Factor analysis of behavioral traits
We registered 1217 behavioral events. A comprehensive check list of 20
behavioral traits displayed by the lizards during the male tournaments
is presented in Table 1.
Statistical analyses revealed that the frequency of these two behaviors
in the dyadic trials (i.e. 42.8% vs. 23.8%) in the lab did not
significantly differ (χ2 = 1.71, P = 0.19).
However, there were significant differences in the distance between
opponents (U = 762, P < 0.0001 – lateral
compressions were displayed at closer distance, see above), and in the
likelihood of subsequently eliciting an aggressive response from the
opponent (χ2 = 21.24, P < 0.0001).
Lizards were significantly more likely to receive an aggressive response
after performing a lateral compression than after push-ups. In contrast,
there was no significant difference in their duration (U = 471.5,P = 0.70).
The factor analysis performed on the 20 behavioral traits extracted five
factors that together explained 62.78% of the variance (Table 2).
Factor 1 explained 22.05% of the variance in behavioral traits
(eigenvalue = 4.41) and the factor loadings indicated that push-ups,
lateral compression, and lunge behaviors were the most important
behavioral traits in this factor. Factor 2 explained 18.34% of the
variance (eigenvalue = 3.67) and climbing on top of the rock was the
most important behavioral traits in this factor. However, tongue flicks
(0.77) and rubbing the base of the tail onto the substrate (0.65) also
had high correlation coefficients (Table 2). Factor 3 explained 8.68%
(eigenvalue = 1.73) with side hop and retreat representing the most
important behavioral traits in this factor. Factor 4 explained 7.58%
(eigenvalue = 1.51) where tail waving was the most important behavioral
traits in this factor. Finally, factor 5 explained 6.11% (eigenvalue =
1.22) where exploring the arena and trying to climb the walls was the
most important behavioral trait.
The comparison of the SELF and the RIVAL models explaining Factor 1
suggested that the RIVAL model was more informative (AICc = -22.84) than
the SELF model (AICc = 47.12). Opponent’s factors 1 (importance = 0.92,β = 0.14, z = 4.79, P < 0.001), 3 (importance =
1.00, β = 0.22, z = 8.26, P < 0.001), and 4
(importance = 0.98, β = 0.07, z = 3.34, P <
0.001) had positive effects on Factor 1 of the focal male (Table 3 and
Fig. 1). Thus, the rivals’ behaviors summarized in Factors 1, 3, and 4
increased the intensity of the aggressive behavior of the focal males,
although the behavioral traits summarized in Factor 4 may contribute
very little to explain the variance in Factor 1 of focal lizards (Fig.
1d). Meanwhile rivals’ Factor 2 (importance = 0.79, β = -0.05, z
= 2.33, P = 0.020) and the chroma of their blue patches
(importance = 0.82, β = -0.76, z = 2.08, P = 0.037) were
negatively related to Factor 1 (Table 3 and Fig. 2). Thus, rivals’
behaviors summarized in Factor 2 and the chroma of their blue patch
reduced the aggression intensity of focal males, although these
behavioral traits may contribute very little to explain Factor 1 of
focal males.
Interestingly, the SELF model suggested that there was a significant
effect of haemococcidians and tick load on Factor 1. The effect of the
infection by the haemococcidian genus Lankesterella was negative
(importance = 0.88, β = 0.08, z = 2.70, P = 0.007);
infected lizards displayed less push-ups, lateral compressions, and
lunge behaviors (Fig. 3a). The number of ticks had a positive effect on
Factor 1 (importance = 0.73, β = 0.05, z = 2.18, P =
0.028) (Table 3). However, this positive relationship was only at low
levels of infestation (< 4) and not when lizards had more
ticks (> 6) (Fig. 3b).