Establishment of a coastal fish in the Azores: recent colonisation or sudden expansion of an ancient relict population?

Abstract

The processes and timescales associated with ocean-wide changes in the distribution of marine species have intrigued biologists since Darwin's earliest insights into biogeography. The Azores, a mid-Atlantic volcanic archipelago located >1000 km off the European continental shelf, offers ideal opportunities to investigate phylogeographic colonisation scenarios. The benthopelagic sparid fish known as the common two-banded seabream (Diplodus vulgaris) is now relatively common along the coastline of the Azores archipelago, but was virtually absent before the 1990s. We employed a multiple genetic marker approach to test whether the successful establishment of the Azorean population derives from a recent colonisation from western continental/island populations or from the demographic explosion of an ancient relict population. Results from nuclear and mtDNA sequences show that all Atlantic and Mediterranean populations belong to the same phylogroup, though microsatellite data indicate significant genetic divergence between the Azorean sample and all other locations, as well as among Macaronesian, western Iberian and Mediterranean regions. The results from Approximate Bayesian Computation indicate that D. vulgaris has likely inhabited the Azores for ∼40 (95% confidence interval (CI): 5.5–83.6) to 52 (95% CI: 6.32–89.0) generations, corresponding to roughly 80–150 years, suggesting near-contemporary colonisation, followed by a more recent demographic expansion that could have been facilitated by changing climate conditions. Moreover, the lack of previous records of this species over the past century, together with the absence of lineage separation and the presence of relatively few private alleles, do not exclude the possibility of an even more recent colonisation event.

Historical gene flow constraints in a northeastern Atlantic fish: phylogeography of the ballan wrasseLabrus bergyltaacross its distribution range

“…Although the results from the slow evolving S7 gene do not show such a clear cut, Azores keeps its singularity, being isolated (with no migration) from the remaining European locations (average Nm of 0.160 between Azorean locations and the remaining ones). Similar findings related to the peripheral position of Azorean haplotypes were also reported for several other species [62,68]. …”

“…This trend for the genetic isolation of the Azores can be occasionally reversed by severe or atypical weather events (e.g. [68]).…”

Unravelling population genetic structure with mitochondrial DNA in a notional panmictic coastal crab species: sample size makes the difference

“…Due to the marginal and isolated position of the Azores (approximately 1500 km from mainland Portugal), this result is rather unexpected. Many genetic studies on fishes reported strong genetic segregations of Azores’ population from continental ones [58]. However, we cannot disregard that only two haplotypes, one of which a singleton, were sampled in individuals from this archipelago.…”

Genetic diversity and population structure of the blue jack mackerel Trachurus picturatus across its western distribution

“…These islands, just off the coast of Europe and Africa, are formed by volcanic seamounts and were never part of a continent. This makes the biogeography of the islands very attractive for phylogeographic studies (Quinteiro et al, ; Stefanni et al, ; Whittaker, ). The marine environment is very often characterised as having complex oceanic currents and no physical barriers, which greatly increase a species’ dispersal potential, promoting high gene flow over large scales (Selkoe et al, ).…”

“…Indeed, several phylogeographic studies have reported a low population genetic differentiation in the Macaronesian region for different taxa, including gastropods (De Wolf et al, ), crustaceans (Faria et al, ; Quinteiro et al, ) and fishes (Francisco et al, ; Stefanni et al, ). On the other hand, the Macaronesia archipelagos are also characterised by different upwellings zones, habitat discontinuities and ecotones between areas with different environmental properties and areas with historical sea level drops ( e.g ., Stefanni et al, ). These features seem to be responsible for maintaining discrete subpopulations over a species’ range, suggesting stable currents in Macaronesia that promote these genetic differences.…”