A particular case and a general pattern: hyperaggressive behaviour by one species may mediate avifaunal decreases in fragmented Australian forests

We quantitatively assessed edge effects associated with elevated abundance of a hyper aggressive bird species, the noisy miner Manorina melanocephala, in fragmented eucalypt forest adjoining developed land. Long‐term data from Toohey Forest, subtropical Australia, show that noisy miner colonies intensively occupy a zone of 20 m from the forest edge, with frequent use occurring up to 100 m from the edge, but little beyond 200 m. Within noisy miner colonies, the abundance and species richness of other birds were both about half those recorded at nearby transects which were outside the colonies' main activity area. Bird species smaller than noisy miners, which are also those with similar diets, were collectively 20–25 times more abundant, and their species richness tenfold greater, outside miner colonies than within them, whereas larger species, which have less dietary overlap, did not differ. Exclusion of small insectivorous birds has been hypothesised to cause elevated insect herbivore density, but we found no difference between tree crown defoliation or dieback rates within versus outside miner colonies. Aggression by noisy miners can be viewed as a mechanism of interspecific competition, since miners have a relatively large body size for their diet and are hence able to exclude virtually all potential competitors at relatively little cost. We examine evidence indicating that reduced bird diversity in eucalypt forest fragments of eastern Australia is often simply the effect of noisy miner occupancy of edges, acting directly on the densities of other species through their aggressive behaviour. With an edge effect 200 m deep, a remnant 10 ha in size is likely to become entirely occupied by noisy miners, and this is a size threshold that has been commonly reported in association with area‐standardised avian diversity reductions. Convergent patterns of species loss from small forest fragments in different continents are the result of different underlying ecological processes.     

Carotenoid status signaling in captive and wild red-collared widowbirds: independent effects of badge size and color

Carotenoid-based plumage ornaments are typically consideredto be sexually selected traits, functioning as honest condition-dependentsignals of phenotypic quality, but few studies have addressedthe function of carotenoid color variation in male contestcompetition. Using two experiments, we investigated the statussignaling function of the variable (ranging from yellow tored) carotenoid throat patch (collar) in the polygynous, sexually dimorphic red-collared widowbird (Euplectes ardens). First,we tested if the red collar functions as a dominance signalby painting spectrometrically controlled collar patches ontothe brown plumage of nonbreeding males and staging dyadic malecontests over food resources. Red-collared males dominatedorange males, which in turn dominated the control brown andnovel blue collars. Red dominance persisted when the collar manipulations were reversed within dyads and also when testedagainst testosterone implanted males. In the second experimentthe collar size and color of breeding males were manipulatedin the field before and after territories were established.All males with enlarged red and most with enlarged orange orreduced red collars obtained territories, whereas most maleswith reduced orange and all with blackened (removed) collarsfailed to establish or retain territories. In addition, amongthe territorial males, those with reduced signals defendedsmaller territories, received more intrusions, and spent moretime in aggressive interactions. Redness and, to a lesser extent,size of the carotenoid ornament both seem to independently indicate male dominance status or fighting ability in male contest competition.     

The ZbYME2 gene from the food spoilage yeast Zygosaccharomyces bailii confers not only YME2 functions in Saccharomyces cerevisiae, but also the capacity for catabolism of sorbate and benzoate, two major weak organic acid preservatives

A factor influencing resistances of food spoilage microbes to sorbate and benzoate is whether these organisms are able to catalyse the degradation of these preservative compounds. Several fungi metabolize benzoic acid by the beta-ketoadipate pathway, involving the hydroxylation of benzoate to 4-hydroxybenzoate. Saccharomyces cerevisiae is unable to use benzoate as a sole carbon source, apparently through the lack of benzoate-4-hydroxylase activity. However a single gene from the food spoilage yeast Zygosaccharomyces bailii, heterologously expressed in S. cerevisiae cells, can enable growth of the latter on benzoate, sorbate and phenylalanine. Although this ZbYME2 gene is essential for benzoate utilization by Z. bailii, its ZbYme2p product has little homology to other fungal benzoate-4-hydroxylases studied to date, all of which appear to be microsomal cytochrome P450s. Instead, ZbYme2p has strong similarity to the matrix domain of the S. cerevisiae mitochondrial protein Yme2p/Rna12p/Prp12p and, when expressed as a functional fusion to green fluorescent protein in S. cerevisiae growing on benzoate, is largely localized to mitochondria. The phenotypes associated with loss of the native Yme2p from S. cerevisiae, mostly apparent in yme1,yme2 cells, may relate to increased detrimental effects of endogenous oxidative stress. Heterologous expression of ZbYME2 complements these phenotypes, yet it also confers a potential for weak acid preservative catabolism that the native S. cerevisiae Yme2p is unable to provide. Benzoate utilization by S. cerevisiae expressing ZbYME2 requires a functional mitochondrial respiratory chain, but not the native Yme1p and Yme2p of the mitochondrion.