Changes in voltinism in a pine moth <Emphasis Type="Italic">Dendrolimus spectabilis</Emphasis> (Lepidoptera: Lasiocampidae) population: implications of climate change

Climate change induces an alteration in the life cycle of many poikilothermic organisms, resulting in changes in the structure and function of communities. Changes in voltinism in the pine moth Dendrolimus spectabilis (Butler), which is known to be univoltine in South Korea, were studied to elucidate the effects of climate change on their voltinism. The developmental stages of the pine moth were evaluated through field surveys, and the developmental rate was estimated at five different temperatures: 17, 20, 25, 28, and 32°C. Field surveys showed that the moths completed two generations per year, indicating that the phenology of the pine moth in this area had changed from univoltinism to bivoltinism. Laboratory experiments showed that increasing the temperature could induce a change in voltinism in the pine moth population. Generations of the bivoltine population displayed phenotypic plasticity: the fitness of the first generation was greater than that of the second generation with regard to size and fecundity. The difference in fitness between the first and second generations could be due to the influence of factors such as low food quality and heat stress on the second generation. Therefore, changes in thermal conditions due to climate change have offered this species the chance to develop a bivoltine population, but they have also exerted ecological costs, especially for the second generation of the pine moth.     

Projecting insect voltinism under high and low greenhouse gas emission conditions

We develop individual-based Monte Carlo methods to explore how climate change can alter insect voltinism under varying greenhouse gas emissions scenarios by using input distributions of diapause termination or spring emergence, development rate, and diapause initiation, linked to daily temperature and photoperiod. We show concurrence of these projections with a field dataset, and then explore changes in grape berry moth, Paralobesia viteana (Clemens), voltinism that may occur with climate projections developed from the average of three climate models using two different future emissions scenarios from the International Panel of Climate Change (IPCC). Based on historical climate data from 1960 to 2008, and projected downscaled climate data until 2099 under both high (A1fi) and low (B1) greenhouse gas emission scenarios, we used concepts of P. viteana biology to estimate distributions of individuals entering successive generations per year. Under the low emissions scenario, we observed an earlier emergence from diapause and a shift in mean voltinism from 2.8 to 3.1 generations per year, with a fraction of the population achieving a fourth generation. Under the high emissions scenario, up to 3.6 mean generations per year were projected by the end of this century, with a very small fraction of the population achieving a fifth generation. Changes in voltinism in this and other species in response to climate change likely will cause significant economic and ecological impacts, and the methods presented here can be readily adapted to other species for which the input distributions are reasonably approximated.     

Responses of insects to the current climate changes: from physiology and behavior to range shifts

