Climate change-driven elevational changes among boreal nocturnal moths.

Climate change has shifted geographical ranges of species northwards or to higher altitudes on elevational gradients. These changes have been associated with increases in ambient temperatures. For ectotherms in seasonal environments, however, life history theory relies largely on the length of summer, which varies somewhat independently of ambient temperature per se. Extension of summer reduces seasonal time constraints and enables species to establish in new areas as a result of over-wintering stage reaching in due time. The reduction of time constraints is also predicted to prolong organisms' breeding season when reproductive potential is under selection. We studied temporal change in the summer length and its effect on species' performance by combining long-term data on the occurrence and abundance of nocturnal moths with weather conditions in a boreal location at Värriötunturi fell in NE Finland. We found that summers have lengthened on average 5 days per decade from the late 1970s, profoundly due to increasing delays in the onset of winters. Moth abundance increased with increasing season length a year before. Most of the species occurrences expanded upwards in elevation. Moth communities in low elevation pine heath forest and middle elevation mountain birch forest have become inseparable. Yet, the flight periods have remained unchanged, probably due to unpredictable variation in proximate conditions (weather) that hinders life histories from selection. We conclude that climate change-driven changes in the season length have potential to affect species' ranges and affect the structure of insect assemblages, which may contribute to alteration of ecosystem-level processes.

Phytochemical Shift from Condensed Tannins to Flavonoids in Transgenic Betula pendula Decreases Consumption and Growth but Improves Growth Efficiency of Epirrita autumnata Larvae.

Despite active research, antiherbivore activity of specific plant phenolics remains largely unresolved. We constructed silver birch (Betula pendula) lines with modified phenolic metabolism to study the effects of foliar flavonoids and condensed tannins on consumption and growth of larvae of a generalist herbivore, the autumnal moth (Epirrita autumnata). We conducted a feeding experiment using birch lines in which expression of dihydroflavonol reductase (DFR), anthocyanidin synthase (ANS) or anthocyanidin reductase (ANR) had been decreased by RNA interference. Modification-specific effects on plant phenolics, nutrients and phenotype, and on larval consumption and growth were analyzed using uni- and multivariate methods. Inhibiting DFR expression increased the concentration of flavonoids at the expense of condensed tannins, and silencing DFR and ANR decreased leaf and plant size. E. autumnata larvae consumed on average 82% less of DFRi plants than of unmodified controls, suggesting that flavonoids or glandular trichomes deter larval feeding. However, larval growth efficiency was highest on low-tannin DFRi plants, indicating that condensed tannins (or their monomers) are physiologically more harmful than non-tannin flavonoids for E. autumnata larvae. Our results show that genetic manipulation of the flavonoid pathway in plants can effectively be used to produce altered phenolic profiles required for elucidating the roles of low-molecular weight phenolics and condensed tannins in plant-herbivore relationships, and suggest that phenolic secondary metabolites participate in regulation of plant growth.

Elucidating mechanisms for insect body size: partial support for the oxygen-dependent induction of moulting hypothesis.

Body size is a key life history trait, and knowledge of its mechanistic basis is crucial in life history biology. Such knowledge is accumulating for holometabolous insects, whose growth is characterised and body size affected by moulting. According to the oxygen-dependent induction of moulting (ODIM) hypothesis, moult is induced at a critical mass at which oxygen demand of growing tissues overrides the supply from the tracheal respiratory system, which principally grows only at moults. Support for the ODIM hypothesis is controversial, partly because of a lack of proper data to explicitly test the hypothesis. The ODIM hypothesis predicts that the critical mass is positively correlated with oxygen partial pressure (PO2 ) and negatively with temperature. To resolve the controversy that surrounds the ODIM hypothesis, we rigorously test these predictions by exposing penultimate-instar Orthosia gothica (Lepidoptera: Noctuidae) larvae to temperature and moderate PO2  manipulations in a factorial experiment. The relative mass increment in the focal instar increased along with increasing PO2 , as predicted, but there was only weak suggestive evidence of the temperature effect. Probably owing to a high measurement error in the trait, the effect of PO2  on the critical mass was sex specific; high PO2  had a positive effect only in females, whereas low PO2  had a negative effect only in males. Critical mass was independent of temperature. Support for the ODIM hypothesis is partial because of only suggestive evidence of a temperature effect on moulting, but the role of oxygen in moult induction seems unambiguous. The ODIM mechanism thus seems worth considering in body size analyses.

