Microtus californicus toothrow and molar .tps files

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.