Floral mimicry Johnson, Steven D; Schiestl, Florian P
2016.
eBook
This text on floral mimicry discusses the functions of visual, olfactory, and tactile signals, integrating them into a broader theory of organismal mimicry that will help guide future research in the ...field. It addresses the fundamental question of whether the evolutionary and ecological principles that were developed for protective mimicry in animals can also be applied to floral mimicry in plants. The book also deals with the functions of floral rewardlessness, a condition which often serves as a precursor to the evolution of mimicry in plant lineages.
The long-standing notion that most angiosperm flowers are specialized for pollination by particular animal types, such as birds or bees, has been challenged recently on the basis of apparent ...widespread generalization in pollination systems. At the same time, biologists working mainly in the tropics and the species-rich temperate floras of the Southern hemisphere are documenting pollination systems that are remarkably specialized, often involving a single pollinator species. Current studies are aimed at understanding: (1) the ecological forces that have favoured either generalization or specialization in particular lineages and regions; (2) the implications for selection on floral traits and divergence of populations; and (3) the risk of collapse in plant–pollinator mutualisms of varying specificity.
1 Flowering patterns in the species-rich and largely endemic flora of the southern and south-western Cape Province, South Africa, are described. 2 Analysis of the flowering times of 7075 Cape species ...(83% of the flora) showed that flowering peaks in spring and then gradually tails off, reaching a trough in autumn and early winter. 3 Flowering seasonality varies along a climatic gradient from winter rainfall in the west, where species show a spring peak, to nonseasonal rainfall in the east, where species show an early summer flowering peak. 4 At least 20% of the flora in the winter rainfall half of the Cape region is in flower at any time of the year. This contrasts with other winter rainfall regions worldwide where very little flowering takes place outside of spring. 5 Strong differences in flowering seasonality between some families and some genera were found, particularly in monocotyledons. 6 Differences in flowering time among lineages are often attributable to the degree to which flowering is constrained by the timing of other phenophases such as growth, seed dispersal and seed germination. Lineages in which these phenophases are uncoupled show more flexibility in flowering time.
It has been debated whether pollination success in nonrewarding plants that flower in association with nectar-producing plants will be diminished by competition for pollinator visits or, ...alternatively, enhanced through increased local abundance of pollinators (the magnet species effect). We experimentally evaluated these effects using the nonrewarding bumblebee-pollinated orchid Anacamptis morio and associated nectar-producing plants at a site in Sweden. Pollination success (estimated as pollen receipt and pollen removal) in A. morio was significantly greater for individuals translocated to patches of nectar-producing plants (Geum rivale and Allium schoenoprasum) than for individuals placed outside (∼ 20 m away) such patches. These results provide support for the existence of a facilitative magnet species effect in the interaction between certain nectar plants and A. morio. To determine the spatial scale of these interactions, we correlated the visitation rate to flowers of A. morio with the density of sympatric nectar plants in 1-m2and 100-m2plots centered around groups of translocated plants, and at the level of whole meadows (∼ 0.5-2 ha). Visitation rate to flowers of A. morio was not correlated with the 1-m2patch density of G. rivale and A. schoenoprasum, but showed a significant positive relationship with density of these nectar plants in 100-m2plots. In addition, visitation to flowers of A. morio was strongly and positively related to the density of A. schoenoprasum at the level of the meadow. Choice experiments showed that bees foraging on the purple flowers of A. schoenoprasum (a particularly effective magnet species) visit the purple flowers of A. morio more readily (47.6% of choices) than bees foraging on the yellow flowers of Lotus corniculatus (17% of choices). Overall similarity in flower color and shape may increase the probability that a pollinator will temporarily shift from a nectar-producing "magnet" plant to a nonrewarding plant. We discuss the possibility of a mimicry continuum between those orchids that exploit instinctive food-seeking behavior of pollinators and those that show an adaptive resemblance to nectar-producing plants.
Cytotoxic CD4+ T cells (CD4+ CTLs) limit HIV pathogenesis, as evidenced in elite controllers (a subset of individuals who suppress the virus without the need for therapy). CD4+ CTLs have also been ...shown to kill HIV-infected macrophages. However, little is known about their contribution towards HIV persistence, how they are affected following exposure to immune modulators like morphine, and what factors maintain their frequencies and function. Further, the lack of robust markers to identify CD4+ CTLs in various animal models limits understanding of their role in HIV pathogenesis. We utilized various PBMC samples obtained from SIV infected and cART treated rhesus macaques exposed to morphine or saline and subjected to flow cytometry evaluations. Thereafter, we compared and correlated the expression of CD4+ CTL-specific markers to viral load and viral reservoir estimations in total CD4+ T cells. We found that CD29 could be reliably used as a marker to identify CD4+ CTLs in rhesus macaques since CD29hi CD4+ T cells secrete higher cytotoxic and proinflammatory cytokines following PMA/ionomycin or gag stimulation. In addition, this immune cell subset was depleted during untreated SIV infection. Strikingly, we also observed that early initiation of cART reconstitutes depleted CD29hi CD4+ T cells and restores their function. Furthermore, we noted that morphine exposure reduced the secretion of proinflammatory cytokines/cytotoxic molecules in CD29hi CD4+ T cells. Lastly, increased functionality of CD29hi CD4+ T cells as depicted by elevated levels of either IL-21 or granzyme B hi T Bet+ gag specific responses were linked to limiting the size of the replication-competent reservoir during cART treatment. Collectively, our data suggest that CD4+ CTLs are crucial in limiting SIV pathogenesis and persistence.
