Life-history Traits In Response Research Articles

Quantitative genetic analysis of responses to larval food limitation in a polyphenic butterfly indicates environment‐ and trait‐specific effects

Different components of heritability, including genetic variance (VG), are influenced by environmental conditions. Here, we assessed phenotypic responses of life-history traits to two different developmental conditions, temperature and food limitation. The former represents an environment that defines seasonal polyphenism in our study organism, the tropical butterfly Bicyclus anynana, whereas the latter represents a more unpredictable environment. We quantified heritabilities using restricted maximum likelihood (REML) procedures within an “Information Theoretical” framework in a full-sib design. Whereas development time, pupal mass, and resting metabolic rate showed no genotype-by-environment interaction for genetic variation, for thorax ratio and fat percentage the heritability increased under the cool temperature, dry season environment. Additionally, for fat percentage heritability estimates increased under food limitation. Hence, the traits most intimately related to polyphenism in B. anynana show the most environmental-specific heritabilities as well as some indication of cross-environmental genetic correlations. This may reflect a footprint of natural selection and our future research is aimed to uncover the genes and processes involved in this through studying season and condition-dependent gene expression.

Rapid evolution in response to increased temperature maintains population viability despite genetic erosion in a tropical ectotherm

Climate change is predicted to increase the average global air temperature by up to 4.0 °C by the end of the century. This increased temperature could have negative effects on many life history traits that are closely linked to fitness. Many species will therefore have to adapt to the warmer environment, but life history traits often have limited additive genetic variance. Here, we investigated population demographics and the evolutionary response of life history traits, as well as genetic diversity in guppies (Poecilia reticulata), in response to an experimentally increased temperature. There were fewer successful pregnancies, smaller brood sizes, and males matured earlier at a higher temperature as compared to control populations. However, there was no sign of an evolutionary response in these traits after 24 months of exposure to the increased temperature. We also found that population size, brood survivorship, sex ratio, and male length at maturity were unaffected by the increased temperature. Genetic diversity decreased rapidly in the increased temperature populations at a rate equivalent to an effective population size of only one quarter of the controls, revealing a clear signature of selection in response to increased temperature. This genetic erosion, however, could hamper the adaptive potential of the populations to other environmental changes associated with climate change.

Increased Phenotypic Plasticity to Climate May Have Boosted the Invasion Success of Polyploid Centaurea stoebe

Phenotypic plasticity may allow organisms to cope with altered environmental conditions as e.g. after the introduction into a new range. In particular polyploid organisms, containing more than two sets of chromosomes, may show high levels of plasticity, which could in turn increase their environmental tolerance and invasiveness. Here, we studied the role of phenotypic plasticity in the invasion of Centaurea stoebe (Asteraceae), which in the native range in Europe occurs as diploids and tetraploids, whereas in the introduced range in North America so far only tetraploids have been found. In a common garden experiment at two sites in the native range, we grew half-sibs of the three geo-cytotypes (native European diploids, European tetraploids and invasive North American tetraploids) from a representative sample of 27 populations. We measured the level and the adaptive significance of phenotypic plasticity in eco-physiological and life-history traits in response to the contrasting climatic conditions at the two study sites as well as three different soil conditions in pots, simulating the most crucial abiotic differences between the native and introduced range. European tetraploids showed increased levels of phenotypic plasticity as compared to diploids in response to the different climatic conditions in traits associated with rapid growth and fast phenological development. Moreover, we found evidence for adaptive plasticity in these traits, which suggests that increased plasticity may have contributed to the invasion success of tetraploid C. stoebe by providing an advantage under the novel climatic conditions. However, in invasive tetraploids phenotypic plasticity was similar to that of native tetraploids, indicating no evolution of increased plasticity during invasions. Our findings provide the first empirical support for increased phenotypic plasticity associated with polyploids, which may contribute to their success as invasive species in novel environments.

