When Anthropogenic River Disturbance Decreases Hybridisation between Non-Native and Endemic Cyprinids and Drives an Ecomorphological Displacement towards Juvenile State in Both Species

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.

Climate, Demography, and Zoogeography Predict Introgression Thresholds in Salmonid Hybrid Zones in Rocky Mountain Streams

“…For aquatic species, main-stem to headwater gradients in habitat structure, flow regimes, productivity, and temperature are likely to influence freshwater species distributions [23] and thus hybrid zone position and characteristics [20,24,25]. Also contributing to hybridization is propagule pressure [26], which reflects the frequency and amount of dispersal of either parental form from source populations and is dependent on the strength and proximity of those populations.…”

Microbiota associated with the skin, gills, and gut of the fish Parachondrostoma toxostoma from the Rhône basin

“…In particular, the Ardèche river basin, in the Mediterranean region, is little managed by anthropogenic structures and is characterised by changes in flow regime, with sudden floods in the autumn and long periods in which water volume remains low during the summer. By contrast, the Durance river basin is geographically situated in the Alpine and Mediterranean climatic regions, with a large positive temperature gradient from up‐ to downstream (Corse et al, ). The Durance River is heavily managed, with its water flow regulated by successive dams and weirs that buffer climatic changes and maintain a minimum flow depth, particularly during long dry periods in summer.…”

“…Climatic conditions are similar for the Durance, but this river basin is heavily managed and drains large urbanised and agricultural areas, with a flow regime strongly regulated by successive dams and connected man‐made canals (Guivier et al, ). Furthermore, the Pt populations of the Ardèche and Durance basins use different food resources, with the diet of individuals from the Ardèche containing a much higher proportion of invertebrates, and that of individuals from the Durance containing a higher proportion of diatoms (Corse et al, ). We used high throughput sequencing of the 16S rRNA gene to investigate the effects of these contrasting environmental conditions and specific dietary regimes on the taxonomic and functional variation of the bacterial communities composition associated with the skin, gills and gut in these wild Pt populations inhabiting the two river basins.…”

Unclogging improvement based on interdate and interreach comparison of water release monitoring (Durance, France)

“…During studies prior to the definition of the new instream flow of the Durance, unclogging of the riverbed was recommended to improve conditions for fish reproduction. It was in this context that the decision was made to implement annual water releases, with the aim of unclogging potential spawning grounds for target species ( Salmo trutta fario , zingel, Barbus barbus , and Chondrostoma nasus ), as their reproduction could be adversely affected by excessive clogging (Cazaubon & Giudicelli, ; Corse et al, ). A test period for these water releases has therefore been in progress since 2014 and will be completed in 2019.…”