Abstract
The co-existence of males, females and hermaphrodites, a rare mating system known as trioecy, has been considered as an evolutionarily transient state. In nematodes, androdioecy (males/hermaphrodites) as found in Caenorhabditis elegans, is thought to have evolved from dioecy (males/females) through a trioecious intermediate. Thus, trioecious species are good models to understand the steps and requirements for the evolution of new mating systems. Here we describe two new species of nematodes with trioecy, Auanema rhodensis and A. freiburgensis. Along with molecular barcodes, we provide a detailed analysis of the morphology of these species, and document it with drawings and light and SEM micrographs. Based on morphological data, these free-living nematodes were assigned to a new genus, Auanema, together with three other species described previously. Auanema species display convergent evolution in some features with parasitic nematodes with complex life cycles, such as the production of few males after outcrossing and the obligatory development of dauers into self-propagating adults.
Highlights
Natural selection has favored the evolution of diverse modes of reproduction
The results of our molecular phylogenetic analyses with 19 Rhabditina species (Fig. 1) confirmed the phylogenetic position of SB347 (A. rhodensis n. sp.) by Kiontke, et al.[16] and van Megen, et al.[37] as sister taxon to Rhabditella and Cephaloboides, and placed SB372 (A. freiburgensis n. sp.) as its sister species with 100% statistical support
Phenotypic evidence suggests that A. viguieri is closely related to A. freiburgensis n. sp. and A. rhodensis n. sp
Summary
Natural selection has favored the evolution of diverse modes of reproduction. Organisms have evolved to reproduce sexually or asexually, self-fertilize or outcross, and exist as either separate sexes or hermaphrodites. There are only two stable states in mating system evolution: predominant outcrossing with strong inbreeding depression or predominant selfing with weak inbreeding depression[7, 9] This assumption led to the suggestion that mixed mating types are transitional and short-lived[7, 10]. Like the model nematode Caenorhabditis elegans, these species have a short life cycle, large number of progeny, and are transparent, which facilitate their use as models for studying the evolution of mating systems Several of their biological features, such as vulva development[14, 15], phylogeny[16], early embryogenesis[17], ecology[18], sex determination[19,20,21] and mating dynamics[22] have been studied in the last few years. We define and describe a new genus, Auanema, to accommodate the new species along with A. viguieri and two further species with similar phenotypic characteristics
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