Dendrophyllia

Aurelle, Didier, Haguenauer, Anne, Blaise, Chloé, Reynes, Lauric, Arnaud-Haond, Sophie, Boavida, Joana, Cabau, Cédric, Klopp, Christophe, Lundalv, Tomas, Noûs, Camille, Sartoretto, Stéphane, Wienberg, Claudia, Jiménez, Carlos E. & Orejas, Covadonga, 2024, On the specific status of eastern Mediterranean Dendrophyllia corals (Cnidaria, Anthozoa): Genetic characterization and speciation scenarios, Zoologica Scripta 53 (2), pp. 235-247 : 241

4.1 | Species identity of Dendrophyllia corals from Cyprus

Morphological characteristics, especially at the skeleton level, have initially been the main characteristics used in the systematics of corals ( Kitahara et al., 2016). The information supplied by morphology in coral systematics can be limited by several factors: intra-specific polymorphism, intra-colony variability, and morphological plasticity ( Kitahara et al., 2016; Paz-García et al., 2015). The integration of genetic information is then useful for species delimitation in corals ( Gélin et al., 2017).

Here, both morphological and genetic data agreed on the identification of Cyprus samples as D. ramea . From a genetic point of view, the COI mitochondrial sequence clearly linked the samples of Cyprus to D. ramea , with a grouping with other sequences from this species obtained here from Sagres (Atlantic). Conversely, other samples used here, and identified morphologically as D. cornigera , grouped separately from D. ramea and were identical to another D. cornigera sequence from GenBank. One can note that the divergence among Dendrophyllia species was quite low with COI. This low inter-specific divergence was also observed for the Caryophyllia species studied here. This relatively low divergence is consistent with the generally low rate of evolution of mitochondrial DNA observed in anthozoans ( Calderón et al., 2006; Shearer et al., 2002), though with exceptions ( Muthye et al., 2022).

The phylogeny obtained with mitochondrial sequences was not well-resolved, with several nodes lacking support, and several genera did not appear monophyletic. This lack of monophyly of genera in the Dendrophylliidae family has already been observed with two mitochondrial and one nuclear markers ( Arrigoni et al., 2014). Nevertheless, our results also underline the need to go further than mitochondrial sequences to work on species delimitation in this family. Here, the transcriptome data clearly separated D. ramea and D. cornigera and agreed with the identification of Cyprus samples as D.ramea . Unfortunately, we did not get any transcriptome sequences for D. ramea samples from Portugal, which would be useful for a better understanding of the phylogeography of this species. This would be especially interesting to test for the divergence between Atlantic and Mediterranean populations observed in various marine species ( Patarnello et al., 2007).

Regarding morphology, the colonies in the Cyprus population appeared slender when compared to other D.ramea populations. Despite this observation, the characteristics analysed here in Cyprus samples were different from those observed in D.cornigera and confirmed their identification as D.ramea . Specifically, in contrast to D.ramea , D.cornigera has five septal cycles with all septa of similar size; calices stem from the base, never arranged in series, and they are smaller and less numerous than in D.ramea .

The morphological differences observed between colonies of D.ramea from Cyprus and from other locations could be explained by two, non-mutually exclusive hypotheses. First, these morphological variations could be driven by developmental plasticity in response to different environmental factors, such as sediment regimes and depth. The effect of sediment in the singular morphology of the specimens from Cyprus can be hypothesized due to the singular growth that the polyps of D. ramea display in the most distal part of the branches (see figure 23. 1c in Orejas, Jiménez, et al., 2019). To the best of our knowledge, the Cypriot D.ramea population (dozens if not hundreds of colonies) and the few colonies off Tarablus/ Batroum in Lebanon are the deepest in the Mediterranean, and both are thriving on soft bottom and exhibit similar morphologies. A soft substrate might influence the growth pattern with a constraint for polyps not to be covered by sediments (Orejas, Gori, et al., 2019; Orejas, Jiménez, et al., 2019); such a morphological diversity according to the environment has also been proposed in the solitary species C. smithii ( Zibrowius, 1971) . Secondly, the morphological differences could also be determined by genetic differences in a context of the same or different related species. A more extended study of D. ramea populations in the Mediterranean, especially in the eastern basin, would be useful to go further on this question as well.