Environment-dependent regime of longevity selection in the chromosomally polymorphic species Leptysma argentina (Acrididae: Orthoptera)

Abstract

In previous papers it was reported that a Robertsonian translocation (centric fusion) affected external phenotype in the grasshopper Leptysma argentina and that thorax height was the target of adult viability selection. In the present paper two populations of L. argentina at different latitudes, with different centric fusion frequencies, were studied. It was demonstrated that selection acts on roughly the same targets but in opposite directions. In the northernmost population longevity selection acted primarily on thorax height (TH), leading to an increase of that variable. In the southern population, longevity selection leads to an increased femur length (FL) but to a decreased body size (including TH). Longevity selection affects karyotype frequency, leading to an increase of fusion homozygote frequency; however, fusion 3/6 significantly increases FL. This is consistent with an increase in fusion frequency along the season. The fact that longevity selection in one population increases and in another decreases body size is interpreted as an interaction between environment and body size, of the sort already detected in laboratory strains of Drosophila melanogaster.