Inbreeding, Developmental Stability, and Canalization in the Sand Cricket Gryllus Firmus

Abstract

Inbreeding, the mating of close relatives, is known to have deleterious effects on fitness traits in organisms. Developmental stability (DS) and canalization may represent two processes that allow an organism to maintain a stable development that will produce the fittest phenotype. Inbreeding is thus expected to affect either DS or canalization. We tested if inbreeding affects DS and canalization using an inbreeding experiment on the cricket Gryllus firmus. We compared mean length, fluctuating asymmetry (as an index of DS), and morphological variation (as an index of canalization) of four limb traits between seven highly inbred lines, their F1 crosses, and outbred lines originated from the same stock population and maintained in the same environmental conditions. We show evidence for moderate inbreeding depression on the four measures of leg length. The nonsystematic difference in fluctuating asymmetry indices between breed types indicates that inbreeding or heterozygosity did not affect DS, or that fluctuating asymmetry is not a reliable index of DS. In contrast, inbreeding appears to affect canalization, as shown by the significantly higher variation in inbred lines compared to other lines. Identical low variation values in the crossbred and outbred lines indicate that heterozygosity could affect canalization. High variation in morphological variation and fluctuating asymmetry within crossbred or inbred lines, however, suggest the effect of recessive deleterious alleles on both canalization and DS. Although the strong correlation in morphological variation among traits suggests that identical genetic mechanisms govern canalization for all the limb traits, the absence of significant correlation in fluctuating asymmetry among traits causes us to reject this hypothesis for DS. For most of the traits, morphological variation and fluctuating asymmetry were not significantly correlated, which support the hypothesis that canalization and DS consist in two distinct mechanisms.

No relationship between canalization and developmental stability of the skull in a natural population ofMastomys natalensis(Rodentia: Muridae)

“…Willmore, Klingenberg & Hallgrimsson (2005) analysed the relationship between FA and environmental variance in the skull of rhesus macaque Macaca mulatta, reporting significant but low correlations. Studies on wing shape reported high correlations in Drosophila melanogaster, tsetse fly (Glossina palpalis gambiensis) and bumblebee (Bombus empatiens) (Klingenberg & McIntyre, 1998;Klingenberg et al, 2001;Santos, Iriarte & Céspedes, 2005;Breuker, Patterson & Klingenberg, 2006) as well as for other traits in 11 invertebrate species (Clarke, 1998); whereas the opposite result was found for cricket limbs (Reale & Roff, 2003). Studies involving the alteration of the heat shock protein 90 (Hsp90) considered a specific mechanism for canalization (Rutherford & Lindquist, 1998;Rutherford, 2000), by either a mutational or pharmacological approach, resulted in an increase of phenotypic variance but did not show any increase of FA, leading to the conclusion that two distinct mechanisms for DS and canalization exist (Milton et al, 2003).…”

Evolution of Adaptation and Mate Choice: Parental Relatedness Affects Expression of Phenotypic Variance in a Natural Population

“…While the effect of intraindividual genetic diversity on sensitivity to environmental variation has been suggested in earlier work (Mitton and Grant 1984;Deng 1997;Réale and Roff 2003;Kristensen et al 2005), this study provides novel insights in several respects. First, whereas the necessity for detailed pedigrees has largely constrained previous studies to inbred laboratory lines, the use of molecular marker-derived estimates of relatedness in this study allowed us to examine naturally occurring variation in inbreeding.…”

“…In particular, inbred offspring often exhibit greater morphological variation compared to outbred individuals (Yezerinac et al 1992;David et al 1997;Deng 1997;Réale and Roff 2003). And while theory predicts that natural selection should strongly favor behaviors that minimize inbreeding (Blouin and Blouin 1988;Pusey and Wolf 1996), matings between relatives might nevertheless occur when individual mate choice is constrained, suggesting that any effect of inbreeding on developmental variation should be particularly relevant in natural systems where mate sampling is costly (e.g., Johnsen et al 2000;Foerster et al 2003) and opportunities to breed are limited (e.g., Keller and Arcese 1998;Kruuk et al 2002).…”

Phenotypic Variability: Its Components, Measurement and Underlying Developmental Processes

“…The general idea has been that different underlying processes govern developmental stability and canalization. However, the results from empirical tests (studied using patterns of phenotypic variation) have been contradictory, some studies indicating that developmental stability and canalization are separate phenomena governed by separate mechanisms (Waddington 1957;Rutherford and Lindquist 1998;Debat et al 2000;Milton et al 2003;Réale and Roff 2003) while others have indicated that they represent similar phenomena that at least partly share underlying developmental processes (Clarke 1993(Clarke , 1998Klingenberg and McIntyre 1998;Woods et al 1999;Hallgrímsson et al 2002;Santos et al 2005;Breuker et al 2006;Debat et al 2006). A recent study by Breuker and colleagues (2006) compares among-individual variation with FA in the wings of 115 different strains of Drosophila melanogaster.…”