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ScienceWeek
EVOLUTION: ON SOCIAL SELECTION FOR ECCENTRICITY
The following points are made by Michel Chapuisat (Current Biology 2004 14:1003):
1) In nature, colorful patterns usually constitute a signal; they may deter competitors, frighten predators, or attract mates. The standard view on animal signaling is that variation in ornamentation carries information about the condition and quality of the signaler [1,2]. For example, the black-and-yellow stripes of wasps are a signal of danger to other species. But there is more to it than that. Recently, Tibbetts [3] reported an experimental study showing that paper wasps use intraspecific variation in facial and abdominal markings to recognize individuals. A new comparative analysis by the same author [4] has revealed that species with a flexible nest-founding strategy have more variable markings than those with obligate single or multiple foundresses. This new work suggests that complex social interactions may select for individual distinctiveness and raises interesting questions about the costs and benefits of revealing individuality in social groups.
2) Polistes paper wasps form a widespread, species-rich group of social insects [5]. They build small, open paper nests in protected places. All paper wasps are eusocial: one or a few individuals monopolize reproduction, while other individuals defend the colony, forage, and care for the brood. After overwintering, mated females -- the queens -- found new nests. The species differ in their nest-founding habits, following one of three possible strategies: they may have an obligate single foundress, where only one queen starts a nest; they may have obligate multiple foundresses, where two or more queens start a nest together; or they may show flexible nest-founding, where either a single queen or multiple queens start a nest.
3) Paper wasp colonies are well known for having a dominance hierarchy [5]. In species with an obligate single foundress or obligate multiple foundresses, dominant queens usually monopolize all reproduction, and other females behave as workers. In species with a flexible nest-founding strategy, the social interactions tend to be more complex. There are even some theoretical and empirical indications that queens engage in reproductive transactions whereby they yield part of the reproductive potential to other females in order to make them stay and cooperate peacefully. Complex alliances of this kind require that wasps are able to accurately recognize individuals.
4) Polistes fuscatus individuals have highly variable markings on their face and abdomen, such as the presence or absence of conspicuous yellow eyebrows [3]. Together, these markings yield dozens of unique patterns, suggesting they may serve for visual recognition of individuals. Indeed, wasps that had experimentally altered markings were found to receive more aggression than control wasps that had been painted without altering their markings [3]. Importantly, the aggression was transient and declined with time as wasps became familiar with the new markings. This elegant study showed that wasps use visual cues to distinguish individuals. Further, it suggested that variable markings might undergo selection for improved individual recognition in species with complex social interactions.
References (abridged):
1. Maynard Smith, J. and Harper, D. (2003). Animal signals. (Oxford: Oxford University Press)
2. In Animal signals: signalling and signal design in animal communication. (2000). Espmark, Y., Amundsen, T. and Rosenqvist, G. eds. (Trondheim, Norway: Tapir, Academic Press)
3. Tibbetts, E.A. (2002). Visual signals of individual identity in the wasp Polistes fuscatus. Proc. R. Soc. Lond. B 269, 1423-1428
4. Tibbetts, E.A. (2004). Complex social behavior can select for variability in visual features: a case study in Polistes wasps. Proc. R. Soc. Lond. B 271, 1955-1960
5. In Natural history and evolution of paper-wasps. (1996). Turillazzi, S. and West-Eberhard, M.J. eds. (Oxford: Oxford University Press)
Current Biology http://www.current-biology.com
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Related Material:
ON HONEYBEE SOCIAL BEHAVIOR, GENES, AND THE ENVIRONMENT
Notes by ScienceWeek:
The so-called social insects live in societies that rival human societies in complexity and internal cohesion. Honey bees, for example, apparently always follow 3 rules: a) they live in colonies with overlapping generations; b) they care cooperatively for offspring other than their own; and, c) they maintain a reproductive division of labor.
The following points are made by Gene E. Robinson (American Scientist 1998 86:456):
1) Genes do not play an exclusive role in regulating behavior: biologists have long realized that behavior is influenced by genes, the environment, and interactions between the two.
2) Genes never act alone. They must operate in an environment where they code for proteins that participate in many systems in an organism, with these systems in turn influencing the expression of genes. Consequently, biologists must take a broad approach in assessing the impact of any gene.
3) The research group of the author uses the Western honey bee, Apis mellifera. Honey bees pass through different life stages as they age, and their behavioral responses to environmental and social stimuli change in predictable ways. Although worker bees go through a consistent path of behavioral development, this path is not rigidly determined. Bees can accelerate, retard, or even reverse their behavioral development in response to changing environmental and colony conditions.
4) Experimental evidence indicates that juvenile hormone, one of the most important hormones influencing insect development, helps time the pace of behavioral maturation in honey bees. The rate of endocrine-mediated behavioral development is influenced by inhibitory social interactions. Older bees inhibit the behavioral development of younger bees: the rate of behavioral development is negatively correlated with the proportion of older bees in a colony. Inhibitory social interactions that influence the rate of behavioral development involve chemical communication between colony members.
5) Evidence from the laboratory of the author in 1993 indicated the so-called mushroom bodies in the bee brain are involved in the behavioral changes occurring during maturation, the volume of the bodies increasing, and the volume increase associated with an increase in synapses with neurons from brain regions devoted to sensory input. The author suggests this was the first report of brain plasticity in an invertebrate.
6) The author suggests that, in general, two-way interactions between the nervous system and the genome contribute fundamentally to the control of social behavior. Information about social conditions that is acquired by the nervous system is likely to induce changes in genomic function that in turn produce adaptive modifications of the structure and function of the nervous system.
7) The author proposes a new research initiative called "sociogenomics", defined as a "wide-ranging approach to identify genes that influence social behavior, determining the influence of these genes on underlying neural and endocrine mechanisms, and exploring the effects of the environment -- particularly the social environment -- on gene action."
American Scientist http://www.americanscientist.org
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Related Material:
ON GENES AND COMPLEX SOCIAL BEHAVIOR
The following points are made by M.J. Krieger and K.G. Ross (Science 2002 295:328):
1) The evolution of complex social behavior is among the most important events in the history of life. Interest in the genes underlying the expression of key social traits is strong because knowledge of the genetic architecture will lead to increasingly realistic models of social evolution, while identification of the products of major genes can elucidate the molecular bases of social behavior. Few studies have succeeded in showing that complex social behaviors have a heritable basis, and fewer still have suggested that variation in these behaviors is attributable to the action of one or few genes of major effect. No candidate genes with major effects on key social polymorphisms have been identified previously.
2) The fire ant Solenopsis invicta displays a fundamental social polymorphism that appears to be under simple genetic control. A basic feature of fire ant colony social organization, the number of egg-laying queens, is associated with variation at the gene Gp-9. In the US, where this species has been introduced, colonies composed of workers bearing only the (B) allele at Gp-9 invariably have a single queen (monogyne social form), whereas colonies with workers bearing the alternate (b) allele have multiple queens (polygyne social form). The two social forms differ in many key reproductive and life history characteristics.
3) The authors report they sequenced the gene Gp-9 and found that it encodes a pheromone-binding protein, a crucial molecular component in same-species (conspecific) chemical recognition. The authors suggest this indicates that differences in worker Gp-9 genotypes between social forms may cause differences in the abilities of workers to recognize queens and regulate their numbers. The authors conclude: "This study demonstrates that single genes of major effect can underlie the expression of complex behaviors important in social evolution."
Science http://www.sciencemag.org
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