Life History Plasticity Research Articles

Quantifying importance of marine prey in the diets of two partially anadromous fishes

The importance of marine prey sources for partially anadromous fishes has received little study and is complicated by considerable plasticity in life history. We determined proportional contributions of marine, freshwater benthic, and freshwater pelagic prey to anadromous and resident Arctic char (Salvelinus alpinus) and lake trout (Salvelinus namaycush) from several partially anadromous populations in the Canadian Arctic. Bayesian mixing models (MixSIR) applied to δ34S and δ13C ratios in lake-specific models indicated that marine prey accounted for 90%–91% of anadromous Arctic char diet and 60%–66% of anadromous lake trout diet. When these estimates were combined with proportion of anadromous individuals in partially anadromous populations, marine food sources accounted for 31%–44% of Arctic char population productivity and 16%–26% of lake trout population productivity. Although future research is needed to refine and quantify variability around these estimates, our results will allow better predictions of the effects of anthropogenic stressors on partially anadromous fishes.

Effects of food availability on reproductive output, offspring quality and reproductive efficiency in the apple snail Pomacea canaliculata

Phenotypic plasticity in life history traits favors the establishment of invaders and may magnify their ecological impacts. Pomacea canaliculata, the only freshwater snail listed among the 100 worst invaders worldwide, is able to complete its life cycle within a wide range of conditions, a capacity attributed to its life history plasticity. Using snails from their native range in Argentina we investigated the changes in fecundity, egg mass traits, offspring quality, and efficiency of food conversion into eggs in response to different levels of food availability throughout different life stages. Pre-maturity mortality was not affected by chronic reductions of up to 80% in food availability. Females fed ad libitum demonstrated no significant reproductive output differences when mated with males raised at different food availability levels. For females, the number and total weight of eggs and the size of egg masses decreased at high levels of food deprivation. Their efficiency of conversion into eggs of the food ingested during the reproductive period increased with deprivation, as did the survival time of their offspring. In contrast, the egg mass laying rate and the individual egg weight did not differ under different food availability regimes. Reductions in food availability have been suggested as a control method but our results indicate that fecundity would be lessened only at deprivation levels higher than 50% and would be partially compensated by an increase in hatchling survival.

Life history and morphological plasticity of the soybean aphid, Aphis glycines

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is a pest of soybean, Glycine max (L.) Merr. (Fabaceae), from eastern Asia that was first reported in North America in 2000. The influence of temperature on plasticity of life history and morphological traits of the soybean aphid has not been tested despite observable differences in population growth and morphology among isolates in laboratory colonies. Therefore, we used three isolates of the aphid to test whether lifespan, growth rate, fecundity, and morphology were plastic at 16, 24, and 28 °C. Population size of the aphid was influenced by temperature, probably because two reproductive traits, maximum number of offspring in 1 day and total fecundity, were plastic and increased in successive generations at 24 °C. All morphological traits were plastic, including lengths of body parts, number of antennal segments and caudal hairs, and color of siphunculi and body, and they were differentially influenced by isolate and temperature. Knowledge about the life history and morphology of the soybean aphid may help identify its capacity for phenotypic plasticity in heterogeneous temperatures and identify how temperature influences its survival, population growth, and diversity.

Phenotypic plasticity of life history traits in relation to reproductive strategies in Boa constrictor occidentalis

The close connection between reproductive ecology and life history in snakes leads to trade-offs between reproductive and other life-history traits. Optimal energy allocation to growth and reproduction is a key factor to determine life history structure. Therefore, elucidating the relationship between body size variations and reproductive characters is essential for a better understanding of life-history plasticity. The aim of this work was to determine to what extent life-history differs among populations of Boa constrictor occidentalis and to identify possible life-history trade-offs between morphological and reproductive traits. We compared two populations from areas that are separated latitudinally, with different climatic conditions and vegetation landscape structure. Reproductive and morphological data of specimens were recorded. Although populations had a similar mean length of mature snakes, the frequency of some size classes tended to be different. Size at sexual maturity differed between populations for females, generating variations in the proportion of mature individuals. Reproductive threshold and follicular size also varied, but female reproductive frequency was similar between populations. Reproductive frequency of males varied between populations although their body condition was similar. We discussed two major issues: (1) implications of size at sexual maturity for body size and fecundity; (2) trade-offs in reproductive characters.

