Coral Genetics

PRESENT:  Trans-Pacific gene flow and species delimitation in Porites. The reef-building Porites found in the Eastern Pacific are a subset of more diverse Central and Western Pacific coral assemblages. Are these faunal similarities the vestiges of past (pre-Pleistocene) connections, or the result of ongoing genetic exchange, perhaps aided by current reversals during El Nino events? In collaboration with Iliana Baums, we have generated nuclear sequence and microsatellite markers that show:

– populations in the eastern Pacific are not experiencing ongoing gene flow with the central Pacific (Baums et al. 2012)

– nominal P. lobata in the eastern Pacific include a cryptic species.  The two are ecologically differentiated, both in terms of habitat and their interactions with other reef organisms (Boulay et al. 2014).

– three named Caribbean species of Porites do not appear to be genetically isolated, suggesting they may instead be habitat-specific morphs (Prada et al. 2014).

– Eastern Pacific and Hawaiian populations of P. lobata appear to have split about 1.8 Mya, consistent with an early Pleistocene recolonization of American reefs.

PREVIOUS:  Large-scale (100-3000 km) genetic subdivision in a coral with limited larval dispersal potential was extensive, but not as great as predicted by stepping stone models. The discrepancy between observed levels of gene flow between populations of Balanophyllia elegans (estimated using allozyme markers) and computer simulations suggests nonequilibrium conditions prevail. Relatively low numbers of alleles per locus in parts of Balanophyllia‘s range recently covered by glaciers supports this idea (Hellberg 1994). To further test this idea, I looked at gene flow at a smaller spatial scale (1-50 km) and found gene flow matched equilibrium stepping stone expectations (Hellberg 1995). Gene flow in a coral with planktonically dispersed larvae was high, and did not decrease with geographic distance (Hellberg 1996).

MtDNA variation (not) in Balanophyllia elegans
A geographic survey of mtDNA sequences from B. elegans revealed greatly depressed mtDNA mutation rates, over 100x slower than those of most other animals (Hellberg 2006). We would like to look for repair genes that might be responsible. We are also interested in resurveying the original B. elegans population samples for DNA sequence variation underlying observed allozyme differentiation.

Species status of Oculina varicosa
O. varicosa forms large deep water reefs off the eastern Florida coast that provide valuable nursery habitat for several fisheries. These fragile reefs have been much damaged by fishing dredges. Using sequence data from three nuclear markers, we showed that deep water populations of O. varicosa are distinct from congeners that occur along the southeastern US (Eytan et al. 2009). As part of work funded by NOAA carried out in collaboration with Marshall Hayes, we have generated EST’s for O. varicosa and have found a candidate gene that may be involved in defending corals against microbial pathogens (Hayes et al. 2010).  Karine Posbic is presently expanding this work to the Mediterranean, where an Oculina species of questionable origin has been expanding over the past few decades.

Clonal reproduction and population connectivity in Acropora
Acropora palmata is a branching hermatypic coral that is a hallmark of healthy Caribbean reefs. Because the geographic distribution of A. palmata spans many national boundaries, estimating levels of population connectivity is a critical first step to any management plan. As part of her Ph.D. thesis, Iliana Baums found a genetic break between A. palmata populations in the western and eastern Caribbean occurring near the Mona Passage (Baums et al. 2005).  Western populations show higher levels of clonality than eastern ones (Baums et al. 2006).  In part because of this work, A. palmata has now been listed as “threatened” under the U.S. Endangered Species Act, the first marine invertebrate to be so designated. Margaret Miller is a collaborator on this work, which was funded by NOAA.