Microbiota associated with echinoid eggs and the implications for maternal provisioning

Mothers impact the survival and performance of their offspring through the
resources they provision, and the degree of maternal investment in an
individual offspring can be broadly estimated by egg size for organisms
that lack parental care. Animals may also actively maintain symbiotic
partnerships with microorganisms through the germ line, but whether
microbes are a fundamental component of maternal provisioning is an
untested hypothesis in evolutionary symbiosis. We present a preliminary
test of this by comparing the egg-associated microbiota of 10 sea urchin
species with ecological factors known to influence egg size. We found that
the microbiota associated with sea urchin eggs had a phylogenetic signal
in both composition and richness, which varied between years but not
between individuals or within a clutch. Moreover, we found a negative
correlation between microbiome richness and taxonomic dominance, and that
community diversity covaried with egg size and energetic content but not
with pelagic larval duration or latitude. These data suggest that there
are multiple parallels between the ecological factors that govern changes
in egg size and microbiome composition and diversity, implying that
microbial symbionts may be another constituent potentially provided by the
mother.