The global trade of species promotes diverse human activities but also facilitates the introduction of potentially invasive species into new environments. As species ignore national boundaries, unilateral national decisions concerning species trade set the stage for transnational species invasion with significant conservation, economic and political consequences. The need for a coordinated approach to species importation policies is demonstrated by the introduction of two bumblebee species into Chile for crop pollination, despite Argentina banning commercial importation of alien bumblebees based on expert opinion. The large garden bumblebee, Bombus ruderatus, was first introduced in 1982, and the buff-tailed bumblebee, Bombus terrestris, has been continually introduced since 1997 as part of the burgeoning bumblebee trade. Both species have subsequently invaded southern South America. Today, the consequences of the growth of the bumblebee trade for agricultural pollination ranks among the top 15 emerging environmental issues likely to affect global diversity. Documented impacts of these invasions include the severe decline and local extinctions of the sole native Patagonian bumblebee, Bombus dahlbomii, pathogen transmission, flower damage and nectar robbing of native and cultivated plants. Policy implications. The South American bumblebee invasions portrayed here should alert governments to the unintended consequences of the booming international bee trade. More broadly, this case demonstrates that one country's importation decisions can have policy implications for its neighbours without consultation. Regrettably, coordinated international measures to prevent species invasions are seldom considered in South America or elsewhere, despite existing legal frameworks. The bumblebee case and others provide stark evidence of the pressing need for coordinated specific and general international policies concerning global species trade and their implementation.

For hermaphroditic angiosperms with multiple flowers the sex roles can be exclusively combined in bisexual flowers (monocliny), strictly separated among different flowers (monoecy), or arrayed in mixtures of bisexual flowers with female flowers (gynomonoecy) or male flowers (andromonoecy). The hypothesized benefits favoring the evolution of these contrasting hermaphroditic sexual systems are typically examined individually, usually by assessing success through only one sex role. We tested predictions of most hypotheses experimentally with an andromonoecious species, Anticlea occidentalis (Melanthiaceae), based on the performance of intact plants (andromonoecy) and those with emasculated bisexual flowers (functionally monoecious) or emasculated male flowers (functionally monoclinous with sterile peripheral flowers). Andromonoecy in this species enables efficient, size-dependent resource allocation, emphasizing female function in large plants. Emasculation revealed that anthers in male flowers promote female mating quality (outcrossing rate and mate diversity), whereas anthers in bisexual flowers promote male mating quantity (pollen dispersal distance and probability of any siring success). Thus, different hermaphroditic sexual systems likely evolve to capitalize on suites of benefits, rather than just one, and provide compromises between quantitative and qualitative reproductive components. These compromises apparently maximize an individual’s combined genetic contributions through female and male functions, rather than separate contributions through each sex role.

Why are some traits and trait combinations exceptionally common across the tree of life, whereas others are vanishingly rare? The distribution of trait diversity across a clade at any time depends on the ancestral state of the clade, the rate at which new phenotypes evolve, the differences in speciation and extinction rates across lineages, and whether an equilibrium has been reached. Here we examine the role of transition rates, differential diversification (speciation minus extinction), and non-equilibrium dynamics on the evolutionary history of angiosperms, a clade well known for the abundance of some trait combinations and the rarity of others. Our analysis reveals that three character states (corolla present, bilateral symmetry, reduced stamen number) act synergistically as a key innovation, doubling diversification rates for lineages in which this combination occurs. However, this combination is currently less common than predicted at equilibrium because the individual characters evolve infrequently. Simulations suggest that angiosperms will remain far from the equilibrium frequencies of character states well into the future. Such non-equilibrium dynamics may be common when major innovations evolve rarely, allowing lineages with ancestral forms to persist, and even outnumber those with diversification-enhancing states, for tens of millions of years.

