Analysis of body size and fecundity in a grasshopper

Abstract

We used linear regression, nonlinear regression and principal component analysis to examine the relationships among morphology, fecundity, and mating variables for lab-reared adult female Romalea microptera (Beauvois) (fam. Romaleidae) grasshoppers. Morphological variables included head width, pronotum length, femur length, adult eclosion mass, maximum mass reached before the 1st oviposition, and maximum mass reached before the 2nd oviposition. Fecundity (= reproductive) variables included clutch size Pod 1, clutch size Pod 2, total eggs Pods 1 2, mass Pod 1, mass Pod 2, time between adult eclosion and Pod 1, time between Pod 1 and Pod 2, and time between eclosion and Pod 2. Mating variables included number of matings and age of 1st mating. Most morphological variables were strongly positively correlated, and morphological variables (especially femur length, eclosion mass, and maximum body mass reached prior to oviposition) predicted many fecundity variables. Maximum body mass reached prior to laying Pod 1 was highly correlated with maximum body mass reached prior to laying Pod 2 (r =0 .93), and clutch size Pod 1 predicted clutch size Pod 2 (r = 0.72). However, time to oviposit (= interval between adult eclosion and oviposition) was generally unrelated to body size, body mass, or clutch size or mass. Hence, clutch size and pod mass are strongly determined by body size and mass at adult eclosion, but timing of oviposition is independent of body size and mass at eclosion. The results also suggest that early mating speeds oviposition, but that excessive mating reduces female fecundity, as measured by clutch size.