Life-history and thermal tolerance traits display different thermal plasticities and relationships with temperature in the marine polychaete Ophryotrocha labronica La Greca and Bacci (Dorvilleidae)

In order to gain insights into links between fitness and physiological function, the phenotypic plasticity of life-history traits and thermal tolerances has been investigated in a laboratory strain of the polychaete Ophryotrocha labronica acclimated to a broad range of temperatures. Reproductive pairs were kept in isolation for two months at one of six temperatures (10, 15, 20, 25, 30 and 35°C), and survival and a number of life-history traits recorded. Tolerance to heat and cold was assessed in individuals that survived the acclimation period by measuring upper and lower thermal limits. Life-history and thermal tolerance traits showed different relationships with temperature: generally non-monotonic for life-history and monotonic for thermal limits. The thermal history of the strain used in the study seemed to be partly responsible for this pattern, affecting the thermal responses of most life-history traits, but not those of the upper and lower thermal limits. Survival correlated positively with tolerance to cold but not with heat tolerance. This result supports the idea that tolerance to heat is under stronger selection in O. labronica, resulting in a lower level of plasticity for this trait. Some life-history features positively co-varied with tolerance to heat (e.g. body size), whilst in other cases reproductive traits showed apparent trade-offs with thermal limits. In all cases correlations amongst traits were apparently driven by their relationship with temperature. Even if we found no evolutionary trade-offs among the thermal responses of life-history traits and thermal limits, the strategies evolved by organisms to cope with thermal variability result from the mutual interaction of these traits, which plays a key role in defining organisms' responses to temperature changes and fluctuations.

Warming leads to divergent responses but similarly improved performance of two invasive thistles

AbstractPlants’ responses to climate change are complex. Even the same net performance changes may involve different responses of multiple life history traits. Here we show that two congeneric thistles, Carduus nutans and Carduus acanthoides, both grew taller under increased temperature, albeit following divergent response patterns. For C. nutans, warming advanced bolting more than flowering, leading to a longer growing period before flowering and ultimately taller plant height at the end of the growing season. Carduus acanthoides maintained the same length of growing period because of equally shifted events in the phenological sequence, however, post‐flowering growth rate was increased, which also led to enhanced final plant height. As seeds from taller plants disperse farther, their responses imply that future invasion spread rates of these two species will increase. Similar consequences due to divergent responses in life history traits, as demonstrated in this study, suggest that considering only ultimate performance outcomes, and not the underlying processes generating such outcomes, is not enough to understand the impacts of climate change.

Life history of an invasive and unexploited population of Nile tilapia (Oreochromis niloticus) and geographical variation across its native and non-native ranges

Although the life history traits of Nile tilapia, Oreochromis niloticus have been studied since the early 20th century, the potential range of life history parameters in unexploited populations and geographical variability in life history traits are still poorly understood. We explored life history traits (age composition, growth rate, mortality, size, and age at maturity) of an invasive and unexploited population in the Tabaru River, Yonaguni-jima Island, southwestern Japan, through comparisons with exploited populations across the species’ global distribution. Analysis of sectioned otoliths from 307 fish revealed that growth and maximum age were sexually dimorphic (females growing less but having greater longevity). Large-scale comparisons with exploited populations revealed that the unexploited Tabaru River population had a greater life span than exploited populations in other regions, but the growth rate was in the middle of the range of observed values. Although a high variation in life history parameters was observed among populations (L∞, K, maximum age), we found no significant variation in life history traits by latitude or between African and non-African populations. Such a combination of long life span and high variability in life history traits in response to environmental and fishing pressures may aid the success of non-native Nile tilapia in various environments.

