Kim Lisa Hoke - US grants

Differences in reproductive behaviors can prevent interbreeding between populations, thereby promoting the formation of new species (speciation). How do differences in the brain contribute to behavioral divergence and speciation? This project combines functional neuroanatomy, genetics, and behavioral experiments to study differences in the brain that may lead to different mating decisions between populations in a single species. The researcher will focus on variation within a species of a frog, Physalaemus petersi. The experiments will test which sensory cues the females in the two populations of P. petersi are using to make their divergent mating decisions, and identify which brain regions function differently to cause these behavioral differences. The proposal is a novel attempt to understand fundamental questions about the neural mechanisms of natural decisions. The proposed work will take significant steps in linking evolution of the brain to the behavioral differences that, by promoting reproductive isolation between populations, may contribute to speciation. The proposed work will include numerous opportunities for training. Four US undergraduates and four Ecuadorian undergraduates will participate in the project and receive training in neuroscience, behavior, and field experiments. One of the Ecuadorian students will spend a semester in the US working with the researcher and the US undergraduates to experience the laboratory side of research in neuroethology.

This award addresses the evolution of sensory system reductions, that is, the decreases in structural size or complexity or functional changes that limit an animal?s capacity to sense the environment. Most terrestrial tetrapods have tympanic ears that convert the external vibrations of air particles to vibrations within the fluid-filled inner ear cavity containing the sensory end organs via middle ear structures. Diverse frogs and toads, however, have secondarily lost the outer and middle ears in independent evolutionary events, despite the general tendency for anurans to use acoustic signals for the social interactions that facilitate reproduction. This award supports an international collaboration designed to integrate natural history, auditory physiology, functional morphology, and evolutionary development to detail the causes and consequences of evolutionary transitions. The study system chosen is Pristimantis in Ecuador. Initial trips will provide the opportunity to locate populations of earless Pristimantis frogs, describe basic natural history of the earless species, and collect specimens for preliminary genetic and morphological analyses. The intention is to expand on this preliminary information in future studies.

The multi-disciplinary, international team will include scientists from Ecuador, Denmark, and The Netherlands. This award will support two female graduate students from the US in for trips to Ecuador, introducing them to fieldwork in South America and to the diverse expertise of the collaborating key individuals. Furthermore, Ecuadorian researchers and students would have a unique opportunity to learn about auditory physiology via an educational workshop. Results of this project are to be shared with the broader public via undergraduate teaching and lectures for the public in the US and in Ecuador. Finally this work will aid in frog conservation efforts.

Biologists still don't understand the mechanisms by which genetic and environmental influences interact to produce well-functioning organisms. This project takes advantage of the wealth of research on stress hormones in the Trinidadian guppy (Poecilia reticulata) to ask how differences in stress hormones coordinate favorable changes in traits influenced by these hormones such as behavior, color, and body size. To address these questions, the project measures hormone levels and various behaviors in fish reared in the laboratory using a breeding design that distinguishes the effects of genetic background and rearing environment. The project will reveal how long- and short-term environmental differences alter hormone levels and the consequences of changes in hormone levels on traits that influence guppy survival. The results will reveal the hormonal mechanisms by which genes and the environment interact to shape multiple traits. In addition, hormone levels - in particular stress hormone levels - are often used to predict health and fitness in wild and domestic animals, and understanding how genetics and environment interact to modify levels in natural populations will improve predictions of how animals respond to novel or changing environments, such as habitat degradation, invasive species, and climate change. This dissertation improvement grant will support the training of a graduate student and research involvement of multiple undergraduate students. The project will also reach out to local middle and high schools using guppies as a model for inquiry-based science in the classroom.

Most frogs and toads vocalize to communicate, and females typically use hearing to locate mates. Despite how essential tympanic ears are for hearing sound in air, outer and middle ear structures have been lost and regained many times in frogs and toads. This project integrates anatomy, physiology, development, and phylogenetic analyses to investigate the independent gains and losses of ear structures. Relating ear morphology to hearing ability will reveal novel mechanisms of hearing and will characterize the costs and benefits of various anatomical features for hearing low and high pitch sounds. Because the development of ear structures is linked to the development of other skull features, this project will identify changes in the size and shape of skull bones that accompany changes in ear structures. Moreover, developmental analyses will determine specific genetic and cellular changes that cause the loss of outer and middle ear structures, a type of ear defect that is a common cause of human deafness.

