Genome-Wide Loss of Diversity in the Critically Endangered Hawaiian Monk Seal

Abstract

Threatened species often exhibit low genetic diversity as a result of selective sweeps, historical bottlenecks, or persistent small population size. Whereas selective sweeps create localized reduction of variation at a chromosome, population bottlenecks result in the loss of rare alleles throughout the genome. Heterozygosity is lost more slowly and is severely impacted only when populations are small for an extended period of time. We test the hypotheses of selective sweep, historical bottleneck and persistently small population size to explain extremely low genetic diversity in the critically endangered Hawaiian monk seal (Monachus schauinslandi). Of 163 microsatellite loci isolated from the species' genome, only 17 are polymorphic. Mapping 98 monomorphic and 12 polymorphic loci to 35 chromosomes throughout the dog genome, we reject the selective sweep hypothesis. Genotyping 2,423 Hawaiian monk seals at the 17 polymorphic loci plus a locus previously isolated from another pinniped species, we find evidence for a recent bottleneck (P = 0.04). This is consistent with historical records describing intense hunting in the 19th century; however, the bottleneck was not of sufficient severity and duration to explain the genome-wide depletion of genetic diversity (H O = 0.05; A = 1.1). Long-term population size restriction is a more likely explanation. Though at least two of the OPEN ACCESSDiversity 2010, 2 864 polymorphic loci appear to be candidates for selection, the low genetic diversity of the species may further threaten chances for survival of this critically endangered species in a changing world.

Demographic histories and genetic diversities of Fennoscandian marine and landlocked ringed seal subspecies

“…; Schultz et al. ; Valtonen et al. ; see also O'Corry‐Crowe ), especially remembering that the reduced nuclear variation is paralleled by losses in mitochondrial haplotype (33.9%) and nucleotide (89.4%) diversity (Valtonen et al.…”

“…The worst phase of the current bottleneck has lasted as little as five generations, which evidently is not enough to have left a clear signal in the population‐genetic parameters of the studied subspecies (see also Schultz et al. ; Peery et al. ).…”

Culture, Conservation, and Conflict: Assessing the Human Dimensions of Hawaiian Monk Seal Recovery

“…comm. to J. N. Kittinger, 31 January 2011), and additional research on the genetics of the species is helping to further understanding of historical and contemporary population dynamics (e.g., Kretzmann et al, 1997;Schultz et al, 2008Schultz et al, , 2010. More historical research is needed to elucidate past population sizes and biogeographic distributions, which could help inform more appropriate recovery goals for the species.…”

“…Using genetic analyses, Schultz et al (2008Schultz et al ( , 2010 estimated a minimum population size of 23 seals at the nadir of the population bottleneck and postulated that extremely low genetic diversity in the population may be attributed to long-term harvesting pressure. The monk seal may have survived extinction because the last remaining rookery on Pearl & Hermes Reef in the NWHI remained undiscovered until after petroleum products eclipsed marine mammal oil as the primary product for lubricants and lighting (Atkinson & Bryan, 1914;Blackman, 1941), and because decreases in whale populations in the Pacific led many of the major whaling business interests out of the Hawaiian Islands (Beechert, 1991).…”

Tempering Expectations of Recovery for Previously Exploited Populations in a Fully Protected Marine Reserve

“…Further research is required to determine the impact of inbreeding depression on the population [36]. Genetic diversity has been virtually lost throughout the genome, likely as a result of long-term population reduction [36,[43][44][45][46]. Though genetic diversity is essential for population persistence and to mount an effective immune response [47], its contribution to the current decline of the species remains unknown.…”