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Causes and consequences of phenotypic plasticity in body size: The case of the yellow dung fly scathophaga stercoraria (diptera: scathophagidae)


Blanckenhorn, Wolf U (2009). Causes and consequences of phenotypic plasticity in body size: The case of the yellow dung fly scathophaga stercoraria (diptera: scathophagidae). In: Whitman, D W; Ananthakrishnan, T N. Phenotypic Plasticity of Insects: Mechanism and Consequences. Enfield, NH, USA: Science Publishers, 369-422.

Abstract

Phenotypic plasticity occurs when a particular genotype assumes different phenotypes depending on its environment. In this article, I focus on phenotypic plasticity in body size and associated life history traits, primarily growth rate and development time, thus taking a trait-centered view. First, I discuss and review phenotypic plasticity in body size in insects in general, centering on its environmental causes and its behavioral and fitness consequences. Plasticity in body size can be caused by a variety of environmental variables, most notably food availability, predators, temperature, season length, photoperiod and humidity, producing recurrent patterns. Food limitation generally results in small body sizes. High temperatures often result in rapid growth but smaller body sizes (Bergmann’s and the temperature-size rule). Short growing seasons limit growth and thus final body size, particularly in species with long development (the converse Bergmann rule). This is often proximately mediated by photoperiod. Predators also limit foraging and hence growth and final body size of prey species, and sometimes induce particular morphological adaptations (induced defenses). For an evolutionary ecologist, the central question is whether or not the phenotypic plasticity exhibited is adaptive. This requires demonstration of heritable variation of the trait and the existence of environment-specific fitness trade-offs. Based on these criteria, growth and body size plasticity in response to seasonal constraints and predators can often be shown to be adaptive, while size reductions due to food limitation typically represent merely the ‘best of a bad situation’. Whether temperature-mediated size plasticity (i.e., Bergmann’s rule) is adaptive remains unclear and contended.
Plasticity in adult body size influences plasticity in adult behavior. Small individuals are forced to use particular strategies in order to overcome their handicap and successfully compete against larger conspecifics to augment their fitness. This is most prominently seen in species with discrete sizedependent alternative foraging or reproductive strategies, but equally necessary when body size variation is continuous. Again, the question is addressed whether small size is merely the ‘best of a bad situation,’ or whether there are environments in which small individuals can match the fitness of larger conspecifics, in which case small size would be adaptive. Evidence suggests that in most cases it is the former. Behavioral plasticity can be classified according to the proximate mechanism, time scale, frequency of occurrence, and the variance component where variation may be detected. In the second part of this chapter, I present a long-term case study of phenotypic plasticity in body size and associated traits of the yellow dung fly Scathophaga stercoraria (Diptera: Scathophagidae). I discuss various environmental causes and behavioral consequences, and conclude that although the extent of body size plasticity of yellow dung flies may not be untypical, the degree of adaptive plasticity perhaps is unusually high. This may be related to the particular ephemeral larval habitat (cow dung), the occurrence and size of which is variable and unpredictable in space and time. Furthermore, high adult mobility promotes extensive gene flow, preventing local adaptation of populations. Long-term case studies of diverse species well suited for this purpose will elucidate which specific conditions foster the evolution of adaptive plasticities, be they morphological, life history, physiological or behavioral.

Abstract

Phenotypic plasticity occurs when a particular genotype assumes different phenotypes depending on its environment. In this article, I focus on phenotypic plasticity in body size and associated life history traits, primarily growth rate and development time, thus taking a trait-centered view. First, I discuss and review phenotypic plasticity in body size in insects in general, centering on its environmental causes and its behavioral and fitness consequences. Plasticity in body size can be caused by a variety of environmental variables, most notably food availability, predators, temperature, season length, photoperiod and humidity, producing recurrent patterns. Food limitation generally results in small body sizes. High temperatures often result in rapid growth but smaller body sizes (Bergmann’s and the temperature-size rule). Short growing seasons limit growth and thus final body size, particularly in species with long development (the converse Bergmann rule). This is often proximately mediated by photoperiod. Predators also limit foraging and hence growth and final body size of prey species, and sometimes induce particular morphological adaptations (induced defenses). For an evolutionary ecologist, the central question is whether or not the phenotypic plasticity exhibited is adaptive. This requires demonstration of heritable variation of the trait and the existence of environment-specific fitness trade-offs. Based on these criteria, growth and body size plasticity in response to seasonal constraints and predators can often be shown to be adaptive, while size reductions due to food limitation typically represent merely the ‘best of a bad situation’. Whether temperature-mediated size plasticity (i.e., Bergmann’s rule) is adaptive remains unclear and contended.
Plasticity in adult body size influences plasticity in adult behavior. Small individuals are forced to use particular strategies in order to overcome their handicap and successfully compete against larger conspecifics to augment their fitness. This is most prominently seen in species with discrete sizedependent alternative foraging or reproductive strategies, but equally necessary when body size variation is continuous. Again, the question is addressed whether small size is merely the ‘best of a bad situation,’ or whether there are environments in which small individuals can match the fitness of larger conspecifics, in which case small size would be adaptive. Evidence suggests that in most cases it is the former. Behavioral plasticity can be classified according to the proximate mechanism, time scale, frequency of occurrence, and the variance component where variation may be detected. In the second part of this chapter, I present a long-term case study of phenotypic plasticity in body size and associated traits of the yellow dung fly Scathophaga stercoraria (Diptera: Scathophagidae). I discuss various environmental causes and behavioral consequences, and conclude that although the extent of body size plasticity of yellow dung flies may not be untypical, the degree of adaptive plasticity perhaps is unusually high. This may be related to the particular ephemeral larval habitat (cow dung), the occurrence and size of which is variable and unpredictable in space and time. Furthermore, high adult mobility promotes extensive gene flow, preventing local adaptation of populations. Long-term case studies of diverse species well suited for this purpose will elucidate which specific conditions foster the evolution of adaptive plasticities, be they morphological, life history, physiological or behavioral.

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Additional indexing

Item Type:Book Section, refereed, original work
Communities & Collections:07 Faculty of Science > Institute of Evolutionary Biology and Environmental Studies
Dewey Decimal Classification:570 Life sciences; biology
590 Animals (Zoology)
Language:English
Date:January 2009
Deposited On:27 Mar 2009 14:03
Last Modified:06 Dec 2017 19:21
Publisher:Science Publishers
ISBN:978-1-57808-423-4
Official URL:http://www.scipub.net/entomology/phenotypic-plasticity-insects.html
Related URLs:http://www.recherche-portal.ch/primo_library/libweb/action/search.do?fn=search&mode=Advanced&vid=ZAD&vl%28186672378UI0%29=isbn&vl%281UI0%29=contains&vl%28freeText0%29=978-1-57808-423-4

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