Abstract
Blood flukes within the genus Schistosoma still remain a major cause of disease in the tropics and subtropics and the study of their evolution has been an area of major debate and research. With the advent of modern molecular and genomic approaches deeper insights have been attained not only into the divergence and speciation of these worms, but also into the historic movement of these parasites from Asia into Africa, via migration and dispersal of definitive and snail intermediate hosts. This movement was subsequently followed by a radiation of Schistosoma species giving rise to the S. mansoni and S. haematobium groups, as well as the S. indicum group that reinvaded Asia. Each of these major evolutionary events has been marked by distinct changes in genomic structure evident in differences in mitochondrial gene order and nuclear chromosomal architecture between the species associated with Asia and Africa. Data from DNA sequencing, comparative molecular genomics and karyotyping are indicative of major constitutional genomic events which would have become fixed in the ancestral populations of these worms. Here we examine how modern genomic techniques may give a more in depth understanding of the evolution of schistosomes and highlight the complexity of speciation and divergence in this group.
Highlights
Members of the genus Schistosoma are digenean (Strigeiformes: Schistosomatidae) blood flukes of mammals, comprising of 23 known species, with at least 7 of these contributing to the neglected medically important disease schistosomiasis [1]
This review aims to discuss some of the evidence generated from molecular biology and genomics that has contributed to the generally accepted “out of Asia” hypothesis, and aims to
Attwood et al [1] suggested that reinvasion of Asia by the ancestral stock of the S. indicum group probably occurred about 2-3 million years ago as large ungulates migrated across the Sinai-Levant dispersal tract between the Pliocene and Pleistocene, and the emergence of the Bovidae during this period, probably facilitated diversification of the S. indicum group giving rise to both S. nasale and S. spindale (Figure 5)
Summary
Members of the genus Schistosoma are digenean (Strigeiformes: Schistosomatidae) blood flukes of mammals, comprising of 23 known species, with at least 7 of these contributing to the neglected medically important disease schistosomiasis [1]. Davis [2,3] proposed that the genus Schistosoma arose before the separation of the super continent Gondwanaland (which was made up of what is today Africa, South America, Antarctica and Australia) more than 150 million years ago (MYA) and had already begun to exploit pulmonate and pomatiopsid snails, of which extensive fossil records suggest a Gondwanan origin This implies that the spread of these parasites was due to continental drift and that the ancestor of the Asian schistosomes was carried across to Asia as India separated from Africa and moved towards Asia 70-148 MYA, giving rise to the S. indicum and S. japonicum groups [2].
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