Meeting Abstract
Thyroid hormone activity is of particular importance to anadromous fishes that face osmotic and metabolic challenges while migrating long distances prior to spawning and immediately after hatching. Differences in adult hypothalmic-pituitatary-thyroid (HPT) axis function have been postulated to be adaptive traits in divergent population of stickleback, yet little is known about how genetic background versus developmental environment affects thryoid morphology and function. We investigated morphological and functional development in genetically divergent populations from anadromous (RS) and fresh water (BL) habitats. We raised fish for eight generations under identical environmental conditions. Fish from each population were sacrificed at time intervals from 8 to 100 days postfertilization (dpf), and we examined histological sections for thyroid morphology, circulating thyroid hormone levels, thyroglobulin production, and expression of genes important to thyroid cell function (SLC5A5 and SLC5A8). Morphologically, anadromous fish had more follicles and follicular epithelial cells than freshwater fish. Freshwater fish had larger follicular epithelial cells, however, and higher circulating thyroid hormone levels at 100dpf. Our gene expression data suggest that anadromous fish express genes more important to early metabolism and activity, while freshwater fish express genes of mineralization and craniofacial mineralization earlier and more broadly. Adult fitness in the face of pollutants or environmental perturbations that disrupt thyroid function may therefore be affected by developmental environment, as well as genetic background of a given population.
