Symposium
Symposium on Ecology and Evolution of Plant Reproduction
The two-day symposium (April 24 and 25, 2017) at UFMS campus in Campo Grande will be limited to 200 attendees. Registration will be accepted up to this limit, according to the order of registration dates.
Along the meeting, we will have ten plenary talks that will be presented by the international speakers. Please see below the topics related to each speaker and titles and abstracts for the talks:
Pollination, mating and floral evolution, plenary speaker Lawrence Harder
Title of the talk: Limits on seed production by flowering plants: diversity, ecological dependence, and evolutionary consequences
The limits on seed production by flowering plants have both ecological and evolutionary consequences, as they can determine population dynamics and contribute to the opportunities for selection on plant traits. Consideration of the processes responsible for seed production leads to recognition of a greater diversity of possible constraints than the dichotomy between pollen receipt and seed resources that has dominated studies of plant reproduction, including limitation by pollen quantity and quality, ovule number, offspring quality, seed resources and predispersal seed predation. Although only the single constraint that acts most restrictively sets the effective limit on a flower’s seed production, effective limits can differ among a plant’s flowers and during flowering seasons. Furthermore, for perennials, flexibility in inter-year resource dynamics allow plants to relax the resource limitation on seed production to capitalize on unusually high embryo quantity and quality. The variety of seed-production constraints and their respective uncertainty influence the nature and consequences of selection on reproductive traits, resource allocation and mating systems.
Title of the talk: The population ecology of male gametophytes
The fate of male gametophytes after pollen reaches stigmas links pollination to ovule fertilization, thereby governing subsequent siring success and seed production. Although pollen germination and pollen-tube growth fundamentally involve biochemical and physiological processes, an ecological analogy may provide insights into the nature of this linkage. As independent haploid organisms, male gametophytes of angiosperms complete their lives in localized populations in the complex and dynamic environment provided by the pistils of conspecific sporophytes. Styles represent a competitive arena for such populations by providing “resources” required for pollen-tube growth, including nutrition and/or space. Consequently, progamic success likely involves both density-independent processes associated with pollen viability and tube-specific interactions with the style, and density-dependent competition among male gametophytes governed by resource availability and the density and activity of competitors. If stylar resources are limiting, male gametophytes can compete in manners that depend on their own characteristics and those of the resource supply (i.e., the pistil). “Contest”, or exploitative, competition should arise if pollen grains differ extensively in the timing of their arrival on a stigma or germination, and/or tube growth rates; whereas “scramble”, or interference, competition could occur when germination time differs little and pollen tubes grow at equal rates, so they compete as an advancing front. Models based on this ecological analogy demonstrate that the mode of resource competition and the timing and severity of density-independent mortality together create characteristic relations of the mean and among-stigma variation in pollen-tube success to pollen receipt on the stigma. Observed differences among species in the relation of the number of pollen-tubes entering ovaries or seed production to pollen receipt support the contrasting expectations of contest and scramble competition. Furthermore, consideration of the implications of progamic resource competition reveals explanations for enigmatic aspects of plant reproduction, including limits on the evolution of pollinator attraction, and enriches understanding of the incidence and nature of sexual selection in plant populations.
Gender strategies and the evolution of plant sexual systems, plenary speaker John Pannell
Title of the talk: Gender strategies and the evolution of plant sexual systems
Our understanding of the function and evolution of plant sexual systems benefited enormously through the elaboration of a quantitative perspective of plant gender. According to this view, females and males represent only two extremes along a continuum in the way plants invest resources in, and transmit genes through, their male versus female functions. In this presentation, I will consider how a quantitative and functional perspective of plant gender can help to interpret transitions between hermaphroditism and dioecy (i.e., combined versus separate sexes) in flowering plants. I will review the major evolutionary paths that plant populations have likely followed in making these transitions, emphasising the evolution of hermaphroditic gender under fluctuating frequency-dependent selection. I will illustrate the ideas presented by drawing on insights we have gained from analysis of sexual-system variation in the European annual plant Mercurialis annua. A combination of field observations, phylogenetic and phylogeographic reconstruction, manipulative experiments, experimental evolution, and the analysis of genomic and transcriptomic variation reveal a highly dynamic picture of gender evolution in M. annua. Importantly, demographic processes at local to continental scales have played a key role in shaping quantitative genetic variation in both gender and other traits that are expected to influence sexual-system evolution in plants.
