Genetic and phenotypic consequences of local transitions between sexual and parthenogenetic reproduction in the wild

Transitions from sexual to asexual reproduction have occurred in numerous
lineages across the tree of life, but many questions remain about how such
transitions occur and why asexual populations rarely persist. In
facultatively parthenogenetic animals, all-female populations can arise
when males are absent or become extinct and, if such populations can
persist asexually for many generations, they could ultimately give rise to
obligately asexual species. However, the initial stages of this process
remain poorly understood. The facultatively parthenogenetic Australian
phasmid Megacrania batesii exhibits a spatial mosaic of mixed-sex
populations that reproduce predominantly sexually and all-female sites
that reproduce exclusively via parthenogenesis. We used this system to
compare genetic and phenotypic parameters among multiple natural
populations that vary in reproductive mode and geographic location.
Analysis of single nucleotide polymorphisms (SNPs) collected from reduced
representation whole genome data showed populations grouping by geographic
location rather than reproductive mode, with little gene-flow between
them. Mixed-sex populations had drastically higher heterozygosities than
all-female populations. Phenotypic analysis revealed considerable
inter-population variation in rates of deformities in (non-functional)
wings, with higher mean frequency and severity of deformities in
all-female sites. All-female sites also harbored more parasites, but only
in swamp habitats. However, reproductive mode did not explain variation in
mean female fecundity, egg hatching success, or missing appendages. These
results indicate that local transitions to parthenogenetic reproduction
can lead to increased rates of developmental abnormalities and increased
vulnerability to disease but can also occur without substantial fitness
consequences despite dramatic reductions in genetic diversity and
heterozygosity.