Introgression and rapid species turnover in sympatric damselflies

Abstract

BackgroundStudying contemporary hybridization increases our understanding of introgression, adaptation and, ultimately, speciation. The sister species Ischnura elegans and I. graellsii (Odonata: Coenagrionidae) are ecologically, morphologically and genetically similar and hybridize. Recently, I. elegans has colonized northern Spain, creating a broad sympatric region with I. graellsii. Here, we review the distribution of both species in Iberia and evaluate the degree of introgression of I. graellsii into I. elegans using six microsatellite markers (442 individuals from 26 populations) and five mitochondrial genes in sympatric and allopatric localities. Furthermore, we quantify the effect of hybridization on the frequencies of the genetically controlled colour polymorphism in females of both species.ResultsIn a principal component analysis of the microsatellite data, the first two principal components summarised almost half (41%) of the total genetic variation. The first axis revealed a clear separation of I. graellsii and I. elegans populations, while the second axis separated I. elegans populations. Admixture analyses showed extensive hybridization and introgression in I. elegans populations, consistent with I. elegans backcrosses and occasional F1-hybrids, suggesting hybridization is on-going. More specifically, approximately 58% of the 166 Spanish I. elegans individuals were assigned to the I. elegans backcross category, whereas not a single of those individuals was assigned to the backcross with I. graellsii. The mitochondrial genes held little genetic variation, and the most common haplotype was shared by the two species.ConclusionsThe results suggest rapid species turnover in sympatric regions in favour of I. elegans, corroborating previous findings that I. graellsii suffers a mating disadvantage in sympatry with I. elegans. Examination of morph frequency dynamics indicates that hybridization is likely to have important implications for the maintenance of multiple female morphs, in particular during the initial period of hybridization.

Environmental and Climatic Determinants of Molecular Diversity and Genetic Population Structure in a Coenagrionid Damselfly

“…in temperature and precipitation) together with fluctuations in population size (due to stochastic events and habitat fragmentation) are responsible for the heightened genetic differentiation of peripheral populations relative to the rest of the populations (Table 2). Moreover, the previously documented on-going hybridization between I. elegans and I. graellsii in Spain [25], [28] could potentially affect the degree of genetic differentiation of the Spanish I. elegans populations versus the other I. elegans populations in Europe [67]. Our statistical analyses provided evidence for a significant longitudinal cline of genetic diversity between I. elegans populations (Figure 2), while we found no evidence for latitudinal clines.…”

Developing diagnostic SNP panels for the identification of true fruit flies (Diptera: Tephritidae) within the limits of COI-based species delimitation

“…Furthermore, they have geographically partly overlapping distribution ranges and have been shown to hybridize in nature [22]. Provided the voltinism periods are at least partly overlapping, these are conditions that may favour mitochondrial introgression, i.e., the introduction of a mitochondrial genotype from another species by “accidental” pairing of two different species, a mechanism not uncommon in insects (e.g., [45-47]) and which should result in shared haplotypes. We therefore performed a haplotype network analysis to assess if the different taxa share identical haplotypes.…”

Transcriptome profiling in the damselfly Ischnura elegans identifies genes with sex-biased expression

“…The colour polymorphism in I. elegans females [22, 23] is controlled by a Mendelian locus with three alleles in a dominance hierarchy [16]. Males are monomorphic in colour, whereas females occur in three different colour forms: the male-mimicking androchrome morph and the two more cryptic and female-like gynomorphs: infuscans and infuscans-obsoleta (Fig.…”