Factors affecting egg production in the selfing mangrove rivulus (Kryptolebias marmoratus).

The mangrove rivulus, Kryptolebias marmoratus, is one of two known vertebrate species with preferentially self-fertilizing hermaphrodites. Males also exist, and can outcross with hermaphrodites. Outcrossing events vary across wild populations and occur infrequently in laboratory settings. This study sought to add dimension to our understanding of mangrove rivulus reproductive habits by probing the effects of male presence on hermaphroditic unfertilized egg production. Specifically, we quantified egg production of solitary hermaphrodites compared to hermaphrodites exposed to males and exposed to other hermaphrodites. Hermaphrodites tended to produce more fertilized eggs in the presence of males but unfertilized eggs were produced relatively rarely and did not vary significantly among treatments. The probability that hermaphrodites would produce eggs changed as a function of genetic dissimilarity with their partner and in a season-dependent manner. In the fall, the probability of laying eggs decreased as a function of increased genetic dissimilarity, regardless of the sex of the partner. In the winter/spring, however, the probability of laying eggs increased markedly with increased genetic dissimilarity, regardless of the sex of the partner. Our findings indicate that reproductive decisions are modulated by factors beyond male presence, and we discuss a number of alternative hypotheses that should be tested in future studies.

Chromium(VI) transport and fate in unsaturated zone and aquifer: 3D Sandbox results.

The simulation of Cr(VI) behavior in an unsaturated zone and aquifer, using a 3D experimental set-up were performed to illustrate the distribution, transport and transformation of Cr(VI), and further to reveal the potential harm of Cr(VI) after entering the groundwater. The result indicated that chromium(VI) was transported in the vertical direction, meanwhile, was transported in the horizontal direction under the influence of groundwater flow. The direction and distance away from the pollution source zone had great effect on the chromium(VI) concentration. At the sampling sites near the pollution source zone, there was a sudden increase of chromium(VI) concentration. The concentration of chromium(III) concentration in some random effluent samples was not detected. Chromium had not only transported but also had fraction and specie transformation in the unsaturated zone and aquifer. The relative concentration of residue fraction chromium was decreased with time. The content of Fe-Mn oxide fraction chromium was increased with time. The relative content of exchangeable and carbonate-bound fraction chromium was lower and the content variations were not obvious. Chromium(VI) (91-98%) was first reduced to chromium(III) rapidly. The oxidation reaction occurred later and the relative content of chromium(VI) was increased again. The presence of manganese oxides under favorable soil conditions can promote the reoxidation of Cr(III) to Cr(VI).