Morales Medina, Jeffry
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Publication Restricted Reproductive biology of two ecomorphs of the Caribbean coral Montastraea cavernosa in La Parguera, Puerto Rico(2020-12-09) Morales Medina, Jeffry; Weil Machado, Ernesto F.; College of Arts and Sciences - Sciences; Cruz Motta, Juan J.; Schizas, Nikolaos V.; Department of Marine Sciences; Villanueva Vega, MariénThe reproductive success of corals is an important element for the maintenance of populations, community and ecosystem function. The common Caribbean reef-building scleractinian Montastraea cavernosa has two distinct, coexisting morphotypes (i.e. ectomorphs), a small-polyped morph (SP), that is active during the day, and a large-polyped (LP), deeper morph, which is active at night. Significant differences in morphometric, behavioral, and ecological traits suggest two separate species. Molecular data has been inconclusive, and previous reproductive studies mixed samples from both ecomorphs. The goal of this study was to characterize the sexual pattern, reproductive mode, gametogenetic cycle and timing of reproduction of coexisting colonies of both ectomorphs. The working hypothesis was that the two morphs belong to the same species. Twenty colonies of each morph living side by side were tagged on two reefs (Turrumote and Media Luna) in La Parguera Natural Reserve (LPNR), southwest coast of Puerto Rico. Ten colonies of each morph were sampled one month and the other ten the next moth to reduce physical impact on colonies and the reproductive cycle. Standard histological techniques were used. Results confirmed that both morphs had gonochoric colonies (one sex) and broadcast gametes, however, over the course three years, several tagged colonies changed sex (from male to female and vice versa), indicating that both morphs are in fact, bi-directional, sequential hermaphrodites, a reproductive pattern never reported for this or any other coral species in the Caribbean. Overall, the female/male ratio was variable over time for both morphs (SP= 1:2, LP= 1:1 in 2015; SP=1:2, LP= 1:2 in 2016, and SP= 1:1, LP= 2:1 in 2017), a result colonies changing sex. The two morphs have a single annual gametogenetic cycle; oocytes developing approximately 6 months prior to spermatocytes; beginning in November, with the pick maturation stage in August-September. No significant differences in the overall gametogenesis process were observed, but the LP morph had significantly (T-test, p = 0.0345) larger mean fecundity compared to the SP morph. We could not check if the LP and SP morphs had different spawning times, which could be a mechanism for reproductive isolation between them. Eggs have zooxanthellae while in the mesenteries, presumably translocated from the mother polyp, a new finding not reported before, which is an evolutionarily advantage for successful larvae dispersion, recruitment and early survivorship for both morphs, a possible explanation for the high abundance of juveniles and adult colonies in most reefs. Overall, with the exception of fecundity,, no significant differences were fund in any of the reproductive phases cycle to support two different species in the genus at this time. However, the clear differences in other traits indicates that more research is needed to ID other potential pre- or post-zygote isolation mechanisms, and/or to establish molecular differences that could resolve the taxonomic status of these morphotypes.