College of Science and Health Theses and Dissertations

Date of Award

Winter 3-22-2019

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Biological Science

First Advisor

Dr. Windsor E. Aguirre

Second Advisor

Dr. Jalene LaMontagne

Third Advisor

Dr. Caleb McMahan

Abstract

Western Ecuador is considered a biodiversity hotspot. Nevertheless, studies of population genetic structure and variation are rare, especially in aquatic species. The genus Rhoadsia is an endemic freshwater fish in this region with two recognized species, Rhoadsia minor and R. altipinna. Little is known about the evolutionary relationships of their populations, and due to morphological similarities, their validity as distinct species has been questioned. The present study uses a phylogeographic approach to examine the evolutionary history of the genus and the validity of the two described species. Furthermore, I investigated the possible geographical origin of the genus based on patterns of genetic diversity and genetic distance from two sister genera. I also estimated potential zoogeographic breaches based on patterns of genetic divergence that could reflect points of genetic divergence between populations of other freshwater fishes. I used several molecular markers with different rates of evolution: cytochrome oxidase I (COI) and cytochrome b (Cyt-b) from the mitochondrial genome (mtDNA) and 12 microsatellite loci from the nuclear genome (nDNA). Sampling was conducted in drainages across Western Ecuador and an effort was made to sample at different elevations (from 30 to 1260 m above sea level), given the known patterns of morphological divergence associated with elevation. The phylogenetic tree resolved with the mtDNA data confirmed the presence of two species exhibiting genetic introgression at the border between the species ranges (Northern Guayas). A Bayesian-based analysis of the microsatellite data revealed the existence of ten populations of Rhoadsia divided into three main groups (I, II, and III). Group I coincided with the distribution of R. minor while group II and III seemed to represent geographic subgroups of R. altipinna. Patterns of genetic divergence and diversity were used to suggest potential evolutionarily significant units within both species for conservation efforts. The most likely geographical origin of the genus appeared to be in the Guayas drainage. However, this result is a hypothesis and should be examined more carefully in the future using other approaches. Two major zoogeographic breaches were identified: the first one was between the two largest drainages (Esmeraldas and Guayas) and the second one was located farther south cutting through the Jubones drainage and isolating the central Guayas and drainages just south from the southernmost drainages of western Ecuador. Future research should include biological and ecological data to reinforce the validity of the species. I also suggest looking for signals of adaptive divergence between species or between populations from contrasting habitats like low and high elevations. This study provides a baseline for future studies examining biogeographic relationships of freshwater species in Western Ecuador.

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