The effects of endangered freshwater pearl mussels on channel morphology and flow in a low-gradient sandy river

Conservation of ecosystem engineers, which modulates the surrounding habitat by causing physical state changes in biotic or abiotic materials, is important for maintaining the functional integrity of ecosystems. This study examined the effects of endangered freshwater pearl mussels (Margaritifera laevis and M. togakushiensis) on channel morphology and flow in a low-gradient sandy river. For this, we performed a field removal experiment of mussels using three treatments in twelve 10-m reaches. Mussel abundance and biomass, and three physical variables were measured before, immediately after, and two months to one year after the treatments. Mussel removal resulted in channel degradation with a 60% increase in flow depth, a 30% decrease in current velocity, and a 50% reduction in the width-to-depth ratio two months after the treatments, whereas minimal changes were measured in reaches with mussels. The results indicated that pearl mussels act as an ecosystem engineer affecting the channel morphology and flow of sandy rivers. The conservation of the pearl mussel populations is key to preserving their far-reaching benefits in ecosystem integrity including habitats for other various organisms

The mechanisms underlying the effects of AMH on Mullerian duct regression in male mice

Anti-Mullerian hormone (AMH) produced in the developing testis induces the regression of the Mullerian duct, which develops into the oviducts, uterus and upper vagina. In our true hermaphrodite mouse with an ovary on one side and a testis on the other (O/T), the oviduct and uterus are present only on the ovary side, and nothing derived from the Mullerian duct is present on the testis side. Here, we investigate the mechanism underlying the unilateral Mullerian duct regression and the mode of AMH signaling, by performing immunohistology, Western blotting, and organ culture analyses. The histological analysis revealed that during the start of the Mullerian duct regression, the duct in the O/T mice was clearly regressed on the AMH-positive testis side compared to the AMH-negative ovary side. The immunohistochemistry showed a diffuse immunoreaction of AMH in the interstitium surrounding the testis cord and boundary region between the testis and mesonephros, especially in the cranial portion. Western blotting revealed that the amount of AMH in the cranial half of the mesonephros was larger than that in the caudal half. AMH injected into the gonads in organ culture induced the regression of the Mullerian duct via the interstitium of the organ. These results suggest that AMH acts on the Mullerian duct in male mice by exuding into the interstitium surrounding the testis cord and infiltrating through the cranial region from the testis to the mesonephros

Genetic differences between C57BL/6 substrains affect the process of testis differentiation in Y-POS mice

C57BL/6J-XYPOS (B6J-XYPOS) mice, which have the Y chromosome derived from Mus musculus poschiavinus on a B6J genetic background, form ovotestes or ovaries. Previously, we replaced the genetic background of B6J-XYPOS mice with B6N and found that individuals with testes also appeared in addition to those with ovaries or ovotestes. To investigate the effect of the B6J genetic sequence on the testis differentiation, the genetic background of B6N-XYPOS mice was replaced with B6J again. The recovery of the B6J genetic background significantly decreased the incidence of testes; only ovaries developed. These results indicate that the testicular differentiation process tends to be perturbed especially in the B6J substrain. This shows the importance of substrain differences in mice usually treated as B6 collectively