Hare Kelly M, Yeong Charlene, Cree Alison
Department of Zoology, University of Otago, Dunedin, New Zealand.
J Exp Zool A Ecol Genet Physiol. 2011 Apr 1;315(4):215-21. doi: 10.1002/jez.667. Epub 2011 Feb 11.
Prenatal sex ratio (through exposure to hormones from siblings in utero) can influence sexually dimorphic traits of many mammals; but research on viviparous reptiles has contrasting outcomes, which have yet to be resolved. The thermal environment experienced during gestation has a strong effect on the phenotype of reptiles, but whether this thermal effect overrides that of prenatal sex ratio has yet to be explored. We experimentally investigated whether the gestation temperature, or litter sex ratio, influences sexually dimorphic traits (head width and axilla-groin length) in a viviparous skink (Oligosoma maccanni). We found that gestation temperature had a significant influence on sexually dimorphic traits of neonates, and at 3 months of age still influenced head width. We found no evidence that traits in either sex were masculinized or feminized in response to litter sex ratio. The development of external sexual dimorphisms increased gradually (all thermal regimes pooled), with neonates showing no sexual dimorphism, 3-month-old juveniles showing some sexual dimorphism in head width, and adults having stronger, but incompletely separated, sexual dimorphism for both traits. We suggest that the overlap in sexually dimorphic traits of adult O. maccanni (and perhaps other reptiles) may be better explained by natural variation in temperatures experienced during embryonic development, rather than hormonal effects arising from litter sex ratio. The interaction of hormones and temperature during gestation and the effect of these factors on sexual dimorphism within reptiles deserve further exploration.
产前性别比例（通过子宫内接触来自兄弟姐妹的激素）会影响许多哺乳动物的两性异形特征；但关于胎生爬行动物的研究结果却相互矛盾，尚未得到解决。妊娠期经历的热环境对爬行动物的表型有很大影响，但这种热效应是否会超过产前性别比例的影响尚待探索。我们通过实验研究了妊娠温度或窝仔性别比例是否会影响胎生石龙子（Oligosoma maccanni）的两性异形特征（头部宽度和腋窝-腹股沟长度）。我们发现，妊娠温度对新生儿的两性异形特征有显著影响，并且在3个月大时仍对头部宽度有影响。我们没有发现任何证据表明，任一性别的特征会因窝仔性别比例而出现雄性化或雌性化。外部两性异形的发育逐渐增加（所有热环境汇总），新生儿没有两性异形，3个月大的幼体在头部宽度上表现出一些两性异形，而成体在这两个特征上具有更强但未完全分离的两性异形。我们认为，成年O. maccanni（也许还有其他爬行动物）两性异形特征的重叠，可能更好地用胚胎发育期间经历的温度自然变化来解释，而不是窝仔性别比例产生的激素效应。妊娠期激素与温度的相互作用以及这些因素对爬行动物两性异形的影响值得进一步探索。
