Can ultraviolet cues function as aposematic signals?
The fact that birds are sensitive to ultraviolet light (UV, 320–400 nm) has been largely ignored by previous studies of aposematism. Therefore, in the present article we investigated whether great tits preferred ultraviolet-reflecting colors compared to colors without UV reflection and whether UV cues alone could function as aposematic signals. We were able to manipulate prey visibility in UV light by changing the UV reflectance of prey items as well as altering the lighting conditions. In order to perform a preference experiment we used three pairs of colors (green UV vs. green, gray UV vs. gray, yellow UV vs. yellow) on a black background. The birds ate both UV types equally for all three…
The importance of pattern similarity between Müllerian mimics in predator avoidance learning
Müllerian mimicry, where unpalatable prey share common warning patterns, has long fascinated evolutionary biologists. It is commonly assumed that Müllerian mimics benefit by sharing the costs of predator education, thus reducing per capita mortality, although there has been no direct test of this assumption. Here, we specifically measure the selection pressure exerted by avian predators on unpalatable prey with different degrees of visual similarity in their warning patterns. Using wild-caught birds foraging on novel patterned prey in the laboratory, we unexpectedly found that pattern similarity did not increase the speed of avoidance learning, and even dissimilar mimics shared the educatio…
Resting metabolic rate can vary with age independently from body mass changes in the Colorado potato beetle, Leptinotarsa decemlineata.
Temperature and mass dependency of insect metabolic rates are well known, while less attention has been given to other factors, such as age. Among insect species that experience seasonal variation in environmental conditions, such as in temperate latitudes, age may also have indirect effects on the metabolic rate. We examined the effect of age on the resting metabolic rate of Leptinotarsa decemlineata during 11 days after adult emergence by using flow-through respirometry. Age had a significant mass-independent effect on metabolic rate of beetles. A twofold increase in metabolic rate occurred during the first 2 days of adult life after which metabolic rate decreased with age relatively slow…
Photoperiodic effects on diapause-associated gene expression trajectories in EuropeanLeptinotarsa decemlineatapopulations
Behavioural and physiological changes during diapause, an important strategy of insects for surviving harsh seasonal conditions, have been intensively studied. The genetic and molecular mechanisms underpinning diapause development are less well known. We took a candidate gene approach to study prediapause gene expression patterns in the Colorado potato beetle (Leptinotarsa decemlineata), an invasive insect that has rapidly spread northwards to high seasonality environments. Newly eclosed beetles originating from southern (Italy) and northern (Russia) Europe were reared under short- [12 h light (L):12 h dark (D)] and long-day (18L:6D) photoperiods for 10 days. This time period includes the s…
Sublethal effects of deltamethrin exposure of parental generations on physiological traits and overwintering inLeptinotarsa decemlineata
Although the evolution of insecticide resistance has received a lot of attention, less is known about sublethal effects of insecticide stress experienced by the preceding generations on the performance of pest populations. We investigated whether three generations of parental exposure to a deltamethrin insecticide influences physiological traits and overwintering success of offspring in Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae). Beetles descending from insecticide-exposed parents had lower adult body mass but higher relative lipid content and resting metabolic rate than those descending from non-insecticide-exposed parents. Also, a higher proportion of beetles descending f…
University of Jyväskylä research evaluation report 2018
Pre-invasion history and demography shape the genetic variation in the insecticide resistance-related acetylcholinesterase 2 gene in the invasive Colorado potato beetle
Abstract Background Invasive pest species offers a unique opportunity to study the effects of genetic architecture, demography and selection on patterns of genetic variability. Invasive Colorado potato beetle (Leptinotarsa decemlineata) populations have experienced a rapid range expansion and intense selection by insecticides. By comparing native and invasive beetle populations, we studied the origins of organophosphate (OP) resistance-associated mutations in the acetylcholinesterase 2 (AChE2) gene, and the role of selection and demography on its genetic variability. Results Analysis of three Mexican, two US and five European populations yielded a total of 49 haplotypes. Contrary to the exp…
Does predation maintain eyespot plasticity in Bicyclus anynana?
