Latitudinal Patterns of Egg Size and Maternal Investment Trade‐offs in Reef Corals

Aim: The aims were to test the role of temperature in latitudinal patterns of egg size and investigate maternal investment trade -offs among coral taxa.Location: Global, from 34 degrees S to 34 degrees N.Time period: 1981- 2020.Major taxa studied: Reef coral species from the order Scleractinia.Methods: We compiled a comprehensive geo-referenced global dataset of egg sizes (diameter or volume) and fecundity (number of eggs per area) for colonial corals (Scleractinia; 123 species, 5359 observations and 39 localities), substantially enhanced by new field collections (> 88% of observations). We used Bayesian phylogenetic multilevel models to test for Rass' rule (a hypothesized negative relationship between egg size and temperature); we also included other environmental variables and life history traits. We also tested whether a trade -off exists between egg size and fecundity in broadcast spawning hermaphroditic corals with horizontal symbiont transmission (HHT).Results: We found a significant relationship between coral egg size and symbiont transmission. Eggs from coral species with vertical symbiont transmission werec. 18.8% smaller than those from species with horizontal symbiont transmission. We also found non-significant relationships between egg size and sea surface temperature (SST) for broadcast spawning corals and between egg size and fecundity specifically for HHT species.Main conclusions: Contrary to recognized latitudinal patterns of egg size across taxa, our study does not provide support for Rass' rule in corals. Additionally, our findings do not support a maternal investment trade -off between egg size and fecundity for HHT species. Our study used a phylogenetic framework that should be a standard practice when studying interspecific variation, including investigation of maternal investment and identification of the influence of multiple predictors on larval fitness (egg size), in addition to trade -offs affecting propagule influx (fecundity). Both these functional traits are vital and have direct consequences for population maintenance and connectivity in sessile organisms, such as corals.