1. Fish sampling and parasite identification
We used unbaited minnow traps to collect adult threespine stickleback
from lake, river, and estuary sites on Vancouver Island in late May and
early June 2009. Collections were approved by the University of Texas
IACUC (07-032201) and a Scientific Fish Collection Permit from the
Ministry of the Environment of British Columbia (NA07-32612). Fish were
euthanized in MS-222 and then preserved in formalin, after the caudal
fin of each individual fish was removed and preserved in pure ethanol
for genotyping. Details are provided in Bolnick & Ballare (2020). These
samples were used to examine within- and between-population variation in
diet (Bolnick & Ballare, 2020), parasite community composition
(Bolnick, Resetarits, Ballare, Stuart, & Stutz, 2019), and parasite
species richness (Bolnick, Resetarits, Ballare, Stuart, & Stutz, 2020).
The parasite infection data for this study are archived at Dryad Digital
Repository (Bolnick and Ballare, 2020). Here, we focus on a random
subset of 26 sampling sites (N = 1437 stickleback) for which we also
genotyped individuals for MHC IIβ. For each stickleback individual, we
recorded sex and body length and then dissected each fish to count and
identify macroparasites as described in (Stutz & Bolnick, 2017).