A trade-off between early growth rate and fluctuating asymmetry in Brazilian boys

Background: Right-left discrepancies in normally symmetrical traits are assumed to result from inability of the individual to buffer environmental and genetic stresses. Fluctuating asymmetry (FA) may therefore signal the quality of an individual to potential mates, or to parents during early life. FA could signal the heritable ability to buffer stress - the 'good genes' hypothesis. Alternatively, FA could signal the degree of within-lifetime exposure to stress, in particular during specific sensitive periods of development - the 'good development' hypothesis. Aim: We tested the hypotheses that FA at 9 years of age is positively related to (a) fetal growth rate, (b) early infant growth rate, and (c) total post-natal growth rate. Methods: FA, weight and height were measured in a sample of 172 boys aged 9 years from Pelotas, Brazil, who had previous measurements of weight and height at birth and 6 months. Results: Fetal growth was not related to FA, however FA was positively related to total weight gain after birth ( p <0.05). This association could be broadly attributed to weight gain in the first 6 months of post-natal life ( p = 0.075). Those currently obese had significantly greater FA than those non-obese ( p <0.05). Conclusions: Our results support the 'good development' hypothesis, and suggest that growth rate during an early post-natal critical window, previously linked to numerous health outcomes, also has long-term effects on FA.