Variations in body shape between two sympatric haplochromine species:
Implications for evolution of the fish species in Lake Kivu
Abstract
Patterns of intra- and interspecific variation based on environmental
conditions in which populations live may reflect adaptive responses to
their habitat. This is particularly relevant in a lake habitat where
closely related species occur sympatrically. This study was aimed at
determining consistency in morphological traits in head and body shapes
in two haplochromine species (Haplochromis insidiae and Haplochromis
kamiranzovu) in littoral and/ pelagic zones and to estimate the extent
to which the habitats affect variations between the species. Specimens
of both species were taken from littoral and pelagic zones, in the
northern and southern parts of Lake Kivu. Morphometrics and
landmark-characteristics were recorded and compared within and between
habitats. The results showed that differences were found among the two
species, among the two zones and for both. The most prominent difference
was in the head; including the relative size of the jaws, head length
and position of the pectoral fin insertion. Variation in head morphology
is normally related to feeding. Changes in body shape can be linked to
differences in environment and food availability between the two
habitats which could have enabled the species to co-exist. This capacity
is important in lakes like Kivu which have low habitat diversity
compared to other African Great lakes like Malawi, Tanganyika and
Victoria and provide some explanation in the differences in the number
of haplochromine species in these lakes. The genetic basis of these
phenotypic changes should be examined in future research.