Historical process lead to false genetic signal of current connectivity among populations.

Identification of the effects of historical processes on spatial genetic variation is of major importance in landscape genetics, especially in recent systems where the signal of recent isolation is often hardly perceptible. The goal of this study was to assess how differences in colonization patterns could influence spatial genetic variation using two centrarchidae species, the pumpkinseed sunfish (Lepomis gibbosus) and the rock bass (Ambloplites rupestris), from two adjacent drainage systems. The striking difference between the spatial genetic variations of the two species suggests completely opposite patterns of colonization. Rock bass colonized the drainage system from a downstream source, which resulted in a loss of diversity in upstream populations and a strong differentiation between drainage systems. In contrast, the reduction of genetic diversity and increase of differentiation toward downstream populations that were observed among sunfish populations suggest colonization from upstream to downstream. The colonization pattern observed in sunfish, which result in low differentiation between upstream most sites of the two drainages, leads to a false genetic signal of current inter-drainage gene flow. The present study demonstrates through empirical evidence that colonization patterns may impede the capacity to estimate current connectivity.