Fluctuating asymmetry-indicator of what?

Abstract

In a population the optimal phenotype is promoted by buffering mechanisms that keep inter- and intra-individual variation low. A link exists between canalization, that controls phenotypic variation, and developmental stability, mostly measured as fluctuating asymmetry of bilateral traits (FA). Both types of variation are associated with the functional importance of a trait, and both are increased by stress of various kinds. But there are also several instances of non-congruence. The concept of developmental stability has been found elusive, and low FA is not the unambiguous measure of well being and good genes that has been claimed. It can be concluded that developmental stability is partly governed by specific, as yet unknown, molecular processes.

Fluctuating asymmetry and genetic variability in the roe deer (Capreolus capreolus): a test of the developmental stability hypothesis in mammals using neutral molecular markers

“…Although there is still a general controversy about the value of FA as an estimator of an organism's fitness (e.g., Rasmuson, 2002), a long-held theory, going back at least to Lerner (1954), connects developmental stability with genetic variability. More heterozygous individuals, the argument goes, more efficiently stabilize their development by buffering against environmental insults.…”

Nutritional Stress Causes Heterogeneous Relationships with Multi-Trait FA in Lesser Black-Backed Gull Chicks: An Aviary Experiment

“…A trait is said to be vulnerable to environmental stressors only during certain developmental stages, leading to the production of visible aberrant phenotypes. These windows of opportunity may vary among traits [43,44]; the tarsi and wings may have experienced only restricted levels of energetic stress during the vulnerable period of their development. However, given that stress exposure was nearly constant throughout our experiment, this is not a very likely explanation of our results.…”

“…Trait-specific susceptibility to FA may also be related to the functional importance of a trait [10,44,46]. Traits of higher functional value should be subjected to stronger stabilizing selection, as minor reductions in their symmetry can impose a substantial fitness cost.…”

Symmetry is beauty – or is it?

“…Ces éléments ont largement altéré la confiance que la communauté pouvait avoir dans ces études. Les biais de publication, rendant la littérature difficile à évaluer, ont sérieusement discrédité l'utilisation de l'asymétrie fluctuante comme marqueur de quoi que ce soit [31], et l'enthousiasme initial a fait place à une certaine désillu-sion [36]. Ainsi, la courbe du nombre (relatif) de publications diminue très sensiblement à partir de 1997 (Figure 3).…”