Large variation in mitochondrial DNA of sexual and parthenogenetic Dahlica triquetrella (Lepidoptera: Psychidae) shows multiple origins of parthenogenesis

Abstract

Background: Obligate parthenogenesis is relatively rare in animals. Still, in some groups it is quite common and has evolved and persisted multiple times. These groups may provide important clues to help solve the 'paradox of sex'. Several species in the Psychidae (Lepidoptera) have obligate parthenogenesis. Dahlica triquetrella is one of those species where multiple transitions to parthenogenesis are postulated based on intensive cytological and behavioural studies. This has led to the hypothesis that multiple transitions from sexuals to diploid parthenogens occurred during and after the last glacial period, followed by transitions from parthenogenetic diploids to parthenogenetic tetraploids. Our study is the first to test these hypotheses using a molecular phylogeny based on mtDNA from multiple sexual and parthenogenetic populations from a wide geographic range.

Results: Parthenogenetic (and sexual) D. triquetrella are not monophyletic, and considerable sequence variation is present suggesting multiple transitions to parthenogenesis. However, we could not establish ancestral sexual haplotypes from our dataset. Our data suggest that some parthenogenetic clades have evolved, indicating origins of parthenogenesis before the last glacial period.

Conclusions: Multiple transitions to parthenogenesis have taken place in Dahlica triquetrella, confirming previous hypotheses. The number of different parthenogenetic clades, haplotypes and their apparent evolutionary age, clearly show that parthenogenesis has been a very successful reproductive strategy in this species over a long period.

Figure 1

Sampling locations where Dahlica triquetrella individuals were collected. Sites where sexual individuals were found are indicated in grey. ^# Confirmed tetraploid population [35].

Figure 2

Haplotype network for COI and COII in Dahlica triquetrella. Haplotype network for the concatenated sequences of COI (658 bp) and COII (331 bp) sequences showing the number of variable sites. Haplotypes from sexual individuals are indicated in red. See Table 1 and Figure 3 for the geographic origin of each haplotype. ^# Confirmed tetraploid population [35].

Figure 3

Phylogenetic concensus tree of mtDNA from Dahlica triquetrella. Post-burnin majority rule phylogenetic concensus tree of COI and COII concatenated sequences of sexual and parthenogenetic haplotypes and other Naryciinae species based on a GTR + I + G model of nucleotide substitution. Two branch support values are indicated. Left, the posterior probabilities obtained from a Bayesian analysis with partitioned sequences (four runs, each with 30.000 trees). Right, the likelihood values obtained from a Maximum Likelihood analysis with 500 bootstraps. For each haplotype, its geographic origin (see Table 1), the number of sequenced individuals, and the reproductive mode (red is sexual, white is parthenogenetic) are indicated. Note that D. fennicella is known only as parthenogenetic.^# Confirmed tetraploid population [35].