Sokolowski Socio-Genetics

1. Auflage 2009
ISBN: 978-0-08-095393-9
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, Band Volume 68, 110 Seiten

Reihe: Advances in Genetics

Socio-Genetics seeks to understand both the genetic and environmental contributions to individual variations in behavior. Behaviors, like all complex traits, involve multiple genes, a reality that complicates the search for genetic contributions. As with much other research in genetics, studies of genes and behavior require analysis of families and populations for comparison of those who have the trait in question with those who do not. The result commonly is a statement of 'heritability,' a statistical construct that estimates the amount of variation in a population that is attributable to genetic factors. The explanatory power of heritability figures is limited, however, applying only to the population studied and only to the environment in place at the time the study was conducted. If the population or the environment changes, the heritability most likely will change as well. Focused on the genetics of complex traits in a variety of organisms-honeybees, mice, and nematodes-this volume discusses environmental influence on genetic programs and evolutionary genetics. Such research is proving important in furthering our understanding of the genetic basis of such diseases as obesity, schizophrenia, multiple sclerosis, and autism, to name a few. - Most recent research findings on gene-environment interaction and complex behavior, allows researchers to make predictions about the genetic mechanisms that underlie some basic behaviors-eating, for example-leading to new and novel treatments for some genetically based abnormal behaviors - Reviews environmental programming of phenotypic diversity in female reproductive strategies, providing important insight into fertility and in developing therapeutic strategies to treat infertility

Autoren/Hrsg.

Sokolowski, Marla

Inhaltsverzeichnis

1;Front Cover
;1
2;Advances in Genetics
;4
3;Copyright
;5
4;Contents
;6
5;Contributors
;8
6;Preface;10
7;Chapter 1: C. elegans: Social Interactions in a "Nonsocial" Animal
;12
7.1;I. Male-Mating
;16
7.2;II. Aggregation
;19
7.3;III. Conclusion
;29
7.4;References;30
8;Chapter 2: Molecular Social Interactions: Drosophila melanogaster Seminal Fluid Proteins as a Case Study
;34
8.1;I. Drosophila Sfps and Molecular Social Interactions: An Interplay in Four Acts
;39
8.2;II. Behind the Scenes: Evolutionary Dynamics
;51
8.3;III. Discussion and Future Directions
;57
8.4;Acknowledgments;58
8.5;References;58
9;Chapter 3: Sleeping Together: Using Social Interactions to Understand the Role of Sleep in Plasticity
;68
9.1;I. Introduction
;69
9.2;II. Social Enrichment Induces Plastic Mechanisms
;70
9.3;III. Functional Effects of Social Enrichment
;72
9.4;IV. Using Social Enrichment to Investigate Functions of Sleep
;74
9.5;V. Future Directions
;83
9.6;References;87
10;Chapter 4: Approaching the Genomics of Risk-Taking Behavior
;94
10.1;I. Introduction
;95
10.2;II. Challenges and Approaches for Studying the Genetics of Risk-Taking Behavior in Humans and Other Animals
;96
10.3;III. Approaching the Genomics of Risk-Taking Behaviors in Stickleback Fish
;98
10.4;IV. Future Directions and Conclusions
;110
10.5;Acknowledgments;110
10.6;References;110
11;Index
;116
12;Color Plates
;120

