Intraspecific Variation in the Alkaloids of Adalia decempunctata (Coleoptera, Coccinellidae): Sex, Reproduction and Colour Pattern Polymorphism.

In this paper, we examine intraspecific variation in the quantity of alkaloid chemical defence in field collected individuals of the polymorphic ladybird beetle Adalia decempunctata (10-spot ladybird). Like its more widely studied relative Adalia bipunctata (2-spot ladybird), A. decempunctata possesses the alkaloids adaline and adalinine, which are, respectively, the major and minor alkaloids of A. bipunctata. We focused especially on alkaloid concentration in relation to colour pattern morph, sex, and the relationship between female and egg parameters. There was a marked sexual dimorphism in the balance of the two alkaloids, with adaline predominating in females and adalinine predominating in males: in males, on average, over 70% of total alkaloid was adalinine. Females had a lower proportion of adalinine (< 10%) than their eggs (> 15%) and relationships between egg alkaloid and female alkaloid or fecundity were weak or non-existent. Colour pattern morph had a borderline (although not) significant relationship with adaline concentration and total alkaloid concentration, which could be further explored with laboratory reared individuals. The sexual dimorphism in alkaloid content, which seems likely due to differences in synthesis, might be related to their relative costs to the two sexes and might provide insight into the evolution of alkaloid diversity in ladybirds.

The spatial arrangement of sexes is related to reproductive allocation in mosses: a comparative study of reproductive allocation in three different monoicous sexual systems.

BACKGROUND AND AIMS: We examined the relationship between reproductive allocation and vegetative growth in three monoicous sexual systems of bryophytes. The sexual systems show a gradient of increasing distance between the sexes, from gonioautoicous to cladautoicous to rhizautoicous. Here, we investigated the following two hypotheses: (1) reproductive allocation differs between sexes and sexual systems, and male reproductive allocation increases with increasing distance between male and female gametangia; and (2) reproductive allocation is negatively related to vegetative growth. METHODS: We sampled the three sexual systems, represented by three moss species of the genus Fissidens in the Atlantic Forest of Southeastern Brazil. Ramets were washed in the laboratory; the reproductive structures were detached from the vegetative ramets and sorted regarding sex and individual, dried at 70 °C for 72 h, and weighed in an ultramicrobalance. We calculated the mean reproductive and vegetative mass and reproductive allocation and used generalized linear models to test our predictions. KEY RESULTS: Reproductive allocation differed between species and sexes. It was higher in the rhizautoicous than in the cladautoicous and gonioautoicous species. Mean reproductive allocation was greater in males than in females of the rhizautoicous species, greater in females than males of the cladautoicous species, and did not differ between the sexes in the gonioautoicous species. Estimates of reproductive and vegetative mass were positively related in females of the rhizautoicous species. Vegetative mass was not related to reproductive allocation in the gonioautoicous species, but negatively related to reproductive allocation in the male and female branchlets of the cladautoicous species and in the female ramets of the rhizautoicous species. CONCLUSIONS: The reproductive allocation patterns differ between the rhizautoicous species and the 'truly' monoicous species, with shorter intersexual distances, which implies that our hypotheses were supported only in part. We suggest that the hypotheses should be reformulated and tested further by comparing 'truly' monoicous species with dioicous species and by including other genera.

Reproductive senescence and mating tactic interact and conflict to drive reproductive success in a passerine.

An understanding of the drivers of individual fitness is a fundamental component of evolutionary ecology and life-history theory. Reproductive senescence, mate and mating tactic choice and latent heterogeneity in individual quality interact to affect individual fitness. We sought to disentangle the effects of these fitness drivers, where longitudinal data are required to understand their respective impacts. We used reproductive allocation and success data from a long-term (1989-2018) study of white-throated dippers Cinclus cinclus in Switzerland to simultaneously examine the effects of female and male age, mating tactic, nest initiation date and individual heterogeneity on reproductive performance. We modelled quadratic and categorical effects of age on reproductive parameters. The probability of polygyny increased with age in both sexes before declining in older age classes. Similarly, hatching probability in monogamous pairs and the number of nestlings hatched in both monogamous and polygynous pairs increased with female age before declining later in life. As predicted, offspring survival in monogamous pairs increased with male age before declining in older age classes, but male age had no effect on offspring survival in polygynous nesting attempts. Our results demonstrate that parental age, mating tactic and individual heterogeneity all affect reproductive success, and that the impacts of senescent decline are expressed across different demographic components as a function of sex-specific senescent decline and mating tactic.

