Genetic Evidence on the Historical Biogeography of Central American Howler Monkeys

Abstract

The study described in this chapter aimed to elucidate the historical biogeography of howler monkeys in Central America. We expected to find evidence supporting an invasion from a common ancestor of the three species proceding northward from South America into Central America, with mantled howlers and black howlers being sister species that diverged after the northward invasion of a common source population. We examined patterns of variation at eight microsatellite loci across three populations of mantled howler monkeys ranging from Southern Mexico to Panama, and one population each of black howlers (Belize) and red howlers (Venezuela). The data reveal a broad pattern of declining genetic variation from south to north in mantled howlers, and a closest relationship between the two most northerly sampling sites, consistent with the hypothesis of an historical invasion from the south. These populations are also genetically distinctive, indicating limited gene flow among them. Another result that matched our a priori expectations was that the red howler population exhibited the greatest genetic diversity in our comparisons. We were surprised, however, to find that black howlers were the most genetically distinctive population in our data set, suggesting that they are not the sister species of mantled howlers. We suggest to hypotheses that could explain this result. First, black howlers may have decended from a different invasion of Central America that predated the one leading to mantled howlers. Second, black howlers may have arrived in Central America via a different route than that taken by the ancestors of matled howlers. Specifically, they may have used the islands of the Caribbean archipelago as stepping stones to reach their current location without moving up the Isthmus of Panama.