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| Researcher: Roger Blahnik | |
One of the things that particularly intrigue me is that the current distribution of organisms on this planet can sometimes be traced to events of almost unimaginable antiquity. The distribution of taxa in the family Philopotamidae may be an example of the long lasting influence of ancient events. The most successful and species diverse genus, Chimarra, currently with about 450 described species, is almost world wide in distribution, but is especially diverse in tropical regions, both in terms of the total number of species present and also the diversity of lineages represented. I began my studies of Chimarra with the New World fauna, but my current interest has shifted to the phylogenetic relationships among Old World taxa. A genus of this size, whose members are relatively poor long distance dispersers, has the potential to tell us about historical events that affected the distribution of species. Morphological and molecular evidence suggest that Old and New World species belong to different lineages. A plausible hypothesis is that the lineages date back to the break up of the southern hemisphere supercontinent of Gondwana almost 80 million years ago, suggesting an original Brazilian-equatorial Africa distribution for the genus. However, the genus is also widespread in Asia, extending to Indonesia, the Philippines, New Guinea,, and Australia. One lineage has even spread to the New World, where it is currently rapidly speciating and co-occurs with endemic New World lineages. Within this range various species lineages are geographically localized. The relationships among surviving lineages and their current geographical distribution may tell us something about the events that allowed the Old World representatives to spread so far. Of particular interest is the relationship of African species to those of India and Asia. An impediment to phylogenetic analyses that would tell us something about the biogeographic history of the group is that many species are still undescribed. With various colleagues I am currently involved in the description of many new Old World species, including those of equatorial Africa (with Trond Andersen) and Sabah in northern Borneo (with Jolanda Huisman). I have also recently begun working on the Chimarra of India, where the fauna is still mostly unknown. The specimens for the latter study were collected over 40 years ago by the late Fernand Schmid of the Canadian National Collection. My eventual goal is to extend my studies from descriptive taxonomy to a phylogenetic analyses of Old World species based on morphological and molecular characters. |
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The other genera in Philopotamidae may trace their distribution to an even more ancient event. Compared to Chimarra, most of the other genera have an almost relictual distribution. Some genera (or subgenera) are individually restricted to the temperate or subtropical regions of the southern hemisphere, including the Chilean region of South America, southeastern Brazil, the southern tip of South Africa, Madagascar, southeastern Australia, and New Zealand. This distribution suggests a southern Gondwanan distribution before the supercontinet broke up. Other genera (or subgenera) are found predominantly in the temperate parts of the northern Hemisphere, including Europe, North America, and Asia. This distribution suggests an original Pangean distribution for the family Philopotamidae, with the elements of the fauna restricted to Lauasia and Gondwana after their separation almost 180 million years ago still maintining their original relative geographic distributions. An additional research research interest of mine is to test this hypothesis against a phylogenetic analysis of the various genera and subgenera with the use of molecular sequence data. This will hopefully also clear up what at present seems to be a very confused taxonomy for the genera and subgenera of Philopotamidae. |
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