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Alloparapatric species meeting in secondary contact zones are evolutionary witnesses to how reproductive isolation progresses over time and space. Western Palearctic tree frogs (Hyla) are phenotypically similar and all the species pairs tested can hybridize and eventually admix at range margins. All except one. The early-diverged Hyla meridionalis exhibits sharp phenotypic differences: a “long” breeding call and the absence of a lateral stripe. In southwestern Europe, this species co-occurs with the “short-call” striped tree frogs H. arborea and H. molleri, two expanding lineages that admix at their parapatric margins. We estimated local gene flow between these three taxa at several syntopic breeding sites in western France. We congruently matched genotypes to phenotypes: the “short-call” striped individuals were a nuclear mixture of H. arborea and H. molleri; the “long-call” stripeless individuals all featured pure H. meridionalis nuclear ancestry and mtDNA, confirming complete genetic isolation from H. arborea/molleri. Yet, we documented an F1 hybrid between a female H. arborea/molleri and a male H. meridionalis: an incompletely-striped male with an intermediate breeding call. These findings suggest H. meridionalis is still able to reproduce with parapatric congeneric species despite 20My of divergence and strong phenotypic differentiation, but that intrinsic incompatibilities (sterility) prevent genetic introgression.

Artificial stocking practices are widely used by resource managers worldwide, in order\ud to sustain fish populations exploited by both recreational and commercial activities,\ud but their benefits are controversial. Former practices involved exotic strains, although\ud current programs rather consider artificial breeding of local fishes (supportive breeding).\ud Understanding the complex genetic effects of these management strategies is an\ud importan t challenge with economic and conservation implications, especially in the\ud context of population declines. In this study, we focus on the declining Arctic charr\ud (Salvelinus alpinus) population from Lake Geneva (Switzerland and France), which has\ud initially been restocked with allochtonous fishes in the early eighties, followed by supportive\ud breeding. In this context, we conducted a genetic survey to document the\ud evolution of the genetic diversity and structure throughout the last 50 years, before\ud and after the initiation of hatchery supplementation, using contemporary and historical\ud samples. We show that the introduction of exotic fishes was associated with a genetic\ud bottleneck in the 1980–1990s, a break of Hardy–Weinberg Equilibrium (HWE),\ud a reduction in genetic diversity, an increase in genetic structure among spawning sites,\ud and a change in their genetic composition. Together with better environmental conditions,\ud three decades of subsequent supportive breeding using local fishes allowed to\ud re-establish HWE and the initial levels of genetic variation. However, current spawning\ud sites have not fully recovered their original genetic composition and were extensively\ud h omogenized across the lake. Our study demonstrates the drastic genetic\ud consequ e nces of different restocking tactics in a comprehensive spatiotemporal\ud framewo rk and suggests that genetic alteration by nonlocal stocking may be partly\ud reversible through supportive breeding. We recommend that conservation-based programs\ud consider local diversity and implement adequate protocols to limit the genetic\ud homogenization of this Arctic charr population.