African Zoology - Volume 35, Issue 2, October 2000

Copadichromis chrysonotus is a zooplanktivorous cichlid member of the diverse fish community inhabiting Lake Malawi's rocky, littoral habitat. Like most Lake Malawi cichlids, this species' reproductive strategy is based on maternal mouthbrooding, but it is the only littoral species known to spawn in the open water without a substrate-based territory. This study investigated length at maturity, sexual dimorphism, spawning behaviour, breeding seasonality, fecundity, fertility, egg size, and brooding habits of C. chrysonotus in southern Lake Malawi. Males in breeding colouration aggregated in sheltered areas at least several metres deep, and each male defended a mobile breeding territory near the surface while attempting to attract females. Breeding was mostly continuous from August to May, with peaks in August-September and January-March. A major lull in breeding activity occurred in May and June. Mean fecundity and fertility increased significantly with female total length, while mean egg length, mean egg mass and gonadosomatic index did not increase significantly with female total length. Females brooded their young up to 15-16 mm total length before abandoning them. Open-water spawning by C. chrysonotus may be an adaptation to reduce both egg predation during spawning and competition for substrate-based breeding territories.

Skull morphometrics of two populations of Subantarctic fur seal (Arctocephalus tropicalis) were compared in order to identify possible geographic variation as an indicator of gene flow between the populations, as well as a potential tool to identify the source of vagrant seals. Nineteen metric variables were recorded from skulls of adult male seals from Marion Island (n=31) and Gough Island (n=41). Comparative univariate and multivariate statistical analyses conducted on the two population samples included standard statistics (mean, standard deviation, coefficient of variation, range), multivariate analysis of variance, stepwise discriminant function analysis, cluster analysis and principal component analysis. No significant separation between the two island groups, based on cranial characteristics of adult males, was found. These findings suggest that gene flow is occurring between these populations.We conclude that skull morphometrics cannot be used to identify the origins of vagrant Subantarctic fur seals.

The intertidal population structure of the large edible gastropod Turbo sarmaticus was examined at four sites along the Eastern Cape Province of South Africa. One site was free from exploitation, two were subjected to low levels of exploitation and one was heavily exploited. Within the intertidal zone at all sites there was a size-related distribution, with smaller animals being found towards the upper mid-shore and larger animals occurring in a downshore direction. The mean shore densities (1.2-animals/m²) and biomass (4.4-9.4 g/m²) of T. sarmaticus at the sites where there was no, or minimal, exploitation of animals were not significantly different (P < 0.001). However, the largest animals (up to 110mm shell length) were found at the unexploited site, an offshore island. The lowest density (0.2 animals/m²) and biomass (0.4 g/m²) of T. sarmaticus was recorded at the site where the exploitation of this gastropod was intense. In addition, no animals of a legally exploitable size (>70 mm shell length) were found. It is suggested that intense over-exploitation is threatening the population at this site.

Kroyeria deetsi n.sp. (Kroyeriidae: Siphonostomatoida) is described from both sexes collected from the gills of spinner sharks, Carcharhinus brevipinna (Müller & Henle, 1839), captured in the Indian Ocean off the coast of South Africa. Kroyeria deetsi n.sp. can easily be distinguished from all of its congeners because the third endopod segments of legs 1-4 of the new species are about twice (legs 1, 2 and 4), or more than twice (leg 3), as long as the corresponding second endopod segments in the female.

The terrestrial invertebrate fauna of an intermittent stream was examined in the absence of surface flows within the context of the flood pulse concept. Terrestrial invertebrates were collected from three sites on the Kruis River in the Western Cape Province, South Africa, using pitfall traps within the dry stream bed over summer months (Jan-Feb). 9848 individuals representing 19 different orders were collected. Taxa were separated and biomass determined for aerial and non-aerial invertebrates. Significantly greater (P < 0.05) numbers of aerial than non-aerial taxa and individuals suggest that most individuals could use flight to escape the onset of surface flows. The absence of significant differences between the biomass (wet weights) of aerial and non-aerial individuals (P > 0.05) suggests, however, that a large proportion of the biomass is confined to the main channel. The inability of a large portion of the biomass to escape the onset of flow through the use of flight suggests that periodically inundated areas of the stream channel constitute an ecologically significant component of temporary stream ecosystems. The concept of the flood pulse should be expanded to include a seasonal and secular variations in flow which in temporary streams create lateral movements that provide the driving mechanism for the entrainment of organic material.