Larval melanism in a geometrid moth: promoted neither by a thermal nor seasonal adaptation but desiccating environments.

Spatiotemporal variation in the degree of melanism is often considered in the context of thermal adaptation, melanism being advantageous under suboptimal thermal conditions. Yet, other mutually nonexclusive explanations exist. Analysis of geographical patterns combined with laboratory experiments on the mechanisms of morph induction helps to unveil the adaptive value of particular cases of polyphenism. In the context of the thermal melanism hypothesis and seasonal adaptations, we explored an array of environmental factors that may affect the expression and performance of nonmelanic vs. melanic larval morphs in different latitudinal populations of the facultatively bivoltine moth Chiasmia clathrata (Lepidoptera: Geometridae). Geographical variation in larval coloration was independent of average temperatures experienced by the populations in the wild. The melanic morph was, however, more abundant in dry than in mesic habitats. In the laboratory, the melanic morph was induced especially under a high level of incident radiation but also at relatively high temperatures, but independently of photoperiod. Melanic larvae had higher growth rates and shorter development times than the nonmelanic ones when both temperature and the level of incident radiation were high. Our results that melanism is induced and advantageous in warm desiccating conditions contradict the thermal melanism hypothesis for this species. Neither has melanism evolved to compensate time constraints due to forthcoming autumn. Instead, larvae solve seasonal variation in the time available for growth by an elevated growth rate and a shortened larval period in the face of autumnal photoperiods. The phenotypic response to the level of incident radiation and a lack of adaptive adjustment of larval growth trajectories in univoltine populations underpin the role of deterministic environmental variation in the evolution of irreversible adaptive plasticity and seasonal polyphenism.

Diet shift induced rapid evolution of size and function in a predatory bird.

A predator's body size correlates with its prey size. Change in the diet may call for changes in the hunting mode and traits determining hunting success. We explored long-term trends in sternum size and shape in the northern goshawk by applying geometric morphometrics. Tetraonids, the primary prey of the goshawk, have decreased and been replaced by smaller birds in the diet. We expected that the size of the goshawk has decreased accordingly more in males than females based on earlier observations of outer morphology. We also expected changes in sternum shape as a function of changes in hunting mode. Size of both sexes has decreased during the preceding decades (1962-2008), seemingly reflecting a shift in prey size and hunting mode. Female goshawks hunting also mammalian prey tend to have a pronouncedly "Buteo-type" sternum compared to males preying upon birds. Interestingly, the shrinkage of body size resulted in an increasingly "Buteo-type" sternum in both sexes. In addition, the sternum shape in birds that died accidentally (i.e., fit individuals) was more Buteo-type than in starved ones, hinting that selection was towards a Buteo-type sternum shape. We conclude that these observed patterns are likely due to directional selection driven by changes in the diet towards smaller and more agile prey. On the other hand, global warming is predicted to also cause a decrease in size, thus these two scenarios are inseparable. Because of difficulties in studying fitness-related phenotypic changes of large raptors in the field, time series of museum exemplars collected over a wide geographical area may give answers to this conundrum.

Size of an interspecific competitor may be a source of information in reproductive decisions.

