Divergence between sea urchins and their microbiota following speciation

Animals have a deep evolutionary relationship with microbial symbionts,
such that individual microbes or an entire microbial community can diverge
alongside the host. Here, we explore these host-microbe relationships in
Echinometra, a sea urchin genus that speciated with the Isthmus of Panama
and throughout the Indo-West Pacific. We find that the eggs from five
Echinometra species generally associate with a species-specific bacterial
community and that the relatedness of these communities is largely
congruent with host phylogeny. Microbiome divergence per million years was
higher in more recent speciation events than in older ones. We, however,
did not find any bacterial groups that displayed co-phylogeny with
Echinometra. Together, these findings suggest that the evolutionary
relationship between Echinometra and their microbiota operates at the
community level. We find no evidence suggesting that the associated
microbiota is the evolutionary driver of Echinometra speciation. Instead,
divergence between Echinometra and their microbiota is likely the
byproduct of ecological, geographic, and reproductive isolations.