Reproductive traits of the freshwater oyster Etheria elliptica (Bivalvia: Etheriidae) in the Pendjari River,Benin: implications for conservation

The African freshwater oyster Etheria elliptica, which is of great economic importance throughout the continent, is facing overharvesting in many fisheries in West Africa. Its reproductive traits (sex ratio, size at sexual maturity, oocyte diameter and fecundity) were studied at four stations located along the Pendjari River, northern Benin, in April 2013. Histological techniques were implemented to identify sex and gonad development stages. Oocyte sizes were measured based on the histological images and mean oocyte diameter was 38 µm. Fecundity, estimated by counting the developing eggs, averaged 106 724 eggs and increased significantly with shell size. The average sex ratio was approximately 1:1. Hermaphrodites were rare. Males reached sexual maturity at 57.6 mm dorsoventral height, earlier than females at 64.7 mm. The majority of the oyster specimens were in ripe-spawning stages, indicating that reproductive activities partly took place towards the end of the dry season. Both mature and immature individuals were subjected to harvesting at all the investigated fishing sites. The mean size of exploited oysters was 60.6 mm, lower than the size of females at maturity. Management strategies must enforce the minimum size of 65 mm required for harvesting, particularly in open access sites where juveniles are mostly harvested.     

Location of the stigmatic areas in Mutisia speciosa Aiton ex Hook. a new floral feature in Asteraceae

In Mutisieae species, the style branches are described as short and the stigmatic areas cover the inside of the style branches. As shown in preliminary observations, the Mutisia speciosa florets had long style branches (7 mm), bifurcate only at the apex (about 1.5 mm) and juxtaposed along the remaining length. The objective was to locate the stigmatic areas in M. speciosa. For this purpose, neutral red, 3% hydrogen peroxide and hand pollinations were used. For the pollinations, florets with cut apical portion of the branches (about 2 mm) and florets with intact branches were used. In the first group of florets, the pollen was deposited along the margins of the juxtaposed branches (about 5 mm), and in the second, the pollen was ventrally deposited on the bifurcated apical portion. Some of these florets were left on the plant until fruiting and others were analyzed under a fluorescence microscope to check pollen tube growth. The neutral red test defined two ventro-marginal bands fused at the apex of each style branch, consisting of papillose cells. Intense bubbling in the hydrogen peroxide test showed that only the bands are receptive. The pollinations resulted in fruit sets and growth of pollen tubes, confirming that the bands are receptive along their entire length. This result is new and indicates the need for further studies on the floral biology of tropical Asteraceae species to improve the understanding of their reproductive attributes.     

Rheological properties of cross-linked hyaluronan-gelatin hydrogels for tissue engineering

Hydrogels that mimic the natural extracellular matrix (ECM) are used in three-dimensional cell culture, cell therapy, and tissue engineering. A semi-synthetic ECM based on cross-linked hyaluronana offers experimental control of both composition and gel stiffness. The mechanical properties of the ECM in part determine the ultimate cell phenotype. We now describe a rheological study of synthetic ECM hydrogels with storage shear moduli that span three orders of magnitude, from 11 to 3 500 Pa, a range important for engineering of soft tissues. The concentration of the chemically modified HA and the cross-linking density were the main determinants of gel stiffness. Increase in the ratio of thiol-modified gelatin reduced gel stiffness by diluting the effective concentration of the HA component.