Signal Evolution and the Origins of Biodiversity in African Mormyridae Fishes

点击翻译按钮获取中文摘要

During a pilot project funded by the NSF International Program, researchers at Cornell University, working in Gabon in Central West Africa, have discovered a new species flock of weakly electric fishes in the genus Brienomyrus of the family Mormyridae. So far they have discovered approximately 34 new species. All of these new fishes were uncovered during two field trips to the river basins of Gabon, in West Africa's equatorial rainforests. They are often morphologically cryptic, so they cannot be easily distinguished. What makes it possible to recognize different forms is their distinctive electric organ discharges (EODs) that facilitate identification in the field. EODs are essential for species recognition and reproductive isolation. There are three goals for the research program. First, the researchers hope to continue the successful fieldwork in Africa with new studies in Gabon, Ivory Coast, and the Congo in order to more extensively document the biodiversity of this species flock. They will collect specimens, make biogeographic distribution maps, make EOD recordings, and collect tissue samples for DNA analysis. Second, they will study the nature of sensory processing of the species-specific EOD waveforms of these fishes by making electrophysiological recordings from electroreceptors, when the receptors are presented with naturalistic electric discharges. Finally, they will do behavioral studies using the technique of playback to explore the stimulus preferences of females to EODs of electric fishes from conspecific and heterospecific individuals.Proposed Research. The researchers will use DNA sequences derived from multiple loci including both mitochondrial and nuclear genes to produce a species-level phylogeny for the newly discovered Gabon clade of Brienomyrus. They propose using multi-locus DNA fingerprinting techniques with amplified fragment length polymorphisms (AFLP) to provide hundreds of binary allelic characters for phylogenetic analysis. The species-level phylogenies will be used to reconstruct the evolution of the electric organs within these clades. A centerpiece of the study of the evolution of this species flock is a good molecular understanding of the evolutionary relationships of existing forms. From this, patterns in the evolution of signal diversity can be explored. In addition to the species-level phylogenies the field data will provide the first detailed information on geographical distribution patterns of these electric fishes. Integration of biogeography with phylogeny and electrical recordings will permit a detailed analysis of reproductive character displacement in EODs and geographic variation in EOD waveforms within species. A complete taxonomic revision of the genus Brienomyrus will be done to recognize the 34 putatively new taxa in a group that currently lists only 11. Recognizing the importance of international cooperation, the Cornell researchers will initiate collaboration with Gabonese fish researchers. Because of the central importance of electric signals in the systematic biology of mormyrids, the researchers will also create a web-site database of electric organ discharges that researchers can access to obtain field recordings of EODs from voucher specimens. The database will be used to archive and catalogue thousands of similar EODs collected during more than 20 years of field work in Africa, and it will set a national standard for recording signals tied to a systematic collection.Impact. These studies should have broad interest to researchers working in evolutionary and systematic biology. To discover a new species flock has intrinsic interest, especially when it concerns a well-known vertebrate group, but this particular group has potential interest to neurobiologists interested in comparative sensory and motor systems biology. The studies of behavior, neurobiology, systematics, and evolution of the Gabon-clade mormyrids will give us a better understanding of the mechanisms of evolution of new species.