Conservation genomics of California towhee (Melozone crissalis) in
relation to the official list of endangered and threatened wildlife
Abstract
The Inyo County population of California towhee, now recognized as
Melozone crissalis, was officially listed as Threatened under the U.S.
Endangered Species Act in 1987. This isolated population in the Argus
Mountains was then estimated to consist of less than 175 individuals.
Its major threats were habitat destruction caused by grazing, mining,
water exporting, and human recreational activities but stakeholders
eventually developed a recovery plan to mitigate habitat damage. Due to
the demographic success of the recovery plan, the U.S. Fish and Wildlife
Service (USFWS) proposed to remove the California towhee from their
formal list of threatened and endangered species in 2013. Herein, we
generated a high-quality reference genome assembly for a typical
representative of the California towhee (N50 = 22 Mb among 627 contigs,
max contig size 89.1Mb), then conducted whole genome resequencing on
birds sampled from geographic sites across much of the species’ range.
Our findings indicate that the California towhee gene pool is relatively
deep (i.e., diverse; mean individual heterozygosity = 0.0021, range =
0.0013-0.0026) and that moderately low levels of autozygosity in
isolated populations are due to a combination of historic and
contemporary inbreeding. Our population, landscape, and phylogeographic
analyses indicate that the shallower (less diverse) regions of the gene
pool are likely due to a combination of natural geography, anthropogenic
impacts, and demographic histories associated with isolated habitats.
None of our findings are inconsistent with the 2013 USFWS proposal and
we see no reason to protest the delisting petition based exclusively on
genetic/genomic data.