Much of what we know about human colour perception has come from psychophysical studies conducted... more Much of what we know about human colour perception has come from psychophysical studies conducted in tightly-controlled laboratory settings. An enduring challenge, however, lies in extrapolating this knowledge to the noisy conditions that characterize our actual visual experience. Here we combine statistical models of visual perception with empirical data to explore how chromatic (hue/saturation) and achromatic (luminant) information underpins the detection and classification of stimuli in a complex forest environment. The data best support a simple linear model of stimulus detection as an additive function of both luminance and saturation contrast. The strength of each predictor is modest yet consistent across gross variation in viewing conditions, which accords with expectation based upon general primate psychophysics. Our findings implicate simple visual cues in the guidance of perception amidst natural noise, and highlight the potential for informing human vision via a fusion be...
Coloration mediates the relationship between an organism and its environment in important ways, i... more Coloration mediates the relationship between an organism and its environment in important ways, including social signaling, antipredator defenses, parasitic exploitation, thermoregulation, and protection from ultraviolet light, microbes, and abrasion. Methodological breakthroughs are accelerating knowledge of the processes underlying both the production of animal coloration and its perception, experiments are advancing understanding of mechanism and function, and measurements of color collected noninvasively and at a global scale are opening windows to evolutionary dynamics more generally. Here we provide a roadmap of these advances and identify hitherto unrecognized challenges for this multi- and interdisciplinary field.
This is an open access article under the terms of the Creative Commons Attribution License, which... more This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Specular reflection appears as a bright spot or highlight on any smooth glossy convex surface and... more Specular reflection appears as a bright spot or highlight on any smooth glossy convex surface and is caused by a near mirror-like reflectance off the surface. Convex shapes always provide the ideal geometry for highlights, areas of very strong reflectance, regardless of the orientation of the surface or position of the receiver. Despite highlights and glossy appearance being common in chemically defended insects, their potential signalling function is unknown. We tested the role of highlights in warning colouration of a chemically defended, alpine leaf beetle, Oreina cacaliae. We reduced the beetles' glossiness, hence their highlights, by applying a clear matt finish varnish on their elytra. We used blue tits as predators to examine whether the manipulation affected their initial latency to attack, avoidance learning and generalization of warning colouration. The birds learned to avoid both dull and glossy beetles but they initially avoided glossy prey more than dull prey. Inter...
Synergistic selection can promote the evolution of aposematism. This requires, however, that pala... more Synergistic selection can promote the evolution of aposematism. This requires, however, that palatable prey without signals do not benefit from their aposematic neighbours. In order to test this requirement, we designed an experiment using artificially aposematic mealworm larvae and palatable control larvae. As a predator we used great tits. Birds encountered five types of groups: pure groups of aposematic or palatable prey items and mixed groups of palatable and aposematic items or single palatable and single aposematic preys. Survival of aposematic items both in pure groups and for solitary items was high. Unexpectedly, birds also avoided mixed groups. Survival of palatable prey with aposematic neighbors was significantly higher compared to solitary palatables and to those with palatable neighbors. Thus, our results suggest that the protection through association gained by palatable individuals should be taken into account when evaluating evolutionary consequences of synergism for the evolution of aposematism.
Ten polymorphic microsatellite loci were isolated and characterized for the Wood Tiger Moth (Para... more Ten polymorphic microsatellite loci were isolated and characterized for the Wood Tiger Moth (Parasemia plantaginis), a nocturnal moth of the Arctiidae family distributed throughout the globe at mid to northerly latitudes. Characterization of 25 P. plantaginis individuals form central Austria showed moderate to high allelic diversity ranging from 2 to 14 alleles per locus. One locus showed significant departures from Hardy-Weinberg equilibrium presumably due to null alleles. No evidence of linkage disequilibrium was found for any locus pair. Polymorphism is also reported in four related Arctiidae species. This set of markers can be useful for the evaluation of genetic composition, conservation, population genetics and might prove useful in other phylogenetically close species of the Arctiidae family.
