Browsing by Author "Contrafatto, Giancarlo."

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Chromosomal evolution in the Vlei Rat Otomys irroratus.
(1996) Contrafatto, Giancarlo.; Meester, Jurgens Anthonie Jansen.; Campbell, Glen Kerry.; Grace, James H.
Proponents of the recognition concept of species hold that isolating mechanisms, including chromosome rearrangements, play no role in speciation while the more commonly accepted biological species concept proposes that isolation mechanisms are instrumental in the formation of new species. Moreover, some adherents of the biological concept of species, reject the hypothesis that chromosomal rearrangements can be instrumental in causing reproductive isolation and, hence, speciation. Evidence to the causative role played in speciation by chromosome changes can be obtained from cytogenetic investigations of sibling species, in parallel with analyses of gene products, DNA polymorphism and premating behaviour. This study reports the results of a cytogenetic investigation of 97 specimens of the vlei rat 0. irroratus, from 18 South African localities, and 11 samples of the Angoni vlei rat 0. angoniensis from two geographically distant populations. All 0. angoniensis individuals showed a constant karyotype with 56 acrocentric chromosomes but extensive variation was detected in 0. irroratus. Five cytotypes could be recognized within the latter. In the south-eastern parts of its South African range, 0. irroratus had a diploid number (2n) of 30 chromosomes in whicll all autosomes were acrocentric (cytotype A) while further east (cytotype A2), the diploid number was 30-32 with, again, acrocentric autosomes, A further acrocentric cytotype (AI) with 2n = 24-27 occupied the southern and south-eastern slopes of the Drakensberg range. A type with 2n = 28-30 (cytotype B), with eight pairs of biarmed autosomes, was found in the southern Cape region while in the Cape of Good Hope and in the north-eastern parts of South Africa, 0. irroratus had 2n = 28 with only four pairs of biarmed autosomes (cytotype C). Most of the numerical changes were due to variation in the number of copies of Bchromosomes which were small, biarmed and partly heterochromatic. C-banding analysis revealed that the short arms of bianned autosomes were totally heterochromatic. On the other hand, G-banding patterns of acrocentric autosomes were, with two exceptions (AI and A2 types), similar in all cytotypes while G~banding of the long arms VII of biarmed chromosomes matched the pattern of their homologues in acrocentric cytotypes. A potentially heterotic rearrangement was detected in the Al localities where a unique acrocentric autosome was identified as the product of a fusion between chromosomes 7 and 12. The geographic distribution of these groups of karyotypes correlated, by Discriminant Function Analysis, with bioclimatic regions of South Africa. The Al cytotype was shown to occupy the coldest and wettest region of the montane Drakensberg while the B type is found in the hot area of the eastern Cape with an unpredictable rainfall pattern: group C occupies regions of intermediate climate. Gene product analysis was carried out using the novel approach of subjecting liver homogenates to "Western blotting". This method was first assessed at supraspecilic level using specimens of various southern African rodents, and allowed the generation of phylogenies essentially similar to those produced by allozyme studies of the same taxa. At intraspecilic level, immunobloHing analysis did not reveal synapomorphies congruent with karyotype groups. This was interpreted, in conjunction with available allozyme data from the same populations, as evidence of low genetic differentiation between 0. irroratus cytotypes, A measure of genetic divergence was indicated in two populations from the Cape province and this was in agreement with existing data from allozyme electrophoresis and mitochondrial DNA polymorphism. The cytogenetic results were related to available data on breeding and premating behaviour concerning some of the O. irroratus populations investigated here. The presence of the 7/12 chromosome fusion in the Al cytotype correlated with a dramatic reproductive impairment of FI individuals originated from Al/A2 and Al/B cytotype crosses. Evidence of partial premating behavioural barriers has been reported by others, but information on premating behaviour between populations which are not chromosomally isolated is lacking. Therefore, it was not possible to establish if behavioural premating barriers preceded, or followed, the fixation of negatively heterotic chromosomal rearrangements. It was, nevertheless, suggested that the existence of such impaired mate recognition may be an example of reproductive character displacement which may have followed the fixation of the t(7: 12) typiVIII cal of the Al populations. In conclusion, the existence of chromosome changes in the AI, and possibly A2, populations accompanied by low genetic divergence and severely impaired hybrid reproductive success, are consistent with a hypothesis whereby chromosomal reproductive isolation causes speciation. Nonetheless, other speciation mechanisms mediated by genetic divergence and/or mate recognition failure, are possible in other populations where no chromosome changes of negatively heterotic potential were found.
A microbal study of water quality in the marine environment off Durban : 1964-1988.
(1989) Livingstone, Douglas James; Contrafatto, Giancarlo.
wastewater from the harbour mouth with the outgoing tides, while the discharge from a sewer on the Bluff into the surf-zone amounted to 20 x 103 m3 /day. In addition, there existed more than 90 beach pipes and storrnwater drains (not all of them legal) , about one third of which carried contaminative material on to the beaches and into the surf. Twenty-eight sampling stations were established between the Mgeni River and Isipingo and subjected to detailed bacteriological surveillance, prior to the construction of a pair of submarine outfalls to serve the region's disposal requirements . A microbial system of evaluating seawater quality was developed using Escherichia coli I, parasite ova, staphylococci, salmonellae (including Salmonella typhi) and the salinity as indicators. A comprehensive "before" picture was therefore created against which to measure future changes in the sea off Durban. In 1968/69 the pair of submarine pipelines was commissioned with their attendant treatment plants. The harbour effluent was diverted to the new complex , and pollution from the minor outfalls was progressively halted with their wastes similarly joined to the new works. The system of water quality gradation was applied to the surf-zone and out to sea to measure the efficacy of the new pipelines, providing an "after" picture . Throughout the subsequent engineering innovation of sludge disposa l via the outfalls (which proved successful), and during climatic extremes involving a severe drought (with stringent water consumption restrictions), cyclones and catastrophic floods, the classification system continued to function satisfactorily , covering 25 years in all: alterations in the water quality were shown to be invariably a consequence of changes effected upon the shore or meteorological events. The system has also proved useful in identifying and measuring the impact of contaminative foci in Cape waters and at Richards Bay. The relevant oceanography and current dynamics, the rationale for the selection of the indicators used and the methodology, along with more general aspects of marine pollution and associated risks are discussed. Finally, the feasibility is examined of curtailing the numbers of parameters measured and simplifying the classification system while retaining its usefulness and serviceability as an instrument for assessing the impact of domestic effluent on the marine environment off Durban.