Does it pay to delay? Flesh flies show adaptive plasticity in reproductive timing

Life-history plasticity is widespread among organisms. However, an important question is whether it is adaptive. Most models for plasticity in life-history timing predict that animals, once they have reached the minimal nutritional threshold under poor conditions, will accelerate development or time to reproduction. Adaptive delays in reproduction are not common, especially in short-lived species. Examples of adaptive reproductive delays exist in mammalian populations experiencing strong interspecific (e.g., predation) and intraspecific (e.g., infanticide) competition. But are there other environmental factors that may trigger an adaptive delay in reproductive timing? We show that the short-lived flesh fly Sarcophaga crassipalpis will delay reproduction under nutrient-poor conditions, even though it has already met the minimal nutritional threshold for reproduction. We test whether this delay strategy is an adaptive response allowing the scavenger time to locate more resources by experimentally providing supplemental protein pulses (early, mid and late) throughout the reproductive delay period. Flies receiving additional protein produced more and larger eggs, demonstrating a benefit of the delay. In addition, by tracking the allocation of carbon from the pulses using stable isotopes, we show that flies receiving earlier pulses incorporated more carbon into eggs and somatic tissue than those given a later pulse. These results indicate that the reproductive delay in S. crassipalpis is consistent with adaptive post-threshold plasticity, a nutritionally linked reproductive strategy that has not been reported previously in an invertebrate species.

Rapid weight gain after birth predicts life history and reproductive strategy in Filipino males

Ecological cues during prenatal and postnatal development may allow organisms to adjust reproductive strategy. The hypothalamic-pituitary-gonadal (HPG) axis is a prime candidate for adaptive plasticity as a result of its critical period of birth to 6 mo (B6M) in humans and the role of testosterone in the development and maintenance of costly sexually dimorphic somatic and behavioral traits. We hypothesized that weight velocity specific to B6M would predict male life history characteristics, including maturational timing, reproductive hormones, adult size, strength, and sexual activity. Data come from 770 Filipino men (age 20.5-22.5 y) followed since birth, with predictor variables including birth weight and weight velocities calculated at 6-mo intervals during the first 2 y of life. As expected, infants who were breastfed experienced less diarrhea, lived in wealthier households with better hygiene, and grew faster from B6M. Males with rapid B6M growth reached puberty earlier and, as young adults, had higher testosterone levels, were taller, more muscular, and had higher grip strength. They also had sex earlier and were more likely to report having had sex in the past month, resulting in more lifetime sex partners. Relationships between B6M weight gain and physical outcomes were generally not present or weaker in female subjects. We conclude that rapid weight gain specific to the brief postnatal hypothalamic-pituitary-gonadal critical period predicts early maturation and sexual activity, elevated hormone production, and more costly adult somatic characteristics among the male subjects in this sample. These findings provide evidence for early life developmental plasticity in male life history and reproductive strategy in humans.

Nutrient mediation of behavioral plasticity and resource allocation in a xylem-feeding leafhopper

