DNA Barcoding—a Windfall for Tropical Biology?

'I AM STANDING IN A COSTA RICAN RAIN FOREST', writes tropical ecologist and conservationist Dan Janzen (2005). 'There are a thou sand species of plants within a long stone's throw. Nearly every one of them is a described species with a proper scientific name, a handle that you can plug into Google and come up with something.... And I cannot identify a single species. Imagine what it would do to any and all aspects of human interactions with wild plants if you could walk up to any plant anywhere-seedling, sapling, 40 m tree, grass, root, pressed leaf, or fallen log-and know in a few seconds its scientific name'. Janzen, one of tropical biology's more ardent advocates, po etically describes the taxonomic impediment that exists today for many ecologists and evolutionary biologists working in the field: determining the correct species identification for any plant sample in a fast and repeatable fashion. In fact Janzen knew when he wrote this passage that a rapid and accurate method is now being devel oped and refined for the quick identification of plant species based on extracting DNA sequence from a tiny tissue sample from any part of a plant. Appropriately called 'DNA barcoding', referring to the coded labels one finds on commercial products, DNA barcodes consist of a standardized short sequence of DNA between 400 and 800 base pairs long that can be easily generated and characterized for all species on the planet (Savolainen et al. 2005). These genetic barcodes will be stored in an open access digital library that can be used to compare the DNA barcode sequence of an unidentified sample from the field, garden, or market by matching it to a known sequence with an associated species name in the data base. DNA barcoding has the potential to greatly advance our access to the col lective knowledge of biodiversity and in turn our understanding of Nature. By harnessing advances in molecular genetics, sequencing technology, and bioinformatics, DNA barcoding will allow users to quickly and cheaply recognize known species and retrieve informa tion about them. It may also speed the discovery of the thousands of species yet to be named. Barcoding, if developed sufficiently, will be a vital new tool for appreciating and managing the Earth's immense and changing biodiversity (Cowan et al. 2006). And most of that diversity is in the tropics. Some of the basic questions about tropical ecosystems that biologists have been attempting to answer over the last century re quire an estimate of species diversity. Why do tropical biomes have greater species diversity than temperate zone habitats? How is this species richness maintained in time and space? What are the ecolog ical and evolutionary processes that influence species composition in tropical forests? Answers to some of these broad questions ini tially require accurate assessments of the level of species diversity in a particular habitat. These assessments must have accurate species identifications and, ideally, a uniform species definition. As tropical biologists, we all know how difficult it is to obtain accurate identifi cation of organisms in species-rich tropical forests. DNA barcoding will provide a new tool that will supplement traditional methods and allow us to more independently assess this overwhelming species diversity.