Changes In Life History Research Articles

Maternal thermal environment induces plastic responses in the reproductive life history of oviparous lizards.

Adaptive plasticity may shift phenotypic traits close to a new optimum for directional selection and probably facilitates adaptive evolution in new environments. However, such plasticity has rarely been reported in life-history evolution, despite overwhelming evidence of life-history variation both among and within species. In this study, the temperatures experienced by gravid females of Scincella modesta were manipulated to identify maternally induced plasticity in reproductive traits and the significance of such changes in the evolution of life history. Consistent with the geographic pattern of life history, the study demonstrated that low temperatures delayed egg oviposition, resulting in a more advanced embryonic developmental stage at oviposition and shorter incubation periods compared with warm temperatures. In addition, females maintained at low temperatures produced larger eggs and hence heavier hatchlings than those at warm temperatures. This study demonstrated that environmental temperatures can induce plastic responses in egg retention and offspring size, and these maternally mediated changes in reproductive life history seem to be adaptive in the light of latitudinal clines of these traits in natural populations.

Insect herbivores associated with an evergreen tree Goniorrhachis marginata Taub. (Leguminosae: Caesalpinioideae) in a tropical dry forest

Goniorrhachis marginata Taub. (Leguminosae: Caesalpinioideae) is a tree species found in Brazilian tropical dry forests that retain their leaves during the dry season. That being, we addressed the following question: i) How do insect diversity (sap-sucking and chewing), leaf herbivory and defensive traits (tannin and leaf sclerophylly) vary on the evergreen tree species G. marginata between seasons? The abundance of sap-sucking insects was higher in the dry season than in the rainy season. However, we did not verify any difference in the species richness and abundance of chewing insects between seasons. Leaf herbivory was higher in the rainy season, whereas leaf sclerophylly was higher in the dry season. However, herbivory was not related to sclerophylly. Insect herbivores likely decrease their folivory activity during the dry season due to life history patterns or changes in behaviour, possibly entering diapause or inactivity during this period. Therefore, G. marginata acts as a likely keystone species, serving as a moist refuge for the insect fauna during the dry season in tropical dry forest, and the presence of this evergreen species is crucial to conservation strategies of this threatened ecosystem.

Bayesian fitting of probabilistic maturation reaction norms to population-level data

Probabilistic maturation reaction norms (PMRNs) are an important tool for studying fisheries-induced evolution and environmental effects on life history. To date there has been no way to fit a PMRN to population-level fisheries data; instead individual-level data must be used. This limits the stocks and time periods that can be studied.We introduce a Bayesian method for fitting PMRNs to population-level data. The method is verified against both an existing result and simulated data, and applied to historical Barents Sea cod data which combines observations of population-level variation in age, size and maturity status from Russia and Norway.The method shows a clear and rapid trend towards greater probability of maturation at smaller lengths in the Barents Sea cod.The new model fitting algorithm allows us to study historic changes in life history despite the lack of individual-level data seen in much long term data. Access to more data will aid the study of evolutionary hypotheses in a wide range of organisms.

A multivariate approach to the analysis of within lifetime variation in life history

Summary Ecological and environmental gradients create varying selective pressures on organisms that result in differences in optimal life history tactics. Moreover, life histories are inherently multivariate, consisting of a coordinated suite of life history traits that vary over an organism's lifetime. Such variation can be described as a trajectory of phenotypic change through time in multivariate space defined by a set of life history traits. We demonstrate the use of phenotypic trajectory analysis as a multivariate analytical approach for quantifying and comparing phenotypic change in life history throughout an organism's life. Life history trajectories have attributes – magnitude, direction, and shape – that can be quantified and statistically compared. We demonstrate the construction of trajectories using levels characterized by individuals with the same age or similar state, and we show how this approach can be used to evaluate the evolution of life history strategies given predictions from life history theory. We demonstrate the utility of phenotypic trajectory analysis for life histories using two examples. We compare life history trajectories of burying beetles and show that females balance costs of reproduction differently based on resource availability. We also characterize life history trajectories of livebearing fish in different predation environments. We show that females in non‐predator environments, but not predator environments, exhibit trajectories consistent with the terminal investment hypothesis. While analysing life history variation in a multivariate framework is not novel, we show that phenotypic trajectory analysis provides a method to statistically test age‐ and state‐based predictions of life history theory.

Selection for narrow gate of emergence results in correlated sex-specific changes in life history of Drosophila melanogaster.

