Environmental stress, inbreeding, and the nature of phenotypic and genetic variance inDrosophila melanogaster

Abstract

Fifty-two lines of Drosophila melanogaster founded by single-pair population bottlenecks were used to study the effects of inbreeding and environmental stress on phenotypic variance, genetic variance and survivorship. Cold temperature and high density cause reduced survivorship, but these stresses do not cause repeatable changes in the phenotypic variance of most wing morphological traits. Wing area, however, does show increased phenotypic variance under both types of environmental stress. This increase is no greater in inbred than in outbred lines, showing that inbreeding does not increase the developmental effects of stress. Conversely, environmental stress does not increase the extent of inbreeding depression. Genetic variance is not correlated with environmental stress, although the amount of genetic variation varies significantly among environments and lines vary significantly in their response to environmental change. Drastic changes in the environment can cause changes in phenotypic and genetic variance, but not in a way reliably predicted by the notion of 'stress'.

Changes in mortality patterns and temperature dependence of lifespan in Drosophila melanogaster caused by inbreeding

“…Several studies have confirmed that inbreeding depression is more pronounced in a stress environment (Bijlsma et al, 2000 and references therein). Other studies however failed to find this (Armbruster et al, 2000;Fowler and Whitlock, 2002).…”

“…Inbreeding is known to lead to general decreases in various fitness measures, and also to very specific linespecific effects in Drosophila (Fowler and Whitlock, 2002) and in Tribolium (Pray and Goodnight, 1995). In a similar fashion, lifespan can be affected by inbreeding in these two different ways.…”

“…In recent years, interest has been kindled in the large influence that environmental factors can exert on the amount of inbreeding depression (Bijlsma et al, 1999;Fowler and Whitlock, 2002). Such issues are relevant to conservation biology, which deals with the fate of small populations in a rapidly changing environment, and also to research directed towards elucidating the genetic determination of life history characters.…”

Effect of inbreeding on reproduction and juvenile performance in two marine gastropods with contrasting reproductive patterns

“…I: inbred juveniles; O: outbred juveniles; Pa: parental generation juveniles; < : significantly lower; = : not significantly different; > : significantly higher; na: no significant difference overall, therefore Bonferroni post hoc test was not performed (Table 2). For example, in C. convexa, inbreeding substantially decreased mean female fecundity (>11% reduction, Fowler & Whitlock 2002), an effect not seen in C. fornicata. Inbreeding also largely decreased mean growth rates for juveniles of C. convexa reared at all 3 temperatures and both food levels tested, but had no effect on juvenile growth rates for C. fornicata reared under the same conditions.…”

Comparing the intersex genetic correlation for fitness across novel environments in the fruit fly, Drosophila serrata

“…That is, observed environmental differences in the magnitude of the correlation could be simply attributable to the environmental effects on the respective (sex-specific) genetic variances. Predicting the effects of a novel environment on the expression of genetic variance is difficult because there are numerous theoretical (and biologically plausible) possibilities and empirical data are equivocal, with documented instances of both inflation and contraction of variances attributable to environmental effects (e.g., Hoffmann, 1998, 2004;Hoffmann and Merilä, 1999;Fowler and Whitlock, 2002;Charmantier and Garant, 2005). However, a simple expectation is that r w FM may vary as a function of absolute fitness, with the extent of sexually concordant genetic variance being positively related to distance from the optimum (e.g., a positive r w FM when a population is far from a fitness peak, and hence at low fitness, characteristic of the early stages of adaptation).…”