Rhodes University

The Biology of Terrestrial Molluscs

"The Biology of Terrestrial Molluscs." African Zoology, 37(2), p. 259

Sperm Biology: an Evolutionary Perspective

Aspects of the biology of Tilapia mossambica Peters (Pisces: Cichlidae) in a natural freshwater lake (Lake Sibaya, South Africa)

An account is given of some aspects of the biology of Tilapia mossambica Peters in Lake Sibaya, South Africa. Lake Sibaya is a warm shallow coastal lake with extensive shallow terraces in the littoral which shelve abruptly into underwater valleys. The substrate is predominantly sandy. Aquatic macrophytes are generally restricted to water 1–7 m deep. Adult fishes (over 8 cm standard length) are usually absent from water deeper than 12m and shallower than 0–5 m, whereas juveniles may occur at all depths, and fry only in very shallow water. T. mossambica inhabits the littoral and sublittoral in the warm and transition periods (August–April) but moves into deep water in the cool season (May–July). Exposed and sheltered areas are utilized for different purposes by adult fishes, the former for nesting, and latter for feeding and mouth–brooding. Habitat selection by males is governed by the availability of suitable nest sites. Nests are most common in sparsely–vegetated sheltered areas. Brooding females preferred sheltered littoral areas but ventured onto the terrace to release the fry. Juveniles and fry inhabited exposed shores with a temperature gradient which reversed diurnally. The breeding, shoaling and feeding behaviour is described. The biology of T. mossambica in Lake Sibaya is compared to data on the same, and similar species, in other systems. The utilization of available resources in the lake by T. mossambica is discussed and reference is made to the importance of the retention of generalized characters for the successful habitation of the cyclically–renewed habitat of the littoral.

Beyond the various contrivances by which orchids are pollinated: global patterns in orchid pollination biology

Abstract Orchidaceae show remarkable diversity in pollination strategies, but how these strategies vary globally is not entirely clear. To identify regions and taxa that are data-rich and lend themselves to rigorous analyses or are data-poor and need attention, we introduce a global database of orchid reproductive biology. Our database contains > 2900 species representing all orchid subfamilies and 23 of 24 tribes. We tabulated information on habit, breeding systems, means of pollinator attraction and the identity of pollinators. Patterns of reproductive biology by habit, geography and taxonomy are presented graphically and analysed statistically. On the basis of our database, most orchid species sampled are pollinator dependent (76%) and self-compatible (88%). Pollinator attraction based on rewards occurs in 54% of the species, whereas 46% use some means of deceit. Orchids generally have highly specific pollinator interactions (median number of pollinator species = 1). Nonetheless, on average, specificity is lower for species offering rewards, occurring in multiple continental regions or Northern America (as defined by the Taxonomic Database Working Group Level 1 regions). Although our database reveals impressive knowledge gains, extensive gaps in basic observations of orchid reproductive biology exist, particularly in tropical regions and diverse lineages of fly-pollinated species. The database is expected to facilitate targeted studies, further elucidating the ecological and evolutionary drivers of orchid diversity.