Evolution of meiosis genes in sexual vs. asexual Potamopyrgus antipodarum

Abstract

Department, and the National Science Foundation for their support. Lastly I'd like to thank my thesis committee for their insight and assistance in the completion of my research. iii ABSTRACT How asexual reproduction affects genome evolution, and how organisms that are ancestrally sexual alter their reproductive machinery upon becoming asexual are both central unanswered questions in evolutionary biology. While these questions have been addressed to some extent in organisms such as asexual clams, rotifers, ostracods, arthropods, and fungi, the most powerful and direct tests of how sex and its absence influence evolution requires direct comparisons between closely related and otherwise similar sexual and asexual taxa. Here, I quantify the rates and patterns of molecular evolution in the meiosis-specific genes Msh4, Msh5, and Spo11 in multiple sexual and asexual lineages of Potamopyrgus antipodarum, a New Zealand freshwater snail. Because asexual P. antipodarum reproduce apomictically (without recombination), genes used only for meiosis should be under relaxed selection relative to meiosis-specific genes in sexual P. antipodarum,allowing me to directly study how asexuality affects the evolution of meiosisspecific genes. Contrary to expectations under relaxed selection, I found no evidence that these meiosis-specific genes are degrading in asexual P. antipodarum; instead they display molecular patterns consistent with purifying selection. The presence of intact meiosis-specific genes in asexual P. antipodarum hints that the asexuals may maintain the ability to perform meiosis despite reproducing apomictically. Asexual meiotic capability suggests that some meiotic components may persist or acquire a new role in these asexuals. iv PUBLIC ABSTRACTHow asexual reproduction affects genome evolution, and how ancestrally sexual organisms alter their reproductive machinery upon becoming asexual are central unanswered questions in evolutionary biology. While these questions have been addressed to some extent in different asexual species, the most powerful tests of how sex and its absence influence evolution requires direct comparisons between closely related and otherwise similar sexual and asexual taxa. I address these questions by studying the evolution of genes critical to sexual reproduction in sexual and asexual lineages of

Reproduction-associated pathways in females of gibel carp (Carassius gibelio) shed light on the molecular mechanisms of the coexistence of asexual and sexual reproduction

“…Our results suggest that all along their evolutionary history, asexual lines of C. gibelio did not lose the genetic toolkit for meiosis, and that the sexual reproduction genetic toolkit is not under relaxed selection, a condition also reported in asexual P. formosa (19) and snails (121). The re-acquisition of sexual reproduction in asexual species is very rare and very few cases have been reported.…”

Reproduction-associated pathways in females of gibel carp (Carassius gibelio) shed light on the molecular mechanisms of the coexistence of asexual and sexual reproduction

“…Our results suggest that all along their evolutionary history, asexual lines of C. gibelio did not lose the genetic toolkit for meiosis, and that the sexual reproduction genetic toolkit is not under relaxed selection, a condition also reported in asexual P. formosa [20] and snails [133]. The re-acquisition of sexual reproduction in asexual species is very rare and very few cases have been reported.…”

Genome evolution and introgression in the New Zealand mud snailsPotamopyrgus estuarinusandPotamopyrgus kaitunuparaoa

“…These inventories discriminate between genes that specifically function in meiosis and genes that are pleiotropic with respect to function outside of meiosis. A combination of NCBI database searches and previously sequenced meiosis genes (Rice 2015) were used to find homologous meiosis genes. We queried the genomes of P. estuarinus and P. kaitunuparaoa using BLASTx to locate each gene's scaffold position.…”