In this study, we investigate whether and how arena design of emergence tests (a commonly used boldness assay where the latency to emerge from a start box is measured) can affect the behaviour of the subject animals. We used two populations of wild brown trout fry, captured on their hatching grounds, and measured emergence latency in arenas with two different sizes of start-box gates and two different environments into which the fish emerges from the start box (barren and complex), in a factorial design. We found that arena design affected the behaviour of the fish, but only in one of the populations. In the affected population, a large start-box gate in combination with a barren environment reduced emergence latency. Furthermore, the time from leaving the box until entering another compartment on the opposite side of the arena was shorter in a barren environment as compared to a more complex environment. We also found that smaller brown trout fry generally showed lower tendency for emerging from the start box at all. The results of this study suggest that direct comparisons among results from experiments using different arena designs may be problematic and highlight the importance of reporting details of arena design in publications.

In recent years, the field of sexual selection has exploded, with advances in theoretical and empirical research complementing each other in exciting ways. This perspective piece is the product of a “stock-taking” workshop on sexual selection and sexual conflict. Our aim is to identify and deliberate on outstanding questions and to stimulate discussion rather than provide a comprehensive overview of the entire field. These questions are organized into four thematic sections we deem essential to the field. First we focus on the evolution of mate choice and mating systems. Variation in mate quality can generate both competition and choice in the opposite sex, with implications for the evolution of mating systems. Limitations on mate choice may dictate the importance of direct vs. indirect benefits in mating decisions and consequently, mating systems, especially with regard to polyandry. Second, we focus on how sender and receiver mechanisms shape signal design. Mediation of honest signal content likely depends on integration of temporally variable social and physiological costs that are challenging to measure. We view the neuroethology of sensory and cognitive receiver biases as the main key to signal form and the ‘aesthetic sense’ proposed by Darwin. Since a receiver bias is sufficient to both initiate and drive ornament or armament exaggeration, without a genetically correlated or even coevolving receiver, this may be the appropriate ‘null model’ of sexual selection. Thirdly, we focus on the genetic architecture of sexually selected traits. Despite advances in modern molecular techniques, the number and identity of genes underlying performance, display and secondary sexual traits remains largely unknown. In-depth investigations into the genetic basis of sexual dimorphism in the context of long-term field studies will reveal constraints and trajectories of sexually selected trait evolution. Finally, we focus on sexual selection and conflict as drivers of speciation. Population divergence and speciation are often influenced by an interplay between sexual and natural selection. The extent to which sexual selection promotes or counteracts population divergence may vary depending on the genetic architecture of traits as well as the covariance between mating competition and local adaptation. Additionally, post-copulatory processes, such as selection against heterospecific sperm, may influence the importance of sexual selection in speciation. We propose that efforts to resolve these four themes can catalyze conceptual progress in the field of sexual selection, and we offer potential avenues of research to advance this progress.

Reported effects of inbreeding vary among taxa and may depend on a number of factors, including what trait is measured, temporal variability, parental effects, or life history stage. To understand the effects of inbreeding during early life history stages, we estimated the effects of individual-level heterozygosity on hatching success and first year survival in a Swedish population of sand lizards (Lacerta agilis) over a period of almost a decade, using over 4000 eggs, 400 clutches, and over 3000 juveniles. Heterozygosity had a positive effect on hatching success, in standardized laboratory conditions, but no effect on first year survival. Also, both of these measures of viability varied across the years of the study, demonstrating the importance of temporal heterogeneity in pre and post-hatching conditions. Finally, we identified both paternal and maternal identity effects on hatching success. Thus, we show that selection on heterozygosity was not consistent across developmental life stages, emphasizing the need of considering a number of ontogenic stages, as well as potential parental and environmental effects, when studying the effects of heterozygosity on viability in natural populations.Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

The field of sexual selection has burgeoned with research into trait evolution in the context of ecology, sociality, phylogeny, natural selection, and sexual conflict. This paper is the product of a “stock-taking” workshop; our aim is to stimulate discussion, not to provide an exhaustive review. We identify outstanding questions organized into four thematic sections. 1) Evolution of mate choice and mating systems. Variation in mate quality can generate mating competition and choice in either sex with implications for the evolution of mating systems. Limitations on mate choice may dictate the importance of direct vs. indirect benefits in mating decisions and consequently, mating systems. Specifically, polyandry evolves in response to the strength of pre- vs. post-copulatory selection. The evolution of polyandry may be related to diversity of pathogens and Major Histocompatibility Complex (MHC) genes. MHC genes are also potential cues of kinship in avoidance of inbreeding. The balance between inbreeding avoidance and inclusive fitness in mating decisions deserves greater attention. 2) Sender and receiver mechanisms shaping signal design. Mediation of honest signal content likely depends on integration of temporally variable social and physiological costs that are a challenge to measure. The neuroethology of sensory and cognitive receiver biases is the main key to signal form and the ‘aesthetic sense’ proposed by Darwin. Since a receiver bias is sufficient to both start and drive ornament or armament exaggeration, without a genetically correlated or even coevolving receiver, this may be the appropriate ‘null model’ of sexual selection. 3) Genetic architecture of sexual selection. Despite advances in modern molecular techniques, the number and identity of genes underlying performance remain largely unknown. A combination of genomic techniques and long-term field studies that reveal ecological correlates of reproductive success is warranted. In-depth investigations into the genetic basis of sexual dimorphism will reveal constraints and trajectories of sexually selected trait evolution. 4) Sexual selection and conflict as drivers of speciation. Population divergence and speciation is often driven by an interplay between sexual and natural selection. To what extent sexual selection promotes or counteracts population divergence may differ depending on the genetic architecture of traits as well as covariance between mating competition and local adaptation, if traits have multiple functions and if sensory systems used in mate choice are locally adapted. Also, post-copulatory processes, e.g. selection against heterospecific sperm, may influence the importance of sexual selection. Sexual conflict can shape speciation processes, since mate choice selection on females can restrict gene flow whereas selection on males is permissive. We propose that efforts to resolve these four themes can catalyze conceptual progress in the field of sexual selection.

Telomeres are the nucleotide-protein caps that constitute the ends of linear chromosomes, protects the chromosomes from end-to-end fusion, and facilitate DNA integrity and stability (Blackburn, 1991;Monaghan & Haussmann, 2006). In recent years, telomeres have become increasingly appreciated biomarkers and indicators of proximate and ultimate health and fitness, reflected in, for example, better parasite resistance (Asghar et al., 2015), lower levels of free radicals (von Zglinicki, 2002), better social health (Epel et al., 2004), and a longer life span (Bauch et al., 2014;Heidinger et al., 2012). One explanation for this could be that individuals with relatively longer telomeres, or those that show slower attrition, are of better phenotypic-or genetic quality, or have better antioxidation against reactive