Phytophthora infestans (Mont.) de Bary is one of the most serious and economically important path... more Phytophthora infestans (Mont.) de Bary is one of the most serious and economically important pathogens in potato fields worldwide, including Estonia. Under favourable conditions it can destroy the whole potato haulm and cause a considerable yield loss. In Estonia, the average yield loss due to late blight can reach 20-25% and in untreated fields, even more. Without control of potato late blight it is not possible to achieve high-quality crop yield. In Estonia, fungicides are used routinely in conventional potato production, but under favourable conditions for the disease, with heavy pressure of the pathogen, protecting large areas is complicated. P. infestans isolated from potato leaves and tubers were collected from a region of Eastern Estonia during 2001-07. In total, 133 isolates were assessed for mating type. The average frequencies of mating types A1 and A2 were 59% and 38% respectively. The data indicate that in the Estonian population of P. Infestans, both mating types occur ...
Kiskluse roll putukate kehasuuruse evolutsioonis erinevate värvusstrateegiate korral Käesoleva do... more Kiskluse roll putukate kehasuuruse evolutsioonis erinevate värvusstrateegiate korral Käesoleva doktoriväitekirja eesmärk on hinnata kehasuurusest positiivselt sõltuva kisklusriski potentsiaali tasakaalustada paljudel putukatel leitud tugevat seost kehasuuruse ja viljakuse vahel. See võimaldaks selgitada niisuguste putukate esmapilgul mitteadaptiivselt lühikesena näivat kasvuperioodi. Uurimisel võeti arvesse eri värvusstrateegiate mõju kisklusriski suurusest-sõltuvuse suunale ja tugevusele. Kehasuurus saab lindude vahendatud kisklusriski mõjutada kas saaklooma silmatorkavuse või kiskja eelistuste kaudu. Laborikatsetes leiti, et linnud (Parus major) ründavad meelsmini suuremaid varjevärvusega, kuid väiksemaid hoiatusvärvusega saakloomi. Saaklooma leidmise kiirus sõltus aga suurusest hoiatusvärvuse puhul tunduvalt tugevamini kui varjevärvuse korral. Hindamaks nende kahe valikusurve reaalset tulemust viidi läbi välikatsed, mis andsid mõlema värvitüübi puhul tulemuseks positiivse sõlt...
Biocontrol providing parasitoids can orientate according to volatile organic compounds (VOCs) of ... more Biocontrol providing parasitoids can orientate according to volatile organic compounds (VOCs) of their host’s plants, the emission of which is potentially dependent on the availability of soil nitrogen (N). This paper aimed at finding the optimal N fertilization rate for oilseed rape (Brassica napus L.) to favor parasitism of pollen beetles (Brassicogethes aeneus Fab. syn. Meligethes aeneus Fab.) in a controlled environment. Pollen beetles preferred to oviposit into buds of plants growing under higher N fertilization, whereas their parasitoids favored moderate N fertilization. As a part of induced defense, the proportion of volatile products of glucosinolate pathway in the total oilseed rape VOC emission blend was increased. Our results suggest that the natural biological control of pollen beetle herbivory is best supported by moderate N fertilization rates.
The characteristics of populations of Phytophthora infestans from organic farms, small convention... more The characteristics of populations of Phytophthora infestans from organic farms, small conventional farms and large conventional farms were determined from isolates collected in northern Estonia in 2004 and 2005. For the population as a whole 41% were A2; all virulence factors to the 11 R genes from Solanum demissum were found; and more than 70% had high or intermediate resistance to metalaxyl. Isolates from organic farms tended to have more complex pathotypes than isolates from either large or small conventional farms, but there was a higher proportion of metalaxyl resistant isolates from large conventional farms than from small conventional farms or from organic farms.
... Late blight is caused by the fungus-like oomycete P. infestans, which can reproduce both sexu... more ... Late blight is caused by the fungus-like oomycete P. infestans, which can reproduce both sexually and asexu-ally. ... The 'new genotypes' also proved to be gener-ally more aggressive than the old clonal lineage (Carlisle et al., 2002; Shattock, 2002). In Estonia, the A2 mating ...
