 2D and 3D landmarks, Newick and NEXUS trees, a choice of Euclidean or Frechet species means, optional anchor-based alignment, and tips backed by a single specimen, and it returns the reconstructed shapes for all nodes together with the tree relabelled at its internal nodes. We demonstrate dicaros on two new datasets: a 2D leaf dataset (217 species) and a 3D guenon skull dataset (22 species).

The general random walk model (GRW) of Hunt (2006) is used to infer directional evolution in mean trait values from sparse fossil data by modeling phenotypic change as the accumulated result of small steps with mean step sizes and step variances. Using simulations and real data cases, Ergon (2026) showed that the step variances can be estimated reasonably well only when the mean trait values have small measurement errors, while for fossil data with realistic measurement errors they appear to be extremely difficult to find, and they are often found to be negative. In the simulations Ergon (2026) assumed that the true phenotypic mean values were known. Here, I essentially repeat these simulations under the assumption that only mean trait values with large measurement errors are known, and based on weighted mean squared error (WMSE) comparisons the conclusion is that weighted least squares (WLS) is a better method than GRW. A second conclusion is that WLS is a better method also in the possibly rare cases with large measurement errors where the GRW parameters are estimated well. The GRW method is simply not flexible enough to handle such cases. A third conclusion is that Akaike Information Criterion (AIC) results for GRW models with large measurement errors relative to the step variance may be overly optimistic.

The human bony labyrinth has attracted increasing interest because of its taxonomic, evolutionary, and functional significance. Although sexual dimorphism has been reported in several aspects of the temporal bone, the extent to which sex, age, size, and allometry contribute to labyrinth shape variation remains poorly understood. Here, we investigated patterns of sexual shape variation in the human bony labyrinth using three-dimensional geometric morphometrics in a sample of 98 archaeological individuals from South America with known genomic sex. Centroid size and allometric effects were assessed in a subset of 90 individuals with comparable metric scaling. In addition to analysing the complete labyrinth, the cochlea and semicircular canals were examined separately to evaluate region-specific patterns of sexual shape variation. Principal Component Analysis showed extensive overlap between females and males, and overall labyrinth shape did not differ significantly between sexes. Males exhibited significantly larger labyrinths than females, and centroid size explained a small but significant proportion of overall shape variation. Regional analyses showed no evidence of significant sexual shape differences in the cochlea or in any individual semicircular canal when analysed separately. In contrast, the combined semicircular canal system exhibited subtle but significant sexual shape variation independent of centroid size, whereas morphological disparity did not differ between sexes. The geometric comparison of the female and male consensus configurations further showed that sexual shape variation was regionally heterogeneous. Whereas the cochlea exhibited a pattern of localized changes with low directional coherence, the semicircular canals displayed more coordinated regional shape changes. The male consensus also exhibited slightly higher canal circularity across all three semicircular canals, particularly the posterior canal, while differences in canal-plane orientation remained minimal. These findings demonstrate that sexual shape variation in the human bony labyrinth is subtle and anatomically partitioned among its components. Although significant sex differences in centroid size were detected across most anatomical regions, overall labyrinth shape and cochlear morphology were primarily influenced by allometry, whereas significant sex-related shape differences were detected only when the semicircular canals were considered as an integrated anatomical system. These findings demonstrate that sexual dimorphism in the human bony labyrinth is subtle but regionally heterogeneous, with the cochlea and semicircular canals exhibiting distinct patterns of shape variation, suggesting that these structures are influenced by different developmental, functional, and evolutionary processes.