The response of life-history traits to a new species in the community: a story of Drosophila parasitoids from the Rhône and Saône valleys

In the present study, we investigated the evolution of life-history traits in the main species of a community, after the arrival of a new competitor. Two parasitoid species, Leptopilina heterotoma and Asobara tabida, are present throughout the Rhone and Saone valleys, whereas a third species, Leptopilina boulardi, is slowly extending its distribution northwards. In the presence of L. boulardi, competing parasitoids experience a higher mortality and lower host availability. Resources should thus be re-allocated between traits according to these new factors. We compared life-history traits of populations of L. heterotoma and A. tabida in areas with and without L. boulardi. As predicted by both Price's balanced mortality hypothesis and the theory of life-history traits, we found that investment in reproduction is higher in southern populations for both native species, coupled with higher travelling abilities. However, only A. tabida paid their higher fecundity by a lower longevity. The absence of a clear trade-off between these traits in L. heterotoma may be explained by a lower metabolic rate in southern populations. These results highlight the importance of the community change over climate in the evolution of life-history traits in this parasitoid community. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 107, 153-165. ADDITIONAL KEYWORDS: Asobara tabida - competition - evolution - global change - Leptopilina boulardi - Leptopilina heterotoma - maintenance - mobility - reproduction - trade-off.

Swim Bladder Nematodes (Anguillicoloides crassus) Disturb Silvering In European Eels (Anguilla anguilla)

The introduced parasite Anguillicoloides crassus is thought to play an important role in the decline of freshwater eel (Anguilla spp.) populations. These nematodes are known to negatively affect many fitness-related traits in eels. We used experimental infections to study the effect of A. crassus on the relative size or mass of organs, and the expression of functionally relevant genes (total of 12 parameters) that are involved in the silvering process of Anguilla anguilla. Our results showed that the liver mass, the hemoglobin α-chain, and androgen receptors α expression levels were significantly higher in infected eels, whereas the freshwater rod opsin expression level and the gut mass were significantly lower in infected eels. Our results suggested that infected eels were at a more advanced stage in the silvering process than uninfected counterparts of similar size. These results may be explained by 2 hypotheses. First, A. crassus could trigger physiological mechanisms involved in the silvering process as a side-effect of infection. Second, eels may adjust their life history traits in response to infection. The implications for eel migration and reproductive success may be either negative or positive, depending on whether the response to A. crassus infection results in an additional cost of the parasite or is due to the phenotypic plasticity of the host.

Seed bank persistence and climate change

The strong mechanistic relationship between climatic factors and seed dormancy and germination suggests that forecast climatic changes will significantly affect seed bank persistence. This review focuses on the potential impact of changing temperature, rainfall and fire regimes on the longevity of long-term persistent seed-banks. Currently, there are few studies investigating the mechanistic responses of demographic processes, such as seed-bank dynamics, to forecast climate change. However, from the work that has been published, several key points have been highlighted. First, increased air temperatures will produce significantly higher soil temperatures in open and sparsely vegetated habitats. Some evidence shows that this could accelerate the decline of seed viability and compromise bet-hedging strategies of species in dryland regions. Second, changes to rainfall season may determine the relative success of recruitment, with lower levels of success producing net losses to seed bank longevity. Finally, higher temperatures are likely to produce increased fire frequency, compromising the persistence of plant populations dependent on long-lived seed banks. Improving our understanding of both the mechanistic response and adaptive capacity of seed banks to climate change will provide a solid basis for improved predictions of future species distributions and risk of extinction, particularly in ecosystems subjected to temporally stochastic disturbances. It is necessary to develop functional groups based on key life-history trait responses to changing environmental conditions, to enable broader-scale predictions of distribution and persistence in the future.