While the study of colour patterns is a traditional subject of evolutionary ecology, there are va... more While the study of colour patterns is a traditional subject of evolutionary ecology, there are various hypotheses which suffer from a lack of experimental evidence. One intriguing possibility is a trade-off between warning efficiency and detectability. After a certain size threshold, the detrimental effect of increased detectability can outweigh the benefits of warning colouration. One may thus expect corresponding patterns at the level of ontogenetic development: as juveniles grow, they should first acquire warning colouration, and then lose it again. We analysed this possibility in Orgyia antiqua, a moth species with hairy larvae which are polyphenic with respect to the intensity of warning colouration. We detected a regular change in colour patterns through larval life. Indeed, the larvae tend to display warning colouration at intermediate sizes while dull colours dominate in fully grown larvae. In aviary experiments, we confirmed that the colourful phenotype is the one that causes the strongest aversion in birds. Nevertheless, the effect was rather weak and most of the larvae were still eventually consumed when found. Unexpectedly, for human subjects, the warningly coloured larvae were harder, and not easier to find among natural vegetation, most likely due to the disruptive effect of the aposematic colour pattern. Importantly, the trend was reversed in the largest size class, suggesting that the disruptive colouration loses its advantage as the larva grows. This is consistent with the actual patterns of size-dependence of colouration. We present evidence against an alternative explanation which relates size-related change in colouration to behavioural changes prior to pupation. We conclude that even if the efficiency of the warning effect plays a role in determining the size-dependence of colouration, the pattern may be largely explained by the effects of size-dependent detectability alone.
... IMPLICATIONS OF COLOUR Master thesis Supervisor: Toomas Tammaru, Ph. D. TARTU 2004 ... positi... more ... IMPLICATIONS OF COLOUR Master thesis Supervisor: Toomas Tammaru, Ph. D. TARTU 2004 ... positively size dependent mortality, which may result from size-selective predation by natural enemies (Teder & Tammaru 2001). However, case studies dealing with size dependent ...
Assumptions about mortality rates form a cornerstone for models of life-history evolution. When s... more Assumptions about mortality rates form a cornerstone for models of life-history evolution. When seeking adaptive explanations for body sizes, the size dependence of predation risk is of particular interest. Here, we review published studies that provide (1) estimates of the daily predation rates experienced by insect larvae feeding on tree leaves or (2) evidence concerning the relationship between predation risk and larval size. Larvae were found to experience an average avian predation rate of 3.1% per day and an average arthropod predation rate of 10.5% per day. In some studies, mortality rates were systematically dependent on parameters of the larvae (e.g. coloration) or of the environment (host plant, season), but not to the extent that would render generalizations meaningless. Nevertheless, mortality rates varied considerably more for arthropod than avian predators, making an estimate of avian predation rate more reliable for use in quantitative models. Moreover, birds tend to be a more important predator guild exploiting the larger larval stages, as indicated by the predominantly positive size dependence of avian predation risk. By contrast, predation by arthropods was generally negatively size dependent. Based on the available data, we estimate that avian predation rates increase approximately 3.6-fold, while arthropod predation rates decrease approximately 4.9-fold, in response to a 2-fold increase in the linear size of prey. A modelling exercise showed that realistic mortality rates-if assumed to be independent of size-cannot serve as a basis for adaptive explanations for observed body sizes. However, by assuming a positive size dependence of mortality risk within the limits observed for bird predation, it is possible to explain a wide range of body sizes within an optimality framework.
To understand the evolution of warning coloration, it is important to distinguish between differe... more To understand the evolution of warning coloration, it is important to distinguish between different aspects of conspicuous color patterns. As an example, both pattern element size and body size of prey have been shown to enhance the effectiveness of warning signals. However, it is unclear whether the effect of body size is merely a side effect of proportionally increasing pattern elements, or if there is an effect of body size per se. These possibilities were evaluated by offering different sized artificial caterpillars with either fixed or proportionally increasing aposematic color signal elements to wild great tits, Parus major L. (Passeriformes: Paridae). The birds' hesitation time to attack each "caterpillar" was used as a measure of the warning effect. The hesitation time showed a significant, positive size-dependence with the caterpillars whose pattern elements increased proportionally with their body size. In contrast, no size dependence was found in the larvae with fixed-size signal elements. Such a difference in mortality curves is consistent with the idea that pattern element size is a more important aspect than body size in enhancing a warning signal. Since no evidence of an effect of body size per se on signal efficiency was found, this study does not support the hypothesis that aposematic insects gain more from large size than cryptic ones.
