Case Study
Submitted By
| Name: | Miguel Vences |
| Institution: | Technical University of Braunschweig, Zoological Institute |
| Country: | Germany |
| Email: | m.vences@tu-bs.de |
Title & Categories
| Case Study Title: | Identifying frog tadpoles by DNA barcoding: applications in ecology, conservation biology and systematics |
| Focus Theme: | Associating life stages/genders |
| Geographic Region: | Africa |
| Habitat Type: | Terrestrial tropical forest |
| Taxonomic Group: | f: Amphibia |
Scope
The scope of this project is to establish DNA barcoding as a tool to identify the larval stages of frogs (tadpoles) from tropical environments. A first step is to morphologically describe the identified tadpoles and assign them to species. A second step will be to develop tools for large-scale identification of tadpoles, ideally by automatized screening of pooled samples, to analyze their role in tropical aquatic environments. A pilot study is underway in Madagascar and gave very promising results. So far a reference database of DNA sequences from over 1000 adult frogs has been built and about 700 individual tadpoles (and attached series of large numbers of individuals) belonging to almost 100 species identified. DNA is taken from available tissue collections which to a great extent have voucher specimens deposited in major natural history museums. New collections will be assembled in the course of fieldwork in Madagascar and SE Asia. While the reference databases of adult frogs from Madagascar will be assembled soon and in the course of ongoing projects, funding is not yet assured for the extension of the project to other tropical environments and for the applications, that is, the screening of large amounts of tadpoles (an estimated minimum of 10,000 - 20,000) to understand their role in tropical aquatic environments and to use them for assessing hotspots of amphibian diversity and endemism in Madagascar and prioritizing conservation.
Purpose
Tadpoles are remarkable in that they represent a larval morphology radically different from the adult, which is exceptional in vertebrates. Most structures of the mouthparts are not at all homologous to those of adult frogs. Furthermore, whereas frogs are strictly carnivorous, most tadpoles are omnivorous suspension feeders, and many have striking trophic specializations. Studies of tadpoles are promising: (a) in ecology and limnology because they are relevant components of many aquatic environments, (b) in evolutionary biology because the large species diversity of frogs may have been triggered by key innovations in larval morphology and reproductive biology rather than adult morphology, (c) in conservation biology because global amphibian declines have been detected and these animals depend both on the quality of the terrestrial environment (in their adult phase) and aquatic environment (in their larval phase), and (d) in systematics because tadpole morphology yields a largely independent data set for morphological studies and species diagnoses. However, so far the identification of tadpoles depended on laborious rearing of eggs obtained from a well-identified mating pair of adults, or even more laborious rearing of wild-caught tadpoles through metamorphosis and tentative assignation of the juveniles to adults. Especially the latter is very error-prone in species-rich amphibian communities in the tropics. Here, DNA barcoding offers a fast and reliable alternative.
Background
The project is, to our knowledge, so far the only major DNA barcoding project in amphibians and uses mantellid frogs as a model group and Madagascar as a model region. The relative rareness of freshwater fishes in many small-scale aquatic habitats in mid-altitude rainforests in Madagascar increases the importance of tadpoles for these ecosystems and may have triggered special adaptations. In addition, tadpoles can be collected in different periods of the year and during the day, whereas adults of many species are only found in the rainy season and at night. Collecting tadpoles could speed up the ongoing process of rapid assessment studies to identify priority areas for biodiversity conservation in Madagascar. The work so far has progressed quickly. Almost 100 possibly new species of frogs have been discovered with the help of DNA barcoding, and for about 100 species the tadpoles were identified. At present a large taxonomic effort is being undertaken to describe the new species and many of the tadpoles are being described morphologically.
We plan to extend the studies to areas of South-East Asia in collaboration with Annemarie Ohler, Museum National d'Histoire Naturelle, Paris, and possibly to areas of South America and continental Africa.Logistics
The project is at present a collaborative effort of several laboratories and scientists who all are participating in different aspects of it. Sequencing has been carried out at the University of Amsterdam, Netherlands (M. Vences), University of Cologne, Germany (M. Thomas, lab of D. Tautz), University of Konstanz, Germany (Y. Chiari, lab of A. Meyer) and University of California at Berkeley (D. R. Vieites, lab of M. Wake). Lab protocols are well-established and no additional expertise is needed. Initial funding was provided by the Volkswagen-Foundation (to M. Vences, F. Glaw and N. Raminosoa) to explore DNA barcoding as a tool for rapid assessments of amphibian diversity in Madagascar. New funding will be needed to proceed with the actual applications of the developed methods.
Amphibians in general are a challenging group for DNA barcoding because of a large intraspecific variability that overlaps with the amount of divergence between closely related species. In several papers we have provieded evidence that this method is nevertheless applicable and very useful to identify larval amphibians, but we use a different marker (the mitochondrial 16S gene) to complement COI because it is more universally applicable in amphibians. However, we also build up a COI database for our model groups as a contribution to the effort of CBOL.