Phenotype-fitness relationships and pollen-transfer efficiency of five orchid species with different pollination strategies.

PREMISE: Deceptive pollination, a fascinating mechanism that independently originated in several plant families for benefiting from pollinators without providing any reward, is particularly widespread among orchids. Pollination efficiency is crucial in orchids due to the aggregated pollen in a pollinarium, which facilitates pollen transfer and promotes cross-pollination as pollinators leave after being deceived. METHODS: In this study, we compiled data on reproductive ecology from five orchid species with different pollination strategies: three deceptive-strategy species (shelter imitation, food deception, sexual deception), one nectar-rewarding species, and one shelter-imitation but spontaneously selfing species. We aimed to compare the reproductive success (female fitness: fruit set; male fitness: pollinarium removal) and pollination efficiency of species representing these strategies. We also investigated pollen limitation and inbreeding depression among the pollination strategies. RESULTS: Male and female fitness were strongly correlated in all species but the spontaneously selfing species, which had high fruit set and low pollinarium removal. As expected, pollination efficiency was highest for the rewarding species and the sexually deceptive species. Rewarding species had no pollen limitation but did have high cumulative inbreeding depression; deceptive species had high pollen limitation and moderate inbreeding depression; and spontaneously selfing species did not have pollen limitation or inbreeding depression. CONCLUSIONS: Pollinator response to deception is critical to maintain reproductive success and avoid inbreeding in orchid species with non-rewarding pollination strategies. Our findings contribute to a better understanding of the trade-offs associated with different pollination strategies in orchids and highlight the importance of pollination efficiency in orchids due to the pollinarium.

Sugars and sucrose transporters in pollinia of Phalaenopsis aphrodite (Orchidaceae).

The pollen grains of Phalaenopsis orchids are clumped tightly together, packed in pollen dispersal units called pollinia. In this study, the morphology, cytology, biochemistry, and sucrose transporters in pollinia of Phalaenopsis orchids were investigated. Histochemical detection was used to characterize the distribution of sugars and callose at the different development stages of pollinia. Ultra-performance liquid chromatography-high resolution-tandem mass spectrometry data indicated that P. aphrodite accumulated abundant saccharides such as sucrose, galactinol, myo-inositol, and glucose, and trace amounts of raffinose and trehalose in mature pollinia. We found that galactinol synthase (PAXXG304680) and trehalose-6-phosphate phosphatase (PAXXG016120) genes were preferentially expressed in mature pollinia. The P. aphrodite genome was identified as having 11 sucrose transporters (SUTs). Our qRT-PCR confirmed that two SUTs (PAXXG030250 and PAXXG195390) were preferentially expressed in the pollinia. Pollinia germinated in pollen germination media (PGM) supplemented with 10% sucrose showed increased callose production and enhanced pollinia germination, but there was no callose or germination in PGM without sucrose. We show that P. aphrodite accumulates high levels of sugars in mature pollinia, providing nutrients and enhanced SUT gene expression for pollinia germination and tube growth.

Pollen viability of Euro-Mediterranean orchids under different storage conditions: The possible effects of climate change.

The future impact of climate change and a warmer world is a matter of great concern. We therefore aimed to evaluate the effects of temperature on pollen viability and fruit set of Mediterranean orchids. The in vitro and controlled pollination experiments were performed to evaluate the ability of pollinia stored at lower and higher temperatures to germinate and produce fruits and seeds containing viable embryos. In all of the examined orchids, pollen stored at -20 °C remained fully viable for up to 3 years, reducing its percentage germination from year 4 onwards. Pollinia stored at higher temperatures had a drastic reduction in vitality after 2 days at 41-44 °C, while pollinia stored at 47-50 °C did not show any pollen tube growth. The different levels of pollen viability duration among the examined orchids can be related to their peculiar reproductive biology and pollination ecology. The germinability of pollinia stored at lower temperatures for long periods suggests that orchid pollinia can be conserved ex situ. In contrast, higher temperatures can have harmful effects on the vitality of pollen and consequently on reproductive success of the plants. To our knowledge, this is the first report demonstrating the effects of global change on orchid pollen, and on pollen ability to tolerate, or not, higher air temperatures. Although vegetative reproduction allows orchids to survive a few consecutive warm years, higher temperatures for several consecutive years can have dramatic effects on reproductive success of orchids.

Specialized cockroach pollination in the rare and endangered plant Vincetoxicum hainanense in China.

