Haplotype diversity of the nematode Pristionchus pacificus on Réunion in the Indian Ocean suggests multiple independent invasions

Abstract

Pristionchus pacificus has been established as a nematode model system in evolutionary developmental biology and evolutionary ecology. Field studies in North and South America, Asia, Africa and Europe indicated that nematodes of the genus Pristionchus live in association with scarab beetles. Here, we describe the first account of soil-and beetle-associated nematodes on an island setting by investigating the island of Réunion in the Indian Ocean. Réunion has high numbers of endemic insects and is one among several attractive islands for biodiversity studies. Being of volcanic origin, Réunion is 2-3 million years old, making it the youngest of the Mascareigne islands. We show that beetle-and soil-derived nematodes on Réunion are nearly exclusively hermaphroditic, suggesting that selfing is favoured over gonochorism (outcrossing) during island colonization. Among members of four nematode genera observed on Réunion, Pristionchus pacificus was the most prevalent species. A total of 76 isolates, in association with five different scarab beetles, has been obtained for this cosmopolitan nematode. A detailed mitochondrial haplotype analysis indicates that the Réunion isolates of P. pacificus cover all four worldwide clades of the species. This extraordinary haplotype diversity suggests multiple independent invasions, most likely in association with different scarab beetles. Together, we establish Réunion as a case study for nematode island biogeography, in which the analysis of nematode population genetics and population dynamics can provide insight into evolutionary and ecological processes.

Cryptic variation in vulva development by cis-regulatory evolution of a HAIRY-binding site

“…Control animals show gonad-independent differentiation in 30-60% of the VPCs according to the RS5275/BOL genetic background. Controls include non-transgenic sisters (*) that have lost the transgenic array of both constructs (8,10), Ppa-egl-20::RFP transgenic animals (11), or RS5275/BOL wild-type animals (12). Error bars denote standard deviation.…”

“…All strains used in this study were inbred for at least 10 generations and are described elsewhere 10,11 . Cell-ablation experiments were carried out using standard techniques 27 , by ablating the gonad 0-1 h after hatching of the larvae (20°C).…”

“…In the nematode Pristionchus pacificus genetic studies can be coupled to natural variation 9 owing to the availability of hundreds of strains that have been recently isolated from the wild 10,11 . The formation of the vulva, the egg-laying structure of nematode hermaphrodites, represents an attractive system for studies on robustness and cryptic variation given the detailed knowledge and the complexity of vulval patterning mechanisms.…”

Opposing Forces of A/T-Biased Mutations and G/C-Biased Gene Conversions Shape the Genome of the Nematode Pristionchus pacificus

“…Potential support for a role of oxidative stress comes from the known ecosystem of P. pacificus and related nematodes. Unlike C. elegans, Pristionchus lives in tight association with scarab beetles in a necromenic interaction (Herrmann et al 2007(Herrmann et al , 2010. Nematodes rest on the living beetle in the dauer stage (Weller et al 2010) and resume development on the beetle carcass only to feed on all types of microbes (McGaughran et al 2013).…”

“…A subset of 104 P. pacificus wild isolates had their genome of 169 Mb resequenced, which revealed strong divergence, resulting in .6 million single-nucleotide polymorphisms (SNPs) (Rödelsperger et al 2014). Furthermore, the patterns of divergence and global dispersal between the four P. pacificus clades and the repeated invasion of the geologically young volcanic island of La Reunion (Herrmann et al 2010;McGaughran et al 2013) indicated that the P. pacificus genome is shaped by weakly deleterious mutations and linked selection (Rödelsperger et al 2014). These studies provide a genomic and phylogenetic framework for evolutionary comparisons of mutational patterns.…”