Plant volatile organic compounds (VOCs) elicited in response to herbivory serve as cues for paras... more Plant volatile organic compounds (VOCs) elicited in response to herbivory serve as cues for parasitic and predatory insects. Knowledge about quantitative relationships between the extent of herbivore-induced damage and the quantities of VOCs released is scarce. We studied the kinetics of VOC-emissions from foliage of the deciduous tree Alnus glutinosa induced by feeding activity of larvae of the geometrid moth Cabera pusaria. Quantitative relationships between the intensity of stress and strength of plant response were determined. Intensity of biotic stress was characterized by herbivore numbers (0-8 larvae) and by the amount of leaf area eaten. The strength of plant response was characterized by monitoring (i) changes in photosynthesis, (ii) leaf ultrastructure, and (iii) plant volatiles. Net assimilation rate displayed compensatory responses in herbivore-damaged leaves compared with control leaves. This compensatory response was associated with an overall increase in chloroplast size. Feedinginduced emissions of products of the lipoxygenase pathway (LOX products; (E)-2-hexenal, (Z)-3-hexenol, 1-hexanol, and (Z)-3-hexenyl acetate) peaked at day 1 after larval feeding started, followed by an increase of emissions of ubiquitous monoterpenes peaking on days 2 and 3. The emission of the monoterpene (E)-β-ocimene and of the nerolidol-derived homoterpene 4,8-dimethyl-nona-1,3,7-triene (DMNT) peaked on day 3. Furthermore, the emission kinetics of the sesquiterpene (E,E)-α-farnesene tended to be biphasic with peaks on days 2 and 4 after start of larval feeding. Emission rates of the induced LOX products, of (E)-β-ocimene and (E,E)-α-farnesene were positively correlated with the number of larvae feeding. In contrast, the emission of DMNT was independent of the number of feeders. These data show quantitative relationships between the strength of herbivory and the emissions of LOX products and most of the terpenoids elicited in response to feeding. Thus, herbivory-elicited LOX products and terpenoid emissions may convey both quantitative and qualitative signals to antagonists of the herbivores. In contrast, our data suggest that the feeding-induced homoterpene DMNT conveys the information "presence of herbivores" rather than information about the quantities of herbivores to predators and parasitoids.
1. Body size is positively correlated with fecundity in various animals, but the factors that cou... more 1. Body size is positively correlated with fecundity in various animals, but the factors that counterbalance the resulting selection pressure towards large size are difficult to establish. Positively sizedependent predation risk has been proposed as a selective factor potentially capable of balancing the fecundity advantage of large size. 2. To construct optimality models of insect body size, realistic estimates of size-dependent predation rates are necessary. Moreover, prey traits such as colouration should be considered, as they may substantially alter the relationship between body size and mortality risk. 3. To quantify mortality patterns, we conducted field experiments in which we exposed cryptic and conspicuous artificial larvae of different sizes to bird predators, and recorded the incidence of bird attacks. 4. The average daily mortality rate was estimated to vary between 4% and 10%. In both cryptic and conspicuous larvae, predation risk increased with prey size, but the increase tended to be steeper in the conspicuous group. No main effect of colour type was found. All the quantitative relationships were reasonably consistent across replicates. 5. Our results suggest that the size dependence of mortality risk in insect prey is primarily determined by the probability of being detected by a predator rather than by a size-dependent warning effect associated with conspicuous colouration. Our results therefore imply that warningly coloured insects do not necessarily benefit more than the cryptic species from large body size, as has been previously suggested.
1. The majority of general life-history models treat the environment as being invariable through ... more 1. The majority of general life-history models treat the environment as being invariable through time, even though temporal variation in selective agents could dramatically change the outcomes, e.g. in terms of optimal size and time at maturity. For but seasonal dynamics of top-down selective forces are poorly documented.
