College of Science and Health Theses and Dissertations

Date of Award

Summer 8-21-2022

Degree Type


Degree Name

Master of Science (MS)


Biological Science

First Advisor

Caleb D. McMahan, PhD

Second Advisor

Windsor E. Aguirre, PhD


Rocio is a small genus of Neotropical freshwater fishes that is distributed in Atlantic drainages of northern Middle America. Two species in the genus exhibit sympatry in the Río Dulce basin (in Izabal, Guatemala), where one species is endemic (R. spinosissima), while the other only includes this area as part of a larger geographic range (R. octofasciata). Unfortunately, the ecology of these species has been poorly studied. This study sought to determine the ecological and morphological differences between these two closely related sympatric freshwater fishes. We hypothesized that R. octofasciata would exhibit greater ecological and morphological variation, showing an overlap with R. spinosissima. We also hypothesized that morphological divergence would be associated with character displacement. Local-scale environmental data suggest habitat characteristics overlap between the two species, with a greater use of slow-flowing to lentic, poorly oxygenated and with a larger range of pH, environments by R. spinosissima, and R. octofasciata inhabiting areas with a greater range of environmental characteristics. Drainage-scale data also indicate that land cover, soil, precipitation and temperature largely define the distribution of both species, with some noticeable differences. Additionally, the mean body shape is different between specimens from the two species when they are in sympatry, while specimens from outside of the sympatric area tend to show similar shape characteristics between the two species, following a pattern of character displacement.

SLP Collection


Included in

Biology Commons