DIFFERENTIAL RATES OF EVOLUTION WITHIN HIGHLY FOSSORIAL MOLES (TALPINAE) CONSTRAIN TRAJECTORIES AND EVOLUTIONARY ALLOMETRIES OF HUMERAL MORPHOLOGY

The subfamily Talpinae includes two tribes, Talpini and Scalopini, whose most recent common ancestor traces back to the late Eocene. Both a North American and Eurasian origin have been proposed for this clade. During the Neogene, Talpinae spread across all the Paleartic. One of the most investigated skeletal elements is the humerus, as it is particularly well-preserved and abundant in the fossil record. The humeral morphology of the entire subfamily is highly modified and adapted for complex tunnel digging. However, the two tribes still show morphological differences mainly related to the teres tubercle, the bicipital tunnel, and the pectoral crest. Here we used 2D geometric morphometrics to assess for the first time the humeral morphological disparity and evolution of Talpinae by comparing all extant and extinct species for which at least one complete humerus is known. We built a synthetic phylogeny including a total of 53 species, i.e., 19 Scalopini and 34 Talpini, that was entered in comparative analyses to test explicit hypotheses about their rates of evolution. When performing ANOVA and MANOVA for size and shape, we found non-significant and significant differences among Talpini and Scalopini respectively. The phylogenetic versions of these analyses returned non significant results thus indicating a strong phylogenetic conservativism for the two tribes. A neat negative shift in morphological evolutionary rate was found in correspondence of derived Late Miocene Talpa spp. This evidence stressed the differences in morphological evolutionary rates between Talpini and Scalopini. Significant evolutionary allometries were found in both tribes showing different multivariate slopes, even when controlling for phylogeny through phylogenetic ANCOVA. An ontogenetic convergence test on evolutionary allometric trajectories suggests a significant convergence between the two trajectories, with the Scalopini humeral morphology more related to size than that of Talpini. Evolutionary trajectories traced on the phylogenetic tree using ancestral state reconstruction highlighted that Talpini followed a significant phenotypic channeling while the Scalopini tribe showed no relationships between phenotype and time during their evolution. In conclusion, we found differences in evolutionary rates and disparity between clades that appear very similar and highly constrained by the same adaptation, thus suggesting different evolutionary canalizations in the humeral morphology of Talpini and Scalopini.