Phenotypic plasticity may be critical for nutrient-limited organisms that allocate ingested nutrients to the competing demands of reproduction and survivorship. Leafhoppers that feed on xylem fluid allow assessment of plasticity in response to the constant selective pressure of nutritional inadequacy. We examined feeding behavior (host selection and consumption rates) and nutrient allocation (fecundity, change in body mass and composition) of the xylem fluid-feeding leafhopper Homalodisca vitripennis (Hemiptera:Cicadellidae) on ten genotypes of related Prunus germplasm when adults first seasonally appear, and later during population peaks, to examine the effects of genotypes and season on plasticity of life history and behavioral traits. Behavior and resource allocation to life history traits were both mediated by xylem nutrients, although nutrients impacting behavior differed from those mediating life history. Host selection and consumption varied with genotype between June and July, yet behavior consistently reflected concentrations of dietary glutamine. Resource allocations also increased linearly with nutrient concentrations, but were best correlated to ingested essential amino acids rather than glutamine. Body mass and composition were highly correlated to dietary essential amino acids in June; 6 weeks later, fecundity was instead proportional to essential amino acids. The discrepancy in nutrients which impact behavior versus those mediating life history may explain the weak preference-performance linkage documented for many insects. The demarcation in allocating resources to biomass in June to fecundity in July suggests increased allocation to reproduction during periods of nutrient stress as predicted by the theory of optimal resource allocation; other contributing biotic and abiotic factors are also discussed.

Exploring plastic and genetic responses to temperature variation using copper butterflies

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 43:17-30 (2010) - DOI: https://doi.org/10.3354/cr00892 Exploring plastic and genetic responses to temperature variation using copper butterflies K. Fischer*, I. Karl Zoological Institute and Museum, University of Greifswald, Johann-Sebastian-Bach-Str. 11/12, 17489 Greifswald, Germany *Email: klaus.fischer@uni-greifswald.de ABSTRACT: Variable thermal environments experienced by most organisms warrant mechanisms to adjust the expression of phenotypic values to environmental needs. Here we explored short- (mainly developmental plasticity) and long-term effects (genetic differentiation across altitudes) of temperature variation using copper butterflies as model organisms. Lower compared to higher developmental temperatures yielded predictable variation by increasing development time, body size, total food consumption, the efficiency of converting digested food into body matter, and cold stress resistance, but decreasing daily food consumption, assimilation efficiency, body fat and protein content, weight loss at metamorphosis, the proportion of directly developing individuals, pupal melanisation and heat stress resistance. While variation in temperature stress resistance and developmental pathways is likely to reflect adaptive phenotypic plasticity, the reasons underlying variation in other traits are less clear. High-altitude populations showed increased development time, egg size, flight performance, wing and pupal melanisation and cold stress resistance, but decreased body fat content and heat stress resistance, compared to low-altitude populations. The differences seem to be mainly caused by thermal adaptation and seasonal time constraints. Cold stress resistance was related to variation at the phosphoglucose isomerase locus, and variation in heat stress resistance showed patterns similar to variation in the expression of stress-inducible heat shock proteins. High-altitude populations showed clearly reduced plasticity in heat stress tolerance, which may pose a substantial problem, given the rising temperatures at a global scale. KEY WORDS: Thermal adaptation · Altitudinal variation · Temperature stress resistance · Temperature–size rule · Life-history plasticity · Lycaena sp. · Phosphoglucose isomerase · PGI Full text in pdf format PreviousNextCite this article as: Fischer K, Karl I (2010) Exploring plastic and genetic responses to temperature variation using copper butterflies. Clim Res 43:17-30. https://doi.org/10.3354/cr00892 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 43, No. 1-2. Online publication date: August 05, 2010 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2010 Inter-Research.

Geographic variation in thermal plasticity of life history and wing pattern in Bicyclus anynana

Temperature is one of the main environmental cues regulating seasonal plasticity in insects. Global climate change may lead to a change in the predictive value of temperature for sea- sonal conditions, potentially resulting in a mismatch of phenotypic form and environment. The afrotropical butterfly Bicyclus anynana shows striking seasonal plasticity for wing patterns and life history traits. This polyphenism is an adaptation to contrasting patterns of rainfall over wet and dry seasons, and is mainly determined by temperature. To investigate the extent of local adaptation of the developmental plasticity response to regional climate, we compared the thermal reaction norms for several life history traits and wing pattern of 2 distant populations from regions with different tem- perature-rainfall associations. We found little to no population differentiation for the life history traits, while wing pattern showed substantially more geographic variation. Broad-sense heritabilities and cross-environment correlations for wing pattern and 2 life history traits indicated a potential for adaptation of the plasticity response of these traits. Our results indicate that thermal plasticity of wing pattern can be population-specific; thus climate change may lead to a mismatch of wing pattern to seasonal environment. Traits that can be further modified by acclimation during the butterfly's adult life span (starvation resistance, resting metabolic rate and egg size) showed no geographic differen- tiation for their developmental plasticity. This indicates that for these traits, adult acclimation plays an important role in coping with local climate.

