The Evolutionary Genetics of an Adaptive Maternal Effect: Egg Size Plasticity in a Seed Beetle

Abstract

In many organisms, a female's environment provides a reliable indicator of the environmental conditions that her progeny will encounter. In such cases, maternal effects may evolve as mechanisms for transgenerational phenotypic plasticity whereby, in response to a predictive environmental cue, a mother can change the type of eggs that she makes or can program a developmental switch in her offspring, which produces offspring prepared for the environmental conditions predicted by the cue. One potentially common mechanism by which females manipulate the phenotype of their progeny is egg size plasticity, in which females vary egg size in response to environmental cues. We describe an experiment in which we quantify genetic variation in egg size and egg size plasticity in a seed beetle, Stator limbatus, and measure the genetic constraints on the evolution of egg size plasticity, quantified as the genetic correlation between the size of eggs laid across host plants. We found that genetic variation is present within populations for the size of eggs laid on seeds of two host plants (Acacia greggii and Cercidium floridum; h ranged between 0.217 and 0.908), and that the heritability of egg size differed between populations and hosts (higher on A. greggii than on C. floridum). We also found that the evolution of egg size plasticity (the maternal effect) is in part constrained by a high genetic correlation across host plants (r > 0.6). However, the cross-environment genetic correlation is less than 1.0, which indicates that the size of eggs laid on these two hosts can diverge in response to natural selection and that egg size plasticity is thus capable of evolving in response to natural selection.

Foundations of Gregariousness: A Dispersal Polymorphism Among the Planktonic Larvae of a Marine Invertebrate

“…Alternatively, the response to selection observed in our study could be the result of intergenerational effects similar to that documented in such taxonomically diverse organisms as insects (e.g., Smith et al 1995;Fox et al 1999;Wedell andTregenza 1999), plants (e.g., Lacey 1996;Thiede 1998), and humans (e.g., Foster et al 1993;Ramakrishman et al 1999). Direct additive genetic covariances between parental performance and the trait of interest in the offspring are frequently found to be strongly negative (e.g., Baker 1980;Meyer 1992a, b;Robinson 1996;Lee and Pollack 1997), and the general outcome of selection is simply difficult to elucidate in these cases: selection may have no apparent effect or even a counter-intuitive effect on the response of a trait subjected to selection under these circumstances depending on the strength of the covariance between the traits (e.g., Lande 1989, 1992;Lande and Price 1989;Lande and Kirkpatrick 1990).…”

Fates of Rare Species under Siege from Invasion: Persistence of Coccinella novemnotata Herbst in Western North America alongside an Invasive Congener

“…While adult body size of individual insects is generally strongly influenced by genetics (e.g., Dingle, 1984;Fox et al, 1999), it also generally reflects environmental conditions, including food availability, during growth of the individual as an immature (e.g., Gullan and Cranston, 2014). Thus the success of lady beetles as larvae in finding and consuming sufficient numbers of aphids and similar prey typically has great influence on their body size upon molting to adults (Hodek et al, 2012).…”

Effects of maternal diet and host quality on oviposition patterns and offspring performance in a seed beetle (Coleoptera: Bruchidae)

“…For instance, if seed size is associated with host quality for larval development, females may use seed size as a cue for adjusting their oviposition pattern in such a way that resources are allocated optimally (Fox et al 1997;Cope and Fox 2003;Yang et al 2006). Plasticity in egg size in response to host quality has been described for the seed beetle Stator limbatus, where females lay larger eggs on seeds of the poor-quality host Cercidium floridum and smaller eggs on the high-quality host Acacia greggii (Fox et al 1997;Fox et al 1999). In S. limbatus, females respond adaptively to the available host by varying egg size to assure high larval survival (Fox et al 1997).…”