Climate change (first of all the rise in temperature) is currently considered one of the most serious global challenges facing mankind. Here we review the diversity of insect responses to the current climate warming, with particular focus on true bugs (Heteroptera). Insects as ectotherms are bound to respond to the temperature change, and different species respond differently depending on their specific physiological and ecological traits, seasonal cycle, trophic relations, etc. Insect responses to climate warming can be divided into six categories: changes in (1) ranges, (2) abundance, (3) phenology, (4) voltinism, (5) morphology, physiology, and behavior, and (6) relationships with other species and in the structure of communities. Changes in ranges and phenology are easier to notice and record than other responses. Range shifts have been reported more often in Lepidoptera and Odonata than in other insect orders. We briefly outline the history and eco-physiological background of the recent range limit changes in the Southern green stink bug Nezara viridula (Heteroptera, Pentatomidae) in central Japan. Range expansion in individual species can lead to enrichment of local faunas, especially at high latitudes. Phenological changes include not only advances in development in spring but also shifts in phenology later in the season. The phenophases related to the end of activity usually shift to later dates, thus prolonging the period of active development. This may have both positive and negative consequences for the species and populations. As with any other response, the tendencies in phenological changes may vary among species and climatic zones. The proven cases of change in voltinism are rare, but such examples do exist. Application of models based on thermal parameters of development suggests that a rise in temperature by 2°C will result in an increased number of annual generations in many species from different arthropod taxa (up to three or four additional generations in Thysanoptera, Aphidoidea, and Acarina). The warming-mediated changes in physiology, morphology, or behavior are difficult to detect and prove, first of all because of the absence of reliable comparative data. Nevertheless, there are examples of changes in photoperiodic responses of diapause induction and behavioral responses related to search of shelters for summer diapause (aestivation). Since (1) individual species do not exist in isolation and (2) the direction and magnitude of responses even to the same environmental changes vary between species, it may be expected that in many cases the current stable relationships between species will be affected. Thus, unequal range shifts in insects and their host plants may disrupt their trophic interactions near the species?? range boundaries. Studies of responses to climate warming in more than one interrelated species or in entire communities are extremely rare. The loss of synchronism in seasonal development of community members may indicate inability of the higher trophic levels to adapt fully to climate warming or an attempt of the lower trophic level to escape from the pressure of the higher trophic levels. It is generally supposed that many insect species in the Temperate Climate Zone will benefit in some way from the current climate warming. However, there is some experimental evidence of an opposite or at least much more complex response; the influence of warming might be deleterious for some species or populations. It is suggested that species or populations from the cold or temperate climate have sufficient phenotypic plasticity to survive under the conditions of climate warming, whereas species and populations which already suffer from stress under extreme seasonal temperatures in warmer regions may have a limited ??maneuver space?? since the current temperatures are close to their upper thermal limits. Without genetic changes, even moderate warming will put these species or populations under serious physiological stress. The accumulated data suggest that responses of insects and the entire biota to climate warming will be complex and will vary depending on the rate of warming and ecological peculiarities of species and regions. Physiological responses will vary in their nature, direction, and magnitude even within one species or population, and especially between seasons. The responses will also differ in different seasons. For example, warming may negatively affect nymphal development during the hot season but at the same time accelerate growth and development during the cold season and/or ensure milder and more favorable overwintering conditions for adults. All these factors will affect population dynamics of particular species and relationships among the members of ecosystems. We should keep in mind that (1) not only selected insect species but almost all the species will be affected, (2) temperature is not the only component of the climatic system that is changing, and (3) responses will be different in different seasons. Host plants, phytophagous insects, their competitors, symbionts, predators, parasites, and pathogens will not only respond separately to climate changes; individual responses will further affect the responses of other species, thus making reliable prediction extremely complicated. Responses are expected to (1) be species- or population-specific, (2) concern basically all the aspects of organism/ species biology and ecology (individual physiology, population structure, abundance, local adaptations, phenology, voltinism, and distribution), and (3) occur at scales ranging from an undetectable cellular level to major distribution range shifts or regional extinctions. The scale of insect responses will depend on the extent and rate of climate warming. Slight to moderate warming may cause responses only in a limited number of species with more flexible life cycles, whereas a substantial increase in temperature may affect a greater number of different species and ecological groups.     

Developmental trap or demographic bonanza? Opposing consequences of earlier phenology in a changing climate for a multivoltine butterfly

A rapidly changing climate has the potential to interfere with the timing of environmental cues that ectothermic organisms rely on to initiate and regulate life history events. Short‐lived ectotherms that exhibit plasticity in their life history could increase the number of generations per year under warming climate. If many individuals successfully complete an additional generation, the population experiences an additional opportunity to grow, and a warming climate could lead to a demographic bonanza. However, these plastic responses could become maladaptive in temperate regions, where a warmer climate could trigger a developmental pathway that cannot be completed within the growing season, referred to as a developmental trap. Here we incorporated detailed demography into commonly used photothermal models to evaluate these demographic consequences of phenological shifts due to a warming climate on the formerly widespread, multivoltine butterfly (Pieris oleracea). Using species‐specific temperature‐ and photoperiod‐sensitive vital rates, we estimated the number of generations per year and population growth rate over the set of climate conditions experienced during the past 38 years. We predicted that populations in the southern portion of its range have added a fourth generation in recent years, resulting in higher annual population growth rates (demographic bonanzas). We predicted that populations in the Northeast United States have experienced developmental traps, where increases in the thermal window initially caused mortality of the final generation and reduced growth rates. These populations may recover if more growing degree days are added to the year. Our framework for incorporating detailed demography into commonly used photothermal models demonstrates the importance of using both demography and phenology to predict consequences of phenological shifts.     

