Fig 1.
Map indicating approximate range boundaries for Douglas squirrels (blue), red squirrels (red), and the hybrid zone (purple) in the North Cascades region.
Range shapefiles developed from published descriptions [49, 50] by A.S. Chavez. Symbols indicate sampling localities. Some specimens within the hybrid zone geographically overlap, see S1 Table for complete specimen details. Basemap reprinted from Terrain With Labels under a CC BY license, with permission from ESRI, original copyright 2016.
Fig 2.
Boxplot showing variation in bite force quotient (BFQ) for each group of squirrels.
Values on comparison bars represent significant p-values from pairwise comparisons. Outliers are indicated by black dots. Abbreviations: Allopatric Douglas squirrel, Allo Doug; Hybrid Zone Douglas squirrel, HZ Doug; Hybrid Zone red squirrel, HZ Red; and allopatric red squirrel, Allo Red.
Fig 3.
Suture complexity comparisons between Tamiasciurus groups.
Values on comparison bars represent significant p-values from pairwise comparisons. Outliers are indicated by black dots. Abbreviations are provided in Fig 2. (A) Principal component analysis for all five sutures. (B) ANCOVA for the premaxillofrontal suture. (C) ANCOVA for the nasofrontal suture. (D) ANCOVA for the maxillofrontal suture. (E) ANCOVA for the coronal suture. (F) ANCOVA for the sagittal suture.
Fig 4.
Principal component analysis of mandible shape in lateral view.
Deformation grids for principal component axes accompany their respective axis and were based on the graphed extremes for the figure. Abbreviations are provided in Fig 2.
Fig 5.
Variation in log10-transformed mandible centroid size across squirrel groups.
Values on comparison bars represent significant p-values from pairwise comparisons. Outliers are indicated by black dots. Abbreviations are provided in Fig 2.
Table 1.
Procrustes ANOVA of lateral view mandible shape data.
Relationships assessed were for squirrel group, sex, log transformed centroid size, and the interactions size by group and size by sex. Significant p-values are shown in bold.
Fig 6.
The probability of mandible morphospace overlap between squirrel groups for geometric morphometric principal components 1 and 2 representing shape and log10-transformed centroid size representing size.
Data shown are a posterior histogram of 3000 iterations of overlap metric calculations, whereby the x-axis of each pairwise comparison is the range of overlap probabilities in percentage, and the y-axis is the frequency of that probability having been observed in the calculation. Mean overlap probability is shown as a solid black line, and 95% confidence intervals are shown as dashed lines for all pairs. The plots shown here represent key comparisons for this study; additional comparisons are shown in S1 Fig.
Fig 7.
(A) Measurements of incisors in lateral and occlusal views and equation of the incisor strength index (labeled Zi) used as a proxy for bite force. (B) Schematic of cranial sutures used in this study with the nasofrontal suture (labeled NF) in red, the premaxillofrontal suture (labeled PMF) in brown, the maxillofrontal suture (labeled MF) in yellow, the coronal suture (labeled C) in pink, and the sagittal suture (S) in green. (C) Position of landmarks (large red circles) and semilandmarks (small black circles) on the mandible in lateral view. Descriptions of landmarks and semilandmarks are provided in S2 and S3 Tables.