Clarifying the taxonomy of some cryptic blennies (Blenniidae) in their native and introduced range

Abstract

Omobranchus punctatus is native to the Indo-Pacific region and invasive in the Atlantic region, currently being considered one of the most widely distributed blenny species. However, recent molecular studies indicated that O. punctatus is a complex of species, with three divergent mtDNA lineages identified to date, stressing the need for a taxonomic revision. In this study, we used an integrative approach, combining morphological and genetic data, to shed light on the taxonomy and distribution of O. punctatus. Moreover, we provide the first genetic records of introduced populations in Brazil and discuss the introduction pattern of this species in this region. Morphological data shows that O. punctatus consists of at least five distinct and geographically restricted species: O. punctatus sensu stricto, O. dispar, O. sewalli, O. cf. kochi, and O. cf. japonicus. Species delimitation analyses performed using the mtDNA data available confirmed that O. punctatus sensu stricto, O. dispar and O. sewalli correspond to different species that started to diverge about 2.6 Mya. Furthermore, O. sewalli was identified as the invasive species colonizing Atlantic shores. The existence of historical oceanographic barriers, such as the emergence of the Sunda Shelf in the Eastern Indian Ocean during the Pleistocene, and the biological traits of these blennies are the most likely factors responsible for their genetic differentiation and subsequent speciation.

Figure 1

Current global distribution of Omobranchus punctatus group including its native (in yellow) and introduced range (in red). See Tables S2–S4 for further details for each location (year of the first record, reference collection, sources, and genetic data availability). Records of introduced populations in the Western Atlantic Ocean (WAO) would correspond to Omobranchus sewalli, and that from the Western Indian Ocean (WIO) and the Mediterranean Sea to Omobranchus cf. sewalli (see Table 2).

Figure 2

Bayesian consensus tree of Omobranchus punctatus group, based on COI sequences. Bayesian posterior probabilities (BPP) over 0.99 are represented by red circles at nodes and values correspond to bootstrap support (>75%) given by the maximum likelihood analyses. Clades A-C are identified. The tree was rooted with O. woodi (sequences available in GenBank: JF494019, HQ561537, HQ561538). Vertical black bars represent results from the species delimitation analyses: Barcode Index Number (BIN), Assemble Species by Automatic Partitioning (ASAP) and Bayesian Poisson Tree Process model (bPTP).

Figure 3

Median-joining network of all COI sequences for the Omobranchus punctatus group. Localities are coded by filling patterns (see legend). Each circle represents a haplotype, and its size is proportional to the observed haplotype frequency. Non-observed haplotypes are represented by small white circles. Every crossbeam on the connecting lines between haplotypes represents a single mutational step. Distinct clades (A-C) are depicted as dashed-lines circles.

Figure 4

Bayesian time tree for Omobranchus punctatus group as inferred by BEAST. Scale bar in Mya. The green clade represents the samples sequenced in this study. Clades A-C are identified. Bayesian posterior probabilities are represented by colour and node size (red values by nodes are strongly supported). Values by nodes indicate the estimated age of the split event and horizontal blue bars represent 95% of the highest posterior density (HPD) interval. H denotes Holocene. Photo of O. punctatus from Venezuela by James Van Tassell (American Museum of Natural History) and Ross Robertson (Smithsonian Tropical Research Institute).

Figure 5

Principal Component Analysis (PCA) based on 10 meristic characters analysed in 36 populations (localities) of Omobranchus punctatus group. 1: Omobranchus cf. kochi, 2: Omobranchus sewalli; 3: Omobranchus punctatus sensu stricto, 4: Omobranchus cf. japonicus, and 5: Omobranchus dispar. Populations analysed are listed in Table S6. First (Dim 1) and second (Dim 2) principal components accounted for nearly 70% of the total variance.

Figure 6

Sampling locations of the putative species Omobranchus punctatus (species considered in this work as Omobranchus sewalli) along the Atlantic coast of South America. See Table 1 for additional information.