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No evidence of genetic structure in a sky island endemic: implications for population persistence under a shrinking thermal niche
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  • Krista Oswald,
  • Shelley Edwards,
  • Alan Lee,
  • Susan Cunningham,
  • Ben Smit
Krista Oswald
Rhodes University

Corresponding Author:[email protected]

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Shelley Edwards
Rhodes University
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Alan Lee
University of KwaZulu-Natal
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Susan Cunningham
Percy FitzPatrick Institute of African Ornithology Niven Library
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Ben Smit
Rhodes University Department of Zoology and Entomology
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Mountain habitats physically isolated from one another (“sky islands”) represent a unique system for studying dispersal in seemingly isolated populations. The Cape Fold Belt of southwest South Africa forms a sky island archipelago of high-altitude mountain fynbos of which the Cape Rockjumper Chaetops frenatus is an avian-endemic. Continued contraction of habitat due to increasing temperatures may be causing further isolation of C. frenatus populations beyond their dispersal capacities, resulting in currently declining populations in warmer areas of their habitat. In this study, we sequenced two mitochondrial loci and one nuclear locus of 73 C. frenatus samples from 13 localities representing 8 mountain ranges. We found (1) low overall genetic diversity, (2) no evidence for geographically-based genetic structuring, and (3) no evidence for inbreeding within localities. While this may indicate birds are effectively dispersing, it may also indicate strong selective pressure is being placed on their specific genotype. Haplotype networks suggested that C. frenatus may have experienced a bottleneck or founder effect in their recent genetic past —- a result supported by a significantly negative Tajima’s D value. As the first avian genetic study to arise from a range-restricted species of the Cape Fold Belt sky islands, our results show no evidence that C. frenatus are unable to disperse across inhospitable lowland habitat, and thus may not experience isolation due to climate change. We thus potentially found further support that selective pressure in species with highly specialized habitat niches may have a stronger effect than dispersal limitations.