Genetic and Environmental Contributions to Geographic Variation in the Ovipositor Length of a Cricket

Abstract

Females of many insects posses an ovipositor, which in crickets is usually used to place eggs deep into the soil. Ovipositor length in female striped ground crickets (Allonemobius socius) increased at higher latitudes and altitudes in North America, despite an opposing trend in overall body size. Crickets inhabiting regions with short growing seasons and long, cold winters invariably had longer ovipositors than crickets inhabiting warmer regions. The only exception to this observation was for first generation crickets in bivoltine populations where there was no pattern of geographic variation in ovipositor length. However, second generation females from these same populations always had longer ovipositors than their first generation ancestors,and followed a pattern of geographic variation similar to that found for univoltine crickets. Overall, these results support Masaki's (1986) model, which predicts that longer ovipositors will evolve in northern cricket populations as an evolutionary response to the selective advantages of overwintering eggs being oviposited deep in the soil in cold habitats. In order to determine the mechanisms underlying patterns of phenotypic variation in the wild, and to test the hypothesis that interpopulation variation reflects genetic differentiation while intergeneration variation within a population reflects environmentally induced phenotypic plasticity, crickets from eight populations were brought to the laboratory and reared through three generations in a common garden. It was found that laboratory—reared populations varied significantly in ovipositor length, with the pattern of variation mimicking that found for field—collected crickets. This finding supports the hypothesis that geographic variation in the wild has a significant genetic basis. The influence of environment on ovipositor length was examined in 20 full—sib families from a bivoltine population. Crickets reared in "autumn—like" conditions (30°C, 15:9 h, L:D), such as might be experienced by second generation bivoltine crickets in the wild, were generally larger and had significantly longer ovipositors than siblings reared under "spring—like" conditions (27°C 11:13 h, L:D). This pattern corresponds to that observed for bivoltine populations in the wild and suggests the importance of environmental cues for phenotypic plasticity, or polyphenism in ovipositor length in bivoltine populations of this cricket.

The coadaptation of female morphology and offspring size: a comparative analysis in crickets

“…A similar relationship may exist between seed size and the emergence potential of seedlings (McGinley et al 1987). The present evidence for a coadaptation of egg size and ovipositor length provides a way to unify studies that had independently considered the evolution of offspring size (Bradford et al 1993; and ovipositor length (Masaki 1986;Mousseau and Roff 1995) in crickets.…”

“…Moreover, Masaki conjectured that protection of diapausing eggs from harsh winter conditions is another selective factor affecting ovipositor length. This hypothesis was supported by the pattern of geographic variation in relative ovipositor length in four egg-overwintering species; crickets from populations experiencing a long and cold winter had longer ovipositors than individuals inhabiting warmer regions (Masaki 1986;Mousseau and Roff 1995).…”

Geographic Variation in Size and Oviposition Depths ofRomalea microptera(Orthoptera: Acrididae) is Associated with Different Soil Conditions

“…If soil conditions vary spatially and select for body size and oviposition behavior, then a cline in body size could arise from continuous geographic variation in soil conditions. In terms of physical capacity, evidence indicates that large body size, greater ovipositor length, and longer abdominal stretching in soil-ovipositing species are positively correlated with depth of egg pod deposition (Zimin 1938, Uvarov 1966, Masaki 1979, Braker 1989, Mousseau and Roff 1995. Previous research suggests that the optimal oviposition depth is a balance between the beneÞts of increased egg and hatchling survival and the costs of deep oviposition (e.g., female time, energy, and exposure to enemies; hatchlingÕs ability to excavate from deeply laid eggs) and imply females should choose depths that optimize this trade-off (Bradford et al 1993, Mousseau 2000, Branson and Vermeire 2007.…”

Interaction between maternal effects and temperature affects diapause occurrence in the cricket Allonemobius socius

“…This group shows clines in morphological characteristics (Mousseau and Roff 1995;Olvido et al 2003) and life history traits (Mousseau and Roff 1989;Bradford and Roff 1993;Roff and Bradford 1996) in response to latitudinal variation in temperature and seasonality, indicating adaptation to specific environmental cues (Bradford and Roff 1993;Mousseau and Roff 1995). These crickets have a relatively short generation time of approximately 2 months, allowing several generations to be studied in a short period of time.…”