Diversity is perhaps , the most outstanding feature of the living world. Traditionally, biological diversity was thought to arise mainly through de nova mutations that increase in frequency through natural selection or genetic drift. However, it is now recognized that hybridization between already divergent populations constitutes another important source of genetic and phenotypic variation, upon which natural and/or sexual selection can operate. Hence, the idea that hybridization can actually promote diversification is becoming increasingly supported. In this thesis work, I explore the role of hybridization in the origin of biological diversity. In particular, I have studied the structure of two overlapping hybrid zones between races of two mimetic species of Heliconius butterflies: Heliconius melpomene and H. erato, in Eastern Ecuador, South America. This thesis work is composed of four empirical studies: 1) a characterization of the phenotypic effects caused by the major wing colour-pattern loci that segregate in the studied hybrid zones, 2) a characterization of the hybrid zones in the field, 3) a field experiment to test whether frequency-dependent selection is maintaining the distinctiveness of the hybridizing races in spite of gene flow, and whether it explains the high abundance of one particular H. erato hybrid form, and 4) a quantification of continuous colour-pattern variation using a novel morphometric technique, which was then used for a preliminary QTL mapping analysis of colour-pattern at the chromosome level. The most outstanding finding of this thesis was the fact that the allele frequency dines for the two major colour-pattern loci segregating in the hybrid zone (D and Ac/ScfJ are significantly displaced from each other in both studied species. This dine displacement is associated with the high abundance of one particular hybrid form of H. erato. This hybrid phenotype is one of the possible homozygote hybrids (i.e. homozygote for the allele from one of the parental populations at one locus, but homozygote for the allele of the other parental population at the other locus). As a result, this hybrid breeds true when mated to its own kind, and could potentially form a self-sustaining population. It was hypothesised then that this particularly abundant hybrid phenotype might constitute a diverging hybrid form (i.e. a sort of incipient race). The implications of this hypothesis led to the field � � . experiment aimed at testing whether frequency-dependent selection was favouring the highly abundant hybri'd phenotype in the zone of cline mismatch. The results of this experiment were mixed but enlightening: even though I could not detect differences in attack rates associated with colour-pattern, I found that all tested colour morphs were significantly more attacked in the hybrid zone than in the parental .zones. This finding suggested that predation against all colour morphs is stronger in t~e hy�b�nd ~one. The implications of all these results for the role of hybridization in biological d1vers1f1cat10n are discussed extensively in this thesis. By studying the genetic bases of colour-pattern as well as the dynamics of hybridization in the wild, this thesis work is making important contributions to the understanding of the role of hybridization in biological diversification including thee reconstructin of a possible route through which novel hybrid phenotypes could be established in nature.

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Includes bibliographical references. / Francolins (Francolinus spp.) are small to medium-sized, sedentary, Old World, partridge/quail-like, terrestrial gamebirds (Order Galliformes) that occupy diverse habitats ranging from dry/open/scrubby lowland and montane grasslands, bushveld and savanna/woodland to mesic montane/lowland forests and forest edges. Some francolins have complex distribution patterns and also are morphologically, ecologically and behaviourally diverse. At the start of this research, Francolinus Stephens, 1819 was considered a monophyletic galliform genus comprising 41 species (36 African and five Asiatic) divided among eight putatively monophyletic species groups and four taxonomically enigmatic species. However, different taxonomic revisions, especially post Hall's (1963) classic monograph, challenged the monophyletic status of the genus and that of some of its designated species groups differed markedly in the number of recognized subspecies. Furthermore, there was debate concerning the geographical origin of the genus: Asia versus Africa. Some of the early molecular research on a few exemplar francolin species based on partial mitochondrial Cytochrome-b DNA sequences and Restriction Fragment Length Polymorphisms (RFLPs) also challenged the monophyly of the genus and that of some of Hall's (1963) species groups. These findings suggested that francolins may form at least two distantly related lineages called 'patryse' (partridges) and 'fisante' (pheasants) by Afrikaans-speaking people. Patryse, or 'true' francolins, had been divided into as many as five genera (Francolinus, Ortygornis, Dendroperdix, Peliperdix, Scleroptila) and fisante, or spurfowls, all grouped into a single genus, Pternistis. Research in this thesis is based on: mitochondrial and nuclear DNA sequences (5554 base pairs), organismal and vocal characters of francolins and spurfowls.

