Browsing by Author "Hoffmann, Lelanie"
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- ItemGenetic diversity and mating systems in a mass-reared black soldier fly (Hermetia illucens) population(Stellenbosch : Stellenbosch University, 2021-03) Hoffmann, Lelanie; Rhode, Clint; Bester-van der Merwe, Aletta Elizabeth; Stellenbosch University. Faculty of AgriSciences. Dept. of Genetics.ENGLISH ABSTRACT: Black soldier flies are gaining popularity as an alternative source of protein in animal feed. They have a high feed conversion ratio and can be reared on biowaste, reducing the energy input required for mass-rearing. As the number of mass-reared colonies is increasing worldwide, the importance of genetic management in commercial populations is becoming clear. This study aimed to determine the effects of domestication and mating behaviour on the genetic diversity of a mass-reared black soldier fly population. Eight microsatellite markers were used to estimate genetic diversity in two temporally separated samples of a wild black soldier fly colony (Wild2015 and Wild2018) and three distinct generations of a mass-reared black soldier fly colony (F28, F48 and F52). Diversity estimates decreased significantly in the mass-reared colony over time, when compared to the two wild samples. The mass-reared colony also saw an increase in relatedness over time, with a relatedness coefficient as high as 0.430 in generation F48. These results indicate severe inbreeding in the mass-reared colony. Effective population sizes of between 22.6 and 59.0 in the mass-reared colony are also a cause for concern, as populations with low effective population sizes are more vulnerable to inbreeding depression and extinction. The high levels of genetic diversity observed in the two wild samples provide the potential for the wild colony to become a donor population, providing immigrants to introduce genetic diversity into the mass-reared colony. However, based on FST estimates, the two populations appear to be diverging from each other over time. Moderate differentiation was observed between Wild2015 and F28 (FST=0.062; p=0.000), while great differentiation was observed between Wild2018 and F52 (FST=0.161; p=0.000). To minimise the risk of outbreeding depression, the compatibility of wild individuals with the artificial environment would therefore need to be tested before immigrants are introduced into the mass-reared population. To study the mating behaviour of the black soldier fly, five mating pairs were randomly sampled in copula from generation F48 of the mass-reared colony. All candidate parents and 25 offspring from each clutch were genotyped and subjected to parentage analysis. Multiple paternity was detected in two of the five families, providing evidence for polyandry. This was a novel finding, as observation had previously led to the hypothesis that this species is monogamous. The occurrence of polyandrous mating provides evidence that adult flies can mate multiply despite being unable to replenish energy through feeding, thereby creating the potential for polygynous mating. Additionally, polyandrous mating has positive implications for the genetic management of commercial black soldier fly populations. However, these results are limited to mass-reared colonies, as the higher population densities found in captive populations increase the probability of remating. Finally, diversity estimates and inbreeding estimates were calculated for the candidate parents, offspring, and the population the parents were sourced from. Individual parent pairs showed increased levels of relatedness when compared to the source population, indicating positive assortative mating. As markers from random genomic regions were used for this study, the observed increase in relatedness may provide additional evidence for inbreeding in the mass-reared population. However, inbred populations show greater genome wide linkage disequilibrium, meaning that mate selection for desirable traits could potentially be detected in markers not directly related to traits of interest.