Riverscape genetics to assess habitat connectivity in riverine organisms.

Abstract

To prevent extinction of species in currently threatened stream ecosystems, it is important not only to increase the number of high-quality habitats, but also to ensure the connectivity of these habitats. Gene flow (exchange of genes between populations) is the "functional connectivity" of habitats and can be assessed using population/landscape genetics approaches. In this paper, I have (i) checked the function of gene flow on species and regional populations, (ii) reviewed methods for estimating gene flow that have been developed in the field of landscape genetics, and (iii) discussed the applicability of these approaches for riverine organisms. Gene flow has been shown to enhance population resilience in a changing environment and to have a positive effect on the viability of species and regional populations. Regarding the approaches to estimating gene flow, many methods have been proposed, most of which are based on the idea that interpopulation genetic differentiation decreases with an increasing number of migrants, while there were also multiple methods inferring recent and/or bidirectional gene flow using individual information. Each proposed method for estimating genetic differentiation and gene flow has assumptions; it should be important to use the appropriate method according to the characteristics of the data and the purpose of research. Stream ecosystems are unique systems with up-down-stream asymmetry and hierarchical and dendritic structures, sometimes making it difficult to apply the same methods developed in landscape genetics for riverine organisms. This led to the establishment of an exceptional field called "riverscape genetics", where some analysis methods specialized for riverine organisms are being developed. As an example of riverscape genetics, I introduced the case of fluvial sculpin in the upper reaches of the Sorachi River, confirming that the estimation of gene flow can provide useful knowledge for conservation.