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. / Thesis (M.Sc.)-University of Natal, 1994.

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. / Thesis (M.Sc.)-University of Natal, Durban, 1993.

This work investigated two important evolutionary processes - speciation and adaptive variation - in two chromosomally-distinct allopatric Natal Midlands populations of the vlei rat Otomys irroratus. The two populations, at Kamberg and Karkloof, differ in the presence of a tandem fusion between chromosomes seven and 12 in the Kamberg karyotype. Speciation studies considered possible reproductive isolating mechanisms. In studies of adaptive variation, socio-ecological characteristics of both populations were investigated. Data on breeding and postnatal development provided evidence of post-zygotic barriers. Interpopulation pairs had reduced breeding success compared to intrapopulation pairs, and some hybrids died before weaning. Surviving hybrids had reduced growth rates, and almost all were sterile. In tests of pre-mating reproductive isolation, ethological barriers were emphasized. Individuals preferred same-population mates, suggesting the existence of mate recognition, which was achieved by means of population-specific courtship behaviour and communication, particularly olfactory, tactile and visual cues. No evidence of population-specific acoustic signals was found, although acoustic cues were associated with agonistic interaction, complementing other communicatory cues to promote increased aggression during interpopulation pairings. Laboratory studies of behaviour and morphology and field work (trapping and habitat assessment) provided information about socio-ecological parameters. The Kamberg habitat was harsher than the Karkloof one, as revealed by differences in seasonal and spatial availability of food and·cover. Cover was the key determinant of the level of sociability of both populations. Sparse, patchy cover selected for a partially communal social system in Kamberg o. irroratus: females were intrasexually tolerant and males were intrasexually highly aggressive. This, in conjunction with male-biased sexual dimorphism, implied that mating was polygynous. Abundant, uniform cover selected for a dispersed social system in Karkloof o. irroratus: females were intrasexually less tolerant than males. Ritualized aggression between males and a low degree of male-biased sexual dimorphism suggested that male may have overlapping home ranges in nature and that mating is promiscuous. Females possibly mated with dominant males, however. Contrasting social systems suggest that adaptation to local environmental circumstances has occurred in allopatry, and that Kamberg and Karkloof o. irroratus are undergoing adaptive speciation. Post-zygotic and pre-mating reproductive barriers appear to have evolved independently in both populations, and could potentially impede gene flow between the populations should they become sympatric. The presence of the tandem fusion in the Kamberg karyotype which, together with genetically-determined factors, may have caused hybrid sterility, suggests that this population is a chromosomally-determined incipient sibling species. / Thesis (Ph.D.)-University of Natal, Durban, 1993.

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. / Thesis (Ph.D.)-University of Natal, 1996.

The ecology and life history of the vlei rat, Otomys irroratus (Brants, 1827), were studied in a population on the Van Riebeeck Nature Reserve near Pretoria. Two main procedures were used to collect the basic information and material for the project. First, a permanent live-trapping grid was established where 333 animals were captured, marked, released, and recaptured over a period of 26 months, Second, snap-trapping and live-trapping were conducted elsewhere in the study area for supplementary material. Because Otomys angoniensis Wroughton, 1906, a sibling species of 0. irroratus, also occurred in the study area and grid, it was necessary to define the differences in morphology and ecological distribution between the two species. The ecology and life history of 0. irroratus are described and discussed in regard to the following major topics: taxonomy and morphology, distribution, population dynamics, reproduction, postnatal growth and development, activity, behavior, and economic importance. In addition to the presently used means of distinguishing 0. irroratus and 0. angoniensis, it was found that the hind foot length of the two species differed, being 29-34 mm in 0. irroratus and 25-28 mm in O. angoniensis. The baculum of the two species was also found to be distinct in both shape and size. In Southern Africa 0. irroratus occurs primarily in the grassland subregion of the Southern Savanna biotic zone, while O. angoniensis occurs primarily in the woodland subregion of the same biotic zone. The preferred habitats of the two species on the study grid were determined. There was little overlap of niches and each species had a high degree of association with a different veld type, O. irroratus being associated with the more mesic habitat. The population size of O. irroratus reached a peak in May and a low in September. The population also fluctuated considerably from one year to the next, with rainfall possibly being the main contributing cause. The ratio of juveniles, subadults, and adults fluctuated primarily in respect to the season when the young were born. The sex ratio did not depart significantly from 1:1. Males comprised 49,5 per cent of the total and females 50,5 per cent. The rate of disappearance after one month from first capture was 41 per cent, indicating that a large number of transients and individuals dispersing from their birth site were involved. The overall rate of disappearance, excluding the high first month rate of disappearance, was 3,1 per cent per month. The mortality rate appeared to be at its highest between August and September when the food and cover were of very poor quality and quantity. This was also the period when males demonstrated a significant loss in body weight. The major factors causing mortality appeared to be flooding of the habitat and owl predation. Floods not only reduced the population but significantly interrupted breeding. Otomys irroratus was one of the most prominent prey species of both barn and grass owls. The major factors causing mortality appeared to be flooding of the habitat and owl predation. Floods not only reduced the population but significantly interrupted breeding. Otomys irroratus was one of the most prominent prey species of both barn and grass owls. Recapture data revealed that the mean home range size was 1 443m2, while that of males (1 730 m2) was highly significantly different (P<O,Ol) from that of females (1 252m2). Home range size decreased significantly in winter but only slightly in relation to a doubling of the population size. Of 18 individuals recaptured after a flood, 12 (66,7 per cent) had returned to their previously determined home range. Despite a small mean litter size (2,33) and relatively long gestation period (about 40 days), the long breeding season (nine months) and precocial birth, rapid development, and nipple-clinging behavior of the young together give O. irroratus a good reproductive potential. Several litters of young were reared. They are precocial at birth and development proceeds rapidly. At birth the incisors are erupted, enabling the young to cling firmly to the nipples of the mother, thereby reducing mortality losses. Most adult behavior patterns are developed before weaning at 13 days of age. Sexual maturity is reached at approximately three months of age. Otomys irroratus is primarily crepuscular, but activity tests conducted in the field and laboratory indicated some activitv throughout the day and night. Individual and social behavior are described and discussed. The vlei rat is shy and retiring in captivity and in nature is not easily captured by the use of snap-traps. Interactions of adults were tested and they were found to be antisocial, with intrasexual aggression occurring when caged. Complex threat and communication patterns exist, a feature of asocial behavior. Mating failed to occur in captivity, probably as a result of their antisocial nature. Marking behavior is very distinctive and, combined with urination and possibly defecation, would appear to be useful in delineating territories. It would also appear from their social habits, marking behavior, and considerable overlap of home ranges that their interactions with conspecifics in nature are represented by a dominance hierarchy. The influence of O. irroratus upon the environment was found to be slight. The species serves as a common prey item for a number of predators and was found to harbor several endo- and ectoparasites of public health importance. / Thesis (DSc)--University of Pretoria, 1973. / gm2013 / Zoology and Entomology / Unrestricted