Abstract
This study was performed to analyse the genetic and morphological diversity of the sabellid annelid genus Branchiomma, with special emphasis on a taxon so far identified as Branchiomma bairdi. This species, originally described from Bermuda, has frequently been reported as an invader in the Mediterranean, the Atlantic and the Eastern Pacific, but recent observations have raised some taxonomic questions. Samples of this taxon were collected from five sites in the Mediterranean Sea, two sites in the original distribution area of B. bairdi in the Gulf of Mexico and four localities in the east Pacific and Atlantic Oceans where B. bairdi has been reported as invasive. The molecular results revealed a conspicuous genetic divergence (18.5% K2P) between the sampled Mediterranean populations and all the other ones that led to a re-evaluation of their morphological characters. The latter showed that the Mediterranean and extra-Mediterranean populations also differ in some discrete morphological and reproductive features. Consequently, the Mediterranean samples were re-designated as B. boholense, another non-indigenous species originally described from Philippines. Branchiomma bairdi and B. boholense differ in body size, development and shape of micro and macrostylodes, size of radiolar eyes and body pigmentation. Genetic diversity was high in B. boholense from the Mediterranean as well as in B. bairdi from the Gulf of Mexico, but low in B. bairdi populations outside their native range. The phylogenetic analysis revealed the presence of connections between the Mediterranean localities as well as between native and introduced B. bairdi populations that focus the attention on the Panama Canal as important passage for the introduction of the species from the Gulf of Mexico to the north-east Pacific Ocean.
Highlights
Introductions of marine non-indigenous species (NIS) have occurred for centuries, but in the last decades the increasing maritime traffic and aquaculture activities have favoured the spread of marine species, with irreversible and devastating impact on global biodiversity [1,2,3,4,5,6,7]
Four haplotypes were shared by individuals collected from distinct populations and sampling sites, two of which resulted the most common haplotypes: haplotype 1 was present just in the Mediterranean Sea and was shared by 35 individuals belonging to all the sampled Mediterranean populations, while haplotype 9 was shared by 67 individuals collected from different populations in both the Pacific Ocean, the Gulf of Mexico and the Atlantic Ocean (S1 Table)
This study revealed significant genetic differentiation in the mitochondrial gene c oxidase subunit I (COI) between Mediterranean and extra-Mediterranean Branchiomma populations, strongly suggesting that they represent two different species
Summary
Introductions of marine non-indigenous species (NIS) have occurred for centuries, but in the last decades the increasing maritime traffic and aquaculture activities have favoured the spread of marine species, with irreversible and devastating impact on global biodiversity [1,2,3,4,5,6,7] Under this framework, biological invasions are becoming an increasingly more pressing problem. In order to achieve these purposes, a better knowledge of both the invasion process, the status and biology of the introduced species are needed This is crucial in regions with a high number of alien species such as the Mediterranean Sea that it is highly susceptible to marine bioinvasion. The Mediterranean area accounted the highest number of established and invasive polychaete taxa in the world’s ocean, suggesting the need of further investigations in this area of knowledge for exhaustive regulatory programs
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