Abstract
Population variation, particularly genetic variation, is the ultimate source of diversification and adaptation to variable environments. However, habitat specialist species living on patchy habitats with high levels of population structure, small effective population size, and low genetic diversity, can face potentially high rates of local extinction both historically and in the face of contemporary environmental change. In my dissertation, I studied the phylogeography and the population genetics of a river specialist species, the torrent duck (<i>Merganetta armata</i>), at multiple spatial scales. This duck is a whitewater species with at least three recognized subspecies or ecotypes that inhabit altitudinal gradients on suitable rivers along the longest mountain system in the world, the Andes. I used mitochondrial and genomic DNA markers obtained from field-collected blood samples to understand the mechanisms associated with species diversification, dispersal, and population persistence. This species is an ideal non-model organism to study ecological and evolutionary processes related to diversification, population demography, and adaptation in traits associated with higher elevations.
I used only live subjects for this study. To collect the blood samples, I refined an active mist-net method that was used to captured 372 individuals from the three subspecies corresponding to eight elevational transects. The torrent duck is a highly elusive species that is difficult to capture alive due to their always-vigilant territorial behavior, constantly diving underwater to evade being seen, and the challenge of working in fast-moving torrential river habitats. Despite these conditions, each captured individual was measured, marked with a numbered leg-band. Blood samples were collected for DNA analysis. Multiple individuals also were recaptured within the same year and across multiple years.
To study the torrent duck population subdivision at larger geographic scales, I examined the phylogeography and population structure of two subspecies of torrent duck, (<i>M. a. leucogenis</i> in Peru and <i>M. a. armata</i> in Argentina) from four independent riverine populations. I found that the South American Arid Diagonal is likely the most significant biogeographic barrier between these old divergent subspecies in the Andes. In addition, I found that adult territoriality and breeding site fidelity behaviors likely contribute to their strong riverine population structure. Moreover, the genetic diversity in torrent ducks was not qualitatively different from other Andean duck species with larger population sizes, and falls somewhere in the middle of genetic diversity compared with a much broader survey of species.
Finally, to understand population subdivision and connectivity at a finer scale, I studied the population structure, relatedness among individuals, and indirect and direct estimates of dispersal of the Peruvian torrent duck (<i>M. a. leucogenis</i>). For this part of the study, I used subjects from three adjacent rivers on the western Andean slope near Lima, Peru. I found a weak population structure with infrequent evidence of indirect and direct dispersal among the low and middle elevations of the rivers; and I found high levels of contemporary dispersal and gene flow across different elevations within rivers. Thus, these results support a complex metapopulation structure, where the rivers contained subpopulations connected by low frequency dispersal (sometimes driven by extreme climatic events such as the El Niño event of 2017). The identification of this metapopulation structure has important consequences; it may indicate the evolutionary potential for change of each subpopulation in the face of natural and anthropogenic disturbances, because it could favor the maintenance of genetic diversity under variable environmental conditions.
In summary, this research provides specific new information about geographic range, population size, behavior, and an individual occupancy response to disturbances (future study section). These findings may assist in the management and conservation of habitat specialist species that inhabit fragile riverine ecosystems, such as the Andes. Overall, I highlight the importance of considering multiple spatial and temporal scales of habitat variation and species behavior; in paying closer attention to these differentiations, studies like this can reveal the role ecological and evolutionary processes in determining species diversification and population persistence.<p class="MsoNormalCxSpFirst" style="text-align:justify;text-indent:17.85pt;