Heritability, Fecundity, and Sexual Size Dimorphism in Four Species of Bark Beetles (Coleoptera: Curculionidae: Scolytinae)

Abstract

Abstract Body size is a key biological trait frequently used to assess fitness. Variation in body size stems from genetic and environmental factors and can have strong affects on reproduction. Here, we quantify narrow-sense heritability of size, fecundity, and sexual size dimorphism in four bark beetle species across two genera: Ips pini (Say), Ips lecontei Swaine, Dendroctonus frontalis Zimmermann, and Dendroctonus brevicomis LeConte. For each species, we conducted rearing experiments pairing parents of large or small size classes and measuring body length of all progeny. There was significant narrow-sense heritability of body size in Ips, but not Dendroctonus. Male parent size in I. pini, I. lecontei, and D. frontalis was positively correlated with progeny production and female parent size was positively correlated with gallery length in I. pini, D. frontalis, and D. brevicomis. All species exhibited sexual size dimorphism (SSD), with males being larger than females (male-biased SSD) in Ips and females larger than males (female-biased SSD) in Dendroctonus. Although mean differences in body length between sexes was small, ≈l–2% for Ips and 2–4% for Dendroctonus, the pioneer sex (first colonizer) was statistically larger than the nonpioneer sex in all species. In addition, the pioneer sex displayed greater phenotypic variation in body length than the nonpioneer sex, and Dendroctonus exhibited greater phenotypic variation in body length than Ips. Differing selection pressures within species and even between sexes likely affect body size and heritability patterns exhibited by bark beetles.