The lost generation hypothesis: could climate change drive ectotherms into a developmental trap?

Climate warming affects the rate and timing of the development in ectothermic organisms. Short‐living, ectothermic organisms (including many insects) showing thermal plasticity in life‐cycle regulation could, for example, increase the number of generations per year under warmer conditions. However, changed phenology may challenge the way organisms in temperate climates deal with the available thermal time window at the end of summer. Although adaptive plasticity is widely assumed in multivoltine organisms, rapid environmental change could distort the quality of information given by environmental cues that organisms use to make developmental decisions. Developmental traps are scenarios in which rapid environmental change triggers organisms to pursue maladaptive developmental pathways. This occurs because organisms must rely upon current environmental cues to predict future environmental conditions and corresponds to a novel case of ecological or evolutionary traps. Examples of introduced, invasive species are congruent with this hypothesis. Based on preliminary experiments, we argue that the dramatic declines of the wall brown Lasiommata megera in northwestern Europe may be an example of a developmental trap. This formerly widespread, bivoltine (or even multivoltine) butterfly has become a conundrum to conservationist biologists. A split‐brood field experiment with L. megera indeed suggests issues with life‐cycle regulation decisions at the end of summer. In areas where the species went extinct recently, 100% of the individuals developed directly into a third generation without larval diapause, whereas only 42.5% did so in the areas where the species still occurs. Under unfavourable autumn conditions, the attempted third generation will result in high mortality and eventually a lost or ‘suicidal’ third generation in this insect with non‐overlapping, discrete generations. We discuss the idea of a developmental trap within an integrated framework for assessing the vulnerability of species to climate change.     

Historical and projected interactions between climate change and insect voltinism in a multivoltine species

Climate change can cause major changes to the dynamics of individual species and to those communities in which they interact. One effect of increasing temperatures is on insect voltinism, with the logical assumption that increases in surface temperatures would permit multivoltine species to increase the number of generations per year. Though insect development is primarily driven by temperature, most multivoltine insect species rely on photoperiodic cues, which do not change from year‐to‐year or in response to climate warming, to initiate diapause. Thus, the relationship between climate change and voltinism could be complex. We use a phenology model for grape berry moth, Paralobesia viteana (Clemens), which incorporates temperature‐dependent development and diapause termination, and photoperiod‐dependent diapause induction, to explore historical patterns in year‐to‐year voltinism fluctuations. We then extend this model to predict voltinism under varying scenarios of climate change to show the importance of both the quality and quantity of accumulated heat units. We also illustrate that increases in mean surface temperatures > 2 °C can have dramatic effects on insect voltinism by causing a shift in the ovipositional period that currently is subject to diapause‐inducing photoperiods.     

Modelling as a tool for analysing the temperature‐dependent future of the Colorado potato beetle in Europe

A warmer climate may increase the risk of attacks by insect pests on agricultural crops, and questions on how to adapt management practice have created a need for impact models. Phenological models driven by climate data can be used for assessing the potential distribution and voltinism of different insect species, but the quality of the simulations is influenced by a range of uncertainties. In this study, we model the temperature‐dependent activity and development of the Colorado potato beetle, and analyse the influence of uncertainty associated with parameterization of temperature and day length response. We found that the developmental threshold has a major impact on the simulated number of generations per year. Little is known about local adaptations and individual variations, but the use of an upper and a lower developmental threshold gave an indication on the potential variation. The day length conditions triggering diapause are known only for a few populations. We used gridded observed temperature data to estimate local adaptations, hypothesizing that cold autumns can leave a footprint in the population genetics by low survival of individuals not reaching the adult stage before winter. Our study indicated that the potential selection pressure caused by climate conditions varies between European regions. Provided that there is enough genetic variation, a local adaption at the northern distribution limit would reduce the number of unsuccessful initiations and thereby increase the potential for spreading to areas currently not infested. The simulations of the impact model were highly sensitive to biases in climate model data, i.e. systematic deviations in comparison with observed weather, highlightening the need of improved performance of regional climate models. Even a moderate temperature increase could change the voltinism of Leptinotarsa decemlineata in Europe, but knowledge on agricultural practice and strategies for countermeasures is needed to evaluate changes in risk of attacks.     