Mediation of vertebrate life historiesviainsulin‐like growth factor‐1

Life-history traits describe parameters associated with growth, size, survival, and reproduction. Life-history variation is a hallmark of biological diversity, yet researchers commonly observe that one of the major axes of life-history variation after controlling for body size involves trade-offs among growth, reproduction, and longevity. This persistent pattern of covariation among these specific traits has engendered a search for shared mechanisms that could constrain or facilitate production of variation in life-history strategies. Endocrine traits are one candidate mechanism that may underlie the integration of life history and other phenotypic traits. However, the vast majority of this research has been on the effects of steroid hormones such as glucocorticoids and androgens on life-history trade-offs. Here we propose an expansion of the focus on glucocorticoids and gonadal hormones and review the potential role of insulin-like growth factor-1 (IGF-1) in shaping the adaptive integration of multiple life-history traits. IGF-1 is a polypeptide metabolic hormone largely produced by the liver. We summarize a vast array of research demonstrating that IGF-1 levels are susceptible to environmental variation and that IGF-1 can have potent stimulatory effects on somatic growth and reproduction but decrease lifespan. We review the few studies in natural populations that have measured plasma IGF-1 concentrations and its associations with life-history traits or other characteristics of the organism or its environment. We focus on two case studies that found support for the hypothesis that IGF-1 mediates adaptive divergence in suites of life-history traits in response to varying ecological conditions or artificial selection. We also examine what we view as potentially fruitful avenues of research on this topic, which until now has been rarely investigated by evolutionary ecologists. We discuss how IGF-1 may facilitate adaptive plasticity in life-history strategies in response to early environmental conditions and also how selection on loci controlling IGF-1 signaling may mediate population divergence and eventual speciation. After consideration of the interactions among androgens, glucocorticoids, and IGF-1 we suggest that IGF-1 be considered a suitable candidate mechanism for mediating life-history traits. Finally, we discuss what we can learn about IGF-1 from studies in free-ranging animals. The voluminous literature in laboratory and domesticated animals documenting relationships among IGF-1, growth, reproduction, and lifespan demonstrates the potential for a number of new research questions to be asked in free-ranging animals. Examining how IGF-1 mediates life-history traits in free-ranging animals could lead to great insight into the mechanisms that influence life-history variation.

Experimental demography and the vital rates of generalist and specialist insect herbivores on native and novel host plants

1. Colonization success of species when confronted with novel environments is of interest in ecological, evolutionary and conservation contexts. Such events may represent the first step for ecological diversification. They also play an important role in adaptive divergence and speciation. 2. A species that is able to do well across a range of environments has a higher plasticity than one whose success is restricted to a single or few environments. The breadth of environments in which a species can succeed is ultimately determined by the full pattern of its vital rates in each environment. 3. Examples of organisms colonizing novel environments are insect herbivores expanding their diets to novel host plants. One expectation for insect herbivores is that species with specialized diets may display less plasticity when faced with novel hosts than generalist species. 4. We examine this hypothesis for two generalist and two specialist neotropical beetles (genus Cephaloleia: Chrysomelidae) currently expanding their diets from native to novel plants of the order Zingiberales. Using an experimental approach, we estimated changes in vital rates, life-history traits and lifetime fitness for each beetle species when feeding on native or novel host plants. 5. We did not find evidence supporting more plasticity for generalists than for specialists. Instead, we found similar patterns of survival and fecundity for all herbivores. Larvae survived worse on novel hosts; adults survived at least as well or better, but reproduced less on the novel host than on natives. 6. Some of the novel host plants represent challenging environments where population growth was negative. However, in four novel plant-herbivore interactions, instantaneous population growth rates were positive. 7. Positive instantaneous population growth rates during initial colonization of novel host plants suggest that both generalist and specialist Cephaloleia beetles may be pre-adapted to feed on some novel hosts. This plasticity in host use is a key factor for successful colonization of novel hosts. Future success or failure in the colonization of these novel hosts will depend on the demographic rates described in this research, natural selection and the evolutionary responses of life-history traits in novel environments.

EVIDENCE FOR STRONG INTRALOCUS SEXUAL CONFLICT IN THE INDIAN MEAL MOTH, PLODIA INTERPUNCTELLA

Males and females share a genome and express many shared phenotypic traits, which are often selected in opposite directions. This generates intralocus sexual conflict that may constrain trait evolution by preventing the sexes from reaching their optimal phenotype. Furthermore, if present across multiple loci, intralocus sexual conflict can result in a gender load that may diminish the benefits of sexual selection and help maintain genetic variation for fitness. Despite the importance of intralocus sexual conflict, surprisingly few empirical studies conclusively demonstrate its operation. We show that the pattern of multivariate selection acting on three sexually dimorphic life-history traits (development time, body size, and longevity) in the Indian meal moth, Plodia interpunctella, is opposing for the sexes. Moreover, we combined our estimates of selection with the additive genetic variance-covariance matrix (G) to predict the evolutionary response of the life-history traits in the sexes and showed that the angle between the vector of responses and the vector of sexually antagonistic selection was almost orthogonal at 84.70°. Thus, G biases the predicted response of life-history traits in the sexes away from the direction of sexually antagonistic selection, confirming the presence of strong intralocus sexual conflict in this species. Despite this, sexual dimorphism has evolved in all of the life-history traits examined suggesting that mechanism(s) have evolved to resolve this conflict and allow the sexes to reach their life-history optima. We argue that intralocus sexual conflict is likely to play an important role in the evolution of divergent life-history strategies between the sexes in this species.

