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Abstract:
Rhabditid nematodes are one of a few animal taxa in which androdioecious reproduction, involving hermaphrodites and males, is found. In the genus Pristionchus, several cases of androdioecy are known, including the model species P. pacificus. A comprehensive understanding of the evolution of reproductive mode depends on dense taxon sampling and careful morphological and phylogenetic reconstruction. In this article, two new androdioecious species, P. boliviae n. sp. and P. mayeri n. sp., and one gonochoristic outgroup, P. atlanticus n. sp., are described on morphological, molecular, and biological evidence. Their phylogenetic relationships are inferred from 26 ribosomal protein genes and a partial SSU rRNA gene. Based on current representation, the new androdioecious species are sister taxa, indicating either speciation from an androdioecious ancestor or rapid convergent evolution in closely related species. Male sexual characters distinguish the new species, and new characters for six closely related Pristionchus species are presented. Male papillae are unusually variable in P. boliviae n. sp. and P. mayeri n. sp., consistent with the predictions of "selfing syndrome." Description and phylogeny of new androdioecious species, supported by fuller outgroup representation, establish new reference points for mechanistic studies in the Pristionchus system by expanding its comparative context.
