Kenji Suetsugu

Host Range and Selectivity of the Hemiparasitic Plant Thesium chinense (Santalaceae)

BACKGROUND AND AIMS Thesium chinense is a hemiparasitic plant that is common in grassland habitats of eastern Asia. Although the physiology of Thesium has been well studied in attempts to control its weedy habit, there have been few ecological investigations of its parasitic life history. Thesium chinense is thought to parasitize species of Poaceae, but evidence remains circumstantial. METHODS A vegetation survey was conducted to test whether any plant species occurs significantly more often in plots with T. chinense than expected. In addition, haustorial connections were examined directly by excavating the roots and post-attachment host selectivity was evaluated by comparing the observed numbers of haustoria on different hosts against those expected according to the relative below-ground biomass. Haustorium sizes were also compared among host species. KEY RESULTS Only two of the 38 species recorded, Lespedeza juncea and Eragrostis curvula, occurred more often in plots with Thesium than expected. In contrast to this, T. chinense parasitized 22 plant species in 11 families, corresponding to 57.9 % of plant species found at the study site. Haustoria were non-randomly distributed among host species, suggesting that there is some post-attachment host selectivity. Thesium chinense generally preferred the Poaceae, although haustoria formed on the Fabaceae were larger than those on other hosts. CONCLUSIONS This is the first quantitative investigation of the host range and selectivity of hemiparasitic plants of the Santalales. The preference for Fabaceae as hosts may be linked to the greater nutrient availability in these nitrogen-fixing plants.

Autogamous fruit set in a mycoheterotrophic orchid Cyrtosia septentrionalis

Non-photosynthetic mycorrhizal plants (i.e. mycoheterotrophs) have long attracted interest due to their bizarre morphological features. Nonetheless, few studies have reported on the reproductive biology of these mycoheterotrophs. In the present study, the pollination mechanism of the mycoheterotrophic orchid Cyrtosia septentrionalis (Rchb.f.) Garay in central Japan was investigated. In spite of their showy appearance, flowers of C. septentrionalis failed to attract pollinators and possessed an effective self-pollination system, in which the rostellum was poorly developed and lost the ability to physically separate the stigma and pollinia, thus allowing contact between them. Comparable fruit set ratio was also obtained in bagged plants and following induced autogamous and xenogamous pollinations. These results indicate that the species is capable of outbreeding, but self-compatible and not pollinator-limited for fruit set under natural condition. These pollination mechanisms may be adaptations to survive the shaded and sparse herbaceous understory, where insect-pollinators are limited.

Pollination biology of the endangered orchid Cypripedium japonicum in a fragmented forest of Japan

Pollination biology studies of the endangered orchid Cypripedium japonicum were conducted in its natural habitat using pollinator observation and hand-pollination experiments. The observed fruit set was as follows: artificial outcross-pollinated, 100%; artificial self-pollinated, 100%; pollinator-excluded, 0%; and emasculated flowers, 0%. These results show that this species, although self-compatible, is neither autogamous nor agamospermous. The fruit set for open-pollinated flowers was 14.9%, which suggests that the study population was subject to pollinator limitation. The nectarless flowers of C. japonicum were exclusively visited and pollinated by the queens of two bumblebee species (Bombus ardens and B. diversus diversus). It is probable that the nectarless flowers of C. japonicum attract pollinators through a generalized food deceptive system.

Consumption of Habenaria sagittifera pollinia by juveniles of the katydid Ducetia japonica

While Habenaria (Orchidaceae) is a species‐rich genus and the orchid diversification is considered to be tightly related to its diverse pollination system, floral visitors of few Habenaria spp. have been studied. Here, we investigated the diurnal floral visitors of Habenaria sagittifera. While Orthoptera have not been considered a regular floral visitor, we observed that juvenile katydid Ducetia japonica (Tettigoniidae) regularly visited and consumed the pollinia and anther caps of H. sagittifera. The relationship between Habenaria and Ducetia would not be a tight mutualism. However, the regular visitation and pollinia consumption may showcase the evolutionary route to Orthoptera–orchid pollination mutualism.

Avian seed dispersal in a mycoheterotrophic orchid Cyrtosia septentrionalis

Orchids produce remarkably small seeds lacking endosperm, which are considered to be predominantly wind-dispersed. Here, we report avian seed dispersal in a mycoheterotrophic orchid Cyrtosia septentrionalis, which occurs under closed canopies where wind is less dependable. Because some orchids occupy similar habitats and have fleshy fruits, shifts in seed dispersal strategy may be a previously unnoticed mechanism promoting the orchids evolutionary success.

Autonomous self-pollination and insect visitors in partially and fully mycoheterotrophic species of Cymbidium (Orchidaceae)

Few studies have examined the reproductive ecology of mycoheterotrophic plants, but the existing literature hypothesizes that they adopt a self-pollinating strategy. Although growing evidence indicates that some rewarding mycoheterotrophic plants depend (at least partially) on an insect-mediated pollination system, it remains unclear whether some mycoheterotrophic plants can attract pollinators without nectar or other rewards. Moreover, in a broader evolutionary/ecological context, the question of whether the evolution of mycoheterotrophy induces a shift in pollination pattern is still unknown. Here I present a comparative investigation into the breeding system of two fully mycoheterotrophic orchids, Cymbidium macrorhizon and C. aberrans, and their closest extant relative, the mixotrophic C. lancifolium. Pollination experiments were conducted to determine the breeding system of these plants. In addition, flower visitors that might contribute to pollination were recorded. Flowers at different maturity stages were examined to investigate mechanisms enabling or limiting self-fertilization. While nectarless flowers of C. lancifolium and C. macrorhizon can successfully attract potential pollinator honeybees, all three Cymbidium possess an effective self-pollination system in which the rostellum that physically separates the stigma and pollinia is absent. Because mixotrophic and mycoheterotrophic Cymbidium occupy low-light niches, pollinator foraging would be negatively influenced by low-light intensity. In partial and fully mycoheterotrophic Cymbidium, autogamy would likely be favoured as a reproductive assurance to compensate for pollinator limitation due to their lack of nectar and pollinators’ hostile habitat preferences.

