Pollination by fungus gnats in four species of the genus Mitella (Saxifragaceae)

The first example of pollination by fungus gnats in the eudicots is reported. The genus Mitella (Saxifragales) is characteristically produces minute, inconspicuous, mostly dull-coloured flowers with linear, sometimes pinnately branched, petals. To understand the function of these characteristic flowers, we studied the pollination biology of four Mitella species with different floral traits and different sexual expression: dioecious M. acerina , gynodioecious M. furusei var. subramosa , and hermaphroditic M. stylosa var. makinoi and M. integripetala. Flower-bagging experiments showed that wind pollination did not occur in the dioecious and gynodioecious species. Two years of observations of flower visitors at six study sites in Japan revealed that the principal pollinators of all four Mitella were specific species of fungus gnats (Mycetophilidae), which landed on the flowers with their long spiny legs settling on the petals. Characteristically, numerous pollen grains were attached to the fungus gnats in specific locations on the body. Although, on average, 1.3–2.6 fungus gnats visited each inflorescence per day, the fruit set of both bisexual and female flowers exceeded 63%. These results suggest that fungus gnats are highly efficient pollinators of Mitella spp., and that Mitella flowers are morphologically adapted to pollination by fungus gnats.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 144 , 449–460.     

LOCALIZATION AND SEGREGATION OF MATERNAL RNA'S DURING EARLY CLEAVAGE OF XENOPUS LAEVIS EMBRYOS

The localization and segregation of maternal RNA's during early cleavage of Xenopus laevis embryos were studied. Blastomeres and hemispheres of eggs and early embryos were separated manually and the amounts of ribosomal RNA and poly(A) ⁺RNA extracted from each blastomere and hemisphere were determined by optical density measurement and by ³H-poly(U) hybridization, respectively. It was found that both kinds of the maternal RNA's were more abundant (two-thirds of the total) in the animal hemisphere (cells), while they were evenly distributed between the dorsal and ventral halves. This pattern of localization remained unchanged from the egg to the blastula stage, indicating that these maternal RNA's were segregated into blastomeres quite simply by cell division. Gel electrophoresis showed that the size distributions of poly(A) ⁺RNA and poly(A) sequences obtained from different blastomeres of 8-cell embryos did not differ greatly. It was also found that cytoplasmic polyadenylation of maternal RNA, which occurs during early cleavage and blastulation, took place equally in all regions of the cleaving embryos, suggesting no regional difference in the localization of maternally inherited nonpolyadenylated RNA. These observations are discussed in relation to previous findings on differences along the animal-vegetal and dorsal-ventral axes of the early amphibian embryo.     

Coexistence of two congeneric tree species of Lauraceae in a secondary warm‐temperate forest on Miyajima Island,south‐western Japan

We analyzed the spatial distributions of two congeneric tree species, Neolistea aciculata and Neolistea sericea (Lauraceae), in a warm‐temperate forest on Miyajima Island, south‐western Japan. Both species were mainly found in valley sites on the island. Hence, these species shared the same topographic habitat niche. However, we found a clear difference between the spatial distributions of the two species in relation to the light environment. Neolistea aciculata was predominantly found in stands with low light, such as beneath the canopy of dense evergreen broadleaved forest. In contrast, N. sericea was predominantly associated with ample light, such as in secondary Pinus densiflora forest. In stands with moderate light conditions, both species were found. This habitat niche segregation in relation to light conditions presumably allows the coexistence of these two species in the predominantly successional forest on Miyajima Island.     

