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The question of species delineation continues to be a controversial topic, compounded in the oceans by our limited accessibility and lack of strong vicariant barriers. Long before molecular genetic evaluations, coloration was a basis for many species descriptions, especially for congeneric reef fishes. Most of these designations have held up to scrutiny, but coloration can be a tricky basis for taxonomy in this group (e.g., Gaither et al. 2014). The controversy addressed by DiBattista et al. (2016) and Delrieu-Trottin et al. (2017) revolves around species’ identities for the lemonpeel angelfish Centropyge flavissima. This coral reef fish was formerly recognized as a single species with a disjunct distribution, its Pacific Ocean and Indian Ocean forms occupy ranges separated by over 3000 km. Dr Gerry Allen, a taxonomic authority on Centropyge, first recorded the Indian Ocean morph of C. flavissima more than 40 years ago (Allen et al. 1998), but declined to describe it as a species due to a lack of supporting evidence. Shen et al. (2016) subsequently describe the Indian Ocean C. flavissima as a distinct species (C. cocosensis) based on subtle differences in color, an isolated distribution and a lack of shared mitochondrial DNA (mtDNA) haplotypes. DiBattista et al. (2012) previously appraised relationships within the entire C. flavissima complex (including both forms of C. flavissima, Indian Ocean Centropyge eibli and western Pacific Centropyge vrolikii; also see Figure 1) with mtDNA cytochrome b (cyt b) and 3 nuclear introns. This study found that the Indian Ocean C. flavissima was genetically distinctive from the Pacific Ocean form, but genetically indistinguishable from sympatric C. eibli. This species complex sorted into 3 monophyletic lineages well-defined by geography but only imperfectly matching color-based taxonomy. With expanded sampling, DiBattista et al. (2016) again show shared haplotypes between C. eibli and “Centropyge cocosensis,” and therefore question the validly of the latter designation. Our seemingly conflicting results are due in part to differences in sample availability. Based on N = 6 “C. cocosensis” and N = 5 C. eibli 16S rDNA and mtDNA cytochrome oxidase I (COI) samples, Shen et al. (2016) observed a single, nondiagnostic base pair substitution in the former locus and no shared haplotypes in the latter locus. None of the variation was parsimony-informative, indicating no diagnostic difference distinguishing putative “C. cocosensis.” DiBattista et al. (2016) based their conclusions on N = 88 “C. cocosensis” and N = 20 C. eibli at the cyt b locus, a faster evolving marker that revealed multiple shared haplotypes. Hence, the much larger data set contradicted the conclusion of genetic differentiation presented by Shen et al. (2016). Additional lines of evidence cast doubt on the species status of “C. cocosensis.” Field observations spanning 15 years reveal that throughout their entire geographic range (Christmas and CocosKeeling Islands), “C. cocosensis” forms stable and persistent harems (i.e., spanning at least 6 consecutive years) with C. eibli and C. vrolikii (Hobbs and Allen 2014; Hobbs et al. in preparation). The resulting hybrids cohabit and form harems with each other and the parental species, and backcross with “C. cocosensis,” resulting in a continuum of color morphs between “C. cocosensis,” C. eibli and C. vrolikii across the entire range of “C. cocosensis,” with some individuals possessing color characteristics of all 3 putative species (Figure 1d–l). We agree with Shen et al. (2016) and Delrieu-Trottin et al. (2017) that C. flavissima in the Indian Ocean is not the same as C. flavissima in the Pacific Ocean; instead we refer to them as “color forms” and “color morphs” in DiBattista et al. (2016), as well as acknowledge that they are distinct based on mtDNA (DiBattista et al. 2012). In their Figure 1, Delrieu-Trottin et al. (2017) reiterate the most interesting conclusion from DiBattista et al. (2012), that the mtDNA indicates incongruence between molecular data and body

Response to Delrieu-Trottin et al.: Hybrids, Color Variants and the Consistently Devilish Taxonomy of Pygmy Angelfishes