Consequences of habitat fragmentation on genetic diversity and structure of Salix alba L. populations in two major river systems of Turkey
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Salix alba L. (white willow) is an indicator species of a healthy riparian ecosystem with great renewable energy potential in Turkey though habitats of the species in many river ecosystems are highly degraded or fragmented. Impacts of this degradation of river ecosystems on the magnitude and pattern of genetic diversity are not known. This study was aimed at assessing the genetic structure of S. alba populations in two highly degraded and fragmented river systems (the Goksu and Kzlrmak rivers) in Turkey with the use of 20 nuclear simple sequence repeat (SSR) loci. Fifteen of them were used for the first time in this study. Out of the 20 SSR loci, 10 loci significantly deviated from the Hardy-Weinberg equilibrium frequencies and five of them contributed greatly to the differentiation of populations. Generally, high levels of genetic diversity were found in populations of both Goksu and Kzlrmak river systems and moderate genetic differentiation (F-ST=0.07) between the river systems. On the contrary to expectations, genetic diversity was higher in middle populations of the rivers (Ho=0.67 of GRMID(Goksu river middle population), Ho=0.68 in KRMID1(Kzlrmak river middle population 1), and 0.65 in KRMID2 (Kzlrmak river middle population 2)) than in downstream populations (Ho=0.65 in GRDOWN(Goksu river downstream population), Ho=0.62 in KRDOWN1, 2 (Kzlrmak downstream populations 1, 2)). These could be due to experienced past bottlenecks, extensive vegetative material movements, and habitat fragmentation by constructed dams in the natural ecosystems of the two river systems. The genetic structure results revealed that the white willow populations in the two different river systems may have evolved from two different founder populations. A low level of genetic admixture between the river systems but high admixture within the river systems were observed due to extensive human-mediated vegetative material movements. The current study has provided valuable genetic data and information that could contribute insights to efficient conservation, management, utilization, and breeding of genetic resources of the species.