Correlated development, organism-wide asymmetry and patterns of asymmetry in two moth species

Understanding the mechanisms that determine the development of a bilaterall y symmetrical trait is crucial to the interpretation of patterns of fluctua ting asymmetry (FA). Experimental and theoretical studies have indicated th at feedback mechanisms both within and between developing traits, may parti cipate in the developmental control of asymmetry. This study provides evide nce that naturally occurring patterns of FA are affected by interactions be tween different traits. We found positive between-trait correlations in sig ned FA values for tibia lengths on different legs, but not between wing and tibia FA in two moth species. Further research should investigate if trait functionality is related to this presumed correlated development. An exten sion of the Rashevsky-Turing model of morphogenesis further showed that cor relations between the signed FA values can be generated by feedback mechani sms that regulate growth patterns between traits. We argue that such feedba ck mechanisms can be expected to be widespread and show that between-trait correlations in the unsigned FA then become confounded with correlations in the signed FA. In addition, correlated development appeared to invalidate the use of the hypothetical repeatability to translate correlations between the unsigned FA values into correlations in the presumed underlying develo pmental instability. In conclusion, the presence of an organism-wide asymme try, which are most frequently found in morphologically integrated traits, may be even less common than previously thought.