In the wolf spider Hygrolycosu rubrofusciata, males court females by drumming dry leaves with the... more In the wolf spider Hygrolycosu rubrofusciata, males court females by drumming dry leaves with their abdomen. Females prefer to mate with the most actively drumming males, and courtship drumming activity is also positively correlated with male viability. However, body mass of the males seems to have only a minor, if any, effect on female choice or male viability. There is also no correlation between male body mass and courtship drumming activity. We studied the effect of body mass and courtship drumming activity on the outcome of agonistic encounters between male H. rubrofasciata. For this purpose, males and females were randomly placed in a plastic arena, where male courtship drumming activity and agonistic encounters were recorded. Large differences in body mass and drumming activity between two rivals seemed to independently increase the probability of the larger or more active males winning. We conclude that while courtship drumming activity affects the fighting success of the males, and body mass more so, male-male interactions may not be of major importance in sexual selection of H. rubrofasciata. RCsurnC : Les miles de la lycose Hygrolycosa rubrofaciata courtisent les femelles en tambourinant sur les feuilles skches avec leur abdomen. Les femelles s'accouplent de preference aux miles les plus tambourinants et l'activite de tambourinage est egalement en correlation positive avec la viabilite des miles. Cependant, la masse des miles semble rester sans effet ou n'avoir qu'un effet negligeable sur le choix des femelles ou sur la viabilite des miles. I1 n'y a pas non plus de correlation entre la masse corporelle des miles et l'intensite du comportement de cour par tambourinage. Au cours de cette etude, nous avons CtudiC l'effet de la masse corporelle et du tambourinage sur le denouement de rencontres agonistiques entre miles d'H. rubrofasciutu. Dans ce but, des miles et des femelles ont kt6 mis en contact de faqon aleatoire dans une arkne de plastique; I'activite de cour par tambourinage et les affrontements agonistiques ont ete notes. De grandes differences de masse et des differences importantes dans le tambourinage jouent de faqon independante sur la probabilite de victoire des miles plus gros et plus actifs. Bien que le comportement de cour par tambourinage et, de faqon encore plus particulikre, la masse corporelle affectent les chances de victoire de miles en combat, les interactions mile-mile ne semblent pas influencer considerablement la selection sexuelle chez H. rubrofasciata. [Traduit par la Rkdaction]
In invertebrates, the size at maturation is considered to be important for adult ®tness. In the w... more In invertebrates, the size at maturation is considered to be important for adult ®tness. In the wolf spider Hygrolycosa rubrofasciata, however, it is only females that clearly bene®t of larger size through augmented egg production, while male mating success is determined by display activity not related to size. Thus, we can expect con¯icting growth patterns for the sexes. Additionally, populations dier greatly in adult size: individuals from dry habitats are smaller than those from wet habitats. To study the sexual dierences in reaction norms of growth, we reared spiderlings from seven populations at two food levels under controlled laboratory conditions and compared size at sexual maturity. The shapes of reaction norms for adult size diered between the sexes. In females, the reaction norms were parallel, but individuals from dry habitats tended to grow larger at the given food levels. In males, there was a signi®cant interaction between food level and population without any consistent dierences between populations. Maturation time was a plastic character in both sexes with no genetic dierences among populations. However, females on low food level matured later and signi®cantly smaller in size than those on high food level. Males also matured later on low food level, but they were nearly of the same size as males that received more food. Female growth patterns re¯ected the strong selection for large size at maturity. However, the patterns for males were highly variable, which could be explained by the weak overall selection on male size, which means that any environmental factors can aect male growing patterns.
Müllerian mimicry, by definition, is the visual resemblance between two or more aposematic prey s... more Müllerian mimicry, by definition, is the visual resemblance between two or more aposematic prey species. According to classical Müllerian mimicry theory, comimics draw mutual benefits from the resemblance because predators have to learn to avoid only one colour pattern. In contrast, the relatively untested quasi-Batesian mimicry theory suggests that, because of differences in unpalatablility, the less toxic mimic acts like a parasite on the more defended prey, decreasing its fitness. We tested predation pressures on artificial mimicry complexes in which comimics varied both in visual similarity and in taste. Both signal and taste were important for the survival of comimics. Predators learned to avoid two similarly conspicuous comimics differently when they were presented alone, suggesting that the signals were unequal. Despite the discrepancy in signal, imperfect visual mimicry did not increase the total number of comimics eaten, as suggested by the classical theory. Great tits, Parus major, learned to avoid highly unpalatable prey faster than mildly unpalatable prey. However, variation in palatability did not unequivocally increase the total mortality of models; instead, the effects depended on the signal of the prey. These results indicate that Müllerian mimicry dynamics may change depending on the configuration of mimicry complexes.
