Junior synonymy of Mulloides armatus and intraspecific comparisons of the yellowstripe goatfish Mulloidichthys flavolineatus (Mullidae) using a comprehensive alpha-taxonomy approach
The main objectives of this study were to clarify the taxonomic status of Mulloides armatus, listed as incertae sedis in current taxonomic literature, and to examine the extent of phenotypic differentiation among subspecies and populations of the yellowstripe goatfish Mulloidichthys flavolineatus (Mullidae) in the Indo-Pacific. In total, 53 quantitative morphometric and meristic characters and the visual detectability of the first dorsal-fin spine were gathered from 116 specimens split according to size into juveniles and adults. In addition, fresh colour imagery was studied. The Mulloides armatus holotype, which is broken into two pieces, could be identified as M. flavolineatus after reconstruction of standard length and detailed comparisons involving specimens from nearby the assumed type locality in the Southwestern (SW) Pacific. Then, the recently described subspecies M. f. flavicaudus of the Red Sea and populations of the nominal subspecies M. f. flavolineatus from the Indian Ocean and the Pacific, with additional subdivision into four smaller populations (SW Pacific, Wake Atoll, Hawaiian Archipelago and remaining Pacific), were studied by direct comparisons and uni- and multivariate statistical methods. For the first time, marked size differences (i.e. allometry) in morphometric characters in M. flavolineatus were documented. Mulloidichthys f. flavicaudus overlaps in all characters, singly and in combination, and under consideration of a whitish-grey vs. yellow caudal-fin colour (a diagnostic character used in the original description) with M. f. flavolineatus. These results do not support the elevation to species level in a recently published list of Red Sea fish species. Our data suggest a well-differentiated population in agreement with genetic data presented in the original description of Mulloidichthys f. flavicaudus. Statistical differences in morphometric and meristic characters were also found between the Indian Ocean and Pacific populations of M. f. flavolineatus, though at a much lower degree than between the two subspecies. Interestingly, considerable variation occurs within the Pacific populations with three specimens from Wake Atoll being distinct from nearly all other conspecifics, in having larger heads and eyes and longer barbels and pectoral fins. Therefore, we stress the significance of intraspecific differentiation in populations from remote oceanic island and atoll areas and the need to collect more data. Important is also to use results on intraspecific regional or local differentiation in widely distributed species such as M. flavolineatus in fisheries management and conservation efforts at biologically relevant scales, as well as adopting appropriate common names to facilitate the information exchange with local stakeholders.