Carter P A
Department of Environmental, Population and Organismic Biology, Campus Box 334, University of Colorado, Boulder, CO 80309, USA.
Heredity (Edinb). 1997 Jan;78(Pt 1):101-9. doi: 10.1038/sj.hdy.6881230.
Populations of gilled tiger salamanders (Ambystoma tigrinum nebulosum) living in ephemeral ponds were studied in order to determine what evolutionary processes might be affecting genetic variation at the alcohol dehydrogenase (Adh) locus. Ponds frequently dried in late summer; salamanders that did not metamorphose and leave drying ponds died of desiccation. Low levels of water oxygen significantly slowed metamorphosis of tiger salamanders in both natural and laboratory populations. Adh- SS frequency was significantly positively correlated with daily oxygen maxima in ponds, Adh-FF frequency demonstrated a nonsignificant trend to be negatively correlated with this measure, and Adh-SF frequency was unrelated to pond oxygen. Genotype frequency changes across the season in hypoxic and supersaturated ponds suggested that differential mortality of genotypes might explain the relationships with pond oxygen, although other mechanisms cannot be ruled out. Individuals of the Adh-SS genotype metamorphosed more slowly in hypoxic water than in normoxic water in the laboratory, and Adh-FF individuals metamorphosed more slowly in supersaturated water in the field, and in hypoxic water in the laboratory, than they did in normoxic water. Adh-SF individuals metamorphosed at the same rate in all oxygen environments. These data suggest that the Adh polymorphism in tiger salamanders is being maintained by selection for Adh or for a linked locus through differential metamorphosis in extreme oxygen environments.
为了确定哪些进化过程可能影响酒精脱氢酶（Adh）基因座的遗传变异，对生活在临时性池塘中的带纹虎螈（Ambystoma tigrinum nebulosum）种群进行了研究。池塘在夏末经常干涸；未变态并离开干涸池塘的蝾螈会死于脱水。低水平的水中氧气显著减缓了自然种群和实验室种群中虎螈的变态。Adh-SS频率与池塘中的每日最高氧气含量显著正相关，Adh-FF频率显示出与该指标负相关的不显著趋势，而Adh-SF频率与池塘氧气无关。缺氧和过饱和池塘中基因型频率随季节的变化表明，基因型的差异死亡率可能解释了与池塘氧气的关系，尽管不能排除其他机制。在实验室中，Adh-SS基因型的个体在缺氧水中比在常氧水中变态更慢，Adh-FF个体在野外过饱和水中以及在实验室缺氧水中比在常氧水中变态更慢。Adh-SF个体在所有氧气环境中变态速率相同。这些数据表明，虎螈中的Adh多态性是通过在极端氧气环境中的差异变态，对Adh或一个连锁基因座进行选择而得以维持的。