ABSTRACTSince the ability to time rhythmic behaviours in accordance with cyclic environments is likely to confer adaptive advantage to organisms, the underlying clocks are believed to be selected for stability in timekeeping over evolutionary time scales. Here we report the results of a study aimed at assessing fitness consequences of a long-term laboratory selection for tighter circadian organisation using fruit fly Drosophila melanogaster populations. We selected flies emerging in a narrow window of 1 h in the morning for several generations and assayed their life history traits such as pre-adult development time, survivorship, adult lifespan and lifetime fecundity. We chose flies emerging during the selection window (in the morning) and another window (in the evening) to represent adaptive and non-adaptive phenotypes, respectively, and examined the correlation of emergence time with adult fitness traits. Adult lifespan of males from the selected populations does not differ from the controls, whereas females from the selected populations have significantly shorter lifespan and produce more eggs during their mid-life compared to the controls. Although there is no difference in the lifespan of males of the selected populations, whether they emerge in morning or evening window, morning emerging females live slightly shorter and lay more eggs during the mid-life stage compared to those emerging in the evening. Interestingly, such a time of emergence dependent difference in fitness is not seen in flies from the control populations. These results, therefore, suggest reduced lifespan and enhanced mid-life reproductive output in females selected for narrow gate of emergence, and a sex-dependent genetic correlation between the timing of emergence and key fitness traits in these populations.

Less means more: nutrient stress leads to higher δ15N ratios in fish

Summary Isotopic ratios of nitrogen are often used in food‐web studies to determine trophic position (including food chain length) and food sources, with greater ratios of 15N/14N (δ15N) usually considered indicative of higher trophic position. However, fasting and starving animals may also show a progressive increase in δ15N over time as they catabolise their own tissues. To determine the importance of starvation, we conducted a 4‐month laboratory experiment testing effects of starvation on body condition and isotope ratios in the muscle tissue of freshwater guppies (Poecilia reticulata). We also compared laboratory results and conclusions with analyses of body condition and isotope ratios in various small species of fish collected in four seasons from the Kansas River in north‐eastern Kansas, U.S.A. Fish starved in our laboratory experiment had significantly higher 15N values and poorer body condition than those fed more regularly. The diverse group of fish species collected in summer (July) from the Kansas River had higher weight‐to‐length ratios and lower 15N values than those retrieved in other seasons. Overall body condition resulting from reduced food consumption explained 44 and 53% of the variability in 15N for field and laboratory fish, respectively. These results are applicable to a wide variety of food‐web research but are especially pertinent to studies of organisms that undergo large changes in life history, dormancy, extended fasts or periods of significant nutritional allocation to young.

Light intensity controls anti-predator defences inDaphnia: the suppression of life-history changes

A huge variety of organisms respond to the presence of predators with inducible defences, each of which is associated with costs. Many genotypes have the potential to respond with more than one defence, and it has been argued that it would be maladaptive to exhibit all possible responses at the same time. Here, we test how a well-known anti-fish defence in Daphnia, life-history changes (LHC), is controlled by light. We show that the kairomone-mediated reduction in size at first reproduction is inversely coupled to the light intensity. A similar effect was found for the kairomone-mediated expression of candidate genes in Daphnia. We argue that the light intensity an individual is exposed to determines the degree of LHC, which allows for plastic adjustment to fluctuating environments and simultaneously minimizes the associated costs of multiple alternately deployable defences. It is hypothesized that this allows for a coupling of multiple defences, i.e. LHC and diel vertical migration.

Artificial light at night causes diapause inhibition and sex-specific life history changes in a moth.

Rapidly increasing levels of light pollution subject nocturnal organisms to major alterations of their habitat, the ecological consequences of which are largely unknown. Moths are well-known to be attracted to light at night, but effects of light on other aspects of moth ecology, such as larval development and life-history, remain unknown. Such effects may have important consequences for fitness and thus for moth population sizes. To study the effects of artificial night lighting on development and life-history of moths, we experimentally subjected Mamestra brassicae (Noctuidae) caterpillars to low intensity green, white, red or no artificial light at night and determined their growth rate, maximum caterpillar mass, age at pupation, pupal mass and pupation duration. We found sex-specific effects of artificial light on caterpillar life-history, with male caterpillars subjected to green and white light reaching a lower maximum mass, pupating earlier and obtaining a lower pupal mass than male caterpillars under red light or in darkness. These effects can have major implications for fitness, but were absent in female caterpillars. Moreover, by the time that the first adult moth from the dark control treatment emerged from its pupa (after 110 days), about 85% of the moths that were under green light and 83% of the moths that were under white light had already emerged. These differences in pupation duration occurred in both sexes and were highly significant, and likely result from diapause inhibition by artificial night lighting. We conclude that low levels of nocturnal illumination can disrupt life-histories in moths and inhibit the initiation of pupal diapause. This may result in reduced fitness and increased mortality. The application of red light, instead of white or green light, might be an appropriate measure to mitigate negative artificial light effects on moth life history.