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Harvesting of Aloeferox was estimated (in 1996) to bring in an annual income ofR4 million per year to rural communities alone - a vital source of income for full-time tappers who rely solely on Aloe ferox as their only form of financial survival. They are joined on occasion by casual-tappers who rely on tapping to supplement their incomes in times of hardship (Newton and Vaughan 1996). Landowner's also benefit by allowing harvesting on their land in exchange for a percentage of the harvest (Newton and Vaughan 1996). Trade in bitters sap or gel far outweighs that of other plant parts so care is taken by harvesters to keep the plants alive for future tapping. Leaves from only the lower third of the leaf rosette ( 10 - 15 leaves) are harvested, and 2 - 4 cm at the base of the leaves are left to prevent damage to vascular tissues (Newton and Vaughan 1996, Mac Farlane 2004). Populations are only harvested every 18 - 36 months allowing plants to recover from the loss of leaf material. Plants suffering from insect-infestation or disease are not harvested to avoid weakening the plant further and possibly causing death (Newton and Vaughan 1996). Effort is also made by landowners to relocate plants growing in areas they plan to transform and to monitor harvesting activities on their properties (Newton and Vaughan 1996). The vested interest in keeping the plants alive has inadvertently assured the preservation of populations at past harvesting levels although no formal conservation or resource management policy presently exists for A. ferox (Newton and Vaughan 1996). Effects of harvesting, which are not limited to the direct effect of leaf removal on the plant but include indirect effects - such as reduced reproductive output, reduced sap production and even trampling of recruits - have nonetheless raised concern for the long-term survival of populations (Newton and Vaughan 1996). This study addressed some of the indirect effects of harvesting on Aloe ferox on both population and individual plants levels. On the population level plant density, mortality, susceptibility to disease and sizeclass structure was compared between unharvested and harvested populations. On the individual plant level vegetative traits, flower production and sap production were compared between unharvested and harvested plants. One of few other studies on ecology of A. ferox by Hoffman (1988) assessed some of these characteristics for a population in Port Elizabeth, South Africa.

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This report investigates the potential for the culture of G. gracilis, an indigenous red alga, into the west coast mariculture farm Jacobs Bay Sea Products Pty. Various methods for cultivating Gracilaria as well as environmental parameters, which influence growth of Gracilaria, are disltussed below. From these optimal conditions for the polycultivation of G. gracilis are determined. Cultivation can take place either, in open waters, or on land. Open water systems are generally less intensive than land based operations. Open water systems can be either bottom planted or suspended. Suspended cultivation has the advantage of maintaining the plant thalli in optimal light intensities. Land based systems can make use of ponds, raceways or tanks. Tanks and raceways are more productive than ponds, but require higher flow rates and regulated nutrient regimes.

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The hybrid zone between Calendulauda albescens and C. barlowi, located near the Orange River, contains a wide range of phenotypically intermediate individuals. This study examines the mitochondrial DNA of some of these individuals to determine if possible introgression is occuring from C. albescens to C. barlowi. Mitochondrial DNA from 13 lark individuals found in the C. albescens/C. barlowi hybrid zone was analysed. A 358 base pair cytochrome-b sequence was obtained. The neighbour-joining phylogenetic tree obtained revealed two distinct clades, a C. albescens and C. barlowi clade. The C. barlowi clade was supported with a bootstrap value of 100. The C. albescens clade contained individuals of intermediate morphology, as represented by their hybrid index scores, indicating that intermediates between the two species contain the mitochondrial DNA of only one species, C. albescens. These results point at introgression from C. albescens to C. barlowi, with female C. albescens choosing to mate with male C. barlowi.

No description available.