Differential adult survival and phenotypic variation in a chromosomally polymorphic population of the grasshopper Sinipta dalmani

摘要

Natural selection is considered the force that drives biological evolution. Evolutionary biologists have concentrated to detect, quantify and visualise selection in nature (Lande and Arnold 1983; Endler 1986).Because most traits of evolutionary importance exhibit phenotypic variation, multiple phenotypic selection has been well studied. In insects, phenotypic selection on body size related traits have been well documented (Taylor and Kekic 1988; Gilburn and Day 1992; Colombo 1993; Hasson et al. 1993; Norry et al. 1995; Martín-Alganza et al. 1997; Norry and Colombo 1999; Rodriguez et al. 1999; Remis et al. 2000). These studies have demonstrated differences in survival, mating success and fertility under laboratory conditions. Rather few of them have been made in nature. As a matter of fact, the detection of selection in the wild is a difficult task. As Endler (1986) points out, the most efficient method to detect natural selection is a direct analysis of fitness components, which evaluate the differences in a certain trait between two or more age classes. Natural populations of grasshoppers seem to be natural laboratories since they have synchronised generations. This synchrony gives an opportunity to study the differences in a certain trait between life-history stages in the wild (Colombo 1993).Here I study the effect of phenotypic variation on male adult survival in the grasshopper Sinipta dalmani (Orthoptera: Acrididae) by analysing samples of young and aged males. Natural populations of S. dalmani are polymorphic for a pericentric inversion in the M4 pair. This inversion has a negative average effect on body size related traits, so that considerable phenotypic variation in populations is caused by the polymorphism (Remis 1989, 1990, 1997). There are chromosomal and phenotypic differences in male mating success favouring the standard sequence and larger individuals. The target of sexual selection was identified to be third tibia; the effect of other body size related traits and chromosome dosage are indirect ones caused by correlated selection (Remis et al. 2000).Here I analyse the possible relationships among adult male survival and body size and shape in a chromosomally polymorphic population of S.dalmani.