The reaction norm of size and age at maturity under multiple predator risk

1. Two major theories underpin our understanding of how predation risk shapes life history. The first is centred around predator induced changes in activity that subsequently reduce food intake and thus growth. The second is centred around size selective, predator induced changes in development. 2. Here, we challenge these theories using experiments and probabilistic models of maturation reaction norms to investigate predator induced life history in the water flea Daphnia pulex facing two different predators. 3. We combine this reaction norm investigation with an assessment of growth rate, development rate, moult number and moult duration to uncover the mechanisms controlling predator induced life history plasticity when D. pulex face either large or small size selective predators. 4. The probabilistic reaction norms reveal predator specific norms of reaction in size and age along a food gradient. Fish cues reduce age and size, with a bias in age, and do so by reducing moult number and duration. Midge cues increase age and size, with a bias in size, and do so by fine scale modulation of early growth rates. 5. These data contribute towards developing a unified view of how predation risk from multiple predators shapes life history evolution.

Extreme life history plasticity and the evolution of invasive characteristics in a native ant

Disturbance resulting from urbanization is a leading cause of biotic homogenization worldwide. Native species are replaced with widespread non-native species and ants are among the world’s most notorious invaders. To date, all documented cases of ant invasions involve exotic introduced species that are spread around the world by human-mediated dispersal. I investigated the effect of urbanization on the evolution of invasive characteristics in a native ant species, the odorous house ant, Tapinoma sessile (Say). Colony social structure, life history traits, and the spatial pattern of nest distribution were compared by sampling T. sessile across a gradient of three distinct habitats: natural, semi-natural, and urban. Results demonstrate a remarkable transition in colony social and spatial structure and life history traits between natural and urban environments. In natural habitats, T. sessile colonies are comprised of small, monogyne (single queen), and monodomous (single nest) colonies. In urban areas, T. sessile often exhibit extreme polygyny and polydomy, form large supercolonies, and become a dominant pest. Results also suggest that urban T. sessile colonies may have a negative impact on native ant abundance and diversity. In the natural environment T. sessile coexisted with a wide array of other ant species, while very few ant species were present in the urban environment invaded by T. sessile. Habitat degradation and urbanization can lead to extreme changes in social and spatial colony structure and life history traits in a native ant species and can promote the evolution of invasive characteristics such as polygyny, polydomy, and supercolonial colony structure.

Life-history plasticity and inbreeding depression under mate limitation and predation risk: cumulative lifetime fitness dissected with a life table response experiment

Environmental effects on the evolution of mating systems are increasingly discussed, but we lack many examples of how environmental conditions affect the expression and consequences of alternative mating systems. Variation in mate availability sets up a trade-off between reproductive assurance and inbreeding depression, but the consequences of both mate limitation and inbreeding may depend on other environmental conditions. Predation risk is common under natural conditions, and known to affect allocation to reproduction, but we know little about the effects of isolation and inbreeding under predation risk. We reared selfed and outcrossed hermaphroditic freshwater snails (Physa acuta) in four environments (predator cues present or absent crossed with mating partners available or not) and quantified life-history traits and cumulative lifetime fitness. Our results confirm that isolation from mates can increase longevity and growth, resulting in higher lifetime fecundity. Thus, we observed no evidence for mate limitation of reproduction. However, reproduction under isolation (i.e., selfing) resulted in inbreeding depression, which should counteract the benefits of selfing. Inbreeding depression in fitness occurred in both predator and no-predator environments, but there was no overall change in inbreeding depression with predator cues. This represents, to our knowledge, the first empirical estimate of the effect of predation risk on inbreeding depression in an animal. Cumulative fitness was most influenced by early survival and especially early fecundity. As predation risk and inbreeding (both ancestral and due to a lack of mates) reduced early fecundity, these effect are predicted to have important contributions to population growth under natural conditions. Therefore life-history plasticity (e.g., delayed reproduction) is likely to be very important to overall fitness.

