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Evolution in changing environments revealed by fire melanism in pygmy grasshopper
Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences. (Evolutionär Ekologi)
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
Keyword [en]
Evolution Melanism Polymorphism Pygmy grasshoppers
National Category
Biological Sciences
Research subject
Natural Science, Evolutionary Biology
Identifiers
URN: urn:nbn:se:hik:diva-2457ISBN: 978-91-86491-05-5 (print)OAI: oai:DiVA.org:hik-2457DiVA, id: diva2:288109
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
List of papers
1. Dynamics of colour polymorphism in a changing environment: Fire melanism and then what?
Open this publication in new window or tab >>Dynamics of colour polymorphism in a changing environment: Fire melanism and then what?
2008 (English)In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 154, no 4, p. 715-724Article in journal (Refereed) Published
National Category
Biological Sciences
Research subject
Natural Science, Evolutionary Biology
Identifiers
urn:nbn:se:hik:diva-2445 (URN)
Available from: 2010-01-22 Created: 2010-01-20 Last updated: 2017-12-12Bibliographically approved
2. No evidence for developmental plasticity of colour patterns in response to rearing substrate in pygmy grasshoppers
Open this publication in new window or tab >>No evidence for developmental plasticity of colour patterns in response to rearing substrate in pygmy grasshoppers
2009 (English)In: Canadian Journal of Zoology, ISSN 0008-4301, E-ISSN 1480-3283, Vol. 87, no 11, p. 1044-1051Article in journal (Refereed) Published
Abstract [en]

Color polymorphisms in animals may result from genetic polymorphisms, developmental plasticity, or a combination where some phenotypic components are under strong genetic control and other aspects are influenced by developmental plasticity. Understanding how color polymorphisms evolve demands knowledge of how genetic and epigenetic environmental cues influence the development and phenotypic expression of organisms. Pygmy grasshoppers (Orthoptera, Tetrigidae) vary in color pattern within and among populations. Color morphs differ in morphology, behavior, and life history, suggesting that they represent alternative ecological strategies. Pygmy grasshoppers also show fire melanism, a rapid increase in the frequency of black and dark-colored phenotypes in populations inhabiting fire-ravaged areas. We examined the influence of plasticity on color polymorphism in the pygmy grasshopper Tetrix subulata (L., 1761) using a split-brood design. Individuals were experimentally raised in solitude on either crushed charcoal or white aquarium gravel. Our analyses uncovered no plasticity of either color pattern or overall darkness of coloration in response to rearing substrate. Instead, we find a strong resemblance between maternal and offspring color patterns. We conclude that pygmy grasshopper color morphs are strongly influenced by genetic cues or maternal effects, and that there is no evidence for developmental plasticity of coloration in response to rearing conditions in these insects.

National Category
Biological Sciences
Research subject
Natural Science, Evolutionary Biology
Identifiers
urn:nbn:se:hik:diva-2447 (URN)10.1139/Z09-097 (DOI)
Available from: 2010-01-20 Created: 2010-01-20 Last updated: 2017-12-12Bibliographically approved
3. Rapid parallel evolution of fire melanism in pygmy grasshoppers.
Open this publication in new window or tab >>Rapid parallel evolution of fire melanism in pygmy grasshoppers.
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Biological Sciences
Research subject
Natural Science, Evolutionary Biology
Identifiers
urn:nbn:se:hik:diva-2454 (URN)
Available from: 2010-01-22 Created: 2010-01-20 Last updated: 2015-09-04Bibliographically approved
4. Is melanism in pygmy grasshoppers induced by crowding?
Open this publication in new window or tab >>Is melanism in pygmy grasshoppers induced by crowding?
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.

National Category
Biological Sciences
Research subject
Natural Science, Evolutionary Biology
Identifiers
urn:nbn:se:lnu:diva-6912 (URN)10.1007/s10682-010-9399-9 (DOI)2-s2.0-77955770021 (Scopus ID)
Available from: 2010-07-29 Created: 2010-07-29 Last updated: 2017-12-12Bibliographically approved
5. Diversity and relatedness enhance survival in colour polymorphic grasshoppers
Open this publication in new window or tab >>Diversity and relatedness enhance survival in colour polymorphic grasshoppers
2010 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 5, no 5, article id e10880Article in journal (Refereed) Published
Abstract [en]

Evolutionary theory predicts that different resource utilization and behaviour by alternative phenotypes may reduce competition and enhance productivity and individual performance in polymorphic, as compared with monomorphic, groups of individuals. However, firm evidence that members of more heterogeneous groups benefit from enhanced survival has been scarce or lacking. Furthermore, benefits associated with phenotypic diversity may be counterbalanced by costs mediated by reduced relatedness, since closely related individuals typically are more similar. Pygmy grasshoppers (Tetrix subulata) are characterized by extensive polymorphism in colour pattern, morphology, behaviour and physiology. We studied experimental groups founded by different numbers of mothers and found that survival was higher in low than in high density, that survival peaked at intermediate colour morph diversity in high density, and that survival was independent of diversity in low density where competition was less intense. We further demonstrate that survival was enhanced by relatedness, as expected if antagonistic and competitive interactions are discriminately directed towards non-siblings. We therefore also performed behavioural observations and staged encounters which confirmed that individuals recognized and responded differently to siblings than to non-siblings. We conclude that negative effects associated with competition are less manifest in diverse groups, that there is conflicting selection for and against genetic diversity occurring simultaneously, and that diversity and relatedness may facilitate the productivity and ecological success of groups of interacting individuals.

National Category
Biological Sciences Ecology
Research subject
Ecology, Evolutionary Biology
Identifiers
urn:nbn:se:lnu:diva-6046 (URN)10.1371/journal.pone.0010880 (DOI)2-s2.0-77956542364 (Scopus ID)
Available from: 2010-06-11 Created: 2010-06-11 Last updated: 2017-12-12Bibliographically approved

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