Abstract
Understanding the impact of non-native species on native species is a major challenge in molecular ecology, particularly for genetically compatible fish species. Invasions are generally difficult to study because their effects may be confused with those of environmental or human disturbances. Colonized ecosystems are differently impacted by human activities, resulting in diverse responses and interactions between native and non-native species. We studied the dynamics between two Cyprinids species (invasive Chondrostoma nasus and endemic Parachondrostoma toxostoma) and their hybrids in 16 populations (from allopatric to sympatric situations and from little to highly fragmented areas) corresponding to 2,256 specimens. Each specimen was assigned to a particular species or to a hybrid pool using molecular identification (cytochrome b and 41 microsatellites). We carried out an ecomorphological analysis based on size, age, body shape, and diet (gut vacuity and molecular fecal contents). Our results contradicted our initial assumptions on the pattern of invasion and the rate of introgression. There was no sign of underperformance for the endemic species in areas where hybridisation occurred. In the unfragmented zone, the introduced species was found mostly downstream, with body shapes similar to those in allopatric populations while both species were found to be more insectivorous than the reference populations. However, high level of hybridisation was detected, suggesting interactions between the two species during spawning and/or the existence of hybrid swarm. In the disturbed zone, introgression was less frequent and slender body shape was associated with diatomivorous behaviour, smaller size (juvenile characteristics) and greater gut vacuity. Results suggested that habitat degradation induced similar ecomorphological trait changes in the two species and their hybrids (i.e. a transition towards a pedomorphic state) where the invasive species is more affected than the native species. Therefore, this study reveals a diversity of relationships between two genetically compatible species and emphasizes constraints on the invasion process in disturbed areas.
Highlights
Understanding how non-native species modify the ecological and genetic features of native biodiversity at local and global scales is a major challenge in conservation biology and of critical importance when dealing with global changes and local exacerbations due to anthropogenic activities [1,2]
In the Durance, the middle section of the river was mainly dominated by P. toxostoma (95.74% at Pertuis and 87.34% at Manosque), whereas the upstream and downstream parts of the river were dominated by C. nasus (57.76% at Buech and 80.23% at Avignon)
In terms of ecological interactions we found that C. nasus and P. toxostoma display similar feeding behaviours, with a majority (53%) of the specimens being omnivorous, which suggests a high inter-species overlapping of prey
Summary
Understanding how non-native species modify the ecological and genetic features of native biodiversity at local and global scales is a major challenge in conservation biology and of critical importance when dealing with global changes and local exacerbations due to anthropogenic activities [1,2]. If the interactions concern genetically compatible species, natural hybridisation can happen In this case, the presence of invasive alleles into the endemic species may lead to its extinction by introgression [7], a situation that has crucial implications for conservation strategies. River disturbing by human activity is traditionally seen as a major factor imposing constraints because of habitat loss (e.g. spawning site), thereby triggering hybridisation intensity [12,13,14] Because these two types of constraints (non-native species pressure and human disturbance pressure) may be simultaneously operating when the impact of invasion is investigated, it is only by including a wide range of conditions that their effects can be dissociated [10]
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