Abstract
The contribution of phenotypically plastic traits to evolution depends on the degree of environmental influence on the target of selection (the phenotype) as well as the underlying genetic structure of the trait and plastic response. Likewise, maternal effects can help or hinder evolution through affects to the response to selection. The sacoglossan sea slug Alderia willowi exhibits intraspecific variation for developmental mode (= poecilogony) that is environmentally modulated with populations producing more yolk‐feeding (lecithotrophic) larvae during the summer, and more planktonic‐feeding (planktotrophic) larvae in the winter. I found significant family‐level variation in the reaction norms between 17 maternal families of A. willowi when reared in a split‐brood design in low (16 ppt) versus high (32 ppt) salinity, conditions which mimic seasonal variation in salinity of natural populations. I documented a significant response to selection for lecithotrophic larvae in high and low salinity. The slope of the reaction norm was maintained following one generation of selection for lecithotrophy. When the maternal environment was controlled in the laboratory, I found significant maternal effects, which reduced the response to selection. These results suggest there is standing genetic variation for egg‐mass type in A. willowi, but the ability of selection to act on that variation may depend on the environment in which the phenotype is expressed in preceding generations.
Highlights
The evolutionary role of plasticity is highly context-dependent, sometimes fueling evolution by moving the mean phenotype in the direction favored by selection and other times hindering evolution through the lack of a genetic response to selection on a variable phenotype
This paper presents data from two experiments, one designed to evaluate the response to selection in high and low salinity, and the other to determine the role of maternal effects and effect of selection on phenotypic plasticity
The sacoglossan sea slug A. willowi exhibits variation in egg size leading to two developmental modes, lecithotrophy and planktotrophy, with differing developmental durations and dispersal potentials
Summary
The evolutionary role of plasticity is highly context-dependent, sometimes fueling evolution by moving the mean phenotype in the direction favored by selection and other times hindering evolution through the lack of a genetic response to selection on a variable phenotype (see Pfennig et al, 2010). Lecithotrophy (nonfeeding) is the most common alternative to planktotrophic development, in which a few relatively large larvae contain substantial amounts of yolk, such that they do not need to feed on plankton before metamorphosis (Marshall et al, 2017; McEdward & Janies, 1997) These two modes can have drastically different influences on larval dispersal and may impact micro-and macro-evolutionary patterns and processes, including gene flow, local adaptation, and speciation and extinction (Ellingson & Krug, 2016; Fobert et al, 2019; Grosberg & Cunningham, 2001; Krug et al, 2015). I use pooled data from both experiments to explore trait lability, whether individual slugs change the type of egg mass laid
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