Island properties dominate species traits in determining plant colonizations in an archipelago system

The extrinsic determinants hypothesis emphasizes the essential role of environmental heterogeneity in species’ colonization. Consequently, high resident species diversity can increase community susceptibility to colonizations because good habitats may support more species that are functionally similar to colonizers. On the other hand, colonization success is also likely to depend on species traits. We tested the relative importance of environmental characteristics and species traits in determining colonization success using census data of 587 vascular plant species collected about 70 yr apart from 471 islands in the archipelago of SW Finland. More specifically, we explored potential new colonization as a function of island properties (e.g. location, area, habitat diversity, number of resident species per unit area), species traits (e.g. plant height, life-form, dispersal vector, Ellenberg indicator values, association with human impact), and species’ historical distributions (number of inhabited islands, nearest occurrence). Island properties and species’ historical distributions were more effective than plant traits in explaining colonization outcomes. Contrary to the extrinsic determinants hypothesis, colonization success was neither associated with resident species diversity nor habitat diversity per se, although colonization was lowest on sparsely vegetated islands. Our findings lead us to propose that while plant traits related to dispersal and establishment may enhance colonization, predictions of plant colonizations primarily require understanding of habitat properties and species’ historical distributions.     

Spatial pattern of pine wilt disease caused byBursaphelenchus xylophilus (Nematoda: Aphelenchoididae) within aPinus thunbergii stand

To understand the mechanism of spread of pine wilt disease caused by the pinewood nematode, Bursaphelenchus xylophilus, which is vectored by a cerambycid, Monochamus alternatus, the spatial distribution of trees weakened by the nematode was examined within a Pinus thunbergii stand from June to October for 4 years. The weakened trees were distributed in a clumped pattern in 1980 and 1981, at an early stage of infestation. In many cases, they showed a double-clumped pattern. The degree of aggregation was higher in June or July than after August. They were uniformly distributed in June or July 1982 and in June 1983 whereas they showed a double-clumped pattern after August. The trees were frequently weakened in June or July when they were near the trees weakened during the previous year. At quadrat sizes of more than 25 m², spatial overlapping was pronounced between trees weakened during June–July of the current year and those weakened in the previous year. The seasonal changes in spatial distribution of weakened trees were explained by the interaction among M. alternatus, B. xylophilus and Pinus trees.     

Dorsal and Ventral Hippocampal Sharp-Wave Ripples Activate Distinct Nucleus Accumbens Networks

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A range wide geographic pattern of genetic diversity and population structure of Hexinia polydichotoma (Asteraceae) in Tarim Basin and adjacent areas

In order to investigate the genetic diversity and influence of climate oscillations on evolutionary processes of organisms in northwest China, we selected Hexinia polydichotoma, a species endemic to China, and examined the geographic pattern of genetic variation in its entire cover range, Tarim Basin and adjacent areas. In the study, 22 chloroplast (cp) haplotypes were identified based on two cpDNA sequences (trnH–psbA and ycf6–psbM), and five ITS sequence variations were found. Shown in the cp haplotype network, the two common cp haplotypes mainly distributed along the northern and southern rims of the basin respectively and intersected in the center of the basin, whereas in the ITS network, ITS genotype 1 was widespread across the whole distribution area, and rare genotypes were concentrated in the western rim of the basin. Genetic variation primarily occurred among populations and SAMOVA groups. Fragmented desert habitat may have caused gene flow barrier among populations or groups far from each other, leading to significant genetic differentiation at these levels. It appears that expansion and contraction cycles of river systems and oases during the middle Pleistocene was the source of the observed fragmentation. Geographic range expansion in H. polydichotoma was supported by the significant value for Tajima's D, Fu's F_S, and by a unimodal mismatch distribution. It was possible that the enlargement of the Taklimakan Desert during the middle Pleistocene may have provided appropriate conditions for the range dispersal. We identified western rim of the basin as the center of genetic diversity of H. polydichotoma based on the present dataset.     

Goldfish use the visual angle of a familiar landmark to locate a food source

Three goldfish were trained to search for food buried 20 cm from a perspex tower. In the absence of food, all fish still searched in the correct location, revealing that fish can use a landmark to locate food. Halving either the width or height of the landmark resulted in searches significantly closer to the tower, suggesting that fish determined their position relative to the landmark using its horizontal and vertical visual angles.