| Genetic isolation-by-distance describes a pattern driven by dispersal-limiting processes, whereby genetic variants sampled closer together in space are, on average found to be more genetically related than variants sampled at further distances. Many studies of population genetic patterns in corals, however, do not fit this pattern. Furthermore, increasing evidence on the primacy of local retention of larvae for marine systems as well as for the existence of locally adaptive genetic variation in corals warranted a new sampling and statistical approach. To gain insight into this "coral population genetic paradox", I present a near-exhaustive (n = 2352) assessment of individual-level spatial genetic patterns for the widely-studied, cosmopolitan, pan-Pacific coral, Pocillopora damicornis, within a single coral reef (Reef 19; diameter ∼40 m) in Kane'ohe Bay, O'ahu, Hawai'i. Genetic and spatial data from three neighboring reefs are also included to allow for cross-scale comparisons. As environmental variation could potentially be influencing genetic patterns on this scale, I also present a reef-wide characterization of environmental heterogeneity in terms of depth, habitat cover, and temperature, drawing from a two-year dataset of in situ temperature variation across a 4 m grid on Reef 19. Overall, I demonstrate: (1) the existence of intra-reef, biologically-significant environmental heterogeneity, (2) that for this species, spatial patterns of individual-level genetic relatedness found within a reef do not scale up to an inter-reef level, (3) the importance of intense sampling efforts in assessing genetic diversity and revealing spatial genetic patterns in highly clonal species, and (4) the possibility of intra-reef, depth-dependent adaptation in this species. Throughout, results are discussed within the context of past studies of P. damicornis' genetic diversity as well as within the context of global climate change and coral reef conservation. |
