Evolutionary and Systematic Significance of Temporal Variation in the Fox Sparrow

Morphometric variation was studied among samples of fox sparrows taken in 1926- 1927 and 1978-1980 at seven sites in California. Samples of males were taken at two of the seven sites in both 1978 and 1979, and five samples of males were measured a second time to assess measurement error. Thus, 21 groups of males (14 "main" samples, 2 samples one year apart, and 5 remeasured samples) and 14 groups of females were used in this study. Thirty-one measurements of skeletal characters were taken on 317 males and 142 females, plus on the 101 males that were remeasured. The main objective was to determine if phenotypic change had occurred over a half century, and to quantify the extent of such temporal change relative to levels and patterns of geographic variation. In the temporal samples, an average of 2.2 (7.1%) significant character differences per site was observed. Hence, most characters showed no signif- icant differences over 50 years. Character differences between remeasured, temporal, and geo- graphic samples were quantified by computing average percentage differences between char- acter means. Taxonomic distances were computed between all pairs of samples (sexes separate). Ten characters were excluded from analyses due to relatively high levels of measurement error. Percentage differences for the remaining 21 character means for remeasured samples averaged 0.33 ? SD of 0.31% and resulted in an average taxonomic distance between replicates of 0.25. Average percentage differences in character means over 50 years (0.98 ? 0.79%) were similar to geographic differences (1.14 ? 0.88%) among samples taken during the same time period. Av- erage taxonomic distance between samples taken 50 years apart (0.71 ? 0.21) was somewhat less than that between temporally comparable samples from different sites (0.84 ? 0.16). However, samples taken 50 years apart at a site can be as different as those from sites 100 to 200 km apart and assigned to different subspecies. Multivariate analysis of variance revealed that temporal samples at two (of seven) sites differed significantly, and generalized discriminant analysis obtained significant differences between temporal samples at two additional sites. Temporal phenotypic stability was evident in that the same two groupings of samples were obtained in analyses of both old and new samples. However, patterns of variation in the two time periods, within these two main groupings of samples, are not concordant because of phe- notypic change over time. That is, temporal change altered geographic patterns. Males and females showed different patterns of variation. No clear temporal trends in morphological change were identified, either in individual characters across sites, or in suites of characters within population samples. Characters with the largest relative differences over 50 years did not tend to show large geographic differences. The average taxonomic distance among old samples did not differ from that computed between recent samples; therefore, the populations at these sites are not diverging phenetically. Although the genetic basis of the phenotypic variation measured here is unknown, temporal variation could be adaptive either through phe- notypic response to environmental change or by maintaining a store of morphological vari- ability. (Sparrows; morphometrics; measurement error; temporal variation; geographic variation; microevolution.)