Pathogens evolve in a close antagonistic relationship with their hosts. The conventional theory p... more Pathogens evolve in a close antagonistic relationship with their hosts. The conventional theory proposes that evolution of virulence is highly dependent on the efficiency of direct host-to-host transmission. Many opportunistic pathogens, however, are not strictly dependent on the hosts due to their ability to reproduce in the free-living environment. Therefore it is likely that conflicting selection pressures for growth and survival outside versus within the host, rather than transmission potential, shape the evolution of virulence in opportunists. We tested the role of within-host selection in evolution of virulence by letting a pathogen Serratia marcescens db11 sequentially infect Drosophila melanogaster hosts and then compared the virulence to strains that evolved only in the outside-host environment. We found that the pathogen adapted to both Drosophila melanogaster host and novel outside-host environment, leading to rapid evolutionary changes in the bacterial life-history trait...
The phenomenon of Batesian mimicry, where a palatable animal gains protection against predation b... more The phenomenon of Batesian mimicry, where a palatable animal gains protection against predation by resembling an unpalatable model, has been a core interest of evolutionary biologists for 150 years. An extensive range of studies has focused on revealing mechanistic aspects of mimicry (shared education and generalization of predators) and the evolutionary dynamics of mimicry systems (co-operation vs. conflict) and revealed that protective mimicry is widespread and is important for individual fitness. However, according to our knowledge, there are no case studies where mimicry theories have been applied to conservation of mimetic species. Theoretically, mimicry affects, for example, frequency dependency of predator avoidance learning and human induced mortality. We examined the case of the protected, endangered, nonvenomous smooth snake (Coronella austriaca) that mimics the nonprotected venomous adder (Vipera berus), both of which occur in the Åland archipelago, Finland. To quantify the added predation risk on smooth snakes caused by the rarity of vipers, we calculated risk estimates from experimental data. Resemblance of vipers enhances survival of smooth snakes against bird predation because many predators avoid touching venomous vipers. Mimetic resemblance is however disadvantageous against human predators, who kill venomous vipers and accidentally kill endangered, protected smooth snakes. We found that the effective population size of the adders in Åland is very low relative to its smooth snake mimic (28.93 and 41.35, respectively).Because Batesian mimicry is advantageous for the mimic only if model species exist in sufficiently high numbers, it is likely that the conservation program for smooth snakes will fail if adders continue to be destroyed. Understanding the population consequences of mimetic species may be crucial to the success of endangered species conservation. We suggest that when a Batesian mimic requires protection, conservation planners should not ignore the model species (or co-mimic in Mullerian mimicry rings) even if it is not itself endangered.
Aposematic organisms have warning signals advertising their unpalatability to predators, and beca... more Aposematic organisms have warning signals advertising their unpalatability to predators, and because signal efficiency is better in higher densities, positive frequencydependent selection is expected to select against less common signals. The wood tiger moth (Parasemia plantaginis) occurs across the Holarctic and its conspicuous hindwings serve as warning signals to predators. It also has conspicuous black and white forewing patterns that could act as warning signals, or help to hide the moth by preventing predators from seeing the outline of the moth's body (a strategy known as disruptive coloration). In Alaska, the predominant forewing pattern changes distinctly between the regions around Fairbanks and Anchorage, suggesting local predators may maintain differences if the pattern functions as a warning signal. Alternatively, restricted gene flow along with drift could be responsible. We placed artificial moths with both local dominant and foreign forewing patterns in each of the two regions to test if predators select against the foreign forewing types, which would suggest the warning signal function of forewing patters. We also manipulated the level of disruptiveness in the forewing patterns to see if disruptiveness works in concert with the warning signal. The locally dominant forewing type was better protected in Fairbanks, but not in Anchorage where morphs were attacked equally. Manipulating the level of disruptiveness in the forewing pattern did not influence predation. Population genetic analyses from specimens caught during fieldwork showed the existence of two populations and restricted gene flow. Our results suggest that positive frequency dependent selection may be partially responsible for maintaining local signal differences, although predators seem to avoid both forewing patterns in Anchorage.
