Toll-like Receptor genes in Southern ground hornbill (Bucorvus leadbeateri)

Project: Research

Project Details


Southern Ground-Hornbills, (Bucorvus leadbeateri) are globally listed as Vulnerable (BirdLife International, 2016) and are regionally listed as Endangered within the southern extent of their range (Simmons et al., 2015; Taylor & Kemp, 2015). The species faces several threats including persecution for window breaking, being trapped for the aviculture trade or for traditional cultural rituals and medicines, poisoning by bait meant for pest species as rats, jackals, feral dogs, leopards and hyenas, electrocution on transformer boxes (Jordan, 2011a), lead toxicosis from spent lead ammunition (Koeppel et al., 2015) and disease. An additional threat includes loss and fragmentation of suitable habitat, with its habitat increasingly transformed by the expansion of human settlements, subsistence farming, large-scale monoculture, and charcoal production, and degraded by bush encroachment and afforestation (BirdLife International, 2016). As the species is resident on permanent territories, local losses due to anthropogenic threats create gaps in an otherwise contiguous population. These threats may contribute to reduced population fitness due to decreased genetic diversity which may result in inbreeding depression and could lead to a reduction in the survival of the species (Gilroy et al., 2017). Understanding the genetic diversity of threatened species is essential for conservation and management purposes (Lei et al, 2016). Neutral markers such as microsatellite and mitochondrial DNA have been used to investigate genetic diversity, genetic structure and demographic history in this species, however they cannot determine reveal how a population will adapt in a changing environment (Grueber et al, 2012; Dalton et al, 2016; Xu et al, 2020). In recent years, research as included the used of adaptive genes such as Major histocompatibility (MHC) and toll-like receptors (TLRs) which are influenced by both demographic and selective pressures to investigate adaptive diversity. Many studies have focused on the analysis of the MHC which provides information for individual and population viability due to their direct association with immune function. However, the analysis of MHC loci is challenging especially when analysing loci in non-model organisms due to the high number of pseudogenes and duplications which may affect genetic diversity estimates. TLRs are a family of innate-immunity genes that recognize and bind to a variety of Pathogen-Associated Molecular Patterns (PAMPs). These genes are highly conserved and are responsible for initiating the innate and acquired immune responses due to recognition of a wide variety of pathogens. TLRs are therefore an important tool to investigate specific loci relevant for immune system function (Grueber et al., 2015). Sequence variations in the TLRs have been associated with variation in resilience to disease and infection and can influence the survival of species (Świderská et al., 2018). Compared to MHC, TLRs are relatively easy to sequence and can be more advantageous in assaying immune-gene heterozygosity by allowing diversity estimates for multiple genes. In birds, ten avian TLRs (TLR1LA, TLR1LB, TLR2A, TLR2B, TLR3, TLR4, TLR5, TLR7, TLR15 and TLR21) have been reported of which four genes (TLR3, 4, 5 and 7) have orthologs in other vertebrate groups (Roach et al., 2005; Khan et al., 2019). To date, ten avian TLR family members have been identified based on their functions and sequences in the red jungle fowl (Gallus gallus, NCBI: NC_006091.5) and other avian species (Wang et al, 2016). TLR15 appears to be unique to avian and reptile species, however it is phylogenetically related to TLR2.

The overall aim of this study is to investigate toll-like receptor diversity in Bucorvus leadbeateri. This information will contribute to a more comprehensive understanding of innate immunity, as well as measures of functional diversity to assist in the management of this species.
Effective start/end date1/08/1831/12/22


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