Global Population Genetic Structure of Caenorhabditis remanei Reveals Incipient Speciation

Abstract

Mating system transitions dramatically alter the evolutionary trajectories of genomes that can be revealed by contrasts of species with disparate modes of reproduction. For such transitions in Caenorhabditis nematodes, some major causes of genome variation in selfing species have been discerned. And yet, we have only limited understanding of species-wide population genetic processes for their outcrossing relatives, which represent the reproductive state of the progenitors of selfing species. Multilocusmultipopulation sequence polymorphism data provide a powerful means to uncover the historical demography and evolutionary processes that shape genomes. Here we survey nucleotide polymorphism across the X chromosome for three populations of the outcrossing nematode Caenorhabditis remanei and demonstrate its divergence from a fourth population describing a closely related new species from China, C. sp. 23. We find high genetic variation globally and within each local population sample. Despite geographic barriers and moderate genetic differentiation between Europe and North America, considerable gene flow connects C. remanei populations. We discovered C. sp. 23 while investigating C. remanei, observing strong genetic differentiation characteristic of reproductive isolation that was confirmed by substantial F 2 hybrid breakdown in interspecific crosses. That C. sp. 23 represents a distinct biological species provides a cautionary example of how standard practice can fail for mating tests of species identity in this group. This species pair permits full application of divergence population genetic methods to obligately outcrossing species of Caenorhabditis and also presents a new focus for interrogation of the genetics and evolution of speciation with the Caenorhabditis model system.

Anthropogenics: Human Influence on Global and Genetic Homogenization of Parasite Populations

“…However, additional works concluded that although genetic differentiation is strong in relative terms among the different groups, it remains quite modest in absolute magnitude, further supporting low species-wide polymorphism (F´elix et al, 2013). High gene flow and recombinations were also observed in Caenorhabditis remanei (Dey et al, 2012) except in 1 population of worms obtained from Germany, which can be genetically differentiated from the North American populations, suggesting some degree of isolation by distance. In 1 case, substantial genetic differentiation was observed between a strain collected from China (Caenorhabditis sp.…”

Reproductive isolation in the Elegans-Group of Caenorhabditis

“…To date, nematodes in general, and Caenorhabditis in particular, have contributed little to these studies [13][14][15][16][17][18][19][20]. However, in recent years, a number of new Caenorhabditis species have been discovered [18,21].…”

“…However, in recent years, a number of new Caenorhabditis species have been discovered [18,21]. With these new species, four pairwise combinations that yield fertile F1 hybrids have been described [17][18][19]. With these new resources, Caenorhabditis is poised to become an important speciation genetics model system.…”

“…Phylogenetic relationships within the Elegans-Group of Caenorhabditis [18,21]. C.oncomelaniae, C. formosana and C. clavopapillata are included within the ElegansGroup based on morphological characters [37].…”

“…In most cross-fertile combinations, F1 hybrids arrest during embryogenesis [13,14,21]. In six combinations, F1 adults are obtained (Table 1) [13,[16][17][18]. In four of these combinations, fertile F1 adults are obtained [17,18].…”