Phytophthora infestans (Mont.) de Bary is one of the most serious and economically important path... more Phytophthora infestans (Mont.) de Bary is one of the most serious and economically important pathogens in potato fields worldwide, including Estonia. Under favourable conditions it can destroy the whole potato haulm and cause a considerable yield loss. In Estonia, the average yield loss due to late blight can reach 20-25% and in untreated fields, even more. Without control of potato late blight it is not possible to achieve high-quality crop yield. In Estonia, fungicides are used routinely in conventional potato production, but under favourable conditions for the disease, with heavy pressure of the pathogen, protecting large areas is complicated. P. infestans isolated from potato leaves and tubers were collected from a region of Eastern Estonia during 2001-07. In total, 133 isolates were assessed for mating type. The average frequencies of mating types A1 and A2 were 59% and 38% respectively. The data indicate that in the Estonian population of P. Infestans, both mating types occur ...
Kiskluse roll putukate kehasuuruse evolutsioonis erinevate värvusstrateegiate korral Käesoleva do... more Kiskluse roll putukate kehasuuruse evolutsioonis erinevate värvusstrateegiate korral Käesoleva doktoriväitekirja eesmärk on hinnata kehasuurusest positiivselt sõltuva kisklusriski potentsiaali tasakaalustada paljudel putukatel leitud tugevat seost kehasuuruse ja viljakuse vahel. See võimaldaks selgitada niisuguste putukate esmapilgul mitteadaptiivselt lühikesena näivat kasvuperioodi. Uurimisel võeti arvesse eri värvusstrateegiate mõju kisklusriski suurusest-sõltuvuse suunale ja tugevusele. Kehasuurus saab lindude vahendatud kisklusriski mõjutada kas saaklooma silmatorkavuse või kiskja eelistuste kaudu. Laborikatsetes leiti, et linnud (Parus major) ründavad meelsmini suuremaid varjevärvusega, kuid väiksemaid hoiatusvärvusega saakloomi. Saaklooma leidmise kiirus sõltus aga suurusest hoiatusvärvuse puhul tunduvalt tugevamini kui varjevärvuse korral. Hindamaks nende kahe valikusurve reaalset tulemust viidi läbi välikatsed, mis andsid mõlema värvitüübi puhul tulemuseks positiivse sõlt...
Biocontrol providing parasitoids can orientate according to volatile organic compounds (VOCs) of ... more Biocontrol providing parasitoids can orientate according to volatile organic compounds (VOCs) of their host’s plants, the emission of which is potentially dependent on the availability of soil nitrogen (N). This paper aimed at finding the optimal N fertilization rate for oilseed rape (Brassica napus L.) to favor parasitism of pollen beetles (Brassicogethes aeneus Fab. syn. Meligethes aeneus Fab.) in a controlled environment. Pollen beetles preferred to oviposit into buds of plants growing under higher N fertilization, whereas their parasitoids favored moderate N fertilization. As a part of induced defense, the proportion of volatile products of glucosinolate pathway in the total oilseed rape VOC emission blend was increased. Our results suggest that the natural biological control of pollen beetle herbivory is best supported by moderate N fertilization rates.
The characteristics of populations of Phytophthora infestans from organic farms, small convention... more The characteristics of populations of Phytophthora infestans from organic farms, small conventional farms and large conventional farms were determined from isolates collected in northern Estonia in 2004 and 2005. For the population as a whole 41% were A2; all virulence factors to the 11 R genes from Solanum demissum were found; and more than 70% had high or intermediate resistance to metalaxyl. Isolates from organic farms tended to have more complex pathotypes than isolates from either large or small conventional farms, but there was a higher proportion of metalaxyl resistant isolates from large conventional farms than from small conventional farms or from organic farms.
... Late blight is caused by the fungus-like oomycete P. infestans, which can reproduce both sexu... more ... Late blight is caused by the fungus-like oomycete P. infestans, which can reproduce both sexually and asexu-ally. ... The 'new genotypes' also proved to be gener-ally more aggressive than the old clonal lineage (Carlisle et al., 2002; Shattock, 2002). In Estonia, the A2 mating ...
