Origins of the genus Poecilia

Abstract of Fred N. Poeser's lecture in the POECILIA Holland symposium

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Maarn (The Netherlands), 17 & 18 November 2000

It is now almost the year 2001, which means: almost 200 years since Poecilia vivipara was described for the first time. Yet, there is still no complete evidence about the identity of Poecilia. What is it that characterizes this genus? Where does it come from? What developments did the genus go through to become what it is now? These are the questions this lecture deals with.

Nomenclature, taxonomy

During its initial development the genus Poecilia existed of five different species. Four of these species have been transferred to other genera in the meantime because they are totally different fishes. The only remaining Poecilia, Poecilia Vivipara, has become the name giver of a confusing genus.

The second Poecilia species that was described immediately caused one of the longest controversies. In 1821, Mollienesia Latipinna was described. One page further we find Poecilia Multilineata, the female of the same species, which was placed in another genus. Female examples were often placed in Poecilia: for instance Poecilia reticulata by Peters, based on females, while the men were put in Lebistes poeciloides (by De Fillippi) and in Girardinus Guppyi (by Günther).

The difference between Poecilia and Mollienesia concerned only the shape and size of the dorsal fin. In 1866, Günter described Poecilia petenensis and Mollienesia petenensis, a short finned molly and a sailfin molly. It all started when Regan discovered in 1913 that the short fin of the molly was not that short at all. The difference between Mollienesia and Poecilia was not big enough and Regan combined both genera into Poecilia. With the consequence that Mollienesia petenensis suddenly was called Poecilia petenensis. At the same time Poecilia petenensis was called Poecilia sphenops like almost all the short finned mollies and therefore Rosen and Bailey (1963) decided to call Mollienesia petenensis Poecilia petenensis. Rosen and Baily have done this more than once.

For example, they have put together all the Poecilia, Mollienesia, Lebistes, Micropoecilia, Limia, Pamphorichtys, Psychropoecilia, Allopoecilia and Curtipenis. They did not know it anymore.

In more recent versions Pamphorichtys, Limia and Micropoecilia are considered as genera by several people, but the arguments are not very convincing. In addition, Mollienesia came back again, as a subgenerus of Poecilia. Concerning the taxonomic status of guppies people have been debating for more than a year. Is it a genus or a subgenus and does Micropoecilia belong to it or does not it?

To find an answer we will have to know more about the biology and the ancestry of different groups.

Biology

The genuine generic name Poecilia came from the name vivipara because of the fact that this species is a livebearer. In the body of the first caught Poecilia there were eggs in a far developed stadium. That this is a confusing but interesting fact is described in taxonomic history.

The young are born almost completely developed and are able to fend for themselves. This has its advantages but also its drawbacks. In many areas where poeciliids live, the years have wet and dry seasons. In wet periods, there is no problem at all; there is enough space for everyone. In the dry period, there is not much space to survive and the hungry young are not very welcome. This explains the ubiquitous cannibalistic hunting of the young:

· If there is enough space, the young can easily find a safe place

· If there is enough food, the parents have less appetite and the young have a small chance to grow up.

Lineage

The poeciliids descend from sail fish [Latin name], which means that they descend from a marine branch of bonefish. Poeciliids are, generally speaking, salt acceptant.

The age of the group might be ascertained when the range of distribution is studied carefully. The species that are next of kin to the poeciliinae are located in South America and even in Africa. The African branch has gone after the continents of Africa and South America drifted apart more than 65 million years ago (end of Cretaceous period). In Africa, there are no original livebearers any more, so this branch must have developed AFTER the rift 65 million years ago.

North and South America have not always been attached to each other. On the contrary, during the last 65 million years they were oftener separate than attached. If we consider the poeciliids in Central America, which have originally come from South America (as a group), then there must have been a time when they migrated to the North. One moment, about 40-50 million years ago, the Great Antilles like Hispaniola were ‘floating’ between the two continents. As the genus Poecilia was located in Hispaniola, together with the genus Limia, that must have been the same time when Poecilia went north. We also know that Poecilia and Limia were already separated in that period. The Poecilia species P. elegans, P. dominicensis and P. hispaniola still have primitive traits.

Poecilia has developed enormously in Central America. The stay-behind Poecilia look-alikes, like the Pamphorichtys species, have developed further. After the heyday in Central America, a land bridge developed about 4 million years ago in the area that is now called Panama. Along the coastlines of this land bridge, the genus was spread to the South; Poecilia vandepolli en Poecilia vivipara are the results of this. In addition, the subgenera Micropoecilia and Lebistes were formed at the newly conquered continent.

Conclusion

The followed method is an analysis called area cladistics. To this end, both anatomic details to construct a phylogeny and the geologic knowledge of the area are used. I can tell you now in short that the Poeciliini consist of Poecilia, Limia, Pamphorichtys, a new to be formed genus of what is now called Poecilia heterandria and maybe Alfaro. The genus Poecilia is to be divided in Poecilia, Lebistes, Micropoecilia and the groups of the Hispaniola: Curtipenis and Psychropoecilia