F.H. van der Bank

A comparative biochemical genetic study of three populations of domesticated and wild African catfish (Clarias gariepinus)

Abstract 1. 1. Gene products of 22 protein coding loci in two commercially used (domesticated) and one wild population of African catfish, Clarias gariepinus, were examined by horizontal starch-gel and vertical polyacrylamide-gel electrophoresis. 2. 2. Average heterozygosities of 0.0759 and 0.0033 for the domesticated and 0.0467 for the wild catfish population were calculated. 3. 3. Genetic distances indicated a greater similarity between geographically isolated (hatchery) populations than between hatchery and wild populations. 4. 4. Selection of breeding stock for aquaculture practices based on the above information is discussed.

Genetic and morphological variation in four populations of the surf clam Donax serra (Roding) from southern African sandy beaches

The surf clam Donax serra (Bivalvia, Donacidae) dominates sandy beach communities of two southern African biogeographical regions, a cold (Benguela current) and warm province (Agulhas current). Morphometric and behavioural differences led to a controversial discussion of whether or not populations from the two provinces belong to the same species. Shell size measurements confirmed morphological differences: clams from the cold province were significantly rounder, flatter and less wedge-shaped than clams from the warm province. In this study a genetic approach was used to relate phenotypic differences to genetic variability of four populations of D. serra separated by up to 2 500 km of shoreline. Genetic analysis of twenty-two protein-coding loci was carried out by starch-gel electrophoresis. Populations studied are conspecific (genetic distances range from 0.003 to 0.044) and possess genetic variation (alleles per locus: 1.73 - 1.91; mean heterozygosity: 18 - 22%; percentage polymorphism: 45.5 - 59.1%) in the range of most other marine bivalves, which allows for potential adaptation to environmental changes. Wrights fixation indices show little to moderate genetic divergence among the subpopulations relative to the limiting amount under complete fixation (FST = 0.016 - 0.089), moderate divergence of individuals relative to the total population (FIS = 0.265 - 0.452), and comparably high divergence of individuals relative to the compound population (FIT = 0.300 - 0.473). The effective number of individuals exchanged between populations in each generation is high enough (1.44 - 8.65) to counteract genetic drift. We propose that the observed differences represent phenotypic plasticity enabling this species to inhabit different biogeographic regions. Gene flow, balanced selective pressure and evolutionary inertia are discussed as explanations for similarities of the two outlying populations. The substantial subdivision of the two Namibian populations indicates a potential biotic barrier and requires separate studies of the population dynamics.

The suitability of using cryopreservation of spermatozoa for the conservation of genetic diversity in African catfish (Clarias gariepinus)

Abstract 1. 1. The effect of cryopreservation of semen on expected Hardy-Weinberg proportions in the f1 progeny of selected breeding pairs was evaluated. 2. 2. Four different African catfish breeding pairs were selected, each pair displaying different heterozygous alleles at the glucose-6-phosphate isomerase-1 or 2 loci. 3. 3. Equal volumes of ova from each female were artificially inseminated with cryopreserved or fresh semen obtained from males possessing corresponding genotypes. 4. 4. A comparison of growth rates between f1 groups of offspring produced from fresh and cryopreserved semen was made. 5. 5. The G-test for goodness of fit showed no significant differences from expected Hardy-Weinberg proportions for allele frequencies obtained in the f1 progeny. 6. 6. The application of cryopreservation for the conservation of genetic diversity is discussed.

Phylogenetic relationships between eight African species of Mormyriform fish (Teleostei, Osteichthyes): Resolution of a cryptic species, and reinstatement of Cyphomyrus Myers, 1960

Phylogenetic relationships between seven elephantfish species from five genera (Mormyridae) that are endemic to southern Africa, and the Nile knifefish of the sister family, Gymnarchidae, were determined using biochemical genetic data, behaviour (the waveforms of the electric organ discharge), morphology, and habitat and food preferences. The results confirmed the existence of an undescribed species of Hippopotamyrus, and that H. ansorgii and H. discorhynchus are not congeners. These distinctions had been suggested by differences in electric organ discharge waveforms and are here substantiated by morphological and genetic data. We recommend the reinstatement of Cyphomyrus discorhynchus (Peters, 1852). Genetic distance (D, Nei, 1972) values suggest confamilial genera (D average of 1.09 for all species studied, and 0.715 for southern African species), with the exception of the sympatric and congeneric species: H. ansorgii and H. sp. (D=0.423). Phylogenies based on morphological and electrophoretic data are congruent.

