Agricultural intensification alters marbled newt genetic diversity and gene flow through density and dispersal reduction
Résumé
Recent agricultural intensification threatens global biodiversity with amphibians being
one of the most impacted groups. Because of their biphasic life cycle, amphibians are
particularly vulnerable to habitat loss and fragmentation that often result in small,
isolated populations and loss of genetic diversity. Here, we studied how landscape
heterogeneity affects genetic diversity, gene flow and demographic parameters in the
marbled newt, Triturus marmoratus, over a hedgerow network landscape in Western
France. While the northern part of the study area consists of preserved hedged farm-
land, the southern part was more profoundly converted for intensive arable crops
production after WWII. Based on 67 sampled ponds and 10 microsatellite loci, we
characterized regional population genetic structure and evaluated the correlation
between landscape variables and (i) local genetic diversity using mixed models and
(ii) genetic distance using multiple regression methods and commonality analysis.
We identified a single genetic population characterized by a spatially heterogeneous
isolation- by- distance pattern. Pond density in the surrounding landscape positively
affected local genetic diversity while arable crop land cover negatively affected gene
flow and connectivity. We used demographic inferences to quantitatively assess dif-
ferences in effective population density and dispersal between the contrasted land-
scapes characterizing the northern and southern parts of the study area. Altogether,
results suggest recent land conversion affected T. marmoratus through reduction
in both effective population density and dispersal due to habitat loss and reduced
connectivity.
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