No evidence for the ‘Meselson effect’ in parthenogenetic oribatid mites (Oribatida, Acari)

Abstract

It has been hypothesized that in ancient apomictic, nonrecombining lineages the two alleles of a single copy gene will become highly divergent as a result of the independent accumulation of mutations (Meselson effect). We used a partial sequence of the elongation factor‐1α (ef‐1α) and the heat shock protein 82 (hsp82) genes to test this hypothesis for putative ancient parthenogenetic oribatid mite lineages. In addition, we tested if the hsp82 gene is fully transcribed by sequencing the cDNA and we also tested if there is evidence for recombination and gene conversion in sexual and parthenogenetic oribatid mite species. The average maximum intra‐specific divergence in the ef‐1α was 2.7% in three parthenogenetic species and 8.6% in three sexual species; the average maximum intra‐individual genetic divergence was 0.9% in the parthenogenetic and 6.0% in the sexual species. In the hsp82 gene the average maximum intra‐individual genetic divergence in the sexual species Steganacarus magnus and in the parthenogenetic species Platynothrus peltifer was 1.1% and 1.2%, respectively. None of the differences were statistically significant. The cDNA data indicated that the hsp82 sequence is transcribed and intron‐free. Likelihood permutation tests indicate that ef‐1α has undergone recombination in all three studied sexual species and gene conversion in two of the sexual species, but neither process has occurred in any of the parthenogenetic species. No evidence for recombination or gene conversion was found for sexual or parthenogenetic oribatid mite species in the hsp 82 gene. There appears to be no Meselson effect in parthenogenetic oribatid mite species. Presumably, their low genetic divergence is due to automixis, other homogenizing mechanisms or strong selection to keep both the ef‐1α and the hsp82 gene functioning.

Reevolution of sexuality breaks Dollo's law

“…Much of what has been written about large parthenogenetic clusters in oribatid mites has focused on Desmonomata (9,10,14), especially Camisiidae, Malaconothridae, and Trhypochthoniidae. Our data support monophyly of species-rich parthenogenetic taxa within Desmonomata and therefore that parthenogenetic lineages of oribatid mites are not evolutionary ''dead-ends''; they have persisted and radiated to form clusters, e.g., the parthenogenetic genus Nothrus with 67 species.…”

“…Why this is not true has been debated for decades, with so many answers having been proposed (3-5) that a second enigma has emerged: How could a few animal lineages have maintained parthenogenetic reproduction over considerable evolutionary time, avoiding extinction long enough to radiate and form monophyletic clades? The most studied examples of such ''ancient asexual scandals'' (1) are darwinulid ostracods (6), bdelloid rotifers (7), and several large clusters within oribatid mites (8)(9)(10)(11).…”

A molecular study of the tardigrade Echiniscus testudo (Echiniscidae) reveals low DNA sequence diversity over a large geographical area

“…The parthenogenetic bdelloid rotifers, darwinulid ostracods and some lineages of oribatid mites are regarded as ancient asexuals (Mark-Welch & Meselson 2000;Schön & Martens 2003;Maraun et al 2004). However, this ancient asexual status has recently been questioned for the mites and ostracods (Schaefer et al 2006;Smith et al 2006).…”

Thelytokous parthenogenesis in the damselfly Ischnura hastata (Odonata, Coenagrionidae): genetic mechanisms and lack of bacterial infection

“…Furthermore, a preliminary test of microsatellite loci amplification in a sample of parthenogenetic females from the Azores detected only one clone , which suggests that recombination does not take place and that asexual populations from the Azores probably arose from a single event. Absence of recombination has been found to occur in Bdelloid rotifers (Welch and Meselson, 2000), in the parthenogenetic wasp Trichogramma cacoeciae (Vavre et al, 2004) and in parthenogenetic oribatid mites (Schaefer et al, 2006). In addition, in thelytokous females of Apis mellifera capensis, recombination rates are lower than in sexually reproducing females of the same species.…”