Western pine beetle voltinism in a changing California climate

1. Recent hot droughts in California resulted in ponderosa pine (Pinus ponderosa) mortality attributed to drought and western pine beetle (WPB, Dendroctonus brevicomis). While drought alone can cause tree death, direct warming effects on WPB are a contributing factor. Research on WPB generation timing (voltinism), however, is lacking.
2. We monitored WPB tree attacks and adult emergence timing at two California sites and developed a degree-day model from field-observed data. Historical, contemporary, and future temperatures for several California sites were used with the model to examine trends in WPB voltinism.
3. Field data showed a single summer and an overwinter generation at a northern California site. As summer temperatures increased beyond 1900–1980 averages, the predicted number of full and partial WPB generations by 2021 had increased from ~2 annual (one summer and one overwinter) generations historically to ~2.3 at two northern California sites and from ~2.3 to ~3.2 at two warmer California sites.
4. Historical and contemporary data suggest winter warming was not sufficient for an additional generation overwinter. Instead, increases in generations were driven by summer and fall temperatures.
5. Unconstrained increases in the number of future annual generations will be limited by complex, but not well understood, WPB thermal adaptations. Increased knowledge of temperature-driven WPB population growth will improve forest vegetation models aimed at predicting ponderosa pine mortality in a changing climate.

     

Developmental synchrony in multivoltine insects: generation separation versus smearing

Many insect species undergo multiple generations each year. They are found across biomes that vary in their strength of seasonality and, depending on location and species, can display a wide range of population dynamics. Some species exhibit cycles with distinct generations (developmental synchrony/generation separation), some exhibit overlapping generations with multiple life stages present simultaneously (generation smearing), while others have intermediate dynamics with early season separation followed by late season smearing. There are two main hypotheses to explain these dynamics. The first is the ‘seasonal disturbance’ hypothesis where winter synchronizes the developmental clock among individuals, which causes transient generation separation early in the season that erodes through the summer. The second is the ‘temperature destabilization’ hypothesis where warm temperatures during the summer cause population dynamics to become unstable giving rise to single generation cycles. Both hypotheses are supported by detailed mathematical theory incorporating mechanisms that are likely to drive dynamics in nature. In this review, we synthesize the theory and propose a conceptual framework—where each mechanism may be seen as an independent axis shaping the developmental (a)synchrony—that allows us to predict dynamic patterns from insect life-history characteristics. High fecundity, short adult life-span and strong seasonality enhance synchrony, while developmental plasticity and environmental heterogeneity erode synchrony. We further review current mathematical and statistical tools to study multi-generational dynamics and illustrate using case studies of multivoltine tortrix moths. By integrating two disparate bodies of theory, we articulate a deep connection among temperature, stability, developmental synchrony and inter-generational dynamics of multivoltine insects that is missing in current literature.     

A population model for diapausing multivoltine insects under asymmetric cannibalism

Pupa-eating cannibalism occurs naturally in several insect species. Byasa alcinous is a multivoltine species of Red-bodied Swallowtail butterfly found in East Asia, which diapauses as pupa over the winter and whose larvae cannibalize eggs and pupae. We investigate the effects on population dynamics of increasing the asymmetric cannibalistic attack rate of a general insect species in different environmental conditions. We do this by theoretically formulating a generalized system of univoltine and bivoltine larvae over two generations in the spring and summer months. We predict that a lack of resources over the summer can force the population to become entirely univoltine, unless the second-generation bivoltine larvae increase their cannibalistic attack rate, and consume the diapausing pupae from the first generation. The model shows that under extreme environmental conditions, the persistence of univoltine larvae is favoured when faced with the threat of extinction. The model also predicts the conditions for the coexistence of both univoltine and bivoltine larvae, and the degree to which they can both coexist, which decreases as the resource in the second generation increases. This work provides the grounding for future theoretical and experimental consideration of the role of cannibalism in determining insect voltinism.     