Animals use inter-specific cues as a source of information in decisions-making, but the full costs and benefits of inter-specific information use are unknown. We tested whether pied flycatchers use the body size and clutch size of great tits as cues in their reproductive decisions and what are the possible fitness consequences as a function of great tit size. The size of great tit females associated positively with flycatcher's probability to settle near a tit nest over a territory further away. Flycatcher egg mass was positively correlated with great tit female size regardless of flycatcher territory choice. However, in flycatchers that had chosen to nest near great tits, the size of nestlings decreased in relation to increasing great tit female size. Our results demonstrate the use of size of inter-specifics as a cue in reproductive decisions and the trade-off between the value of information and costs of competition information users face when using inter-specific information in decision-making.

Geographic variation in resource allocation to the abdomen in geometrid moths.

A resource allocation trade-off is expected when resources from a common pool are allocated to two or more traits. In holometabolous insects, resource allocation to different functions during metamorphosis relies completely on larval-derived resources. At adult eclosion, resource allocation to the abdomen at the expense of other body parts can be seen as a rough estimate of resource allocation to reproduction. Theory suggests geographic variation in resource allocation to the abdomen, but there are currently no empirical data on it. We measured resource allocation to the abdomen at adult eclosion in four geometrid moths along a latitudinal gradient. Resource (total dry material, carbon, nitrogen) allocation to the abdomen showed positive allometry with body size. We found geographic variation in resource allocation to the abdomen in each species, and this variation was independent of allometry in three species. Geographic variation in resource allocation to the abdomen was complex. Resource allocation to the abdomen was relatively high in partially bivoltine populations in two species, which fits theoretical predictions, but the overall support for theory is weak. This study indicates that the geographic variation in resource allocation to the abdomen is not an allometric consequence of geographic variation in resource acquisition (i.e., body size). Thus, there is a component of resource allocation that can evolve independently of resource acquisition. Our results also suggest that there may be intraspecific variation in the degree of capital versus income breeding.

Latitudinal insect body size clines revisited: a critical evaluation of the saw-tooth model.

1. Insect body size is predicted to increase with decreasing latitude because time available for growth increases. In insects with changing voltinism (i.e. number of generations per season), sharp decreases in development time and body size are expected at season lengths where new generations are added to the phenology of a species, giving rise to saw-tooth clines in these traits across latitudes. Growth rate variation may affect the magnitude of variation in body size or even reverse the saw-tooth cline. 2. In this study, we analyse latitudinal body size clines in four geometrid moths with changing voltinism in a common laboratory environment. In addition to body size, we measured larval development time and growth rate and genetic correlations among the three traits. 3. The patterns of clinal variation in body size were diverse, and the theory was not supported even when saw-tooth body size clines were found. Larval development time increased and growth rate decreased consistently with increasing season length, the clines in these traits being uniform. 4. The consistencies of development time and growth rate clines suggest a common mechanism underlying the observations. Such a mechanism is discussed in relation to the complex interdependencies among the traits.

Geographical variation in host use of a blood-feeding ectoparasitic fly: implications for population invasiveness.

Invasive generalist ectoparasites provide a tool to study factors affecting expansion rates. An increase in the number of host species may facilitate geographic range expansion by increasing the number of suitable habitats and by affecting local extinction and colonization rates. A geographic perspective on parasite host specificity and its implications on range expansion are, however, insufficiently understood. We conducted a field study to explore if divergent host specificity could explain the observed variation in expansion rates between Fennoscandian populations of the deer ked (Lipoptena cervi), which is a blood-feeding ectoparasitic fly of cervids. We found that the rapidly expanding eastern population in Finland appears to specialize on moose, whereas the slowly expanding western population in Norway breeds successfully on both moose and roe deer. The eastern population was also found to utilize the wild forest reindeer as an auxiliary host, but this species is apparently of low value for L. cervi in terms of adult maintenance, reproductive output and offspring quality. Abundant numbers of roe deer and white-tailed deer were observed to be apparently uninfected in Finland, suggesting that host use is not a plastic response to host availability, but rather a consequence of population-level evolutionary changes. Locally compatible hosts were found to be the ones sharing a long history with the deer ked in the area. Cervids that sustained adult deer keds also allowed successful reproduction. Thus, host use is probably determined by the ability of the adult to exploit particular host species. We conclude that a wide host range alone does not account for the high expansion rate or wide geographic distribution of the deer ked, although loose ecological requirements would increase habitat availability.

