Food web structure of the fungivorous insect community on bracket fungi in a Bornean tropical rain forest

1. If fungivorous insect diversity is maintained by host specialisation on particular fungi, it should be higher in the tropics than in temperate or boreal regions owing to high macrofungus species diversity. 2. To reveal the community and food web structure of fungivorous insects on bracket fungi, fungivorous insects were collected from 427 fruiting bodies belonging to 22 genera throughout the development and deterioration process in a 3‐ha plot of lowland dipterocarp tropical rain forest on Borneo Island. 3. Eight hundred and twenty‐nine individuals of 82 coleopteran species in 13 families from 111 fruiting bodies of 15 fungal genera were collected. Tenebrionidae and Staphylinidae were most common. Fifty‐three and 19 insect species were observed on Ganoderma and Phellinus, respectively. The numbers of insect species and individuals on a particular fungal genus were positively correlated with the abundance of that fungal genus. 4. Quantitative food web analysis revealed a high degree of specialisation at the whole‐community level. At least 65% of insect individuals were observed on Ganoderma at every stage of development and deterioration. Diverse insects coexist on one dominant fungal genus, Ganoderma, in contrast to our hypothesis. 5. The high abundance of Ganoderma fruiting bodies, which lack obvious defences against insect feeding, probably influences the bracket fungus–insect food web in this tropical rainforest.     

The oxygen supply to thermogenic flowers

Thermogenic flowers produce heat by intense respiration, and the rates of O₂ consumption (?o₂) in some species can exceed those of all other tissues of plants and most animals. By exposing intact flowers to a range of O₂ pressures (Po₂) and measuring ?o₂, we demonstrate that the highest respiration rates exceed the capacity of the O₂ diffusive pathway and become diffusion limited in atmospheric air. The male florets on the inflorescence of Arum concinnatum have the highest known mass‐specific ?o₂ and can be severely diffusion limited. Intact spadices of Japanese skunk cabbage Symplocarpus renifolius are diffusion limited in air only when ?o₂ is maximal, but not at lower levels. True flowers of the sacred lotus Nelumbo nucifera and the appendix of Arum concinnatum are never diffusion limited in air. ?o₂ – Po₂ curves are evaluated quantitatively with the ‘Regulation Index’, a new tool to measure dependence of ?o₂ on ambient Po₂, as well as the conventional ‘Critical Po₂’. The study also includes measurements of Po₂ within thermogenic tissues with O₂‐sensitive fibre optics, and reveals that the diffusion pathway is complicated and that O₂ can be provided not only from the surface of the tissues but also from the pith of the flower's peduncle.     

Hybridization involving independent gametophytes in the Vandenboschia radicans complex (Hymenophyllaceae): a new perspective on the distribution of fern hybrids

To test our hypothesis of hybrid formation involving the ‘independent gametophyte’ phenomenon in ferns, we identified the genomic formulae and ploidy level of gametophytes of the Vandenboschia radicans complex at the periphery of a sporophyte population. We identified haploid gametophytes of V. kalamocarpa (one of the two putative parents of V.×stenosiphon) in a hybrid sporophyte population in Japan that lacks fertile non‐hybrid individuals. Furthermore, diploid sporophytes of the species were not found within a 50‐km radius. This finding supports a hypothesis of hybridization involving the ‘independent gametophyte’ phenomenon and provides a new perspective on the geographical distribution of fern hybrids.     

Life-history traits in insect inclusions associated with bamboo galls

We examined the life-history traits of insect inclusions in bamboo galls induced by the gall maker, Aiolomorphus rhopaloides Walker (Hymenoptera: Eurytomidae) in a bamboo stand. Eight hymenopteran and one dipteran species were detected using soft X-ray photography of the galls and insect emergence from the galls. Aiolomorphus rhopaloides was the gall maker and Diomorus aiolomorphi Kamijo (Torymidae) was its inquiline.Homoporusjaponicus Ashmead (Pteromalidae) and Eupelmus sp. (Eupelmidae) are likely to be primary parasitoids of the larva ofA. rhopaloides. Eurytoma sp. (Eurytomidae),Sycophila sp. (Eurytomidae) and Norbanus sp. (Pteromalidae) are thought to be facultative hyperparasitoids. Cecidomyiidae sp. is thought to be the inquiline ofA. rhopaloides galls.Leptacis sp. (Platygastridae) probably parasitizes the larvae of Cecidomyiidae sp. Larvae of A. rhopaloides appeared in galls in July with the percentage of larvae decreasing in September, before overwintering as pupae. The growth ofD. aiolomorphi larvae within galls may be faster than that ofA. rhopaloides. The percentage of parasitoids in galls was low in July, but increased until winter. Aiolomorphus rhopaloides and D. aiolomorphi emerged from mid-April to early May, and from late April to early June, respectively. From overwintering galls, six other hymenopteran species emerged between late May and late June; one dipteran Cecidomyiidae sp. emerged between mid-April and early May.     

Airborne‐pollen pool and mating pattern in a hybrid zone between Pinus pumila and P. parviflora var. pentaphylla

The reproductive isolation barriers and the mating patterns among Pinus pumila, P. parviflora var. pentaphylla and their hybrids were examined by flowering phenology and genetic assays of three life stages: airborne‐pollen grains, adults and seeds, in a hybrid zone on Mount Apoi, Hokkaido, Japan. Chloroplast DNA composition of the airborne‐pollen was determined by single‐pollen polymerase chain reaction. Mating patterns were analysed by estimating the molecular hybrid index of the seed parent, their seed embryos and pollen parents. The observation of flowering phenology showed that the flowering of P. pumila precedes that of P. parviflora var. pentaphylla by about 6 to 10 days within the same altitudinal ranges. Although this prezygotic isolation barrier is effective, the genetic assay of airborne‐pollen showed that the two pine species, particularly P. pumila, still have chances to form F₁ hybrid seeds. Both parental species showed a strong assortative mating pattern; F₁ seeds were found in only 1.4% of seeds from P. pumila mother trees and not at all in P. parviflora var. pentaphylla. The assortative mating was concluded as the combined result of flowering time differentiation and cross‐incompatibility. In contrast to the parental species, hybrids were fertilized evenly by the two parental species and themselves. The breakdown of prezygotic barriers (intermediate flowering phenology) and cross‐incompatibility may account for the unselective mating. It is suggested that introgression is ongoing on Mount Apoi through backcrossing between hybrids and parental species, despite strong isolation barriers between the parental species.