Climate change and voltinism of Mythimna sequax: the location and choice of phenological models matter

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Explaining the sawtooth: latitudinal periodicity in a circadian gene correlates with shifts in generation number

Many temperate insects take advantage of longer growing seasons at lower latitudes by increasing their generation number or voltinism. In some insects, development time abruptly decreases when additional generations are fit into the season. Consequently, latitudinal ‘sawtooth’ clines associated with shifts in voltinism are seen for phenotypes correlated with development time, like body size. However, latitudinal variation in voltinism has not been linked to genetic variation at specific loci. Here, we show a pattern in allele frequency among voltinism ecotypes of the European corn borer moth (Ostrinia nubilalis) that is reminiscent of a sawtooth cline. We characterized 145 autosomal and sex‐linked SNPs and found that period, a circadian gene that is genetically linked to a major QTL determining variation in post‐diapause development time, shows cyclical variation between voltinism ecotypes. Allele frequencies at an unlinked circadian clock gene cryptochrome1 were correlated with period. These results suggest that selection on development time to ‘fit’ complete life cycles into a latitudinally varying growing season produces oscillations in alleles associated with voltinism, primarily through changes at loci underlying the duration of transitions between diapause and other life history phases. Correlations among clock loci suggest possible coupling between the circadian clock and the circannual rhythms for synchronizing seasonal life history. We anticipate that latitudinal oscillations in allele frequency will represent signatures of adaptation to seasonal environments in other insects and may be critical to understanding the ecological and evolutionary consequences of variable environments, including response to global climate change.     

Integrating ancient patterns and current dynamics of insect–plant interactions: Taxonomic and geographic variation in herbivore specialization

Abstract The search for pattern in the ecology and evolutionary biology of insect–plant associations has fascinated biologists for centuries. High levels of tropical (low-latitude) plant and insect diversity relative to poleward latitudes and the disproportionate abundance of host-specialized insect herbivores have been noted. This review addresses several aspects of local insect specialization, host use abilities (and loss of these abilities with specialization), host-associated evolutionary divergence, and ecological (including “hybrid”) speciation, with special reference to the generation of biodiversity and the geographic and taxonomic identification of “species borders” for swallowtail butterflies (Papilionidae). From ancient phytochemically defined angiosperm affiliations that trace back millions of years to recent and very local specialized populations, the Papilionidae (swallowtail butterflies) have provided a model for enhanced understanding of localized ecological patterns and genetically based evolutionary processes. They have served as a useful group for evaluating the feeding specialization/physiological efficiency hypothesis. They have shown how the abiotic (thermal) environment interacts with host nutrirional suitability to generate “voltinism/suitability” gradients in specialization or preference latitudinally, and geographical mosaics locally. Several studies reviewed here suggest strongly that the oscillation hypothesis for speciation does have considerable merit, but at the same time, some species-level host specializations may lead to evolutionary dead-ends, especially with rapid environmental/habitat changes involving their host plants. Latitudinal gradients in species richness and degree of herbivore feeding specialization have been impacted by recent developments in ecological genetics and evolutionary ecology. Localized insect–plant associations that span the biospectrum from polyphenisms, polymorphisms, biotypes, demes, host races, to cryptic species, remain academically contentious, with simple definitions still debated. However, molecular analyses combined with ecological, ethological and physiological studies, have already begun to unveil some answers for many important ecological/evolutionary questions.     