Title of the talk: Evolution of plant mating systems in metapopulations and fragmented landscapes
The mating opportunities of species that inhabit fragmented landscapes, and that establish new populations by long-distance dispersal, will often differ from those that usually occur in large, demographically stable populations. First, a paucity of mates and/or pollinators during phases of low population density is expected to select for an ability to self-fertilize, e.g., during episodes of colonisation. And second, bottlenecks caused by colonisation and subsequent population growth are expected to affect local genetic diversity at loci that influence the mating system, the sex allocation, and patterns of inbreeding depression. In this presentation, I will discuss the effects that colonisation in metapopulations and range expansions can have on the evolution of plant mating systems, emphasising the breakdown of outcrossing mechanisms as a result of mate limitation and the loss of inbreeding depression. I will illustrate these ideas with data from computer simulations of metapopulation dynamics and range expansions, as well as empirical observations from two studies: (1) the selection of combined versus separate sexes in an annual colonising plant; and (2) the selection of self-compatibility in an otherwise self-incompatible long-lived perennial herb
Genetics and genomics of plant reproduction, plenary speaker Stephen Wright
Title of the talk: Evolution of sex chromosomes: Y go Backward
The degeneration of Y chromosomes represents one of the most striking patterns of genome evolution, but the relative role of neutral genetic drift, positive selection, and inefficient selection remains unclear. Because of their recent origin, dioecious plants provide an outstanding opportunity to investigate the early stages of sex chromosome evolution, and to disentangle the key evolutionary forces involved. Here, we conduct comparative genomic and transcriptomic analysis of sex chromosome evolution in the genus Rumex. We show that gene loss precedes dosage compensation, and is not associated with genes subject to positive selection. In contrast, genes subject to early gene loss experience weaker purifying selection, and are less expressed. Combined with evidence for strong loss of neutral diversity, our results suggest that Hill-Robertson interference plays a predominant role in the degeneration of Y chromosomes.
Title of the talk: Population Genomics of Mating System Transitions in Capsella
The shift from outcrossing to selfing is one of the most common evolutionary transitions, but the demographic context in which these transitions occur, the evolutionary dynamics of adaptation to a selfing mating system, and the genomic consequences of evolving selfing remain poorly understood. Studying recent evolutionary transitions provides a unique opportunity to investigate the early stages of this process, and gain unique insights into the causes and consequences of mating system evolution. We have been using comparative and population genomics to investigate the evolution of selfing in the genus Capsella, which has experienced a recent and rapid shift from outcrossing to selfing. Our results suggest that the transition to selfing was accompanied by a severe reduction in effective population size and rapid reduction in the efficacy of natural selection. Despite these negative consequences, the shift to selfing occurred rapidly through morphological changes originating by a combination of standing genetic variation from ancestral outcrossing populations and new mutations. Evidence for ongoing introgression between selfing and outcrossing lineages highlights that mating system transitions do not drive complete reproductive isolation and highlight the potential importance of selection against gene flow in maintaining species boundaries following mating system transitions.
Applied reproductive biology, plenary speaker Marcelo Aizen.
Title of the talk: The impact of invasive bees on agriculture
Management of crop pollination is mainly based on a relatively few domesticated bee species, most notably Apis mellifera and different species of bumble bees, that have been transported across the world and introduced in regions outside their native ranges. A few of these species have become phenomenal invaders in several continents; the most impressive examples are the Africanized honeybee (i.e. a hybrid between the African Apis mellifera scutellata and the European honeybee subspecies) in the Americas and the European bumble bee Bombus terrestris in Southern South America, New Zealand, Tasmania and Japan. Because of their high abundances, these invasive bees can change the nature, from mutualistic to antagonistic, of many of the flower-pollinator interactions they usurp, with negative consequences even for crop pollination. This is exemplified with a study of the effect of B. terrestris on raspberry pollination in southern South America, where it has been recorded that fruit quality decreases above a few bumble bee visits because of increasing style breakage. Also, nectar robbing of raspberry flower buds by bumble bees decreases nectar availability for more legitimate pollinator. At a continental scale, evidence on a supposedly positive effect of the invasion of the Africanized honeybee in coffee yield is put into question, showing that temporal trends in yield vary greatly among countries and that yield declines have occurred in some Neotropical countries during the last decades. It is concluded that invasive bees can have several direct and indirect negative effects on pollination services and further introductions should be discouraged.
