Variation in adult longevity in a polymorphic grasshopper species

Abstract

Life-history theory suggests that the existence and persistence of phenotypic variation within species must be maintained through some advantage accruing to an individual following one developmental pathway over another. Here, we consider the adult lifespan of two highly differentiated male morphs and the female in the bladder grasshopper species Bullacris membracioides (Orthoptera: Pneumoroidea). Our results show that the adult longevity of small, uninflated males is twice that of both the larger inflated male and mature females. Uninflated males have a type II survivorship curve, whereas inflated males and adult females both have type I survivorship curves. This difference indicates that the latter two morphs die due to senescence, while the uninflated male does not. The longevity difference between the male morphs shows that while the volant inflated males have the ability to locate many females, they can do so only over a short term, whereas the flightless uninflated male has comparatively limited mobility, but twice as much time to search for mates. This lifespan extension may impart some reproductive advantage for the uninflated male in the longer term, allowing for more female encounters, and increasing its chances for reproduction.