The butterfly Bicyclus anynana exhibits phenotypic plasticity involving the wet-season phenotype, which possesses marginal eyespots on the ventral surface of the wings, and the dry-season form, which lacks these eyespots. We examined the adaptive value of phenotypic plasticity of B. anynana in relation to the defence mechanisms of crypsis and deflection. We assessed the visibility differences between spotless and spotted butterflies against backgrounds of brown (dry season) or green (wet season) leaves. Spotless butterflies were highly cryptic and less predated by adult bird predators than were spotted ones when presented against brown leaf litter. However, the advantage of crypsis disappea…
Selection for cryptic coloration in a visually heterogeneous habitat.
We studied selection by predators for cryptic prey coloration in a visually heterogeneous habitat that consists of two microhabitats. It has been suggested that the probability of escaping detection in such habitats might be optimized by maximizing crypsis in one of the microhabitats. However, a recent model indicates that a coloration that compromises the requirements of different microhabitats might sometimes be the optimal solution. To experimentally study these hypotheses, we allowed great tits (Parus major L.) to search for artificial prey items in two different microhabitats (background boards): small patterned and large patterned. On each board there was one prey item that was either…
Stress for invasion success? Temperature stress of preceding generations modifies the response to insecticide stress in an invasive pest insect
Adaptation to stressful environments is one important factor influencing species invasion success. Tolerance to one stress may be complicated by exposure to other stressors experienced by the preceding generations. We studied whether parental temperature stress affects tolerance to insecticide in the invasive Colorado potato beetle Leptinotarsa decemlineata. Field-collected pyrethroid-resistant beetles were reared under either stressful (17°C) or favourable (23°C) insecticide-free environments for three generations. Then, larvae were exposed to pyrethroid insecticides in common garden conditions (23°C). Beetles were in general tolerant to stress. The parental temperature stress alone affect…
Variation in Hsp70 Levels after Cold Shock: Signs of Evolutionary Responses to Thermal Selection among Leptinotarsa decemlineata Populations
Individuals of widely spread species are expected to show local adaption in temperature tolerance as they encounter a range of thermal conditions. We tracked thermal adaptations of the Colorado potato beetle (Leptinotarsa decemlineata) that invaded Europe within the last 100 years. It has occupied various conditions although, like the majority of invasive species, it lost a measurable amount of neutral genetic variation due to bottleneck effect when it invaded Europe. We exposed diapausing beetles originated from three different latitudes (54°N, 59°N, 60°N) to cold shock (−5°C, 1.5 hrs) in order to test if beetles from the northern populations express differential levels of cold-induced and…
Northward range expansion requires synchronization of both overwintering behaviour and physiology with photoperiod in the invasive Colorado potato beetle (Leptinotarsa decemlineata)
Abstract. Photoperiodic phenological adaptations are prevalent in many organisms living in seasonal environments. As both photoperiod and growth season length change with latitude, species undergoing latitudinal range expansion often need to synchronize their life cycle with a changing photoperiod and growth season length. Since adaptive synchronization often involves a large number of time-consuming genetic changes, behavioural plasticity might be a faster way to adjust to novel conditions. We compared behavioural and physiological traits in overwintering (diapause) preparation in three latitudinally different European Colorado potato beetle (Leptinotarsa decemlineata) populations reared u…
Energy use, diapause behaviour and northern range expansion potential in the invasive Colorado potato beetle
Summary 1. As organisms expand their range towards northern latitudes they will encounter selective factors like harsh winter conditions. The ability to cope with and adapt to harsh winters may depend on the variability and evolutionary potential of relevant traits. 2. One adaptation in insects is winter diapause. It is characterized by changes in physiology, behaviour or in both. Physiological changes include lowered metabolic rate that enhances survival by saving limited energy reserves during overwintering. Active behavioural changes like burrowing into the soil allow individuals to escape harsh conditions. 3. We examined variation in overwintering body mass, resting metabolic rate (CO2 …
Strong antiapostatic selection against novel rare aposematic prey
The evolution of aposematism, a phenomenon where prey species conspicuously advertise their unprofitability to predators, is puzzling. How did conspicuousness evolve, if it simultaneously increased the likelihood of an inexperienced predator to detect the prey and presumably kill it? Antiapostatic selection, where rare prey is predated relatively more often, is considered as another major difficulty for aposematism to evolve. However, the risk of being conspicuous in low frequencies has not been experimentally tested. We designed an experiment to test how frequency (4%, 12%, 32%) of conspicuous aposematic prey and its dispersion type (solitary vs. aggregated) affect an initial predation ri…
Relative importance of taste and visual appearance for predator education in Müllerian mimicry
Mullerian mimicry, by definition, is the visual resemblance between two or more aposematic prey species. According to classical Mullerian 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 learne…
The voyage of an invasive species across continents: genetic diversity of North American and European Colorado potato beetle populations
The paradox of successful invading species is that they are likely to be genetically depauperate compared to their source population. This study on Colorado potato beetles is one of the few studies of the genetic consequences of continent-scale invasion in an insect pest. Understanding gene flow, population structure and the potential for rapid evolution in native and invasive populations offers insights both into the dynamics of small populations that become successful invaders and for their management as pests. We used this approach to investigate the invasion of the Colorado potato beetle (Leptinotarsa decemlineata) from North America to Europe. The beetles invaded Europe at the beginnin…
Is a change in juvenile hormone sensitivity involved in range expansion in an invasive beetle?
