Metamorphosis imposes variable constraints on genome expansion

Abstract

AbstractGenome size varies ∼ 100,000-fold across eukaryotes. Genome size is heavily shaped by transposable element accumulation, the dynamics of which are increasingly well understood. However, given that traits like cell size and rate of development co-vary strongly with genome size, organism-level trait evolution likely shapes genome size diversity as well. Metamorphosis — a radical transformation of morphology — has been hypothesized to impact genome size because it can be a vulnerable part of the life cycle. Thus, selection may act to limit metamorphic duration, indirectly constraining the rate of development as well as genome and cell sizes. Salamanders have large and variable genomes — 3 to 40 times that of humans — and species exhibit a range of metamorphic and non-metamorphic life histories. Using salamanders, we test the hypothesis that different types of metamorphic repatterning during the life cycle impose different constraints on genome expansion. We show that metamorphosis during which animals are unable to feed imposes the most severe constraint against genome expansion. Other types of metamorphosis that differ in energetic provisioning impose less severe constraints. More generally, our work demonstrates the utility of phylogenetic comparative methods in testing the role of constraint in shaping phenotypic evolution.