Phylogenetic ecology of gall crabs (Cryptochiridae) as associates of mushroom corals (Fungiidae)

Abstract

Coral‐associated fauna is a relatively understudied topic. Hence, the nature of the relationship between an associated organism and its host is usually unknown. In the present study, the obligate associations between gall crabs (Decapoda: Cryptochiridae) and mushroom corals (Scleractinia: Fungiidae) are reviewed from a phylogenetic perspective. Based on field surveys, examination of museum material and a literature review, a total of 35 fungiid species have been found that act as hosts for four gall crab species. Fungiid‐associated gall crabs appear to be more geographically widespread than previously known, with new records showing their occurrences from the Red Sea and western Indian Ocean all the way to the central Pacific Ocean. The obligate nature of the association between cryptochirids and their hosts makes them an ideal model taxon to test for possible cospeciation events. The congruence between their phylogenies was tested by using the program Jane 4.0, resulting in cospeciation and duplication events between the crabs and their host corals. The sharing of several closely related host coral species by the same gall crab species or genus may provide support to models indicating phylogenetic relationships within the Scleractinia.

A New Host and Range Record for the Gall CrabFungicola fageias a Symbiont of the Mushroom CoralLobactis scutariain Hawai‘i

“…The elongated pits were wedged in between the host's septa, with the crabs themselves in perpendicular position (Figure 1f ). These dwellings were similar to those made by Fungicola crabs in corals of Cycloseris and Pleuractis (van der Meij, Fransen, et al 2015: fig. 1).…”

“…Until now, the easternmost record of F. fagei is from New Caledonia and Vanuatu (Figure 4), where it was reported from the corals Podabacia motuporensis Veron, 1990, andSandalolitha robusta (Quelch, 1886), respectively (van der Meij 2015a; van der Meij, Fransen, et al 2015). Hawai'i is about 6,000 km away from the nearest locality of F. fagei at Vanuatu (Figure 4).…”

“…For the purpose of molecular identification, a Neighbor-Joining tree was constructed to show the phylogenetic affinities of the crabs from Hawai'i, along with all three Fungicola species recognized so far (van der Meij, Fransen, et al 2015). Data are derived from GenBank ( NCBI ) based on specimens from Southeast Asia and the West Pacific (van der Meij 2015a).…”

“…Finally, van der Meij, Fransen, et al (2015) reported on empty galls of cryptochirids found in museum specimens of L. scutaria from Hawai'i, which were assigned to Fungicola sp. In an earlier review paper, Hoeksema et al (2012) reported on two gall crab species, Fungicola fagei (Fize & Serène, 1956) and F. utinomi (Fize & Serène, 1956), in association with L. scutaria, but they did not give specific locality data or references.…”

“…In an earlier review paper, Hoeksema et al (2012) reported on two gall crab species, Fungicola fagei (Fize & Serène, 1956) and F. utinomi (Fize & Serène, 1956), in association with L. scutaria, but they did not give specific locality data or references. In a successive, more elaborate study on cryptochirids associated with mushroom corals, van der Meij, Fransen, et al (2015) mentioned that F. fagei crabs were known to dwell only in Podabacia and Sandalolitha corals and that F. utinomi crabs were hosted by Ctenactis, Danafungia, Fungia fungites (Linnaeus, 1758), Halomitra, Lithophyllon, and Sandalolitha corals, whereas F. syzygia van der Meij, 2015, was predominantly associated with Cycloseris and Pleuractis. Hence, there was no certainty about which gall crab species lived in association with Lobactis in the Hawaiian Islands, and no occurrence records of this association are known from elsewhere.…”