REVISION OF FROM THE "" EMPODISMA GROUP

REVISION OF THE SPECIES (TELEOSTEI, CICHLIDAE) FROM . PART II

by

R. J. C. HOOGERHOUD+ and F. WITTE+ (HaplochromisEcology Survey Team, Mwanza, Tanzania; Division of & Evo- lutionaryBiology and MorphologyDepartment, Zoologisch Laboratorium, Universityof Leiden, The Netherlands)

SUMMARY

The endemic haplochromine from Lake Victoria are estimated to comprise 200 to 250 species. This estimate is mainly based on collections from two opposite ends of the Lake, i.e. the area around Jinja (Uganda) in the north and the area around Mwanza (Tanzania) in the south. An ecological and taxonomic survey of the from the Mwanza area was recently started by the Haplochromis Survey Team (HEST). The collection of HEST contains several species groups of which the members closely resemble each other as well as their congeners known from the northern part of the Lake. One such case, the "H." empodismagroup, has been analysed in this paper. The study was focussed on two new colour forms of this group, which were discovered in the Mwanza area, and on two previously described species, "H." empodismaand "H." obtusidens,which closely resemble them. It is demonstrated that the two species plus the two colour forms can be distinguished from each other on the basis of (small) morphological differences (other than male colouration). The two Mwanza forms are described as new species. The species rank is corroborated by ecological data.

INTRODUCTION AND METHODS S

In the course of their fieldwork on haplochromine the Haplo- Ecology Survey Team (HEST), distinguished a large number of forms*, most of which (iL70%) could not be identified to any described species. Initial distinction of most forms was based on extensive experience of (including the study of the museum-collections) and above all on the inspection of the many haplochromine cichlids caught by HEST in Lake Victoria. The distinct

+ c/o Drs. C. D. N. Barel, Zoologisch Laboratorium, Kaiserstraat 63, Postbus 9516, 2300 RA Leiden, The Netherlands. * The word "form" in this paper is used to designate a morphologically defined group of which the systematic position is as yet unknown. 233 morphology of each form was determined by the measurement and description of specimens, using standard taxonomic techniques (BAREL et al., 1977), as well as by using new characters that appeared to be useful (e,g, the new measurements defined on p. 235). Ideally a form description should be unequivocal, i.e. with the help of the descrip- tion it should be possible with each specimen caught to decide whether or not it belongs to a particular form. For the majority of forms, HEST succeeded in providing such objective descriptions, but there remained a number of problematic cases. In these it was felt that a particular form was characteristic, but that it could not be described objectively because the current technique was insufficient. Such a frustrating con- flict between feeling and quantification is only too well known to taxonomists. The present paper demonstrates that for cichlids too techniques other than the taxonomic standard ones may be instrumen- tal in corroborating form distinction between forms with only very minor morphological differences. Naturally the first and major biological question of form distinction is whether the forms represent species. A biologically meaningful species concept requires information on the degree of reproductive isolation. In the context of this investigation that information was most easily derived from the current ecological research of HEST. When no indication of reproductive isolation can be obtained, the possibility of a more limited biological meaning of the form should be considered: does it for instance indicate a functional morphological, genetic, geographic or ecological entity (other than a species) ? Finally the possibility of an artificial or inconsistent distinction should not be overruled. An example of such an inconsistency is found in BENDA & MAINGA (1977). The authors attempted to sort haplochromine trawl- catches into various trophic groups and to determine their depth distributions. Based on morphological characters, colour and promi- nent markings, 69 groups with more than one specimen were dis- tinguished. However, as the authors noticed themselves, 56 of these groups turned out to be monosexual, suggesting that the intended trophic grouping was biased by inadvertently applying sexual charac- teristics as classification-criteria. From the more than 150 new forms we carefully selected two to serve as a test case for the questions outlined above. Diagnostic descrip- tion of these two forms is the major subject of the present paper. The two forms are morphologically similar and indicate the lower limits of form distinction made by HEST. The only obvious morphological difference between the two forms is the difference in the male coloura- tion. The two forms closely resemble two species (re)described by GREENWOOD (1960): "Haplochromis" empodisma and "H." obtusidens. The