Evolution and biogeography of the Zanclea-Scleractinia symbiosis

Abstract

Scleractinian corals provide habitats for a broad variety of cryptofauna, which in turn may contribute to the overall functioning of coral symbiomes. Among these invertebrates, hydrozoans belonging to the genus Zanclea represent an increasingly known and ecologically important group of coral symbionts. In this study, we analysed 321 Zanclea colonies associated with 31 coral genera collected from 11 localities across the Indo-Pacific and Caribbean regions, and used a multi-disciplinary approach to shed light on the evolution and biogeography of the group. Overall, we found high genetic diversity of hydrozoans that spans nine clades corresponding to cryptic or pseudo-cryptic species. All but two clades are associated with one or two coral genera belonging to the Complex clade, whereas the remaining ones are generalists associated with both Complex and Robust corals. Despite the observed specificity patterns, no congruence between Zanclea and coral phylogenies was observed, suggesting a lack of coevolutionary events. Most Zanclea clades have a wide distribution across the Indo-Pacific, including a generalist group extending also into the Caribbean, while two host-specific clades are possibly found exclusively in the Red Sea, confirming the importance of this peripheral region as an endemicity hotspot. Ancestral state reconstruction suggests that the most recent common ancestor of all extant coral-associated Zanclea was a specialist species with a perisarc, occurring in what is now known as the Indo-Pacific. Ultimately, a mixture of geography- and host-related diversification processes is likely responsible for the observed enigmatic phylogenetic structure of coral-associated Zanclea.

Diversification and distribution of gall crabs (Brachyura: Cryptochiridae: Opecarcinus) associated with Agariciidae corals

“…Agaricia) in the Atlantic. This result is in contrast with a study on coralassociated hydrozoans of the genus Zanclea Gegenbaur, 1856, where the Caribbean harbours the same generalist hydrozoan species as the Indo-Pacific (Maggioni et al 2020), highlighting the suitability of Cryptochiridae crabs for co-evolutionary studies.…”

Integrative systematics illuminates the relationships in two sponge-associated hydrozoan families (Capitata: Sphaerocorynidae and Zancleopsidae)

“…Indeed, the morpho-molecular approach enabled us to accurately characterise the analysed species, to identify the previously unknown polyp stages of Euphysilla and Zancleopsis, to describe a new sphaerocorynid genus and species (both authored by Maggioni), and to assess the phylogenetic position of the two families within the Capitata. Molecular species delimitations concordantly revealed the presence of ten species hypotheses in the investigated dataset, and also genetic distances between species were always moderate to high, not overlapping with intraspecific distances, with values comparable to other closely related capitate species (e.g., Miglietta et al, 2019;Maggioni et al, 2020aMaggioni et al, , b, 2021. Morphological analyses identified diagnostic and easy-to-detect features of sphaerocorynid polyps, mostly related to the colour of hydranths, tentacles organisation, inclusions in capitula, and organisation of medusa buds.…”

“…However, with a few exceptions for S. bedoti and E. pyramidata, all other samples analysed in this work were associated with sponges. Capitate hydrozoans often establish symbiotic associations with benthic invertebrates, such as scleractinian corals, octocorals, bryozoans, and bivalves (Cerrano et al, 1997;Maggioni et al, 2016Maggioni et al, , 2020c, in some cases with high specificity (e.g., Montano et al, 2017a;Maggioni et al, 2020a) and hypothesised important ecological roles for their hosts (Montano et al, 2017b). On the other hand, they can also be hosts themselves to anthoathecate hydrozoans (Montano et al, 2020).…”

“…In the same way, it is also possible that Zancleopsis species are generalist symbionts of poriferans, with Z. cabela hosted by three different sponge species in the Maldives and Red Sea (Maggioni et al, 2017). Future increased efforts in sponge host identification will likely shed light on the degree of specificity of these associations and may also help with the delineation of species boundaries in the associated hydrozoans, as in other species (Maggioni et al, 2020a(Maggioni et al, , 2021.…”

“…Total genomic dna was extracted from ethanol-fixed samples using the protocols described in Maggioni et al (2020a) and Schuchert (2005). Briefly, dna was extracted from a single polyp or medusa by digesting the specimen in a mixture of proteinase K and MilliQ water in the first case, or following the CTAB protocol (Coffroth et al, 1992) in the second case.…”