Genetic differentiation reflects geological history in the Azorean land snail, Leptaxis azorica

Abstract

The land snail Leptaxis azorica, endemic on the Azores, was subjected to an electrophoretic (allozymes) and morphometric (genital tract) analysis. Genetic distances suggest the presence of four distinct lineages and are compatible with colonisation proceeding from the eastern, older islands (Santa Maria and Sã o Miguel) to the west (Flores and Corvo). On Sã o Miguel, genetic and morphometric differentiation is concordant with the separate colonisation of two islands that gave rise to the current island 50 000 years ago. The maximum time available for differentiation in isolation (0.55 million years) suggests a high rate of allozyme change between the two lineages on Sã o Miguel. This may be related to population isolation and bottlenecks caused by human and volcanic activity on Sã o Miguel in relatively recent times. This is more prominent in the eastern region where populations are also characterised by reduced genetic variation (loss of alleles and heterozygosity) compared to populations elsewhere.

Phylogeography and molecular phylogeny of Macaronesian island Tarphius (Coleoptera: Zopheridae): why are there so few species in the Azores?

“…2). Inter‐island colonization and isolation on different islands have also been acknowledged as important mechanisms responsible for the evolution of Azorean endemic land snails (Van Riel et al. , 2003, 2005; Jordaens et al.…”

Speciation on the Azores islands: congruent patterns in shell morphology, genital anatomy, and molecular markers in endemic land snails (Gastropoda, Leptaxinae)

“…7). Finally, the molecular data (Van Riel et al. , 2003, 2005) and our morphological data show that the OTUs within the azorica and within the caldeirarum shell‐type may represent distinct species.…”

“…7). The congruence of morphological and molecular differentiation was already demonstrated among the three OTUs within L. a. azorica on different islands (Flores, West, and East São Miguel) (Van Riel et al. , 2003, 2005).…”

“…Geographical isolation appears to be an important mechanism underlying morphological and molecular differentiation in the Azorean Leptaxini (Van Riel et al. , 2003, 2005) instead of adaptive radiation through ecological differentiation.…”

“…(2005) suggested a major role of allopatric differentiation via the successive colonization of younger islands, whereas a major role for adaptive evolution was not supported. Interestingly, Van Riel et al. (2003) found four distinct lineages within L. a. azorica that were compatible with colonization proceeding from the eastern, older islands [Santa Maria ( L. a. minor ) and São Miguel ( L. a. azorica )] to the west ( Leptaxis a. azorica from Flores).…”