Consequences of outbreeding on phenotypic plasticity in Drosophila mercatorum wings

Abstract

A multivariate morphometric investigation was conducted on wings of two parthenogenetic Drosophila mercatorum strains and offspring (F1) of crosses between these parthenogenetic strains with highly inbred sexual individuals of the same species. The parental flies and F1 offspring were reared at three different temperatures: 20, 25, or 28°C. This design allows a comparison of completely homozygous individuals (parental generation) with identical heterozygote offspring (F1), which makes an analysis of phenotypic plasticity of morphometric traits possible, without a potentially confounding effect of genotype-environment interactions, which can increase the phenotypic variability. The same pattern of phenotypic plasticity of wing size between the homozygous parental strains and the heterozygous offspring was found in both strains with an apparent heterotic effect for wing size in the F1 at 25°C. At 20 and 28°C flies from the parental generation had the biggest wings. Phenotypic plasticity of shape was found to be strain dependent. A reduced level of developmental instability (DI) was found in the F1 as compared to the parental strain only in strain 1 reared at 20°C for the wing size and 25°C for the wing shape. For all the other treatments higher DI was found in the F1 when the difference was significant, which is suggestive of outbreeding depression. These findings are difficult to interpret since an apparent heterotic effect of size at 25°C is accompanied by higher DI (though not significant in strain 2) and complex changes in wing shape. Hence, we cannot conclude whether outbreeding lowers or increases the capacity to respond to environmental change via plastic responses and via changes of the level of DI. The degree of change of Kristian Krag and Hans Thomsen have contributed equally. phenotypic plasticity and DI is trait specific, depending on the environment and on the genotypes which are hybridizing.

Temperature–maternal age interactions on wing traits in outbred Drosophila mercatorum

“…We used 2 facultative parthenogenetic lines of Drosophila mercatorum, referred to as Strains 1 and 2, and a sexually reproducing, highly inbred strain (see Krag et al 2009 for further details). The flies were maintained on instant Drosophila medium (Carolina Biological Supply) and a 12 h light:12 h dark cycle.…”

“…After mating, the vials with eggs were randomly assigned to 20, 25 and 28°C, respectively, and left to develop the F 1 generation, giving a total of 12 treatments: 2 lines, 2 age classes and 3 temperatures. The offspring from the young mothers were previously analysed in a study on the effect of outbreeding on young females (Krag et al 2009). Since the present study compared all female parthenogenetic offspring with the outcome of the same lines reproducing sexually, we only used females in the present experiment.…”

A Study of Canalization and Developmental Stability in the Sternopleural Bristle System of Drosophila Melanogaster

“…Andersen et al 2002Andersen et al , 2006Garnier et al 2006). One commonly used measure of DI is fluctuating asymmetry (FA), or the difference in value between paired bilateral traits, which is known to be elevated due to environmental stresses and genetic factors such as hybridization (Andersen et al 2002(Andersen et al , 2006(Andersen et al , 2008Kristensen et al 2003Kristensen et al , 2004Røgilds et al 2005;Pertoldi et al 2006a;Petavy et al 2006;Lens et al 2000;Soderman et al 2007;Krag et al 2009). The reason for the increased FA in intraspecific hybrids has been attributed to a breakdown in co-adapted gene complexes (Andersen et al 2002), whereas in interspecific hybrids increased FA has more often been attributed to genetic incompatibilities causing meiotic irregularities or physiological and developmental abnormalities (Andersen et al 2006;Burke and Arnold 2001;Pialek et al 2001;Rego et al 2006;Kurbalija et al 2010).…”

The phenotypic variance gradient – a novel concept

“…; Krag et al. ). Differences among the slopes of reaction norms (the regression of the mean on the environmental gradient) for different traits are interpreted as differences of the degree of phenotypic plasticity (Pigliucci ; Krag et al.…”

“…Differences among the slopes of reaction norms (the regression of the mean on the environmental gradient) for different traits are interpreted as differences of the degree of phenotypic plasticity (Pigliucci ; Krag et al. ). Genotype × environment interactions for a trait within populations, which suggest, genetic variation for phenotypic plasticity, will increase the phenotypic variance of the traits, which will depress the response to a selective pressure (Pigliucci ; Pertoldi and Bach ).…”