Plant functional connectivity of Nymphoides fallax in geographically isolated temporary wetlands in Mexican highlands

Abstract

Plant functional connectivity integrates species-environment interactions, dispersal vectors, and landscape structure variables to understand species’ spatial responses to habitat fragmentation. Functional connectivity is still poorly understood for aquatic plants despite the promise it holds for informing wetland conservation across landscapes. Through a landscape genetics approach, we quantified plant functional connectivity among geographically isolated wetlands by genotyping seven nuclear microsatellite loci in 18 populations of Nymphoides fallax, a tetraploid aquatic plant endemic to Mexican and Guatemalan highland wetlands. We tested if wetland connectivity, quantified with three connectivity indices, translated to high genetic diversity within populations and if geographical distance per se explained gene flow among wetlands. We also tested if landscape features such as vegetation and surface water cover explained gene flow among N. fallax populations. Our results show that wetland connectivity is positively associated with genetic diversity over threshold distances up to 5 km. The Si Hanski connectivity index, with wetland area incorporated, was the best predictor explaining the effective number of alleles, allelic richness, and expected heterozygosity. Population-specific FST, as a proxy for gene flow, was better explained by a model including forest cover than by geographical distance or water cover. Our findings highlight the importance of forest conservation to maintain gene flow at the landscape scale for N. fallax and allows the detection of key populations to maintain genetic diversity and connectivity. Understanding wetland connectivity is critical to address wetland loss in human-impacted landscapes.