Gs. Spicer et J. Jaenike, PHYLOGENETIC ANALYSIS OF BREEDING SITE USE AND ALPHA-AMANITIN TOLERANCE WITHIN THE DROSOPHILA-QUINARIA SPECIES GROUP, Evolution, 50(6), 1996, pp. 2328-2337
The Drosophila quinaria group is unusual within the genus in that it c
omprises both mycophagous and nonmycophagous species. DNA sequence dat
a from three regions of the mitochondrial genome were used to infer re
lationships among four mycophagous species and three that breed on dec
aying water plants. Phylogenetic analysis of these species show that b
reeding in mushrooms and tolerance of high levels of alpha-amanitin we
re the ancestral states within the group. Thus, breeding in decaying w
ater plants and intolerance of alpha-amanitin are derived conditions.
We also found that the D. quinaria species group does not comprise sep
arate mycophagous and nonmycophagous clades, but rather that (1) the s
hift from mushrooms to decaying plants occurred on at least two occasi
ons; or (2) mycophagy reevolved within a lineage that had previously s
hifted to breeding on plants. The correlation between mycophagy and al
pha-amanitin tolerance is perfect across the species we have examined,
indicating that there is no detectable time lag between an ecological
shift to a new breeding site and correlated changes in biochemical ad
aptation. The genetic distance between the mycophagous D. recens and t
he nonmycophagous D. quinaria indicates that these species split only
about 1 M.Y.B.P. In terms of alpha-amanitin tolerance, D. recens and D
. quinaria are typical of other ecologically similar species within th
e group. Thus, evolutionary changes in alpha-amanitin tolerance can ev
idently occur on the order of about 1 million yr. Our data also indica
te that, in comparison to other groups of Drosophila, the quinaria spe
cies group may be undergoing an adaptive radiation.