Evidence of sexual dimorphism in skeletal morphology of a gonochoric reef coral

Abstract

In the emerald coral Porites panamensis, the rates of elongation and calcification of colonies are higher in males than in females, probably because of the higher energetic demands of the latter in order to cope with the development of the large planulae produced throughout the year. This differing energetic demand could also be reflected in the sexual dimorphism of the calyces; hence, to test this hypothesis, 11 morphological traits of the corallite were assessed from 63 colonies that were collected in the southern Gulf of California, Mexico. Three traits showed statistical differences between sexes, enabling accurate distinction of males from females. Our results confirm for the first time the existence of external sexual dimorphism in a reef-building coral, opening the possibility that sex-related morphological differences may occur generally in gonochoric scleractinians. These findings can be very useful for the correct classification and characterization of recent and fossil records, helping to improve the historical and evolutive understanding of reef-building corals facing threats under environmental changes.

Sexual dimorphism in corallite size and modularity of a broadcast spawning coral, Porites lobata

“…Sexual dimorphism is widespread among animals but has been considered rare in colonial marine taxa (Levitan, 2010). Recent studies on scleractinian corals, however, have found sexual dimorphism in size (Kramarsky-Winter and Loya and Sakai, 2008), calcification rates (Cabral-Tena et al, 2013;Tortolero-Langarica et al, 2016;Tortolero-Langarica et al, 2017;Mozqueda-Torres et al, 2018;Cruz-Ortega et al, 2020), skeletal isotopic signals (Cabral-Tena et al, 2013), and corallite morphologies (Gonzaĺez-Espinosa et al, 2018). From these studies (Table 1), corallite differences have been found for only one species (Gonzaĺez-Espinosa et al, 2018), leading us to ask whether the dimorphism previously observed (primarily in growth) could be seen in corallite's traits.…”

“…Five morphological traits were selected for analysis (Table 2) based on their potential to delimit between Porites species (Brakel, 1977;Weil, 1992;Budd et al, 1994) and reveal sexual dimorphism in P. panamensis (Gonzaĺez-Espinosa et al, 2018). A Nikon D5300 digital camera was used to capture images for corallite density (Figure 2A).…”

“…In brooding gonochoristic corals, females both capture sperm for internal fertilization and, critically, brood larvae within their polyps, while males merely release sperm (Baird et al, 2009;Harrison, 2011). These differences may explain the divergent morphologies of their corallites (Gonzaĺez-Espinosa et al, 2018). Meanwhile, in gonochoristic broadcast spawning corals, both sexes release their gametes and fertilization occurs externally (Baird et al, 2009;Harrison, 2011), with females freed of any larval care beyond provisioning eggs.…”

“…Meanwhile, P. panamensis broods its larvae (Carpizo-Ituarte et al, 2011). Its corallites show sexual dimorphism in their diameter, density, and number of neighboring corallites (Gonzaĺez-Espinosa et al, 2018) but the integration of these traits has not been analyzed before.…”

Sex estimation from morphology in living animals and dinosaurs

“…The remaining species were then tested for sexual dimorphisms using Multivariate Analysis of Variance (MANOVA) based on all morphological measurements, and species with at least weakly significant differences between the sexes (p < 0.1) were retained. This left 139 species in the data (Table 1), containing 53 arthropods (38 arachnids (Buzatto et al, 2014), 4 crustacean (Fernandes Martins et al, 2017;Sørdalen et al, 2020), 7 insects (Punzalan & Rowe, 2015)), 1 cnidarian (González-Espinosa et al, 2018), and 89 vertebrates (1 amphibian (De Lisle, Paiva, & Rowe, 2018), 2 birds (Hsu et al, 2014;Poissant et al, 2016), 6 mammals (Christiansen & Harris, 2012;Roseman et al, 2020), 8 osteichthyes (Ronco, Roesti, & Salzburger, 2019;Garcia & Zuanon, 2019), and 72 reptiles (Sanger et al, 2013;Massetti et al, 2017;Burbrink, 2019)).…”