Fennoscandian distribution of an important parasite of cervids, the deer ked (Lipoptena cervi), revisited.

The deer ked [Lipoptena cervi (L. 1758) (Dipt., Hippoboscidae)] is a blood-sucking ectoparasite of cervids. The species has been resident in Sweden for more than two centuries, whereas in Finland ( approximately 50 years) and Norway ( approximately 30 years), it has established itself relatively recently. L. cervi may cause serious health problems in its natural hosts, act as a vector for zoonotic diseases, and pose a socioeconomic threat to forest-based activity. In this paper, we review the distribution and former expansion of the species in Fennoscandia. The current distribution of L. cervi appears bimodal, and the geographical range expansion of the species shows notable differences across Fennoscandia. The western population in Norway and Sweden has its northern edge of range at respective latitudes of 61 degrees N and 62 degrees N, whereas the eastern population in Finland reaches 65 degrees N. The future expansion of L. cervi is dependent on several interdependent extrinsic and intrinsic factors. International multidisciplinary collaboration is needed to achieve a synthesis on the factors affecting expansion rates and to understand the effects of L. cervi on wildlife, human health, and the rural societies of Fennoscandia.

Seasonal clines of evolutionarily stable reproductive effort in insects.

For ectotherms, growth and reproduction are possible only during a limited period of the year in seasonal environments. In insects, fitness is generally maximized by producing as many generations as possible within a season, and in many species, the number of generations produced (voltinism) increases with increasing season length. In this study, we analyzed variation in adult life histories in insects along a climatic gradient. The analyzed trait is reproductive effort (resource allocation to reproduction). We begin by formalizing the trade-off between current reproduction and subsequent survival generated by reproductive effort. It appeared that reproductive effort is correlated positively with early fecundity and negatively with lifetime fecundity and life span. Then, deriving from that trade-off, we analyze the evolutionary stability of different schedules of age-specific fecundity that are generated by divergent reproductive effort. The analysis was carried out in season lengths that promote either univoltine or bivoltine phenology. The evolutionarily stable reproductive effort decreases with increasing season length in both phenologies, with a sudden increase when a change from univoltine to partially bivoltine phenology takes place. Reproductive effort responds strongly to changing phenology when density-dependent mortality occurs during diapause and weakly when juvenile mortality is density dependent.

From feces to data: A metabarcoding method for analyzing consumed and available prey in a bird-insect food web.

Diets play a key role in understanding trophic interactions. Knowing the actual structure of food webs contributes greatly to our understanding of biodiversity and ecosystem functioning. The research of prey preferences of different predators requires knowledge not only of the prey consumed, but also of what is available. In this study, we applied DNA metabarcoding to analyze the diet of 4 bird species (willow tits Poecile montanus, Siberian tits Poecile cinctus, great tits Parus major and blue tits Cyanistes caeruleus) by using the feces of nestlings. The availability of their assumed prey (Lepidoptera) was determined from feces of larvae (frass) collected from the main foraging habitat, birch (Betula spp.) canopy. We identified 53 prey species from the nestling feces, of which 11 (21%) were also detected from the frass samples (eight lepidopterans). Approximately 80% of identified prey species in the nestling feces represented lepidopterans, which is in line with the earlier studies on the parids' diet. A subsequent laboratory experiment showed a threshold for fecal sample size and the barcoding success, suggesting that the smallest frass samples do not contain enough larval DNA to be detected by high-throughput sequencing. To summarize, we apply metabarcoding for the first time in a combined approach to identify available prey (through frass) and consumed prey (via nestling feces), expanding the scope and precision for future dietary studies on insectivorous birds.