While the study of colour patterns is a traditional subject of evolutionary ecology, there are va... more While the study of colour patterns is a traditional subject of evolutionary ecology, there are various hypotheses which suffer from a lack of experimental evidence. One intriguing possibility is a trade-off between warning efficiency and detectability. After a certain size threshold, the detrimental effect of increased detectability can outweigh the benefits of warning colouration. One may thus expect corresponding patterns at the level of ontogenetic development: as juveniles grow, they should first acquire warning colouration, and then lose it again. We analysed this possibility in Orgyia antiqua, a moth species with hairy larvae which are polyphenic with respect to the intensity of warning colouration. We detected a regular change in colour patterns through larval life. Indeed, the larvae tend to display warning colouration at intermediate sizes while dull colours dominate in fully grown larvae. In aviary experiments, we confirmed that the colourful phenotype is the one that causes the strongest aversion in birds. Nevertheless, the effect was rather weak and most of the larvae were still eventually consumed when found. Unexpectedly, for human subjects, the warningly coloured larvae were harder, and not easier to find among natural vegetation, most likely due to the disruptive effect of the aposematic colour pattern. Importantly, the trend was reversed in the largest size class, suggesting that the disruptive colouration loses its advantage as the larva grows. This is consistent with the actual patterns of size-dependence of colouration. We present evidence against an alternative explanation which relates size-related change in colouration to behavioural changes prior to pupation. We conclude that even if the efficiency of the warning effect plays a role in determining the size-dependence of colouration, the pattern may be largely explained by the effects of size-dependent detectability alone.
... IMPLICATIONS OF COLOUR Master thesis Supervisor: Toomas Tammaru, Ph. D. TARTU 2004 ... positi... more ... IMPLICATIONS OF COLOUR Master thesis Supervisor: Toomas Tammaru, Ph. D. TARTU 2004 ... positively size dependent mortality, which may result from size-selective predation by natural enemies (Teder & Tammaru 2001). However, case studies dealing with size dependent ...
Assumptions about mortality rates form a cornerstone for models of life-history evolution. When s... more Assumptions about mortality rates form a cornerstone for models of life-history evolution. When seeking adaptive explanations for body sizes, the size dependence of predation risk is of particular interest. Here, we review published studies that provide (1) estimates of the daily predation rates experienced by insect larvae feeding on tree leaves or (2) evidence concerning the relationship between predation risk and larval size. Larvae were found to experience an average avian predation rate of 3.1% per day and an average arthropod predation rate of 10.5% per day. In some studies, mortality rates were systematically dependent on parameters of the larvae (e.g. coloration) or of the environment (host plant, season), but not to the extent that would render generalizations meaningless. Nevertheless, mortality rates varied considerably more for arthropod than avian predators, making an estimate of avian predation rate more reliable for use in quantitative models. Moreover, birds tend to be a more important predator guild exploiting the larger larval stages, as indicated by the predominantly positive size dependence of avian predation risk. By contrast, predation by arthropods was generally negatively size dependent. Based on the available data, we estimate that avian predation rates increase approximately 3.6-fold, while arthropod predation rates decrease approximately 4.9-fold, in response to a 2-fold increase in the linear size of prey. A modelling exercise showed that realistic mortality rates-if assumed to be independent of size-cannot serve as a basis for adaptive explanations for observed body sizes. However, by assuming a positive size dependence of mortality risk within the limits observed for bird predation, it is possible to explain a wide range of body sizes within an optimality framework.
To understand the evolution of warning coloration, it is important to distinguish between differe... more To understand the evolution of warning coloration, it is important to distinguish between different aspects of conspicuous color patterns. As an example, both pattern element size and body size of prey have been shown to enhance the effectiveness of warning signals. However, it is unclear whether the effect of body size is merely a side effect of proportionally increasing pattern elements, or if there is an effect of body size per se. These possibilities were evaluated by offering different sized artificial caterpillars with either fixed or proportionally increasing aposematic color signal elements to wild great tits, Parus major L. (Passeriformes: Paridae). The birds' hesitation time to attack each "caterpillar" was used as a measure of the warning effect. The hesitation time showed a significant, positive size-dependence with the caterpillars whose pattern elements increased proportionally with their body size. In contrast, no size dependence was found in the larvae with fixed-size signal elements. Such a difference in mortality curves is consistent with the idea that pattern element size is a more important aspect than body size in enhancing a warning signal. Since no evidence of an effect of body size per se on signal efficiency was found, this study does not support the hypothesis that aposematic insects gain more from large size than cryptic ones.