ABSTRACT Prey use many strategies to avoid being detected by their predators. However, once detec... more ABSTRACT Prey use many strategies to avoid being detected by their predators. However, once detected and identified as potentially palatable, prey must employ a second line of defence such as performing a deimatic (startle) display. During the predation sequence, composed of the stages encounter, detection, identification, approach, subjugation and consumption, such defences should be deployed as the predator approaches, but before prey are brought under the predator's control (i.e. before subjugation). We tested this assumption in the mountain katydid (or bush cricket), which is cryptic at rest, but when disturbed flashes spectacular abdominal colours by lifting its wings, and is chemically defended. We experimentally determined which visual, auditory and tactile stimuli trigger their deimatic display via six treatments. Contrary to expectations of the predation sequence katydids required tactile cues before performing their deimatic display, that is, it was performed only after attempted subjugation. Field experiments also showed that katydids perform their deimatic display after experiencing tactile stimuli. Mountain katydid natural history may explain this counterintuitive behaviour. Being slow and cryptic, katydids cannot effect a fast escape after performing their deimatic display but their tough cuticle and chemical defences make survival of initial subjugation attempts likely. Holding their deimatic display until after initial subjugation may prevent continued attack and avoid the potentially large cost of revealing themselves to predators that have not yet noticed them. Performance of deimatic display after subjugation may be more common than currently recognized and we encourage further investigation.
Insect communities consist of aposematic species with efficient warning colours against predation... more Insect communities consist of aposematic species with efficient warning colours against predation, as well as abundant examples of crypsis. To understand such coexistence, we here report results from a field experiment where relative survival of artificial larvae, varying in conspicuousness, was estimated in natural bird communities over an entire season. This takes advantage of natural variation in the proportion of naive predators: naivety peaks when young birds have just fledged. We show that the relative benefit of warning signals and crypsis changes accordingly. When naive birds are rare (early and late in the season), conspicuous warning signals improve survival, but conspicuousness becomes a disadvantage near the fledging time of birds. Such temporal structuring of predator-prey relationships facilitates the coexistence of diverse antipredatory strategies and helps explain two patterns we found in a 688-species community of Lepidoterans: larval warning signals remain rare and occur disproportionately often in seasons when predators are educated.
The coincidental virulence evolution hypothesis suggests that outside-host selection, such as pre... more The coincidental virulence evolution hypothesis suggests that outside-host selection, such as predation, parasitism and resource competition can indirectly affect the virulence of environmentally-growing bacterial pathogens. While there are some examples of coincidental environmental selection for virulence, it is also possible that the resource acquisition and enemy defence is selecting against it. To test these ideas we conducted an evolutionary experiment by exposing the opportunistic pathogen bacterium Serratia marcescens to the particle-feeding ciliate Tetrahymena thermophila, the surface-feeding amoeba Acanthamoeba castellanii, and the lytic bacteriophage Semad11, in all possible combinations in a simulated pond water environment. After 8 weeks the virulence of the 384 evolved clones were quantified with fruit fly Drosophila melanogaster oral infection model, and several other life-history traits were measured. We found that in comparison to ancestor bacteria, evolutionary tre...
Lytic bacteriophages and protozoan predators are the major causes of bacterial mortality in natur... more Lytic bacteriophages and protozoan predators are the major causes of bacterial mortality in natural microbial communities, which also makes them potential candidates for biological control of bacterial pathogens. However, little is known about the relative impact of bacteriophages and protozoa on the dynamics of bacterial biomass in aqueous and biofilm phases. Here, we studied the temporal and spatial dynamics of bacterial biomass in a microcosm experiment where opportunistic pathogenic bacteria Serratia marcescens was exposed to particle-feeding ciliates, surface-feeding amoebas, and lytic bacteriophages for 8 weeks, ca. 1300 generations. We found that ciliates were the most efficient enemy type in reducing bacterial biomass in the open water, but least efficient in reducing the biofilm biomass. Biofilm was rather resistant against bacterivores, but amoebae had a significant long-term negative effect on bacterial biomass both in the open-water phase and biofilm. Bacteriophages had ...
