Salmonid fish have become important models in evolution and ecology, but possible effects of embryo or larval sex are mostly ignored, probably because morphological gonad formation starts only months after hatching and sexual maturation years later. However, recent gene expression studies and first observations in domestic strains suggest that sex-specific life histories could already start at an embryonic stage. Here we test this hypothesis in embryos and larvae of lake char (Salvelinus umbla). We sampled wild char and used their gametes to produce embryos of 40 different families. Embryos were raised singly in a stress or a non-stress environment until a late larval stage (stress was induced by allowing remainders of ovarian fluids to support microbial growth). Genetic markers were then used to sex the fish and reconstruct paternity (N = 1,463, including dead embryos). Primary sex ratio did not differ among families and was about 1:1. Female embryos hatched on average later and showed lower stress tolerance than male embryos. There were significant parental effects on offspring growth and mortality, but the sex differences in embryo performance were not family specific. We conclude that the sexes differ in their life history and susceptibilities to environmental stress already at embryonic stages. Environmental stress during incubation can therefore affect population sex ratio and hence population growth and genetics.

Fish often spawn eggs with ovarian fluids that have been hypothesized to support sperm of some males over others (cryptic female choice). Alternatively, sperm reactions to ovarian fluids could reveal male strategies linked to their likely roles during spawning. Sperm of males who would usually be close to females during spawning are then expected to be better adapted to the presence of ovarian fluids than to water only, while the reverse would be expected for males that typically spawn at larger distance to the females. We tested these predictions with gametes and ovarian fluids from wild-caught lake char (Salvelinus umbla). We found that sperm of more colorful males showed increased sperm velocity in diluted ovarian fluids while sperm of paler males were fastest in water only. We then let equal numbers of sperm compete for fertilizations in the presence or absence of ovarian fluids and used microsatellite markers to assign in total 1,464 embryos (from 70 experimental trials) to their fathers. Overall, sperm of more colorful males reached higher fertilization success than sperm of pale males. This difference was enhanced by the presence of ovarian fluids and best explained by the increased sperm velocity. Sperm competitiveness was not enhanced with decreasing genetic distance to a given female, although parallel stress tests on embryos had revealed that females would profit more from mating with least related males rather than most colored ones. We conclude that sperm of more colorful males are best adapted to ovarian fluids, and that the observed reaction norms reveal male strategies rather than cryptic female choice.

Most vertebrates host a wide variety of haematophagous parasites, which may play an important role in the transmission of vector-borne microorganisms to hosts. Surveillance is usually performed by collecting blood and/or tissue samples from vertebrate hosts. There are multiple methods to obtain samples, which can be stored for decades if properly kept. However, blood sampling is considered an invasive method and may possibly be harmful to the sampled individual. In this study, we investigated the use of ectoparasites as a tool to acquire molecular information about the presence and diversity of infectious microorganism in host populations. We tested the presence of three distinct vector-borne microorganisms in both bat blood and bat flies: Bartonella bacteria, malaria-like Polychromophilus sp. (Apicomplexa), and Trypanosoma sp. (Kinetoplastea). We detected the presence of these microorganisms both in bats and in their bat flies, with the exception of Trypanosoma sp. in South African bat flies. Additionally, we found Bartonella sp. in bat flies from one population in Spain, suggesting its presence in the host population even if not detected in bats. Bartonella and Polychromophilus infection showed the highest prevalence in both bat and bat fly populations. Single, co- and triple infections were also frequently present in both. We highlight the use of haematophagous ectoparasites to study the presence of infectious microorganism in host blood and its use as an alternative, less invasive sampling method.

Fish often spawn eggs with ovarian fluids that have been hypothesized to support sperm of some males over others (cryptic female choice). Alternatively, sperm reactions to ovarian fluids could reveal male strategies linked to their likely roles during spawning. Sperm of males who would usually be close to females during spawning are then expected to be better adapted to the presence of ovarian fluids than to water only, while the reverse would be expected for males that typically spawn at larger distance to the females. We tested these predictions with gametes and ovarian fluids from wild-caught lake char (Salvelinus umbla). We found that sperm of more colorful males showed increased sperm velocity in diluted ovarian fluids while sperm of paler males were fastest in water only. We then let equal numbers of sperm compete for fertilizations in the presence or absence of ovarian fluids and used microsatellite markers to assign in total 1,464 embryos (from 70 experimental trials) to their fathers. Overall, sperm of more colorful males reached higher fertilization success than sperm of pale males. This difference was enhanced by the presence of ovarian fluids and best explained by the increased sperm velocity. Sperm competitiveness was not enhanced with decreasing male inbreeding coefficients or decreasing genetic distance to a given female, although parallel stress tests on embryos revealed that females would profit more from mating with least related males rather than most colored ones. We conclude that sperm of more colorful males are best adapted to ovarian fluids, and that the observed reaction norms reveal male strategies rather than cryptic female choice.

Mating is rarely random in nature, but the effects of mate selection on offspring performance are still poorly understood, even in well-established models such as salmonid fish. We sampled wild lake char (Salvelinus umbla) and used their gametes to investigate the genetic consequences of different mating scenarios. In a first study, we used full-factorial breeding to experimentally separate additive genetic from maternal environmental effects. This led to 60 families and in total 1,073 embryos that were raised singly after sublethal exposures to the pathogen Aeromonas salmonicida, the common pollutant ethinylestradiol, or water only. Contrary to predictions of ‘good genes’ sexual selection, offspring of more yellow males were less tolerant to the pathogen than offspring of pale males, while male coloration did not predict offspring tolerance to ethinylestradiol. However, increased kinship between the parents had strong negative effects on embryo development in all treatment groups. In a second experiment, we monitored 1,464 singly-raised embryos that resulted from 70 pair-wise sperm competition trials. These embryos were raised in an environment that supports the growth of symbiotic microbes (sublethal stress) or in a clean environment. Offspring of yellow males were again less stress tolerant than those of pale males, and embryo development was again slowed down with increasing genetic similarity between the parents. We conclude that genetic benefits of mate selection would be strongest if females avoided genetic similarity during mate selection, for example based on MHC-linked signals, while male breeding colors seem more relevant in intra-sexual selection.