Plants need not participate passively in their own mating, despite their immobility and reliance on pollen vectors. Instead, plants may respond to their recent pollination experience by adjusting the ...number of flowers that they display simultaneously. Such responsiveness could arise from the dependence of floral display size on the longevity of individual flowers, which varies with pollination rate in many plant species. By hand-pollinating some inflorescences, but not others, we demonstrate plasticity in display size of the orchid Satyrium longicauda. Pollination induced flower wilting, but did not affect the opening of new flowers, so that within a few days pollinated inflorescences displayed fewer flowers than unpollinated inflorescences. During subsequent exposure to intensive natural pollination, pollen removal and receipt increased proportionally with increasing display size, whereas pollen-removal failure and self-pollination accelerated. Such benefit-cost relations allow plants that adjust display size in response to the prevailing pollination rate to increase their attractiveness when pollinators are rare (large displays), or to limit mating costs when pollinators are abundant (small displays). Seen from this perspective, pollination-induced flower wilting serves the entire plant by allowing it to display the number of flowers that is appropriate for the current pollination environment.
One explanation for the widespread absence of floral nectar in many orchids is that it causes pollinators to visit fewer flowers on a plant, and thus reduces self-pollination. This, in turn, could ...increase fitness by reducing inbreeding depression in progeny and promoting pollen export. The few previous investigations of this hypothesis have all involved bee-pollinated orchids and some have given contradictory results. We studied the effects of adding artificial nectar (sucrose solution) to the spurs of a non-rewarding long-proboscid fly-pollinated orchid, Disa pulchra. Addition of nectar significantly increased the number of flowers probed by flies (2.6-fold), the time spent on a flower (5.4-fold), the number of pollinia removed per inflorescence (4.8-fold) and the proportion of removed pollen involved in self-pollination (3.5-fold). The level of self-pollination increased dramatically with the number of flowers probed by flies. Experimental self-pollination resulted in fruits with only half as many viable seeds as those arising from cross-pollination. Pollinators were more likely to fly long distances (>40 cm) when departing from non-rewarding inflorescences than when departing from rewarding ones. These findings provide support for the idea that floral deception serves to reduce pollinator-mediated self-pollination.
Darwin's mechanistic model whereby selection favours plants with flower tubes that exceed the tongue length of the primary pollinator, was tested using unmanipulated plants of the hawkmoth-pollinated ...South African iris, Gladiolus longicollis. The study population was characterized by exceptionally large phenotypic variation in flower-tube length (range 56-129 mm). Directional selection on tube length was revealed by a significant positive relationship between this trait and both fruit and seed set. Selection was attributed to the effect of tube length on pollen receipt, as supplemental hand pollinations showed fruit and seed set in the population to be pollen limited. Indirect selection on tube length may also occur through the correlation of this trait with inflorescence height, although direct selection on the latter trait was significant only for seed set. The main pollinators at the study site were individuals of the large hawkmoth Agrius convolvuli that had tongue lengths of 85-135 mm. Other hawkmoths had tongues that were much too short to reach the nectar in G. longicollis flowers and seldom carried pollen of G. longicollis. Flowers with tubes shorter than the tongues of A. convolvuli are apparently not effectively pollinated because stigmas do not contact the moth's head effectively. This study demonstrates that selection may occur among plants with natural phenotypic variation in flower-tube length, and supports Darwin's model of pollinator-mediated selection.
According to Baker's Rule, plant species capable of uniparental reproduction are more likely to be successful colonists than are self-incompatible or dioecious species. Controlled pollination ...experiments carried out on 17 invasive alien plant species in South Africa revealed that 100% were either self-compatible or apomictic, and that 72% of these were capable of autonomous self pollination. The distribution of breeding systems among these invasive aliens is thus strongly skewed towards uniparental reproduction. While all 13 woody species in our survey showed a capacity for uniparental reproduction, this mode of reproduction is very rare among woody plants in general. Thus Baker's rule, which has generally been considered for short-lived herbaceous plants, may also apply to invasive shrubs and trees. The study species exhibited high levels of fruit set (median = 71.5%). Supplemental hand-pollination experiments carried out on five of the species showed that pollen availability did not limit fruit set. Further work is needed to establish the exact role of uniparental reproduction in various stages of the invasion process. In particular, we need to know whether uniparental reproduction provides reproductive assurance at the population establishment stage (as originally envisaged by Baker) or whether it plays a further role in alleviating pollen limitation in small and established populations.
Flowers of the parthenocarpic knuckles mutant are conditionally male sterile and contain ectopic stamens and carpels that originate from placental tissue within developing gynoecia. The mutation was ...mapped to a 123 Kb interval on chromosome 5 using molecular markers. All aspects of the knuckles phenotype could be complemented by a genomic fragment from the region which contained the annotated MAC12.2 gene. A guanine to adenine transition within a predicted C2H2 zinc finger-encoding region of MAC12.2 causes the second of two critical zinc-binding cysteine residues to be replaced by a tyrosine. Transgenic plants in which translational fusions of the GUS reporter to KNUCKLES were driven by the presumptive KNUCKLES promoter indicate that the gene is expressed first in developing carpel primordia, and later in stamens and ovules of flower buds. In situ hybridization experiments showed a broader pattern of transcript localization, suggesting that post-transcriptional regulatory mechanisms may limit KNUCKLES protein accumulation and localization. Based on genetic evidence and the presence of a carboxy-terminal motif demonstrated by others to function as an active repression domain, we propose that KNUCKLES might function as a transcriptional repressor of cellular proliferation that regulates floral determinacy and relative size of basal pattern elements along the proximo-distal axis of the developing Arabidopsis gynoecium.
PDF