Anuran life history plasticity: Variable practice in determining the end-point of larval development

AbstractPlasticity in the timing of life history events and their impact on individual fitness, particularly the timing of and size at metamorphosis in animals with complex life cycles such as anuran amphibians, has long been of interest to ecologists. For different studies on life history plasticity to be comparable, there must be clearly defined and commonly agreed transition points, but it is unclear how consistently this is being performed in studies using anuran amphibians. In a review of 157 published studies, I found considerable variation in defining the end point of the larval phase. While a slight majority used the emergence of the forelimbs as the conclusion of the larval phase, some used a period within the developmental phase of metamorphic climax and others used the resorption of the tail. Studies included in this review, that assessed the same life history variable at two different developmental stages, reported some differences in results depending on which developmental stage was used. Recent evidence also shows that metamorphic climax is itself a period which can vary with environmental conditions, but, even in studies that included part or all of metamorphic climax in the larval phase, the treatment of individuals during metamorphic climax was not reported. Therefore, I argue that life history studies on anuran amphibians should distinguish the following phases: larval, metamorphic climax, juvenile, adult; that the end of the larval phase is best defined in ecological studies by forelimb emergence and that conditions under which individuals undergo metamorphic climax should be fully described.

Structural and proteomic analyses reveal regional brain differences during honeybee aging

Among insects, learning is particularly well studied in the fruit fly Drosophila melanogaster and the honeybee Apis mellifera. A senescence-dependent decline in classic pavlovian conditioning is demonstrated for both species. To understand how aging affects learning, genetic approaches used with Drosophila can benefit from complementary studies in Apis. Specifically, honeybees have a larger brain size allowing for compartment-specific approaches, and a unique life-history plasticity. They usually perform within-nest tasks early in life (nest bees) and later they collect food (foragers). Senescence of learning performance is a function of the bees' foraging duration but underlying causes are poorly understood. As cognitive aging is commonly associated with structural and biochemical changes in the brain, we hypothesized that brain areas implicated in learning change in synaptic and biochemical composition with increased foraging duration. First, we used synapse-specific immunohistochemistry and proteomics to screen for alterations in the calyx region of the mushroom body, a key structure for memory formation. Using proteomics, we next profiled the central brain, which comprises all higher-order integration centers. We show that, with increased foraging duration, levels of kinases, synaptic- and neuronal growth-related proteins decline in the central brain while the calyx region remains intact both in structure and biochemistry. We suggest that proteome-level changes within major anatomical sites of memory formation other than the calyx region could be central to learning dysfunction. These include large compartments of the central brain, such as the mushroom body's output regions and the antennal lobes. Our data provide novel information toward heterogeneity in the aging insect brain, and demonstrate advantages of the honeybee for invertebrate neurogerontological research.

Life history plasticity magnifies the ecological effects of a social wasp invasion

