Differences in reproductive success between laboratory and wild-derived golden hamsters (Mesocricetus auratus) as a consequence of inbreeding

All laboratory golden hamsters (Mesocricetus auratus) originated from a sibling pairing back in 1930. Due to this extreme founder event, domestic golden hamsters are presumed to be one of the most bottlenecked animal populations. Nevertheless, domestic hamsters show no obvious signs of inbreeding depression in commonly used breeding stocks. To explore the existence of potentially masked inbreeding effects, we compared the reproductive success of laboratory (lab) and wild-derived (wild) golden hamsters. We allowed oestrus females to mate consecutively with lab and wild males. The resulting offspring was genotyped using microsatellites to assess paternity. Finally, we compared male reproductive success to genetic variability, sexual behaviour and different sperm characteristics. Both hamster strains exhibited the expected large difference in genetic diversity (H _wild =0.712±0.062 vs H _lab =0.007±0.007. The reproductive success of wild males dramatically exceeded that of lab males (87% of pups were sired by wild males). Sexual behaviour of wild and lab males only varied in the number of long intromissions (intromissions without ejaculation at the end of the mating). No significant differences were observed in relation to mounting, ejaculation and intromission. There were also no apparent differences in sperm motility, velocity and density or testis histology between wild and lab hamsters. We conclude that the reduced reproductive success of lab males represents a hidden inbreeding effect, although its precise physiological cause remains unclear. These results provide first evidence for a major fitness disadvantage in captive golden hamsters.     

Organic carbon oxidation induced by large-scale shallow water intrusion into a vertical fracture zone at the Äspö Hard Rock Laboratory (Sweden)

Entrance tunnel construction at the Äspö Hard Rock Laboratory opened a conductive vertical fracture zone at a depth of 70 m on March 13, 1991. Three weeks later a sharp dilution front corresponding to 80% shallow water inflow to the originally saline fracture zone arrived at the entrance tunnel depth. In spite of this large inflow of shallow water, the fracture zone has remained persistently anoxic over a subsequent period. Results from gas sampling and ¹⁴C dating of dissolved organic and inorganic carbon conclusively show that recent organic carbon is being transported into the fracture zone and oxidized to carbon dioxide. These results are important when considering possible changes of redox status in the deep groundwater environment during construction and operation of a repository for spent nuclear fuel. Opening this fracture zone to large-scale surface water inflow adds reducing capacity in the form of organic carbon. This implies that the soil cover may provide important protection against input of dissolved oxygen to fractures being drained during the open phase of the repository.     

An automatic sampler for measurement of dust-deposition rates around fugitive sources

A wind-directional sampler for determination of dust-deposition rates has been developed, enabling the measurement of dust-deposition caused by a specific source and, at the same time, providing information on the dust-deposition rate for the background area. The sampler is called METDUST. This paper describes the results of a field evaluation of the METDUST sampler. The field evaluation was performed in a village in Southern Jutland, Denmark, where complaints of dust-deposition had occurred close to a power plant with large stockpiles of coal. The results showed that, out of a 9-month period, increased dust-deposition occurred downwind from the stockpiles during 4 months. Episodes were identified by comparison with the background deposition rate. The METDUST sampler offers an opportunity to measure the dust-deposition rate contributed by the source and the background simultaneously. It can, therefore, be used by environmental authorities to identify the "likelihood of complaint" and to define a suitable guideline for the case in question.     

Toxicity of a complex mixture of atmospherically transported pesticides to Ceriodaphnia dubia

The presence of several anthropogenic chemicals has been documented in the atmosphere of the Canadian prairies. The deposition of these chemicals as a mixture is of importancesince little is known of the combined effects of these chemicalson aquatic organisms. This study was designed to evaluate theacute and chronic toxicity of a complex mixture of nineatmospherically transported pesticides to Ceriodaphniadubia. The nine selected pesticides (bromoxynil, dicamba, 2,4-D,MCPA, triallate, trifluralin, pentachlorophenol, lindane, and4,4-DDT) were detected in appreciable quantities in dryatmospheric deposits. The concentration of each pesticide in themixture was based on maximum measured daily dry deposition ratesfor central Canada, except for pentachlorophenol, which wasestimated based on atmospheric concentrations. The 48-h LC50estimate for C. dubia exposed to the pesticide mixture was174.60 g L^-1 (340 times the measured total dry deposition concentration). The estimated NOEC and LOEC for bothsurvival and reproduction, as determined in the 7-d chronic toxicity test, were 51.3 (100 times) and 154 g L^-1 (300 times), respectively. A basic risk assessment, using the toxic unit approach, suggested that the toxicity of the pesticide mixture was mainly due to 4,4-DDT. Overall, this atmospherically transported complex mixture of pesticides appearsto pose a negligible toxicological risk to non-target aquatic invertebrates such as zooplankton.     

Social encapsulation of beetle parasites by Cape honeybee colonies (Apis mellifera capensis Esch.)

Worker honeybees (Apis mellifera capensis) encapsulate the small hive beetle (Aethina tumida), a nest parasite, in propolis (tree resin collected by the bees). The encapsulation process lasts 1-4 days and the bees have a sophisticated guarding strategy for limiting the escape of beetles during encapsulation. Some encapsulated beetles died (4.9%) and a few escaped (1.6%). Encapsulation has probably evolved because the small hive beetle cannot easily be killed by the bees due to its hard exoskeleton and defensive behaviour.