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Personality variation, defined as among‐individual differences in behaviour that are repeatable across time and context, is widely reported across animal taxa. From an evolutionary perspective, characterising the amount and structure of this variation is useful since differences among individuals are the raw material for adaptive behavioural evolution. However, behavioural variation among individuals also has implications for more applied areas of evolution and ecology—from invasion biology to ecotoxicology and selective breeding in captive systems. Here, we investigate the structure of personality variation in the red cherry shrimp, Neocaridina heteropoda, a popular ornamental species that is readily kept and bred under laboratory conditions and is emerging as a decapod crustacean model across these fields, but for which basic biological, ecological and behavioural data are limited. Using two assays and a repeated measures approach, we quantify behaviours putatively indicative of shy–bold variation and test for sexual dimorphism and/or size‐dependent behaviours (as predicted by some state‐dependent models of personality). We find moderate‐to‐high behavioural repeatabilities in most traits. Although strong individual‐level correlations across behaviours are consistent with a major personality axis underlying these observed traits, the multivariate structure of personality variation does not fully match a priori expectations of a shy–bold axis. This may reflect our ecological naivety with respect to what really constitutes bolder, more risk‐prone, behaviour in this species. We find no evidence for sexual dimorphism and only weak support for size‐dependent behaviour. Our study contributes to the growing literature describing behavioural variation in aquatic invertebrates. Furthermore, it lays a foundation for further studies harnessing the potential of this emerging model system. In particular, this existing behavioural variation could be functionally linked to life‐history traits and invasive success and serve as a target of artificial selection or bioassays. It thus holds significant promise in applied research across ecotoxicology, aquaculture and invasion biology. [ABSTRACT FROM AUTHOR]

Social interactions can give rise to indirect genetic effects (IGEs), which occur when genes expressed in one individual affect the phenotype of another individual. The evolutionary dynamics of traits can be altered when there are IGEs. Sex often involves indirect effects arising from first‐order (current) or second‐order (prior) social interactions, yet IGEs are infrequently quantified for reproductive behaviors. Here, we use experimental populations of burying beetles that have experienced bidirectional selection on mating rate to test for social plasticity and IGEs associated with focal males mating with a female either without (first‐order effect) or with (second‐order effect) prior exposure to a competitor, and resource defense behavior (first‐order effect). Additive IGEs were detected for mating rate arising from (first‐order) interactions with females. For resource defense behavior, a standard variance partitioning analysis provided no evidence of additive genetic variance—either direct or indirect. However, behavior was predicted by focal size relative to that of the competitor, and size is also heritable. Assuming that behavior is causally dependent on relative size, this implies that both DGEs and IGEs do occur (and may potentially interact). The relative contribution of IGEs may differ among social behaviors related to mating which has consequences for the evolutionary trajectories of multivariate traits. Behavioral traits involved in sexual selection can have similar phenotypically plastic responses to a change in social environment but may have quite different underlying architecture so will respond differently to selection. This highlights the importance of quantifying indirect genetic effects (IGEs) as well as direct genetic effects (DGEs) of suites of related traits to understand how they will evolve. [ABSTRACT FROM AUTHOR]

It is widely expected that physiological and behavioral stress responses will be integrated within divergent stress-coping styles ( SCS) and that these may represent opposite ends of a continuously varying reactive-proactive axis. If such a model is valid, then stress response traits should be repeatable and physiological and behavioral responses should also change in an integrated manner along a major axis of among-individual variation. While there is some evidence of association between endocrine and behavioral stress response traits, few studies incorporate repeated observations of both. To test this model, we use a multivariate, repeated measures approach in a captive-bred population of Xiphophorus birchmanni. We quantify among-individual variation in behavioral stress response to an open field trial ( OFT) with simulated predator attack ( SPA) and measure waterborne steroid hormone levels (cortisol, 11-ketotestosterone) before and after exposure. Under the mild stress stimulus ( OFT), (multivariate) behavioral variation among individuals was consistent with a strong axis of personality (shy-bold) or coping style (reactive-proactive) variation. However, behavioral responses to a moderate stressor ( SPA) were less repeatable, and robust statistical support for repeatable endocrine state over the full sampling period was limited to 11-ketotestosterone. Although post hoc analysis suggested cortisol expression was repeatable over short time periods, qualitative relationships between behavior and glucocorticoid levels were counter to our a priori expectations. Thus, while our results clearly show among-individual differences in behavioral and endocrine traits associated with stress response, the correlation structure between these is not consistent with a simple proactive-reactive axis of integrated stress-coping style. Additionally, the low repeatability of cortisol suggests caution is warranted if single observations (or indeed repeat measures over short sampling periods) of glucocorticoid traits are used in ecological or evolutionary studies focussed at the individual level. [ABSTRACT FROM AUTHOR]