DOI: 10.5061/dryad.bzkh189cx
title: Characterizing phenotypic diversity in marine populations of the threespine stickleback

description: The threespine stickleback (Gasterosteus aculeatus) is an important model
 for studying the evolution of vertebrate morphology. Sticklebacks inhabit
 freshwater, brackish, and marine northern hemisphere waters. Anadromous
 and marine populations (hereafter marine) are assumed to have remained
 unchanged morphologically from ancestral marine sticklebacks, despite
 marine environments varying on regional and local scales. Recent studies
 suggest that genetic and phenotypic structure exists in marine
 populations, yet the scale of this variation, and its ecological causes
 remain unclear. Our goal was to assess morphological trait variation in
 marine stickleback populations around Southern British Columbia (BC) and
 determine if oceanographic and habitat characteristics were associated
 with this variation. Between May-July 2019, we sampled 534 sticklebacks
 from 15 sites around Vancouver Island, a region characterized by a large
 diversity of oceanographic and habitat features. We characterized trait
 variation using two-dimensional (2D) geometric morphometric analysis,
 comparing individuals between oceanographic regions and habitats. We
 focused on head and body shape. We found that marine sticklebacks varied
 morphologically among and between regions and habitats, but the variation
 did not appear to be related to environmental variation. Sexual dimorphism
 was the largest source of variation, but oceanographic and habitat
 variables influenced differences between sexes. We concluded that marine
 sticklebacks offer abundant opportunities for expanding our knowledge of
 drivers of morphology.
description: General Methodology of the Project Between
 May – July 2019, a total of 534 fish were collected from 15 sites around
 Vancouver Island and Southern BC, Canada. At each site, sticklebacks were
 caught with beach seines at 1–2m depth and 2–3m offshore, or with
 un-baited minnow traps. We sampled in all four oceanographic regions of
 Vancouver Island: the Strait of Georgia, the Juan de Fuca Strait, and the
 western and northern coasts of Vancouver Island. Within each region, we
 sampled from three different coastal habitat types: tidal flats, salt
 marshes, and lagoons. Stickleback Head and Body
 Photograph Files The original image files were
 converted into tps format using the software <em>tps.Util</em>
 version 1.61, and then organized into files for superimposition. The tps
 images were uploaded into <em>tps.Dig </em>version 2.05 to
 digitize landmarks on the head and body photographs. The TPS files are
 included as well, labelled as “All_Body_Fraser_El-Sabaawi.TPS” and
 “All_Head_Fraser_El-Sabaawi.TPS”. For the head photographs 13 anatomical
 landmarks were placed around the left side of the head in tps.Dig. For
 body photographs, 15 landmarks were placed on the left side of the
 body. After the landmarks were digitized, landmark
 coordinates (X and Y positions) were uploaded into R. We extracted linear
 distances from each image using the “linear.dist” function in the
 <em>landvR</em> package for R. Head length (mm) was extracted
 from headshots (landmarks 1 and 12) as a proxy for head size. Standard
 length (cm) was extracted from body shots (landmarks 1 and 8) as a proxy
 for body size. These lengths, plus individual ID tag,
 sex, site names, habitat type, oceanographic region, plate morphology,
 salinity, temperature, mean head length/mean standard length and latitude
 were included in classifier Excel spreadsheets to upload into R. There is
 one for the head size/shape analysis and another classifier file for body
 size/shape analysis. Generalized Procrustes
 Analysis The head and body shape coordinates were
 analyzed separately. In the <em>geomorph</em> package, the
 “gpagen” function was used to perform a Generalized Procrustes Analysis
 (GPA), which is the most common approach for separating shape from size. 
 Following GPA, 26 vectors of shape were produced for the head dataset (X
 and Y coordinates for 13 landmarks), while 30 vectors of shape were
 produced for the body dataset (X and Y coordinates for 15 landmarks). 
 Additionally, an extra vector was produced for each dataset which
 described the geometric size of each specimen’s head or body (i.e.
 CS).
description: Programs:
 <em style="text-indent:48px;">tps.Util</em> version 1.61 and
 <em style="text-indent:48px;">tps.Dig</em> version
 2.05.  In R, we used
 the <em style="text-indent:48px;">landvR </em>package and
 the <em style="text-indent:48px;">geomorph</em> package.