Many iteroparous angiosperms may benefit from flexible annual resource allocation in response to variable reproductive opportunities induced by external conditions. If maximal reproductive investment is fixed, lack of reproductive sinks would cause resource redistribution to other sinks. Alternatively, reproductive investment may vary depending on the demand of reproductive sinks, changing source-sink relations. In particular, differential responses by males and females to the demands of flower and seed production may cause sexual dimorphism. We assess the occurrence of demand-driven seed allocation by females and its implications for sexual differences in reproductive investment, including the dynamics of mass and carbon allocation and the physiological cost of reproduction, for a dioecious, perennial herb, Thalictrum occidentale. We specifically quantified allocation responses to partial defoliation, which reduced current resource supply, and partial flower/fruit removal, which reduced the aggregate demand of reproductive sinks. During flowering, males preferentially invested carbon and mass in flowers at the expense of vegetative organs, whereas females allocated less mass to flowers and invested more in new-rhizome production for future performance than males. In contrast, during early fruiting, both sexes had new rhizomes of similar size and a doubling of reproductive mass by females after flowering resulted in similar total reproductive investment for both sexes. Manipulation of the source-sink balance did not influence carbon allocation, except that partial fruit removal increased new-rhizome mass compared to intact plants. Females with many fertilized ovules invested proportionally more in seed number and mass per seed than females with few fertilized ovules, indicating both demand-driven seed maturation and its elimination of seed size-number trade-off. Furthermore, males consistently exhibited size-dependent flower production, whereas females exhibited size-dependent flower production only if they had not reproduced during the previous year. Synthesis: This study demonstrates that sexual differences in policies of reproductive investment and the timing of the physiological costs of reproduction impose contrasting allocation schedules. Males invested in reproduction proportionally with their size, whereas females invested flexibly in seeds in response to the demand of developing embryos. Thus, the contrasting certainty and timing of reproductive resource requirements between the sexes contribute to sexual dimorphism.

Local adaptation occurs when different environments are dominated by different specialist genotypes, each of which is relatively fit in its local conditions and relatively unfit under other conditions. Analogously, ecological species sorting occurs when different environments are dominated by different competing species, each of which is relatively fit in its local conditions. The simplest theory predicts that spatial, but not temporal, environmental variation selects for local adaptation (or generates species sorting), but this prediction is difficult to test. Although organisms can be reciprocally transplanted among sites, doing so among times seems implausible. Here we describe a reciprocal transplant experiment testing for local adaptation or species sorting of lake bacteria in response to both temporal and spatial variation in water chemistry. The experiment used a −80 °C freezer as a ‘time machine’. Bacterial isolates and water samples were frozen for later use, allowing transplantation of older isolates ‘forward in time’ and newer isolates ‘backward in time’. Surprisingly, local maladaptation predominated over local adaptation in both space and time. Such local maladaptation may indicate that adaptation, or the analogous species sorting process, fails to keep pace with temporal fluctuations in water chemistry. This hypothesis could be tested with more finely-resolved temporal data.

Inbreeding depression can reduce the performance of offspring produced by mating between relatives, with consequences for population dynamics and sexual-system evolution. In flowering plants, inbreeding depression commonly acts most intensely during seed development. This predispersal component is typically estimated by comparing seed production following exclusive self- and cross-pollination, but such estimates are unbiased only if seed production is limited by ovule availability, rather than by pollen receipt or seed-development resources. To overcome this problem, we propose experimental and statistical methods based on a model of ovule fertilization and seed development that accounts for differential fertilization by self- and cross-pollen, limited ovule viability or receptivity, differential survival of self- and cross-zygotes and limited resource availability. Simulations illustrate that the proposed methods eliminate bias in estimated predispersal inbreeding depression caused by pollen limitation and can improve estimates under resource limitation. Application of these methods to two orchid species further demonstrates their utility in identifying and estimating diverse influences on reproductive performance under typical conditions. Although our theoretical results raise questions about the reported intensity of predispersal inbreeding depression, our proposed methods guard against bias while also providing insight into plant reproduction.