Data from: Genetic drift or natural selection? Hybridization and asymmetric mitochondrial introgression in two Caribbean lizards (Anolis pulchellus and Anolis krugi)

Hybridization and gene introgression can occur frequently between closely
related taxa, but appear to be rare phenomena among members of the
species-rich West Indian radiation of Anolis lizards. We investigated the
pattern and possible mechanism of introgression between two sister species
from Puerto Rico, Anolis pulchellus and Anolis krugi, using mitochondrial
(ND2) and nuclear (DNAH3, NKTR) DNA sequences. Our findings demonstrated
extensive introgression of A. krugi mtDNA (k-mtDNA) into the genome of A.
pulchellus in western Puerto Rico, to the extent that k-mtDNA has mostly
or completely replaced the native mtDNA of A. pulchellus on this part of
the island. We proposed two not mutually exclusive scenarios to account
for the interspecific matings between A. pulchellus and A. krugi. We
inferred that hybridization events occurred independently in several
populations, and determined that k-mtDNA haplotypes harboured in
individuals of A. pulchellus can be assigned to four of the five major
mtDNA clades of A. krugi. Further, the spatial distribution of k-mtDNA
clades in the two species is largely congruent. Based on this evidence, we
concluded that natural selection was the probable driving mechanism for
the extensive k-mtDNA introgression into A. pulchellus. Our two nuclear
data sets yielded different results. DNAH3 showed reciprocal monophyly of
A. pulchellus and A. krugi, indicating no effect of hybridization on this
marker. In contrast, the two species shared nine NKTR alleles, probably
due to incomplete lineage sorting. Our study system will provide an
excellent opportunity to experimentally assess the behavioural and
ecological mechanisms that can lead to hybridization in closely related
taxa.