An unresolved question in ecology concerns why the ecological effects of invasions vary in magnitude. Many introduced species fail to interact strongly with the recipient biota, whereas others profoundly disrupt the ecosystems they invade through predation, competition, and other mechanisms. In the context of ecological impacts, research on biological invasions seldom considers phenotypic or microevolutionary changes that occur following introduction. Here, we show how plasticity in key life history traits (colony size and longevity), together with omnivory, magnifies the predatory impacts of an invasive social wasp (Vespula pensylvanica) on a largely endemic arthropod fauna in Hawaii. Using a combination of molecular, experimental, and behavioral approaches, we demonstrate (i) that yellowjackets consume an astonishing diversity of arthropod resources and depress prey populations in invaded Hawaiian ecosystems and (ii) that their impact as predators in this region increases when they shift from small annual colonies to large perennial colonies. Such trait plasticity may influence invasion success and the degree of disruption that invaded ecosystems experience. Moreover, postintroduction phenotypic changes may help invaders to compensate for reductions in adaptive potential resulting from founder events and small population sizes. The dynamic nature of biological invasions necessitates a more quantitative understanding of how postintroduction changes in invader traits affect invasion processes.

Life history plasticity and fitness in a caddisfly in response to proximate cues of pond-drying

Pond-drying is a model for understanding the causes of life history variation in metamorphic organisms. However, we know relatively little about how interactions among specific proximate cues of pond-drying affect juvenile life history, how those responses might be mitigated by diet, and the post-metamorphic consequences for adult fitness. I manipulated larval diet, water depth, and water temperature during the aquatic larval stage of a temporary pond-dwelling caddisfly, Limnephilus indivisus. I predicted that shallow depths and warm temperatures (depth x temperature) associated with pond-drying would have negative effects on larval survival, growth, development, adult size, female fecundity, and adult longevity, but that supplementation of the larval diet should mitigate the trade-off between juvenile growth and pre-reproductive mortality risk by ameliorating the negative effects of pond-drying (diet x depth, diet x temperature) on these traits. Larval survival was enhanced by diet supplementation but was not affected by depth or temperature. Larval diet and water temperatures acted independently on growth, development, and female size, and growth rates were higher when larval diets were supplemented relative to ambient diets; development times were shorter when temperatures were warmer relative to colder; adult females were larger when larvae were fed a supplemented diet but smaller when reared in warm water. Larval growth and development were not affected by depth, but female size was reduced under shallow relative to deep conditions. Female longevity and fecundity were affected by the larval diet x female size interaction. Surprisingly, this was independent of the depth x temperature interaction on female longevity and fecundity suggesting that reductions in adult fitness due to juvenile abiotic conditions can be independent of size-at-maturity. Future studies should quantify the effect of proximate cues of pond-drying on juvenile survival and life history as well as adult fitness correlates.

Plant research accelerates along the (bio)informatics superhighway

The Keystone Symposium on Plant Sensing, Response and Adaptation to the Environment took place between 11 and 16 January 2009, at Big Sky, Montana, USA, and was organized by S.A. Kay & J. Chory. ![][1] See Glossary for abbreviations used in this article In spite of the fanfare surrounding the two‐hundredth anniversary of the birth of Charles Darwin, and the one‐hundred and fiftieth anniversary of his most celebrated book ‘ On the Origin of Species ’ (Darwin, 1859), many people would still be surprised to learn that Darwin wrote a nearly 600 page book entitled ‘ The Power of Movement in Plants ’ (Darwin, 1880). As most plants have their location fixed as soon as their roots enter the soil, non‐specialists might wonder how much movement plants can make. However, movement is not limited to locomotion, and many of the movements studied by Darwin probably evolved in response to the unique challenges imposed by the rooted habit. Unable to change location, plants have developed exquisite abilities to sense, respond to and adapt to their local environment. One example that captured Darwin's attention is the navigation of the radicle (root) tip through the complex soil environment to optimize water and nutrient acquisition. He stated, “It is hardly an exaggeration to say that the tip of the radicle thus endowed, and having the power of directing the movements of the adjoining parts, acts like the brain of one of the lower animals[…].” These root‐growth movements were but one of many environmental responses discussed by plant biologists gathered at the recent Keystone Symposium on Plant Sensing, Response and Adaptation to the Environment. Root growth is controlled by gravity, water and nutrient acquisition; whereas growth of the aerial shoot is regulated primarily by the light environment. Various photoreceptors allow plants to judge light intensity, direction … [1]: /embed/graphic-1.gif

