Interspecific interactions influence contrasting spatial genetic structures in two closely related damselfly species.

Spatial genetic structure (SGS) is largely determined by colonization history, landscape and ecological characteristics of the species. Therefore, sympatric and ecologically similar species are expected to exhibit similar SGSs, potentially enabling prediction of the SGS of one species from that of another. On the other hand, due to interspecific interactions, ecologically similar species could have different SGSs. We explored the SGSs of the closely related Calopteryx splendens and Calopteryx virgo within Finland and related the genetic patterns to characteristics of the sampling localities. We observed different SGSs for the two species. Genetic differentiation even within short distances in C. splendens suggests genetic drift as an important driver. However, we also observed indication of previous gene flow (revealed by a negative relationship between genetic differentiation and increasing potential connectivity of the landscape). Interestingly, genetic diversity of C. splendens was negatively related to density of C. virgo, suggesting that interspecific interactions influence the SGS of C. splendens. In contrast, genetic differentiation between C. virgo subpopulations was low and only exhibited relationships with latitude, pointing to high gene flow, colonization history and range margin effects as the drivers of SGS. The different SGSs of the two ecologically similar species caution indirect inferences of SGS based on ecologically similar surrogate species.