Life-history traits and density dependence in metapopulations of a tropical moss: a monoicous species that is almost dioicous.

Life-history traits, such as reproductive allocation, sexual expression, sex ratio, and reproductive success, are central aspects of a species' ecology and evolution. For example, bias in male and female sex expression may play a large role in determining the viability of populations in the face of environmental pressures, such as population fragmentation, climate change and habitat occupancy. Thus, in this study, we investigated reproductive traits in 10 meta-populations of Fissidens flaccidus Mitt. From each meta-population, 30 patches were randomly selected, and 1 cm2 samples were collected form each patch. A total of 20,173 ramets were analyzed and classified into male, non-sporophytic female, sporophytic female, and non-sex expressing. In addition, population density in each patch was quantified. Our results showed that relative reproductive allocation in perigonia and sporophytes is greater than perichaetia. Trade-off between sexual relative reproductive allocation and asexual gemma production was observed, suggesting an important role of female ramets in asexual reproduction. The number of male ramets does not influence the reproductive success observed in each patch, and ramet density may induce male sex expression. Thus, we concluded that reproductive allocation in male function is efficient, since fewer male ramets can assure a considerable reproductive success. Furthermore, our results suggest that there may be a habitat preference between the sexes, since male ramets are found in patches with high density and mostly below female ramets, suggesting an avoidance of direct sunlight by male ramets.

Forest regeneration within Earth system models: current process representations and ways forward.

Earth system models must predict forest responses to global change in order to simulate future global climate, hydrology, and ecosystem dynamics. These models are increasingly adopting vegetation demographic approaches that explicitly represent tree growth, mortality, and recruitment, enabling advances in the projection of forest vulnerability and resilience, as well as evaluation with field data. To date, simulation of regeneration processes has received far less attention than simulation of processes that affect growth and mortality, in spite of their critical role maintaining forest structure, facilitating turnover in forest composition over space and time, enabling recovery from disturbance, and regulating climate-driven range shifts. Our critical review of regeneration process representations within current Earth system vegetation demographic models reveals the need to improve parameter values and algorithms for reproductive allocation, dispersal, seed survival and germination, environmental filtering in the seedling layer, and tree regeneration strategies adapted to wind, fire, and anthropogenic disturbance regimes. These improvements require synthesis of existing data, specific field data-collection protocols, and novel model algorithms compatible with global-scale simulations. Vegetation demographic models offer the opportunity to more fully integrate ecological understanding into Earth system prediction; regeneration processes need to be a critical part of the effort.

Sex-specific differences in reproductive life-history traits of the moss Weissia jamaicensis.

PREMISE: We investigated sex-specific differences in the life-history traits of a metapopulation of the dioicous moss Weissia jamaicensis. Field observations revealed high rates of fertilization, which is uncommon for most dioicous bryophytes. We raised four hypotheses associated with the way the reproductive traits are related to the fertilization rate in this metapopulation. METHODS: We sampled 10 patches of the metapopulation and quantified sexual expression, sex ratio, reproductive success, and reproductive allocation. The ramets were classified as male, non-sporophytic female, sporophytic female, or non-sex-expressing. Thirty ramets from each of the categories expressing sex were placed for regeneration to test the effect of reproductive allocation on this trait. RESULTS: We found greater expression of the female function in all patches, implying a female bias in the metapopulation. The number of male ramets was variable in each patch and did not affect reproductive success. At the prezygotic level, the allocation of resources to the male function was higher. However, the large allocation of resources to sporophyte development in sporophytic females, which exceeded allocations at prezygotic levels, was related to the higher mortality rate of these ramets, suggesting reproductive cost. CONCLUSIONS: The prezygotic ramets that allocated the greatest amount of resources to reproduction expressed sex less frequently, biasing the sex ratio toward the sex that allocated the least amount of resources to reproduction. Overall, the ramets that allocated the greatest amount of resources to reproduction had the lowest regeneration rate, suggesting reproductive cost.

Experimental manipulation of body size alters life history in hydra.

