Sex-Specific Stress Tolerance in Embryos of Lake Char (Salvelinus umbla)

Abstract

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.

Genetic compatibility exceeds possible ‘good genes’ effects of sexual selection in lake char

“…All embryos and larvae that had died before were also genotyped. A sex-specific marker was added to the first multiplex of 3 microsatellite markers to test for sex-specific effects on embryo development that are reported in Nusbaumer et al [100].…”

Sperm of more colorful males are better adapted to ovarian fluids in lake char (Salmonidae)

“…Embryo mortality, the timing of hatching, hatchling size, and hatchling growth was monitored from then on in the course of two parallel studies, one that combines these data with further stress experiments (by a pathogen and a chemical pollutant) on embryos produced in a regular full-factorial breeding design to test for parental effects on embryo performance (Garaud et al . 2022), and another one on sex-specific stress tolerance (Nusbaumer et al . 2021).…”

“…In the first multiplex PCR, the sdY sex marker (Yano et al . 2013) was included to sex offspring (Table S3) for a parallel study on sex-specific stress tolerance (Nusbaumer et al . 2021).…”

“…No visible embryo at this stage was interpreted as non-fertilized egg. Embryo mortality, the timing of hatching, hatchling size, and hatchling growth was monitored from then on in the course of two parallel studies, one that combines these data with further stress experiments (by a pathogen and a chemical pollutant) on embryos produced in a regular full-factorial breeding design to test for parental effects on embryo performance (Garaud et al 2022), and another one on sex-specific stress tolerance (Nusbaumer et al 2021). Embryos and larvae that died during the observational period were transferred to individual microtubes and stored in 96% ethanol at -20°C for further analysis.…”

“…A second multiplex PCR of 3 further microsatellite markers (Savary et al 2017) was used for to assign the remaining offspring (Table S3). In the first multiplex PCR, the sdY sex marker (Yano et al 2013) was included to sex offspring (Table S3) for a parallel study on sex-specific stress tolerance (Nusbaumer et al 2021). Multiplex PCR were run on a Biometra thermocycler in 20 µL reaction volume using HotStarTaq DNA Polymerase (Qiagen, Germany) reagents (i.e.…”