Photoperiod affects compensating developmental rate across latitudes in the damselflyLestes sponsa

1. Although there is a great deal of theoretical and empirical data about the life history responses of time constraints in organisms, little is known about the latitude‐compensating mechanism that enables northern populations' developmental rates to compensate for latitude. To investigate the importance of photoperiod on development, offspring of the obligatory univoltine damselflyLestes sponsafrom two populations at different latitudes (53°N and 63°N) were raised in a common laboratory environment at both northern and southern photoperiods that corresponded to the sites of collection.2. Egg development time was shorter under northern photoperiod regimes for both populations. However, the northern latitude population showed a higher phenotypic plasticity response to photoperiod compared with the southern latitude population, suggesting a genetic difference in egg development time in response to photoperiod.3. Larvae from both latitudes expressed shorter larval development time and faster growth rates under northern photoperiod regimes. There was no difference in phenotypic plastic response between northern and southern latitude populations with regard to development time.4. Data on field collected adults showed that adult sizes decreased with an increase in latitude. This adult size difference was a genetically fixed trait, as the same size difference between populations was also found when larvae were reared in the laboratory.5. The results suggest phenotypic plasticity responses in life history traits to photoperiod, but also genetic differences between north and south latitude populations in response to photoperiod, which indicates the presence of a latitudinal compensating mechanism that is triggered by a photoperiod.

Response of daily and annual shell growth patterns of the intertidal bivalve Phacosoma japonicum to Holocene coastal climate change in Japan

It is well known that the latitudinal distribution of shallow-marine mollusks around the Japanese Islands has changed episodically during the Holocene in response to climate change; however, few studies have investigated the biotic response of individual species to Holocene climate change at daily to annual scales of temporal resolution. Holocene shells of the venerid Phacosoma japonicum recovered from various sites in Japan preserve lunar daily and annual growth increments in the outer shell layer and hinge plate, as also observed in modern shells. Sclerochronological analysis of 29 shells with known 14C ages revealed that the life history traits (e.g., length of the growth period and the mean lunar daily growth rate at a given age) have changed markedly over the past 8000 years. The intra-annual patterns of lunar daily increments and shell oxygen isotope records of the fossil shells can be compared with those of modern specimens from various locations, which are constrained by annual patterns of seawater temperature and summer–autumn precipitation rates. Furthermore, the temporal trends recorded in the fossil shells show a strong correlation with climate change in mid-latitude parts of East Asia over the past 8000 years, indicating that P. japonicum has changed its life history traits in response to Holocene terrestrial and coastal climate change.

Convergent life-history shifts: toxic environments result in big babies in two clades of poeciliids

The majority of studies on ecological speciation in animals have investigated the divergence caused by biotic factors like divergent food sources or predatory regimes. Here, we examined a system where ecological speciation can clearly be ascribed to abiotic environmental gradients of naturally occurring toxic hydrogen sulfide (H(2)S). In southern Mexico, two genera of livebearing fishes (Poeciliidae: Poecilia and Gambusia) thrive in various watercourses with different concentrations of H(2)S. Previous studies have revealed pronounced genetic differentiation between different locally adapted populations in one species (Poecilia mexicana), pointing towards incipient speciation. In the present study, we examined female reproductive life-history traits in two species pairs: Gambusia sexradiata (from a nonsulfidic and a sulfidic habitat) and Gambusia eurystoma (sulfide-endemic), as well as P. mexicana (nonsulfidic and sulfidic) and Poecilia sulphuraria (sulfide endemic). We found convergent divergence of life-history traits in response to sulfide; most prominently, extremophile poeciliids exhibit drastically increased offspring size coupled with reduced fecundity. Furthermore, within each genus, this trend increased with increasing sulfide concentrations and was most pronounced in the two endemic sulfur-adapted species. We discuss the adaptive significance of large offspring size in toxic environments and propose that divergent life-history evolution may promote further ecological divergence through isolation by adaptation.

