Patterns of pollen quantity and quality limitation of pre‐zygotic reproduction in Mimulus guttatus vary with co‐flowering community context

Pollen quantity limitation has been widely recognized as one of the main causes of plant reproductive failure in nature. However, its negative effects on fruit and seed production have been often confounded with those of low pollen quality (i.e. low conspecific pollen viability and/or slow pollen tube growth rate). The lack of differentiation between these two aspects of pollen limitation has resulted not only in a potential overestimation of the incidence of pollen quantity limitation but has led to a poor understanding of the factors and mechanisms that affect pollen quality limitation. Knowledge of the relative importance and underlying causes of both aspects of pollen limitation (quantity and quality) is required to fully understand the ecological and evolutionary consequences of pollen limitation in natural populations. Co‐flowering community context (e.g. species richness and conspecific density), in particular, can be an important driver of overall pollen limitation. However, how pollen quantity and quality limitation vary separately with the community context has not previously been examined, even though they may vary differently as they arise from different mechanisms, e.g. insect visitation rate versus inbreeding depression. Here we evaluate the effect of co‐flowering diversity and conspecific density on the relative importance of pollen quantity and quality limitation for Mimulus guttatus pre‐zygotic reproduction (i.e. pollen tube success) at serpentine seeps in California over two years. We found overall pollen limitation of pre‐zygotic reproductive success at all seeps regardless of the co‐flowering context. However, plants in high‐diversity/low‐ conspecific density communities were mostly limited by pollen quantity, whereas plants in low‐diversity/high‐conspecific density ones experienced stronger quality limitation – a pattern that was consistent across years. These results not only highlight the importance of conducting comprehensive studies on pollen limitation that evaluate both, its quantity and quality aspects, but are the first to show how their relative contribution to overall pollen limitation can vary with extrinsic factors such as the co‐flowering community context.     

Pollen limitation,fruit abortion,and autonomous selfing in three populations of the perennial herb Ruellia nudiflora

Multiple factors determine plant reproductive success and their influence may vary spatially. This study addresses several factors influencing female reproductive success in three populations of Ruellia nudiflora, specifically we: (i) determine if fruit set is pollen‐limited and if pollinator visitation rates are related to this condition; (ii) estimate fruit set via autonomous self‐pollination (AS) and relate it to the magnitude of herkogamy; and (iii) evaluate if fruit abortion is a post‐pollination mechanism that determines the magnitude of pollen limitation. At each site we marked 35 plants, grouped as: unmanipulated control (C) plants subjected to open pollination, plants manually cross‐pollinated (MP), and plants excluded from pollinators and only able to self‐pollinate autonomously (AS). Fruit set was greater for MP relative to C plants providing evidence for pollen limitation, while a tendency was observed for lower fruit abortion of MP relative to C plants suggesting that fruit set is influenced not only by pollen delivery per se, but also by subsequent abortion. In addition, although pollinator visits varied significantly among populations, the magnitude of pollen limitation did not, suggesting that pollinator activity was not relevant in determining pollen limitation. Finally, fruit set tended to decrease with the degree of herkogamy for AS plants, but this result was inconclusive. These findings have contributed to identify which factors influence reproductive success in populations of R. nudiflora, with potentially relevant implications for population genetic structure and mating system evolution of this species.     

Can plants evolve tolerance mechanisms to heterospecific pollen effects? An experimental test of the adaptive potential in Clarkia species

Flowering plants do not occur alone and often grow in mixed‐species communities where pollinator sharing is high and interactions via pollinators can occur at pre‐ and post‐pollination stages. While the causes and consequences of pre‐pollination interactions have been well studied little is known about post‐pollination interactions via heterospecific pollen (HP) receipt, and even less about the evolutionary implications of these interactions. In particular, the degree to which plants can evolve tolerance mechanisms to the negative effects of HP receipt has received little attention. Here, we aim to fill this gap in our understanding of post‐pollination interactions by experimentally testing whether two co‐flowering Clarkia species can evolve HP tolerance, and whether tolerance to specific HP ‘genotypes’ (fine‐scale local adaptation to HP) occurs. We find that Clarkia species vary in their tolerance to HP effects. Furthermore, conspecific pollen performance and the magnitude of HP effects were related to the recipient's history of exposure to HP in C. xantiana but not in C. speciosa. Specifically, better conspecific pollen performance and smaller HP effects were observed in populations of C. xantiana plants with previous exposure to HP compared to populations without such exposure. These results suggest that plants may have the potential to evolve tolerance mechanisms to HP effects but that these may occur not from the female (stigma, style) but from the male (pollen) perspective, a possibility that is often overlooked. We find no evidence for fine‐scale local adaptation to HP receipt. Studies that evaluate the adaptive potential of plants to the negative effects of HP receipt are an important first step in understanding the evolutionary consequences of plant–plant post‐pollination interactions. Such knowledge is in turn crucial for deciphering the role of plant–pollinator interactions in driving floral evolution and the composition of co‐flowering communities.     

