Growth overshoot and seasonal size changes in the skulls of two weasel species

R Soc Open Sci. 2017 Jan 25;4(1):160947. doi: 10.1098/rsos.160947. eCollection 2017 Jan. LaPoint S1, Keicher L2, Wikelski M3, Zub K4, Dechmann DK3. Author information 1 Department of Migration and Immuno-Ecology , Max Planck Institute for Ornithology , Am Obstberg 1, Radolfzell 78315 , Germany. 2 Department of Biology , University of Konstanz , Universitätsstrasse 10, Konstanz 78457 , Germany. 3 Department of Migration and Immuno-Ecology, Max Planck Institute for Ornithology, Am Obstberg 1, Radolfzell 78315, Germany; Department of Biology, University of Konstanz, Universitätsstrasse 10, Konstanz 78457, Germany. 4 Mammal Research Institute , Waszkiewicza 1, Białowieża 17-230 , Poland. Abstract Ontogenetic changes in mammalian skulls are complex. For a very few species (i.e. some Sorex shrews), these also include seasonally driven, bidirectional size changes within individuals, presumably to reduce energy requirements during low resource availabilities. These patterns are poorly understood, but are likely most pronounced in high-metabolic species with limited means for energy conservation. We used generalized additive models to quantify the effect of location, Julian day, age and sex on the length and depth of 512 and 847 skulls of stoat (Mustela erminea) and weasel (M. nivalis) specimens collected throughout the northern hemisphere. Skull length of both species varies between sexes and geographically, with stoat skull length positively correlated with latitude. Both species demonstrate seasonal and ontogenetic patterns, including a rare, absolute growth overshoot in juvenile braincase depth. Standardized braincase depths of both species peak in their first summer, then decrease in their first winter, followed by a remarkable regrowth that peaks again during their second summer. This seasonal pattern varies in magnitude and timing between geographical regions and the sexes, matching predictions of Dehnel's phenomenon. This suggests implications for the evolution of over-wintering strategies in mammals, justifying further research on their mechanisms and value, with implications for applied osteology research. KEYWORDS: Dehnel's phenomenon; Mustela; body size; morphology; ontogeny; sexual dimorphism PMID: 28280592 PMCID: PMC5319358 DOI: 10.1098/rsos.160947 Free PMC Article