Tibayrenc M, Ward P, Moya A, Ayala F J
Proc Natl Acad Sci U S A. 1986 Jan;83(1):115-9. doi: 10.1073/pnas.83.1.115.
We have studied 15 gene loci coding for enzymes in 121 Trypanosoma cruzi stocks from a wide geographic range--from the United States and Mexico to Chile and southern Brazil. T. cruzi is diploid but reproduction is basically clonal, with very little if any sexuality remaining at present. We have identified 43 different clones by their genetic composition; the same genetic clone is often found in very distant places and in diverse hosts. There is much genetic heterogeneity among the different clones, and they cannot be readily classified into a few discrete groups that might represent natural taxa. These findings imply that the biological and medical characteristics need to be ascertained separately for each natural clone. The evidence indicates that clonal evolution is very ancient in T. cruzi. We propose two alternative hypotheses concerning the relationship between the biochemical diversity and the heterogeneity in other biological and medical characteristics of T. cruzi. One hypothesis is that the degree of diversity between strains simply reflects the time elapsed since their last common ancestor. The second hypothesis is that biological and medical heterogeneity is recent and reflects adaptation to different transmission cycles. A decision between the two hypotheses can be reached with appropriate studies, with important medical consequences.
我们研究了来自广泛地理区域（从美国、墨西哥到智利和巴西南部）的121株克氏锥虫中15个编码酶的基因位点。克氏锥虫是二倍体，但繁殖基本上是克隆性的，目前几乎没有有性生殖。我们根据其基因组成鉴定出了43个不同的克隆；相同的基因克隆常常在非常遥远的地方以及不同的宿主中被发现。不同克隆之间存在很大的基因异质性，并且它们不能轻易地被分类为可能代表自然分类群的几个离散组。这些发现意味着需要针对每个自然克隆分别确定其生物学和医学特征。证据表明克隆进化在克氏锥虫中非常古老。我们提出了两个关于克氏锥虫生化多样性与其他生物学和医学特征异质性之间关系的替代假说。一个假说是菌株之间的多样性程度仅仅反映了自它们最近的共同祖先以来所经过的时间。第二个假说是生物学和医学异质性是最近出现的，并且反映了对不同传播周期的适应。通过适当的研究可以在这两个假说之间做出抉择，这具有重要的医学意义。