The nautilus (Nautilus sp.) is an early-branching cephalopods. It retains several conchiferan synapomorphies, including an external planispiral biomineralized shell. The shells complex structure allows it to withstand hydrostatic pressure, control buoyancy, and protect against external hazards. In this study, we comprehensively examined shell microstructures across different shell components and regions representing various ontogenetic stages in two adult museum shell specimens. We found that the nautilus shell is composed of five microstructural types (spherulitic, prismatic, nacreous, semi-prismatic, and irregularly oriented prismatic structures) organized into layered architectures within individual shell components and coordinated across the shell as an integrated system. Our observations highlight transitions between distinct microstructures within and across shell components and local variation within individual components such as the dorsal and ventral shell walls, suggesting that these patterns may contribute to shell strength and overall mechanical performance. Variation in caecum morphology suggests that this structure may be developmentally plastic and subject to relatively relaxed structural constraints. These findings show that the Nautilus shell is an integrated biomineral system in which diverse microstructures are organized across shell components to meet functional demands and provide the mechanical strength needed for survival.

Gliding enables mammals to forage and escape from predators by moving between discontinuous forests. Its benefits depend not only on glide distance but also on the ability to decelerate and land safely. This study developed a theoretical framework linking glide distance, gliding velocity, aerodynamic braking, body mass, and braking distance. Twenty-two representative distance-velocity observations from eight studies and five species were compiled. Among distance-velocity models, log-distance and saturated with V0 models received nearly equivalent support. Both models predicted increasing velocity with glide distance, with the rate of increase declining at longer distances. For a 1 kg animal undergoing a 60% reduction in velocity, predicted kinetic energy remaining immediately before contact increased from 4.80-5.14J at 20 m to 8.13-8.90 J at 80 m. This velocity reduction corresponded to a dissipation of 84% of approach kinetic energy before contact. Over a braking distance of 1 m, the required mean deceleration increased from 2.57-2.75 g at 20 m to 4.35-4.77 g at 80 m. At 80 m, shortening the braking distance from 4 to 0.5 m increased the required deceleration from 1.09-1.19 to 8.70-9.53 g. These results indicate that the absolute energetic and deceleration requirements of landing increase with glide distance, even when velocity is close to an asymptote. These results provide a quantitative basis for considering aerodynamic braking and landing requirements alongside conventional measures of glide performance. Summary statementModels quantify how glide distance, aerodynamic braking, and braking distance affect pre-contact kinetic energy and deceleration requirements in gliding mammals.

Animal personality is the expression of consistent among-individual variation in a behavioural trait across time and context. The application of this theory to behavioural research provides a valuable framework to investigate the among- and within-individual variation in behaviour. The animal personality theory is particularly relevant to understand and diagnostic fish welfare. It can be integrated within the nature-based welfare framework, which emphasizes the expression of species-specific behaviours and the maintenance of consistent behavioural patterns over time. Because behavioural trait such as boldness may be closely linked to other functional phenotypes, such associations reflect the broader concept of animal personality, whereby a behavioural trait can covary with another phenotypic trait to support an adaptive responses to environmental conditions. Although these relationships are both species and context dependent, they are consistently shaped by environmental conditions and environmental complexity tend to promote species specific behaviours and reduce maladaptive traits. Here we examined how structural environmental complexity shapes personality in Arctic charr and their covarying functional phenotypes, specifically growth rate and brain size. We propose that environmental complexity promotes alternative behavioural and functional phenotypes through multivariate phenotypic plasticity. We found that environmental complexity did not influence mean boldness between both treatments, but repeatability of boldness in the complex environment was remarkably consistent over a longer-term period, while estimates collapse after seven days in the plain treatment. Our findings are a clear evidence that environmental complexity foster stable behavioural trait expression and that a plain environment may suppress personality. Our results provide compelling evidence that behavioural structure and dynamics are embedded within patterns of behavioural variance. Although we found no support for behavioural covariation or associations with growth rate and brain size, we suggest that the animal personality framework may offer a valuable approach for diagnosing fish welfare issues through the partitioning of behavioural variance.

