Figure 2.
Rates of amino acid replacement for GPDH, SOD, and XDH in dipterans. Time (abscissa) is in million years × 10−1. White dots indicate comparisons made between Drosophila species, gray dots between the drosophilid genera, and black dots between dipteran families. Averages (with their standard errors) are calculated to minimize the impact of the phylogenetic structure shown in Fig. 1. Thus, for example, for the D. melanogaster species-group, the average amino acid distance used for XDH is 0.0855 ± 0.0243, the arithmetic mean of the pair-wise distances Drosophila ananassae to D. melanogaster (0.0971) and D. ananassae to Drosophila erecta (0.0723). The rates on the right are for replacements × 10−10 per site per year. Da is the rate for comparisons between Drosophila species (2, 32, and 32), Di for drosophilid genera (5, 45, and 34), and Ce for dipteran families (23, 49, and 33) for GPDH, SOD, and XDH, respectively. These rates are obtained by linear regression with the intercept constrained to be the origin. The rate 5 to the right of the SOD graphic corresponds to the comparisons within the melanogaster and obscura groups.