Body size has fundamental impacts on animal ecology and physiology but has been strongly influenced by recent climate change and human activities, such as size-selective harvesting. Understanding the ecological and life history consequences of body size has proved difficult due to the inseparability of direct effects of body size from processes connected to it (such as growth rate and individual condition). Here, we used the cnidarian Hydra oligactis to directly manipulate body size and understand its causal effects on reproduction and senescence. We found that experimentally reducing size delayed sexual development and lowered fecundity, while post-reproductive survival increased, implying that smaller individuals can physiologically detect their reduced size and adjust life history decisions to achieve higher survival. Our experiment suggests that ecological or human-induced changes in body size will have immediate effects on life history and population dynamics through a growth-independent link between body size, reproduction and senescence.

Rapid adaptive evolution to drought in a subset of plant traits in a large-scale climate change experiment.

Rapid evolution of traits and of plasticity may enable adaptation to climate change, yet solid experimental evidence under natural conditions is scarce. Here, we imposed rainfall manipulations (+30%, control, -30%) for 10 years on entire natural plant communities in two Eastern Mediterranean sites. Additional sites along a natural rainfall gradient and selection analyses in a greenhouse assessed whether potential responses were adaptive. In both sites, our annual target species Biscutella didyma consistently evolved earlier phenology and higher reproductive allocation under drought. Multiple arguments suggest that this response was adaptive: it aligned with theory, corresponding trait shifts along the natural rainfall gradient, and selection analyses under differential watering in the greenhouse. However, another seven candidate traits did not evolve, and there was little support for evolution of plasticity. Our results provide compelling evidence for rapid adaptive evolution under climate change. Yet, several non-evolving traits may indicate potential constraints to full adaptation.

Increased allocation to reproduction reduces future competitive ability in a burying beetle.

The existence of a trade-off between current and future reproduction is a fundamental prediction of life history theory. Support for this prediction comes from brood size manipulations, showing that caring for enlarged broods often reduces the parent's future survival or fecundity. However, in many species, individuals must invest in competing for the resources required for future reproduction. Thus, a neglected aspect of this trade-off is that increased allocation to current reproduction may reduce an individual's future competitive ability. We tested this prediction in the burying beetle, Nicrophorus vespilloides, a species where parents care for their offspring and where there is fierce competition for resources used for breeding. We manipulated reproductive effort by providing females with either a small brood of 10 larvae or a large brood of 40 larvae and compared the ability of these females, and virgin females that had no prior access to a carcass, to compete for a second carcass against a virgin competitor. We found that increased allocation to current reproduction reduced future competitive ability, as females that had cared for a small brood were more successful when competing for a second carcass against a virgin competitor than females that had cared for a large brood. In addition, the costs of reproduction were offset by the benefits of feeding from the carcass during an initial breeding attempt, as females that had cared for a small brood were better competitors than virgin females that had no prior access to a carcass, whilst females that had cared for a large brood were similar in competitive ability to virgin females. Our results add to our understanding of the trade-off between current and future reproduction by showing that this trade-off can manifest through differences in future competitive ability and that direct benefits of reproduction can offset some of these costs.

Long-term research and hierarchical models reveal consistent fitness costs of being the last egg in a clutch.

Maintenance of phenotypic heterogeneity in the face of strong selection is an important component of evolutionary ecology, as are the consequences of such heterogeneity. Organisms may experience diminishing returns of increased reproductive allocation as clutch or litter size increases, affecting current and residual reproductive success. Given existing uncertainty regarding trade-offs between the quantity and quality of offspring, we sought to examine the potential for diminishing returns on increased reproductive allocation in a long-lived species of goose, with a particular emphasis on the effect of position in the laying sequence on offspring quality. To better understand the effects of maternal allocation on offspring survival and growth, we estimated the effects of egg size, timing of breeding, inter- and intra-annual variation, and position in the laying sequence on gosling survival and growth rates of black brant Branta bernicla nigricans breeding in western Alaska from 1987 to 2007. We found that gosling growth rates and survival decreased with position in the laying sequence, regardless of clutch size. Mean egg volume of the clutch a gosling originated from had a positive effect on gosling survival (ß = 0.095, 95% CRI: 0.024, 0.165) and gosling growth rates (ß = 0.626, 95% CRI: 0.469, 0.738). Gosling survival (ß = -0.146, 95% CRI: -0.214, -0.079) and growth rates (ß = -1.286, 95% CRI: -1.435, -1.132) were negatively related to hatching date. These findings indicate substantial heterogeneity in offspring quality associated with their position in the laying sequence. They also potentially suggest a trade-off mechanism for females whose total reproductive investment is governed by pre-breeding state.

