| 1. |
- Forsman, Anders, 1962-, et al.
(författare)
-
Rapid evolution of fire melanism in replicated populations of pygmy grasshoppers
- 2011
-
Ingår i: Evolution. - : Wiley. - 0014-3820 .- 1558-5646. ; 65:9, s. 2530-2540
-
Tidskriftsartikel (refereegranskat)abstract
- Evolutionary theory predicts an interactive process whereby spatiotemporal environmental heterogeneity will maintain genetic variation, while genetic and phenotypic diversity will buffer populations against stress and allow for fast adaptive evolution in rapidly changing environments. Here, we study color polymorphism patterns in pygmy grasshoppers (Tetrix subulata) and show that the frequency of the melanistic (black) color variant was higher in areas that had been ravaged by fires the previous year than in nonburned habitats, that, in burned areas, the frequency of melanistic grasshoppers dropped from ca. 50% one year after a fire to 30% after four years, and that the variation in frequencies of melanistic individuals among and within populations was genetically based on and represented evolutionary modifications. Dark coloration may confer a selective benefit mediated by enhanced camouflage in recently fire-ravaged areas characterized by blackened visual backgrounds before vegetation has recovered. These findings provide rare evidence for unusually large, extremely rapid adaptive contemporary evolution in replicated natural populations in response to divergent and fluctuating selection associated with spatiotemporal environmental changes.
|
|
| 2. |
- Karpestam, Einat, et al.
(författare)
-
Body size influences differently the detectabilities of colour morphs of cryptic prey
- 2014
-
Ingår i: Biological Journal of the Linnean Society. - : Oxford University Press (OUP). - 0024-4066 .- 1095-8312. ; 113:1, s. 112-122
-
Tidskriftsartikel (refereegranskat)abstract
- Body size and coloration may contribute to variation in performance and fitness among individuals, for instance by influencing vulnerability to predators. Yet, the combined effect of size and colour pattern on susceptibility to visual predators has received little attention, particularly in camouflaged prey. In the colour polymorphic pygmy grasshopper Tetrix subulata (Linnaeus, 1758) females are larger than males although there is a size overlap between sexes. We investigated how body size and colour morph influenced detection of these grasshoppers, and whether differences in protective value among morphs change with size. We conducted a computer-based experiment and compared how human ‘predators’ detected images of large, intermediate or small grasshoppers belonging to black, grey or striped colour morphs when embedded in photographs of natural grasshopper habitats. We found that time to detection increased with decreasing size, that differences in time to detection of the black, grey and striped morphs depended differently on body size, and that no single morph provided superior or inferior protection in all three size classes. By comparing morph frequencies in samples of male and female grasshoppers from natural populations we also examined whether the joint effects of size and colour morph on detection could explain evolutionary dynamics in the wild. Morph frequency differences between sexes were largely in accordance with expectations from the results of the detection experiment. Our results demonstrate that body size and colour morph can interactively influence detection of camouflaged prey. This may contribute to the morph frequency differences between male and female pygmy grasshoppers in the wild. Such interactive effects may also influence the dynamics of colour polymorphisms, and contribute to the evolution of ontogenetic colour change and sexual dichromatism.
|
|
| 3. |
- Karpestam, Einat
(författare)
-
Causes and consequences of niche differentiation between color morphs of pygmy grasshoppers
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, I used the color polymorphic pygmy grasshopper, Tetrix subulata, as a model system in order to investigate the degree of niche differentiation between alternative color morphs that are present within a single population. First, I hypothesized that individuals belonging to different color morphs differ in their innate food preference due to somewhat dissimilar physiology, and in their actual food consumption due in part to differential habitat use. I found that alternative morphs differ in their preferred food (multiple-choice experiment in the lab), and in long-term consumption of food in the wild (stable isotopes analysis). Next, I investigated what kind of ecological constraints may result in differential habitat use? Firstly, by painting grasshoppers either black or white in order to influence their thermal properties, I demonstrated that thermoregulatory behavior results in differential microhabitat use in a way that may increase fitness. Secondly, in computer based experiments in which human ‘predators’ were asked to detect images of grasshoppers implemented in images of various environments, I further demonstrated that the degree to which a specific body coloration supply protection, changes across backgrounds, and that no single color pattern provides superior protection against all visual backgrounds. Thus, predator avoidance behavior may result in differential habitat use as well. Can these findings translate into an advantage of polymorphic relative to monomorphic populations? I then evaluated one prediction from theory that posits that more variable founder groups will be more successful in establishing population in new environments. Indeed, I found higher number of individuals the following year in more variable founder groups in semi-natural conditions in field experiment. This thesis demonstrates, niche differentiation along several dimensions between alternative color morph in a generalist invertebrate. It provides experimental evidence supporting the notion that visual predation may be driving force behind evolutionary change in morph frequencies, and points to a possible advantage for color polymorphic relative to monomorphic groups in terms of a higher establishment success.
