iii) Gregariousness evolves semi-linearly and is preceded
by host specialisation
Estimates from our Phylogenetic Path Analysis (PPA) revealed that, from
a solitary ancestor, G1 and G2 are both equally likely to evolve next
(pathway coefficients: solitary to G1 = -4.303; solitary to G2 =
-4.146). Our model also supports the pathway in which G1 evolves before
G2 (G1 to G2 = -2.652), and G2 precedes the evolution of G3 (G2 to G3 =
5.117, Figure 3A, Table A3). When host plant number is included in the
model set, a solitary ancestor is estimated to precede G1 (solitary to
G1 = -3.580) and there is strong support for G2 preceding G3 (G2 to G3 =
5.693), but these character state pairs are independent of one another.
Our second model also suggests that a decrease in host use number
precedes transitions to G1 (host number to G1 = -0.394, Figure 3B, Table
A3).