Mitochondrial DNA variability between selected populations of Otomys irroratus (Muridae:Otomyinae)
(1993) Raubenheimer, Janine.; Lamb, Jennifer Margaret.; Contrafatto, Giancarlo.
An interpopulation study was done on the rodent species Otamys irroratus (Muridae:Otomyinae) using restriction fragment length Polymorphisms to examine the mitochondrial DNA (mtDNA) of 30 vlei rats (Otamys irroratus) from three South African locations and 12 Angoni vlei rats (O.angoniensis) from two locations which were included as an outgroup. The three O.irroratus Populations originated from Karkloof and Kamberg in the Natal midlands and from Rietvlei in the Southern Transvaal. Mitochondrial DNA was extracted and purified by cesium-chloride/ethidium-bromide ultracentrifugation and digested with 19 class 11 restriction endonucleases. The fragments were end-labelled with 32P-dCTP, separated by electrophoresis on horizontal 1% agarose gels and the bands detected by autoradiography. The resultant individual-specific fragment patterns were analysed using the Restsite analysis program (v 1.1; Nei and Miller, 1990) to obtain a measure of the percent sequence divergences between and within the 3 POpulations of O.irroratus as well as between this species and the outgroup. The 19 endonucleases detected 19 distinct O.irroratus mtDNA maternal lineages and 3 O.angoniensis lineages. The O.irroratus lineages were clearly geographical ly structured and most closely reflected the Avise et al. (1987) category I (phylogenetic discontinuity with spatial separation). The only exception was a possible ancestral lineage represented by single individuals from Kamberg and Karkloof. Phylogenetic affinities between the most diverse lineages found at Kamberg and most Karkloof clones appear to be consistent with the finding of Pillay et al. (1993) and Contrafatto et al. (1992b) that Kamberg O.irroratus is an incipient sibling species of Karkloof O.irroratus. The mtDNA data indicates that the O.irroratus Populations at Karkloof and Kamberg last shared a common ancestor approximately 365 000 years ago. By contrast, O.angoniensis showed no evidence of geographic mtDNA structuring and is best described by the Avise et al. (1987) category Ill, which reflects phylogenetic continuity with spatial separation. These classifications must be regarded with caution given the limited distributional range of each species covered by this investigation. The interspecific mtDNA sequence divergence between O.irroratus and O.angoniensis of 11.57% substaniates morphological, karyotypic and allozymic evidence that these two sympatric species are also sibling species and they appear to have last shared a common ancestor between 1.2 and 2.4 million years ago.
Restriction patterns of mitochondrial DNA in natural populations of the murid species Otomys irroratus.
(1994) Rimmer, Alison.; Lamb, Jennifer Margaret.; Contrafatto, Giancarlo.
Mitochondrial DNA (mtDNA) was isolated from 8 different natural populations of the rodent species Otomys irroratus (Muridae: Otomyinae) and from one population of the species 0. angoniensis occurring in South Africa. MtDNA samples were cleaved with five different restriction endonucleases, end-labelled with phosphorous-32, separated by electrophoresis on horizontal 1 % agarose gels and the resulting fragment bands were detected by autoradiography. The individual-specific fragment banding patterns were analysed and compared among the various populations. The percent sequence divergence among and between the populations was calculated using the formula of Nei (1979). A matrix of sequence divergence values for all intergenomic pairwise comparisons was subjected to a clustering analysis by the unweighted pair group method with arithmetic means (UPGMA, Sneath and Sokal, 1973), using the computer programme NTSYS (Rohlf: 1988). The results of these analyses allowed for a preliminary identification of phenetic groupings in the data set. A matrix generated by scoring the restriction endonuclease fragments as present or absent was used to generate a phylogenetic dendogram using the BIOSYS (Swofford and Selander, 1989) programme. The overall restriction fragment variation uncovered in this study revealed 15 different mtDNA haplotypes within the 20 individuals examined. This corresponded to a high degree of polymorphism in the populations where more than one specimen was available, as well as within the species 0. irroratus. There were no clones that were shared between any of the populations sampled. The intrapopulation sequence divergence values uncovered in this study were high (range 0.35 % to 5.08 %), but also consistent with some other reports in the literature for intrapopulation variation. The outgroup, 0. angoniensis revealed the highest divergence values when compared to the mtDNA clones found in 0. irroratus. The phenetic and cladistic cluster diagrams revealed overall similarity with one another. There appeared to be little correlation between the topology of the mtDNA haplotype phenograms and the geographic distance of the sample localities. There was, however, a marked congruence between the distribution of mtDNA haplotypes and the distribution of three distinct cytotypes occurring over the species range. A possible polyphyletic evolution of populations of 0. irroratus was inferred from the cladistic analysis.
Systematic revision of Southern African species in the genera Eptesicus, Neoromicia, Hypsugo and Pipistrellus (Chiroptera: Vespertilionidae).
(2005) Kearney, Teresa Catherine.; Contrafatto, Giancarlo.; Taylor, Peter John.
Abstract available in PDF file.