Leaf Anatomy and Carbon Discrimination in NAD-malic Enzyme Panicum Species and their Hybrids Differing in Bundle Sheath Cell Ultrastructure

The relationship between leaf anatomy, ultrastructure and carbondiscrimination was investigated in leaves of two F₁hybrids (F₁-1and F₁-2) between two different types of the grassPanicum [anNAD-malic enzyme (ME) C₄species], which differ in bundle sheathultrastructure. The female parent was Kabulabula grass, whichhas centrifugal chloroplasts in bundle sheath cells and is designatedan NAD-ME(F) species, while the male parent was Makarikari grass,which has centripetal chloroplasts in the bundle sheath cellsand is designated an NAD-ME(P) species. Suberin lamellae arepresent in Kabulabula grass but are lacking in Makarikari grass.Both F₁hybrids had the same chromosome number (2n =36) as theparents but exhibited both univalent (about 45%) and bivalent(about 55%) chromosome pairing which was the major basis forthe identification of F₁hybrids. In F₁-1, elongated bundle sheathcell chloroplasts are arranged mainly in a centripetal position,similar to those in the male parent, Makarikari grass. In contrast,most of the bundle sheath cells in F₁-2 are packed with starch-containingchloroplasts, although in some cells chloroplasts tended tobe centripetally arranged. In both F₁hybrids, suberin lamellaewere found in the bundle sheath cell walls, similar to the femaleparent, Kabulabula grass. The ¹³C values of both F₁hybrids were-11.4 to -11.7, almost the same as those of Kabulabula grass(-11.4), but significantly higher than those of Makarikari grass(-12.7). These results indicate that the chloroplast orientationin the bundle sheath cells and the presence of suberin lamellaeare not obligatorily linked in their expression and suggestthat suberin lamellae may play an important role in discriminationagainst¹³C. Panicum ; NAD-malic enzyme species; hybrid; chloroplast position; ¹³C discrimination; suberin lamellae     

Parasitoid aggregation and interference in host–parasitoid dynamics

1. Parasitoids do not distribute themselves evenly among available patches, which has an important bearing on the dynamics of host–parasitoid interactions. This study examined the density‐dependent nature of aggregation of the parasitoid Dirhinus giffardii Silvestri on the oriental fruit fly host, Bactrocera dorsalis (Hendel) distributed among discrete patches. 2. Four artificial patches were created in a cage, and the number of hosts in each patch was manipulated. Parasitoids were released into the cage, and whether parasitoid density and host density influence the degree of parasitoid aggregation was examined. 3. Parasitoid aggregation became stronger (e.g. uneven distribution among patches) as the parasitoid density decreased and also as the host density increased. The index of parasitoid aggregation was not influenced by the distribution of hosts among patches. 4. The empirically characterised aggregation pattern was incorporated in a host–parasitoid model that consists of one host and one parasitoid species. The analysis of the model shows that an unstable system (i.e. the coexistence of the host and parasitoid is impossible) can be stabilised (i.e. coexistence is possible) when the parasitoid aggregates in a way that is consistent with the pattern found in the experiment.     

Seedling Establishment of a Canopy Tree Species in Malaysian Tropical Rain Forests

Abstract Unlike many other canopy tree species in tropical rain forests, Dryobalanops aromatica (Dipterocar-paceae, local name: Kapur) establishes monospecific dominant (monodominant) forests in Peninsular Malaysia. In natural conditions, monodominance of Kapur does not necessarily mean low species diversity of the Kapur forests. While the emergent canopy layer is occupied by Kapur, many other plant species, which are common to lowland dipterocarp primary forests in the same region, are found in lower canopy layer and understory.
To understand the ecological implications of the monodominance of Kapur, we monitored post dispersal survival and seedling establishment in a pure stand of Kapur in a plantation in Kepong, near Kuala Lumpur. Immediately after seed fall, seeds and cotyledon-stage seedlings suffered high predation by vertebrates such as rodents. The predation pressure was higher in a more general fruiting year (1991) than in a sporadic fruiting year (1992). In contrast to the high mortality of seeds and newly emerged seedlings, seedlings surviving to the six-leaf stage showed low mortality, which allowed the establishment of a sapling bank.
The occurrence of saplings of Kapur with a wide range of size classes in natural forests indicates that this species is more shade tolerant than other dipterocarp species such as the Shorea group and that it could well respond to enhanced light conditions caused by canopy opening. These characteristics may partly contribute to maintaining monodominance of Kapur.