Restructuring of the 'Macaronesia' biogeographic unit: A marine multi-taxon biogeographical approach

The Azores, Madeira, Selvagens, Canary Islands and Cabo Verde are commonly united under the term “Macaronesia”. This study investigates the coherency and validity of Macaronesia as a biogeographic unit using six marine groups with very different dispersal abilities: coastal fishes, echinoderms, gastropod molluscs, brachyuran decapod crustaceans, polychaete annelids, and macroalgae. We found no support for the current concept of Macaronesia as a coherent marine biogeographic unit. All marine groups studied suggest the exclusion of Cabo Verde from the remaining Macaronesian archipelagos and thus, Cabo Verde should be given the status of a biogeographic subprovince within the West African Transition province. We propose to redefine the Lusitanian biogeographical province, in which we include four ecoregions: the South European Atlantic Shelf, the Saharan Upwelling, the Azores, and a new ecoregion herein named Webbnesia, which comprises the archipelagos of Madeira, Selvagens and the Canary Islands.

Multilocus molecular systematics of the circumtropical reef-fish genus Abudefduf (Pomacentridae): history, geography and ecology of speciation

We investigated a pantropical sub-family and genus of damselfishes, the sergeant-majors (Pomacentridae: Abudefdufinae: Abudefduf), to identify the tempo and mechanisms of speciation in the lineage. We examined sequence capture data from 500 loci and 20 species, with multiple individuals sampled from across the geographic ranges of widespread species. Utilizing a maximum likelihood framework, as well as a time-calibrated Bayesian phylogeny, the following key questions are addressed: What is the historical tempo of speciation? What are the relative contributions of vicariant, peripatric and parapatric speciation to sergeant-major diversity? How is speciation related to major variation in trophic ecology? The approximately 20 species of sergeant-majors fall into three main lineages. The ancestral condition appears to be benthivory, which is predominant in two lineages comprising six species. The remaining species of sergeant-majors, of which there are at least 15, fall within a clade composed entirely of planktivores. This clade is sister to a benthivore clade that included one species, Abudefduf notatus, in transition to planktivory. Most speciation of sergeant-majors, which appeared ∼24 million years ago, occurred in the last 10 million years. Present distributional patterns indicate vicariant speciation precipitated by the closure of land barriers between both sides of the Atlantic and the Pacific, and the emergence of land between the Indian and Pacific Oceans. Within this backdrop, frequent oscillations in sea level over the last 10 million years also appear to have generated conditions suitable for both peripatric and vicariant speciation, and most speciation within the genus appears linked to these changes in sea level. Diversification within the genus has been concentrated in planktivorous seargeant-majors rather than benthivores. The root cause is unclear, but does not appear to be related to differences in dispersal potential, which is greater in the planktivorous species, due to the ability of their post-larval juveniles to raft with floating debris. This elevated speciation rate in planktivores and their propensity to form local endemics may reflect relaxation of selective pressures (e.g., on crypticity) that limit speciation in benthivorous sergeant-majors. Finally, our data allow us to clarify relationships of geminate sergeant-major species, indicating that there are subdivisions within the Atlantic for both benthivore and planktivore geminate pairs that may have misled previous studies.

Analysing morphological variation of appendages and labrum in 10 species of Heterocypris Claus, 1893 (Podocopida : Cyprididae) with additional description of Heterocypris exigua

Natural selection can lead to speciation, but its effects depend on amount of morphological variation within populations. In Ostracoda, the appendages enclosed within the calcified carapace are less influenced by environmental conditions in comparison with carapace valves. Here, we explored morphological variation of appendages and labrum in cosmopolitan genus Heterocypris, investigating the species occurring in Europe. With the aim to overcome taxonomical problems, both traditional and geometric morphometrics were applied. The relative lengths were analysed by one-way ANOVA and post-hoc tests to determine interspecific variation and sexual dimorphism. Significant traits were further analysed by Canonical Variate Analysis separately for males and females as segment width/length ratios and relative length of claws and setae ratios. Landmark-based geometric morphometrics were applied to analyse shape variation of the labrum and traits of the maxillular palp. From this, a new perspective on morphological variation within this genus emerged. Relative measurements of the second segment of the maxillular palp, and relative lengths of the natatory setae were found to be the characters that contribute most to discrimination among Heterocypris species. The most important discriminant traits in females are the relative lengths of the G2 and G1 claws. Heterocypris exigua is additionally described, as all findings demonstrated that this is the most distinctive species, the most similar to H. gevgelica. In conclusion, we found that in comparison with maxillular palp and other analysed characters, labrum traits showed as more reliable and deserve more attention in descriptions of new species.

Phylogeography of the sergeants Abudefduf sexfasciatus and A. vaigiensis reveals complex introgression patterns between two widespread and sympatric Indo-West Pacific reef fishes

On evolutionary timescales, sea level oscillations lead to recurrent spatio-temporal variation in species distribution and population connectivity. In this situation, applying classical concepts of biogeography is challenging yet necessary to understand the mechanisms underlying biodiversity in highly diverse marine ecosystems such as coral reefs. We aimed at studying the outcomes of such complex biogeographic dynamics on reproductive isolation by sampling populations across a wide spatial range of a species-rich fish genus: the sergeants (Pomacentridae: Abudefduf). We generated a mutlilocus data set that included ten morpho-species from 32 Indo-West Pacific localities. We observed a pattern of mito-nuclear discordance in two common and widely distributed species: Abudefduf sexfasciatus and Abudefduf vaigiensis. The results showed three regional sublineages (Indian Ocean, Coral Triangle region, western Pacific) in A. sexfasciatus (0.6-1.5% divergence at cytb). The other species, A. vaigiensis, is polyphyletic and consists of three distinct genetic lineages (A, B and C) (9% divergence at cytb) whose geographic ranges overlap. Although A. vaigiensis A and A. sexfasciatus were found to be distinct based on nuclear information, A. vaigiensis A was found to be nested within A. sexfasciatus in the mitochondrial gene tree. A. sexfasciatus from the Coral Triangle region and A. vaigiensis A were not differentiated from each other at the mitochondrial locus. We then used coalescent-based simulation to characterize a spatially widespread but weak gene flow between the two species. We showed that these fishes are good candidates to investigate the evolutionary complexity of the discrepancies between phenotypic and genetic similarity in closely related species.

An investigation of the genusMesacanthus(Chordata: Acanthodii) from the Orcadian Basin and Midland Valley areas of Northern and Central Scotland using traditional morphometrics

Mesacanthus is a common and speciose genus of acanthodian fish from Lower Old Red Sandstone and Middle Old Red Sandstone assemblages (representing the Lower Devonian and Middle Devonian respectively) and is well represented in many palaeoichthyology collections in the UK. Based upon descriptions given during the 19th century, specimens of the genus Mesacanthus from the Orcadian Basin and Midland Valley areas of Northern and Central Scotland have historically been referred to a number of different species; of these, the most frequently discussed in the literature are M. mitchelli, M. peachi and M. pusillus. In order to test the validity of these three species, traditional morphometric analyses were carried out on over 100 specimens of Mesacanthus, from both the Lower Devonian and the Middle Devonian, that cover the full range of known localities for these taxa in Northern and Central Scotland. Based upon morphological and morphometric comparisons, this investigation has found that at least two species of Mesacanthus are valid (M. mitchelli and M. pusillus) as specimens from the Lower Devonian and Middle Devonian have been shown to differ significantly in a number of important ways. However, no evidence has been found for the validity of the second and distinct Middle Devonian species, M. peachi.