Valkonen, Janne K. Warning signalling in European vipers and their mimics: implications for conse... more Valkonen, Janne K. Warning signalling in European vipers and their mimics: implications for conservation of the smooth snake Jyväskylä:
Much of what we know about human colour perception has come from psychophysical studies conducted... more Much of what we know about human colour perception has come from psychophysical studies conducted in tightly-controlled laboratory settings. An enduring challenge, however, lies in extrapolating this knowledge to the noisy conditions that characterize our actual visual experience. Here we combine statistical models of visual perception with empirical data to explore how chromatic (hue/saturation) and achromatic (luminant) information underpins the detection and classification of stimuli in a complex forest environment. The data best support a simple linear model of stimulus detection as an additive function of both luminance and saturation contrast. The strength of each predictor is modest yet consistent across gross variation in viewing conditions, which accords with expectation based upon general primate psychophysics. Our findings implicate simple visual cues in the guidance of perception amidst natural noise, and highlight the potential for informing human vision via a fusion be...
Coloration mediates the relationship between an organism and its environment in important ways, i... more Coloration mediates the relationship between an organism and its environment in important ways, including social signaling, antipredator defenses, parasitic exploitation, thermoregulation, and protection from ultraviolet light, microbes, and abrasion. Methodological breakthroughs are accelerating knowledge of the processes underlying both the production of animal coloration and its perception, experiments are advancing understanding of mechanism and function, and measurements of color collected noninvasively and at a global scale are opening windows to evolutionary dynamics more generally. Here we provide a roadmap of these advances and identify hitherto unrecognized challenges for this multi- and interdisciplinary field.
This is an open access article under the terms of the Creative Commons Attribution License, which... more This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Specular reflection appears as a bright spot or highlight on any smooth glossy convex surface and... more Specular reflection appears as a bright spot or highlight on any smooth glossy convex surface and is caused by a near mirror-like reflectance off the surface. Convex shapes always provide the ideal geometry for highlights, areas of very strong reflectance, regardless of the orientation of the surface or position of the receiver. Despite highlights and glossy appearance being common in chemically defended insects, their potential signalling function is unknown. We tested the role of highlights in warning colouration of a chemically defended, alpine leaf beetle, Oreina cacaliae. We reduced the beetles' glossiness, hence their highlights, by applying a clear matt finish varnish on their elytra. We used blue tits as predators to examine whether the manipulation affected their initial latency to attack, avoidance learning and generalization of warning colouration. The birds learned to avoid both dull and glossy beetles but they initially avoided glossy prey more than dull prey. Inter...
Synergistic selection can promote the evolution of aposematism. This requires, however, that pala... more Synergistic selection can promote the evolution of aposematism. This requires, however, that palatable prey without signals do not benefit from their aposematic neighbours. In order to test this requirement, we designed an experiment using artificially aposematic mealworm larvae and palatable control larvae. As a predator we used great tits. Birds encountered five types of groups: pure groups of aposematic or palatable prey items and mixed groups of palatable and aposematic items or single palatable and single aposematic preys. Survival of aposematic items both in pure groups and for solitary items was high. Unexpectedly, birds also avoided mixed groups. Survival of palatable prey with aposematic neighbors was significantly higher compared to solitary palatables and to those with palatable neighbors. Thus, our results suggest that the protection through association gained by palatable individuals should be taken into account when evaluating evolutionary consequences of synergism for the evolution of aposematism.
Ten polymorphic microsatellite loci were isolated and characterized for the Wood Tiger Moth (Para... more Ten polymorphic microsatellite loci were isolated and characterized for the Wood Tiger Moth (Parasemia plantaginis), a nocturnal moth of the Arctiidae family distributed throughout the globe at mid to northerly latitudes. Characterization of 25 P. plantaginis individuals form central Austria showed moderate to high allelic diversity ranging from 2 to 14 alleles per locus. One locus showed significant departures from Hardy-Weinberg equilibrium presumably due to null alleles. No evidence of linkage disequilibrium was found for any locus pair. Polymorphism is also reported in four related Arctiidae species. This set of markers can be useful for the evaluation of genetic composition, conservation, population genetics and might prove useful in other phylogenetically close species of the Arctiidae family.
