Reduced sperm counts in guppies (Poecilia reticulata) following exposure to low levels of tributyltin and bisphenol A

There is increasing evidence that normal male reproductive function can be disrupted by exposure to pollutants in the environment that can exogenously mimic, antagonize or block sex-hormone function. One possible consequence of exposure to these xenobiotics is disruption to spermatogenesis, but results thus far provide only indirect and inconsistent evidence. In this study we exposed adult male guppies (Poeciliidae: Teleostei) to environmentally relevant levels of the common xenobiotics tributyltin (11.2-22.3 ngl-1) and bisphenol A (274-549 micrograms l-1) in experimental aquaria. After 21 days of exposure, we found significant declines (by 40-75%) in total sperm counts for male fishes exposed to tributyltin and bisphenol A compared with controls. This short-term decline in sperm count is unlikely to be the result of endocrine-mediated alteration of the germ line, and we found no change in testis size or sperm lengths between treatments. However, Sertoli cells, which facilitate the transport of maturing sperm into the testicular deferent duct (where they are stored prior to ejaculation), are directly sensitive to xenobiotic action and it is therefore possible that spermatogenesis was inhibited through in vivo interference with normal Sertoli-cell function.

Concentration effects of selected insecticides on brain acetylcholinesterase in the common carp (Cyprinus carpio L.)

The differential inhibition of acetylcholinesterase (AChE) by organophosphate (OP) and carbamate (C) is followed by the distinct duration of exposure effect on common carp AChE. Hence, in the present study in vivo exposure period effect and in vitro concentration-response of chlorfenvinphos, chlorpyrifos diazinon, and carbofuran were investigated on Cyprinus carpio L. AChE. Individuals of 1-year-old carp were exposed for 96 h to different concentrations of insecticides, after which AChE activity was measured in the brain. The highest concentrations of carbofuran (2.44 mg x L(-1)), chlorfenvinphos (2.9 mg x L(-1)), and diazinon (2.5 mg x L(-1)) killed all the test animals after only 4 h, although there was no statistically significant difference from the control group's brain AChE activity. The lowest concentration significantly inhibited brain AChE after 96 h. Chlorfenvinphos was the most potent inhibitor in vivo and chlorpyrifos the least active inhibitor after 96 h of exposure time. In vitro experimentation with the same pesticide indicated that several concentrations inhibited 50% of the AChE activity (I50), ranging from 4.1x10(-7) to 8.12x10(-4) M in both single inhibitory action and joint inhibitory effect. The results suggest that in biomonitoring programs carp brain AChE can be a good diagnostic tool for chronic OP nd C pollution.

MATING BEHAVIOUR AND MALE MATE CHOICE IN TRIBOLIUM CASTANEUM (COLEOPTERA, TENEBRIONIDAE)

Mate choice by males has received less attention than female choice, despite the recognition that males can incur non-trivial reproductive costs through mating. In this study we investigate male mate choice in the red flour beetle, Tribolium castaneum. We determine whether male beetles have evolved sensitivity that enables them to discriminate between females and we then examine how males discriminate between females that present different reproductive potentials. Recently-emerged adult females are immature, and we investigate when egg-laying maturity develops, and whether male mating attempts with immature females provide reproductive pay-offs. We show that males are the sex most likely to initiate mating attempts (more than 85% of male-female contacts are male-initiated). Therefore, we test male mating initiations when presented with choices between: (i) immature and mature virgin females; (ii) mature virgin females and previously mated mature females; and (iii) mature females previously mated either with different male or with the test males. Last male sperm precedence exists in T. castaneum and females are polyandrous. Matings with immature females are therefore likely to generate lower fertilization successes than matings with mature females. Furthermore, males are likely to achieve higher total fertilization success when they mate if they precede a rival male's sperm than if they precede their own sperm. Accordingly, we find that: (i) males copulate more frequently with mature, than with immature females; (ii) males do differentiate between virgin and mated females; and (iii) males prefer females that have been inseminated by a different male to those previously inseminated by the test males themselves. The results demonstrate that male T. castaneum recognise female status, display mate choice, and prefer to inseminate females which provide greater reproductive potential.

DNA polymorphism detection in Tribolium castaneum (HERBST) (Coleoptera: Tenebrionidae): potential use in stored product pest management

Different pairs of oligonucleotide primers have used for the detection of DNA polymorphism between Tribolium castaneum strains. Amplification of a major DNA fragment and two minor was observed in all strains tested excepted for one strain from France which present only two major bands (respectively at 800 bp and 880 bp). Arbitrarily, the major band amplified from a DNA sample of the strain originating from the Philippines was choosen as a probe (sequence of 487 bp in length). The combination of this probe and restriction enzymes permitted the discrimination between strains. Our results show that RAP marker of Tribolium castaneum could be used to study its population genetics.