Abstract
The Azorean barnacle, Megabalanus azoricus (Pilsbry, 1916), is a Macaronesian endemic whose obscure taxonomy and the unknown relationships among forms inhabiting isolated Northern Atlantic oceanic islands is investigated by means of molecular analysis herein. Mitochondrial data from the 16S rRNA and COX1 genes support its current species status, tropical ancestry, and the taxonomic homogeneity throughout its distribution range. In contrast, at the intraspecific level and based on control region sequences, we detected an overall low level of genetic diversity and three divergent lineages. The haplogroups α and γ were sampled in the Azores, Madeira, Canary, and Cabo Verde archipelagos; whereas haplogroup β was absent from Cabo Verde. Consequently, population analysis suggested a differentiation of the Cabo Verde population with respect to the genetically homogenous northern archipelagos generated by current oceanographic barriers. Furthermore, haplogroup α, β, and γ demographic expansions occurred during the interglacial periods MIS5 (130 Kya - thousands years ago -), MIS3 (60 Kya), and MIS7 (240 Kya), respectively. The evolutionary origin of these lineages is related to its survival in the stable southern refugia and its demographic expansion dynamics are associated with the glacial-interglacial cycles. This phylogeographic pattern suggests the occurrence of genetic discontinuity informative to the delimitation of an informally defined biogeographic entity, Macaronesia, and its generation by processes that delineate genetic diversity of marine taxa in this area.
Highlights
The Azorean barnacle belongs to the taxonomically problematic genus Megabalanus [1]
It has been referred to as Megabalanus tintinnabulum [6]. It is cited as M. azoricus when located in the Azores and as M. tintinnabulum when found in the other Macaronesian archipelagos [7]
The individuals sampled throughout the Macaronesian archipelagos, including the Azores type location (Terceira, Azores), exhibit morphological characters that agree with the available descriptive data for M. azoricus [2]
Summary
In the latest major revision of the genus it was classified as Megabalanus azoricus (Pilsbry, 1916) [2]. It was formerly included in Darwin’s [3] subdivision A of the genus Balanus, which contained the larger forms of Balani, as a variety of Balanus tintinnabulum (Linnaeus). Their fouling ability confers a high dispersion capacity, which may have altered their original distribution [9] This occurs in several Megabalanus species, including M. coccopoma, M. rosa, and M. volcano, whose current cosmopolitan distributions are associated with fouling in ocean-crossing vessels [10]
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