Population genomics and geographical parthenogenesis in Japanese harvestmen (Opiliones, Sclerosomatidae, Leiobunum)

Abstract

Naturally occurring population variation in reproductive mode presents an opportunity for researchers to test hypotheses regarding the evolution of sex. Asexual reproduction frequently assumes a geographical pattern, in which parthenogenesis‐dominated populations are more broadly dispersed than their sexual conspecifics. We evaluate the geographical distribution of genomic signatures associated with parthenogenesis using nuclear and mitochondrial DNA sequence data from two Japanese harvestman sister taxa, Leiobunum manubriatum and Leiobunum globosum. Asexual reproduction is putatively facultative in these species, and female‐biased localities are common in habitat margins. Past karyotypic and current cytometric work indicates L. globosum is entirely tetraploid, while L. manubriatum may be either diploid or tetraploid. We estimated species phylogeny, genetic differentiation, diversity, and mitonuclear discordance in females collected across the species range in order to identify range expansion toward marginal habitat, potential for hybrid origin, and persistence of asexual lineages. Our results point to northward expansion of a tetraploid ancestor of L. manubriatum and L. globosum, coupled with support for greater male gene flow in southern L. manubriatum localities. Specimens from localities in the Tohoku and Hokkaido regions were indistinct, particularly those of L. globosum, potentially due to little mitochondrial differentiation or haplotypic variation. Although L. manubriatum overlaps with L. globosum across its entire range, L. globosum was reconstructed as monophyletic with strong support using mtDNA, and marginal support with nuclear loci. Ultimately, we find evidence for continued sexual reproduction in both species and describe opportunities to clarify the rate and mechanism of parthenogenesis.

Genetic diversity and population structure of trifoliate yam (Dioscorea dumetorum Kunth) in Cameroon revealed by genotyping-by-sequencing (GBS)

“…This method infers cytotypes based on the allelic ratios of heterozygous SNPs identified during variant calling within each individual. Data was prepared by acquiring a *.vcf output file for all specimens from iPyrad using VCFConverter2.py (https://github.com/dandewaters/VCF-File-Converter) as in [50]. Cytotypes were estimated in two ways: 1) without reference to accessions of known ploidy and 2) with reference of 17 accessions for which ploidy is known) from flow cytometry as set of triploids and diploids to the 27 remaining accessions.…”

Spermathecal Variation in Temperate Opiliones

“…3). This is a novel result, because L. globosum males are exceedingly rare and absent in most populations (Burns et al 2017;Tsurusaki 1986). Moreover, flow cytometrics support L. globosum males and females to be entirely tetraploid (Burns et al 2017), and gynandromorphs of the species have been collected (Tsurusaki 2001).…”

“…This is a novel result, because L. globosum males are exceedingly rare and absent in most populations (Burns et al 2017;Tsurusaki 1986). Moreover, flow cytometrics support L. globosum males and females to be entirely tetraploid (Burns et al 2017), and gynandromorphs of the species have been collected (Tsurusaki 2001). That spermatozoa were found in the spemathecae of one specimen does not ultimately discount the possibility of hybrid mating, but suggests that sexual behavior in the species is still maintained, even though male density in most populations is very low.…”

“…Two of the three species examined have facultatively parthenogenetic females, and past publications have focused on the antagonistic morphologies found in rare males of these species (Burns & Tsurusaki 2016). Subsequent papers have discussed the uniquely manifest nature of sexual conflict in facultatively parthenogenetic systems (Burke & Bonduriansky 2018;Gerber & Kokko 2016), where we might otherwise expect relaxed selection on males (Jalinsky et al 2019;Schwander et al 2013) given the biases towards females in populations (Burns et al 2017). While males of facultatively parthenogenetic species have larger pedipalps than expected given their body size (Burns & Tsurusaki 2016), females of these species did not have significantly larger or more complex spermatheca than a closely related sexual species.…”

“…In North American leiobunine harvesters, the female barrier and male antagonistic traits have previously been shown to covary, http://mc.manuscriptcentral.com/icbiol suggesting mating system transition towards increasing sexual conflict. Pedipalpal dimorphism is also seen in the Japanese leiobunines Leiobunum globosum and L. manubriatum, in which females are facultatively asexual and may be experiencing a related transition towards sexual antagonism due to reproductive mode switching (Burns et al 2017). In all species, the penis is equipped with a flexible glans stylus that is presumably used to deliver aflagellate spermatozoa (Macías-Ordóñez et al 2010;Moya et al 2007) to the female's spermathecae.…”