Robert L. Jeanne - US grants

It is a general rule among social insects that colony members specialize on different tasks required for the growth, defense, and reproduction of the colony. Most previous studies of division of labor among workers have limited analysis to the level of the "caste," the group of workers performing a given role for a prolonged period of time. However, some recent evidence suggests that behavioral differences among individual members of a caste may play an integral role in how the colony organizes work. Dr. Jeanne's research will take the analysis of the organization of work in social-insect colonies down to the level of the individual. The overall goal is to understand how the colony's response to a contingency, which at the global level appears to be deterministic (certain), is put together from the responses of individual workers, which appear to be idiosyncratic and probabilistic. Dr. Jeanne will analyze nest-construction behavior of a species of tropical wasp on which he has already done detailed preliminary work. He has two objectives within his overall goal. The first objective is to determine the characteristics and behavioral correlates of individual variability in nest construction. Experiments will be conducted on individually marked workers, working within the social context, to determine if their levels of activity are related to age and to different individual thresholds of response to the stimuli that release nest-construction activities. The second objective is to experimentally test for mechanisms hypothesized to regulate nest-construction behavior. The end result will be an understanding of the nest-construction system in terms of responses to stimuli, feedback pathways, and modes of communication among workers engaged in the activity. What we know so far about the coordination of complex activities of social insects suggests a parallel with what Sydney Brenner and his associates are finding out about development in simple organisms, namely that much of the "grammar of assembly" lies in the interaction among the component parts of the system. Specifying this grammar for a social insect is the ultimate goal of this research.

9222108 Jeanne The most remarkable of the social wasps are the tropical species in which new colonies are established by large groups called swarms. The 24 "swarm-founding" genera evolved from a more primitive type, still represented in the tropical fauna, in which colonies are founded by one or a few inseminated queens acting independently, without the help of workers. Not only do the swarm-founding species form the largest, most conspicuous, and most pugnacious colonies, but they dominate the "independent-founders" ecologically, exceeding them in sheer numbers in some localities by several thousand to one. An important reason for the striking success of the swarm-founders is that their entire life cycle is spent as a group. This gives them an advantage in countering the high risk of predation that faces life in the tropics. Swarming cannot work unless the scout wasps, who choose a site suitable for a new nest, can communicate its location to the rest of the swarm. How this is done is known for one species only: the scouts lay a trail of chemical scent-marks, which their swarm-mates follow to the new site. The scent is produced by a particular gland on the abdomen in this species. A number of other swarm- founding genera have the same gland, but in some of these the form of the gland is different, suggesting other functions. In still other species the gland is entirely lacking, suggesting other means of recruiting swarm members. These facts suggest (1) that chemical trails are not universal among swarm-founders and (2) that swarm-founding itself may have had two or more independent origins. The ultimate objective of Dr. Jeanne's research is to determine the specific swarm-recruitment mechanisms utilized by seven key swarm-founding genera and to use the results to test among several hypotheses on the evolution of these mechanisms. The results will yield a much-improved picture of the varieties of communication evolved among the swarm-founding genera and provide an explicit phylogenetic model for the evolution of swarm-recruitment mechanisms. This will make it possible to conduct rigorous comparative studies on the adaptive significance of these mechanisms. Finally, the research will contribute significantly to understanding the evolution of an extraordinarily successful form of social behavior in insects.

Abstract Jeanne 9514010 The number of workers in some social insect colonies can reach millions, yet they cooperate with one another and the colonies smoothly accomplish all their necessary tasks. It has recently been discovered for a tropical social wasp that the larger the colony, the greater its productive output per worker. This pattern contradicts previous understanding and has direct implications for the evolution of colony size. The purpose of the proposed research is to learn how the behavior of workers in large colonies is organized differently from that of small colonies and how these differences give rise to the differences in productivity. The research will be conducted on colonies in the field. New colonies are founded by swarms of workers and queens. Newly-founded colonies of different sizes will be made to repair nest damage to provide data on numbers of workers performing each type of work and their individual rates of work. Experimental manipulation of nest repair activity will be used to reveal the behavioral cues workers use to make decisions about whether to become active or idle. At the end of 25 days the colonies will be collected and the size measured (number of workers). The behavioral results will be correlated with colony size to determine how the changes in behavior at different colony size translate into per capita differences in output. The results of this study will explain the relationship between the behavior of group members and group size. The resulting knowledge of the underlying mechanisms will enhance our understanding of the evolution of large colony size in social insects and may provide insights into how human groups organize.

Vibrational behavior in the social wasps with an emphasis on antennal drumming in Polistes (Hymenoptera: Vespidae)

Proposal # IOS-0709869

PI: Dr. Robert L. Jeanne; CO-PI: Sainath Suryanarayanan

The purpose of the dissertation research is to elucidate the function(s) of vibrational signals associated with brood feeding in a wasp. The proposed research will experimentally test the vibrational stress hypothesis according to which, high rates of vibrations induce developmental changes in the brood, causing them to emerge as adults with worker-like traits, whereas low rates of vibrations cause brood to develop with potential-queen-like traits. Polistes is the only wasp group in which vibrational signals have been studied in some detail and offers itself as a promising experimental system. Antennal drumming (AD) is a behavior in which queens rapidly beat their antennae synchronously on the rims of the nest cells. Thirty colonies initiated in the lab will be divided into three treatments: i) those that receive reverse AD signals from a coupled electro-mechanical device, ii) those that receive a random signal, and iii) undisturbed controls. Fat stores and juvenile hormone levels of newly emerged adults will be measured to indicate their behavioral caste: potential queens show high levels of both and workers show low levels. The idea of mechanical stress as a regulator of caste switching is novel and results from this study could have far reaching implications for our understanding of caste development in animal societies. Undergraduate students are participating and will take further part in the research proposed. Results from the proposed research will be used to design instructional material for an Insect Behavior course.

Many studies on humans and rodents have aimed at understanding how maternal care influences the behavior and health of offspring. Because it is hard to separate the effects of maternal behavior itself from effects of the environment, many fundamental questions remain unanswered: To what extent can maternal care itself directly affect the long-term behavior and physiology of offspring? Can maternal care completely or partially overcome environmental stressors? Does maternal care trigger genetic changes in offspring that mediate long-term effects?

Toth and Jeanne will use a new behavioral system to address these questions. Mother paper wasps (Polistes) feed and care for larvae throughout their development. In the process, maternal wasps physically vibrate their larvae by striking their antennae on nest cells. This behavior, which can be simulated using a piezoelectric device, has profound effects on offspring. Vibrated larvae become workers, whereas un-vibrated wasps become queens. This unique system can be used to experimentally dissect how maternal behavior affects offspring.

The researchers will use state-of-the art DNA sequencing methods to characterize what types of genetic changes (e.g. gene activation or chemical DNA modifications) are induced in offspring in response to the interactions of an environmental factor (nutritional stress) and a maternal behavior (vibrations).

This work will provide new information on the extent to which maternal behavior can affect the fate of offspring, how these effects may be modulated by stressors in the environment, and the genetic mechanisms underlying this process. The project will involve the training of a postdoctoral researcher, several undergraduates, and a high school teacher. The results will be disseminated to the scientific community and new insights shared at school and community outreach events.