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Is melanism in pygmy grasshoppers induced by crowding?
Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.ORCID iD: 0000-0001-9598-7618
2010 (English)In: Evolutionary Ecology, ISSN 0269-7653, E-ISSN 1573-8477, Vol. 24, no 5, p. 975-983Article in journal (Refereed) Published
Abstract [en]

Color polymorphisms in animals may result from plasticity of the developmental system in response to genetic cues in the form of allelic variation at polymorphic loci, environmental cues, or a combination of genetic and environmental cues. An increased understanding of the evolution of color polymorphisms requires better knowledge of when we should expect genetic and environmental cues respectively to influence phenotype determination. Theory posits that the developmental systems of organisms should evolve sensitivity to such cues that most accurately predict coming selective conditions. Pygmy grasshoppers (Orthoptera, Tetrigidae) vary in color pattern within and among populations and show fire melanism, i.e., an increased frequency of black and dark colored phenotypes in high density populations inhabiting fire-ravaged areas. We examined if the population density experienced by individuals during development influenced the phenotypic expression of color pattern in Tetrix subulata. Individuals were experimentally reared either in solitude, at intermediate density or under crowded conditions. We found that color patterns of experimental individuals were independent of rearing density but strongly influenced by maternal color pattern. High population density and crowding may not constitute reliable predictors of the selective regime that characterizes post-fire environments.

Place, publisher, year, edition, pages
2010. Vol. 24, no 5, p. 975-983
National Category
Biological Sciences
Research subject
Natural Science, Evolutionary Biology
Identifiers
URN: urn:nbn:se:lnu:diva-6912DOI: 10.1007/s10682-010-9399-9Scopus ID: 2-s2.0-77955770021OAI: oai:DiVA.org:lnu-6912DiVA, id: diva2:332013
Available from: 2010-07-29 Created: 2010-07-29 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Evolution in changing environments revealed by fire melanism in pygmy grasshopper
Open this publication in new window or tab >>Evolution in changing environments revealed by fire melanism in pygmy grasshopper
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

According to theory, genetic diversity can be maintained by environmental variation and the degree of genetic and phenotypic polymorphism may enhance the ability of populations to endure stress imposed by changing environments. In my thesis I used colour polymorphic pygmy grasshoppers (Tetrix subulata) as a model system to explore how environmental variation influenced genetic diversity. I compared population colour morph frequencies between populations in burnt and non-burnt areas and performed experiments to investigate to what extent colour patterns in these insects are determined by genes and influenced by phenotypic plasticity in response to environmental effects experienced during development. My results showed that the frequency of black individuals on average was much higher in recently fire ravaged areas, a condition known as fire melanism. The highest proportion of black individuals was reached within the first year after a fire. After the initial increase, the proportion of black individuals declined again and the distribution among alternative colour morphs became more even. Data for individuals raised in captivity revealed a high correspondence between maternal and offspring colour patterns, indicating a strong genetic influence on colour. Additional experiments demonstrated that the development of colour patterns in pygmy grasshoppers was not influenced by burnt material or high population densities, two environmental cues associated with post fire environments.

To test if reduced competition among alternative colour morphs may contribute to the maintenance of colour pattern polymorphism in these insects I examined if average survival was higher in diverse compared to homogeneous groups of individuals. I found that survival increased with colour pattern diversity, presumably due to reduced competition among alternative colour morphs. Relaxation of competition may explain why the distribution among alternative colour patterns changed and became more even after the initial evolution of fire melanism. My results demonstrate that environmental change may cause extremely rapid and reversible evolution, indicate that fluctuating selection may preserve genetic variation and support the notion that polymorphism may increase average individual success and enable populations to withstand environmental change.

 

Place, publisher, year, edition, pages
Linnaues University Press, 2010
Series
Linnaeus University Dissertations ; 5/2010
Keywords
Evolution Melanism Polymorphism Pygmy grasshoppers
National Category
Biological Sciences
Research subject
Natural Science, Evolutionary Biology
Identifiers
urn:nbn:se:hik:diva-2457 (URN)978-91-86491-05-5 (ISBN)
Public defence
2010-03-12, Fullriggaren, Landgången 4, Kalmar, 09:00 (English)
Opponent
Supervisors
Available from: 2010-01-20 Created: 2010-01-20 Last updated: 2013-03-22Bibliographically approved

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Karlsson, MagnusForsman, Anders

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