Phylogeny and oscillating expression of period and cryptochrome in short and long photoperiods suggest a conserved function in Nasonia vitripennis

Photoperiodism, the ability to respond to seasonal varying day length with suitable life history changes, is a common trait in organisms that live in temperate regions. In most studied organisms, the circadian system appears to be the basis for photoperiodic time measurement. In insects this is still controversial: while some data indicate that the circadian system is causally involved in photoperiodism, others suggest that it may have a marginal or indirect role. Resonance experiments in the parasitic wasp Nasonia vitripennis have revealed a circadian component in photoperiodic time measurement compatible with a mechanism of internal coincidence where a two components oscillator system obtains information from dawn and dusk, respectively. The identity of this oscillator (or oscillators) is still unclear but possible candidates are the oscillating molecules of the auto-regulatory feedback loops in the heart of the circadian system. Here, we show for the first time the circadian oscillation of period and cryptochrome mRNAs in the heads of Nasonia females kept under short and long photoperiods. Period and cryptochrome mRNA levels display a synchronous oscillation in all conditions tested and persist, albeit with reduced amplitude, during the first day in constant light as well as constant darkness. More importantly, the signal for the period and cryptochrome oscillations is set by the light-on signal. These results, together with phylogenetic analyses, indicate that Nasonia’s period and cryptochrome display characteristics of homologous genes in other hymenopteran species.

Natural resilience in Arctic charr Salvelinus alpinus: life history, spatial and dietary alterations along gradients of interspecific interactions.

The Arctic charr Salvelinus alpinus species complex has been shown to be exceptionally vulnerable to rapid abiotic and biotic changes. Salvelinus alpinus, however, inhabit environmental extremes ranging from lakes and rivers in the High Arctic to deep multi-fish species lakes far outside the polar region. Long-term responses to post-glacial environmental variations and successively increased interspecific interactions reveal an essential degree of natural ecological resilience and phenotypic flexibility. Case studies in Scandinavia and Newfoundland illustrate the alternate trophic roles of S. alpinus, and its flexible niche use and life-history changes in order to regain or maintain body size in gradients of lakes with increasing fish species diversity. While allopatric in northern low-productive upland lakes, landlocked populations are commonly structured by cannibalism. In sympatry with other fish species, S. alpinus mostly serve as prey, with their decreasing growth and body size reflecting the successive diet shift from littoral macro-benthos to zooplankton and profundal microbenthos as interspecific competition for food and habitat intensifies. Interactions with natural and introduced superior zooplankton feeders and ultimate predators finally become detrimental. Consequently, the niche of S. alpinus is increasingly compressed in lakes along latitudinal and altitudinal gradients, although certain natural key conditions offer S. alpinus temporary asylum in the inescapable process towards local and regional extinction. The water temperature drop during winter allows S. alpinus to temporarily resume the richer littoral dietary and spatial niche use in low diversity lakes. In southern lowland and coastal lakes with more complex fish communities, access to key prey species such as profundal macro-crustaceans and smelt Osmerus spp. allow S. alpinus to regain its original niche space and characteristics as a large piscivore. In conclusion, S. alpinus along its evolutionary landscape demonstrates associated alterations of life-history characteristics, such as body size and longevity, and thus reproductive traits demonstrating similarities between northern cannibals and southern piscivores. Although including a high degree of natural resilience, obviously differing among S.alpinus populations along its range, differences seen in extreme marginal populations may have been adaptive and the product of an evolutionary response with optimized growth resulting from natural selection due to ultimate intra or inter-specific competition and predation.

