Alternative Life-Histories in Callosobruchus maculatus: Environmental and Genetic Bases
This review considers within- and between-population variation in three traits that mediate intraspecific competition in Callosobruchus maculatus: 1) the production of the “active” or dispersing morph, 2) the tendency to distribute eggs uniformly among seeds, and 3) the competitiveness of larvae confined to the same seed. The proportion of active progeny in different strains ranged from near zero despite intense crowding to > 30% even in the absence of crowding. Similarly, distributions of eggs varied from nearly uniform to nearly random. A strain producing highly uniform egg distributions also exhibited unusually competitive larvae; if two larvae entered a small seed simultaneously, only one adult emerged. In contrast, > 50% of seeds bearing two larvae from a different strain yielded two adults. Each trait was under polygenic control, but differences between strains were caused by both additive (in the case of morph determination) or non-additive (in the case uniform egg-laying) genetic variation. Quantitative-genetic analysis within an outbred strain produced significant heritabilities for body size, development time, fecundity, and egg dispersion. Comprehensive genetic and demographic analyses are needed to determine if morphological, behavioral, and physiological traits in C. maculatus covary in a predictable way to form alternative life-histories.