Abstract
Biogeographic barriers for freshwater biota can be effective at various spatial scales. At the largest spatial scale, freshwater organisms can become genetically isolated by their high mountain ranges, vast deserts, and inability to cross oceans. Isolation by distance of aquatic plants is expected to be stronger across than alongside mountain ridges whereas the heterogeneity of habitats among populations and temporary droughts may influence connectivity and hamper dispersal. Suitable aquatic plant habitats became reduced, even for the widespread submerged Potamogeton pectinatus L. (also named Stuckenia pectinata) giving structure to various aquatic habitats. We compared the level of genetic diversity in a heterogeneous series of aquatic habitats across Iran and tested their differentiation over distances and across mountain ranges (Alborz and Zagros) and desert zones (Kavir), with values obtained from temperate region populations. The diversity of aquatic ecosystems across and along large geographic barriers provided a unique ecological situation within Iran. P. pectinatus were considered from thirty-six sites across Iran at direct flight distances ranging from 20 to 1,200 km. Nine microsatellite loci revealed a very high number of alleles over all sites. A PCoA, NJT clustering and STRUCTURE analysis revealed a separate grouping of individuals of southeastern Iranian sites and was confirmed by their different nuclear ITS and cpDNA haplotypes thereby indicating an evolutionary significant unit (ESU). At the level of populations, a positive correlation between allelic differentiation Dest with geographic distance was found. Individual-based STRUCTURE analysis over 36 sites showed 7 genetic clusters. FST and RST values for ten populations reached 0.343 and 0.521, respectively thereby indicating that allele length differences are more important and contain evolutionary information. Overall, higher levels of diversity and a stronger differentiation was revealed among Iranian P. pectinatus than previously observed for temperate European regions, due to regional differences across mountain ranges over long distances.
Highlights
Biogeographic barriers for freshwater biota can be considered at three spatial scales, namely inter and within basin and continental
Gene flow between populations of aquatic plants is restricted by the discontinuous nature of their habitat embedded in another terrestrial landscape and as such, lakes or rivers could be considered as islands of suitable habitats
As the primers were previously developed and used on European Potamogeton pectinatus populations, we tested these cross-amplified loci with microchecker, but there was no evidence for null alleles, large allele dropout or scoring error due to stuttering
Summary
Biogeographic barriers for freshwater biota can be considered at three spatial scales, namely inter and within basin and continental. At the largest spatial scale, freshwater organisms are isolated by their high mountain ranges, inability to cross oceans and vast deserts [1]. Gene flow between populations of aquatic plants is restricted by the discontinuous nature of their habitat embedded in another terrestrial landscape and as such, lakes or rivers could be considered as islands of suitable habitats. Besides merely distance as a limit to connectivity, especially large deserts and mountain ranges act as additional natural barriers. The flora of the mountains provides many examples of subspecies with populations and very closely related species that show restricted gene flow due to these inherent geographic barriers [7, 8]. Isolation by distance is stronger across than alongside mountain ridges [9, 10, 11]
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