Life-History Variation in a Colonial Ascidian: Broad-Sence Heritabilities and Tradeoffs in Allocation to Asexual Growth and Male and Female Reproduction

Abstract

Intraspecific variation in life-history strategy provides a valuable opportunity for examining how natural selection acts on life-history variants to mold reproductive strategies. Evaluating the consequences of selection requires knowledge of the range of phenotypic variation in life histories, the extent to which variation is genetically based, and possible correlations among different traits that might constrain or promote the effect of selection on individual traits. We explored life-history variation in the colonial ascidian Botryllus schlosseri (a cyclical hermaphrodite) by growing clonal replicates of 18 genotypes in a common-garden experiment. Colonies of this species have previously been shown to vary in egg production and growth rate. We demonstrate that genotypes also vary in sperm production, which is manifested as variation in testis size. We then calculate broad-sense heritabilities for a suite of life-history traits and demonstrate correlations among traits that suggest a three-way tradeoff in resource allocation to asexual growth and sexual reproduction via male and female function. This correlation structure suggests that selection cannot act independently on individual life-history traits.