Recognizing patterns in functional trait evolution is a necessary step in testing macroevolutionary questions. Quantification of these patterns and interpretation of their generative processes relies on an ever-expanding suite of comparative approaches, but current methods oversimplify the process-to-pattern mapping. This simplification may promote binary classifications of patterns and their drivers, such as adaptive versus non-adaptive or constrained versus unconstrained. A potentially more robust and evolutionarily informative alternative is to fit an expanded suite of evolutionary models at different levels of taxonomic or ecological resolution to reveal how evolutionary drivers imprint simultaneously on observed patterns of trait evolution. Here, we perform a clade-wide analysis of functional trait evolution across Anura (frogs and toads). Focusing on three functionally important traits, we quantify the relative fit of random, directional, and bounded models at the intra- and inter-microhabitat levels to explore how changes in trait function across microhabitats translate into different evolutionary regimes. We recover heterogeneous regime-level distributions of model support that imply complex underlying evolutionary dynamics, while also revealing methodological biases and model identifiability issues. These findings underscore the need to develop more robust tools for evolutionary model fitting and advance beyond binary frameworks for interpreting evolutionary processes.

This study investigates the impact temperature-induced vertebral anomalies have on the C-start escape response of Astyanax mexicanus, a model species in evolutionary developmental biology. Employing three temperature treatments to induce varying degrees of skeletal anomalies, we assessed their effects on key swimming performance metrics including, C-start time, curvature coefficient, head displacement distance, and displacement velocity. Through the use of linear mixed models and generalized linear mixed models, our results reveal that specific anomalies such as vertebral fusions and anomalous haemal and neural spines affected the curving ability of C-start escape responses. However, these did not negatively impact other performance parameters, with velocity, distance, and response time showing no significant impacts from any anomaly types, when assessed individually. This suggests a complex interplay between structural deformities and compensatory physiological mechanisms that maintain functional performance. Other variables measured had a stronger and significant impact on swimming performance, including standard length, vertebral number, and temperature treatment, which influenced escape speed, curving ability, and overall locomotor performance. Our findings challenge conventional perceptions about the debilitating impact of vertebral anomalies, indicating that many affected fish can still effectively perform escape maneuvers critical for survival.

Brain size and structure are hypothesized to be adaptively designed to satisfy the behavioral requirements of securing food and living socially. The importance of these socioecological and sociobiological selective forces in brain evolution is constantly debated. Socioecological divergence is striking in the Neotropical ant genus Neoponera: N. apicalis is a generalist solitary predator forming small colonies of ~100 whereas N. commutata colonies are approximately 10 times as large and workers pheromonally organize cooperatively raids only on Syntermes termite colonies. We interspecifically compared the size and structure of the compound eyes, size and number of antennal glomeruli, mosaic brain scaling and synaptic processing (microglomeruli-MG). Our results indicate that N. apicalis workers have a larger number of ommatidia, antennal lobe glomeruli, and allometrically larger antennal and optic lobes than N. commutata. These sensory traits were associated with differences in higher-order processing architectures in the mushroom body (MB) microglomeruli (MG). N. commutata workers had an allometrically larger MB, perhaps due to their socially complex chemical foraging communication, although MG density in N. apicalis was higher in both the MB lip and collar, regions associated with processing olfactory and visual information, respectively. The increase in MG density in N. apicalis may be associated with higher demands for navigation, learning, and memory, as well as a higher density of antennal lobe glomeruli to support prey odor discrimination. In contrast, N. commutata workers had larger ommatidia and antennal lobe glomeruli. Larger ommatidia correlate with their diurnal/nocturnal habits and a larger MB Our findings indicate that differences in behavioral performance demands associated with socioecological differentiation are reflected in variation in visual and olfactory system structure, brain size, mosaicism, and synaptic organization. Our results support both social and ecological brain hypothesis as drivers of mosaic brain evolution.

