H. Carl Gerhardt - US grants

The goal of Dr. Gerhardt's research is to gain knowledge about mechanisms and evolution of acoustic communication in vertebrate animals. In particular, the research will focus on temporal codes, that is, information encoded in the timing of repeated elements in natural communication sounds. Dr. Gerhardt will carry out behavioral studies of signal (sound) structure and the discrimination of these sounds, with both wild-type and hybrid animals, and he will also perform neurophysiological studies of the responses of auditory neurons to time patterns in sounds of biological relevance. Two species of North American gray treefrogs (Hyla chrysoscelis and H. versicolor) will be studied. These frogs are particularly suitable as a model system for vertebrate sound communication because males of each species produce a small set of very stereotyped communication signals. Females reliably respond to natural and synthetic (computer-generated) signals by approaching a loudspeaker, just as they approach a calling male in nature. The timing properties of the male's sounds are not learned, but develop normally when the frogs are raised in acoustic isolation. The two species will be cross-mated artificially to produce viable hybrids, thus affording the opportunity to study genetic mechanisms of both calling and selective approach to sounds. There are extensive areas where just one species occurs, and other areas where both species breed in the same ponds at the same time, at the risk of producing sterile hybrids if they make an error of identification. Thus, the selectivity of females from areas of overlap will be compared with that of frogs from areas where only one species occurs. The auditory system of treefrogs has been well studied, so that a great deal of basic information is already available as a foundation for the neurophysiological studies of time coding that will be done in these two species. In this research the results of the behavioral experiments will guide and complement the neurophysiological work. The results of this research should provide insights into fundamental properties of all acoustic communication systems in vertebrates. The treefrog system is especially powerful in that a combination of genetic and neurophysiological techniques can be used in ways that would be impossible in higher animals.

Polyploidy in higher animals is generally rare, but more than fifteen species of five different families of frogs and toads have been discovered. The subjects of this research are two widely ranging North American gray treefrogs - the polyploid species Hyla versicolor, a tetraploid (2 times normal chromosome number) and its diploid counterpart, h. chrysoscelis. The main goal is to learn if H. versicolor arose more than once from H. chrysoscelis or as a hybrid between ancestral h. chrysoscelis and another diploid, h. avivoca. The multiple-origin hypotheses will be tested by comparing the nucleotide sequences of mitochondrial DNA from frogs of all three species from widespread areas through their distribution. The hypothesis of multiple- origin will be supported if in an evolutionary tree based on sequence data, different populations of H. versicolor occupy different branches. In other words, the two species in the same area of the range would be more similar to each other than individuals of the same species from different parts of the range. A second goal is to compare differences in the acoustic properties of the mating calls of H. versicolor and H. chrysoscelis in areas where they occur together (sympatry) with differences between areas where only one species occurs (allopatry). Because the frogs use mating calls alone to identify correct mates, and because mismatings lead to sterile, triploid hybrids, the working hypothesis is that differences within sympatry will be greater than differences between allopatric populations.

9508741 Gerhardt Explaining how genetic variation arises, is distributed among organisms, and is maintained over time is a major goal of evolutionary biology. Genetic variation in the characteristics that determine an organism's reproductive success is especially important, because it underlies the capacity of species to perpetuate themselves successfully under new environmental challenges. For animal-pollinated plants, one such attribute is flower form. Flower morphology is a complex trait that simultaneously influences plant resource use, the behavior of enemies, and the likelihood of pollination. This proposal addresses the environmental factors maintaining morphological variation in the flowers of one of the most abundant and ecologically dominant flowers of the Rocky Mountains, Polemonium viscosum. Specifically, experiments will test whether the large showy flowers preferred by animal pollinators exact a high cost in resources for future growth and survival and/or make plants more apparent and susceptible to flower predators. Such ecological tradeoffs could explain why genetic variation in flower form persists over time in P. viscosum and nearly every other natural and agricultural plant species that has been studied. Current farming expenditures on crop fertilization, irrigation and chemical pest management are considerable. The research described here could reduce such costs by suggesting how flower form can be genetically optimized to alleviate the amount of resource diverted from plant growth and the number of ovules lost to pest damage, while continuing to ensure adequate pollination. In this way, the proposed studies have the potential to make the cultivation of sunflowers, blueberries, strawberries, alfalfa and rapeseed, among myriad other animal-pollinated crops, more economical and environmentally sound.

This research project addresses the general question of how evolutionary changes in preferences for species-specific calls track changes in the characteristics of those calls. The question is addressed through studies of artificially produced polyploid treefrogs in a complex in which a tetraploid (two extra sets of chromosomes) species has evolved multiple times. The main aim is to determine if the preferences of artificially produced autotriploids (one extra set of chromosomes) and autotetraploids shift in parallel with changes in call characteristics in male polyploids. Parallel change would facilitate rapid speciation and indicate that such coordinated changes in communication systems may occur in all animals experiencing polyploid speciation, including all vertebrates, for which there is evidence of two ancient chromosome-duplication events. Furthermore, a significant consequence of polyploidy is an increase in cell size. A shift in the preferences of artificially produced polyploids would have important implications for studies of the mechanisms of hearing in all vertebrates, including humans, in which some pathologies are correlated with cell-size changes. This research affords educational opportunities for undergraduates and graduate students (including currently enrolled minorities and women) working on this project. This laboratory has a strong record of publishing results in scientific journals and lay publications.

