Biology subjects

Babcock, R. C.

Publications and source records attributed to Babcock, R. C..

2 recordsLinked to original sources

bioRxiv2025

Optimising fertilisation kinetics models for broadcast spawning corals in the genus Acropora

Synchronous spawning is a specialised adaptation to maximise fertilisation success in free spawning sessile invertebrates. There are many factors that drive and limit reproduction in such benthic invertebrates including localised hydrodynamic forcing, adult density dependence, and fine-scale gamete interactions, all of which are difficult to measure in situ. Therefore, measures to manage or restore reproductive populations of sessile invertebrates rely in part on adequate modelling of spawning processes at localised scales. Fertilisation kinetics of spawning events has been modelled for many free spawning marine invertebrate taxa, yet little work has been done to parameterise such models for hermaphroditic corals. This study used experimentally derived coral-specific parameters and optimisation protocols to improve model predictions of fertilisation outcomes for Acropora kenti (formerly A. "Maggie" tenuis) and A. digitifera. Three fine scale parameters that are difficult to measure experimentally - fertilisation efficiency (Fe), egg concentration (E0), and polyspermy block strength (tb) - were estimated using optimisation, and medians and 95% confidence intervals were derived for each parameter and species. For A. kenti the median optimised Fe value was 0.0194 (0.0027-0.0776), and tb was 0.1000 (0.1000-0.1000). For A. digitifera, the median optimised Fe value was 0.0013 (0.0002-0.0030), and tb was 10.0000 (2.4703- 10.0000). Further, sensitivity analyses suggest that kinetics models are the most sensitive to changes in Fe parameter values, as well as species-specific metrics like sperm swimming speed and egg size. Results will inform biophysical coral fertilisation models to better predict reproductive outcomes and support management decisions that safeguard natural reef recovery.

systems biology↗

bioRxiv2024

Allee effects, spawning asynchrony, and mixed reproductive modes in a common mass spawning coral

Understanding strategies of organisms that utilise multiple modes of reproduction presents a complex challenge for evolutionary biologists. Platygyra daedalea, a common reef-building coral with unclear reproductive boundaries between morphological species, illustrates these complexities. Here, we evaluate the contribution of these reproductive modes in the coral P. daedalea at Heron Island, on the southern Great Barrier Reef. We tagged and sequenced eighteen coral colonies, representing various degrees of spatial clustering, along a 130-m stretch of shallow reef slope. During spawning, divers collected eggs from each colony and placed them in mesh containers within the spawn slick, allowing free movement of sperm for fertilisation. High levels of spawning asynchrony were observed, potentially indicating distinct genetic clusters within the putative species, which resulted in low fertilisation success (1.5%). Notably, of those fertilised eggs, paternity assignments revealed that all resulting embryos were self-fertilised, with no cross-fertilisation occurring. The adult population showed evidence of two genetically distinct subpopulations, along with levels of spatial autocorrelation and inbreeding. This evidence supports the notion of small breeding populations within larger assemblages, density-dependent population effects, and localised recruitment. Selfing may serve as a reproductive assurance mechanism in such populations, which may be more hierarchically structured than previously thought. Given the lack of evidence for in situ outcrossed fertilisation in this natural coral population during split spawning, it appears that P. daedalea may rely on limited high-density patches of adults for successful cross-fertilisation, utilise atypical modes of reproduction when at low densities, and/or sustain its population through limited progeny.

ecology↗