Changes in the life history traits of Song Thrushes Turdus philomelos introduced to New Zealand

Capsule Song Thrushes introduced to New Zealand differ in a number of life history traits compared to their source population in Britain.Aim To survey life history traits in an introduced population of Song Thrushes, for comparison with the source population.Methods Nests were monitored near Kaikoura, New Zealand. We recorded clutch size, egg size, length of incubation and nestling stages, hatching success, levels of brood reduction, and nest success. Data on life history traits of Song Thrushes in Britain were collated from the literature.Results Mean clutch size declined from 4.1 eggs in Britain to 3.6 eggs in New Zealand. Egg size, nestling period length, and breeding success of Song Thrushes in New Zealand also decreased, while incubation period lengthened. There were changes in six out of seven life history traits studied.Conclusion The general direction of changes in life history traits suggests that Song Thrushes in New Zealand invest less in each reproductive bout than in their native range. These changes may be the result of the warmer climate and longer breeding season in New Zealand. Understanding the fitness effects of these life history changes may provide insight into how a species adapts to a warmer environment.

Period-Based Mortality Change: Turning Points in Trends since 1950.

We investigate a major turning point in mortality trends at adult ages that occurred for many low‐mortality countries in the late 1960s or early 1970s. We analyze patterns of total and cause‐specific mortality over the past 60 years using data from the Human Mortality Database and the World Health Organization. We focus on four broad categories of causes of death: heart diseases, cerebrovascular diseases, smoking‐related cancers, and all other cancers. We use a two‐slope regression model to assess the timing and magnitude of turning points in mortality trends over this era, making separate analyses by sex, age, and cause of death. The age pattern of temporal changes is given particular attention. Our results demonstrate convincingly that period‐based factors were very significant in the onset of the “cardiovascular revolution” in the years around 1970. In general, although cohort processes cannot be ruled out as a driver of mortality change in recent decades (especially for mortality due to smoking‐related cancers), the evidence reviewed here suggests that period factors have been the dominant force behind the mortality trends of high‐income countries during this era.

Rapid evolution of antimicrobial peptide genes in an insect host–social parasite system

Selection, as a major driver for evolution in host–parasite interactions, may act on two levels; the virulence of the pathogen, and the hosts’ defence system. Effectors of the host defence system might evolve faster than other genes e.g. those involved in adaptation to changes in life history or environmental fluctuations. Host–parasite interactions at the level of hosts and their specific social parasites, present a special setting for evolutionarily driven selection, as both share the same environmental conditions and pathogen pressures.Here, we study the evolution of antimicrobial peptide (AMP) genes, in six host bumblebee and their socially parasitic cuckoo bumblebee species. The selected AMP genes evolved much faster than non-immune genes, but only defensin-1 showed significant differences between host and social parasite. Nucleotide diversity and codon-by-codon analyses confirmed that purifying selection is the main selective force acting on bumblebee defence genes.

On the fate of sexual traits under asexuality

Environmental shifts and life-history changes may result in formerly adaptive traits becoming non-functional or maladaptive. In the absence of pleiotropy and other constraints, such traits may decay as a consequence of neutral mutation accumulation or selective processes, highlighting the importance of natural selection for adaptations. A suite of traits are expected to lose their adaptive function in asexual organisms derived from sexual ancestors, and the many independent transitions to asexuality allow for comparative studies of parallel trait maintenance versus decay. In addition, because certain traits, notably male-specific traits, are usually not exposed to selection under asexuality, their decay would have to occur as a consequence of drift. Selective processes could drive the decay of traits associated with costs, which may be the case for the majority of sexual traits expressed in females. We review the fate of male and female sexual traits in 93 animal lineages characterized by asexual reproduction, covering a broad taxon range including molluscs, arachnids, diplopods, crustaceans and eleven different hexapod orders. Many asexual lineages are still able occasionally to produce males. These asexually produced males are often largely or even fully functional, revealing that major developmental pathways can remain quiescent and functional over extended time periods. By contrast, for asexual females, there is a parallel and rapid decay of sexual traits, especially of traits related to mate attraction and location, as expected given the considerable costs often associated with the expression of these traits. The level of decay of female sexual traits, in addition to asexual females being unable to fertilize their eggs, would severely impede reversals to sexual reproduction, even in recently derived asexual lineages. More generally, the parallel maintenance versus decay of different trait types across diverse asexual lineages suggests that neutral traits display little or no decay even after extended periods under relaxed selection, while extensive decay for selected traits occurs extremely quickly. These patterns also highlight that adaptations can fix rapidly in natural populations of asexual organisms, in spite of their mode of reproduction.