Leseproben

C. elegans
Social Interactions in a “Nonsocial” Animal
Evan L. Ardiel*,† and Catharine H. Rankin*,† *Brain Research Centre, University of British Columbia, Vancouver, British Columbia, Canada V6T 2B5 †Department of Psychology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4 Abstract As self-fertilizing nematodes, Caenorhabditis elegans do not normally come to mind when one thinks of social animals. However, their reproductive mode is optimized for rapid population growth, and although they do not form structured societies, conspecifics are an important source of sensory input. A pheromone signal underlies multiple complex behaviors, including diapause, male-mating, and aggregation. The use of C. elegans in sociogenetics research allows for the analysis of social interactions at the level of genes, circuits, and behaviors. This chapter describes natural polymorphisms in mab-23, plg-1, npr-1, and glb-5 as they relate to two C. elegans social behaviors: male-mating and aggregation. Although it does not form anything resembling a structured society, the power of Caenorhabditis elegans as a model organism makes it an important system in the study of sociogenetics. Some 40 years ago Sydney Brenner chose the worm as the best metazoan in which to investigate development and the nervous system. It was small (approximately 1 mm) with a short life cycle (<4 days) and could be easily cultivated in the laboratory; furthermore, its mode of reproduction was ideal for genetics—self-fertilizing hermaphrodites could be easily inbred or crossed with males. Morphologically, C. elegans is relatively simple and its development is highly deterministic. As a result, the complete cell lineage and neural wiring diagram could be worked out; each adult hermaphrodite has only 959 cells, 302 of which are neurons forming about 5000 chemical synapses, 600 gap junctions, and 2000 neuromuscular junctions (Sulston and Horvitz, 1977, Sulston et al., 1983 and White et al., 1986). The worm's transparency grants easy access to cells for targeted laser ablation and in vivo imaging of fluorescent markers. The genome has now been mapped and sequenced and thousands of mutants and RNAi constructs are readily available. Clearly, a powerful model system, but is it social? Although dense populations are rarely found in nature (Barrière and Félix, 2005), the boom and bust strategy of resource depletion suggest that conspecifics are a particularly salient feature of the environment. Indeed, pheromones influence gene expression and two types of social behavior have been well documented: male-mating and aggregation. Conspecifics can affect one another in a wide variety of ways, ranging from providing simple sensory input (i.e., visual, auditory, or mechanosensory stimulation) to more complex emotional stimulation (nurturing, pair-bonding, dominance, etc.). A constructive and parsimonious approach to study “social” behavior is to ascertain what level/type of stimulation is required from conspecifics and to determine whether some other type of stimulation, rather than a conspecific, can have the same effect. To say this in a different way, the issue is whether the effect/behavior is mediated by a specific drive to interact with a conspecific or whether the conspecific produces some critical/important stimulus conditions that do not actually require conspecifics. A useful approach to studying the importance of a particular sensory input is to remove it and see what happens. For example, Rose et al. (2005) removed all conspecific cues by raising worms in isolation and compared these isolate-reared worms to group reared worms on several measures. They found that worms reared in social isolation were less responsive to mechanical stimulation (Fig. 1.1 A) and had weaker synaptic connections in the underlying neural circuit, as compared to worms reared in colonies of 30–40. These differences were not the result of social deprivation per se, as they could be reversed during development by simply dropping the Petri plate containing an isolated worm (Rai and Rankin, 2007 and Rose et al., 2005). Thus, conspecifics appeared to act as a source of mechanosensory stimulation during the maturation of the neural circuit. The effects of isolation on the mechanosensory response were mediated by a gene, glr-1, which encodes a glutamate receptor subunit. Rose et al. (2005) also noted that isolate-reared worms were smaller (Fig. 1.1 B) and had a delayed onset of egg-laying compared to colony worms. No amount of mechanical stimulation could reverse this effect, but isolated worms did grow larger if they were transferred into colonies before the third larval molt (Rai and Rankin, 2007). This suggests that social interactions with other worms can influence adult body size and that there is a critical period for them to do so. Worms with mutations in glr-1 did show the same effect of isolation on body size as wild-type worms, suggesting that this gene pathway is not involved in the effects of isolation on body size. The current work is attempting to identify the relevant conspecific cues that influence adult body size, the neurons through which these cues are registered, and the genes required to process them. Thus, the effects of isolation on mechanosensory behavior are mediated by simple mechanical stimulation-activating glr-1 receptors; in contrast the effects of isolation on body size appear to be mediated by the physical presence of conspecifics and do not involve glr-1 receptors. Figure 1.1 Worms reared in isolation are less responsive to mechanical stimulation than worms reared in colonies (A). Responsiveness is scored as the distance a worm swims backwards following a tap to the side of its Petri plate. Worms reared in isolation are shorter than worms reared in colonies (B). *p<0.05.
At the other end of the population density continuum, social interactions are also important as populations become overcrowded. Under optimal conditions, C. elegans develops through four larval stages (L1–L4) to egg-laying adult in about 3 days. However, high population density and limited food promote a diversion into a larval diapause state known as dauer, which can last up to 4 months. Population density is assessed indirectly by the concentration of dauer pheromone, which is composed of several structurally related ascarosides (derivatives of the dideoxysugar ascarylose; Butcher et al., 2007) constitutively secreted by worms (see Edison (2009) for an excellent review on C. elegans pheromones). Mutant analysis has identified at least four evolutionarily conserved signal transduction pathways regulating dauer formation. They are a guanylyl cyclase pathway, a TGF?-like pathway, an insulin-like pathway, and a steroid hormone pathway. Morphologically specialized for long-term survival and dispersal, dauer larvae appear thin and dense and exhibit distinctly different behavioral patterns from developing larvae. Pharyngeal pumping is suppressed (Cassada and Russell, 1975) and movement is limited, although they do respond to touch. Dauer larvae may also climb objects and wave their body in the air, a behavior likely leading to insect-mediated dispersal. There is considerable reorganization of the nervous system, as several neurons adopt dauer-specific morphologies and positions. As would be expected, metabolism also changes to meet the demands of long-term survival in the absence of food, and the mouth is closed off. Altering another's life history is the most profound effect that could arise from a social interaction. Robinson et al. (2008) described two key “vectors of influence” linking genes, neural circuits and social behaviors. The first is the effects of social interactions on brain gene expression and behavior. As highlighted above, dauer pheromone can have a profound impact on gene expression, brain function, and behavior. The second key vector of influence is genetic variation on social behaviors. This is the focus of the remainder of our chapter as we discuss research on two behaviors: male-mating and aggregation. I. Male-Mating The interaction of a male and female during sexual reproduction is one of the most ancient of social behaviors. Although derived from an obligate-outcrossing, male–female ancestor, there are no female C. elegans, just males and hermaphrodites. Hermaphrodites produce a limiting amount of sperm and a large number of oocytes. The sperm fertilizes the eggs with nearly 100% efficiency, so a hermaphrodite can sire about 300 self-progeny, but they can also mate with males to sire over 1000 cross-progeny. Copulation is arguably the most complex social behavior of the worm, although the hermaphrodites play a mostly passive role. Male-mating comprises several stereotyped sub-behaviors (Fig. 1.2; Liu and Sternberg, 1995). Males must find a partner, respond to contact, arch around the head or tail, locate the vulva, insert their spicules, and ejaculate (see Fig. 1.2). Step 1: Hermaphrodite localization. Males are attracted to a chemical cue secreted by hermaphrodites (Simon and Sternberg, 2002). Sensed by the ASK and CEM sensory...