Microhabitat preference, body size, and egg allocation in the gill parasite Naobranchia lizae (Copepoda).

The relationships between microhabitat preference, body size, and egg allocation were examined in the copepod Naobranchia lizae, which establishes on the gills of striped mullet Mugil cephalus. A total of 297 individual N. lizae (mean intensity = 5.0 ± 4.8 SD) were recovered from 60 infected hosts collected from the Charleston Harbor Estuarine System, South Carolina USA. For each mullet, we identified 16 microhabitats per gill arch, which yielded 128 microhabitats per host that could potentially be occupied. On average, only 5% of these microhabitats were occupied per host. The distribution pattern of the copepods on the gills revealed that microhabitat preferences occurred both among and within gill arches. For the microhabitats occupied, there was no effect of preference on body size, egg number, or egg size. Similarly, microhabitat sharing, which was more likely to occur at higher infection intensities, was not costly in terms of the copepod body size and egg allocation and there was no detectable trade-off between egg number and egg size. However, results also revealed that about half (48%) of the available microhabitats were never occupied by the copepods. We suggest that the occupancy of these potentially poor quality sites could carry fitness costs not realized in nature since numerous high quality sites are available per host. The findings are consistent with the interpretation that female N. lizae occupy a resource-rich habitat on the gill arches of striped mullet that provides conditions for optimal growth and reproduction.

Comparative response to drought in primitive and modern wheat: a cue on domestication.

MAIN CONCLUSION: Primitive wheat follows an opposite metabolic law from modern wheat with regard to leaf biomass/reproductive growth vs above-ground biomass that is under the regulation of non-hydraulic root signals and that influences resource acquisition and utilization. Non-hydraulic root signals (nHRS) are so far affirmed as a unique positive response to drying soil in wheat, and may imply huge differences in energy metabolism and source-sink relationships between primitive and modern wheat species. Using a pot-culture split-root technique to induce nHRS, four primitive wheat genotypes (two diploids and two tetraploids) and four modern wheat ones (released from different breeding decades) were compared to address the above issue. The nHRS was continuously induced in drying soil, ensuring the operation of energy metabolism under the influence of nHRS. We found that primitive wheat followed an opposite size-dependent allometric pattern (logy = αlogx + logß) in comparison with modern wheat. The relationships between ear biomass (y-axis) vs above-ground biomass (x-axis), and between reproductive biomass (y-axis) and vegetative (x-axis) biomass fell into a typical allometric pattern in primitive wheat (α > 1), and the nHRS significantly increased α (P < 0.01). However, in modern wheat, they turned to be in an isometric pattern (α ≈ 1). Regardless of nHRS, either leaf (i.e., metabolic rate) or stem biomass generally exhibited an isometric relationship with above-ground biomass in primitive wheat (α ≈ 1), while in modern wheat they fell into an allometric pattern (α > 1). Allometric scaling of specific leaf area (SLA) or biomass density showed superior capabilities of resource acquisition and utilization in modern wheat over primitive ones. We therefore proposed a generalized model to reveal how modern wheat possesses the pronounced population yield advantage over primitive wheat, and its implications on wheat domestication.

Explaining the larger seed bank of an invasive shrub in non-native versus native environments by differences in seed predation and plant size.

BACKGROUND AND AIMS: Large, persistent seed banks contribute to the invasiveness of non-native plants, and maternal plant size is an important contributory factor. We explored the relationships between plant vegetative size (V) and soil seed bank size (S) for the invasive shrub Ulex europaeus in its native range and in non-native populations, and identified which other factors may contribute to seed bank variation between native and invaded regions. METHODS: We compared the native region (France) with two regions where Ulex is invasive, one with seed predators introduced for biological control (New Zealand) and another where seed predators are absent (La Réunion). We quantified seed bank size, plant dimensions, seed predation and soil fertility for six stands in each of the three regions. KEY RESULTS: Seed banks were 9-14 times larger in the two invaded regions compared to native France. We found a positive relationship between current seed bank size and actual plant size, and that any deviation from this relationship was probably due to large differences in seed predation and/or soil fertility. We further identified three possible factors explaining larger seed banks in non-native environments: larger maternal plant size, lower activity of seed predators and higher soil fertility. CONCLUSIONS: In highlighting a positive relationship between maternal plant size and seed bank size, and identifying additional factors that regulate soil seed bank dynamics in non-native ranges, our data offer a number of opportunities for invasive weed control. For non-native Ulex populations specifically, management focusing on 'S' (i.e. the reduction of the seed bank by stimulating germination, or the introduction of seed predators as biological control agents) and/or on 'V' (i.e. by cutting mature stands to reduce maternal plant biomass) offers the most probable combination of effective control options.

