Discussion
A major objective of marine molecular ecology is to obtain accurate
estimates of subtle genetic structure, as it can inform efforts to
identify units of management and design effective marine protected areas
(Kelley et al. , 2016; Selkoe et al. , 2016). By comparing
sponge populations in Indo-Pacific marine lakes and lagoons at different
spatial scales, varying in degree of connection to the sea and differing
in local environmental conditions, we were able to study fine-scaled
genetic structure and the drivers of genetic diversity and
differentiation of marine populations. Using a reduced representation
genomic approach, we confirmed broad-scale patterns of structure
identified in a prior single-marker study and provided new evidence of
small-scaled structure for sessile species with a short dispersive
larval stage. Furthermore, we found no associations between sponge host
population patterns and previously studied microbial community patterns,
suggesting that sponge host and associated microbes may be on different
eco-evolutionary tracts. Below, we discuss our findings on population
structure for marine lake sponges, the possible drivers of diversity,
microbe versus host patterns and finally the implications for future
phylogeographic and population genetic studies on sponges.