Dascyllus, Cuvier, 1829

Tang, Kevin L., Stiassny, Melanie L. J., Mayden, Richard L. & DeSalle, Robert, 2021, Systematics of Damselfishes, Ichthyology & Herpetology 109 (1), pp. 258-318 : 277-278

Dascyllus .

— The species of Dascyllus all share a distinctive orbiculate body shape which differentiates them from other chromines. The genus is broadly distributed across the Indo-West Pacific. The composition and limits of Dascyllus have been stable for many years. In their revision, Randall and Allen (1977) recognized nine species: Dascyllus albisella , D. aruanus , D. carneus , D. flavicaudus , D. marginatus , D. melanurus , D. reticulatus , D. strasburgi , and D. trimaculatus . In the intervening four decades, only one new species has been described, D. auripinnis , and one species has been resurrected, D. abudafur ( Randall and Randall, 2001; Borsa et al., 2014). However, possible cryptic diversity has been identified in D. trimaculatus (Bernardi et al., 2001, 2002, 2003; Leray et al., 2010; Hubert et al., 2012, 2017). Species of Dascyllus generally have a conserved or low fundamental chromosome number (NF) but reduced diploid (2n) number (Arai and Inoue, 1976; Ojima and Kashiwagi, 1981; Klinkhardt et al., 1995; Molina, 2007; Arai, 2011), which is likely the result of Robertsonian translocations ( Ojima, 1983; Takai and Ojima, 1995; Molina and Galetti, 2002, 2004b), a phenomenon that is uncommon in teleosts ( Takai and Ojima, 1995).

Following information drawn from Randall and Allen (1977), Godwin (1995) delimited three species complexes based on ‘‘morphology, biogeography, and striking coloration differences.’’ He observed that the smaller species of the aruanus ( D. aruanus and D. melanurus ) and reticulatus ( D. carneus , D. flavicaudus , D. marginatus , and D. reticulatus ) complexes are closely associated with branching corals and often have protogynous sex change and resource-defense polygyny, whereas the larger species of the trimaculatus complex ( D. albisella , D. strasburgi , and D. trimaculatus ) only associate with corals as juveniles and do not exhibit sex change nor polygyny. He hypothesized that the hermaphroditism is linked to a harem-based mating system in which males defend the coral heads where females reside. Our results seem congruent with Godwin’s (1995) hypothesis that protogynous sex change evolved in the ancestor of Dascyllus , as seen in the small-bodied species plus D. flavicaudus , followed by a reversal to gonochorism in the species of the trimaculatus complex. However, Asoh et al. (2001) cautioned that evidence for either gonochorism or protogyny in these species was often equivocal, after they showed evidence for protogyny in D. albisella , a large-bodied species hypothesized to be gonochoristic. Further complicating matters was their discovery that, despite gonadal development transitioning through an ovarian stage in all individuals, the protogyny was non-functional and likely an example of phylogenetic inertia. Asoh and Kasuya (2002) reported a similar pattern of non-functional protogynous gonad development in D. trimaculatus , another large, putatively gonochoristic species. Whether size or phylogenetic inertia was the primary factor in the evolution of protogyny remains unresolved, with different studies finding ambiguous and sometimes conflicting results (Bernardi and Crane, 1999; McCafferty et al., 2002).

Bernardi and Crane (1999) produced the first explicit phylogeny of the genus, inferred from 16S and cytochrome b sequences. They determined that D. aruanus and D. melanurus are sister to the rest of the genus and that species assigned to the reticulatus complex are paraphyletic relative to a clade of D. trimaculatus and its nearest relatives. Subsequent studies generated similar results (e.g., McCafferty et al., 2002; Quenouille et al., 2004), with disagreement mainly in the exact placement of D. reticulatus (see below). All agreed that the four species of the reticulatus complex are paraphyletic to a crown clade comprising D. trimaculatus and its allies.