Moth floral visitors of the three rewarding Platanthera orchids revealed by interval photography with a digital camera

We investigated the insect visitors of Platanthera ussuriensis, Platanthera sachalinensis and Platanthera florentii, which might contribute to pollination, using a digital camera with automatic interval photography. Monitoring was conducted for a total of five nights (45 hours), and during every night, at least one moth species visited. The total number of pictures taken and pictures taken of moths were 3607 and 152, respectively. We concluded, based on our findings, that Geometridae and Noctuidae moths probably pollinated P.florentii and P.sachalinensis, respectively, whereas no pollinia attachment or removal was observed in P. ussuriensis during the intensive visit of the Crambidae moth.

Moths Visiting the Flowers of the Orchid Platanthera japonica

There are approximately 24,500 orchid species already reported, and they are one of the most diverse angiosperm families (Dressler, 2005). Orchids are biologically complex, and as such are proposed as an appealing way to study many of our most fundamental questions on biology. Orchid flowers allow researchers to study the development and evolution of pollination biology and flower forms, as they showcase a great example of the close relationship between plants and their pollinators (Duttke et al., 2012). The orchid’s floral complexity is one of the key factors in the rapid species radiation (Waterman and Bidartondo, 2008). For example, some of the features found on orchids—such as nocturnally emitted fragrance, whitish colorations, and long narrow spurs—are clues to pollination by moths (Hapeman and Inoue, 1997). Despite the great interest in orchid biology and diversity, little is known about their pollination biology in many taxa (Widmer et al., 2000). Therefore, it is primarily important to increase the observations of orchid pollinations in order to expand our understanding of the specificity of orchid-pollinator interactions. It is, unfortunately, challenging to directly observe pollination events in orchids. This is because during a flowering season, the proportion of flowers visited is generally low (Neiland and Wilcock, 1995). The long life-span of individual flowers combined with low population densities con tri butes to making pollination observation particularly time-consuming and tedious (Wid mer et al., 2000). It appears that Platanthera has become extremely diversified, both in its pollination system and its floral form (Hapeman and Inoue, 1997). Platanthera flow ers range in color from purple or orange to green and white. They may have a “fringed” appearance due to the elaborate dissections of the petals and labellum. All species have a nectar spur on the lip, the length of which may be greater than 4cm in some taxa (Hapeman and Inoue, 1997). Though most of the species are pollinated by pyralid and noctuid moths, pollination by mosquitoes, bees, butterflies, beetles and flies have also been observed (Inoue, 1983; Inoue, 1985; Hapeman and Inoue, 1997). The diverse pollination systems within Pla tan thera corresponds to most of the Orchidaceae’s non-deceptive pollination types (Van Der Pijl and Dodson, 1966). Phylogenetic analysis suggests that Pla tanthera’s basal condition can involve generalized pollination by pyralid and noctuid moths, while hawkmoth (Sphigidae) polli nation—which requires only minimal modification from the green to the greenish-white floral syndrome found in most 78 ENTOMOLOGICAL NEWS

Independent recruitment of a novel seed dispersal system by camel crickets in achlorophyllous plants

The seeds of most heterotrophic plants, commonly referred to as dust seeds, are typically dispersed in the air like dust particles. Therefore, little attention has been paid to how seeds of heterotrophic plants are dispersed, owing to the notion that wind dispersal is the dominant strategy. However, inconspicuous but fleshy, indehiscent fruit can be observed in distantly related plants that have independently evolved full heterotrophy. Here I investigated the seed dispersal system in three unrelated fully heterotrophic plants with fleshy, indehiscent fruits (Yoania amagiensis, Monotropastrum humile and Phacellanthus tubiflorus) by direct observation, a differential exclusion experiment of fruit feeders and investigation on seed viability through the digestive tract. The present study revealed that camel crickets are the major seed disperser in three achlorophyllous plants in the study population. This represents the first evidence of seed dispersal by camel crickets in any angiosperm species. These heterotrophic plants grow in the understorey of densely vegetated forests where wind is probably an ineffective seed dispersal agent. Life-history traits of the achlorophyllous plants associated with heterotrophic lifestyles, such as colonization of dark understorey habitats and dust seeds, could facilitate independent recruitment of the novel endozoochorous seed dispersal system by camel crickets.

Autonomous self‐pollination in the nectarless orchid Pogonia minor

The pollination biology of the nectarless orchid Pogonia minor was investigated in central Japan. The investigation revealed that the solitary flowers failed to attract pollinators, while high rates of fruit set were observed in the natural population. Comparable levels of fruit set were obtained in bagged, artificial self-pollinated and artificial cross-pollinated plants, indicating that the species is not pollinator-limited for fruit set under natural conditions. Autonomous self-pollination in P. minor resulted from a reduced rostellum, which allowed contact between the pollinia and the stigma. Self-pollination is thought to be an adaptive response that provides reproductive assurance under conditions of pollinator limitation. Since pollen limitation is generally known to be frequent among deceptive orchids, strong pollen limitation is probably a driving force in the autonomous self-pollination mechanism in the nectarless orchid P. minor.