Drivers and demographic consequences of seasonal mass changes in an alpine ungulate.

We know little about the determinants and demographic consequences of the marked seasonal mass changes exhibited by many northern and alpine mammals. We analysed 43 years of data on individual winter mass loss (the difference between mass in early June and mass in mid-September the previous year) and summer mass gain (the difference between mass in mid-September and in early June of the same year) in adult bighorn sheep (Ovis canadensis). We calculated relative seasonal mass change as a proportion of individual body mass at the start of each season. We first examined the effects of weather and population density on relative changes in body mass. We then assessed the consequences of relative seasonal mass changes on reproduction. Mean April-May temperature was the main driver of relative seasonal mass changes: warm springs reduced both relative winter mass loss and summer mass gain of both sexes, likely partially due to a trade-off between growth rate of plants and duration of access to high-quality forage. Because these effects cancelled each other, spring temperature did not influence mass in mid-September. Mothers that lost relatively more mass during the winter had lambs that gained less mass during summer, likely because these females allocated fewer resources to lactation. Winter survival of lambs increased with their summer mass gain. In males, relative mass loss during winter, which includes the rut, did not influence the probability of siring at least one lamb, possibly indicating that greater mating effort did not necessarily translate into greater reproductive success. Our findings improve our understanding of how weather influences recruitment and underline the importance of cryptic mechanisms behind the effects of climate change on demographic traits.

Photosynthetic opportunity cost and energetic cost of a rapid leaf closure behavior in Mimosa pudica.

PREMISE OF THE STUDY: The rapid leaf movement of Mimosa pudica is expected to be costly because of energetic trade-offs with other processes such as growth and reproduction. Here, we assess the photosynthetic opportunity cost and energetic cost of the unique leaf closing behavior of M. pudica. METHODS: In the greenhouse, we employed novel touch-stimulation machines to expose plants to one of three treatments: (1) untouched control plants; (2) plants touch-stimulated to close their leaves during the day to incur energetic costs associated with leaf movement and reduced photosynthesis; (3) plants touched at night to assess the effects of touch alone. M. pudica is nyctinastic and closes its leaves at night; thus, touching at night does not impart additional costs. We directly assessed costs by comparing physical traits. Leaf re-opening response was measured to assess the potential for plant behavioral plasticity to impact photosynthetic opportunity costs. KEY RESULTS: The cost of rapid leaf closure behavior was expressed as a 47% reduction in reproductive biomass accounting for the effect of touch. Touch itself changed physical traits such as biomass, with touched plants being generally bigger. Plants touched at night re-opened their leaflets 26% quicker than plants touched during the day. CONCLUSIONS: We reason that the reproductive allocation costs incurred by M. pudica can be attributed to a combination of photosynthetic opportunity cost and the energetic cost associated with increased stimulation of leaf movement and that behavioral plasticity has the potential to alter photosynthetic opportunity costs.

Resource Allocation and Seed Size Selection in Perennial Plants under Pollen Limitation.

Pollen limitation may affect resource allocation patterns in plants, but its role in the selection of seed size is not known. Using an evolutionarily stable strategy model of resource allocation in perennial iteroparous plants, we show that under density-independent population growth, pollen limitation (i.e., a reduction in ovule fertilization rate) should increase the optimal seed size. At any level of pollen limitation (including none), the optimal seed size maximizes the ratio of juvenile survival rate to the resource investment needed to produce one seed (including both ovule production and seed provisioning); that is, the optimum maximizes the fitness effect per unit cost. Seed investment may affect allocation to postbreeding adult survival. In our model, pollen limitation increases individual seed size but decreases overall reproductive allocation, so that pollen limitation should also increase the optimal allocation to postbreeding adult survival. Under density-dependent population growth, the optimal seed size is inversely proportional to ovule fertilization rate. However, pollen limitation does not affect the optimal allocation to postbreeding adult survival and ovule production. These results highlight the importance of allocation trade-offs in the effect pollen limitation has on the ecology and evolution of seed size and postbreeding adult survival in perennial plants.

