Sexual dimorphism in the tusked frog, Adelotus brevis (Anura:Myobatrachidae): the roles of natural and sexual selection

At least two adaptive processes can lead to the evolution of sexual dimorphism: sexual selection (e.g. male-male combat) or natural selection (e.g. dietary divergence). We investigated the adaptive significance of a distinctive pattern of sexual dimorphism in a south-eastern Australian frog, Adelotus brevis. Male Adelotus grow larger than female conspecifics, have larger heads relative to body size, and have large paired projections (‘tusks’) in the lower jaw. All of these traits are rare among anurans. We quantified the degree of dimorphism in Adelotus, and gathered data on diets and mating systems of this species to evaluate the possible roles of sexual selection and dietary divergence in favoring die evolution of these sexually dimorphic traits. Analysis of prey items in alimentary tracts revealed significant sex differences in prey types. For example, females ate proportionally more arthropods and fewer molluscs than did males. However, this difference is likely to be a secondary consequence of habitat differences between the sexes (due in turn to their different reproductive roles) rather than a selective force for the evolution of sexual dimorphism. Calling males spend their time in moist habitats where pondsnails are abundant, whereas females are more often encountered in the drier arthropod-rich woodlands. A three-year behavioural ecology study on a field population revealed that reproductive males engage in agonistic interactions, with the sexually dimorphic tusks used to attack rivals. Larger body size contributed to male reproductive success. Small males were excluded from calling sites and, among the calling males, larger animals had higher reproductive success (numbers of matings) than did smaller individuals. Hence, the atypical pattern of sexual dimorphism in Adelotus brevis seems to have resulted from sexual selection for larger body size and tusk size in males, in the context of male-male agonistic behaviour, rather than natural selection for ecological divergence between the sexes.     

Design of a reactor bioleach process for refractory gold treatment

Abstract: CRA has been developing bioleaching for the treatment of low-grade refractory gold resources. In lhe course of dcveloping a biolcach process for a pyrite concentrate at Bougainville Copper Limited (BCL), CRA has confronted the myriad of problems associated with proving a concept at a small scale, to the design of a conceptual flowsheet. A phased programme was initiated to develop the project. Laboratory scale batch studies indicated that the pyrite concentrate was amenable to bacterial leaching and subsequent cyanidatkm gold recovery. Large scale continuous leaching was then performed to delincate the major operating wtriables. In conjunction with this programme, CRA has also been addressing the problem of reactor scale-up. The success of the bioleach process is dependent on the design of large, energy-efficient reactors, with reactor sizes of the order of 1000 m³ contemplated. Results from these scale-up studies are presented in this paper.