Latitudinal variation of life history strategies in the burying beetle, Nicrophorus orbicollis

Brandon Matthew Quinby, Purdue University

Abstract

How organisms allocate resources to growth, reproduction, and body maintenance is expected to vary along latitudinal gradients. Two hypotheses explaining latitudinal variation are local adaptation and counter-gradient variation. The local adaptation hypothesis proposes that populations do best in their source location and, as a result, do less well in other environments. The counter gradient hypothesis proposes that one population out performs others across an environmental gradient because the first population’s source location has greater selective pressure than other locations. Temperature is one selective pressure that varies along latitudinal gradients, and life histories are expected to be sensitive to the variation. We test local adaptation and counter-gradient variation in the burying beetle, Nicrophorus orbicollis. We looked at patterns of reproduction in populations from Wisconsin (high latitude), Indiana (medium latitude) and Oklahoma (low latitude). Carcass preparation, reproductive success, and developmental timelines were quantified at temperatures representing typical environmental conditions of the breeding months for each population. Along a latitudinal range N. orbicollis, show variation in their ability to initiate reproduction, successfully rear offspring, and the number of offspring they are able to raise on a carcass. This variation suggest local adaptation in that, (1) beetles are less likely to initiate breeding at extreme temperatures, especially when that temperature is representative of ones experienced in their source range; (2) once beetles initiate reproduction, source populations produce relatively larger broods, and are more successful at source location temperature extremes. This experiment shows that N. orbicollis is able to use temperature as a reliable environmental cue to determine whether or not reproduction should be initiated, providing unique insight into how behavior modification can be used to avoid costly reproductive attempts. However, all other measurements of developmental timelines in our experiment (i.e. number of days to prepare a carcass, eggs laid, feeding hole, 1st instar arrival on carcass, and days developing on the carcass) were only affected by temperature. This suggests a temperature tolerance constraint that may be shaping reproductive behavior and distribution. This research gives unique insight into how N. orbicollis cope with temperature conditions along latitudinal gradients by behaviorally avoiding costly reproductive attempts.

Degree

M.S.

Advisors

Creighton, Purdue University.

Subject Area

Ecology|Evolution and Development

COinS