Evolution of sprouting versus seeding inAspalathus linearis

We have tested the hypothesis that reseeding is a plesiomorphic character state and that sprouting is a derived state inAspalathus linearis, and that the latter is an adaptation to ensure fire-survival in a fireprone environment. Samples of five seeder and four sprouter populations of A.linearis were examined by horizontal starch gel electrophoresis to assess the amount of genetic differentiation within and between sprouting and seeding populations, and to determine the extent of gene flow between the populations. Leaf extracts were surveyed for ten enzymes and gene products revealed genetic variation at 13 (76%) of 17 protein coding loci. Allele frequency differences were found between sprouting and seeding populations and genetic distance values show that the sprouters are grouped separate from the seeders, thus providing support for the morphological data on which the above mentioned hypothesis is based. It is evident that evolution operates at the population level inA. linearis.

A comparison of growth performance and genetic traits between four selected groups of African catfish (Clarias gariepinus burchell 1822)

1. 1. Fast growing individuals (three groups) in a progeny batch of African catfish were identified and isolated from the main population. 2. 2. At the age of 36 weeks, the mean mass of two fast growing groups (169.6 and 232.0 g) was significantly (P < 0.05) higher than that of the rest of the population (88.8–108.7 g). 3. 3. A comparison of specific growth rates revealed that these differences were the result of superior growth at an early age. 4. 4. An electrophoretic evaluation of the different mass classes showed little or no difference between the LDH allele frequencies of the fast growing groups, but did indicate significant differences between the frequencies of fast and slow growing groups. 5. 5. The present study represents the first attempt to establish the role of genetic characteristics in the control of growth in African catfish, and suggests the feasibility of genetic selection for rapid growth in Clarias gariepinus.

Genetic diversity and isolation in African Buffalo (Syncerus caffer)

Abstract We studied genetic diversity in 58 buffalo from the Kruger National Park (KNP) and Willem Pretorius Nature Reserve (WPNR). Thirty-three protein-encoding loci were resolved; three were polymorphic. Average heterozygosity (H) values did not differ substantially between adult and sub-adult animals from the KNP (2.65 and 2.89%, respectively), but were lower in animals from the isolated WPNR herd (H = 1.48% and only 3% polymorphic loci compared to 9.1%). Representative levels of genetic diversity exist in the large but disease-carrying herd, whereas the smaller disease-free herds available for translocations appear less polymorphic.

Allozyme variation in domesticated African catfish (Clarias gariepinus) from The Netherlands

Abstract 1. 1. Gene products of 20 protein-coding loci of 50 African catfish individuals, imported from The Netherlands, were examined by horizontal starch-gel and vertical polyacrylamide gel electrophoresis. 2. 2. No polymorphism could be detected at any of the loci examined, except at the esterase protein-coding locus which was not examined by previous authors. 3. 3. The loss of genetic variation could be attributed to the combined effects of a small founder population, limited numbers of parents used to produce the next generation and/or accumulation of genetic drift. 4. 4. The results are compared to those obtained by other authors for African catfish population.

Phylogenetic relationships, based on allozyme data, between six cycad taxa indigenous to South Africa

Phylogenetic relationships between Encephaiartos altensteinii Lehmann, E. friderici-guilielmii Lehmann, E. lehmannii Lehmann, E. natalensis Dyer & Verdoorn, E. transvenosus Stapf & Burtt Davy and E. villosus Lemaire were studied, using Cycas revoluta Thunberg as outgroup. Three continuous and one discontinuous buffer systems were used and gene products of 21 enzyme coding loci were examined by horizontal starch gel-electrophoresis. A biochemical key, based on fixed allele differences, is presented. Fixed allele differences at one locus between E. altensteinii and E. natalensis may confirm that these species do not share the same gene pool. However, the genetic distance is the least (0.042) between these two species, compared to the mean genetic distance value of 0.222 for the other ingroup taxa. The results are discussed with reference to affinities based on morphology and distribution.

Allozyme divergence among four representatives of the subfamily Alcelaphinae (family: Bovidae).

We used protein gel electrophoresis to study genetic diversity within and between blue wildebeest (Connochaetes taurinus), black wildebeest (C. gnou), red hartebeest (Alcelaphus buselaphus caama) and blesbok (Damaliscus dorcas phillipsi). Twenty-nine protein encoding loci were resolved, average heterozygosity ranged from 3.25-5.36% and between population gene diversity accounted for the major share of the total relative gene diversity (69.34%). Genetic distance values ranged from 0.021 to 0.132 and 0.029 to 0.136, with closest identity between the two wildebeest species (as expected for congeneric species). The results are discussed with specific reference to taxonomic relationships between species within the subfamily where interbreeding is known to have occurred.