Competition between larvae in a butterfly Pieris napi and maintenance of different life-history strategies.

1. In scramble competition all individuals suffer equally from competition, whereas in contest competition some individuals outperform the others. Generally, larger individuals gain asymmetric advantage in competition over smaller ones. Given the positive correlation between age and size, asynchronous birth may result in asymmetric competition among juveniles. 2. In Pieris napi (Lepidoptera: Pieridae), reproductive rate is determined by the females' intrinsic mating tactic. The early reproductive rate is high in females with a low mating frequency and low in females with a high mating frequency, whereas lifetime fecundity shows the opposite pattern. Thus, offspring of monandrous females start to develop in relatively low densities and they are relatively large when the offspring of highly polyandrous females start to hatch. 3. The purpose of this study was to explore if asymmetry in larval competition could outweigh the late-life benefits of polyandry. In a laboratory experiment, P. napi larvae of different ages were reared together in different densities. 4. Increasing density decreased both larval survival and reachable pupal mass, but had no effect on duration of larval period. Younger larvae suffered from high mortality and reduced size compared with the older larvae. Mortality decreased in the older cohort with increasing age difference between the cohorts, and the reverse occurred in the younger cohort. Increasing age difference between the cohorts was associated with increase in pupal mass in both cohorts. All the variables showed a lot of variation between broods of different females. 5. The results suggest that polyandrous females, or more generally females with a low early reproductive rate, may lose a great proportion of their late-life benefits, which may partly explain the maintenance of polymorphism in reproductive strategies within species.

Evolution of alternative insect life histories in stochastic seasonal environments.

Deterministic seasonality can explain the evolution of alternative life history phenotypes (i.e., life history polyphenism) expressed in different generations emerging within the same year. However, the influence of stochastic variation on the expression of such life history polyphenisms in seasonal environments is insufficiently understood. Here, we use insects as a model and explore (1) the effects of stochastic variation in seasonality and (2) the life cycle on the degree of life history differentiation among the alternative developmental pathways of direct development and diapause (overwintering), and (3) the evolution of phenology. With numerical simulation, we determine the values of development (growth) time, growth rate, body size, reproductive effort, adult life span, and fecundity in both the overwintering and directly developing generations that maximize geometric mean fitness. The results suggest that natural selection favors the expression of alternative life histories in the alternative developmental pathways even when there is stochastic variation in seasonality, but that trait differentiation is affected by the developmental stage that overwinters. Increasing environmental unpredictability induced a switch to a bet-hedging type of life history strategy, which is consistent with general life history theory. Bet-hedging appeared in our study system as reduced expression of the direct development phenotype, with associated changes in life history phenotypes, because the fitness value of direct development is highly variable in uncertain environments. Our main result is that seasonality itself is a key factor promoting the evolution of seasonally polyphenic life histories but that environmental stochasticity may modulate the expression of life history phenotypes.

Seasonality maintains alternative life-history phenotypes.

Many organisms express discrete alternative phenotypes (polyphenisms) in relation to predictable environmental variation. However, the evolution of alternative life-history phenotypes remains poorly understood. Here, we analyze the evolution of alternative life histories in seasonal environments by using temperate insects as a model system. Temperate insects express alternative developmental pathways of diapause and direct development, the induction of a certain pathway affecting fitness through its life-history correlates. We develop a methodologically novel and holistic simulation model and optimize development time, growth rate, body size, reproductive effort, and adult life span simultaneously in both developmental pathways. The model predicts that direct development should be associated with shorter development time (duration of growth) and adult life span, higher growth rate and reproductive effort, smaller body size as well as lower fecundity compared to the diapause pathway, because the two generations divide the available time unequally. These predictions are consistent with many empirical data. Our analysis shows that seasonality alone can explain the evolution of alternative life histories.