The New WorldArtemiaspeciesA. franciscanaandA. persimilisare highly differentiated for chromosome size and heterochromatin content

Chromosomal rearrangements have played a key role in the speciation of the New World sexual Artemia species (Crustacea, Anostraca) A. franciscana and A. persimilis. The species differ by a chromosome duplication (2n+2=44 in A. persimilis vs 2n=42 in A. franciscana), and a greater amount of heterochromatin (HCH) in A. franciscana. To investigate this difference in HCH, four parameters were compared for the first time in Artemia: 1) the absolute sizes of one A. persimilis and four A. franciscana karyotypes; 2) the relative lengths of all chromosome; 3) the number of heterochromatic bands and 4) the relative amounts of HCH per chromosome and its position. The two A.franciscana karyotypes with the largest HCH amount (26%), have twice (139.26 microm and 134.05 microm) the absolute size of the A.persimilis karyotype (64.91 microm; HCH: 1.97%). Interspecific and intraspecific (A. franciscana) differences in chromosome size and HCH were observed, although the two sets of information are not positively correlated. While A. persimilis shares plesiomorphic karyological traits with Old World species, A. franciscana has apomorphic features such as longer chromosomes and greater HCH content, mainly dispersed towards telomeres. The impacts of such chromosome rearrangements are discussed in relation to the wider geographic distribution, greater colonizing ability, and life history plasticity of A. franciscana. An additional, though preliminary, point of this paper is the observation that the female would be the heterogametic sex.

Robustness in life history of the brown seaweed Ascophyllum nodosum (Fucales, Phaeophyceae) across large scales: effects of spatially and temporally induced variability on population growth

Understanding the demography and function of biotope-forming seaweed species is of great importance for the conservation of the target species itself, as well as its associated organisms. The brown seaweed Ascophyllum nodosum is fundamental for the functioning of coastal marine ecosystems in the North Atlantic. In this study, we use a data-based size-classified matrix model to investigate the temporal and spatial variability in demography, and the environment-specific stochastic sensitivity and elasticity, of two A. nodosum populations, one in western Sweden and one on the Isle of Man in the Irish Sea. A significant difference between the two populations was that the Swedish population had comparably low and more variable stochastic population growth rate (λs). This pattern was partly explained by the relatively high and varying mortality rates during extreme ice-years in Sweden, and by the lower survival of small individuals during all years. There were also fewer large individuals in Sweden due to lower transitions to the larger size-classes and higher probability of shrinkage. Sensitivities were analogous in the two populations, and showed a high selection pressure for increased individual growth. Elasticities were also similar, with the exception that survival of the smallest individuals (i.e., transition a1,1), had a higher elasticity on the Isle of Man. Overall, the stochastic growth rate (λs) was most sensitive to proportional changes in loop- (i.e., survival within size-class) and, to some extent, growth-transitions in both study areas. These results show that structurally and demographically diverging A. nodosum populations may be similarly sensitive to changes in vital rates. This, in turn, indicates a plastic life history of A. nodosum that may cope with large environmental variability. The results further suggest that environmental change affecting the survival or growth of the larger, reproductive A. nodosum individuals could have severe and regional effects on the abundance and biomass of this species, with potential negative effects on the biodiversity of the associated communities.

Effects of Genetic Perturbation on Seasonal Life History Plasticity

Like many species, the model plant Arabidopsis thaliana exhibits multiple different life histories in natural environments. We grew mutants impaired in different signaling pathways in field experiments across the species' native European range in order to dissect the mechanisms underlying this variation. Unexpectedly, mutational loss at loci implicated in the cold requirement for flowering had little effect on life history except in late-summer cohorts. A genetically informed photothermal model of progression toward flowering explained most of the observed variation and predicted an abrupt transition from autumn flowering to spring flowering in late-summer germinants. Environmental signals control the timing of this transition, creating a critical window of acute sensitivity to genetic and climatic change that may be common for seasonally regulated life history traits.