Differences among families in craniofacial shape at early life-stages of Arctic charr (Salvelinus alpinus)

Abstract

Background Organismal fitness can be determined at early life-stages, but phenotypic variation at these early life-stages has rarely been considered in studies on evolutionary diversification. The trophic apparatus has been shown to contribute to sympatric resource-mediated divergence in several taxa. However, processes underlying this diversification are poorly understood. Using a phenotypically variable morph of Icelandic Arctic charr (Salvelinus alpinus), we reared offspring from multiple families under standardized laboratory conditions and tested to what extent family (i.e. direct genetic and maternal effects) contributes to offspring morphology at hatching (H) and first feeding (FF). To understand the underlying mechanisms behind early life-stage variation in morphology, we examined how craniofacial shape varied according to family, egg size, offspring size and individual candidate genes related to craniofacial development. Finally, we assessed whether craniofacial shape and expression of genes related to craniofacial development covaried. Results We found effects of family for offspring craniofacial shape at both H and FF, whilst relative expression levels of Sgk1 (a gene involved in craniofacial shape divergence) correlated with craniofacial shape at FF. However, there were no evidence to suggest that mean egg size or individual offspring size influenced offspring morphology. Conclusions This study provides evidence for within population family effects for phenotypic variation in trophic morphology, indicating the potential for genetic and/or maternal effects to facilitate resource polymorphism.

DNA methylation differences during development distinguish sympatric morphs of Arctic charr (Salvelinus alpinus)

“…Multiple epigenetic mechanisms acting across generations have been described, such as epi‐alleles, maternal provisioning and metabolism, or sncRNAs in sperm [mainly tsRNAs (Peng et al, 2012) and miRNA (see Perez & Lehner, 2019)], all of which could possibly impact DNA methylation profiles of the offspring. In fish, specific cytosine methylation has been associated with maternal effects in Chinook salmon (Venney et al, 2020), parental maturation temperature corresponded with DNA methylation patterns in the offspring of Brook charr (Venney et al, 2022) and egg size has already been correlated with craniofacial shape at first feeding in this S. alpinus model (Beck et al, 2020). It would be very interesting to study parental effects and transgenerational epigenetic inheritance (see Baerwald et al, 2016; Heckwolf et al, 2020), with a multigeneration scheme and crosses (for instance, pure and reciprocal crosses of different morphs), for further inquiry into these potential causes.…”

Variation in egg size and offspring phenotype among and within seven Arctic charr morphs

“…Egg size‐mediated changes in feeding behavior (Leblanc et al, 2011) combined with size‐correlated constraints on diet choice (mediated by offspring size and associated mouth gape), can ultimately promote divergence in alternative resource use in the wild, especially in organisms with highly plastic trophic morphologies (Adams & Huntingford, 2004; Parsons et al, 2016; Robinson & Wilson, 1994). Trophic specializations can occur early in development in Arctic charr, as documented between morphs (e.g., þingvallavatn; Kapralova et al, 2015) and even between families (e.g., Vatnshlíðarvatn, Beck et al, 2020). However, even though salmonids are widely studied in evolutionary biology to understand the process of diversification, very little is known about variation between sympatric morphs or populations during early life stages and their ecology (both habitat and feeding) in the wild.…”

“…Developmental (phenotypic) plasticity has been proposed to affect evolution by facilitating adaptive change (West‐Eberhard, 2003), yet the role that egg size may play in the diversification of natural populations is only beginning to be understood (Beck et al, 2019, 2020; Cogliati et al, 2018; Leblanc et al, 2011, 2016; Penney et al, 2018; Pfennig & Martin, 2009, 2010; Smalås et al, 2017). This study characterized egg size and development among seven morphs of Arctic charr.…”

“…Females may thus ‘hedge their bets’ in stochastic environments to maximize fitness (Hutchings, 1997; Koops et al, 2003; Marshall et al, 2008), which can consequently alter developmental processes and associated phenotypic outcomes (Bernardo, 1996a; West‐Eberhard, 2003), as seen in many taxa (e.g., Drosophila [Eizadshenass & Singh, 2015]; fish [Cogliati et al, 2018; Kinnison et al, 2001]; amphibians [Pfennig & Martin, 2009; Räsänen et al, 2005]; and birds [Badyaev, 2008]). For example, differences in embryo size has been found to influence the expression of genes involved in growth and skeletal development (Beck et al, 2019), as well as offspring phenotype (Beck et al, 2020) in a single morph of Arctic charr ( Salvelinus alpinus ) that has large variation in egg size. However, no study to date has examined how variation in egg size changes across multiple wild polymorphic populations that differ in their degree of phenotypic divergence from a proposed ancestral type.…”

“…In Arctic charr, egg size can be highly variable among and within females (Baroudy & Elliott, 1994; Lasne et al, 2018; Leblanc et al, 2016; Wallace & Aasjord, 1984), as well as among morphs (e.g., Smalås et al, 2017). Such variation can contribute toward alternative feeding behavior (Benhaïm et al, 2003; Leblanc et al, 2011, 2016), developmental rates (Eiríksson et al, 1999; Leblanc et al, 2011), body size (Leblanc et al, 2016), gene expression patterns (Beck et al, 2019), and craniofacial shape (Beck et al, 2020). Here, we study seven morphs of Icelandic Arctic charr that vary in magnitude of phenotypic and genetic divergence, including an ancestral anadromous morph.…”