Plectroglyphidodon, Fowler & Ball, 1924

Tang, Kevin L., Stiassny, Melanie L. J., Mayden, Richard L. & DeSalle, Robert, 2021, Systematics of Damselfishes, Ichthyology & Herpetology 109 (1), pp. 258-318 : 284-285

Plectroglyphidodon .

— The species of this genus are predominantly herbivores found on shallow reefs of the Indo-West Pacific (Allen, 1975a, 1991). As currently constituted, the ten species of Plectroglyphidodon are polyphyletic ( Fig. 1 ). Of the eight species represented in the data matrix, seven are paraphyletic relative to a clade of Indo-West Pacific ‘‘ Stegastes ’’ and a single species, P. lacrymatus , is recovered inside Stegastes sensu stricto, sister to S. pelicieri . In their description of the genus, Fowler and Ball (1924) noted the similarity of Plectroglyphidodon to Parma but with larger scales like Abudefduf , which served as a dumping ground at the time for what turned out to be a disparate collection of largely unrelated pomacentrid taxa (Allen and Emery, 1973; Allen, 1975a; Hensley, 1978; Allen and Randall, 1981; Allen and Woods, 1980). Fowler and Ball (1924) differentiated Plectroglyphidodon from Abudefduf on the basis of its plaited lips, analogous to how the enlarged lips of Cheiloprion differentiated that monotypic genus from the equally unruly Pomacentrus of the time. Both Plectroglyphidodon johnstonianus (type species) and Cheiloprion labiatus are corallivores ( Hobson, 1974; Allen, 1975a; Masuda et al., 1975, 1984; Sano et al., 1984a, 1984b; Cole et al., 2008). The modified lips appear to be adaptations for their specialized diet (Allen, 1975a; Huertas and Bellwood, 2018). Although it has been suggested that this distinctive feature indicates some close relationship between the two genera ( Woods and Schultz, 1960: 96–97), other characters do not support such an association (Allen, 1975a: 194).

There are two monophyletic groups of putative Plectroglyphidodon which are paraphyletic relative to the Indo-Pacific ‘‘ Stegastes .’’ One clade includes P. johnstonianus , the type of Plectroglyphidodon . The other includes P. leucozonus , the type of an available name, Negostegastes . Species of the latter group, which is sister to ‘‘ Stegastes ,’’ generally have fewer dorsal- (16) and anal-fin (13) rays than species of the other group (16 and 13, respectively; Allen, 1991). Plectroglyphidodon phoenixensis accounts for the overlap in both counts: it is in a clade with P. johnstonianus and the only species of its clade reported to possess 16 dorsal rays and 13 anal rays; the other species have 17 or more dorsal rays and 14 or more anal rays (Allen, 1991). Both P. johnstonianus and P. phoenixensis have discernible genetic splits between their respective Indian and Pacific populations, represented by reciprocally monophyletic lineages in each ocean basin ( Hubert et al., 2012: fig. S1, table S3; Hubert et al., 2017: fig. A1, tables S3, S4). If this is recognized as cryptic diversity, the Indian Ocean population of P. johnstonianus may have an available name: Plectroglyphidodon nitidus . Species of Plectroglyphidodon and Stegastes ( P. dickii , P. lacrymatus , P. johnstonianus , P. imparipennis , P. sp. [¼ P. lacrymatus ], S. acapulcoensis , S. bicolor [¼ S. partitus ], S. dorsopunicans [¼ S. adustus ], S. diencaeus , S. fasciolatus [¼ S. marginatus ], S. flavilatus , S. fuscus [¼ S. adustus ], S. leucostictus , S. lividus [¼ S. punctatus ], S. planifrons , S. rocasensis , and S. variabilis ; Webb, 1988: appendix II) lack additional pitted scales posterior to the tubed lateral line scales found in other genera, which was suggested as having potential phylogenetic signal ( Webb, 1988: 129). The P. dickii – P. johnstonianus pairing we recovered was suggested by earlier studies ( Randall et al., 1997; Allen and Erdmann, 2012). We found a sister-group relationship between P. imparipennis and P. sagmarius . The latter species was originally considered a color variant of P. imparipennis endemic to the Marquesas Islands (Allen, 1975a, 1991; Randall and Earle, 1999), so their close relationship has been discussed before (Randall, 2005).

