DOI: 10.5061/dryad.v15dv41tk
title: Microtus californicus toothrow and molar .tps files

description: Aim. This study examines how climate shaped Microtus californicus
 (Rodentia: Arvicolinae) ecomorphology throughout the Quaternary. It tests
 three hypotheses: (1) climate corresponds with consistent shape variation
 in M. californicus dentition; (2) Quaternary warming and drying trends
 caused M. californicus morphotypes to predictably shift in range through
 time; (3) Quaternary warming and drying led to predictable changes in
 tooth morphological variation. Finally, we discuss how shifts in
 climate-linked morphological variation may affect the potential of M.
 californicus to react to future climate change. Location. Western United
 States. Taxon. Microtus californicus (Peale, 1848) Methods. Geometric
 morphometrics and partial least squares (PLS) analyses were used to
 discern how climate contributes to consistent variation in the shapes of
 the M. californicus lower first molar (m1), validated for the full
 toothrow. We further corroborate this relationship, reconstructing
 precipitation at fossil localities using m1 morphology and comparing those
 values to paleoclimate-model-derived precipitations. Disparity analyses
 and a MANOVA were performed to examine changes in variation and whether a
 shift in tooth shape occurred through time. Results. M. californicus m1
 and toothrow shapes are narrower and more curved in cooler, wetter
 climates. Morphology-based paleoclimate reconstructions align with
 model-based paleoclimate estimations. When time averaging is accounted
 for, M. californicus demonstrates a 12% reduction in variation from fossil
 to present-day specimens, and these changes in tooth shape correspond with
 climate-related morphotypes. Main conclusions. As California became drier
 and hotter since the late Pleistocene, M. californicus dental morphology
 generally tracked these changes by adapting to the consumption of rougher
 vegetation in drier environments. This resulted in the loss of some
 high-precipitation morphotypes, indicating that ecomorphology, often
 observed at the species and community levels, translates to intraspecific
 variation and dynamically changes in response to changing climates. The
 loss of climate-linked morphological variation since the late Pleistocene
 may limit the ability of M. californicus to respond to future changes in
 climate. These findings portend that other species may have experienced
 similar losses in adaptability.
description: We analyzed 101 fossil m1s, 307 modern m1s, and 361 modern upper
 toothrow specimens of <i>M. californicus</i>. Fossil specimens
 from the 7 localities are housed at the University of California Museum of
 Paleontology (UCMP; Berkeley, USA) or the Los Angeles County Museum of
 Natural History (LACM; Los Angeles, CA; Fig. 1; Supplementary Table 1;
 McGuire & Davis, 2013). Modern specimens are from the Museum of
 Vertebrate Zoology (MVZ; Berkeley, USA) and were evenly sampled from
 throughout the species’ range, with a male and female specimen selected
 from each county and subspecies designation (Fig. 1 &
 Supplementary Table 2). Specimens were photographed using a Nikon D70s and
 AF Micro-NIKKOR 60mm f/2.8D macro lens ensuring, and best practices for
 small-specimen photographing were followed (Fox, Veneracion, &
 Blois, 2020). Left m1s and upper left toothrows were
 digitized on Tiff images using tpsDig 2.10 (Rohlf, 2006), designating 21
 landmarks and 15 semilandmarks for the m1s (after McGuire, 2011
 semilandmark placement) and 34 landmarks for the toothrows (Fig. 2).
 Semilandmark curves were drawn and initially subsampled by length using
 tpsDig 2.10 (Rohlf, 2006). They were slid using bending energy in tps
 Relative Warps 1.45 (Rohlf, 2007) and subsampled again in tps Utility 1.40
 (Rohlf, 2008).
description: The final two points of the molar .tps file are scale points that
 are 5 mm apart. The first two points of the toothrow
 .tps file are scale points that are 5 mm apart.
 "IMAGE=" indicates the museum specimen number. This can
 be cross-referenced with the specimen table in the paper supplements to
 find the online museum record for each tooth or toothrow.