|
|
| 4. |
- Karpestam, Einat, et al.
(författare)
-
Colour polymorphism protects prey individuals and populations against predation
- 2016
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 6
-
Tidskriftsartikel (refereegranskat)abstract
- Colour pattern polymorphism in animals can influence and be influenced by interactions between predators and prey. However, few studies have examined whether polymorphism is adaptive, and there is no evidence that the co-occurrence of two or more natural prey colour variants can increase survival of populations. Here we show that visual predators that exploit polymorphic prey suffer from reduced performance, and further provide rare evidence in support of the hypothesis that prey colour polymorphism may afford protection against predators for both individuals and populations. This protective effect provides a probable explanation for the longstanding, evolutionary puzzle of the existence of colour polymorphisms. We also propose that this protective effect can provide an adaptive explanation for search image formation in predators rather than search image formation explaining polymorphism.
|
|
| 5. |
- Karpestam, Einat, et al.
(författare)
-
Detection experiments with humans implicate visual predation as a driver of colour polymorphism dynamics in pygmy grasshoppers
- 2013
-
Ingår i: BMC Ecology. - : Springer Science and Business Media LLC. - 1472-6785. ; 13, s. Article number 17-
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Animal colour patterns offer good model systems for studies of biodiversity and evolution of local adaptations. An increasingly popular approach to study the role of selection for camouflage for evolutionary trajectories of animal colour patterns is to present images of prey on paper or computer screens to human 'predators'. Yet, few attempts have been made to confirm that rates of detection by humans can predict patterns of selection and evolutionary modifications of prey colour patterns in nature. In this study, we first analyzed encounters between human 'predators' and images of natural black, grey and striped colour morphs of the polymorphic Tetrix subulata pygmy grasshoppers presented on background images of unburnt, intermediate or completely burnt natural habitats. Next, we compared detection rates with estimates of capture probabilities and survival of free-ranging grasshoppers, and with estimates of relative morph frequencies in natural populations. Results: The proportion of grasshoppers that were detected and time to detection depended on both the colour pattern of the prey and on the type of visual background. Grasshoppers were detected more often and faster on unburnt backgrounds than on 50% and 100% burnt backgrounds. Striped prey were detected less often than grey or black prey on unburnt backgrounds; grey prey were detected more often than black or striped prey on 50% burnt backgrounds; and black prey were detected less often than grey prey on 100% burnt backgrounds. Rates of detection mirrored previously reported rates of capture by humans of free-ranging grasshoppers, as well as morph specific survival in the wild. Rates of detection were also correlated with frequencies of striped, black and grey morphs in samples of T. subulata from natural populations that occupied the three habitat types used for the detection experiment. Conclusions: Our findings demonstrate that crypsis is background-dependent, and implicate visual predation as an important driver of evolutionary modifications of colour polymorphism in pygmy grasshoppers. Our study provides the clearest evidence to date that using humans as 'predators' in detection experiments may provide reliable information on the protective values of prey colour patterns and of natural selection and microevolution of camouflage in the wild.
|
|
| 6. |
|
|
| 7. |
- Karpestam, Einat, et al.
(författare)
-
Matching habitat choice by experimentally mismatched phenotypes
- 2012
-
Ingår i: Evolutionary Ecology. - : Springer Science and Business Media LLC. - 0269-7653 .- 1573-8477. ; 26:4, s. 893-907
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 8. |
- Karpestam, Einat, et al.
