%0 Journal Article
%T Natural variation of outcrossing in the hermaphroditic nematode Pristionchus pacificus
%A Arielle Click
%A Chandni H Savaliya
%A Simone Kienle
%A Matthias Herrmann
%A Andre Pires-daSilva
%J BMC Evolutionary Biology
%D 2009
%I BioMed Central
%R 10.1186/1471-2148-9-75
%X Here we determine various parameters that influence outcrossing in the hermaphroditic nematode Pristionchus pacificus and compare them to the better known Caenorhabditis elegans. These nematode species are distinct in terms of genetic diversity, which could be explained by differences in outcrossing rates. We find that, similarly to C. elegans, P. pacificus males are generated at low frequencies from self-fertilizing hermaphrodites and are relatively poor mating partners. Furthermore, crosses between different isolates reveal that hybrids have lower brood sizes than the pure strains, which is a sign of outbreeding depression. In contrast to C. elegans, P. pacificus has lower brood sizes and the male X-bearing sperm is able to outcompete the X-nullo sperm.The results indicate that there is no evidence of any selection acting very strongly on P. pacificus males.The types of mating systems organisms use have important implications for discerning various aspects of the biology of organisms, including genetic diversity, genome evolution, sexual dimorphism and sex ratios [1]. It is therefore crucial to understand the mechanisms and factors that influence the transition of one type of mating system into another. The evolution of mating systems is best understood in flowering plants [2,3], mainly because numerous examples of mating types considered transitory are found in these organisms [4-6]. Hermaphroditism (ie, "cosexuals" or "bisexuals") is considered the ancestral mating system, and selection for outcrossing has been proposed as the main selective force responsible for the evolution of dioecy (male/female) [4,7].Two main transitory mating systems have been recognized: gynodioecy (females/hermaphrodites) and androdioecy (males/hermaphrodites). In plants, gynodioecy is more prevalent than androdioecy, a trend predicted from theory [4,7,8] and confirmed empirically [9]. According to theoretical predictions, hermaphroditic populations can become gynodioecious when a reces
%U http://www.biomedcentral.com/1471-2148/9/75