2.2 Measurement of traits
Spur length was measured of all flowering individuals in each
population, including both red- and yellow-flowered individuals. The
spur lengths of 1–3 randomly selected flowers per plant were measured
with a digital caliper (precision 0.01 mm), and the average length of
the measured spurs was used as the spur length of that individual
(Figure 1c). Corolla diameter and petal width of each individual were
measured at the same time. The variation in floral traits was visualized
by principal component analysis (PCA) and compared among populations.
Preliminary observations showed that the three floral traits did not
differ among flowers within an individual, and petal width did not
differ among the five petals of each flower. We considered spur length
to be the most important trait because of its relation to visitor size.
Therefore, in subsequent analyses we focused on spur length. The
multiple comparison Steel-Dwass test was used to compare average spur
length between populations.
We also examined spatial autocorrelation (i.e., whether the variation in
spur length could be explained by physical distance) by using the
”moran.test” function in the ”spdep” package in the R Software
Environment ver. 4.0.2 (R Core Team, 2013) to run Moran’s I test. This
analysis used the average spur length and the latitude and longitude of
each population.