When Ahl described Labeotropheus fuelleborni in 1927 relatively little was known about the myriad of rock-dwelling cichlids in Lake Malawi—now better known as mbuna. He certainly didn’t know whether the specimens he received from Dr. Fülleborn who had caught all of them at Lumbila in Tanzania, had a lake-wide distribution or were restricted to the locality collected. With the subsequent publications of Trewavas (1935) and Ribbink et al. (1983) a host of new species became known and also that most of the rock-dwelling forms commonly showed geographical variation. Such variation is a logical result of the fact that these small, rock-dwelling cichlids are bound to their protective habitat and almost certainly would lose their lives if they would cross open sandy territory where they would be exposed to predators and to lack of proper food (Aufwuchs). Since rocky outcrops/reefs/shores are separated from each other by hostile (sandy or swampy) habitat, populations evolve independently from each other without much mixing of genetic material. So it is rather normal that a particular population of cichlid has adapted itself to the local environment. Sometimes this means that on average the species can be smaller/larger than the same species in neighboring populations depending on the availability of food at either locality. Other small morphological differences can be caused by the type of algae that is available at either place which can be dependent on how much light penetrates, what type of substrate is available, or what other species live at the same place competing for the same food source. There are usually so many variables that affect the shape of a mbuna that it is sometimes a real problem to regard a certain population as a geographical variant or as a separate species. Over the years I have adopted the following strategy in defining what constitutes a species and what a geographical variant: The “new” species is compared to similar species from neighboring localities. Such comparisons are tedious as you need to measure and compare at least 20 specimens of each population to get a little idea about the variability within each population. If the “new” species only has a different male coloration but largely overlaps in morphology, it would very likely be classified as a geographical variant. Note here that we compare neighboring populations, not populations from the other end of the lake because they are much more likely to be different in morphology and coloration. Logically the nearest relatives of the new species are found in neighboring habitats.
This should sound logical to anybody who is familiar with the variability of mbuna in Lake Malawi; else we are going to be in need of describing every population as a separate species. I was therefore surprised to find in the latest publication from Michael Pauers—a study in which two new species of Labeotropheus, both from Katale Island, Malawi, are described—that he compared his new material with only the type material of L. fuelleborni (5 types from Lumbila, Tanzania) and that of L. trewavasae (12 types from Nkhata Bay, Malawi). Also his new material was obtained through the aquarium trade so precise collection sites can only be surmised. The new species were represented by 9 (L. chlorosiglos) and 5 (L. simoneae) type specimens respectively—not exactly a representative sample for such a common species; even though 16 additional specimens of L. chlorosiglos were available but not used for the description. I have a hard time accepting the validity of these new species because they are only marginally distinguishable from the respective types that were collected 60 and 90 years ago and which are separated from the putative new species by a multitude of populations of either L. trewavasae or L. fuelleborni. In the 1980s I collected many specimens of Labeotropheus from about a dozen different localities (now lodged at the Central Africa Museum in Tervuren, Belgium) and tried to find a characteristic that would separate just the two species, but was unsuccessful. Only when both species of the same locality were compared could a distinction be made. According to Pauers’ reasoning all these populations should represent different species. The problem with such a hypothesis is that none of these many species can be distinguished from the others by morphological characters. Furthermore, every hobbyist knows what is L. fuelleborni or L. trewavasae, but without reading the paper nobody would know whether L. chlorosiglos is a fuelleborni-type or a trewavasae-like species. On the other hand when I write L. fuelleborni Katale almost any Malawi aficionado knows what I mean.
Science has developed a taxonomic system in which we all try to bring clarity in the genetic relationships by grouping the closest related entities in the same group, i.e. populations into species, species into genera, and genera into tribes/families. By placing trewavasae and fuelleborni in the same genus we indicate that they are closely related and we know these are two different species because often both can be found at the same locality. By adding two more species (of the same rank) to this genus one infers that at some point three or all four species can be found sympatric, which certainly is not the case. So, what is the advantage of splitting geographical variants into species? Good question!
- Pauers, Michael J. 2016. "Two new and remarkably similarly colored species of Labeotropheus (Perciformes: Cichlidae) from Lake Malaŵi, Africa". Copeia. v. 104(n. 3), pp. 628-638 (crc07407) (摘要)
- Ribbink, Anthony J & A.C. Marsh, B.A. Marsh, B.J. Sharp. 1983. "The zoogeography, ecology and taxonomy of the genus Labeotropheus Ahl, 1927, of Lake Malawi (Pisces: Cichlidae)". Zoological Journal of the Linnean Society. v. 79(n. 3), pp. 223–243 (crc05458) (摘要)
- Trewavas, Ethelwynn. 1935. "A Synopsis of the Cichlid Fishes of Lake Nyasa". Annals and Magazine of Natural History. Series 10; pp. 65-118 (crc00118)
© Copyright 2016 Ad Konings, all rights reserved
Konings, Ad. (八月 12, 2016). "Labeotropheus, splitting out of context". Cichlid Room Companion. 檢索 七月 16, 2019, 來自: https://www.cichlidae.com/section.php?id=292&lang=zh.