Population genomic analyses of the sea urchin Echinometra sp. EZ across an extreme environmental gradient

Extreme environmental gradients represent excellent study systems to
better understand the variables that mediate patterns of genomic variation
between populations. They also allow for more accurate predictions of how
future environmental change might affect marine species. The
Persian/Arabian Gulf is extreme in both temperature and salinity, whereas
the adjacent Gulf of Oman has conditions more typical of tropical oceans.
The sea
urchin Echinometra sp. EZ inhabits
both of these seas and plays a critical role in coral reef health as a
grazer and bioeroder, but, to date, there have been no population genomic
studies on this or any urchin species in this unique region. E.
sp. EZ’s life history traits (e.g., large population sizes, large
reproductive clutches, and long life spans), in theory, should homogenize
populations unless nonneutral processes are occurring. Here, we generated
a draft genome and a restriction site-associated DNA sequencing data set
from seven populations along an environmental gradient across the
Persian/Arabian Gulf and the Gulf of Oman. The estimated genome size
of E. sp. EZ was 609 Mb and the heterozygosity
was among the highest recorded for an echinoderm at 4.5%. We recovered 918
high-quality SNPs from 85 individuals which we then used in downstream
analyses. Population structure analyses revealed a high degree of
admixture between all sites, although there was population differentiation
and significant pairwise FST values between the two
seas. Preliminary results suggest migration is bidirec- tional between the
seas and nine candidate loci were identified as being under putative
natural selection, including one collagen gene. This study is the first to
investigate the population genomics of a sea urchin from this extreme
environmental gradient and is an important contribution to our
understanding of the complex spatial patterns that drive genomic
divergence.