Sample collection and site characterization
In the Northern Range Mountains in Trinidad, guppies originating from
high predation (HP) environments have been previously transplanted into
guppy-free, low-predation (LP) environments, and monitored as they
evolved towards the LP guppy ecotype, forming one of the best examples
of replicated parallel evolution in the wild to date (Reznick et
al. 1996; Magurran 2005; Gee et al. 2009). Translocations
occurred in six instances (1957, 1976, 1981, 2008, and for two streams
in 2009) across five drainages (Aripo, Campo, El Cedro, Guanapo, Turure;
Fig. 1). In February 2014, we field-collected guppies from each of these
six transplant sites, which we call “Introductions” (LP environments
where HP populations were previously introduced). We also collected fish
from the three original HP populations that served as sources for the
introductions, and from three native LP populations as presumed locally
adapted references (Fig. 1). We divided sites into four categories: HP
source, LP native, old introduction (introduced 30-60 years prior to
sampling), and recent introduction (5-6 years prior to sampling).
We collected 19-35 female guppies from each of these 12 sites. We
sampled three distinct pools that were at least 30 m apart to capture
within-site heterogeneity, and only females to control for possible sex
differences (Bolnick et al. 2014b) and for comparability to
Sullam et al. (2015). Sampling was lower at Naranjo (N= 19)
because rain limited sampling time and Tumbasson (N=21) because of its
small population size. We weighed and euthanized individuals with an
overdose of MS-222 immediately after field capture, and preserved them
in 95% ethanol. We measured stream pH and temperature using a handheld
meter (Hanna Instruments, Smithfield, RI, USA), and recorded GPS
coordinates of each pool. Fish condition was calculated as weight
divided by length.