The effects of population bottlenecks on genetic diversity and rates of molecular evolution in Spheniscus penguins

The penguin genus Spheniscus is comprised of four closely related species that vary in geographic distribution, population sizes and population histories. Population bottlenecks in the Galápagos Penguin (S. mendiculus) and Humboldt Penguin ( S. humboldti) are induced by EI Niño events, while populations of African Penguins (S. detnersus) have decreased only recently due to human pressures. The fourth species, the Magellanic Penguin ( S. magellanicus) lives in large colonies that are not highly affected by El Niño events and have not experienced sharp declines in recent years. Given these different population histories, I predicted the species to show dissimilar levels of genetic diversity and rates of molecular evolution as well.; I used microsatellite markers and mitochondrial DNA to determine whether serial population bottlenecks in the Galápagos and Humboldt Penguins have resulted in relatively low levels of genetic diversity and higher rates of molecular evolution. The Galápagos Penguins do show significantly lower heterozygosity and allelic diversity in microsatellite loci than Magellanic Penguins. For instance, the Galápagos Penguin has only 3% heterozygosity at microsatellite loci, significantly lower that the 37% to 40% in Magellanic Penguins. However the Humboldt Penguins had relatively high diversity at microsatellite loci. The Magellanic Penguins have significantly higher allelic diversity than both Galápagos and African Penguins. Unlike the microsatellite data, the mitochondrial DNA results fit expectations; the Galápagos and Humboldt Penguins had fewer haplotypes than their congeners and lower nucleotide diversity.; Although the serial bottlenecks have resulted in low genetic diversity in Galápagos Penguins, there is no evidence that the bottlenecks have been severe enough to affect rates of molecular evolution. A battery of parsimony and likelihood tests did not indicate significant rate variation among taxa. While the Galápagos population has the genetic signature of a small population at risk for inbreeding, the population has remained large enough for selection to compete with drift at some loci.