9520553 Gerhardt Monocarpy, in which plants grow for several years then undergo one, fatal bout of reproduction, should be favored when a plant experiences a disproportionately large gain in fitness by investing all the resources it has available for reproduction at once. Previous research in plants has focused on how monocarpy might benefit the adult plant during its own lifetime through enhanced mating success. The proposed research will test whether monocarpy also confers fitness benefits by allowing plants to provide maternal care or nurse effects that directly increase offspring survival during seedling establishment. This research will enhance basic understanding of how selection on maternal care shapes the life-history attributes of plants. It will be among the first studies to incorporate consideration of parental care into explanations of plant reproductive strategies.

9727623 Schwartz Animal communication in nature involves detection of important signals in a noisy environment. In gray tree frog mating choruses calling males attempt to attract mates, females must discriminate among large number of competing calls and use this acoustic information to choose among competing males making this an ideal setting in which to investigate such signal discrimination in a noisy environment. The proposed research will also improve our understanding of mate assessment in nature and competition among males. Females of the gray treefrog base their choice of mate solely on acoustic criteria. In the intensely competitive environment of a chorus, males change their calls in a way that laboratory experiments suggestshould improve their attractiveness. However, we don t know how well females can assess males in the complex acoustic environment of a chorus or why certain patterns of calling are preferred. Nor are the fine details of the vocal competition that occurs among males or the relationship between these details and male condition understood. This research, using field-based tests of female choice and laboratory studies of male vocalizations, will help answer these questions in addition to addressing the general problem of signal detection in a noisy environment. Experiments will use a computer-based interactive playback system, that constitutes a new methodology for application to studies of animal communication.

In nature, animals recognize their neighbors. This research will examine the foundation of how psychological mechanisms of recognition play a role in this widespread phenomenon. Territorial male bullfrogs recognize their nearby neighbors by the distinctive properties of their acoustic communication signals, or songs. Three acoustic playback experiments will address four unanswered questions about neighbor recognition: 1) Does the perceived fighting ability of new neighbor's affect the establishment of new territorial borders? 2) What is the relative importance of locational and acoustic cues in mediating recognition of neighbors? 3) How important are physical interactions during the establishment of territorial borders? 4) What is the role of memory in recognizing a neighbor?

The experiments will extend previous investigations to more focused and interesting questions about the psychological mechanisms of recognition, providing an opportunity to gain deeper insight into the operation of these mechanisms in nature. The results will provide a foundation for future studies examining the precise nature of the learning experience involved in neighbor recognition. Because much is known about the processing of acoustic signals by the frog nervous system, the behavioral experiments in this proposal can form the basis for future neurophysiological investigations of neighbor recognition. This proposal continues a recent and important trend toward integrating behavioral, ecological and psychological approaches in the study of animal behavior.

Animal Behavior Program
Nontechnical Abstract

Proposal #: 9816433
PI: H. Carl Gerhardt
Title: Request for Travel Grant for the XXVI International Ethological Conference to be held in Bangalore, India 1999

This request is to provide support for up to 14 young scientists that would help defray the costs of attending the XXVI International Ethological Congress. This is the most important international ethological meeting held. It will attract participants from all over the world. In the past this conference has been extremely well attended and successful.
Attendance at this meeting will be very beneficial to the young scientists who otherwise would be unable to participate in this international gathering. Contacts for future international collaborations will be made and interchange of ideas will occur.

Male animals may use several different behaviors to obtain mates. In the case of the green treefrog, some males remain silently positioned next to a calling male and attempt to intercept females attracted to that caller (satellite mating tactic). Using multiple speaker playbacks of frog calls to simulate and control a socially complex environment, investigations of how a male's ability to compete with other individuals for access to mates influences his use of different mating behaviors
will be conducted. It will also be determined whether males adopting the satellite mating behavior take advantage of female call preferences for mates by becoming satellites of attractive males, thereby maximizing the benefits of the behavior.

Behavioral differences among individuals may have a purely genetic basis; however, individuals in many species are flexible in their behavioral choices and adopt the tactic that best fits their current
needs. Scientists have a relatively poor understanding why individual behavioral variation exists and how the animal's social environment may mediate this behavioral variation. This study will contribute to our understanding of how male-male competition and female mate choice shape
a behaviorally complex mating system.