Age and years to death disparately influence reproductive allocation in a short-lived bird.

Theory predicts that reproduction will change as individuals near the end of their lives by either increasing reproductive allocation (terminal allocation hypothesis) or decreasing allocation (senescence hypothesis) toward the end of life. Although senescence has received more support, few studies examine how both age and years to death influence late-life reproduction. We used a 37-yr study of Song Sparrows (Melospiza melodia) to ask how age and years to death influenced reproductive allocation late in life. We observed both senescence and terminal allocation, and that age and years to death interacted to influence individual variation in allocation tactics. In particular, we observed a decline in allocation in older individuals (senescence), but only when comparing individuals with the same number of years to death. Likewise, we observed terminal allocation, but only in young females. Reproductive tactics were most variable in young females, with many exerting high effort but living 1-2 yr, and others exerting low effort annually and living longer. Our results suggest that late-life reproductive tactics are influenced by both chronological age and years to death, and that short- and long-lived females with differing reproductive tactics exist within this population of Song Sparrows.

Variation in the reproductive strategy of a lichenized fungus along a climatic gradient.

Background and aims: Onset of reproduction and reproductive allocation patterns are key components of plant reproductive strategies. Life history theory predicts that plants in adverse environments for juvenile performance start reproduction at smaller sizes and exhibit higher reproductive allocation compared to their counterparts in favourable environments. Life history theory will gain in generality if its predictions are shown to apply to a broad range of organisms and modes of reproduction. This study tested whether the asexual reproductive strategy of a lichenized fungus changed along a climatic gradient. Methods: The variation in threshold size for asexual reproduction and asexual reproductive allocation of the lichen Lobarina scrobiculata was assessed in 18 populations (9665 individuals) along a climatic gradient spanning 800 km in latitude in Southern Europe. Using generalized linear models and standardized major axis regressions, the allometric relationships and the associated variation in climatic factors according to the changes in the threshold size for reproduction and reproductive allocation patterns were assessed. Key Results: The onset of reproduction was size-dependent and the reproductive allocation increased with individual size. Both the threshold size for reproduction and the reproductive allocation varied along the rainfall gradient. A lower threshold size for reproduction and higher reproductive allocation in drier, adverse locations were found. Therefore, populations in drier locations fitted the predictions of life history theory for sexually reproducing organisms in adverse environments for juvenile performance. Conclusions: This study highlights the applicability of the life history theory to fungi and to modes of reproduction other than sexual reproduction. Based on the intraspecific variation in the asexual reproductive strategy of a fungal organism with climatic factors, these findings expand the scope of life history theory predictions and increase our understanding of life history diversity and reproductive strategies across environments.

Elevated CO2 boosts reproduction and alters selection in northern but not southern ecotypes of allergenic ragweed.

PREMISE OF THE STUDY: Many plants increase reproduction in response to rising levels of atmospheric CO2 . However, environmental and genetic variation across heterogeneous landscapes can lead to intraspecific differences in the partitioning of CO2 -induced carbon gains to reproductive tissue relative to growth. METHODS: We measured the effects of rising atmospheric CO2 on biomass allocation in the allergenic plant Ambrosia artemisiifolia (common ragweed) across a geographic climate gradient. We grew plants from three latitudes at 400, 600, and 800 µL·L-1 CO2 and analyzed biomass allocation and natural selection on flowering phenology and growth. KEY RESULTS: Both the latitude of origin and CO2 treatment had significant effects on allocation and on estimates of selection. Northern plants were under stronger selection than southern plants to flower quickly, and they produced larger seeds and more reproductive mass per unit of growth. Northern plants were under stronger selection than southern plants to flower quickly, and they produced larger seeds and more reproductive mass per unit of growth. While all plants grew larger and produced heavier seeds at higher CO2 , only northern plants increased male flower production. Both size and time to flowering were under selection, with a relaxation of the size-fitness function in northern ecotypes at high CO2 . CONCLUSIONS: Northern ecotypes allocate more CO2 -induced carbon gains to reproduction than do southern plants, pointing to a geographic gradient in future pollen and seed production by this species arising from local adaptation. Relaxed selection on size at elevated CO2 could amplify reproductive enhancements to northern ecotypes, although more growth and seed provisioning can be expected overall. Our results demonstrate potential for ecotypic divergence in ragweed responses to climate change.