Responses of life-history traits of brackish- and freshwater populations of the water strider to NaCl Aquarius paludum (Hemiptera: Gerridae)

The water strider Aquarius paludum inhabits the surfaces of a wide variety of freshwater habitats both temporary and permanent. It can also live on the surface brackish-water around river mouths. Exposure to a brackish rather than freshwater environment may affect a range of adult and offspring life-history traits. In a two-stage experiment A. paludum offspring from fresh- (F) and brackish-water (B) populations were obtained and their offspring reared in either a fresh- or brackish-water (0.45% NaCl) environments. The four offspring treatment groups (F-F, F-B, B-F, B-B) varied in terms of the parental and offspring rearing environments. The effect of parental and offspring rearing environment on longevity, fecundity and flight was assessed. Offspring reared in a brackish environment throughout their larval and adult stages had a reduced longevity and egg production. The flight activity of the offspring originated from the brackish-water population was maintained when they were reared in a brackish environment, but inhibited when they were exposed to freshwater. Our results suggest that the life-history strategies depend critically on the degree of salinity in both the current environment and that of their parents.

DIVERGENT SELECTION, NOT LIFE-HISTORY PLASTICITY VIA FOOD LIMITATION, DRIVES MORPHOLOGICAL DIVERGENCE BETWEEN PREDATOR REGIMES INGAMBUSIA HUBBSI

We recently tested the hypothesis of ecological speciation in a post-Pleistocene radiation of Bahamas mosquitofish (Gambusia hubbsi) inhabiting inland blue holes (vertical, water-filled caves) on Andros Island, the Bahamas (Langerhans et al. 2007). Combining morphological, molecular, and behavioral data, our results suggested that enhanced premating isolation evolved as a byproduct of differences in body shape between predator regimes, due to assortative mating for body shape. Our results strongly supported the hypothesis of ecological speciation, and parallel results were observed across species within the genus, suggesting a past history of such ecological speciation within the Gambusia lineage. Downhower et al. (in press) question the morphological results described for G. hubbsi in our paper, contending that prior work on life-history variation in G. hubbsi (primarily Downhower et al. 2000, 2002) invalidates our conclusions. Here we show that this contention is based on a mischaracterization of our study, inaccurate quotation of our paper, and misinterpretation of the relevance of their life-history data for morphological results observed in our study. Downhower et al. (in press) suggest—without providing any direct evidence—that differences in body shape between predator regimes in G. hubbsi reflect correlative effects of phenotypic plasticity in life-history traits in response to variation in food availability. To make such a conclusion, we would have to set aside the following facts: (1) morphological differences were observed in adult males, who do not exhibit the life-history traits in question (e.g., number and size of offspring), (2) results matched well-supported a priori predictions of body shape variation based on divergent selection on locomotor performance, (3) results matched empirical results observed in other fish presumably experiencing similar forms of divergent selection between predator regimes, (4) the observed morphological differences are known to influence swimming performance in Gambusia fish and consequently influence endurance and survival with predators, (5) consistent results were observed for males both within and between Gambusia species, (6) any differences in food availability among blue holes are unknown, and (7) available evidence to date indicates that differences in body shape partly reflect genetic divergence, and not solely phenotypic plasticity. The criticisms in Downhower et al. (in press) can be summarized as three arguments: (1) incorrect attribution of evidence for divergent selection between predator regimes in G. hubbsi to several previous

