Population diversity and relatedness in Sugarbirds (Promeropidae: Promerops spp.)

Abstract

Sugarbirds are a family of two socially-monogamous passerine species endemic to southern Africa. Cape and Gurney's Sugarbird (Promerops cafer and P. gurneyi) differ in abundance, dispersion across their range and in the degree of sexual dimorphism in tail length, factors that affect breeding systems and potentially genetic diversity. According to recent data, P. gurneyi are in decline and revision of the species' IUCN conservation status to a threatened category may be warranted. It is therefore necessary to understand genetic diversity and risk of inbreeding in this species. We used six polymorphic microsatellite markers and one mitochondrial gene (ND2) to compare genetic diversity in P. cafer from Helderberg Nature Reserve and P. gurneyi from Golden Gate Highlands National Park, sites at the core of each species distribution. We describe novel universal avian primers which amplify the entire ND2 coding sequence across a broad range of bird orders. We observed high mitochondrial and microsatellite diversity in both sugarbird populations, with no detectable inbreeding and large effective population sizes.

Keywords: Conservation genetics; Molecular ecology; Ornithology; Phylogeography; Population genetics; Sexual selection.

Figure 1. Sugarbird species distributions and sampling sites.

Distribution of Cape (red) and Gurney’s (green) Sugarbirds. Large circles show sampling sites at Cape Town (lower left) and Golden Gate Highlands National Park (mid right), respectively. The small circle indicates the single sample of P. gurneyi from Sani Pass. The base map of Southern Africa was QGIS while data on Sugarbird occurrence is from the South African Bird Atlas Project 2 (sabap2.adu.org.za) updated in May 2018.

Figure 2. ND2 haplotype networks for Cape and Gurney’s Sugarbirds.

Mean uncorrected sequence diversity is 0.24% in P. cafer (maximum 0.6%) and 0.12% in P. gurneyi (maximum 0.3%). Net divergence between species is 2.70% (28 nucleotide differences), ranging from 2.70 to 3.07% (28–31 differences).

Figure 3. Distribution of relatedness estimates in Cape and Gurney’s Sugarbirds.

Histograms of Queller & Goodnight’s (1989) relatedness statistic among (A) 49 Gurney’s sugarbirds from Golden Gate Highlands National Park and (B) 63 Cape Sugarbirds from Helderberg Nature Reserve. Columns indicate the rescaled density of pairwise relatedness values in each population, red lines are smoothed curves matching the shape of each distribution. This measure varies from −1 to 1, with 0 representing Hardy-Weinberg expected similarity of multilocus genotypes, negative values indicating genotypes that are less similar than expected from random resampling the data, positive values show genotypes that are more similar than expected under random resampling.