On the Importance of the Study of Past Connectivity to Understand Present and Future Patterns in a Freshwater Fish
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Conceptually, in evolution, the variable “time” is fundamental. Extant populations are the result of long- and short-term historical processes affecting them through time. Populations in areas near the poles have been exposed to extreme changes in landscape during the Quaternary glacial cycles. This is the case for Galaxias platei, a species that survived the Quaternary in the lakes and rivers of Patagonia, a region that experienced significant changes following the Last Glacial Maximum during deglaciation as well as more recently, as a result of the construction of dams and the introduction of invasive salmonids during the Anthropocene. With these processes in mind I used genetic markers to try to (1) elucidate the effect of long- and short-term historical processes on the genetic diversity and divergence of contemporary G. platei populations, and (2) predict what would happen to future populations. I found that while the Quaternary glaciations had a great influence in contemporary populations, most of the configuration of extant populations took place during the Holocene and Anthropocene (Chapters 2, 3, and 4). Dams can have an extremely negative effect, especially for low diversity populations experiencing recent expansion, where population isolation could lead to local extinctions (Chapter 3). The difference in genetic diversity between G. platei populations inhabiting lakes with and without salmonids is similar to that observed in marine species between populations that are pristine and those that are threatened by overfishing (Chapter 4). Finally an analysis of simulated populations demonstrated the importance of spatial arrangement in the prediction of the effects of dams (Chapter 5). Thus, by using G. platei populations as a model species for the region I revealed the importance of interpreting patterns of diversity and population structure considering processes that act over different temporal scales. I thus used information from the past to understand the present and project what would happen with future populations as consequence of landscape modifications induced by humans.