Ecosystem effects of contemporary life-history changes are comparable to those of fishing

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 495:219-231 (2014) - DOI: https://doi.org/10.3354/meps10579 Ecosystem effects of contemporary life-history changes are comparable to those of fishing Asta Audzijonyte1,2,*, Anna Kuparinen2,3, Elizabeth A. Fulton1 1CSIRO Wealth from Oceans Flagship, GPO Box 1538, Hobart, Tasmania 7001, Australia 2Department of Environmental Sciences, University of Helsinki, PO Box 65, Helsinki 00014, Finland 3Department of Biosciences, University of Helsinki, PO Box 65, Helsinki 00014, Finland *Corresponding author: asta.audzijonyte@helsinki.fi ABSTRACT: Recent studies suggest that fishing and climate change can lead to a decrease in body size of fishes. While the effect of fishing on marine ecosystems has been widely explored, much less is known about the ecosystem effects of fish body size decrease. Here we used a marine ecosystem model to compare how fishing and small (<0.1% yr -1) but continuous (50 yr) decreases in the average body sizes of 5 Australian demersal fish species affect ecosystem indicators, biomasses and diets of different species. We found that decreasing growth rate of the 5 species had similar and comparable impact as the introduction of fishing of these 5 species at fishing mortality rate of F = 0.2 yr -1. The same applied when impacts of decrease in size were compared to those of increasing fishing from F = 0.2 to F = 0.4. This suggests that declines in body size alone can lead to ecosystem responses similar in magnitude to those caused by moderate fishing. On average, body size decrease alone caused more qualitative changes in diets of all species and larger changes in the predation mortality of slower growing species than the introduction or intensification of fishing. The overall ecosystem response to fishing and slower growth of fish was largely similar and additive, suggesting that decreasing sizes of harvested fishes are likely to amplify the effects of fishing. KEY WORDS: Diets · Ecosystem indicators · Ecosystem models · Fisheries induced evolution · Growth · Predator–prey interactions Full text in pdf format Supplement 1 Supplement 2 Supplement 3 Supplement 4 PreviousNextCite this article as: Audzijonyte A, Kuparinen A, Fulton EA (2014) Ecosystem effects of contemporary life-history changes are comparable to those of fishing. Mar Ecol Prog Ser 495:219-231. https://doi.org/10.3354/meps10579 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 495. Online publication date: January 09, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.

Life‐history plasticity and sustainable exploitation: a theory of growth compensation applied to walleye management

A simple population model was developed to evaluate the role of plastic and evolutionary life-history changes on sustainable exploitation rates. Plastic changes are embodied in density-dependent compensatory adjustments to somatic growth rate and larval/juvenile survival, which can compensate for the reductions in reproductive lifetime and mean population fecundity that accompany the higher adult mortality imposed by exploitation. Evolutionary changes are embodied in the selective pressures that higher adult mortality imposes on age at maturity, length at maturity, and reproductive investment. Analytical development, based on a biphasic growth model, led to simple equations that show explicitly how sustainable exploitation rates are bounded by each of these effects. We show that density-dependent growth combined with a fixed length at maturity and fixed reproductive investment can support exploitation-driven mortality that is 80% of the level supported by evolutionary changes in maturation and reproductive investment. Sustainable fishing mortality is proportional to natural mortality (M) times the degree of density-dependent growth, as modified by both the degree of density-dependent early survival and the minimum harvestable length. We applied this model to estimate sustainable exploitation rates for North American walleye populations (Sander vitreus). Our analysis of demographic data from walleye populations spread across a broad latitudinal range indicates that density-dependent variation in growth rate can vary by a factor of 2. Implications of this growth response are generally consistent with empirical studies suggesting that optimal fishing mortality is approximately 0.75M for teleosts. This approach can be adapted to the management of other species, particularly when significant exploitation is imposed on many, widely distributed, but geographically isolated populations.

