Environmentally induced (co)variance in sperm and offspring phenotypes as a source of epigenetic effects

Abstract

Traditionally, it has been assumed that sperm are a vehicle for genes and nothing more. As such, the only source of variance in offspring phenotype via the paternal line has been genetic effects. More recently, however, it has been shown that the phenotype or environment of fathers can affect the phenotype of offspring, challenging traditional theory with implications for evolution, ecology and human in vitro fertilisation. Here, I review sources of non-genetic variation in the sperm phenotype and evidence for co-variation between sperm and offspring phenotypes. I distinguish between two environmental sources of variation in sperm phenotype: the prerelease environment and the post-release environment. Pre-release, sperm phenotypes can vary within species according to male phenotype (e.g. body size) and according to local conditions such as the threat of sperm competition. Post-release, the physicochemical conditions that sperm experience, either when freely spawned or when released into the female reproductive tract, can further filter or modify sperm phenotypes. I find evidence that both pre-and post-release sperm environments can affect offspring phenotype; fertilisation is not a new beginning -rather, the experiences of sperm with the father and upon release can drive variation in the phenotype of the offspring. Interestingly, there was some evidence for co-variation between the stress resistance of sperm and the stress resistance of offspring, though more studies are needed to determine whether such effects are widespread. Overall, it appears that environmentally induced covariation between sperm and offspring phenotypes is non-negligible and further work is needed to determine their prevalence and strength.

Heat stress: A risk factor for skin carcinogenesis

“…The stratum basalis, or basal layer, of the epidermis consists of stem cells which continuously undergo mitotic division to provide new keratinocytes (Leung et al, 2015;Marshall, 2015;Sexton-Oates et al, 2015). Daughter cells of basal keratinocytes then detach from the basal membrane and undergo further differentiation as they move towards the epidermal surface, over a period of approximately two weeks (Zitzmann et al, 2015).…”

Contributions of genetic and environmental variance in early development of the Antarctic sea urchin Sterechinus neumayeri in response to increased ocean temperature and acidification

“…The ability to adapt to a changing environment depends on the existence of additive genetic variance present within populations, the proportion of genetic variation that responds to natural selection (Billington and Pelham 1991;Kelly et al 2013). There is increasing evidence, however, that the sire component does not exclusively represent additive genetic variance (Crean and Bonduriansky 2014;Jensen et al 2014;Marshall 2015) and thus estimating genetic variance from paternal lines may not be accurate (Crean and Bonduriansky 2014). It can still offer important insights into adaptive potential by providing evidence of whether different genotypes are present in the population.…”

A study of the transit amplification divisions during spermatogenesis in Oncopetus fasciatus to assess plasticity in sperm numbers or sperm viability under different diets

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