3.1 Morphometric analyses
PC1 for linear body measurements described 86.4% of the variation and
based on factor loadings, was used as a proxy for overall body size
(Table S3). For head shape, PC1 explained 53% and was retained for
further analyses. We found no significant correlation between pairwise
differences in PC1 for linear body measurements and geographic distance
between sites (Mantel r = 0.22; mantel simulated p-value >
0.05). Similarly, there was no relationship between geographic distance
and relative leg length (Mantel r = 0.26; mantel simulated p-value
> 0.05) or PC1 for head shape (Mantel r = 0.10; mantel
simulated p-value > 0.05).
The RF model for body size explained 49% of the total variation.
Significant environmental variables for this RF model comprised two
measures of temperature variation (isothermality and minimum temperature
of the coldest month), two measures of precipitation (precipitation
seasonality and precipitation of the coldest quarter), elevation and
latitude (Fig. S1). Site origin was also significant in the model,
although it was the least important predictor. The results of the
follow-up linear regression indicated that four predictors explained
50% of the variance in body size (R2 =0.50, F(7,143)=22.91,
p<.001). These were: isothermality (β= 0.81,
p<0.001), precipitation seasonality (β= -0.53,
p<0.001), precipitation of the coldest quarter (β= -0.003,
p<0.05), and site (β= -0.44, p<0.01). The RF model
for relative leg length explained 44% of the variation with
isothermality, precipitation seasonality, precipitation of the coldest
quarter, precipitation of the warmest quarter, treecover and latitude as
significant predictors. The RF model for head shape explained 59% of
the variation and was explained by the following variables:
isothermality, mean temperature of the driest quarter, minimum
temperature of the coldest month, precipitation of the warmest quarter,
wettest quarter, and coldest quarter, latitude and longitude (Fig. S1).
Projected variation in body size is greatest across the Cameroon
highlands and forest-savanna ecotone as well as between the coast and
interior of Gabon (Fig. 2a). Body size increases with distance from the
equator with the exception of the southern coast of Gabon where body
size decreased sharply towards the coast. Relative leg length also
generally increased with distance from the equator, however it is
relatively uniform in areas of continuous forest (Fig. 2b). This
phenotypic variable also exhibits the greatest variation from the
southern coast of Gabon moving inland. Head shape shares a similar
pattern of variation across the forest-savanna ecotone of Cameroon as
does body size but also exhibits a shift from wider to narrow heads
moving away from the equator (Fig. 2c). In contrast to body size and
relative leg length, there was little variation in head shape between
the coast and interior of Gabon.