Thermal tolerance of Strongylocentrotus purpuratus early life history stages: mortality, stress-induced gene expression and biogeographic patterns

In this study, we examined the differential thermal tolerance of Strongylocentrotus purpuratus early life history stages by comparing high temperature–induced mortality and the relative levels of the stress-induced gene, hsp70, between S. purpuratus embryos and larvae from adults collected throughout the species range. There was no significant difference between gastrulae and 4-arm plutei mortality from all sites examined. Furthermore, there was little variability in temperature tolerance across the biogeographic range as southern gastrulae and 4-arm plutei exhibited similar tolerances to northern individuals. Relative levels of hsp70 mRNA expression did not differ overall between the two developmental stages at each site. Across sites, all gastrulae and 4-arm plutei exhibited maximum hsp70 expression at approximately 25°C; however, the range of hsp70 expression was narrower in southern individuals, suggesting they are living closer to their upper thermal limit than northern individuals.