Landscape effects of a non-native grass facilitate source populations of a native generalist bug, Stenotus rubrovittatus, in a heterogeneous agricultural landscape.

Non-native plant species can provide native generalist insects, including pests, with novel food and habitats. It is hypothesized that local and landscape-level abundances of non-native plants can affect the population size of generalist insects, although generalists are assumed to be less sensitive to habitat connectivity than specialists. In a heterogeneous landscape in Japan, the relationship between the density of a native pest of rice (Stenotus rubrovittatus (Matsumura) (Heteroptera: Miridae)) and the abundance of Italian ryegrass (Lolium multiflorum Lam. (Poales: Poaceae)), a non-native meadow grass known to facilitate S. rubrovittatus, was analyzed. Statistical analyses of data on bug density, vegetation, and the spatial distribution of fallow fields and meadows dominated by Italian ryegrass, obtained by field surveys, demonstrated that local and landscape-level abundances of Italian ryegrass (the unmowed meadow areas within a few hundred meters of a sampling plot) positively affected bug density before its immigration into rice fields. Our findings suggest that a generalist herbivorous insect that prefers non-native plants responds to spatial availability and connectivity of plant species patches at the metapopulation level. Fragmentation by selective mowing that decreases the total area of source populations and increases the isolation among them would be an effective and environmentally-friendly pest management method.

Behavioural and morphological differences between feral and domesticated strains of common carp Cyprinus carpio.

Morphological and behavioural traits of a feral strain of the common carp Cyprinus carpio from Lake Biwa in Japan were compared with those of two domesticated strains reared in Japan (one commercial strain and one ornamental koi). To compare genetically inherited traits, all fish were reared from eggs under similar environmental conditions. Using these fish, the following five traits were compared among the three strains: body shape, consumption rate of two types of free-swimming shrimp, medaka Oryzias latipes and bottom-dwelling chironomid larvae prey items, preference for a bottom habitat, feeding skills in detecting prey and escape response to predator attack. The feral strain of fish had more streamlined bodies, higher consumption rates for free-swimming prey, a greater preference for a bottom habitat, possessed greater skill in detecting prey and were more cautious of predator attacks, compared with the fish of the two domesticated strains. These characteristics shown by the feral fish are probably adaptive to the natural environment. A genetic analysis based on five nuclear single nucleotide polymorphism markers, however, suggested that the feral strain was relatively recently derived from domesticated stocks. Considering this, the present results appear to indicate the possibility that domesticated C. carpio could re-adapt to the wild environment during a short evolutionary period, although further research using more feral strains is required.

Spatial genetic structure among and within populations of Primula sieboldii growing beside separate streams.

We investigated the hierarchical genetic structure of SSR (simple sequence repeats) and cpDNA (chloroplast DNA) polymorphisms among and within populations of Primula sieboldii, a heterostylous clonal herb. Seven out of eight populations at the study site, located in a mountainous region of Nagano Prefecture, had each developed alongside a different stream, and the other occurred on a flat area 70 m from the nearest stream. The magnitude of genetic differentiation among streamside populations in maternally inherited cpDNA (Phi = 0.341) was much higher than that in biparentally inherited SSRs (Phi = 0.011). This result suggests that seed dispersal among streams was restricted, and pollen was the primary agent of gene flow among streamside populations. In contrast, genetic differentiation among subpopulations within streams were low at both markers (Phi = 0.053 for cpDNA, Phi = 0.025 for SSR). This low differentiation among subpopulations in cpDNA compared with that among streamside populations suggest that seed dispersal occur along the stream probably during flooding. This hypothesis was supported by the fact that in cpDNA haplotypes, no clear genetic structure was detected within the streamside population, while a significant genetic structure was found within 20 m in the nonstreamside population. Furthermore, within the streamside populations, two pairs of ramets with identical multilocus genotypes for eight SSR loci were distantly (> 50 m) distributed along the same streamside, suggesting dispersal of clonal propagule. Our study showed that the heterogeneity of the landscape can influence gene flow and hence spatial genetic structure.

Patterns and consequences of self-pollen deposition on stigmas in heterostylous Persicaria japonica (Polygonaceae).

In order to test the "anti-interference" hypothesis for adaptive significance of reciprocal herkogamy, patterns of illegitimate pollination and effects of self-pollen on the legitimate pollination and fertility were investigated in a naturally pollinated experimental population of distylous Persicaria japonica. Pollen deposition was compared among the emasculation treatments, i.e., emasculation of a single flower from individual inflorescences, emasculation of all the flowers of individual inflorescences, and no emasculation control. In both morphs, considerable illegitimate pollination was found to occur in all the treatments, and there was no significant difference in incompatible pollen load among the treatments. Therefore, it is suggested that herkogamy of P. japonica can sufficiently reduce both intraflower and intra-inflorescence self-pollinations, but not interinflorescence geitonogamous and-or interclonal illegitimate pollination. Measurements of pollen load after the repetitive pollen addition showed that space on the stigma surface may not limit the legitimate pollination under natural pollination conditions. Seed sets after legitimate pollination following prior self-pollination did not differ from the controls without self-pollination. Therefore, there is little possibility that incompatible pollen load interferes with either pollination or fertilization by compatible pollen, suggesting that "anti-interference" is unimportant for adaptive significance of reciprocal herkogamy at least in P. japonica.

Combined effects of light and water availability on photosynthesis and growth of Arisaema heterophyllum in the forest understory and an open site.

Photosynthetic characteristics, leaf longevity and biomass accumulation of a threatened herb species, Arisaema heterophyllum, were studied in the understory of a riparian forest and at a neighboring deforested open site for 3 years in order to understand the combined effects of light and water availability. Light availability was 2- to 4-fold higher at the deforested than at the forest site during the growing season of the species, and precipitation varied considerably over the 3 years. Despite the difference in water availability among the years (dry in 1994 and 1996, and wet in 1995), the species showed a strong acclimation to the different light environments. Light-saturated assimilation rate on a leaf area basis, leaf mass area ratio (LMA), and relative growth rate (RGR) were all higher at deforested site. While a positive correlation between individual RGR and microsite light availability was found in the wet year, no correlation was found in the dry years, and mean RGR was significantly lower in the dry year at both sites. Leaf longevity, photosynthetic capacity on a leaf mass basis, dark respiration rate, and leaf conductance, varied considerably from year to year, especially in the plants at the open site, probably depending on water availability. In the dry years plants at the deforested sites showed a lower photosynthetic rate and leaf conductance under unwatered than under watered conditions. These results suggest that the water availability in a given year may strongly affect light acclimation and annual RGR of the herb species in natural habitats, even under mesic climate conditions.