The recovery of ‘‘ Plectroglyphidodon ’’ lacrymatus apart from other Plectroglyphidodon matches prior studies (Cooper et al., 2009; Cowman and Bellwood, 2011; Hofmann et al., 2012; Litsios et al., 2012a, 2012b; Frédérich et al., 2013; Rabosky et al., 2013, 2018; Lobato et al., 2014; DiBattista et al., 2016; Mirande, 2016; Gaboriau et al., 2018; Delrieu-Trottin et al., 2019). It has more gill rakers on the first arch (21–23) than species of Plectroglyphidodon usually do (10–17; Allen, 1975a: 191), though P. randalli possesses almost as many (17–20; Allen, 1991). Bleeker (1877) placed lacrymatus in Stegastes (as a subgenus of Glyphidodon [¼ Abudefduf ]), but the taxon was used in a different sense than modern Stegastes (sensu Emery and Allen, 1980) . It was the sole Plectroglyphidodon in a clade Cowman and Bellwood (2011: figs. 2b, S6) called ‘‘ Stegastes IP & Plectroglyphidodon .’’ Cooper and Santini (2016) included this species in a group they called ‘‘ Stegastes I/ Plectroglyphidodon I.’’ They stated that it likely would have to be reassigned to Stegastes . Our phylogeny shows a P. lacrymatus – S. pelicieri relationship similar to what was seen in Hubert et al. (2011, 2012, 2017). This is not surprising because the data we used for S. pelicieri were generated by those same barcode sources. Support for this sister-group pairing is robust (100%). This relationship was also described in other studies that compiled the same data from GenBank (DiBattista et al., 2016; Mirande, 2016; Gaboriau et al., 2018; Rabosky et al., 2018). Allen and Emery (1985) reported that ‘‘[j]uvenile specimens of S. pelicieri are remarkably similar in color to’’ P. lacrymatus , differing mainly in their dorsal-spine count (XII vs. XIV). Plectroglyphidodon lacrymatus also maintains algal gardens like many Stegastes ( Kuo and Shao, 1991; Meekan et al., 1995; Ceccarelli, 2007; Hoey and Bellwood, 2010). Based on the relationships recovered in our phylogeny and those reported in the literature, we hereby refer this species to Stegastes , as Stegastes lacrymatus . Plectroglyphidodon and Stegastes are both masculine, so the species name does not need to change for gender agreement. Hubert et al. (2012, 2017) suggested that there may be cryptic diversity in the species after they detected two discrete lineages ( Madagascar and French Polynesia) separated by S. pelicieri , which is found in the western Indian Ocean. The Pacific population was actually more closely related to S. pelicieri in their topologies. Our sample of S. lacrymatus is from Tonga (21801 0 39.0 00 S, 175807 0 21.0 00 W; Supplemental Table 1; see Data Accessibility). If there are separate species within S. lacrymatus , there are two possible available species-group names, Glyphisodon nivosus and Glyphidodon florulentus . However, their type localities are ambiguous: origin not indicated and Indian Ocean, respectively (Hombron and Jacquinot in Jacquinot and Guichenot, 1853; Günther, 1862). Furthermore, there is no type material for G. nivosus (Bauchot et al., 1978: 34) . The status of these populations is beyond the purview of this study.

Of the two species of Plectroglyphidodon that we were unable to examine, P. flaviventris is most likely related to P. johnstonianus , based on their morphological similarity (Allen and Randall, 1974). The affinities of P. sindonis are less clear. The species is endemic to the Hawaiian Islands, where three other species of Plectroglyphidodon also occur ( Randall, 2007), including representatives from both clades. Based on meristic counts, it is most likely in the same clade as P. johnstonianus . Like others of that group, P. sindonis has high dorsal- and anal-fin ray counts (19–20 and 15–16, respectively), its dorsal fin-ray count overlaps with what is reported for P. johnstonianus , its anal fin-ray count matches that of P. flaviventris and overlaps with those of P. dickii and P. johnstonianus , and its gill raker count on the first branchial arch matches that of P. phoenixensis (Allen, 1991; Randall, 2007).

Figures

FIG. 1. The phylogenetic relationships of damselfishes (Teleostei: Pomacentridae): (A) outgroup taxa; (B) subfamilies Microspathodontinae and Glyphisodontinae; (C) subfamily Chrominae; (D) subfamily Pomacentrinae (part I); (E) subfamily Pomacentrinae (part II). The phylogeny is based on the maximum-likelihood topology with the best log likelihood score (ln L ¼ –45,4518.728) recovered from ten independent maximum-likelihood analyses of a data matrix composed of 462 taxa and 6,865 nucleotides. Bootstrap values from 1,000 ultrafast replicates are displayed for each node