Browsing Masters Degrees (Genetics) by Author "Badenhorst, Rozane"
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- ItemGenetic diversity in a commercial black soldier fly, Hermetia illucens (Diptera: Stratiomydiae), population(Stellenbosch : Stellenbosch University, 2017-03) Badenhorst, Rozane; Rhode, Clint; Bester-van der Merwe, Aletta Elizabeth; Stellenbosch University. Faculty of AgriSciences. Dept. of Genetics.ENGLISH ABSTRACT: The applications of black soldier fly (BSF), Hermetia illucens, as a first-generation biotechnology address two global problems - the pressure on food security arising from unsustainable food production practices which exhausting fisheries resources by fishmeal production; and the vast accumulation of organic waste. Understanding the phenotypic and genetic changes experienced when establishing colonies of H. illucens is important for successfully establishing new colonies and managing already existing mass-rearing facilities. The aim of this study was to assess the changes in genetic diversity coupled with the phenotypic changes associated with colony establishment. Commercially-relevant phenotypic parameters were measured; including pupae weight, percentage eclosion, post-mating longevity, hatchability and egg clutch sizes over six successive generations (F0-F5). Hatchability, clutch size and pupae weight increased from F1 to F4, but a decline was apparent from F3 to F4. Post-mating longevity dramatically decreased from F1 (100%) to F4 (33%) and the F5 generation did not develop beyond the pre-pupae stage resulting in colony-collapse. The phenotypic changes can be explained by a combination of environmental, physiological and genetic effects. The positive trends observed during earlier generations (F0-F1) may reflect the population reacting to relaxed natural selection. While, at the end of the study period (F3-F5), natural selection in captivity resulted in a decrease in phenotypic variables. The colony collapse in the final generation, despite constant environmental conditions, possibly reflects the deleterious effects of random genetic drift and inbreeding depression. For the assessment of the genetic processes which may have resulted in the observed phenotypic changes, ten microsatellite markers were developed and characterised. Marker utility was tested on 37 wild individuals using three multiplex-PCR reactions. The number of alleles for each locus ranged from 4 to 21. Polymorphism information content ranged from 0.52 to 0.90, while observed and expected heterozygosity ranged from 0.30-0.65 and 0.55-0.91, respectively. Furthermore, the markers are useful in individual identification (PID = 1.2x10-11and PIDsib = 1.1x10-4) and parentage analysis (P1=1; P2 = 1). The markers proved useful in the assessment of genetic diversity and were used to understand the genetic mechanisms underlying phenotypic trends previously described. The assessment of genetic diversity revealed significant population differentiation as described by FST estimates across the experimental generations (P < 0.01), accompanied by a significant loss of genetic diversity. The final generation indicated a significantly higher number of private alleles and significantly lower observed heterozygosity in comparison to preceding generations (P < 0.05). Population bottlenecks and inbreeding were evident in the estimation of effective population size (Ne) and relatedness. Phenotypic parameters which significantly correlated (Pearson’s r) to changes in genetic diversity were pupation (%), clutch size, pupae weight and female post-mating longevity (P < 0.05). Results indicate the effects of inbreeding depression and genetic drift were amplified by a decrease in effective population size and increased relatedness amongst individuals. In summation, the assessment of changes in phenotypic measurements and genetic diversity during the establishment of an H. illucens colony, gave valuable insight into the genetic processes which occur during colony establishment; and are applicable to colony establishment and the management of already existing colonies.