The amount of venom injected by the spider Cupiennius salei depended on the efficiency of the mechanical defence of the prey species. Spiders were milked for the first venom (i.e. the first microlitre of venom emitted) versus remaining venom, and for venom regenerated from emptied glands. HPLC gel filtration and IEF electrophoresis showed that the protein content of the first venom was only half as compared to that of the remaining venom, and that this was due to a dilution of all proteins. Venom regeneration came in two speeds. The amount of venom was regenerated more rapidly than the protein concentration. Newly regenerated venom as compared to older venom was characterized by a lower concentration of all proteins and by a higher total concentration of free amino acids, whereas histamine and taurine did not follow this trend. K+concentration and pH remained similar during venom regeneration. Crickets injected with the venoms showed less acute symptoms when the protein concentration was lower, namely with the first venom and with newly regenerated venom. Consequently, a spider which modulates the quantity of venom injected into a prey also directly changes the venom quality. The ecological consequences of this are discussed. This paper also discusses which region of a gland (ampulla, extracellular and intracellular parts of the glandular sac) is involved in the changes of the venom quality. © 1995.
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