(författare)
-
Natural levels of colour polymorphism reduce performance of visual predators searching for camouflaged prey
- 2014
-
Ingår i: Biological Journal of the Linnean Society. - : Oxford University Press (OUP). - 0024-4066 .- 1095-8312. ; 112:3, s. 546-555
-
Tidskriftsartikel (refereegranskat)abstract
- Polymorphism, the coexistence of two or more variants within a population, has served as a classic model system to address questions about the evolution and maintenance of intra-specific variation. It has been hypothesized that natural level of colour polymorphism may impair the search efficiency of visually oriented predators. To test this polymorphism protects hypothesis, we asked human participants to search for images of natural black, striped or grey Tetrix subulata grasshopper colour morphs presented against photographs of their natural habitat on computer screens. Fewer grasshoppers were detected when morphs were presented in mixed than in uniform sequences. All three morphs benefitted to comparable degrees, in terms of reduced detection, from being presented in polymorphic sequences. Our findings demonstrate that natural levels of polymorphic variation can impede the efficiency of visually oriented predators and increase survival of prey. This protective effect supports the limited attention hypothesis, explains why predators develop ‘search images’, may account for the spread and establishment of novel colour variants, and contribute to maintenance of polymorphisms.
|
|
| 9. |
- Karpestam, Einat, et al.
(författare)
-
Reduced predation risk for melanistic pygmy grasshoppers in post-fire environments
- 2012
-
Ingår i: Ecology and Evolution. - : Wiley. - 2045-7758. ; 2:9, s. 2204-2212
-
Tidskriftsartikel (refereegranskat)abstract
- The existence of melanistic (black) color forms in many species represents interesting model systems that have played important roles for our understanding of selective processes, evolution of adaptations, and the maintenance of variation. A recent study reported on rapid evolutionary shifts in frequencies of the melanistic forms in replicated populations of Tetrix subulata pygmy grasshoppers; the incidence of the melanistic form was higher in recently burned areas with backgrounds blackened by fire than in nonburned areas, and it declined over time in postfire environments. Here, we tested the hypothesis that the frequency shifts of the black color variant were driven, at least in part, by changes in the selective regime imposed by visual predators. To study detectability of the melanistic form, we presented human “predators” with images of black grasshoppers and samples of the natural habitat on computer screens. We demonstrate that the protective value of black coloration differs between burnt and nonburnt environments and gradually increases in habitats that have been more blackened by fire. These findings support the notion that a black color pattern provides improved protection from visually oriented predators against blackened backgrounds and implicate camouflage and predation as important drivers of fire melanism in pygmy grasshoppers.
|
|
| 10. |
- Karpestam, Einat, et al.
(författare)
-
Size variability effects on visual detection are influenced by colour pattern and perceived size
- 2018
-
Ingår i: Animal Behaviour. - : Elsevier. - 0003-3472 .- 1095-8282. ; 143, s. 131-138
-
Tidskriftsartikel (refereegranskat)abstract
- Most animals including humans use vision to detect, identify, evaluate and respond to potential prey items in complex environments. Theories predict that predators' visual search performance is better when targets are similar than when targets are dissimilar and require divided attention, and this may contribute to colour pattern polymorphism in prey. Most prey also vary in size, but how size variation influences detectability and search performance of predators that utilize polymorphic prey has received little attention. To evaluate the effect of size variability on prey detection we asked human subjects to search for images of black, grey and striped pygmy grasshoppers presented on computer screens in size-variable (large, medium and small) or in size-invariable (all medium) sequences (populations) against photographs of natural grasshopper habitat. Results showed that size variability either increased or reduced detection of medium-sized targets depending on colour morph. To evaluate whether bias in perceived size varies depending on colour pattern, subjects were asked to discriminate between two grasshopper images of identical size that were presented in pairs against a monochromatic background. Subjects more often incorrectly classified one of the two identical-sized targets as being larger than the other in colour-dimorphic than in monomorphic presentations. The distinctly patterned (striped) morph elicited stronger size perception biases than the dorsally grey or black morphs, and striped grasshoppers were incorrectly classified more often as smaller than grey grasshoppers. The direction of the effect of size variability on detection changed across colour patterns as the bias in perceived size increased. Such joint effects of variation in size and colour pattern on detection and perception can impact the outcome of behavioural and evolutionary interactions between visually oriented predators and their camouflaged prey. This may have consequences for population dynamics, evolution of polymorphisms, community species composition and ecosystem functioning. (C) 2018 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
|
|
