Effects of veterinary fences on Wildlife conservation in Zimbabwe

In Zimbabwe, veterinary fences are used to control trypanosomiasis and foot- and-mouth disease, two important diseases that threaten cattle production and beef exports. Wildlife is implicated in both instances and the effects of fences on wildlife conservation and land use are discussed in relation to these two diseases. Advantages and disadvantages related to direct and indirect fence effects are outlined. Although the maintenance of fences for trypanosomiasis control is likely to become obsolete, control of foot- and-mouth disease will rely on fences for the foreseeable future. Most of Zimbabwe's protected wildlife areas are located in marginal agricultural land around the periphery of the country where cattle productivity is low. This land should be excluded from any involvement in the beef export industry rather than attempting its inclusion through cordoning and isolating individual protected areas. Within such land, the need for rigid veterinary restrictions should then disappear and allow more flexible strategies for disease control, including adaptive and imaginative approaches to land-use planning.     

Aversive and avoidance responses of female mice to the odors of males infected with an ectoparasite and the effects of prior familiarity

The detection and avoidance of parasitized males is a component of female mate choice. Here we show that female mice can distinguish between the odors of individual males infected with an ectoparasite, the murine louse, Polyplax serrata, and uninfected males. Female mice displayed aversive responses to, and avoided the odors of, parasitized males. A 15 min exposure to the urinary odors of infected males induced an endogenous opioid-peptide-mediated reduction in pain sensitivity or analgesia, while a brief 1 min exposure to the odors elicited a non-opioid-mediated analgesic response. These neuromodulatory mechanisms facilitate the expression of a variety of anxiety and stress associated responses of which pain inhibition is one component. Females further distinguished between novel and familiar infected males. Prior exposure to the odors of an infected males reduced the degree of analgesia expressed and the associated levels of anxiety and stress and their concomitant costs. In a Y-maze odor preference test females also displayed a marked overall preference for, and initial choice of, the odors of clean, uninfected males and an active discrimination against, and avoidance of, the odors of both familiar and novel infected males. These findings indicate that female mice can distinguish between males infected with an ectoparasite and clean uninfected males and display aversive and avoidance responses to infected males. They also show that females can discriminate between individual infected males and modulate their aversive responses to the odors of infected males on the basis of prior familiarity. This is likely part of the mechanisms whereby females can both reduce the transmission of ectoparasites, such as lice, to themselves and select for parasite-free males.     

Copper and zinc handling during the moult cycle of male and female shore crabs Carcinus maenas

Tissue concentrations and contents of copper and zinc were determined at 11 different stages of the moult cycle in male and female shore crabs Carcinus maenas. Metal concentrations in haemolymph, gills, midgut gland, muscle, and exoskeleton of males and haemolymph, gills, and midgut gland of females were determined, as were haemocyanin concentrations and haemolymph volumes (using ¹⁴C-inulin) in males. The changes in tissue Cu and Zn concentrations and contents that occur throughout the moult cycle can be attributed to muscle breakdown in late premoult, the period of starvation in late premoult and early postmoult, the resorption from and shedding of the old exoskeleton, and the dilution of the haemolymph caused by water uptake around the time of ecdysis. The present study demonstrates that whole-body Cu and Zn contents remain constant during a large part of the moult cycle of male and female C. maenas. This state of whole-body trace metal homeostasis is maintained in spite of major changes in tissue proportions and tissue Cu and Zn concentrations and contents. Previous studies have not carried out the necessary analysis to move from theoretical estimates to quantitative determination of the changes in tissue metal distribution associated with moulting in crustaceans; the data presented illustrate the necessity of measuring both tissue concentrations and contents of metals to avoid misinterpretation of either.     

Seasonal occurrence of the ctenophore Pleurobrachia pileus in the western Dutch Wadden Sea

Due to the short residence time of the water in the western Dutch Wadden Sea the ctenophore Pleurobrachia pileus has to be considered as an allochthonous species, which enters the estuary passively from the North Sea. The seasonal occurrence of this species in the Dutch Wadden Sea is a reflection of its abundance in the coatal zone of the North Sea and is characterized by a pronounced spring peak of up to 17000 individuals per 1000 m³ and a lower autumn peak with numbers up to 400 individuals per 1000 m³. Similar to other areas, predation by Beroë gracilis, another ctenophore species, may be a factor in controlling the P. pileus population in this region, although B. gracilis abundance is low. P. pileus is only important as a predator for a short time, i.e. the month of May, when it reaches maximum biomass values of up to 12 00 mgC per 1000 m³. Both the estimated potential consumption rates in comparison with the available food as well as the observed suboptimal growth rate of the population suggest that in the coastal zone of the North Sea area food conditions may not be optimal for P. pileus.