Oribatid mites are typically terrestrial, though many species of Ameronothroidea are marine intertidal. Marine ameronothroids are cosmopolitan with genera being endemic to the Holarctic, sub-Antarctic, or equatorial Indo-Pacific and tropical Atlantic regions. Recent collections from rocky-shores and mangroves of the subtropical east coast of southern Africa (South Africa and Mozambique) contained specimens of the hitherto monospecific genus, Schusteria Grandjean, 1968, one of ten genera from four families of marine ameronothroid. This article describes two new Schusteria species, S. ugraseni n.sp and S. melanomerus n.sp., and compares them with the known species, S. littorea Grandjean, 1968.

Aethomys namaquensis is a 60 g murid rodent that is an important pollinator of several Protea species in South Africa. We compared the nitrogen requirements of this species on two different protein sources: pollen and casein. Pollen is an important source of nitrogen for specialist flower-feeding mammals in Australia. However, its value for a generalist rodent species such as A. namaquensis had not previously been assessed. Casein is often used as the source of protein in studies of wildlife nutrition, as the use of a single purified protein makes it easier for researchers to compare their results with those from other studies. The apparent digestibility of casein was significantly higher than that of pollen, 75.6 % vs 58.4 %, but the biological value was significantly lower, 39 % vs 49 %. As a result of the lower biological value the truly digestible maintenance nitrogen requirements of A. namaquensis on the casein diet were almost double those on the pollen diet (158 mg N/day vs 66 mg N/day). When these values are compared with those for other non-ruminants on natural diets, the pollen values match those predicted for a 60 g animal, while the casein values exceed the predictions. Because purified proteins, like casein, are unlikely to match an animal's amino acid requirements closely, they may overestimate the nitrogen requirements of wild animals.

Four populations of the bushveld rain frog, Breviceps adspersus, representing three northern populations (B. adspersus adspersus), and a southern population (B. adspersus pentheri), were analysed by electrophoresis to assess the extent of genetic variation and differentiation amongst them. Eighteen protein-coding loci were resolved of which 11 loci (61 %) displayed polymorphism. A low mean heterozygosity ranging between H = 0.009 to H = 0.062 was estimated. Greater genetic differentiation was observed between the B. adspersus pentheri and B. adspersus adspersus populations, than between the three B. adspersus adspersus populations. This supports the subspecific status of both taxa.

Histological examination of gametogenesis revealed that the current staging criteria used to assess gonadal recrudescence of the redeye labeo, Labeo cylindricus, were adequate. Gametogenesis was qualitatively similar to that of freshwater teleosts with a clearly defined seasonal reproductive cycle. L. cylindricus undergoes seasonal gross morphological and cytological gonadal changes with previtellogenesis dominating during the winter, vitellogenic development during spring and summer culminating in large-scale spawning at the end of summer. Post-spawning mass atresia of oocytes was evident in autumn. The histological data presented support macroscopical evidence that L. cylindricus is a synchronous iteroparous spawner, reproducing over a short period each year throughout its life-span.

Significant sexual dimorphism in overall size occurs in the rock agama, Agama atra (Sauria; Agamidae), with males growing larger than females. Geographic variation in the degree of sexual size dimorphism also exists, males growing significantly larger than females in Namaqualand and Namibia compared to populations in other areas. Sexual differences in scaling of head, limb and tail dimensions were mainly the result of differential asymptotic sizes reached by the sexes. Head size was also influenced by a faster increase in head dimensions with increasing snout to vent length in males compared to females, probably as a result of sexual selection. In females, scaling of limb and tail dimensions was decreased compared to males, possibly a result of differential energy allocation to reproduction.

A new genus, Parapsycharium n.gen. and its type species, P. paarlense, are described in Somabrachyidae. A key to the somabrachyid genera Somabrachys Kirby, Psycharium Herrich-Schäffer and Parapsycharium n.gen. is given. The description of the new taxon includes the description of its final instar larva.

Seasonal changes in the diet of Cape clawless otters Aonyx capensis feeding in the surf zone in False Bay,Western Cape Province, South Africa, were investigated by spraint (faecal) analysis. The most common prey species, during all seasons, was the Cape rock crab, Plagusia chabrus. The next most important prey species was the Cape rock lobster, Jasus lalandii, with the fish species Clinus superciliosus being equally important in winter. Other prey were fresh-water crabs, Potamonautes perlatus, octopus, Octopus granulatus, and 17 other species of fish, frogs and mammals. In winter and autumn the most important prey category was fish while in spring and summer, crustaceans were the most important. Diversity of prey was lowest in winter, increasing through the seasons from spring to autumn.

