Distribution of Holtodrilus truncatus, a Branchiobdellidan Ectosymbiotic on Atyid Shrimps in the Kii Peninsula, Western Japan, with Reference to Salinity Tolerance and Host Preference.

The distribution of the branchiobdellidan Holtodrilus truncatus (Liang, 1963), which is symbiotic on atyid shrimps, was surveyed in 26 river catchments, covering almost all of the Kii Peninsula, western Japan. Holtodrilus truncatus has been recorded in 10 rivers located from the southwest to northeast regions of the peninsula. Paratya compressa was the dominant host species in all rivers, with a lower prevalence on Caridina leucosticta, C. multidentata, C. typus, and Neocaridina denticulata. The longitudinal distribution of H. truncatus was limited to the middle and upper reaches, while its main host P. compressa occurred widely from the lower to the upper reaches. The numbers of H. truncatus and their cocoons per host increased in summer and decreased in winter, in accordance with the abundance of the host P. compressa. The body size of P. compressa was larger in individuals with H. truncatus than those without H. truncatus in some rivers, while in another river, sizes of the two groups were not different. A salinity tolerance experiment revealed that the threshold of salinity tolerance of H. truncatus occurred between 0-0.5%. A choice experiment between two host species showed that H. truncatus preferred C. leucosticta to C. multidentata, P. compressa to C. multidentata, and P. compressa to C. leucosticta.

A macro-scale perspective on within-farm management: how climate and topography alter the effect of farming practices.

Organic farming has the potential to reverse biodiversity loss in farmland and benefit agriculture by enhancing ecosystem services. Although the mixed success of organic farming in enhancing biodiversity has been attributed to differences in taxa and landscape context, no studies have focused on the effect of macro-scale factors such as climate and topography. This study provides the first assessment of the impact of macro-scale factors on the effectiveness of within-farm management on biodiversity, using spiders in Japan as an example. A multilevel modelling approach revealed that reducing pesticide applications increases spider abundance, particularly in areas with high precipitation, which were also associated with high potential spider abundance. Using the model we identified areas throughout Japan that can potentially benefit from organic farming. The alteration of local habitat-abundance relations by macro-scale factors could explain the reported low spatial generality in the effects of organic farming and patterns of habitat association.