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Diurnal Variation of Spacing and Foraging Behaviour in Tropheus Moorii (Cichlidae) in Lake Tanganyika, Eastern Africa

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Diurnal Variation of Spacing and Foraging Behaviour in Tropheus Moorii (Cichlidae) in Lake Tanganyika, Eastern Africa DIURNAL VARIATION OF SPACING AND FORAGING BEHAVIOUR IN TROPHEUS MOORII (CICHLIDAE) IN LAKE TANGANYIKA, EASTERN AFRICA by CHRISTIAN STURMBAUER and REINHARD DALLINGER (Departmentof Zoology,University of Innsbruck,Austria) SUMMARY Diurnal variation of behaviour was investigated in the epilithic algae feeder Tropheus mooriiin Lake Tanganyika. Territories, home ranges and four behavioural categories were recorded during the diurnal cycle. All four behavioural categories (foraging, locomotory activity, resting behaviour and total social interactions) followed a diurnal pattern. Foraging activity was maximum between 12.30 h and 16.30 h, and the observed diurnal pattern was similar to the rhythm found in a great number of marine algae feeders. In contrast to previous observations individuals displayed both territorial and non-territorial activities during the day, expressed by specific colour- and behav- iour patterns. The time spent in the own territories also varied with day time and was maximum between 12.30 h and 16.30 h. Non-territorial aggregations of several individ- uals outside territories were particularly observed during dawn and dusk. Territories may primarily function as feeding territories since foraging was the most frequent behaviour. Non-territorial activities may allow individuals to utilize additional food sources and the aggregation of several individuals at dawn and dusk may indicate their behaviour at night. The observed diurnal rhythms of behaviour, together with the previously described complex social behaviour, and the altered mating system of Tro- pheus, may have evolved as a consequence of extreme sedentarity and close association to rocky substrate in order to optimize resource utilization. KEY WORDS:colour patterns, territoriality, non-tcrritoriality, feeding rhythm, algae feeders. INTRODUCTION Since their discovery at the turn of the century (BOULENGER, 1898) the assemblages of cichlid fishes in the East African Lakes Victoria, Ma- lawi and Tanganyika have fascinated evolutionary biologists (FRYER & ILES, 1972; GREENWOOD 1984; LOWE-MCCONNELL, 1987). With an estimated age of 9-20 Mya, Lake Tanganyika is the second oldest lake in the world (TIERCELIN & MONDEGUER, 1991; COHEN et al., 1993) being substantially older than the two other eastern African lakes. In com- parison to the assemblages of cichlid fishes in Lakes Malawi and Victoria, the species flock of Lake Tanganyika exhibits the highest degree of morphological, behavioural and genetic diversification 387 (GREENWOOD, 1984; BARLOW, 1991; STURMBAUER & MEYER, 1992, 1993; STURMBAUER et al., 1994). The littoral communities at rocky shores are the most species-rich assemblages of the lake, dominated by epilithic algae feeders (FRYER & ILES, 1972). As the rocky coasts are divided by sandy areas, swamps and river estuaries, many species are split into numerous distinct populations. The highest number of such populations was reported for Tropheus, almost each continuous line of rocky shore being inhabited by a distinct population (MARLIER, 1959; MATTHES, 1962; BRICHARD, 1989). Although highly variable in coloration, their morphology basically remained unchanged (VERHEYEN, unpublished data). Six nominal spe- cies of Tropheus are presently recognized (NELISSEN, 1975; POLL, 1986). A genetic study of 21 populations of Tropheus (6 species) identified T. duboisi as the most ancestral branch. After this split, six mitochondrial lineages were identified containing T. moorii, T. polli, T. kasabae, T. annectens and T. brichardi. The study revealed surprisingly large genetic divergences among populations, twice exceeding that of the whole Lake Malawi species flock, and five times exceeding that of the whole Lake Victoria flock (STURMBAUER& MEYER, 1992). Since some of the nominal species appear to be paraphyletic, conflicting the present taxonomy, we will use the name of the first described species (T. moorii Boulenger 1898) here. Behavioural studies on captive Tropheus demonstrated a complex system of colour and behaviour patterns, pointing to a highly devel- oped social organization (WICKI,ER, 1969; NELISSEN, 1976). Studies in the natural habitat reported a territorial organization of males and females, and the formation of breeding pairs, both unusual characteris- tics of maternal mouthbrooders (KAWANABE, 1981; YANAGISAWA & NISHIDA, 1991). The high complexity of mouthbrooding in Tropheus was highlighted by the observation of foraging behaviour during mouthbrooding to feed the fry after hatching (YANAGISAWA& SATO, 1990). The present study was carried out on a northern population of T. moorii and focussed on observations on diurnal variation of behav- iours and spacing. MATERIALS AND METHODS ' Studyarea The investigation was carried out during February and March 1988 in Magara (3°44' South, 29° 19' East), 41 km south of Bujumbura, Republic of Burundi. The rocky shores of this area are populated by the red-yellow-red Tropheusmoorii which is genetically closely related to populations at Kiriza (Zaire; STURMBAUER& MEYER, 1992), Minago (Burundi) and the Ubwari peninsula (Zaire; STIJRMBATJER,unpublished data). The study area was located about 500 m south of Cape Magara and had an extension of about 250 .
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