Population Genomics of Early-Splitting Lineages of Metazoans

Abstract

Population genetics/genomics investigates gene flow, genetic diversity within and between populations, inbreeding, and effective population size, among other parameters. We here review the literature available on this topic in early-splitting lineages of metazoans (Porifera, Ctenophora, and Cnidaria). To date, great variation in population genetic patterns has been demonstrated in marine invertebrates, but because genetic structure results from the interplay of both biological and physical factors at different temporal and spatial scales, the complexity of these processes is not yet well known. This knowledge gap limits our ability to predict connectivity patterns according to species’ biological traits and environmental factors. A general conclusion of our review is that in most sponges and brooding cnidarians, the short dispersal potential of the larvae, together with oceanographic circulation, is behind the strong genetic structure observed, whereas species with long pelagic larval duration (e.g., some broadcast spawners) or planktonic adults (jellyfish and ctenophores) display large variation in genetic patterns, from panmixia to local structuring, because a long pelagic life stage does not always ensure connectivity at large spatial scales. Additionally, the contribution of asexual propagation to local recruitment across phyla may also influence a populations’ genetic structure. The future use of genome-wide scans of the species, together with oceanographic modeling and methodologies to measure larval dispersal, will provide us with meaningful data to understand the role of biotic and abiotic factors driving genetic patterns in marine metazoans and allow us to make predictions about genetic trends with implications for conservation and management.