Genetic compatibility underlies benefits of mate choice in an external fertilizer

Authors: J David Aguirre, Mark W Blows, and Dustin J Marshall

Published in: The American Naturalist, volume 187, number 5 (May 2016)

Abstract

Mate choice is a common feature of sexually reproducing species. In sessile or sedentary external fertilizers, however, direct interactions between reproductive partners are minimal, and instead mate recognition and choice must occur at the level of gametes.

It is common for some sperm and egg combinations to have higher fertilization success than others, but it remains unclear whether differences in fertilization reflect gamete-level mate choice (GMC) for paternal quality or parental compatibility.

Here, we examine the mechanisms underlying GMC in an externally fertilizing ascidian. A manipulative mate-choice assay confirmed that offspring viability was greater in clutches where we allowed GMC than in clutches where we precluded GMC. A complementary quantitative genetic experiment then revealed that paternal quality effects were generally weaker than parental compatibility effects, particularly for the trait combination underlying the benefits of GMC.

Overall, our data suggest that gametes that are more compatible at fertilization produce more viable offspring than gametes that are less compatible at fertilization. Therefore, although the regalia we typically associate with sexual selection are absent in external fertilizers, mechanisms that allow females to bias fertilization in favor of some males over others produce significant fitness benefits in organisms reproducing via the ancestral strategy.

Citation

Aguirre, JD, Blows MW, Marshall DJ (2016) Genetic compatibility underlies benefits of mate choice in an external fertiliser. The American Naturalist, 187(5) DOI: 10.1086/685892 PDF 672 KB

The genetic covariance between life cycle stages separated by metamorphosis

Authors: David Aguirre, Mark W Blows and Dustin J Marshall

Published in: Proceedings of the Royal Society B, volume 281 number 1788 (July 2014)

Abstract

Metamorphosis is common in animals, yet the genetic associations between life cycle stages are poorly understood.

Given the radical changes that occur at metamorphosis, selection may differ before and after metamorphosis, and the extent that genetic associations between pre- and post-metamorphic traits constrain evolutionary change is a subject of considerable interest. In some instances, metamorphosis may allow the genetic decoupling of life cycle stages, whereas in others, metamorphosis could allow complementary responses to selection across the life cycle.

Using a diallel breeding design, we measured viability at four ontogenetic stages (embryo, larval, juvenile and adult viability), in the ascidian Ciona intestinalis and examined the orientation of additive genetic variation with respect to the metamorphic boundary.

We found support for one eigenvector of G (gobsmax), which contrasted larval viability against embryo viability and juvenile viability. Target matrix rotation confirmed that while gobsmax shows genetic associations can extend beyond metamorphosis, there is still considerable scope for decoupled phenotypic evolution.

Therefore, although genetic associations across metamorphosis could limit that range of phenotypes that are attainable, traits on either side of the metamorphic boundary are capable of some independent evolutionary change in response to the divergent conditions encountered during each life cycle stage.

Full paper

Aguirre JD, Blows MW, Marshall DJ (2014) The genetic covariance between life cycle stages separated by metamorphosis. Proceedings of the Royal Society B. 281: 20141091. PDF 554 KB DOI 10.1098/rspb.2014.1091