PREMISE: Species of Apocynaceae are pollinated by a diverse assemblage of animals. Here we report the first record of specialized cockroach pollination in the family, involving an endangered climbing vine species, Vincetoxicum hainanense in China. Experiments were designed to provide direct proof of cockroach pollination and compare the effectiveness of other flower visitors. METHODS: We investigated the reproductive biology, pollination ecology, pollinaria removal, pollinia insertion, and fruit set following single visits by the most common insects. In addition, we reviewed reports of cockroaches as pollinators of other plants and analyzed the known pollination systems in Vincetoxicum in a phylogenetic context. RESULTS: The small, pale green flowers of V. hainanense opened during the night. The flowers were not autogamous, but were self-compatible. Flower visitors included beetles, flies, ants and bush crickets, but the most effective pollinator was the cockroach Blattella bisignata, the only visitor that carried pollen between plants. Less frequent and effective pollinators are ants and Carabidae. Plants in this genus are predominantly pollinated by flies, moths and wasps. CONCLUSIONS: Globally, only 11 plant species are known to be cockroach-pollinated. Because their range of floral features encompass similarities and differences, defining a "cockroach pollination syndrome" is difficult. One commonality is that flowers are often visited by insects other than cockroaches, such as beetles, that vary in their significance as pollinators. Cockroach pollination is undoubtedly more widespread than previously thought and requires further attention.

Honey bees are the dominant diurnal pollinator of native milkweed in a large urban park.

In eastern North America, the field milkweed, Asclepias syriaca L. (Asclepiadaceae), is used in planting schemes to promote biodiversity conservation for numerous insects including the endangered monarch butterfly, Danaus plexippus (Linnaeus) (Nymphalidae). Less is known about its pollinators, and especially in urban habitats where it is planted often despite being under increasing pressure from invasive plant species, such as the related milkweed, the dog-strangling vine (DSV), Vincetoxicum rossicum (Kleopow) Barbar. (Asclepiadaceae). During the A. syriaca flowering period in July 2016, we surveyed bees in open habitats along a DSV invasion gradient and inspected 433 individuals of 25 bee species in 12 genera for pollinia: these were affixed to bees that visited A. syriaca for nectar and contain pollen packets that are vectored (e.g., transferred) between flowers. Of all bees sampled, pollinia were found only on the nonindigenous honeybee, Apis mellifera (43% of all bees identified), as well as one individual bumblebee, Bombus impatiens Cresson. Pollinia were recorded from 45.2% of all honeybees collected. We found no relationship between biomass of DSV and biomass of A. syriaca per site. There was a significant positive correlation between A. syriaca biomass and the number of pollinia, and the proportion vectored. No relationship with DSV biomass was detected for the number of pollinia collected by bees but the proportion of vectored pollinia declined with increasing DSV biomass. Although we find no evidence of DSV flowers attracting potential pollinators away from A. syriaca and other flowering plants, the impacts on native plant-pollinator mutualisms relate to its ability to outcompete native plants. As wild bees do not appear to visit DSV flowers, it could be altering the landscape to one which honeybees are more tolerant than native wild bees.

Visitação de orquídea por Melipona capixaba Moure & Camargo (Hymenoptera: Apidae), abelha ameaçada de extinção / Visitation of orchid by Melipona capixaba Moure & Camargo (Hymenoptera: Apidae), bee threatened with extinction

The stingless bee Melipona capixaba Moure & Camargo is a species restricted to the Atlantic forest in the Domingos Martins, Conceição do Castelo, Venda Nova do Imigrante and Afonso Cláudio County, in the Espírito Santo State, Brazil. Despite its cological importance as pollinator few studies have examined the ecology and biology of this bee. This note relates a case of the M. capixaba workers carrying pollinarium attached to the scuttellum. The pollinaria were identified as belonging to the orchid subtribe Maxillariinae species possibly of the genus Maxillaria sensu lato or Xylobium.

A abelha sem ferrão Melipona capixaba Moure & Camargo é uma espécie restrita à Mata Atlântica nos municípios de Domingos Martins, Conceição do Castelo, Venda Nova do Imigrante e Afonso Cláudio, ES. Apesar de sua importância ecológica como polinizador, poucos estudos têm investigado a biologia e ecologia dessa abelha, popularmente conhecida como uruçu-negra, pé-de-pau, ou uruçu-capixaba. Esta nota relata uma observação de operárias de M. capixaba carregando polinário preso ao escutelo. Os polinários foram identificados como pertencentes a uma espécie da subtribo Maxillariinae e, possivelmente, a um dos gêneros Maxillaria sensu lato ou Xylobium.