Mast Cell Dependent Vascular Changes Associated with an Acute Response to Cold Immersion in Primary Contact Urticaria

Background

While a number of the consequences of mast cell degranulation within tissues have been documented including tissue-specific changes such as bronchospasm and the subsequent cellular infiltrate, there is little known about the immediate effects of mast cell degranulation on the associated vasculature, critical to understanding the evolution of mast cell dependent inflammation.

Objective

To characterize the microcirculatory events that follow mast cell degranulation.

Methodology/Principal Findings

Perturbations in dermal blood flow, temperature and skin color were analyzed using laser-speckle contrast imaging, infrared and polarized-light colorimetry following cold-hand immersion (CHI) challenge in patients with cold-induced urticaria compared to the response in healthy controls. Evidence for mast cell degranulation was established by documentation of serum histamine levels and the localized release of tryptase in post-challenge urticarial biopsies. Laser-speckle contrast imaging quantified the attenuated response to cold challenge in patients on cetirizine. We found that the histamine-associated vascular response accompanying mast cell degranulation is rapid and extensive. At the tissue level, it is characterized by a uniform pattern of increased blood flow, thermal warming, vasodilation, and recruitment of collateral circulation. These vascular responses are modified by the administration of an antihistamine.

Conclusions/Significance

Monitoring the hemodynamic responses within tissues that are associated with mast cell degranulation provides additional insight into the evolution of the acute inflammatory response and offers a unique approach to assess the effectiveness of treatment intervention.     

A Mathematical Study of the Differential Effects of Two SERCA Isoforms on Ca2+ Oscillations in Pancreatic Islets

Cytosolic Ca²⁺ dynamics are important in the regulation of insulin secretion from the pancreatic β-cells within islets of Langerhans. These dynamics are sculpted by the endoplasmic reticulum (ER), which takes up Ca²⁺ when cytosolic levels are high and releases it when cytosolic levels are low. Calcium uptake into the ER is through sarcoendoplasmic reticulum Ca²⁺-ATPases, or SERCA pumps. Two SERCA isoforms are expressed in the β-cell: the high Ca²⁺ affinity SERCA2b pump and the low affinity SERCA3 pump. Recent experiments with islets from SERCA3 knockout mice have shown that the cytosolic Ca²⁺ oscillations from the knockout islets are characteristically different from those of wild type islets. While the wild type islets often exhibit compound Ca²⁺ oscillations, composed of fast oscillations superimposed on much slower oscillations, the knockout islets rarely exhibit compound oscillations, but produce slow (single component) oscillations instead. Using mathematical modeling, we provide an explanation for this difference. We also investigate the effect that SERCA2b inhibition has on the model β-cell. Unlike SERCA3 inhibition, we demonstrate that SERCA2b inhibition has no long-term effect on cytosolic Ca²⁺ oscillations unless a store-operated current is activated.     

Selection on intra‐individual variation in stigma–anther distance in the tropical tree Ipomoea wolcottiana (Convolvulaceae)

• It is well known that animals can exert strong selective pressures on plant traits. However, studies on the evolutionary consequences of plant–animal interactions have mainly focused on understanding how these interactions shape trait means, while overlooking its potential direct effect on the variability among structures within a plant (e.g. flowers and fruits). The degree of within‐plant variability can have strong fitness effects but few studies have evaluated its role as a potential target of selection.
• Here we reanalysed data on Ipomoea wolcottiana stigma–anther distance to test alternate mechanisms driving selection on the mean as well as on intra‐individual variance in 2 years. We found strong negative selection acting on intra‐individual variation but not on mean stigma–anther distance, suggesting independent direct selection on the latter.
• Our result suggests that intra‐individual variance has the potential to be an important target of selection in nature, and that ignoring it could lead to the wrong characterisation of the selection regime.
• We highlight the need for future studies to consider patterns of selection on the mean as well as on intra‐individual variance if we want to understand the full extent of plant–animal interactions as an evolutionary force in nature.