Effects of a population bottleneck on Whooping Crane mitochondrial DNA variation

The Whooping Crane (Grus americana) is an endangered bird that suffered a severe population bottleneck; only 14 adults survived in 1938. We assessed the genetic effect of this human-caused bottleneck by sequencing 314 base pairs (bp) of the mitochondrial DNA control region from cranes that lived before, during and after this bottleneck. The maximum length of DNA amplifiable from museum specimens was negatively correlated with age, and only 10 of 153 specimens yielded the entire 314 bp sequence. Six haplotypes were present among the prebottleneck individuals sequenced, and only one of these persists in the modern population. The most common modern haplotype was in low frequency in the prebottleneck population, which demonstrates the powerful effect of genetic drift in changing allele frequencies in very small populations. By combining all available data, we show that no more than one-third of the prebottleneck haplotypes survived the human-caused population bottleneck. High levels of variation of substitution rates among nucleotide sites prevented us from estimating the prebottleneck population size. Our data will be incorporated into the captive breeding program to allow better management decisions regarding the preservation of current genetic diversity. These data offer the first glimpse into the genetic toll this species has paid for human activities.