Epigenetics as an alternative mode to speciation - The June sucker

Peter C. Searle, Dennis Shiozawa and Mark C. Belk, Biology, Brigham Young University, Provo, UT, R. Paul Evans, Microbiology and Molecular Biology, Brigham Young University, Provo, UT, Arminda Suli and Michael Stark, Physiology and Developmental Biology, Brigham Young University, Provo, UT

Background/Question/Methods
Epigenetic modifications to gene expression can lead to heritable phenotypic variation between genetically similar organisms. Epigenetic effects may explain the confounding phylogenetic status of June sucker (Chasmistes liorus). June sucker are endemic to Utah Lake, UT and have subterminal mouths adapted for pelagic feeding. Utah sucker (Catostomus ardens) also reside in Utah Lake, but have ventral mouths adapted for benthic feeding. As larvae, these suckers have subterminal mouths, however after 15 weeks of development, the Utah sucker’s mouth shifts ventrally. To analyze the role of epigenetic events in altering gene expression during larval development of these suckers—resulting in genetically similar but phenotypically different species—we will 1) Use geometric morphometric analysis of head and premaxilla shape to determine the critical developmental period (i.e. the week before and during) when mouth shape changes the most between these larval suckers; 2) Use transcriptome analysis to determine the transcriptome profiles for the head region and determine what homologous genes associated with jaw development are actively expressed during the critical developmental period; and 3) use in situ hybridization to determine spatiotemporal expression of target genes in the head region of these suckers.
Results/Conclusions
Geometric morphometric analysis of the head and premaxilla reveals that June and Utah sucker exhibit common shape variation from weeks 0-6, with species-specific shape variation present by week 10 (i.e., critical developmental period). Transcriptomes were sequenced from specimens collected before and after this critical developmental period. These transcriptomes are being screened for active functional genes associated with the development of craniofacial structures in the head region. In addition, we are generating the first de novo assembly of June and Utah sucker transcriptomes. Our final objective is to develop tissue-specific tools that will identify regions of specific gene activity in the critical developmental period of these fish. While this study integrates techniques from the fields of evolutionary ecology, molecular biology, and developmental biology to examine epigenetic processes in June sucker, these procedures will be equally applicable for studying other species which exhibit morphological plasticity.