Integrative analyses of skull features will assess whether associated changes in skulls facilitate the diversity of ear structures, with data publicly available at Digimorph (http://www.digimorph.org/) and the CSU Digital Repository (http://lib.colostate.edu/repository/). The research in this proposal includes natural opportunities to better educate the general public and university students about hearing, biodiversity, and conservation. Within the US, this proposal will be integrated into undergraduate classes as part of a new laboratory approach to teach students to conduct and interpret statistical analyses. In addition, US undergraduates will participate in the research efforts and participate in developing a bilingual museum exhibition about frogs that will be displayed at one or more US science museums. The Ecuadorian toad breeding program and a related Ecuadorian museum exhibition will contribute to amphibian conservation at a key moment when road-building and resource extraction threaten to have major impacts on wildlife in Ecuador.

Genes shape how sensitive individuals are to environmental conditions during development, and this environmental sensitivity influences the behaviors produced in adulthood. This project seeks to understand how genes and developmental conditions together influence the brain, and how that alters social behaviors. The planned research takes advantage of extensive information on genetic and environmental influences on behavior of guppies, small fish that have evolved numerous behavioral responses to predators. Guppies that experience high and low levels of predation in the wild will be raised in laboratory conditions with and without predator exposure during development. Genetic and molecular experiments will link the patterns of gene expression in different brain regions to neural activity patterns and the resulting social behaviors. Results will demonstrate the extent to which similar behavioral traits (increased sociality in fish from high-predation sites and in fish exposed to predators) rely on the same gene expression changes and brain activity patterns, or whether similar behaviors may emerge from a variety of neural mechanisms. These findings will also reveal how sensitivity to environmental conditions shapes evolution of behavior. Developing this novel experimental approach will provide a model for other researchers seeking to understand the impacts of gene expression differences on behavior. The PIs will incorporate this research into undergraduate courses and will train graduate students via annual workshops on analysis of gene expression data. The simplicity and availability of guppies also make them amenable to enriching K-12 curricula in evolution and behavior, through development of a guppy module for for the Understanding Evolution resources for teaching evolution (http://evolution.berkeley.edu/). This project will allow the Colorado State University researchers to extend an ongoing program in which lab personnel work with middle school classes to design and implement behavioral experiments using guppies to reach a larger group of students.

Middle and outer ear structures are used for hearing sound and are shared by most land animals. Although frogs and toads use hearing to find a mate, many frogs and toads have lost their middle and outer ear structures. This project aims to discover the genetic changes that have resulted in the evolution of ear loss in toads. Since the middle and outer ears of other land animals (including humans) use similar developmental pathways, understanding the genetic changes that result in ear loss in toads will illuminate potential causes of middle and outer ear loss and malformation in other animals. The genetic data produced by this study will help us better understand the relationships between toad species and provide novel genetic data for future research. In addition to graduate training, interactive museum displays will be created from the specimens and data generated from the project, and a series of K-12 classroom exercises will be developed to explain the ear structure evolution in toads.

This project investigates the selection pressures and genetic constraints that generate convergent loss and potential regain of middle and outer ear structures across the family of true toads (Bufonidae). Sequence data for 60 bufonid species (16 earless, 44 eared) spanning seven ear loss events will be analyzed to identify signatures of selection and parallel genetic changes across 50 genes involved in middle and outer ear development. The dataset will assess the effects of various selection pressures and look for evidence of constraint at the genetic level, complementing the large amount of evidence for selection and constraint at the phenotypic level that has previously been collected by the research team. Results of this project will delineate the roles of selection and constraint in driving ear loss across Bufonidae, and elucidate common genetic pathways by which selection can act in a constrained, potentially costly, trait loss.