Project Title: EAGER: Cavefishes of the Guangzi Karst Region in China Investigator: Soares, Daphne Project Number: IOS 1048820
This research plan investigates how animals adapt to new environments. Specifically, the proposal examines how evolution has changed the sensory modalities that allow vertebrates to thrive in the perpetual world of darkness found in caves. Do species adapt in their own way or there are rules that they must follow? Is there interplay between sensory modalities during evolution? How are nervous systems constrained by their environment? These questions are especially interesting in caves because the harsh quality of the environment provide unique insights into the malleability of nervous systems over time. This proposal compares the behavior, neuroanatomy and genes of many species of cavefishes. These animals have a diverse phylogeny and various completely unrelated species have independently colonized caves all over the world. Examining unrelated animals can point towards general rules of evolution and comparative studies create an intellectual framework for the study of adaptation. China contains the majority of reported cavefishes in the literature and this project funds preliminary work between the University of Maryland and the Shanghai Ocean University. Researchers and students will be examining rare, unique and often undescribed species of cavefish in the Guangxi autonomous region. Aside from studying the organisms themselves results are likely to uncover conservational issues that may impact the long term survival of these animals. This proposal not only addresses unique biological questions in possibly endangered species, establishes a new international collaboration, but also creates a venue for undergraduate students to learn essential aspects of Biology.
Subterranean habitats prevail on the continental mass. In fact, the entirety of air-filled and water-filled cavities beneath the Earth’s surface may even be more common than surface habitats. For example, 97% of all unfrozen freshwater is subsurface, while rivers and lakes account for less than 2%. Subterranean habitats also house a substantial and often underappreciated biodiversity ranging from bacteria and fungi to crustaceans and insects to vertebrates, such as fishes, salamanders and bats. It has even been estimated that up to 40% of the planet’s prokaryotic biomass may be underground. However, subterranean organisms remain one of the least understood faunas, partly because of the difficulty in exploring and sampling the natural cavities found underground. The central south Chinese province of Guizhou is renowned for its Karst environment. The landscape is covered with Karst cones and is deeply incised by fluvial canyons. Caves are mostly of phreatic origin, with both active and multiple high-level fossil systems, indicating a long history of episodic uplift and renewal. This region hosts most of the 92 described cave fishes in China, which represent nearly one third of all described cave fish species in the world. Little is understood about these animals, their microhabitat, behavior, phylogeny and especially nervous systems. The region is the most promising in the world for comparative studies. Extant cavefishes are replicate experiments in adaptation to an extreme environment. Various surface dwelling fish species have independently invaded caves throughout evolutionary time. Thus, the existence of independently derived cavefish forms provides a unique opportunity to examine parallel evolution and convergence. All cavefish ancestors had to outmaneuver and adapt to the harsh constraints imposed by caves and their perpetual darkness. As a result, a suite of unique troglobitic phenotypes emerged, with loss of pigmentation and eyes being the most prominent. Cavefishes however, are outcomes of not just regressive evolution but also constructive adaptation. Cavefishes are especially suited for comparative studies because of their diverse phylogeny and their independent adaption to various cave types. What do these individual adaptation events have in common? What is the most significant constraint after darkness? Are all caves the same? How does the microenvironment of caves, such as rivers with high current, play a role in sensory adaptation? Would sensory preadaptations from ancestors dominate cave adaptation? Only comprehensive studies that span the environment, genotypes and sensory biology phenotypes can begin to answer such questions. The aims of the NSF EAGER 1048820 award were twofold: 1) To examine cavefish exploratory behaviors in complete darkness. 2) To establish the unique morphological characteristics of the brain and mechanosensory organs of cavefish. During the tenure of the award, the PI Soares and the post-doctoral fellow Niemiller spent time in China where they examined the caves in the Guizhou province with collaborators from Shanghai Ocean University and the Guizhou Normal University, as well as analyzed data. Guizhou is the least explored province in the region and little is known about its cavefishes and caves. Although they collected various species of hypogean fishes, the two most notable troglobites were one new species of Triplophysa spp. (Figures 1 and 2) and one species of Synocyclochelus (S. longibarbatus, Figure 3). The new species of Triplophysa is a cave loach and is unique because it has no eyes, small brains and seems to use its lateral line, fins and barbs for tactile sensation. It has no phototactic response and is a true troglobite. The PI achieved all outlined goals for this award: 1) She established a long term relationship with Chinese researchers (she is invited to return in 2014), 2) She mentored a postdoctoral fellow, graduate students (Chinese) and undergraduates, 3) She disseminated information via presentations, interviews and publications; and in addition the team was able to 4) discover a new species of cavefish.
