Genome evolution and consequences of transitions to asexuality

How do genes, genomes, and bodies evolve when a critical life-history trait is suddenly altered? This is a big question that I address by evaluating the evolutionary consequences of a transition from sexual reproduction – involving both males and females – to all-female asexual reproduction. I specifically compare DNA sequence evolution in sexual and asexual lineages of lichenized fungi in the Peltigera genus and in the New Zealand freshwater snail Potamopyrgus antipodarum. Both Peltigera and P. antipodarum are unusual in featuring closely related and otherwise similar sexually reproducing and asexually reproducing lineages, which allows direct comparisons across reproductive modes. I also compare and contrast sperm produced by sexual male P. antipodarum to sperm made by the male P. antipodarum that are occasionally produced by asexual females. I found that asexual lineages of both P. antipodarum and Peltigera have a distinct genomic fingerprint of increased mutation accumulation in genes specific to sex. I also find that asexually produced sperm are much more likely to feature morphological abnormalities than sperm produced by sexual males. Taken together, these discoveries highlight the evolutionary centrality of sexual reproduction in maintaining genes and traits critical for reproduction and suggest that evolutionary transitions back to sexual reproduction might be difficult to impossible for most asexual lineages.