Geography Reference
In-Depth Information
CASE STUDY 7.3 Phylogeographic Predictions of a Weevil Species
of the Canary Islands
Oceanic islands are attractive for evolutionary biogeography for several reasons:
They present discrete geographic entities within defined oceanic boundaries, gene
flow between individual islands is reduced by oceanic barriers, their often small
geographic size has made the cataloguing of their biotas easier than that of con-
tinental systems, despite their small geographic size they can contain a diversity of
habitats, and they are often geologically dynamic, with historical and contempor-
aryvolcanic and erosional activity (Emerson et al. 2006). In addition to the molecu-
lar phylogenetic analyses that have focused on the relationships between species
occurring on two or more oceanic islands, these features make them attractive for
studies of intraspecific phylogeography within individual islands. Emerson et al.
(2006) analyzed the intraspecific phylogeography of the weevil species Brachyde-
res rugatus (Coleoptera: Curculionidae) in La Palma (Canary Islands) in order to
test some predictions about the biotic evolution of this taxon.
The geological history of La Palma is fairly well understood (Carracedo and
Day 2002). The island consists of the northern shield, composed of older volcanic
terrains, and the southern ridge, constituted by terrains of more recent volcanic
origin. Subaerial development of the northern shield began about 1.7-2.0 mya and
continued until about 0.55 mya, being dominated by two volcanos, Garafia (act-
ive from 1.7 to 1.2 mya) and Taburiente (active from 1.2 to 0.4 mya). From 0.8 to
0.7 mya, in the final stages of the Taburiente volcano, the southward migration of
volcanism began through the southern, or Cumbre Nueva, rift of the volcano. At
about 0.56 mya this rift became unstable, and its western flank collapsed into the
sea. After this collapse, the Bejenado volcano dominated activity from 0.56 to 0.40
mya, with possible minor activity continuing until about 0.2 mya. After the end of
the growth of the Bejenado volcano, the entire northern shield became quiescent,
and the island may have entered a period of volcanic calm, but volcanism in the
south of La Palma may have built its submarine and core parts, now concealed by
younger lavas of the eruptive period in the northern shield. It seems reasonable
to assume that a widespread species with limited dispersal abilities, which was
present in the island during its volcanic history, would have been influenced by
these events. Genetic footprints of past range expansions and fragmentations of
a species such as Brachyderes rugatus should be consistent with predictions from
volcanic and erosional events. Emerson et al. (2006) hypothesized that ancestral
haplotypes should be located predominantly in the northern shield, with the new-
er Bejenado and Cumbre Vieja volcanic terrains having more derived haplotypes,
located peripherally in the haplotype network. They also predicted signatures of
population expansion in the areas of the geologically young Cumbre Vieja volcanic
terrains: haplotypes occurring in multiple sampling localities and haplotypes with
multiple derivatives differing by only one or few mutations.
 
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