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Angiosperm pollen, the male gametophyte, plays a crucial role in facilitating fertilization by protecting and transporting male sperm cells to the female pistil. Despite their seemingly simple structure, pollen grains undergo intricate development to produce viable sperm cells capable of fertilizing the egg cell. Factors such as resource limitation and plant aging can disrupt normal pollen development and affect pollen performance. We investigated the influence of plant resources and aging on pollen developmental failure in Azorella nivalis Phil., an exceptionally long-lived high-Andean species that grows in a stressful alpine environment. Leveraging the modular nature of plants, we aimed to identify intra-individual sources of variation in pollen developmental failure. By using pollen viability and variation in viable pollen grain size as indicators of pollen developmental performance, we assessed whether proxies of plant resource availability and aging influenced these pollen traits at the inter-individual, inter-flower and intra-flower levels. Our findings revealed decreased pollen viability in putative resource-depleted flowers and in shoots that experienced higher levels of meristematic divisions from the zygote (i.e., greater cell depth). Additionally, we observed increased variability in the size of viable pollen grains in resource-depleted anthers. Our study suggests that resource availability and shoot aging are critical determinants shaping pollen development in long-lived plants at the intra-individual level. These findings contribute to our understanding of how differences in male fitness can arise in plants, with implications for their evolutionary trajectory., (© 2024 Wiley‐VCH GmbH. Published by John Wiley & Sons Ltd.)

Organism shape changes predictably during ontogeny, resulting in specific patterns of ontogenetic allometry. In several plant and animal lineages, among-species variation in the shape of mature organisms mirrors variation along their growth trajectories. Hence, ontogenetic allometry is an important bias in evolution. This bias should be stronger at reduced evolutionary time scales, in which among-trait correlations had less time to evolve. Nevertheless, it was shown that adaptation of organism shape frequently involved departures from the ancestral ontogenetic allometry. Moreover, only a moderate fraction of shape variation is correlated with size during ontogeny. Hence, nonallometric variation in shape (NAVSh) is likely to contribute to adaptation, even at reduced evolutionary time scales. We explored the contributions of allometric variation in shape (AVSh), NAVSh, and size variation to adaptive evolution in the angiosperm species Calceolaria polyrhiza. This strongly relies on oil-collecting bees for pollination and experienced transitions in the size of pollinators during the last 2 Ma. Using geometric morphometrics, we described corolla morphology in several populations across its distribution range. Variation in corolla shape was decomposed into an allometric and a nonallometric component, and corolla size was estimated. We then looked for the correlation between these aspects of morphology and the pollinator. Our results suggest that adaptation to pollinators with different sizes relied on NAVSh, which resulted from shifts in the allometric slope and from shape changes that occurred early in flower development. We conclude that NAVSh can contribute to adaptation in flowering plants, even at the species-level., (© 2020 Wiley Periodicals LLC.)

Herbivores decrease plant fitness by consuming reproductive tissues, limiting resources, and/or affecting mutualisms. Although these mechanisms were extensively tested in chewing herbivores, the impact of other functional groups (e.g., sap-feeders) remains poorly understood. We investigated whether aphids affect plant reproduction via direct resource limitation on seed production and/or pollination interference. We compared plant traits and the seed set of naturally aphid-free vs. aphid-infested plants and then manipulated aphid presence and pollen receipt. We used path models to examine the links between variables. Nectar volume and seed set of aphid-infested plants was 54% and 42% lower than that of aphid-free plants. 72 h after removing aphids, nectar volume was restored to the level of aphid-free plants. When pollinators were excluded, the seed set of aphid-infested and aphid-free plants did not differ, suggesting that direct resource limitation on seed production was not the cause of reduced plant fitness. Manual addition of pollen restored the seed set of aphid-infested plants to the level of aphid-free plants, evidencing that plants were pollen limited. The path analysis showed a negative link between aphids and the seed set via nectar volume, supporting that nectar shortage caused by aphids may interfere with pollination and reduce plant fitness. Since aphids are crop pests and feed on a large number of animal-pollinated plants, the potential of these insects to influence pollination and plant fitness is high. This study emphasizes the ecological importance of aphids and the need to better understand the links between sap-feeding herbivory, pollination, and plant fitness.

Background and Aims: Geographical variation in foliar and floral traits and their degree of coupling can provide relevant information on the relative importance of abiotic, biotic and even neutral factors acting at geographical scales as generators of evolutionary novelty. Geographical variation was studied in leaves and flowers of Embothrium coccineum, a species that grows along abrupt environmental gradients and exhibits contrasting pollinator assemblages in the southern Andes., Methods: Five foliar and eight floral morphological characters were considered from 32 populations, and their patterns of variation and covariation were analysed within and among populations, together with their relationship with environmental variables, using both univariate and multivariate methods. The relationships between foliar and floral morphological variation and geographical distance between populations were compared with Mantel permutation tests., Key Results: Leaf and flower traits were clearly uncoupled within populations and weakly associated among populations. Whereas geographical variation in foliar traits was mostly related to differences in precipitation associated with geographical longitude, variation in floral traits was not., Conclusions: These patterns suggest that leaves and flowers responded to different evolutionary forces, environmental (i.e. rainfall) in the case of leaves, and biotic (i.e. pollinators) or genetic drift in the case of flowers. This study supports the view that character divergence at a geographical scale can be moulded by different factors acting in an independent fashion.

Background and Aims: Floral nectar concentration and chemical composition of 26 plant species native to the temperate forest of southern South America are reported and the relationships with the flower type are evaluated., Methods: Nectar concentration was measured with a hand refractometer and sugar composition was analysed by gas-liquid chromatography. Plant species were classified into flower type categories based not only on floral features but also on data from the literature and field observations on their pollinators., Key Results: Most data on nectar are new reports at the generic and/or specific level. Plant species in which more than one population was studied showed significant among-population variation in nectar sugar concentration and composition. Results showed a weak relationship between nectar traits and flower type. Many species had nectar containing 50 % or more sucrose (17 of 26 species), independent of the main pollinator., Conclusions: Considering that (a) nectar characteristics did not show a clear association with different flower types or with plant taxonomic membership, and (b) different populations of the same species showed large variability in sugar composition, the results suggest that other factors (e.g. historical and environmental) could be involved in determining the sugar composition of the highly endemic plant species from this region.