Body size divergence in the Plestiodon skiltonianus group

We provide the R code and morphological measurements used to compare body
size divergence in different parts of the range of a monophyletic group of
scincid lizards (Plestiodon skiltonianus species group) in western North
America. Behavioral experiments have shown that successful mating among
members of the group occurs more than 50% of the time if the body size
difference of a male-female pair lies within 10 mm of an optimal threshold
but quickly falls to ~5% once it reaches 15 mm. Beyond 15 mm, individuals
tend to avoid any interaction at all. We used this information to test
whether a greater proportion of heterotypic pairs drawn from inside two
introgression zones fall within the ±10 mm optimum compared to pairs drawn
from outside those areas. To test this hypothesis, we used rangewide
specimen data from Richmond (2005) to calculate the body size difference
(measured as snout-vent-length [SVL] in millimeters) of 500 randomly
sampled pairs in each of four groups: (1) heterotypic pairs from the
Diablo subrange of the inner Coast Ranges (ICR; Fig. 1) of central
California, or introgression zone 1; (2) heterotypic pairs from the
vicinity of the Kern River Valley (KRV), or introgression zone 2; (3)
heterotypic pairs from areas without introgression; and (4) rangewide
within the same morphotype. For heterotypic pairs, we sampled male P.
gilberti and female P. skiltonianus to match the direction of
mitochondrial introgression described in the paper. For group (4), the
male was sampled first and then the female was randomly sampled from the
same morphotype and mitochondrial clade to negate the effects of
geographic variation in body size. We performed the permutation test in R
(R_Core_Team 2021) using a custom script and plotted the distributions of
the body size differences for each of the four groups in the paper.