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Dwarf males of Ostrea jibananandai sp. nov. from the lower Eocene rocks of the Cambay Basin, western India, are found attached inside the anterior end of the hinge of large females. Commonly, one male is found inside a female shell. Equivalent associations are known in the extant oyster Ostrea puelchana and the Neogene “Cubitostrea” alvarezii from Argentina. This association increases successful fertilization of eggs by reducing sperm loss in these spermcasting/brooding oysters. The sperms, released into water, are normally brought in with the inhalant water current before fertilization inside the body of the female in brooding oysters. This male-female association reduces the uncertainty involved in fertilization because sperms are released directly inside the female shell. The phenomenon is christened here as facultative monogamy. With this discovery, its evolution in oysters is pushed back more than 40 myr to over 54 Ma. Facultative monogamy evolved only in these three species over its long history in spite of its obvious advantages. Facultative monogamy reduces evolutionary flexibility by decreasing phenotypic variability. It is argued here that the phenomenon evolved by trading off morphological variability in favour of successful fertilization in response to environmental perturbations that tend to disrupt sperm transport in open water. Rapid global warming is hypothesized to potentially cause environmental perturbation, because two of the three cases of facultative monogamy in oysters, Eocene O. jibananandai sp. nov. and Recent O. puelchana, occurred at the early stages of hyperthermal events.

Dwarf males of Ostrea jibananandai sp. nov. from the lower Eocene rocks of the Cambay Basin, western India, are found attached inside the anterior end of the hinge of large females. Commonly, one male is found inside a female shell. Equivalent associations are known in the extant oyster Ostrea puelchana and the Neogene "Cubitostrea" alvarezii from Argentina. This association increases successful fertilization of eggs by reducing sperm loss in these spermcasting/brooding oysters. The sperms, released into water, are normally brought in with the inhalant water current before fertilization inside the body of the female in brooding oysters. This male-female association reduces the uncertainty involved in fertilization because sperms are released directly inside the female shell. The phenomenon is christened here as facultative monogamy. With this discovery, its evolution in oysters is pushed back more than 40 myr to over 54 Ma. Facultative monogamy evolved only in these three species over its long history in spite of its obvious advantages. Facultative monogamy reduces evolutionary flexibility by decreasing phenotypic variability. It is argued here that the phenomenon evolved by trading off morphological variability in favour of successful fertilization in response to environmental perturbations that tend to disrupt sperm transport in open water. Rapid global warming is hypothesized to potentially cause environmental perturbation, because two of the three cases of facultative monogamy in oysters, Eocene O. jibananandai sp. nov. and Recent O. puelchana, occurred at the early stages of hyperthermal events. [ABSTRACT FROM AUTHOR]

Background: The Caribbean pillar coral Dendrogyra cylindrus was recently listed as a threatened species under the United States Endangered Species Act. One of the major threats to this species is its low, virtually undetectable recruitment rate. To our knowledge, sexually-produced recruits have never been found in over 30 years of surveys of Caribbean reefs. Until recently, the reproductive behavior of D. cylindrus was uncharacterized, limiting efforts to study its early life history, identify population bottlenecks, and conduct outplanting projects with sexually-produced offspring. In Curaçao, we observed the spawning behavior of this species over three years and five lunar cycles. We collected gametes from spawning individuals on three occasions and attempted to rear larvae and primary polyp settlers. Results: Here we describe successful fertilization methods for D. cylindrus and we document rapid embryonic development. We describe the successful propagation of embryos to the swimming larvae stage, the first settlement of larvae in the laboratory, and the survival of primary polyp settlers for over seven months. We show that spawning times are highly predictable from year to year relative to the lunar cycle and local sunset times. We use colony-level data to confirm that males begin spawning before females. We also provide the first reports of split-spawning across months in this species. Conclusions: Together, our findings of consistent spawning times, split-spawning, rapid embryonic development, and remarkable robustness of larvae and settlers now enable expanded research on the early life history and settlement ecology of D. cylindrus. This will help biologists to identify the population bottlenecks in nature that underlie low recruitment rates. Further, the settlement of D. cylindrus larvae in the laboratory now makes out-planting for restoration more feasible. Asynchronous spawning times and rapid embryonic development may have important consequences for population biology, connectivity, and management, by affecting fertilization dynamics and larval dispersal distances. We argue that a precautionary approach to conservation is warranted, given this species' peculiar life history traits and still-unresolved population structure. Overall, the natural history and husbandry contributions presented here should facilitate accelerated research and conservation of this threatened coral. [ABSTRACT FROM AUTHOR]