Ecological speciation and co-evolution of gall-inducing cecidosid moth and Schinus host plants in the Neotropics

BRENTANO, ADRIANA M.; GISLENE L. GONÇALVES; GERMÁN SAN BLAS; GILSON R. P. MOREIRA

Foz do Iguaçu

Congreso; 58º Congresso Brasileiro Do Genética; 2012

Sociedade Brasileira de Genética

Ecological speciation is an evolutionary process in which a polymorphic species splits into two sister lineages as a consequence of divergent selection pressures caused by the use of multiple niches or environment. Such process has been intensively studied in plant-feeding insects, where either sympatric or allopatric shifts onto novel host plants could lead to the diversification. However, a fully understanding of the frequency and relevance of ecological shifts in the formation of new species is still lacking. In this study, we have focused the genus Eucecidoses Brèthes (Lepidoptera: Cecidosidae), whose larvae induces galls on Schinus polygamus (Cavanilles) Cabrera (Anacardiaceae) in southern Brazil, Uruguay and Argentina. Distinct forms of the Schinus were previously identified across this broad region, but its taxonomic status is still under debate. Moreover, Eucecidoses is currently considered a monotypic genus, with only E. minutanus Bréthes formally recognized. However, recent evidences from morphological characters of corresponding immature and adult stages have also raised doubts about its taxonomy status. We therefore hypothesized an ecology-based speciation process in Eucecidoses, associated with spatial changes in the host plant that would be adapted to different environments along the distribution. Thus, our major goal in this study is to investigated the genetic structure of E. minutanus populations across its range of distribution in order to characterize evolutionary patterns of variation. We sequenced 626 base pairs of cytochrome oxidase subunit I in 12 specimens, including three populations located in Argentina (Mendoza) and Southern Brazil (Rio Grande do Sul, RS and Paraná, PR). Overall, 63 variable sites, and four haplotypes, were observed, with an haplotype diversity of 0.77 ±0.07, and nucleotide diversity of 0.05 ±0.005. Population level analysis indicated higher variability in specimens from PR, where 2 distinct haplotypes were found. Mendoza and RS sites presented only one haplotype. All haplotypes observed were unique within each population. Evolutionary divergence estimates using Kimura 2-parameters, indicated high differentiation among populations (>2%). When pairwise comparisons were performed, higher divergence were observed, where Mendoza presented 4% of differentiation in relation to PR, and 3% compared to RS. Similarly, comparison between PR and RS indicated 2% of distance. These estimates suggest high levels of divergence among population within a species, which is above the proposed threshold of species level, indicating a significant accumulation of genetic differences along the evolutionary history. Thus, our genetic data corroborates with previous morphology-based analysis, strongly supporting the existence of different lineages within Eucecidoses. In this context, we plan to add more populations and specimens across the distribution, sequence other loci and evaluate the genetic structure of the host plants as well, to make better inferences about co-evolution of Eucecidoses and its Schinus host plants. Financial Support: CAPES and PPG Ecologia-UFRGS.