Mesoamerican Spider Monkeys: A Case Study

The taxon of Mesoamerican spider monkeys (Ateles geoffroyi sensu lato), which are found throughout southern Mexico and Central America, is presumed to include nine species. The validity of the phylogenetic relationships and their proposed assignment into a taxon has been a source of controversy. An example of this would be the difficulty of determining whether Mesoamerican A. geoffroyi forms a separate clade from Atles fuscipes. In order to determine the phylogenetic relationship of these species, pelage color, cranial measurements and mtDNA sequence data were evaluated. The results were conflicting: pelage color and cranial measurements determined that they represented a distinct species whereas mtDNA determine that they were subspecies.
The study utilizing mtDNA was proven incorrect because they only included samples of one species and none of the subspecies. The study that overcame this proposed phylogenetic relationship that A. geoffroyi and A. fuscipes were different species also utilizing mtDNA data from three neighboring coding regions. This study determined that A geoffroyi and A. fuscipes were indeed separate species and form distinct monophyletic clades. Although the phylogenetic relationships of species within these separate clades is unclear.
Most often pelage color and geography has been used to assign and determine the phylogenetic relationships between species. These methods have been a source of discord between scientists. This is because the variability found in pelage color leads to a range of proposed species. This is combined with the confusion surrounding the existence of some of the species. There are some scientists that have claimed to observe spidermonkeys in unlikely habitats and some have not been observed.
There has been only one previous study performed by Collins and Dubach that utilized genetic data to understand and validate proposed phylogenetic relationships of spider monkey’s. They were found little consensus between the phylogenetic relationships determined by genetic data and pelage. They were able to determine a northern clade and a southern clade but were unable to determine the evolutionary lineages of other presumed spider monkey species and to other different species. This was due to incomplete sampling. In this study, they further explore the phylogenetic relationships within this species utilizing mtDNA sequence data from a control region. This data was from a wide geographic range and from a variety of individuals. It was used to determine if species from sample populations that are supported by a variety of authors, the IUCN Red List of threatened species and presumed subspecies formed separate monophyletic groups.