This research focuses on how the complex chorus environment influences communication in two closely related species of gray treefrogs. Specific objectives are to determine if there are differences between the species in the frequency with which receivers (females) commit errors under less than ideal communication conditions, and to investigate whether male signaling strategies differ between the species in ways predictable by receiver behavior. These objectives will be addressed by (1) monitoring calling behavior of males and mate choice by females in natural and artificial choruses, (2) exposing females to multiple synthetic call sources presented to mimic chorus complexity, and (3) investigating male signaling interactions with artificial signals varied to represent differing social conditions.

How the signals of animals are designed to transfer information to receivers has been of interest to investigators of behavior for some time, but environmental influences on uncertainty in communication have often been ignored. To understand how a communication system may have been evolved, it is necessary to determine how signalers and receivers interact under realistic conditions. Because of their readily observable and stereotyped communication behavior, frogs are ideal for investigating interactions between signalers, receivers and the environment.

Interactions between good genes and the environment in the gray treefrog
H. Carl Gerhardt
University of Missouri

The evolution of mating preferences and of the male displays favored by these preferences can occur if display traits are correlated with genetic quality: offspring of males with attractive displays should then inherit "good genes," resulting in the benefit of high quality offspring for preferring females. Implicit in this scenario is the requirement of ample genetic variation in the display trait and a genetic correlation between the display and components of offspring fitness. How is this genetic variation maintained, and how does the environmental variation that is experienced by most natural populations affect the genetic relationships between female preferences, male traits, and the quality of their offspring?
Using gray tree frogs as a model system, this study will investigate the relationship between an attractive male display trait - call duration - and offspring fitness in different environments. In particular, the study will determine how the genetic quality of the father, assayed in terms of call duration, and the quality of the environment together affect several components of offspring fitness, including condition, expression of the display trait, and allocation of resources to reproduction. This study will also examine the genetic relationship between condition and call duration in offspring; because condition may reflect many genes, and these genes may have different effects in different environments, the relationship between condition and display traits may help explain the persistence of genetic variation in male displays. Thus, a central goal of this study is to understand how environmental variation affects the genetic relationships between display traits and offspring fitness and, ultimately, how genetic variation in sexually-selected traits is maintained.

Acoustic signals are used by many kinds of animals to communicate between members of the same and opposite gender. This research focuses on how acoustic signals used for mate attraction might influence the aggregation and spacing of calling males. The treefrog system is an ideal model system because only males produce long-range sounds, which elicit phonotaxis in females and phonotaxis and vocal responses in other males. Furthermore, much knowledge is already available about the evolutionary significance of this communication and the underlying auditory mechanisms. The experiments will test the idea that calling by a small group of males (simulated by playbacks of recorded calls from speakers) can influence the onset of chorusing and the location of choruses, which are large groups of calling males. Further tests will assess the effects of signal quality on the location of aggregations of calling males within the general chorusing area. The results bear on general hypotheses about the causes and consequences of aggregated displaying, which is a common phenomenon in animals. For example, if playbacks accelerate the onset of chorusing and attractive (to females) rather than unattractive calls influence the location of aggregations within choruses, the hypothesis that males with especially attractive signals are focal points for chorus formation will be supported. If chorus onset is not influenced by playbacks and unattractive and attractive signals are equivalent in influencing location, the hypothesis that favorable locations for attracting females are focal points for chorus formation. These questions will be addressed in three different species in order to generalize the results and to learn if different environmental factors might also influence chorus formation.

Broader Impacts: This research will serve to increase knowledge of animal communication and to further the graduate education of a Hispanic student whose undergraduate education occurred in Puerto Rico. His undergraduate training lacked an opportunity for designing and conducting experiments that address broad theoretically informed research questions. Several undergraduates some of will be from under represented groups will assist the graduate student.

In many animals, aggressive signals, rather than overt physical fighting are used to resolve disputes. Despite intensive research into aggressive signaling, the means by which most animals assess their own status and that of competitors during contests remains unclear: for example, animals may use mutual assessment, in which persistence in a contest is based on assessing their fighting ability relative to that of their opponent, or they may use self-assessment, in which the decision to withdraw is based only on assessing their own accumulated costs, regardless of characteristics of their opponent. Recent theoretical work has provided a method to distinguish between possible means of assessment. This study will use these recent theoretical advances to determine whether male gray treefrogs, Hyla versicolor, use mutual or self assessment during aggressive vocal interactions. Measurements of the duration and level of escalation of staged aggressive encounters between calling males in size-equal and size-unequal pairings will be used to distinguish between these two possibilities. Under mutual assessment, contests are expected to be longer when individuals are more closely matched, regardless of their absolute size, while self-assessment predicts that contest duration is an increasing function of the absolute size of the smaller individual, regardless of size asymmetry.

This experiment will provide important new information on the significance of aggressive signaling that will be important for confirming the results of recent theoretical work. It will also continue the development of H. versicolor as a model for studies of aggressive signaling. Aggressive calling in frogs has been understudied in general, yet frogs offer many advantages to the study of communication. Finally, this project will provide important research experiences for several undergraduate students (including those from underrepresented groups), who will be given the opportunity to participate fully in the project's execution.