year) much greater for comparisons between drosophilid genera (4.4× 10 −^10 ) and still
greater for comparisons between dipteran families (9.31× 10 −^10 ). This heterogeneity
conceals even more disparate actual rates, which become manifest when we take into
account that these rates apply to largely overlapping lineages. Thus, the rate of 4.4× 10 −^10
for comparisons between Chymomyza and Drosophila (row 4 in Table 1.3) needs to be
decomposed into a rate of ≤2.0× 10 −^10 for most of the overlapping period of Drosophila
evolution and a rate >10× 10 −^10 for the 25 million years between the divergence of the
two genera and the time of divergence between the Drosophila subgenera and between the
Chymomyza species (Ayala 1997). The range of rates of evolution is ostensibly greater for
GPDH (from ≤2 to ~40) than for any other gene in this survey.
G6PD
The rate within Drosophila groups (melanogaster group) is 44.1× 10 −^10 /site per year (row 1,
Table 1.3). This rate is about twice as great as the rate between dipteran families (21.
2 × 10 −^10 /site per year; row 6), and four times greater than the rate between animal phyla
(13.4× 10 −^10 /site per year; row 8) or multicellular kingdoms (11.7× 10 −^10 /site per year;
row 9). Note that Drosophila (melanogaster group) evolves ≈10 times faster (44.1× 10 −^10 /
site per year) than rodents (4.6× 10 −^10 /site per year between mouse and rat; not shown in
Table 1.3), and ≈5 times faster than mammals (8.5× 10 −^10 /site per year; row 5).
PGD
The rate of amino acid replacement of PGD generally slows down with increasing
divergence time. Rate differences are, however, less conspicuous than for G6PD. Thus,
the average rate within Drosophila groups (melanogaster group) is 19.7× 10 −^10 /site per year,
just slightly faster than the rate between dipteran families (16.1× 10 −^10 /site per year), but
about twice as great as the rate between animal phyla (9.7× 10 −^10 / site per year) or
multicellular kingdoms (11.7× 10 −^10 /site per year).
SOD
We have noted earlier the baffling contrast between SOD and GPDH. When animals are
compared with plants or fungi, the two enzymes ostensibly evolve at similar rates (12.6
and 13.0), but for comparisons between Drosophila species, SOD evolves as much as 30–
40 times faster than GPDH (Ayala 1997; Rodríguez-Trelles et al. 2001a).
TPI
The rate within Drosophila groups is 4.4× 10 −^10 /site per year (averaged across the
melanogaster and obscura groups). This rate becomes six times greater between Drosophila
groups (26.1× 10 −^10 /site per year), eight times greater between Drosophila subgenera (35.
5 × 10 −^10 ), and 10 times greater between brachyceran families (43.5× 10 −^10 ; between
Drosophila and Calliphora). Compared with this last-named value, the rate decelerates by a
18 FRANCISCO RODRÍGUEZ-TRELLES ET AL.