Meeting Abstract
Conspecific populations may experience substantial variation in thermal environments across the species range and this may result in the evolution of population differences in thermal tolerance. Previous work on the intertidal copepod Tigriopus californicus has shown that southern populations can survive acute thermal stress that is lethal to northern populations. These differences are associated with differences in expression of heat shock protein (HSP) genes. Among these genes, HSP Beta 1 (HSPB1) shows the highest level of upregulation and heat tolerant populations also express more HSPB1 than heat sensitive populations. An RNAi knockdown study found that HSPB1 is essential for T. californicus survival following acute heat stress. Comparison of approximately 1 kb of 5’ flanking region of the HSPB1 gene from populations along the coast revealed variation in Heat Shock Transcription Factor (HSF) binding motifs called Heat Shock Elements (HSEs). HSPB1 promotors from heat tolerant populations contain two canonical HSEs while less tolerant populations have mutations in these conserved motifs. To examine the potential role of sequence divergence in these cis-regulatory elements, we investigated allele specific expression in F1 hybrids between a heat tolerant San Diego population and a less tolerant Santa Cruz population using RNA-seq. The results show biased expression favoring elevated expression of the San Diego allele possessing the canonical HSEs and confirm our prediction of adaptive divergence in cis-regulatory elements. Our results provide an insight on how small changes in cis-regulatory elements could result in different thermal tolerance phenotypes and local adaptation.
