Masters of Science / Although the processes that promote biodiversity and speciation remain poorly understood, ecological factors are thought to be one of the causal agents responsible for promoting variation. Bladder grasshoppers (Orthoptera; Pneumoroidea) are a group of endemic southern African insects that provide an ideal model system to study the role of ecology in speciation. All species rely on acoustic communication for mate location, with males producing an extremely loud advertisement call that is highly species specific. Any alteration to the male call would thus likely have implications for species integrity. In this study, I examined geographic variation as well as potential ecological drivers of biological diversity within Bullacris unicolor, a variable and wide-ranging species of bladder grasshopper. The main aims of the study were to characterise the extent of acoustic and morphological variation among individuals sampled from five geographic locations and to correlate this variation with environmental data and host plant use. At the inter-population level, I found significant differences between populations with respect to both morphological and acoustic characters. Results of multivariate analyses showed significant differences in the body length, pronotum length and head width of males and in the pronotum length, abdomen width and head width of females. Similarly, the acoustic signals of males from the five populations differed significantly in both temporal and frequency components, with all but one variable (peak frequency of the introductory syllables) showing a significant difference. However, there was no correlation between morphological and acoustic variables among populations, and acoustic characters showed far greater divergence among populations than did morphology. In both males and females, the morphological variables that differed among populations were negatively correlated with mean annual temperature, indicating that grasshoppers are larger in areas with lower temperatures. Also, some of the call characteristics of males were correlated with temperature, precipitation, altitude, and slope. Although grasshoppers were observed feeding on a range of host plant species, neither morphology nor signal characteristics were found to vary according to host plant. At the intra-population level, multivariate analyses revealed that all acoustic characters differed significantly among individuals. Morphology may be influencing signal properties within a population to some extent as there were significant correlations between some of the call characters and both abdomen width and tibia length, with lengths of these two morphological variables being positively correlated with temporal components of the call and abdomen width being negatively correlated with frequency components. I also found a significant difference in the carrier frequency of male calls, as well as in some of the morphological characters of males and females, according to host plant. This indicates that host plant use has a greater effect on variation at the intra-population level than at the interpopulation level. In conclusion, the results of my study reveal significant variation in the morphology and acoustic signals of B. unicolor, both within and among populations, and suggest that this variation is at least partially related to ecological factors.

Philosophiae Doctor - PhD / The order Orthoptera contains a wide diversity of species and is the most speciose of the polyneopteran insect lineages. In South Africa, the orthopteran fauna is abundant and diverse, with approximately 88% of all Southern African species occurring in the region. One highly endemic and conservationally important group, the Pneumoridae (commonly known as bladder grasshoppers), is recognized as being an evolutionary distinct lineage, with all species occurring either fully or partially within South Africa. Unfortunately, the understanding of the true extent of diversity for this paleo-relictual group is hampered by inaccuracies in current taxonomic descriptions and the lack of adequate survey data. The last taxonomic revision was undertaken >50 years ago, during which several taxonomic discrepancies and uncertainties were introduced, particularly within the genus Bullacris. Specimens may be difficult to classify due to significant morphological overlap between species, geographic variation within species, and confusion arising from alternative male morphs being designated as separate species rather than conspecific within existing species. Furthermore, paleo-relictual insects are of great evolutionary and biogeographical interest by virtue of being survivors of highly derived lineages, which allows for insights into the paleo-history and phylogenetic diversity of a region. Thus, the aims of this research were, firstly, to investigate the biogeographic patterns of diversity for South African Orthoptera and to place the Pneumoridae family into this context, secondly, to construct a molecular phylogeny for the Pneumoridae and estimate divergence times by genetically analysing the relationships between Pneumoridae species, and lastly, to update taxonomic descriptions in the genus Bullacris. Biogeographic analyses were performed by making use of a national orthopteran database created from historical and current collecting records, and performing hierarchical cluster analyses to delimit zoogeographic regions and centres. A dated phylogeny was created by extracting DNA from fresh and museum specimens, and generating Bayesian Inference, Maximum Likelihood and BEAST phylogenetic trees for the Pneumoridae family. The updated revision of the genus Bullacris included morphological, acoustic and genetic comparisons. Results from the biogeographic analyses showed that there was a clear east (summer-rainfall) and west (winter-rainfall) primary biogeographic division for orthopteran species, which has also been previously noted for other insect taxa. Six zoogeographic centres were retrieved: the Central Nama-Karoo, the Cape Fynbos and the Succulent Karoo centre located in the west and the Savanna, the South-East Tropical and the Indeterminate Summer-Rainfall centre located in the east. Orthopteran species richness was found to be evenly distributed throughout the bladder grasshoppers diverged from other orthopteran species during the early Cretaceous period, at an estimated 134.70 MYA. The first group to have diverged within the pneumorid family were the Forest species at approximately 116.91 MYA, followed by the Fynbos, the Succulent Karoo and then the Savanna species groups. It is suggested that bladder grasshoppers originated in South Africa and dispersed northward due to climatic changes. In addition, the phylogeny of the family showed that the species Physemacris variolosa integrated with members from the Bullacris genus. Lastly, the taxonomic revision of the Bullacris genus indicated that B. discolor and B. serrata were acoustically and morphologically similar, and had relatively low mitochondrial pairwise variation, and could thus possibly be represent sub-species. In addition, B. membracioides and B. intermedia were acoustically similar and also had low mitochondrial pairwise distances; however, statistical analyses showed significant morphological differences. Therefore, there was insufficient combined evidence to amalgamate species. Nevertheless, there are several environmental factors that could explain these variations, and it is therefore suggested that additional data is required to solve these taxonomic discrepancies. The results derived from this research have provided interesting insights into the evolutionary history of the Pneumoridae, the environments in which they occur, and share with other orthopteran species. Together with the newly discovered phylogenetic relationships and biogeographic studies, this information is useful data for conservation management strategies and expands our knowledge on the evolutionary histories of South Africa’s entomofauna.country; however, the Cape Fynbos centre has representatives for most orthopteran families. The dated phylogenetic analyses revealed that