The genetics and evolutionary dynamics of sexual system evolution in tadpole shrimps

Mathers, Thomas C.

Abstract

Sexual reproduction is found throughout the eukaryote tree of life and fundamentally affects the organisms that practice it. In particular, the sexual system of an organism can influence genetic diversity, population structure, genome structure, the evolutionary potential of species and even cause speciation. Understanding the effects of sexual reproduction, and the effects of transitions between its various forms, is therefore a central theme in biology and essential to understanding how populations and species evolve.

In this thesis I investigate the genetics and evolutionary dynamics of sexual system evolution in tadpole shrimps (Notostraca), a group of branchiopod crustaceans with diverse sexual systems. Gonochorism (dioecy), hermaphroditism and androdioecy – the presence of self-­‐fertile hermaphrodites and males within a population – are all found, with this variation occurring both within and between species. In contrast to their variable sexual system, tadpole shrimps exhibit high levels of morphological conservatism, appearing to have changed little since the Early Devonian.

I establish the first resolved phylogeny of Notostraca and find that tadpole shrimps have undergone at least two bouts of diversification in their evolutionary history, with extant species being younger than the fossil record would suggest. Analysis of sexual system across the phylogeny reveals the labile nature of sexual systems within Notostraca with multiple transitions having occurred between separate and combined sexes, driven by selection for reproductive assurance. Finally I use restriction site associated DNA sequencing (RAD-­‐seq) to identify over 1000 high coverage, novel genomic markers for Triops cancriformis, a mixed mating tadpole shrimp. I confirm a Z W chromosomal sex determination system for T. cancriformis, conserved in gonochoric and androdioecious populations and identify significant alterations in the structure of the W and Z chromosomes associated with the transition in sexual system. The results presented within this thesis establish tadpole shrimps as an ideal model to study the evolution of sexual systems and the genomic effects of repeated transitions between sexual systems.

Citation

Mathers, T. C. The genetics and evolutionary dynamics of sexual system evolution in tadpole shrimps. (Thesis). University of Hull. https://hull-repository.worktribe.com/output/4216243

• Thesis Type: Thesis
• Deposit Date: Jan 20, 2015
• Publicly Available Date: Feb 23, 2023
• Keywords: Biological sciences
• Public URL: https://hull-repository.worktribe.com/output/4216243
• Additional Information: The University of Hull
• Award Date: Sep 1, 2013