[Coral-List] Proliferation of Acropora prolifera
nf121 at nova.edu
Tue Sep 10 13:39:46 EDT 2013
My apologies for not responding sooner; I was busy in Belize conducting coral spawning research on questions related to this thread. I will briefly summarize what we currently know about A. prolifera and refer you to some publications. For a wonderful review of coral hybridization see Willis et al.. 2006. Annual Review of Ecology, Evolution, and Systematics 37, 489-517.
1) Acropora prolifera is not a sterile mule. Genetic evidence of unidirectional introgression demonstrate that genes flow from A. cervicornis into A. palmata's genome. In order for this to occur the hybrid (A. prolifera) must mate with A. cervicornis.
- For more info see: van Oppen et al. 2000; Vollmer and Palumbi 2002; Vollmer and Palumbi 2007; Hemond and Vollmer 2010; Palumbi et al. 2012
We also have preliminary evidence of introgression occurring in both directions at one site, and A. prolifera spawned in Belize 2 weeks ago.
However, no molecular evidence has been found of an F2 hybrid generation, which suggest that hybrid breakdown may be occurring or that hybridization is very recent and F2 individuals are rare (see density dependent hypothesis below).
2) There are many sites in Belize where the hybrid was not present 5 years ago but is currently proliferating. Additionally at sites in the Florida Keys, Belize, and Curacao, new single hybrid recruits have been observed. (See Vassil's early post for similar observations in Cuba.)
- Fogarty, ND et al. in prep
3) Genotypic data suggest that hybrid thickets are not only from asexual propagation, but from multiple distinct hybridization events.
- Fogarty, ND et al. in prep.
4) The hybrid does not appear to be inferior at any life history stage and demonstrates some evidence of hybrid vigor.
- Fogarty, ND. 2012. MEPS 446: 145-159.
5) Hybrids have the same zoox clade as shallow acroporids.
- Baums et al. in prep
6) Hybrids can be produced in both directions (i.e., with A. cerv and A. palmata eggs); however, they are more easily produced with A. cervicornis eggs and A. palmata sperm.
- Fogarty, ND et al. PLos One 7(2): e30486.doi:10.1371/journal.pone.0030486
The question remains: Why are hybrids recently increasing in abundance at some locations? My hypothesis is that reproductive isolation between A. cervicornis and A. palmata is density dependent. When these branching corals formed dense thickets (prior to 1980's), eggs were immediately swamped by conspecific sperm leaving very few unfertilized eggs available for heterospecific fertilization. As these species have decreased in abundance in recent decades, eggs (particularly A. cervicornis) will float unfertilized increasing the probability of heterospecific fertilization. Acropora cervicornis eggs are fertilized by A. palmata sperm as easily as conspecific sperm. My lab is currently testing this hypothesis.
- For more information on this density dependent hypothesis see : Fogarty et al. PLos One 7(2): e30486.doi:10.1371/journal.pone.0030486
My laboratory in collaboration with the Baums lab are exploring many of the remaining questions related to acroporid hybridization.
If you have further questions, please feel free to contact me directly.
Nicole D. Fogarty, PhD
Nova Southeastern University Oceanographic Center
Center of Excellence for Coral Reef Ecosystems Research: 405 office, 420 lab
8000 N. Ocean Drive, Dania Beach, FL 33004-3078
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