Introduction: It has been suggested that rapid range expansion could proceed through evolution in the endocrinological machinery controlling life-history switches. Based on this we tested whether the Colorado potato beetle, Leptinotarsa decemlineata, which has rapidly expanded its range across latitudinal regions in Europe, and shows photoperiodic adaptation in overwintering initiation, has different sensitivities to juvenile hormone (JH) manipulation along a latitudinal gradient. Results: A factorial experiment where beetles were reared either under a long or short day photoperiod was performed. Hormone levels were manipulated by topical applications. An allatostatin mimic, H17, was used t…
Population dependent effects of photoperiod on diapause related physiological traits in an invasive beetle (Leptinotarsa decemlineata).
Organisms undergoing latitudinal range expansion face a change in the photoperiod which can lead to a mismatch between the timing of seasonal changes in physiological and life history traits with seasonal environmental changes. This mismatch can lead to lowered survival, for example, due to unsynchronized diapause timing. Successful range expansion even in recent introductions requires that organisms which use the photoperiod for seasonal predictions should show interpopulational differences in photoperiodic responses at different latitudes, as the photoperiod is a function of latitude. We investigated among population differences in photoperiodic responses of life history and physiological…
Ultraviolet reflection and predation risk in diurnal and nocturnal Lepidoptera
According to our extensive data on Lepidoptera (883 species), UV wing patterns are almost three times more common in nocturnal than in diurnal Lepidoptera. This might be due to predation, because the primary diurnal predators, birds, utilize UV light in foraging and even prefer UV-reflecting prey. To test this hypothesis, we conducted a field experiment with tethered living moths whose wings were artificially manipulated to reflect (UV+, reflection at UV wavelength: 15%) or absorb (UV - ) UV light, keeping longer wavelengths identical. Thus, any difference found in survival rates would be the result of the difference in wing patterns in UV spectrum. Significantly more UV+ moths th…
Responses in metabolic rate to changes in temperature in diapausing Colorado potato beetleLeptinotarsa decemlineatafrom three European populations
Many insects survive adverse periods in seasonal environments by entering diapause, a deep resting stage, during which energy consumption is typically low and gas exchange is in the form of a discontinuous gas exchange cycle (DGC). Because insects in high-latitude environments are severely time constrained during summer, an effective diapause termination with careful regulation of metabolic rate is important. The present study examines whether diapausing Colorado potato beetles Leptinotarsa decemlineataSay originating from three latitudinally different regions in Europe differ in their quantitative or qualitative gas exchange patterns in response to an increasing temperature. Overall produc…
Predator experience on cryptic prey affects the survival of conspicuous aposematic prey.