ADULT MALE NUTRITION AND REPRODUCTIVE SUCCESS INDROSOPHILA MELANOGASTER

Explanations for the maintenance of variation in reproductive traits influenced by seminal fluid accessory gland proteins (Acps) in male Drosophila melanogaster include nontransitivity in the outcome of sperm competition and/or condition dependence of the traits involved. We investigated the effects of adult male nutrition (five diets) on the expression of Acp- and sperm- mediated traits. We found novel, nonlinear effects, with females showing lower levels of refractoriness to remating after mating with males held on the lowest and highest yeast diets. There were no significant effects of adult male nutrition on male paternity share, but there was a striking, nonlinear effect on second male progeny production, with males kept on intermediate yeast diets fathering the highest number of offspring. Such "bell shaped" responses of life-history traits to nutrition have only previously been reported for longevity. Consistent with previous reports, males maintained on low protein diets had lower premating success and gained fewer rematings with nonvirgins. We show novel and body size independent effects of adult male nutrition on traits influenced by Acps and sperm, which do not fit current condition-dependent handicap models and can affect the strength of sexual selection acting upon such fitness-related traits.

Host Responses in Life-History Traits and Tolerance to Virus Infection in Arabidopsis thaliana

Knowing how hosts respond to parasite infection is paramount in understanding the effects of parasites on host populations and hence host–parasite co-evolution. Modification of life-history traits in response to parasitism has received less attention than other defence strategies. Life-history theory predicts that parasitised hosts will increase reproductive effort and accelerate reproduction. However, empirical analyses of these predictions are few and mostly limited to animal-parasite systems. We have analysed life-history trait responses in 18 accessions of Arabidopsis thaliana infected at two different developmental stages with three strains of Cucumber mosaic virus (CMV). Accessions were divided into two groups according to allometric relationships; these groups differed also in their tolerance to CMV infection. Life-history trait modification upon virus infection depended on the host genotype and the stage at infection. While all accessions delayed flowering, only the more tolerant allometric group modified resource allocation to increase the production of reproductive structures and progeny, and reduced the length of reproductive period. Our results are in agreement with modifications of life-history traits reported for parasitised animals and with predictions from life-history theory. Thus, we provide empirical support for the general validity of theoretical predictions. In addition, this experimental approach allowed us to quantitatively estimate the genetic determinism of life-history trait plasticity and to evaluate the role of life-history trait modification in defence against parasites, two largely unexplored issues.

Positive effects of cyanogenic glycosides in food plants on larval development of the common blue butterfly

Cyanogenesis is a widespread chemical defence mechanism in plants against herbivory. However, some specialised herbivores overcome this protection by different behavioural or metabolic mechanisms. In the present study, we investigated the effect of presence or absence of cyanogenic glycosides in birdsfoot trefoil (Lotus corniculatus, Fabaceae) on oviposition behaviour, larval preference, larval development, adult weight and nectar preference of the common blue butterfly (Polyommatus icarus, Lycaenidae). For oviposition behaviour there was a female-specific reaction to cyanogenic glycoside content; i.e. some females preferred to oviposit on cyanogenic over acyanogenic plants, while other females behaved in the opposite way. Freshly hatched larvae did not discriminate between the two plant morphs. Since the two plant morphs differed not only in their content of cyanogenic glycoside, but also in N and water content, we expected these differences to affect larval growth. Contrary to our expectations, larvae feeding on cyanogenic plants showed a faster development and stronger weight gain than larvae feeding on acyanogenic plants. Furthermore, female genotype affected development time, larval and pupal weight of the common blue butterfly. However, most effects detected in the larval phase disappeared for adult weight, indicating compensatory feeding of larvae. Adult butterflies reared on the two cyanogenic glycoside plant morphs did not differ in their nectar preference. But a gender-specific effect was found, where females preferred amino acid-rich nectar while males did not discriminate between the two nectar mimics. The presented results indicate that larvae of the common blue butterfly can metabolise the surplus of N in cyanogenic plants for growth. Additionally, the female-specific behaviour to oviposit preferably on cyanogenic or acyanogenic plant morphs and the female-genotype-specific responses in life history traits indicate the genetic flexibility of this butterfly species and its potential for local adaptation.