Predator exposure alters stress physiology in guppies across timescales

In vertebrates, glucocorticoids mediate a wide-range of responses to stressors. For this reason, they are implicated in adaptation to changes in predation pressure. Trinidadian guppies (Poecilia reticulata) from high-predation environments have repeatedly and independently colonized and adapted to low-predation environments, resulting in parallel changes in life history, morphology, and behavior. We validated methods for non-invasive waterborne hormone sample collection in this species, and used this technique to examine genetic and environmental effects of predation on basal glucocorticoid (cortisol) levels. To examine genetic differences, we compared waterborne cortisol levels in high- and low-predation fish from two distinct population pairs. We found that fish from high-predation localities had lower cortisol levels than their low-predation counterparts. To isolate environmental influences, we compared waterborne cortisol levels in genetically similar fish reared with and without exposure to predator chemical cues. We found that fish reared with predator chemical cues had lower waterborne cortisol levels than those reared without. Comparisons of waterborne and whole-body cortisol levels demonstrated that populations differed in overall cortisol levels in the body, whereas rearing conditions altered the release of cortisol from the body into the water. Thus, evolutionary history with predators and lifetime exposure to predator cues were both associated with lower cortisol release, but depended on distinct physiological mechanisms.

Estimating growth from sex ratio-at-length data in species with sexual size dimorphism

Individual growth is one of the main processes which drive the population dynamic and stock productivity. Many fish have differential individual growth by sex. Growth is affected by sexual development, which is frequently reached at different sizes in males and females. Differences in growth per sex after maturity produce different patterns in sex proportions-at-length in the population. If these patterns are the consequence of changes in life history parameters, sex ratio-at-length data can be expected to contain significant information on the population life history. In this paper I first explore how post-maturity changes in life history may shape these patterns in sex ratio-at-length; secondly I explore how these data may be used to estimate growth parameters and finally I discuss how this information may be useful for stock assessment purposes. I use European hake data and life history parameters to model expected sex ratios. The results suggest that reproductive energy allocation leads to a lower growth rate in male hakes than in females. Moreover the sex ratio-at-length may provide useful information for estimating growth parameters in dimorphic species if additional information from other sources is available. Finally, these data can easily be factored into stock assessment models to help provide a better estimation of growth parameters and mortality rates. This valuable, accurate and cheap biological information (sex ratio-at-length) may play an important role in population dynamic models and stock assessment for species with sexual size dimorphism.

Flight muscle breakdown in the soldier caste of the gall-inducing thrips species, Kladothrips intermedius Bagnall

Within the gall-inducing thrips of Australia, genus Kladothrips, is a single origin of a soldier caste. A subsequent radiation has led to at least seven social species, and two species that are likely to have independently lost the soldier caste. Both losses of soldiers are connected to a shift in the insects’ host plant. A third inferred host shift is correlated with life history changes in a species with soldiers, K. intermedius, which might suggest this defensive caste may be in transition. The soldiers of this species have variable wing lengths that overlap with that of the flight-capable dispersers. Our study was designed to assess the possibility that some soldiers in this species retain the ability to disperse by wing. A morphological assessment shows that a proportion of soldiers have body dimensions and wing lengths that fall within the range of dispersers, with males more so than females. However, longer wing length in soldiers (sample of primarily females) did not correspond with a disperser like walking behaviour. Furthermore, histological sections suggest that wing muscles of soldiers are deteriorated or absent, which is similar to what was observed in their foundress mothers. The presence of long wings did not correspond with being flight capable in this caste.

Effect of experimental and seasonal warming on litter decomposition in a temperate stream

Litter decomposition, a fundamental ecosystem process in woodland streams, is potentially affected by the predicted increase in water temperature. Here, we assessed the effects of experimental and seasonal warming on oak litter decomposition and on the relative contributions of microbes and invertebrates to this process. Experimental warming (~3 °C) stimulated litter decomposition in the coldest, but not in the warmest, months. This may be attributed to (1) higher temperature sensitivity of decomposition at lower ambient temperature due to temperature limitation of enzymatic activity, (2) higher relative temperature increase in winter than in warmer months, (3) existence of a previous warming period in winter, and (4) stronger stimulation of the activity of detritivores by warming in winter due to the prevalence of earlier (smaller) instars than in warmer months. The low response of litter decomposition to warming may have been due to the low nutrient availability in the study stream. The 30-day litter decomposition was stimulated over the seasonal gradient (monthly mean temperature: 6–16 °C), which may be attributed to a stimulation of metabolic activities by warming and to changes in detritivore life history over the seasons. The stimulation of litter decomposition with temperature suggests that the rate of CO2 release from freshwaters will increase under global warming. However, invertebrate-driven litter decomposition was more responsive to warming than microbial-driven litter decomposition, suggesting that a larger fraction of litter carbon may be converted into secondary production and stored in the system for longer periods.