Initially, aposematism, which is an unprofitable trait, e.g. noxiousness conspicuously advertised to predators, appears to be a paradox since conspicuousness should increase predation by naive predators. However, reluctance of predators for eating novel prey (e.g. neophobia) might balance the initial predation caused by inexperienced predators. We tested the novelty effects on initial predation and avoidance learning in two separate conspicuousness levels of aposematic prey by using a 'novel world' method. Half of the wild great tits (Parus major) were trained to eat cryptic prey prior to the introduction of an aposematic prey, which potentially creates a bias against the aposematic morph. …
Significance of butterfly eyespots as an anti-predator device in ground-based and aerial attacks
Many butterfly genera are characterised by the presence of marginal eyespots on their wings. One hypothesis to account for an occurrence of eyespots is that these wing pattern elements are partly the outcome of visual selection by predators. Bicyclus anynana (Satyrinae) has underside spotting on its wings but there is also a seasonal form in which the eyespots are reduced in size or totally absent. This natural variation gives us a useful tool to test the hypothesis that marginal eyespot patterns can decoy the attacking predator by, at least sometimes, diverting attack from vital body parts to the edges of the wings. We used lizards, Anolis carolinensis, and pied flycatchers, Ficedula hypol…
Responses of a native plant species from invaded and uninvaded areas to allelopathic effects of an invader
Invaders exert new selection pressures on the resident species, for example, through competition for resources or by using novel weapons. It has been shown that novel weapons aid invasion but it is unclear whether native species co‐occurring with in‐ vaders have adapted to tolerate these novel weapons. Those resident species which are able to adapt to new selective agents can co‐occur with an invader while others face a risk of local extinction. We ran a factorial common garden experiment to study whether a native plant species, Anthriscus sylvestris, has been able to evolve a greater tolerance to the allelochemicals exerted by the invader, Lupinus polyphyllus. Lupinus polyphyllus produces …
Genetic variation in growth and development time under two selection regimes in Leptinotarsa decemlineata
It is possible to predict the potential range of a species on the basis of its ecological characteristics and those of the invaded ecosystem. The existence of genetic variation indicates a species' potential to respond to new environmental conditions, thus facilitating its success as an invader. Accordingly, evolutionary and ecological approaches are needed to identify the factors explaining both species' range and their potential to invade new areas. We combined these two approaches and studied whether genetic variation in life-history traits under abiotic (temperature) and biotic (host plant) selection pressures contributes to the potential range expansion of Leptinotarsa decemlineata Say…
THE EFFECT OF ALTERNATIVE PREY ON THE DYNAMICS OF IMPERFECT BATESIAN AND MÜLLERIAN MIMICRIES
Both Batesian and Müllerian mimicries are considered classical evidence of natural selection where predation pressure has, at times, created a striking similarity between unrelated prey species. Batesian mimicry, in which palatable mimics resemble unpalatable aposematic species, is parasitic and only beneficial to the mimics. By contrast, in classical Müllerian mimicry the cost of predators' avoidance learning is shared between similar unpalatable co-mimics, and therefore mimicry benefits all parties. Recent studies using mathematical modeling have questioned the dynamics of Müllerian mimicry, suggesting that fitness benefits should be calculated in a way similar to Batesian mimicry; that i…
Negatively condition dependent predation cost of a positively condition dependent sexual signalling.
Predation is considered as an important factor constraining the expression of sexual signals. Nevertheless, direct quantitative evidence for predation provoking significant viability costs on individuals signalling at high rates is scarce. Moreover, it is unclear whether high rate signallers are able to balance presumably increased predation costs. We examined whether a condition dependent audible sexual signal, drumming, makes Hygrolycosa rubrofasciata male spiders more prone to predation by pied flycatchers (Ficedula hypoleuca), and whether sexual signalling rate is related to escaping ability once attacked. When birds were given a choice between two spider males manipulated to drum eithe…
Cold tolerance during larval development: effects on the thermal distribution limits of Leptinotarsa decemlineata
Insects' cold tolerance during their development is a surprisingly understudied subject in ecology, despite the fact that subzero temperatures during the growing season are common at high altitudes and latitudes. Subzero temperatures can have detrimental effects on organisms, restricting a species' range. This study addresses the question whether night frosts during the growing season have an instant or delayed negative impact on larval mortality of the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae). We also tested whether populations from the centre (Poland) and margins (Russia) of the distribution range of L. decemlineata differ in their responses to s…
Data from: Stress for invasion success? Temperature stress of preceding generations modifies the response to insecticide stress in an invasive pest insect
Adaptation to stressful environments is one important factor influencing species invasion success. Tolerance to one stress may be complicated by exposure to other stressors experienced by the preceding generations. We studied whether parental temperature stress affects tolerance to insecticide in the invasive Colorado potato beetle Leptinotarsa decemlineata. Field-collected pyrethroid-resistant beetles were reared under either stressful (17°C) or favourable (23°C) insecticide-free environments for three generations. Then, larvae were exposed to pyrethroid insecticides in common garden conditions (23°C). Beetles were in general tolerant to stress. The parental temperature stress alone affect…