Investigating Impacts of Whole Genome Duplication on Immunogenetic Diversity and Parasite Load in Corydoradinae Catfish

Bell, Ellen (2018) Investigating Impacts of Whole Genome Duplication on Immunogenetic Diversity and Parasite Load in Corydoradinae Catfish. Doctoral thesis, University of East Anglia.

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Whole genome duplication (WGD) events have occurred repeatedly in the evolutionary history of plant and, less commonly, animal lineages, but their role as a facilitator of evolution is still not fully understood. Whole genome duplication events have been identified in the early history of vertebrates, teleosts and angiosperms and have been hypothetically linked to the large-scale diversification that has been described in these lineages. The Corydoradinae catfishes are a highly diverse sub-family of Neotropical catfishes with over 170 species described. A key feature of this subfamily is their history of whole genome duplication events.
Previous studies have divided the Corydoradinae into nine distinct lineages and Restriction site Associated DNA (RAD) sequencing data identified that lineages 2 to 9 had undergone a WGD event 35 to 66 MYA and lineages 6 and 9 had undergone a second WGD event 20 to 30 MYA. Species belonging to the Corydoardinae coexist in sympatric and often mimetic mixed species communities with representatives of two or more or the nine lineages. This makes them a novel animal system for exploring the effects of WGD.
It is well understood that hosts derive benefits from carrying immune genes with high levels of diversity. Polymorphisms in immune genes mean that there is a greater probability of detecting a wider range of pathogenic antigens and there is an intrinsic advantage in expanding the pathogenic repertoire that an immune system can respond to. Toll-like receptors (TLRs) are a type of pathogen recognition receptor that function as part of the innate immune system. We have compared TLR2 in single individuals across the nine Corydoradinae lineages. Results show that lineages 2 and 7 had very high levels of TLR2 diversity and that all lineages, except for lineage 1 and lineage 6, had retained more then two haplotypes of this gene. When examining TLR diversity in two TLR genes (TLR1 and TLR2) in two coexisting populations of Corydoras, C. maculifer (a lineage 1, diploid) and C. araguaiaensis (a lineage 9, putative tetraploid) we found greater functional diversity in C. araguaiaensis. We also found that C. araguaiaensis had retained four copies of these TLRs and had not, as is common in polyploids, lost additional haplotypes of the duplicated genes. Conversely C. maculifer had a surprisingly low genetic diversity in TLRs, comparable to that found in endangered and/or bottlenecked populations of other taxa. When looking at a greater suit of immune genes across the C. maculifer genome this lack of diversity in immune genes held true. After assessing the parasite burden of populations of these two species we found that although the proportion of infected individuals in C. maculifer and C. araguaiaensis were similar the intensity of the infection was higher in C. maculifer. The increased immune gene diversity and reduced parasite intensity in the putative tetraploid C. araguaiaensis may be rare direct evidence of the adaptive advantage of whole genome duplication.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Megan Ruddock
Date Deposited: 16 Apr 2019 09:33
Last Modified: 17 Sep 2019 00:39


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