In the wolf spider Hygrolycosu rubrofusciata, males court females by drumming dry leaves with the... more In the wolf spider Hygrolycosu rubrofusciata, males court females by drumming dry leaves with their abdomen. Females prefer to mate with the most actively drumming males, and courtship drumming activity is also positively correlated with male viability. However, body mass of the males seems to have only a minor, if any, effect on female choice or male viability. There is also no correlation between male body mass and courtship drumming activity. We studied the effect of body mass and courtship drumming activity on the outcome of agonistic encounters between male H. rubrofasciata. For this purpose, males and females were randomly placed in a plastic arena, where male courtship drumming activity and agonistic encounters were recorded. Large differences in body mass and drumming activity between two rivals seemed to independently increase the probability of the larger or more active males winning. We conclude that while courtship drumming activity affects the fighting success of the males, and body mass more so, male-male interactions may not be of major importance in sexual selection of H. rubrofasciata. RCsurnC : Les miles de la lycose Hygrolycosa rubrofaciata courtisent les femelles en tambourinant sur les feuilles skches avec leur abdomen. Les femelles s'accouplent de preference aux miles les plus tambourinants et l'activite de tambourinage est egalement en correlation positive avec la viabilite des miles. Cependant, la masse des miles semble rester sans effet ou n'avoir qu'un effet negligeable sur le choix des femelles ou sur la viabilite des miles. I1 n'y a pas non plus de correlation entre la masse corporelle des miles et l'intensite du comportement de cour par tambourinage. Au cours de cette etude, nous avons CtudiC l'effet de la masse corporelle et du tambourinage sur le denouement de rencontres agonistiques entre miles d'H. rubrofasciutu. Dans ce but, des miles et des femelles ont kt6 mis en contact de faqon aleatoire dans une arkne de plastique; I'activite de cour par tambourinage et les affrontements agonistiques ont ete notes. De grandes differences de masse et des differences importantes dans le tambourinage jouent de faqon independante sur la probabilite de victoire des miles plus gros et plus actifs. Bien que le comportement de cour par tambourinage et, de faqon encore plus particulikre, la masse corporelle affectent les chances de victoire de miles en combat, les interactions mile-mile ne semblent pas influencer considerablement la selection sexuelle chez H. rubrofasciata. [Traduit par la Rkdaction]
In invertebrates, the size at maturation is considered to be important for adult ®tness. In the w... more In invertebrates, the size at maturation is considered to be important for adult ®tness. In the wolf spider Hygrolycosa rubrofasciata, however, it is only females that clearly bene®t of larger size through augmented egg production, while male mating success is determined by display activity not related to size. Thus, we can expect con¯icting growth patterns for the sexes. Additionally, populations dier greatly in adult size: individuals from dry habitats are smaller than those from wet habitats. To study the sexual dierences in reaction norms of growth, we reared spiderlings from seven populations at two food levels under controlled laboratory conditions and compared size at sexual maturity. The shapes of reaction norms for adult size diered between the sexes. In females, the reaction norms were parallel, but individuals from dry habitats tended to grow larger at the given food levels. In males, there was a signi®cant interaction between food level and population without any consistent dierences between populations. Maturation time was a plastic character in both sexes with no genetic dierences among populations. However, females on low food level matured later and signi®cantly smaller in size than those on high food level. Males also matured later on low food level, but they were nearly of the same size as males that received more food. Female growth patterns re¯ected the strong selection for large size at maturity. However, the patterns for males were highly variable, which could be explained by the weak overall selection on male size, which means that any environmental factors can aect male growing patterns.
Müllerian mimicry, by definition, is the visual resemblance between two or more aposematic prey s... more Müllerian mimicry, by definition, is the visual resemblance between two or more aposematic prey species. According to classical Müllerian mimicry theory, comimics draw mutual benefits from the resemblance because predators have to learn to avoid only one colour pattern. In contrast, the relatively untested quasi-Batesian mimicry theory suggests that, because of differences in unpalatablility, the less toxic mimic acts like a parasite on the more defended prey, decreasing its fitness. We tested predation pressures on artificial mimicry complexes in which comimics varied both in visual similarity and in taste. Both signal and taste were important for the survival of comimics. Predators learned to avoid two similarly conspicuous comimics differently when they were presented alone, suggesting that the signals were unequal. Despite the discrepancy in signal, imperfect visual mimicry did not increase the total number of comimics eaten, as suggested by the classical theory. Great tits, Parus major, learned to avoid highly unpalatable prey faster than mildly unpalatable prey. However, variation in palatability did not unequivocally increase the total mortality of models; instead, the effects depended on the signal of the prey. These results indicate that Müllerian mimicry dynamics may change depending on the configuration of mimicry complexes.
