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  • 1.
    Forsman, Anders
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Rethinking the thermal melanism hypothesis: rearing temperature and coloration in pygmy grasshoppers2011In: Evolutionary Ecology, ISSN 0269-7653, E-ISSN 1573-8477, Vol. 25, no 6, p. 1247-1257Article in journal (Refereed)
    Abstract [en]

    Selection for efficient conversion of solar radiation to body heat has favored theevolution of dark coloration in many ectotherms. The thermal melanism hypothesis positsthat dark coloration is beneficial under conditions of low ambient temperatures because itresults in faster heating rates and higher body temperatures. Fast heating rates, however,may come at a cost of overheating unless compensated for by thermal physiology orbehaviour. Pygmy grasshopper (Orthoptera, Tetrigidae) populations that inhabit fire-ravagedareas characterized by blackened backgrounds and hot surface temperatures due tohigh absorbance of solar radiation show an increased frequency of black phenotypes. Iraised the progeny of wild-captured Tetrix undulata in cold and hot temperatures and useddata on color patterns and survival in a greenhouse to examine whether a cold thermalenvironment triggered the development of melanic coloration or differently affected survivalof melanic versus non-melanic individuals. My results indicate that melanism was notinfluenced by rearing temperature but by genes or epigenetic maternal effects. Temperaturealso did not affect survival. However, melanic individuals produced by melanic motherssurvived longer than melanic individuals produced by non- melanic mothers, whereas nonmelanicindividuals produced by non-black mothers survived longer than melanic individualsproduced by non-black mothers. This suggests a mismatch between color andphysiology in offspring belonging to a different color morph than their mother. Futureinvestigations into the evolution of melanism should consider conflicting selection pressureson thermal capacity and camouflage as well as the influence of correlated responsesto selection on traits associated with coloration.

  • 2.
    Härlin, Carina
    et al.
    University of Gothenburg.
    Härlin, Mikael
    Södertörn University College.
    Towards a historization of aposematism2003In: Evolutionary Ecology, ISSN 0269-7653, E-ISSN 1573-8477, Vol. 17, no 2, p. 197-212Article in journal (Refereed)
    Abstract [en]

    Aposematism is one of the oldest phenomena in evolutionary biology and still a major puzzle to biologists. Despite its evolutionary nature, most attempts to understand aposematism are devoid of phylogenetic components. In addition, most studies that do take phylogeny into account need to bring the analysis even further. We argue that in order to fully understand aposematism we must have a clear picture of the evolutionary history behind present behaviours. In this paper we frame aposematism in a phylogenetic context and argue that most studies still are wanting in terms of demonstrating aposematism. Aposematism is not an end product but rather evolutionary scenarios including character transformations as well as prey-predator interactions. Finally, we suggest that, regardless how we restrict the concept of aposematism, knowing the directions of events facilitate all kinds of comparisons with a promise of uniting functional and evolutionary aspects into a historization of aposematism.

  • 3.
    Karlsson, Magnus
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Forsman, Anders
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Is melanism in pygmy grasshoppers induced by crowding?2010In: Evolutionary Ecology, ISSN 0269-7653, E-ISSN 1573-8477, Vol. 24, no 5, p. 975-983Article in journal (Refereed)
    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.

  • 4.
    Karpestam, Einat
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Wennersten, Lena
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Forsman, Anders
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Matching habitat choice by experimentally mismatched phenotypes2012In: Evolutionary Ecology, ISSN 0269-7653, E-ISSN 1573-8477, Vol. 26, no 4, p. 893-907Article in journal (Refereed)
    Abstract [en]

    Gene flow is often regarded a random process that homogenizes differencesbetween populations and constrains local adaptation. However, the matching habitat choicehypothesis posits that individuals actively choose those microhabitats that best match theirspecific phenotype to maximize fitness. Dispersal (and possibly gene flow) may thus bedirected. Many studies report associations between habitats and phenotypes, but they mayreflect selection, plasticity or adaptation rather than matching choice. Here, we test twopredictions from the matching habitat choice hypothesis by manipulating the dorsal colourof Tetrix subulata, a pygmy grasshopper. (1) Is microhabitat choice flexible such thatdifferently manipulated phenotypes distribute themselves differently in a microclimaticand solar radiation mosaic? (2) If they do, are their fitness prospects higher in the morepreferred microhabitat? We find that individuals painted white or black do distributethemselves differently, with black individuals residing in habitats with less radiation, onaverage, than white individuals, demonstrating that microhabitat choices are plastic. Furthermore,white females had more hatchlings than black ones in the increased radiationtreatment, and this was mainly due to increased mortality of black females under increasedradiation. These findings provide rare experimental evidence in line with predictions fromthe matching habitat choice hypothesis.

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