Plant volatile organic compounds (VOCs) elicited in response to herbivory serve as cues for paras... more Plant volatile organic compounds (VOCs) elicited in response to herbivory serve as cues for parasitic and predatory insects. Knowledge about quantitative relationships between the extent of herbivore-induced damage and the quantities of VOCs released is scarce. We studied the kinetics of VOC-emissions from foliage of the deciduous tree Alnus glutinosa induced by feeding activity of larvae of the geometrid moth Cabera pusaria. Quantitative relationships between the intensity of stress and strength of plant response were determined. Intensity of biotic stress was characterized by herbivore numbers (0-8 larvae) and by the amount of leaf area eaten. The strength of plant response was characterized by monitoring (i) changes in photosynthesis, (ii) leaf ultrastructure, and (iii) plant volatiles. Net assimilation rate displayed compensatory responses in herbivore-damaged leaves compared with control leaves. This compensatory response was associated with an overall increase in chloroplast size. Feedinginduced emissions of products of the lipoxygenase pathway (LOX products; (E)-2-hexenal, (Z)-3-hexenol, 1-hexanol, and (Z)-3-hexenyl acetate) peaked at day 1 after larval feeding started, followed by an increase of emissions of ubiquitous monoterpenes peaking on days 2 and 3. The emission of the monoterpene (E)-β-ocimene and of the nerolidol-derived homoterpene 4,8-dimethyl-nona-1,3,7-triene (DMNT) peaked on day 3. Furthermore, the emission kinetics of the sesquiterpene (E,E)-α-farnesene tended to be biphasic with peaks on days 2 and 4 after start of larval feeding. Emission rates of the induced LOX products, of (E)-β-ocimene and (E,E)-α-farnesene were positively correlated with the number of larvae feeding. In contrast, the emission of DMNT was independent of the number of feeders. These data show quantitative relationships between the strength of herbivory and the emissions of LOX products and most of the terpenoids elicited in response to feeding. Thus, herbivory-elicited LOX products and terpenoid emissions may convey both quantitative and qualitative signals to antagonists of the herbivores. In contrast, our data suggest that the feeding-induced homoterpene DMNT conveys the information "presence of herbivores" rather than information about the quantities of herbivores to predators and parasitoids.
1. Body size is positively correlated with fecundity in various animals, but the factors that cou... more 1. Body size is positively correlated with fecundity in various animals, but the factors that counterbalance the resulting selection pressure towards large size are difficult to establish. Positively sizedependent predation risk has been proposed as a selective factor potentially capable of balancing the fecundity advantage of large size. 2. To construct optimality models of insect body size, realistic estimates of size-dependent predation rates are necessary. Moreover, prey traits such as colouration should be considered, as they may substantially alter the relationship between body size and mortality risk. 3. To quantify mortality patterns, we conducted field experiments in which we exposed cryptic and conspicuous artificial larvae of different sizes to bird predators, and recorded the incidence of bird attacks. 4. The average daily mortality rate was estimated to vary between 4% and 10%. In both cryptic and conspicuous larvae, predation risk increased with prey size, but the increase tended to be steeper in the conspicuous group. No main effect of colour type was found. All the quantitative relationships were reasonably consistent across replicates. 5. Our results suggest that the size dependence of mortality risk in insect prey is primarily determined by the probability of being detected by a predator rather than by a size-dependent warning effect associated with conspicuous colouration. Our results therefore imply that warningly coloured insects do not necessarily benefit more than the cryptic species from large body size, as has been previously suggested.
1. The majority of general life-history models treat the environment as being invariable through ... more 1. The majority of general life-history models treat the environment as being invariable through time, even though temporal variation in selective agents could dramatically change the outcomes, e.g. in terms of optimal size and time at maturity. For but seasonal dynamics of top-down selective forces are poorly documented.
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