Pathogens evolve in a close antagonistic relationship with their hosts. The conventional theory p... more Pathogens evolve in a close antagonistic relationship with their hosts. The conventional theory proposes that evolution of virulence is highly dependent on the efficiency of direct host-to-host transmission. Many opportunistic pathogens, however, are not strictly dependent on the hosts due to their ability to reproduce in the free-living environment. Therefore it is likely that conflicting selection pressures for growth and survival outside versus within the host, rather than transmission potential, shape the evolution of virulence in opportunists. We tested the role of within-host selection in evolution of virulence by letting a pathogen Serratia marcescens db11 sequentially infect Drosophila melanogaster hosts and then compared the virulence to strains that evolved only in the outside-host environment. We found that the pathogen adapted to both Drosophila melanogaster host and novel outside-host environment, leading to rapid evolutionary changes in the bacterial life-history trait...
The phenomenon of Batesian mimicry, where a palatable animal gains protection against predation b... more The phenomenon of Batesian mimicry, where a palatable animal gains protection against predation by resembling an unpalatable model, has been a core interest of evolutionary biologists for 150 years. An extensive range of studies has focused on revealing mechanistic aspects of mimicry (shared education and generalization of predators) and the evolutionary dynamics of mimicry systems (co-operation vs. conflict) and revealed that protective mimicry is widespread and is important for individual fitness. However, according to our knowledge, there are no case studies where mimicry theories have been applied to conservation of mimetic species. Theoretically, mimicry affects, for example, frequency dependency of predator avoidance learning and human induced mortality. We examined the case of the protected, endangered, nonvenomous smooth snake (Coronella austriaca) that mimics the nonprotected venomous adder (Vipera berus), both of which occur in the Åland archipelago, Finland. To quantify the added predation risk on smooth snakes caused by the rarity of vipers, we calculated risk estimates from experimental data. Resemblance of vipers enhances survival of smooth snakes against bird predation because many predators avoid touching venomous vipers. Mimetic resemblance is however disadvantageous against human predators, who kill venomous vipers and accidentally kill endangered, protected smooth snakes. We found that the effective population size of the adders in Åland is very low relative to its smooth snake mimic (28.93 and 41.35, respectively).Because Batesian mimicry is advantageous for the mimic only if model species exist in sufficiently high numbers, it is likely that the conservation program for smooth snakes will fail if adders continue to be destroyed. Understanding the population consequences of mimetic species may be crucial to the success of endangered species conservation. We suggest that when a Batesian mimic requires protection, conservation planners should not ignore the model species (or co-mimic in Mullerian mimicry rings) even if it is not itself endangered.
Aposematic organisms have warning signals advertising their unpalatability to predators, and beca... more Aposematic organisms have warning signals advertising their unpalatability to predators, and because signal efficiency is better in higher densities, positive frequencydependent selection is expected to select against less common signals. The wood tiger moth (Parasemia plantaginis) occurs across the Holarctic and its conspicuous hindwings serve as warning signals to predators. It also has conspicuous black and white forewing patterns that could act as warning signals, or help to hide the moth by preventing predators from seeing the outline of the moth's body (a strategy known as disruptive coloration). In Alaska, the predominant forewing pattern changes distinctly between the regions around Fairbanks and Anchorage, suggesting local predators may maintain differences if the pattern functions as a warning signal. Alternatively, restricted gene flow along with drift could be responsible. We placed artificial moths with both local dominant and foreign forewing patterns in each of the two regions to test if predators select against the foreign forewing types, which would suggest the warning signal function of forewing patters. We also manipulated the level of disruptiveness in the forewing patterns to see if disruptiveness works in concert with the warning signal. The locally dominant forewing type was better protected in Fairbanks, but not in Anchorage where morphs were attacked equally. Manipulating the level of disruptiveness in the forewing pattern did not influence predation. Population genetic analyses from specimens caught during fieldwork showed the existence of two populations and restricted gene flow. Our results suggest that positive frequency dependent selection may be partially responsible for maintaining local signal differences, although predators seem to avoid both forewing patterns in Anchorage.
