What Fossils Reveal About the Protozoa Progenitors, Geographic Provinces, and Early Hosts of Malarial Organisms

Abstract

In 1991, Robert S. Desowitz asked, “Did the primitive malaria begin as a parasite of some prehistoric reptile that later was picked up by a mosquito, or was it first a parasite of the mosquito that later became established in the reptile?” This question has been debated for years and is addressed in the present work in light of the fossil record of malarial organisms (Haemosporidia). The general consensus is that malaria evolved as a parasite of vertebrates (Manwell 1961, Desportes and Schrevel 2013, Mattingly 1983); however, Huff (1945) felt that the malaria progenitor originated with the vector, and in their discussion of malaria evolution, Di Fiore et al. (2009) recognized that in the digenetic malarial life cycle, the vector is the definitive host and the vertebrate the intermediate host. This question has also been addressed with molecular data, but thus far, only very small DNA segments have been analyzed, resulting in incongruous and poorly resolved gene trees (Di Fiore et al. 2009). In the present analysis, fossils are used to determine the progenitors, ancient hosts, and original geographic provinces of malarial organisms. Malarial vectors are ancient, as demonstrated by the early mid-Cretaceous female biting midge (Diptera: Ceratopogonidae) of the extinct genus Protoculicoides infected with Paleohaemoproteus burmacis Poinar and Telford (2005) (Fig. 1). The abdomen of the Protoculicoides vector had cleared enough to reveal 35 oocysts of P. burmacis in its body cavity (Fig. 2). The oocysts contained developing sporozoites, some of which had broken out of their cysts (Fig. 3), thus showing that the pattern of sexual reproduction (sporogony) was already established in vectors at …