Evolution of Electric Fish
This page describes research completed during my Master's thesis and subsequent technician work at the University of Toronto.
Loss of an Anti-Predator Adaptation
Gymnotiform fishes generate species-specific electric organ discharges (EODs), which they use for both communication and navigation. Gymnotus, the banded electric knifefish, is a diverse genus with a range that extends from Argentina to southern Mexico and includes species distributed both east (cis-Andean) and west (trans-Andean) of the Andes. I proposed a new molecular phylogenetic hypothesis for 35 Gymnotus species based on two mitochondrial (cyt b and 16S) and two nuclear genes (RAG2 and Zic1). I found that the trans-Andean species are distributed in four distinct lineages with varying amounts of divergence from their closest cis-Andean sister taxa. I also evaluated EOD phase number evolution in Gymnotus and found a trend for reduced phase numbers in both cis- and trans-Andean regions.
Evolution of Rhodopsin in Electric Fish
Functional variation in rhodopsin, the dim-light-specialized visual pigment, frequently occurs in species inhabiting light-limited environments. Variation in visual function can arise through two processes: relaxation of selection or adaptive evolution improving photon detection in a given environment. Here, we investigate the molecular evolution of rhodopsin in Gymnotiformes, an order of mostly nocturnal South American fishes that evolved sophisticated electrosensory capabilities. Our initial sequencing revealed a mutation associated with visual disease in humans. As these fishes are thought to have poor vision, this would be consistent with a possible sensory trade-off between the visual system and a novel electrosensory system. To investigate this, we surveyed rhodopsin from 147 gymnotiform species, spanning the order, and analysed patterns of molecular evolution. In contrast with our expectation, we detected strong selective constraint in gymnotiform rhodopsin, with rates of non-synonymous to synonymous substitutions lower in gymnotiforms than in other vertebrate lineages. In addition, we found evidence for positive selection on the branch leading to gymnotiforms and on a branch leading to a clade of deep-channel specialized gymnotiform species. We also found evidence that deleterious effects of a human disease-associated substitution are likely to be masked by epistatic substitutions at nearby sites. Our results suggest that rhodopsin remains an important component of the gymnotiform sensory system alongside electrolocation, and that photosensitivity of rhodopsin is well adapted for vision in dim-light environments.