Our data matrix included all species but D. auripinnis . The tree shows strong support (100% bootstrap) for the monophyly of Dascyllus and for the relationships within the genus ( Fig. 1 ; Supplemental Fig. 1 ; see Data Accessibility). The topology agrees with the consensus that the humbug damselfishes, consisting of D. aruanus and its allies, are monophyletic and sister to the remaining species of Dascyllus (Bernardi and Crane, 1999; McCafferty et al., 2002; Quenouille et al., 2004; Cowman and Bellwood, 2011; Litsios et al., 2012a, 2012b; Frédérich et al., 2013; Rabosky et al., 2013, 2018; DiBattista et al., 2016; Mirande, 2016; Gaboriau et al., 2018; Delrieu-Trottin et al., 2019), and that the domino damselfishes, consisting of D. trimaculatus and its allies, form the crown group (Bernardi and Crane, 1999; McCafferty et al., 2002; Cowman and Bellwood, 2011; Litsios et al., 2012a, 2012b; Frédérich et al., 2013; DiBattista et al., 2016; Mirande, 2016; Gaboriau et al., 2018; Delrieu-Trottin et al., 2019). The separation of the humbug damsels from the rest of Dascyllus is also supported by cytogenetic data, where D. aruanus has distinctive chromosomal rearrangements and fewer chromosomes overall than other species (2n ¼ 28–32 vs. 48 in D. carneus , D. melanurus , and D. trimaculatus ; Arai, 2011; Getlekha et al., 2016b). There is less agreement on the relationships among the remaining species. Several studies (Bernardi and Crane, 1999; Quenouille et al., 2004; Koh and Park, 2007; Cowman and Bellwood, 2011; Litsios et al., 2012a, 2012b; DiBattista et al., 2016) have resolved D. flavicaudus and D. marginatus as sister species, which our results and others ( Frédérich et al., 2013; Mirande, 2016; Gaboriau et al., 2018; Delrieu-Trottin et al., 2019) do not support. Despite finding that pairing themselves, Bernardi and Crane (1999: 1216) remarked that a sister relationship between these two species is unexpected because of their geographic ranges.

The status of D. reticulatus is complicated, in part because its species delimitation is uncertain. A sister-group relationship between D. carneus and D. reticulatus has been suggested in the literature ( Randall and Allen, 1977; Randall, 2005; Allen and Erdmann, 2012) and is supported by some studies ( Quenouille et al., 2004; Cowman and Bellwood, 2011;

Litsios et al., 2012a, 2012b; Frédérich et al., 2013; Mirande, 2016) but contradicted by others (Bernardi and Crane, 1999; Koh and Park, 2007: fig. 1; Rabosky et al., 2013, 2018; DiBattista et al., 2016; Gaboriau et al., 2018; Delrieu-Trottin et al., 2019). This discrepancy may be partially explained by McCafferty et al. (2002), who discovered that individuals traditionally classified as ‘‘ Dascyllus reticulatus ’’ fall into two separate lineages. They resolved a northern population (their reticulatus A) that is paraphyletic relative to D. flavicaudus and a southern population (their reticulatus B) that is sister to D. carneus . Subsequent studies have not accounted for these two populations. Of the previously published phylogenies, Cooper et al. (2009: table 1) drew from the northern population ( Philippines, near Busuanga Island) and Quenouille et al. (2004: table 1) from the southern population ( Australia, Great Barrier Reef). Locality information for the Bernardi and Crane (1999) sample was unknown because it came from the aquarium trade, but McCafferty et al. (2002: 1387) stated that the specimen is phylogenetically equivalent to their reticulatus B, the southern group. Several studies (e.g., Tang, 2001; Tang et al., 2004; Cowman and Bellwood, 2011; Litsios et al., 2012a, 2012b; Frédérich et al., 2013; Rabosky et al., 2013, 2018; Mirande, 2016; Gaboriau et al., 2018; Delrieu-Trottin et al., 2019) have mixed sequences from both populations to represent a single combined ‘‘ D. reticulatus ’’ taxon. Our sample of D. reticulatus (CAS 217404; KU T4945) originates from Fiji (16816 0 54.6 00 S, 179809 0 20.4 00 W) and corresponds to the southern lineage ( reticulatus B). We also mined GenBank sequences ( FJ616340 , FJ616448 , FJ616667 ; Cooper et al., 2009) with known locality data to include a representative of the northern population. In finding two disparate reticulatus lineages, these results corroborate McCafferty et al. (2002), where the northern population ( Philippines) is with D. flavicaudus and the southern population ( Fiji) is with D. carneus ( Fig. 1 ).

Based on the geographical boundaries drawn by McCafferty et al. (2002), the type material of D. reticulatus appears to originate from the northern population: the description only gives ‘‘ China seas’’ as the locality, with Richardson (1846) stating that the two type specimens were brought to him from China. McCafferty et al. (2002) could not find any differences in the molecular data to distinguish between D. flavicaudus and the northern lineage, D. reticulatus sensu stricto. If they were to be placed in synonymy, Dascyllus reticulatus would have priority over Dascyllus flavicaudus . Conversely, the southern ‘‘ D. reticulatus ,’’ which is sister to D. carneus , would require a name if it were to be treated as a separate species. Dascyllus xanthosoma is an available name for the southern lineage based on its type locality of Banda, Indonesia. McCafferty et al. (2002) could find no discernable molecular evidence to distinguish between D. albisella (Hawaiian endemic) and D. trimaculatus . They suggested that the two species should be regarded as part of a trimaculatus species group. The species limits within Dascyllus and their nomenclature merit more detailed examination, but these issues are beyond the scope of this study.

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