ABSTRACT Prey use many strategies to avoid being detected by their predators. However, once detec... more ABSTRACT Prey use many strategies to avoid being detected by their predators. However, once detected and identified as potentially palatable, prey must employ a second line of defence such as performing a deimatic (startle) display. During the predation sequence, composed of the stages encounter, detection, identification, approach, subjugation and consumption, such defences should be deployed as the predator approaches, but before prey are brought under the predator's control (i.e. before subjugation). We tested this assumption in the mountain katydid (or bush cricket), which is cryptic at rest, but when disturbed flashes spectacular abdominal colours by lifting its wings, and is chemically defended. We experimentally determined which visual, auditory and tactile stimuli trigger their deimatic display via six treatments. Contrary to expectations of the predation sequence katydids required tactile cues before performing their deimatic display, that is, it was performed only after attempted subjugation. Field experiments also showed that katydids perform their deimatic display after experiencing tactile stimuli. Mountain katydid natural history may explain this counterintuitive behaviour. Being slow and cryptic, katydids cannot effect a fast escape after performing their deimatic display but their tough cuticle and chemical defences make survival of initial subjugation attempts likely. Holding their deimatic display until after initial subjugation may prevent continued attack and avoid the potentially large cost of revealing themselves to predators that have not yet noticed them. Performance of deimatic display after subjugation may be more common than currently recognized and we encourage further investigation.
Insect communities consist of aposematic species with efficient warning colours against predation... more Insect communities consist of aposematic species with efficient warning colours against predation, as well as abundant examples of crypsis. To understand such coexistence, we here report results from a field experiment where relative survival of artificial larvae, varying in conspicuousness, was estimated in natural bird communities over an entire season. This takes advantage of natural variation in the proportion of naive predators: naivety peaks when young birds have just fledged. We show that the relative benefit of warning signals and crypsis changes accordingly. When naive birds are rare (early and late in the season), conspicuous warning signals improve survival, but conspicuousness becomes a disadvantage near the fledging time of birds. Such temporal structuring of predator-prey relationships facilitates the coexistence of diverse antipredatory strategies and helps explain two patterns we found in a 688-species community of Lepidoterans: larval warning signals remain rare and occur disproportionately often in seasons when predators are educated.
The coincidental virulence evolution hypothesis suggests that outside-host selection, such as pre... more The coincidental virulence evolution hypothesis suggests that outside-host selection, such as predation, parasitism and resource competition can indirectly affect the virulence of environmentally-growing bacterial pathogens. While there are some examples of coincidental environmental selection for virulence, it is also possible that the resource acquisition and enemy defence is selecting against it. To test these ideas we conducted an evolutionary experiment by exposing the opportunistic pathogen bacterium Serratia marcescens to the particle-feeding ciliate Tetrahymena thermophila, the surface-feeding amoeba Acanthamoeba castellanii, and the lytic bacteriophage Semad11, in all possible combinations in a simulated pond water environment. After 8 weeks the virulence of the 384 evolved clones were quantified with fruit fly Drosophila melanogaster oral infection model, and several other life-history traits were measured. We found that in comparison to ancestor bacteria, evolutionary tre...
Lytic bacteriophages and protozoan predators are the major causes of bacterial mortality in natur... more Lytic bacteriophages and protozoan predators are the major causes of bacterial mortality in natural microbial communities, which also makes them potential candidates for biological control of bacterial pathogens. However, little is known about the relative impact of bacteriophages and protozoa on the dynamics of bacterial biomass in aqueous and biofilm phases. Here, we studied the temporal and spatial dynamics of bacterial biomass in a microcosm experiment where opportunistic pathogenic bacteria Serratia marcescens was exposed to particle-feeding ciliates, surface-feeding amoebas, and lytic bacteriophages for 8 weeks, ca. 1300 generations. We found that ciliates were the most efficient enemy type in reducing bacterial biomass in the open water, but least efficient in reducing the biofilm biomass. Biofilm was rather resistant against bacterivores, but amoebae had a significant long-term negative effect on bacterial biomass both in the open-water phase and biofilm. Bacteriophages had ...
Valkonen, Janne K. Warning signalling in European vipers and their mimics: implications for conse... more Valkonen, Janne K. Warning signalling in European vipers and their mimics: implications for conservation of the smooth snake Jyväskylä:
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