Climate-mediated population dynamics enhance distribution range expansion in a rice pest insect

Environmental fluctuations can influence invertebrate population dynamics over large spatial scales, and effects of climate change are of particular importance in understanding phenology. In this study, we tested whether changing climate patterns could increase voltinism and emergence synchrony in Stenotus rubrovittatus and drive the mirid bug’s expansion into currently uninhabited areas of Japan. This expansion could have potentially serious economic consequences for the rice industry. We modelled development of S. rubrovittatus in the field applying the effective accumulated temperature model to calculate the theoretical number of generations and the egg hatching dates from 2003 to 2012 based on a high-resolution, daily weather database. We then performed a regional analysis to assess the relationship between population dynamics and range expansion across the study region and also included a local analysis to evaluate how population parameters affect the presence of S. rubrovittatus at local sites in each year. Results showed that distribution expanded with a relative increase in voltinism and with synchrony of egg hatching date. Moreover, we showed that increased voltinism in the previous year positively influenced local population occurrence. This positive effect suggests that the species’ distribution range expands through increased reproduction at both the regional and local scale. Climate-mediated population dynamics play a significant role in range expansion of the mirid bug.     

Influence of voltine ecotype and geographic distance on genetic and haplotype variation in the Asian corn borer

Diapause is an adaptive dormancy strategy by which arthropods endure extended periods of adverse climatic conditions. Seasonal variation in larval diapause initiation and duration in Ostrinia furnacalis may influence adult mating generation number (voltinism) across different local environments. The degree to which voltine ecotype, geographic distance, or other ecological factors influence O. furnacalis population genetic structure remains uncertain. Genetic differentiation was estimated between voltine ecotypes collected from 8 locations. Mitochondrial haplotypes were significantly different between historically allopatric univoltine and bivoltine locations, but confounded by a strong correlation with geographic distance. In contrast, single nucleotide polymorphism (SNP) genotypes show low but significant levels of variation and a lack of influence of geographic distance between allopatric voltine locations. Regardless, 11 of 257 SNP loci were predicted to be under selection, suggesting population genetic homogenization except at loci proximal to factors putatively under selection. These findings provide evidence of haplotype divergent voltine ecotypes that may be maintained in allopatric and sympatric areas despite relatively high rates of nuclear gene flow, yet influence of voltinism on maintenance of observed haplotype divergence remains unresolved.     

Host plant defences and voltinism in European butterflies

Abstract.  1. With respect to seasonal availability for herbivores, plants defended by synthesising qualitative compounds differ from those protected by accumulation of quantitative macromolecules, leaf toughness, and low water and/or nutrient content. While the palatability of the former plants remains relatively constant during the season, the palatability of the latter group decreases with leaf age.
2. It was hypothesised that in seasonal temperate environments, quantitative plant defences should restrict the annual numbers of insect generations. To test this hypothesis, European butterflies were used as a model, both non-corrected regressions and tests controlling for phylogeny were carried out, and potentially confounding factors such as body size or occurrence in short-season environments were treated as covariables.
3. Non-phylogenetically controlled regressions corroborated that butterflies feeding on quantitatively protected hosts (woody plants + grasses) form fewer generations than species feeding on qualitatively protected forbs. Plant defences fitted voltinism better than butterfly size, and remained significant even after controlling for short seasons. Using independent contrasts, feeding on woody plants plus grasses, and feeding on woody plants only, predicted fewer generations. These patterns, however, applied exclusively for foliage-feeding species.
4. The association between plant defences and voltinism represents a hitherto overlooked pattern in the ecology of temperate herbivores. It may explain why large insects tend to form fewer generations and feed on structurally complex hosts, and why some species remain monovoltine although they are not restricted by short season.     

On the laboratory rearing of green dock leaf beetles Gastrophysa viridula (Coleoptera: Chrysomelidae)

Abstract Leaf beetles Gastrophysa viridula have attracted recently increased research interest from various points of view, since they are: (i) pest insects in rhubarb crops; (ii) potential biocontrol agents of dock plants Rumex spp. in grasslands; and (iii) a model species in ecological studies on insect population dynamics, biochemistry, behavior, biomechanics and biomimetics. The continuous rearing of beetles at standardized conditions may help to unify the fitness state of different individuals, allowing a better comparison of experimental results. The present communication suggests a modular space‐ and time‐saving rearing method of G. viridula in stackable faunariums under laboratory conditions, which has been successfully established and continuously used over the last 5 years. Several developmental stages were kept in separate boxes, and multiple generations were kept simultaneously, depending on the required number of beetles.     

