Lepidozygus, Günther, 1862

Tang, Kevin L., Stiassny, Melanie L. J., Mayden, Richard L. & DeSalle, Robert, 2021, Systematics of Damselfishes, Ichthyology & Herpetology 109 (1), pp. 258-318 : 282

Lepidozygus .

— This is a monotypic genus found throughout the tropical Indo-West Pacific (Allen, 1975a, 1991; Emery, 1983). The classification of the Fuselier Damsel ( Lepidozygus tapeinosoma ) warrants further attention because our results contradict earlier works that assigned Lepidozygus to its own monotypic subfamily (Allen, 1975a, 1991; Cooper et al., 2009; Cooper and Santini, 2016). This taxon has drawn particular interest since it was accorded subfamilial status by Allen (1975a). Cooper et al. (2009) were the first to include Lepidozygus in a molecular phylogeny, and they placed it as the sister group of all pomacentrids except Microspathodontinae (their Stegastinae ). Cooper and Santini (2016) maintained the subfamilial rank for the Lepidozyginae but noted its uncertain status, citing the long branch connecting it to other pomacentrids. Other studies have recovered relationships for Lepidozygus that are at least congruent with its treatment as a separate subfamily (e.g., Cowman and Bellwood, 2011; Litsios et al., 2012a; Frédérich et al., 2013; Rabosky et al., 2013; Lobato et al., 2014; DiBattista et al., 2016; Stieb et al., 2017; Gaboriau et al., 2018; Delrieu-Trottin et al., 2019). However, they all relied on the sequences of Lepidozygus produced by Cooper et al. (2009). In contrast, other studies have recovered a relationship similar to the one that we found: Lepidozygus closely allied with Stegastes sensu stricto ( Litsios et al., 2012b: figs. A1–3; Betancur-R. et al., 2013a: Dryad file ‘‘RAxMLThree_Plus_24_part.tre’’, 2015: fig. S1, 2017: ‘‘12862_2017_958_MOESM6_ESM.pdf’’; Mirande, 2016: fig. S11; Sanciangco et al., 2016: fig. S1; Rabosky et al., 2018: Dryad file ‘‘actinopt_12k_raxml.tre’’). What these latter studies share in common is that they either generated their own independent RAG1 sequence for Lepidozygus ( Rabosky et al., 2018: table S2, Dryad file ‘‘accession_numbers.csv’’) or they did not analyze its RAG1 data ( Litsios et al., 2012b: table A1; Betancur-R. et al., 2013a: table S1; Mirande, 2016: appendix S1; Sanciangco et al., 2016: table S1). For example, Litsios et al. (2012a: additional file 2) used all of Cooper et al.’s (2009) data for Lepidozygus and found a similar result. However, Litsios et al. (2012b: table A1) used many of the same sequences but excluded that specific RAG1 sequence. A reason for the deletion was not given, but, with that removal, the phylogenetic position of Lepidozygus deviated greatly between the two topologies ( Litsios et al., 2012a: fig. 2; 2012b: figs. A1–3). Similarly, Rabosky et al. (2013: supplementary data 1, Dryad file ‘‘Rabosky_et_al_timetree.tre’’) used three sequences from Cooper et al. (2009), including RAG1, and recovered Lepidozygus sister to Chrominae . In contrast, Rabosky et al. (2018) replaced that RAG1 with new data. No explanation was given for the change, but they inferred a sister-group relationship between Lepidozygus and Stegastes sensu stricto. Hofmann et al. (2012: 82) used 12S and RAG1 from Cooper et al. (2009), resolving Lepidozygus inside Chromis sensu stricto, which, in hindsight, gave a clue as to the underlying problem. Despite the apparent disagreement and uncertainty in the literature concerning this taxon, we are confident that our results accurately depict the subfamilial affiliation of Lepidozygus because, following an examination of the available data, we suspect that its placement in Cooper et al. (2009: fig. 1) is the result of an error in a single sequence, possibly from data transposition or PCR contamination. In a GenBank BLAST search, their RAG1 sequence for Lepidozygus tapeinosoma (GenBank FJ616676 ) is identical to their RAG1 sequence for Chromis weberi ( FJ616653 ). The next closest match (99.8% similarity) is another RAG1 sequence from C. weberi ( AY208642 ; Quenouille et al., 2004); the other top ten BLAST results (.97.8%) were all RAG1 sequences from species of Chromis sensu stricto. That RAG1 sequence is a 99.6% match with the RAG1 sequence from our Chromis weberi but has only 91–92% similarity with the RAG1 sequences from our samples of Lepidozygus and that of Rabosky et al. (2018: Dryad file ‘‘alignment.phylip’’). Our RAG1 and Rabosky et al.’s (2018) share 99.1% similarity. Comparing 12S and 16S sequences, the only other genes where our dataset overlaps with Cooper et al. (2009), we found high degrees of similarity between their Lepidozygus data and ours (12S: 97.2%; 16S: 96.8%). Conversely, their 12S and 16S for Lepidozygus showed limited similarity with our C. weberi (12S: 83.8%; 16S: 85.2%). This suggests that misidentification of their voucher specimen is unlikely. When we analyzed their non-RAG1 loci in single-gene tree searches, Lepidozygus was consistently recovered within the Microspathodontinae (not shown). An analysis of their data matrix minus the questionable RAG1 sequence ( FJ616676 ) resolved Lepidozygus as the sister group of Stegastes sensu stricto (not shown), which matches the results of this study ( Fig. 1 ). An analysis that included their sequences of Lepidozygus , excluding their RAG1, in our data matrix found their taxon clustered with our representatives of Lepidozygus (not shown), sister to Stegastes sensu stricto within the Microspathodontinae . All indications are that this single aberrant sequence ( FJ616676 ) produced a misleading topology which resulted in an incorrect classification for Lepidozygus .

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