Sex differences in morphology across an expanding range edge in the flightless ground beetle, Carabus hortensis

Many species experience range shifts, contractions, and/or expansions. Often, morphological traits that increase movement capacity are observed in higher frequencies at the edge of an expanding or shifting range. Although traits observed at the range edge may differ between the sexes, sex differences in the distribution of morphological traits across species’ changing ranges are rarely studied.  Here, we report pronotum width (as a proxy for body size) and body condition data from individual Carabus hortensis ground beetles that were captured at varying proximities to an expanding range edge. The relationships between measures of both body size and body condition and the position along the expansion front with which individuals were captured were assessed for males and females separately. Body size increased with proximity to the range edge in males alone. Body condition (relative to body size) was not predicted by position along the expansion front, but decreased with increasing popula...