Evolution and Development of the Stickleback Lateral Line

Abstract

The lateral line sensory system allows fish to sense water movement. It has been implicated in many behaviors, including schooling, prey detection and capture, and rheotaxis. The number and arrangement of neuromasts in the lateral line varies substantially between populations of the threespine stickleback (Gasterosteus aculeatus). In some cases, variation in the lateral line is correlated with variation in ecological habitat, suggesting that it may be adaptive. Previous work in the Peichel lab identified differences between the adult lateral line patterns of two stickleback populations, a marine population from Japan (JP) and a freshwater benthic lake population from British Columbia (PB), as well as the genetic architecture of those differences. The most striking differences between these two populations are in the number and patterning of neuromasts in the main posterior (Mp) trunk line. For my thesis research, I investigated the developmental and genetic basis of the differences in Mp. PB fish have more neuromasts than JP in the Mp line, and this difference maps to Chromosome XXI. In Chapters 2 and 3, I used a number of techniques to try to identify the gene within the region responsible for the difference in number: recombination mapping, analysis of individual candidate genes, RNA-seq analysis of all genes in the region, and in situ hybridization. I did not identify the causative gene, but I did show that the candidate gene Eya1 is expressed in neuromasts during stickleback development. I also demonstrated that difference in neuromast number between PB and another freshwater population does not map to Chromosome XXI, suggesting that there are other loci that control neuromast number in sticklebacks. A second difference in the Mp line, the arrangement of neuromasts, correlates strongly with the presence of bony lateral plates and maps to Chromosome IV. In Chapter 4, I found that the elaboration of the neuromast pattern coincides with the growth of those plates through postembryonic development. I also used transgenesis to demonstrate that pleiotropic activity of the gene responsible for plate development, Eda, is also responsible for the difference in neuromast pattern.