Shapeshifting Least Shrews: Variability in Body Size Measures with Sex and Toothwear Stage in Cryptotis floridanus (Merriam, 1895) and Cryptotis parvus (Say, 1822) (Mammalia: Eulipotyphla: Soricidae)

Body size is a basic mammalian characteristic that has implications for numerous aspects of a species' physiology and ecology. The most commonly used measure of body size is mass, although other morphological traits are often employed as proxies. I examined four measures of body size (mass, head-and-body length [HB], condylobasal length [CBL], and PC1 scores from a PCA of skull variables [PC1]) from a sample of the Florida least shrew, Cryptotis floridanus (Merriam, 1895) (Mammalia: Eulipotyphla: Soricidae) and eastern and western samples of the North American least shrew, C. parvus (Say, 1823), to determine whether these body size measures were correlated within each sample and how each measure varied with sex and with relative age as estimated by 12 progressive stages of tooth wear. None of the size variables indicated sexual dimorphism in size. In each sample, mass was significantly, but weakly, correlated with HB, and CBL was significantly, but weakly, correlated with PC1 scores. Mass and HB also were correlated with toothwear stage in C. floridanus and the eastern sample of C. parvus, but not in western C. parvus. Growth curves calculated from birth for eastern C. parvus exhibited steep increases of approximately 1438% in mean mass, 289% in mean HB, and 204% in mean CBL between parturition and toothwear stage 1. Growth curves and data partitioned by toothwear stage for only free-ranging individuals (i.e., subadults and adults) exhibited modest continued increases in both mean mass (35–56%) and mean HB (12–29%) through toothwear stage 9 and possibly later in each of the three samples. Mean CBL and mean PC1 increased slightly (3%) through toothwear stage 5 in C. floridanus, after which growth ceased. In contrast, increases in these two measures ceased by toothwear stage 1 in both samples of C. parvus. All three samples were biased toward younger individuals, with toothwear stages 1–5 accounting for 62–81% of the samples. A noticeable decrease in individuals between stages 5 and 6 suggested an increase in mortality at that time. Mean body condition, a measure of relative health, was constant among toothwear stages. It appears from these data that fewer than half of a given age cohort of least shrews survived beyond toothwear stage 5, but those that reached later toothwear stages were generally as healthy as those in earlier stages.