Adult sex ratios in mammals are usually female-biased, but the northern mole vole (Ellobius talpinus) (Pallas, 1770), a cooperatively breeding subterranean rodent, shows a persistent male bias that increases with age. Combining four years of capture-mark-recapture data with radiographic age estimation and genetic parentage data, we modeled apparent survival and state transitions (young-of-the-year, breeder, non-breeder) separately by sex. Young individuals showed significantly lower apparent survival than adults in both sexes, consistent with dispersal occurring predominantly in the first year of life. Within each age class, females showed consistently lower apparent survival than males, and this pattern held within breeding and non-breeding status groups alike, with female breeders showing lower apparent survival than male breeders. These results point to female-biased natal dispersal, an atypical pattern for mammals. We propose that faster turnover of reproductive females than males, in combination with singular breeding, favor female dispersal in search of vacant breeding positions, while promoting male philopatry and facultative polyandry.

Phenotypic differences among populations can arise through heritable genetic divergence, phenotypic plasticity, or both, making it difficult to determine whether trait-environment correlations observed in nature reflect adaptive evolution. Within threespine stickleback (Gasterosteus aculeatus) studies, numerous document morphological differences among allopatric-, parapatric-, and even sympatric populations. These phenotypic differences among populations are often correlated with diet and lake habitat (e.g., lake size), suggesting an adaptive value to the population differences. However, many studies of ecomorphological divergence in stickleback use wild-caught stickleback, which may differ due to evolution or plasticity. Although common garden experiments have confirmed that population differences can be heritable, such experiments typically entail small numbers of populations. Consequently, we still do not know to what extent well-known trait-environment correlations in stickleback are a result of evolution. To address this gap, we reared stickleback embryos from 27 lake populations on Vancouver Island, in a laboratory environment. Morphological differences among populations persist in common-garden fish, confirming a large role for divergent evolution. These heritable differences were associated with environmental variation among lakes, implying an adaptive value. However, some well-known trait-environment relationships in stickleback did not persist in common-garden fish and may be primarily plastic.

Reproductive success requires allocating effort across lifespan in a manner that balances the risk of early mortality against the benefit of higher fecundity or parental expertise that increase with body size or age. Here we report a cross-taxonomic analysis of reproductive schedules in plants, animals, and humans, showing that peak reproductive effort consistently occurs at approximately 1/e (~37%) of species-specific maximum lifespan. The pattern is robust across major phylogenetic groups and independent of absolute lifespan. This convergence is both logically and numerically consistent with the optimal stopping fraction (1/e), which maximizes the probability of selecting a superior option under uncertainty by delaying commitment until 1/e of the available options have been examined. By integrating population dynamics and empirical data with a formal decision-theoretic model, our results suggest a striking previously unrecognized quantitative regularity linking lifespan and reproductive timing. These findings provide a unifying perspective on life-history evolution and suggest that complex biological scheduling strategies are governed by probabilistic principles.

Ecogeographic rules predict that endotherms inhabiting colder environments exhibit larger body sizes and shorter appendages to reduce heat loss. However, these hypotheses have largely been tested using size-based traits, leaving it unclear whether climatic adaptation also alters body proportions that more directly influence surface-area-to-volume ratio. Here, I examined ecogeographic variation in body shape, body size, and relative limb lengths across climatic gradients in three western North American mustelids: American ermine (Mustela richardsonii), American mink (Neogale vison), and Pacific marten (Martes caurina). I then modeled how variation in body shape and size affected surface-area-to-volume ratio. Body size increased in colder climates in all three species, consistently supporting Bergmanns rule. In contrast, only ermines became stouter in colder climates, whereas body shape remained unchanged in minks and martens. Patterns of appendage variation also differed: ermines and martens exhibited relatively longer limbs in colder climates, contrary to Allens rule, whereas only minks exhibited relatively shorter hindlimbs. Modeling showed that increased body size reduced surface-area-to- volume ratio in all species, whereas body shape contributed only in ermines. These findings demonstrate that body shape, body size, and appendage lengths respond independently to climatic gradients, with species-specific ecological and functional constraints shaping thermoregulatory adaptation.

