Bursa tract diverticulum in the hermaphroditic land snail Arianta arbustorum (Stylommatophora: Helicidae): morphology, function, and evolutionary implications

A bursa tract diverticulum is widespread in the female part of the hermaphroditic reproductive system of stylommatophoran pulmonates. However, the ultrastructure of the diverticulum is unknown and there is only anecdotal evidence for a spermatophore-dissolving function for this organ. In the present study, we examined the ultrastructure of the diverticulum and investigated histological, histochemical, and morphometric changes at different time intervals after mating in the simultaneously hermaphroditic land snail Arianta arbustorum. The diverticulum in this species of snail is a prominent organ, consisting of a luminal columnar epithelium surrounded by a thick layer of connective tissue. During mating, the diverticulum functions as the site of spermatophore uptake. Within the lumen of the diverticulum the spermatophore wall is dissolved or at least partly broken down. The digested material is taken up by epithelial cells and accumulated in molluscan-specific cells of the connective tissue, the so-called rhogocytes. Subsequent to copulation, the total diameter of the diverticulum increases markedly, reaching a maximum size 12 h after mating, while at the same time the thicknesses of the diverticulum wall and diverticulum epithelium decrease. The length of the diverticulum shows a positive allometry and a high phenotypic variation compared to snail size, which suggests that the diverticulum is under directional sexual selection. We propose that the diverticulum in A. arbustorum has evolved in response to selection pressures imposed by divergent evolutionary interests between male and female function.     

In situ studies of soil mineral N fluxes: Some comments on the applicability of the sequential soil coring method in arable soils

Is the sequential in situ incubation of undisturbed soil cores, developed for forest stands applicable to arable soils? The incubation of covered and uncovered soil cores allows the estimation of net nitrogen mineralization (NNM), plant nitrogen uptake (N_uptake) and potential leaching losses (N_trans). The amounts and temporal dynamics of these N fluxes were determined at four arable soils in a two-year study. Results suggest that: (i) the method can not be recommended for the estimation of N uptake and leaching losses, but (ii) it is suitable for the estimation of NNM; (iii) incubations should preferably be started when soil is moist; (iv) the length of incubation periods should be reduced (<4 weeks); (v) dynamics of NNM is mainly determined by temperature and moisture conditions if there is no interference by agricultural management. Inputs of straw, manure, slurry or green manure strongly influence the amount and the dynamics of NNM.