Title of the talk: Evidence of widespread pollination-mediated facilitation in south Andean plant communities based on pollen transfer networks
Although plant-plant facilitation via the nurse effects seems to be common in Alpine environments, similar information for plant-plant facilitation via shared pollinators is limited. Pollinator sharing often implies interspecific pollen transfer (IPT). We studied IPT among a total of ~50 plant species distributed across three high-Andean communities at 1600, 1800 and 2000 m a.s.l. in Cerro Challhuaco (Nahuel Huapi NP) to construct networks depicting plant-plant, pollinator-mediated interactions. We analysed the relation between the (a) number of conspecific and number of heterospecific pollen grains deposited on stigmas (quantitative effect), and (b) proportion of germinated pollen and number of heterospecific pollen grains on stigmas (qualitative effect). Using GLMMs, we estimated the sign (positive, neutral or negative) of quantity and quality effects of pollinator sharing for each recipient species and each recipient-donor species pair. Communities were characterized by the presence of pollen hub-donors acting as “magnet species”. In general, facilitative and neutral pollinator-mediated interactions among plants prevailed over competition. Thus, the benefits from pollinator sharing (i.e. increased visitation and conspecific pollen deposition) seem to outweigh the costs (i.e. heterospecific deposition and conspecific pollen loss). The largest proportion of facilitated species was found in the highest elevation community, suggesting that facilitation can be even more common at lower plant densities and under unfavourable conditions for pollination. This evidence indicates that widespread facilitation in stressful environments can not only occur via increasing availability of limited abiotic resources, but also increasing attraction of scarce mutualists.
In addition, there will be two lectures by Spencer Barrett.
Title of the talk: The Unappreciated Botanical Legacy of Charles Darwin
Charles Darwin studied plants for over 40 years, devoted more of his research to this group of organisms than any other, and wrote three books on plant reproduction. This fact is generally not well appreciated because of the zoocentric nature of human interest in Darwin’s contributions and the dominance of animal biology in today’s universities. Yet Darwin’s botanical work provided the conceptual foundation for understanding many aspects of plant form and function including floral adaptations and the mechanisms responsible for evolutionary transitions in plant reproductive systems. Many of Darwin’s insights, gained from careful observations and experiments on diverse flowering plants, remain remarkably durable today and have stimulated much current research on plant reproductive strategies. Here, I review Darwin’s botanical legacy and also address the question of why Darwin become so interested in plant sex. Topics covered will include floral adaptation, the evolution and function of sexual polymorphisms, the costs and benefits of selfing and outcrossing, the evolution of combined versus separate sexes, and the evolution of wind pollination. Darwin made important contributions on all of these topics and can rightfully be considered the founder of plant reproductive biology.
Title of the talk: Some Unresolved Questions in Plant Reproductive Biology
My talk will be unorthodox; instead of focusing on a single question or study system, I will present short vignettes on projects with many unresolved questions. The main emphasis will be on what we do not know, rather than what we know. The projects range in scope from evolutionary ecology to evolutionary genomics and use a variety of species and groups that were specifically chosen to address particular questions in reproductive biology.
My interests largely concern the evolution of mating systems. Mating in seed plants arises from interactions between plant traits and the environmental context in which individuals reside. These interactions commonly cause non-random mating, including selfing and promiscuous outcrossing within local neighborhoods. Extrinsic ecological factors influence all stages of the mating process – pollination, pollen-tube growth, ovule fertilization – as well as seed development, determining offspring quantity and quality. Changes in mating patterns are of particular interest because they can have profound ecological, demographic and genetic consequences. Transitions in reproductive systems generally have important influences on patterns of mating and our work focuses on the three major transitions – the evolution of selfing from outcrossing, separates sexes from combined sexes, and wind- from animal-pollination. Below are some questions I will address.
Evolutionary breakdown of heterostyly to selfing – Why is the inheritance of distyly and tristyly similar given their phylogenetically divergent origins? Do supergenes exist in heterostylous species? What is the genetic and developmental basis of selfing variants that replace outcrossing morphs?
Gender strategies, dioecy and biased sex ratios – When is the gender of a flower determined? What are the mechanisms causing biased sex ratios? How can male- versus female-determining pollen tubes be distinguished to test hypotheses on certation and sex ratio bias?
Evolution of wind pollination from animal pollination – What determines whether lineages evolve selfing versus anemophily through reproductive assurance? What floral traits predispose lineages to evolve anemophily? Is ambophily an intermediate stage in the evolution of anemophily?
My talk will likely raise more questions than are solved.