3.1 Variation in Circadian Period among and within Populations
Families with at least 5 replicates were included in analysis of
variance of circadian period, with the largest number of replicates
within a single family being 18. Both ANOVA and the Welch’s F-test found
highly significant differences among and within populations in mean
circadian period (Table 1). Among the 30 populations analyzed, mean
circadian period varied between 21.91 to 24.92 h, or three hours (Fig.
2). Although most of the populations expressed a circadian period close
to a 24 h, many populations had a period that is much shorter; 10 of the
30 populations had a mean period value that was shorter than 22.5 h, and
only 2 such populations (LEW, LIB) exhibited spatial autocorrelation.
Variation within the populations (among the families within each
population) was similar (variance component for the family within
population effect 0.687, or 21.3 % of total variation) compared to the
variation among the 30 populations (variance component for the
population effect 0.787, or 24.4 % of total variation), which defines
the structure of the populations. Thus, though the range of family
values within many of the populations was large, the populations were
structured with slightly higher variation among the populations
(Table 2).
Within populations, the difference between the family with the shortestvs . longest circadian period length (range) was 3 h on average.
Two populations expressed exceptionally high ranges of >5 h
(Happy Jack Trail, HJT, and Crow Creek, CRW, populations; Table 2). HJT
and CRW exhibited spatial autocorrelation, such that one cannot exclude
the possibility of a founder event and that HJT and CRW are one genetic
population; nevertheless, under this hypothesis, at least one population
exhibits >5 h range. The wide range of values for the HJT
and CRW populations contrasted with another population, Sand Lake, which
had a range of values among families of less than an hour (Fig. 3).
Neither population mean value nor the number of replicates (both
individuals and family lines) had a significant association with the
within-population range, indicating the results for circadian range
within populations are not a consequence of slight differences in
replicate number and potential sampling bias. In sum, the range of
variation among families within some populations (> 5 h) is
greater than the mean difference among populations (3 h).