How climate change affects the seasonal ecology of insect parasitoids

1. In the context of global change, modifications in winter conditions may disrupt the seasonal phenology patterns of organisms, modify the synchrony of closely interacting species and lead to unpredictable outcomes at different ecological scales. 2. Parasites are present in almost every food web and their interactions with hosts greatly contribute to ecosystem functioning. Among upper trophic levels of terrestrial ecosystems, insect parasitoids are key components in terms of functioning and species richness. Parasitoids respond to climate change in similar ways to other insects, but their close relationship with their hosts and their particular life cycle – alternating between parasitic and free-living forms – make them special cases. 3. This article reviews of the mechanisms likely to undergo plastic or evolutionary adjustments when exposed to climate change that could modify insect seasonal strategies. Different scenarios are then proposed for the evolution of parasitoid insect seasonal ecology by exploring three anticipated outcomes of climate change: (i) decreased severity of winter cold; (ii) decreased winter duration; and (iii) increased extreme seasonal climatic events and environmental stochasticity. 4. The capacities of insects to adapt to new environmental conditions, either through plasticity or genetic evolution, are highlighted. They may reduce diapause expression, adapt to changing cues to initiate or terminate diapause, increase voltinism, or develop overwintering bet-hedging strategies, but parasitoids' responses will be highly constrained by those of their hosts. 5. Changes in the seasonal ecology of parasitoids may have consequences on host–parasitoid synchrony and population cycles, food-web functioning, and ecosystem services such as biological pest control.     

Thermodynamics constrains the evolution of insect population growth rates: "warmer is better"

Diverse biochemical and physiological adaptations enable different species of ectotherms to survive and reproduce in very different temperature regimes, but whether these adaptations fully compensate for the thermodynamically depressing effects of low temperature on rates of biological processes is debated. If such adaptations are fully compensatory, then temperature-dependent processes (e.g., digestion rate, population growth rate) of cold-adapted species will match those of warm-adapted species when each is measured at its own optimal temperature. Here we show that cold-adapted insect species have much lower maximum rates of population growth than do warm-adapted species, even when we control for phylogenetic relatedness. This pattern also holds when we use a structural-equation model to analyze alternative hypotheses that might otherwise explain this correlation. Thus, although physiological adaptations enable some insects to survive and reproduce at low temperatures, these adaptations do not overcome the "tyranny" of thermodynamics, at least for rates of population increase. Indeed, the sensitivity of population growth rates of insects to temperature is even greater than predicted by a recent thermodynamic model. Our findings suggest that adaptation to temperature inevitably alters the population dynamics of insects. This result has broad evolutionary and ecological consequences.     

Ecological and genetic factors linked to contrasting genome dynamics in seed plants

The large-scale replacement of gymnosperms by angiosperms in many ecological niches over time and the huge disparity in species numbers have led scientists to explore factors (e.g. polyploidy, developmental systems, floral evolution) that may have contributed to the astonishing rise of angiosperm diversity. Here, we explore genomic and ecological factors influencing seed plant genomes. This is timely given the recent surge in genomic data. We compare and contrast the genomic structure and evolution of angiosperms and gymnosperms and find that angiosperm genomes are more dynamic and diverse, particularly amongst the herbaceous species. Gymnosperms typically have reduced frequencies of a number of processes (e.g. polyploidy) that have shaped the genomes of other vascular plants and have alternative mechanisms to suppress genome dynamism (e.g. epigenetics and activity of transposable elements). Furthermore, the presence of several characters in angiosperms (e.g. herbaceous habit, short minimum generation time) has enabled them to exploit new niches and to be viable with small population sizes, where the power of genetic drift can outweigh that of selection. Together these processes have led to increased rates of genetic divergence and faster fixation times of variation in many angiosperms compared with gymnosperms.