Like mother, like daughter? Phenotypic plasticity, environmental covariation, and heritability of size in a parthenogenetic wasp

Abstract

Dinocampus coccinellae (Hymenoptera:Braconidae, Euphorinae) is a solitary, generalist Braconid parasitoid wasp of over fifty diverse species of coccinellid ladybeetles worldwide that reproduces through thelytokous parthenogenesis, an asexual process in which diploid daughters emerge from unfertilized eggs. Here we utilized a common garden and reciprocal transplant experiment using parthenogenetic lines of D. coccinellae presented with three different host ladybeetle species of varying sizes, across multiple generations to investigate heritability, plasticity, and environmental covariation of body size. Since unilineal (reared on same host species) lines restrict environmental variation on clones, we expected positively correlated parent-offspring parasitoid regressions, indicative of heritable size variation. Whereas multilineal (reared on different host species) lines would quantify phenotypic plasticity of clones reared in varying environments, we expected negatively correlated parent-offspring parasitoid regressions. Contrary to expectations, our results indicate (1) little heritable variation in body size, (2) strong dependence of offspring size on the host environment, (3) a consistent signal of size-host tradeoff wherein small mothers always produced larger offspring, and vice versa, independent of host environment. Our study offers support for a constrained fecundity advantage model of Cope’s Law, wherein D. coccinellae maintains phenotypic plasticity in body size despite parthenogenetic reproduction.