ten Broek Clara Mariquita Antoinette, Bots Jessica, Varela-Lasheras Irma, Bugiani Marianna, Galis Frietson, Van Dongen Stefan
Group of Evolutionary Ecology, University of Antwerp, Antwerp, Belgium ; Department of Terrestrial Zoology, Naturalis Biodiversity Center, Leiden, The Netherlands.
PLoS One. 2013 Nov 27;8(11):e81824. doi: 10.1371/journal.pone.0081824. eCollection 2013.
Fluctuating asymmetry (FA), as an indirect measure of developmental instability (DI), has been intensively studied for associations with stress and fitness. Patterns, however, appear heterogeneous and the underlying causes remain largely unknown. One aspect that has received relatively little attention in the literature is the consequence of direct mechanical effects on asymmetries. The crucial prerequisite for FA to reflect DI is that environmental conditions on both sides should be identical. This condition may be violated during early human development if amniotic fluid volume is deficient, as the resulting mechanical pressures may increase asymmetries. Indeed, we showed that limb bones of deceased human fetuses exhibited increased asymmetry, when there was not sufficient amniotic fluid (and, thus, space) in the uterine cavity. As amniotic fluid deficiency is known to cause substantial asymmetries and abnormal limb development, these subtle asymmetries are probably at least in part caused by the mechanical pressures. On the other hand, deficiencies in amniotic fluid volume are known to be associated with other congenital abnormalities that may disturb DI. More specifically, urogenital abnormalities can directly affect/reduce amniotic fluid volume. We disentangled the direct mechanical effects on FA from the indirect effects of urogenital abnormalities, the latter presumably representing DI. We discovered that both factors contributed significantly to the increase in FA. However, the direct mechanical effect of uterine pressure, albeit statistically significant, appeared less important than the effects of urogenital abnormalities, with an effect size only two-third as large. We, thus, conclude that correcting for the relevant direct factors allowed for a representative test of the association between DI and stress, and confirmed that fetuses form a suitable model system to increase our understanding in patterns of FA and symmetry development.
波动不对称性（FA）作为发育不稳定性（DI）的一种间接测量指标，已被深入研究其与压力和健康状况的关联。然而，相关模式似乎并不一致，其潜在原因在很大程度上仍不为人知。文献中相对较少受到关注的一个方面是直接机械作用对不对称性的影响。FA能够反映DI的关键前提是两侧的环境条件应相同。如果羊水过少，在人类早期发育过程中这一条件可能会被打破，因为由此产生的机械压力可能会增加不对称性。事实上，我们发现，当子宫腔内羊水不足（进而空间不足）时，已故人类胎儿的四肢骨骼会表现出更大的不对称性。由于已知羊水过少会导致显著的不对称性和肢体发育异常，这些细微的不对称性可能至少部分是由机械压力造成的。另一方面，已知羊水过少与其他可能干扰DI的先天性异常有关。更具体地说，泌尿生殖系统异常会直接影响/减少羊水量。我们将对FA的直接机械作用与泌尿生殖系统异常的间接作用区分开来，后者可能代表DI。我们发现这两个因素都对FA的增加有显著贡献。然而，子宫压力的直接机械作用尽管在统计学上具有显著性，但似乎不如泌尿生殖系统异常的作用重要，其效应大小仅为后者的三分之二。因此，我们得出结论，校正相关直接因素能够对DI与压力之间的关联进行有代表性的检验，并证实胎儿是一个合适的模型系统，有助于增进我们对FA模式和对称性发育的理解。
