Anthopleura

Daly, M., Crowley, L. M., Larson, P., Rodríguez, E., Heestand Saucier, E. & Fautin, D. G., 2017, Anthopleura and the phylogeny of Actinioidea (Cnidaria: Anthozoa: Actiniaria), Organisms Diversity & Evolution (New York, N. Y.) 17 (3), pp. 545-564 : 558-560

Phylogeny of Anthopleura

We find no evidence for monophyly of Anthopleura : its members are scattered across the tree, associated with members of other actiniid genera and with members of other actinioidean families ( Fig. 2 ; Supplemental Figs. 1 and 2 ). Genera that have been proposed as closely related to Anthopleura , such as Anthostella , Aulactinia , Bunodactis , Bunodosoma , and Gyractis , are closely related to it in the sense that they group with nominal species of Anthopleura . The type of Anthopleura , A. krebsi , lies within the A clade. The interrelationships among nominal Anthopleura are difficult to determine given the paraphyly of the genus and the relatively low support for internal branches. Of the well-supported and consistent clades, only the A and ST clades contain members of Anthopleura ; the majority of included species of Anthopleura are part of poorly supported clades. Because we have over-sampled Anthopleura relative to other genera, this may reflect sampling depth rather than something more significant about Anthopleura relative to other actinioideans: for example, the support for the L, EA, or P clades may be inflated because many members of those clades have not been included and so the support is not divided among the same number of nodes or subjected to the same number of possible resolutions as clades of Anthopleura .

Previous studies of relationships among species of Anthopleura ( Geller and Walton 2001; Daly 2004a) have not included as many nominal species or as many taxa from outside of Anthopleura . In light of the broad polyphyly of Anthopleura , this difference makes comparing trees difficult. However, we see points of congruence with the results of Geller and Walton (2001), including finding a close relationship between A. handi and A. nigrescens and between these and a clade of Anthopleura from Japan. Geller and Walton (2001) and Daly (2004a) both find that Anthopleura is not monophyletic with respect to Bunodosoma ; the present results extend this finding to include several other genera, but concur in finding a close relationship between Bunodosoma and several species of Anthopleura ( Figs. 2 and 3; Supplemental Figs. 1 and 2 ). Similarity between the present results and those of Geller and Walton (2001) is not surprising given that their focal markers are among those we analyze here. The tree in Daly (2004a) is based on morphological data and is generally less congruent with these new results than is the tree of Geller and Walton (2001); other than the close association between Bunodosoma and Anthopleura , only the proposed relationship between A. dowii and A. elegantissima is seen in our trees and in those of Daly (2004a).

Although the frequency with which species of Anthopleura occur in sympatry is explained in part by the broad polyphyly of the genus, geography provides a means of interpreting and synthesizing the diversity of Anthopleura and its actinioidean relatives, if only because several of the well-supported or consistently recovered subunits have some geographic signature. Of course, because we have not sampled all members of Anthopleura and because the relationships of a few species of Anthopleura are highly labile across data sets, these groups and inferences about them are provisional.

In terms of the biogeography of the North Pacific, based on our results, there are at least two colonization events each in the East and West Pacific ( Fig. 4 ). Species of Anthopleura from the North East Pacific span two groups: the clade that includes A. dowii , A. elegantissima , and A. sola and the clade containing A. xanthogrammica and A. artemisia . These two groups are never siblings. A. xanthogrammica and A. artemisia are generally associated with one another but are not siblings in all analyses. The included species from the Southern and Central West Pacific ( A. handi , A. buddemeieri , A. nigrescens ) are sister to a clade from the North West Pacific ( A. atodai , A. inornata , A. kurogane ( Japan), A. japonica ), together forming the J clade ( Fig. 2 ). Of these, there seem to be two in situ radiations: the dowii / elegantissima / sola group has undergone an in situ radiation on the North American coast and the atodai / inornata / kurogane / japonica group has undergone and in situ radiation in Asia. Our finding of multiple origins for the East and West Pacific Anthopleura was previously predicted by Geller and Walton (2001).

Geography is more predictive of relationship than taxonomy, for species from the Atlantic ( Fig. 4 ). Anthopleura from the Atlantic belong to three clades: A. balli is sister to A. viridis (also an Atlantic species); A. thallia is part of the ST clade; and the remaining species ( A. annae , A. insignis , A. krebsi , A. pallida , Anthopleura sp. South Africa) are part of the A clade, which also contains the Red Sea-Northern Indian Ocean species A. waridi . A. waridi is reported from the Red Sea, Persian Gulf, and the coasts of East Africa and India ( Fautin 2013) and is most closely related to two species from the North Atlantic ( A. krebsi , A. pallida ). The taxa within the B and P clades, which are sister to the A clade, are also primarily Atlantic in their distribution. The distribution of the members of the ABEPP clade suggests an Atlantic (or possibly Tethyan) origin for the group, with B. californicum dispersing into the Pacific and A. waridi dispersing into the Indian Ocean.

The North American and Northern European costs were under ice during the Quaternary glaciation, as were parts of Argentina and Chile. In light of their current restriction to the shallow subtidal and intertidal zones, it is probable that Anthopleura species currently inhabiting these regions are migrants from warmer waters rather than from deepwater refugia.

Figures

Fig. 2 Maximum likelihood tree resulting from analysis of combined data set. Branch lengths are to scale. Bootstrap values (1000 replicates) greater than 75% are indicated. Clade labels apply to taxa within each shaded box

Fig. 4 Recorded occurrences of focal species mapped onto combined data maximum likelihood tree. Distributional data from Fautin (2013). Branch lengths are proportional to change