Sharks exhibit extraordinary morphological diversity across a wide range of ecological niches, yet large-scale, high-resolution digital datasets of their internal anatomy remain limited. Here we present an open-access 3D shark anatomical repository derived from published X-ray computed tomography (CT) data, featuring manually segmented and systematically annotated models of the chondrocranium, visceral arches, axial skeleton, musculature, and viscera in standard STL format. The dataset comprises 117 individuals, representing 72 species across 25 families and all nine extant shark orders, with 115 full-body reconstructions and two head-only models. This open-access dataset offers a comprehensive resource for comparative anatomy, biomechanical simulations, evolutionary developmental biology and biomimetics research of extant sharks.

Tessellated calcified cartilage (TCC) is a hallmark of the chondrichthyan skeleton, yet its development early in ontogeny across the four major groups (batoids, galeomorphs, squalomorphs, and holocephalans) remains poorly understood. Specialised traits of TCC, such as multi-layered TCC and internal mineralised trabeculae, typically develop in response to feeding mechanics. In this study, we evaluated TCC morphology in the jaws of 12 representative taxa to observe its structure at an early ontogenetic stage to determine whether these specialised features had yet developed. Batoids consistently exhibited well-developed, homogeneous, polygonal tesserae early in ontogeny regardless of jaw morphology or feeding habit. In contrast, galeomorphs displayed high morphological heterogeneity. Notably, we document the first report of an extensive internal trabecular network in a non-batoid elasmobranch, observed in Ginglymostoma cirratum, which may serve to resist the mechanical pressures of specialised suction feeding. Furthermore, we identified voussoir tesserae in galeomorphs for the first time, extending their documented presence across all elasmobranch groups, where they display an inverted aspect ratio (wider than tall) compared to mature forms. The durophagous Mustelus mustelus exhibited surprisingly poor TCC development despite being a durophagous feeder, pointing to a pronounced ontogenetic lag. In Squatina oculata, TCC was characterised by large and thick tesserae and extensive fused tesseral regions which may relate to its explosive ambush predation mode, whereas the holocephalan Chimaera exhibited a poorly mineralized, mesh-like structure without resolvable discrete tesserae or trabeculae-matching findings from previous studies. Across all specimens, multi-layered TCC was absent, confirming that multi-layering develops later in ontogeny. These results demonstrate that generalised models of TCC development based on one group or a few taxa fail to capture the broader diversity of TCC morphology. It also opens up many exciting avenues for further study, and forms the basis for comparisons with fossil chondrichthyans, to investigate the evolution of TCC.

Parental qualities can influence the development and fitness of their offspring via genetic and non-genetic effects. Although these effects are often linked to parental phenotypes, the effect of parental genetic variation linked with relevant phenotypes is less well understood. We performed full factorial crosses based on parental genotypes for an age-at-maturity-related gene, vgll3, to investigate how the parental genotypes influence Atlantic salmon (Salmo salar) offspring survival, growth, and development in their early life. Beyond the connection with age at maturity, the additional association between vgll3 and body condition in Atlantic salmon offers a potential pathway by which the maternal vgll3 genotype could influence offspring early life fitness. Combined with measurements of maternal phenotype and egg characteristics, the crossing design therefore allowed us to disentangle the maternal and paternal genetic and non-genetic contributions to variation in offspring survival and phenotypic traits. The phenotypic traits measured were hatching length and yolk sac area, growth, and yolk sac consumption and conversion efficiency. Parental vgll3 genotype did not influence the majority of our measured egg traits or alevin traits except for a genetic effect of paternal vgll3 genotype on offspring survival, whereby the paternal late maturation allele was associated with higher survival. Maternal effects were strongest for survival and for traits associated with hatching and weaker for alevin growth and yolk sac usage. Paternal effects on the measured alevin traits were negligible. The results from our study demonstrate that both maternal and paternal effects have the potential to influence offspring early life fitness traits.