A new species of hyperoliid frog, Heterixalus carbonei n.sp., is described from the Antsingy forest in western Madagascar. It is characterized by an advertisement call consisting of long and regular note series. The only other Heterixalus with a similar call structure, H. betsileo from higher altitudes in eastern Madagascar, has distinctly shorter notes. After recent discoveries of the occurrence of H. luteostriatus and H. tricolor in western Madagascar, the new species brings the number of Heterixalus known from western Madagascar to three.

The active-inactive model predicts temporal variation in the operational sex ratio (OSR) throughout a breeding season, as a function of each male's optimal strategy for finding mates. I tested the model using data for the raucous toad, Bufo rangeri, collected nightly over three breeding seasons. The numbers of active males and fertilizable females were correlated in two of the three breeding seasons. The OSR, defined as the average ratio of sexually active males to fertilizable females, decreased throughout each season, except for the first, when it rose to a peak before decreasing. The OSR fluctuated towards the end of the season in two of the three seasons, and rose again at the end in only one. Although the equal-performance assumption was violated, the temporal pattern of the OSR in this species complied largely with that predicted by the active-inactive model. Reasons for deviations from the model's predictions are discussed. Despite the lack of data on mortality rates, this study represents the most comprehensive test of the model yet, as tests on other species have been based on data collected intermittently, as opposed to nightly, over only two breeding seasons.

The histology of brain neurosecretory cells and the development of the ovary and oocytes of preclitellate, early clitellate and late clitellate stages of Eudrilus eugeniae reared in clay loam soil and pressmud have been studied. E. eugeniae reared in pressmud showed earlier differentiation of lobules in the ovary, and increased oocyte numbers with larger cellular and nuclear volumes than those reared in clay loam soil. This indicates the nutritional superiority of pressmud over clay loam soil in supporting gametogenesis. In the preclitellate stage, the brain neurosecretory cell types (A and B) are small and appear to be laden with secretory substances. The neurosecretory cells become vacuolated and show increased cellular and nuclear volumes and nucleocytoplasmic indices during the reproductively active clitellate stages. Secretory activity of neurosecretory cells occurs earlier in worms reared in nutritively rich pressmud which has greater amounts of nitrogens, phosphorus and sugar, than in worms reared in clay loam soil.

Sexual size dimorphism in the medium-sized lizard Oplurus cuvieri cuvieri, which is endemic to the dry deciduous forest of Madagascar, is presented. Adults are sexually dimorphic in body size, head size, and tail length. Males have a greater snout-vent length (SVL), head depth, head width, jaw length, tail length and body mass than females. Juvenile males have greater annual SVL growth rates than juvenile females, contributing to adult sexual size dimorphism. Moreover, the rates of increase in head depth and width differ significantly between the sexes after reaching maturity so that adult males have larger heads for a given body size than adult females. I suggest three proximate mechanisms that may cause sex-related differences in adult head size of O. c. cuvieri based on natural selection; to reduce intersexual food competition, sexual selection involving mate acquisition in males, and ontogenetic change of allometry to improve reproductive output in females.

Seed removal from bait stations was studied in miombo habitat in western Zimbabwe. Previous studies of seed predation in southern Africa have largely been conducted in desert ecosystems. However, this woodland-savanna habitat is more mesic and has relatively predictable rainfall patterns. The experiment was conducted in grassy and woody microhabitats in the hot, dry season and early wet season, and followed a year in which precipitation was 69%of the long-term average. Birds removed the greatest quantity of seeds, followed by ants and then rodents. Previous studies in northern hemisphere mesic environments emphasize the importance of rodents and minor role of invertebrates in seed predation. Although our site appears to have more in common with southern hemisphere desert sites than with northern hemisphere mesic sites, we recognize that our results are likely to reflect a lower limit of consumption by rodents.

Molluscs play key roles in the ecology of many freshwater communities and ecosystems. This is particularly true in temperate to topical habitats where snails are infamous as intermediate hosts of debilitating parasites. In his book on the ecology of freshwater molluscs, Robert Dillon has adopted an organismal rather than an ecological approach to this large subject.

This book represents the first comprehensive review of the genus Rhipicephalus. Ticks in this genus include many species that are important vectors of disease to man and animals. Unfortunately many of these species are notoriously difficult to identify, particularly as immature stages.

This is one of a series of books from Oxford University Press entitled 'Biology of Habitats'. In a mere 252 pages, Colin Little attempts to cover the biology of both muddy and sandy shores, sublittoral soft sediments, estuaries, saltmarshes, mangroves and human impacts on these ecosystems.