Summary of variation explained by PC axes.

<p>This table shows the percent of variation explained by the first 8 PC axes of mandible and upper jaw shape.</p><p>Summary of variation explained by PC axes.</p

Size differences in mouse upper jaws and mandibles.

<p>All data depict average centroid size, which is calculated using all landmarks included in the morphometric analysis. Figures depict mandible and upper jaw size differences by location and year. Site abbreviations and sample sizes are as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0127218#pone.0127218.t001" target="_blank">Table 1</a>. Sites with greater than or equal to 75% corn-soybean cover in the landscape are depicted in red, while sites with less than or equal to 33% corn-soybean cover are depicted in black. Bottom graphs illustrate the average size and 1 SE by time period.</p

Landmarks used for morphological analysis.

<p>Landmarks follow Myers et al. and McPhee [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0127218#pone.0127218.ref026" target="_blank">26</a>,<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0127218#pone.0127218.ref025" target="_blank">25</a>]. Landmarks follow the same numbering as seen in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0127218#pone.0127218.g002" target="_blank">Fig 2</a>.</p><p>Landmarks used for morphological analysis.</p

Allometry of upper jaws and mandibles by time period.

<p>Prediction lines represent a regression of shape values (common allometric component) within time period on the log of the centroid size [Log(Csize)], based on 150 historic and 160 contemporary specimens. Allometry tests show significant effects of size and year on shape for both structures. Interaction of size:period is significant for upper jaws, but not mandibles. Regression lines are historic upper jaws: CAC = 0.1876*Csize-0.5037; contemporary upper jaws: CAC = 0.08492*log(Csize)- 0.23; historic mandibles: CAC = 0.134*log(Csize)– 0.3886; contemporary mandibles: CAC = 0.1005*log(Csize)– 0.284.</p

Landmarks (circles) and semilandmarks (triangles) digitized onto each specimen.

<p>Landmarks are detailed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0127218#pone.0127218.t002" target="_blank">Table 2</a>.</p

Locations of <i>Peromyscus maniculatus bairdii</i> trapping.

<p>The map illustrates the spatial distribution of corn-soybean agricultural intensity in the Midwestern US. The locations indicated on the map are detailed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0127218#pone.0127218.t001" target="_blank">Table 1</a>. They were chosen because concentrations of historical specimens from before 1910 were available from the region. Three of our locations (NILL, IOWA, and WAMN) are in regions of greater than 75% corn-soybean agriculture cover within the county, while the other three (MAKA, OTKA, and EMND) are in agricultural regions of less than 33% corn and soybean cover within the county. All contemporary specimens were collected from corn-soybean fields. Map available at: <a href="http://www.nass.usda.gov/Charts_and_Maps/Crops_County/cr-pl.asp" target="_blank">http://www.nass.usda.gov/Charts_and_Maps/Crops_County/cr-pl.asp</a>.</p

Location-specific changes in <i>Peromyscus maniculatus bairdii</i> jaw shape.

<p>Thin plate spline (TPS) deformation grids illustrate the changes in shape that have occurred in each location from approximately 1910 to 2012. TPS grids represent a hypothetical change in shape, based on required bending energies associated with making changes to a 2-dimensional object using the least amount of force. If an object is compared to itself, all lines would be parallel or perpendicular to all other lines, and all grid squares would be of equal size. These TPS grids are shown at 3x magnification to clarify changes. Parallel lines represent no change between objects, and all non-parallel lines represent a change in shape. Also, lines further apart represent a relative widening of that region relative to the rest of the structure, whereas lines that are closer together represent a relative shrinking of that region. Landmarks are as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0127218#pone.0127218.g002" target="_blank">Fig 2</a> and specimens are as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0127218#pone.0127218.t001" target="_blank">Table 1</a>.</p

Summary of predictors of jaw morphology.

<p>Location, period, size, and interactions were modeled as predictors of mandible and upper jaw morphology, using a Procrustes distance metric and resampling techniques. Values are mean square errors explained by each parameter, based on all 310 specimens as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0127218#pone.0127218.t001" target="_blank">Table 1</a>. Significance codes are as follows:</p><p>*** p < 0.001,</p><p>** p < 0.01,</p><p>* p < 0.05,. p < 0.10.</p><p>Summary of predictors of jaw morphology.</p

Summary of specimen collection sites.

<p>Historical location is an estimate from museum records and contemporary locations are the coordinates of the sampled field. Percent corn and soybean in 2012 is based on National Agricultural Statistics Service numbers (nass.usda.gov). The number of acres of land planted to corn or soybean was divided by the recorded size of each county in which sampling occurred.</p><p>Summary of specimen collection sites.</p

Tangent space for upper jaws (top) and mandibles (bottom).

<p>PC axes 1 and 2 explain the maximum amount of variation in the data (upper jaws: 27 and 13%, mandibles: 25 and 13%). The thin plate spline deformation grids in each corner represent the largest difference among all specimens, by indicating what each structure looks like at the ends of PC axis 1 relative to a specimen at the origin (0,0), as described in the methods. Colors are locations as follows: Black: EMND; Red: IOWA; Green: MAKA; Blue: NILL; White: OTKA; Grey: WAMN. Sample sizes and abbreviations are as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0127218#pone.0127218.t001" target="_blank">Table 1</a>.</p