Research School of Biology
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Research School of Biology
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| Research Breakthroughs
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In a new paper in Proceedings of the National Academy of Sciences USA, Menna Jones and Andrew Cockburn have collaborated with a large team of scientists from Tasmania and Queensland to investigate the response of Tasmanian devil populations to the ravages of an infective cancer, first detected by Menna while studying devils as an ARC Postdoctoral fellow in BoZo. Before the advent of the cancer, devils bred for the first time at two or three years of age and normally had three years after that in which to breed. However, most devils now contract cancer after mating, and they have responded by breeding at one year of age. This dramatic life history response may offer some hope that the animals can survive the onslaught of this terrible disease Scientific American Science News BBC Cuckoo chicks change calls to mimic hosts N. E. Langmore, G. Maurer, G. J. Adcock, R. M. Kilner Evolution 62: 1689 - 1699
Some media links to this story: Cuckoo chicks are masters of deception Cuckoo Chicks Change Calls to Mimic Host Oz cuckoo chicks copy hosts' voices to be fed by foster parents
Having a helper to assist with the childcare doesn't just make life easier for superb fairy-wren mothers, it can give them longer lives and enable them to breed more. Superb fairy-wrens are 'cooperative breeders', meaning that some pairs are assisted in rearing their young by 1-4 helpers. Helpers are usually the grown-up sons of the breeding female. Although helpers provide lots of food to the nestlings, researchers had previously been unable to detect any benefit to the nestlings in terms of body mass or survival. Our study of fairy-wrens in Canberra revealed the answer to this conundrum; females with helpers laid smaller eggs than females that had no helpers. By laying smaller eggs with disproportionately small yolks, the females could conserve energy for later breeding attempts. The chicks from small eggs were smaller at hatching, but the extra food provided by helpers allowed them to catch up, so that they fledged at a normal weight. The energy conserved during breeding improved the survival odds of females with helpers by 30%, compared to females without helpers. Some media links to this story: ABC online: Science Alert: Sydney Morning Herald: SBS World News Australia: Washington Post: News10 NBC, New York: The Telegraph, U.K.:
Paired female and male Australian magpie-larks, Grallina cyanoleuca , can sing alone or in duets in which individuals alternate notes. The responding bird times its notes with split-second accuracy, so that most duets have almost perfect rhythm and avoid any overlap of notes. What is the benefit of such exquisite timing? In this paper, we tested the idea that coordination signals the quality or motivation of the pair, and so may be more effective at driving away rivals. We found that duets became more coordinated the longer the members of the pair had been together, and that playback of coordinated duets was more threatening to residents then uncoordinated duets. Temporal coordination therefore does appear to signal pair quality. The photo shows a pair of magpie-larks duetting. Abstract: Coordinated displays are widely used to defend shared resources, and may signal coalition strength so that groups can assess the relative competitive ability of rivals and avoid unnecessary fights. Joint vocal displays are known to facilitate numerical assessment of relative group size in some animals, but it is not known whether features of coordinated vocal displays can signal coalition strength independent of coalition size. We show experimentally that precise coordination between partners in avian duets increases the perceived threat of these joint territorial displays, and provide the first evidence that established pairs produce more highly coordinated duets than new pairs. Duet precision thus serves as an honest signal of coalition strength. This is the first reported evidence of cooperative benefits for precise temporal coordination of signals. Supplemental data, including experimental procedures and audios are available at http://www.current-biology.com/cgi/content/full/17/11/r406/DC1/ Some media links to this paper: Magpie larks sing to warn other birds Birds with rhythm sing scary harmonies: Pairs of magpie-larks use choral skills to intimidate rivals Duetting birds intimidate rivals with their song Birds That Sing Together Scare off Invaders Duetting Birds With Rhythm Present A Greater Threat No larking matter: a duet's dire precision Birdsong that puts rivals to flight Good Rhythm Helps Birds Compete Scary singing: precise birds signal, 'Don't mess with us': A pair of magpie-larks can advertise their toughness by the precision of the duets they sing Promiscuous females have healthier babies because of sperm competition
There is a growing consensus that polyandry (mating with multiple males) is beneficial, despite potential costs like disease or injury. One mechanism may be that genetically better males have greater fertilisation success when their sperm compete with those of inferior males. Surprisingly, there is no unequivocal evidence for this because of the difficulties of experimental design. Enter the brown antechinus, Antechinus stuartii. The unusual life history of this mouse-sized marsupial, centred on a mating season of a fortnight, makes it possible to design experiments to resolve the problems. The results show conclusively that polyandry can increase net offspring fitness in the wild, and males that sire more offspring through sperm competition also have much greater offspring survival. Some links to stories about this paper: Scientific American. Marsupial Mating Proves Promiscuity Pays. Livescience. Swinger Marsupials Produce Healthier Offspring. UK Metro. Sleep around for healthier babies (for fans of Little Britain). iafrica.com. Free love breeds better babies. ABC Science. Marsupials sleep around for babies' sake. Fox News / AAP. Promiscuity breeds better babies: study. Podcasts: Nature <http://www.nature.com/nature/podcast/index.html>
Leavesley, A. & Magrath , R. D. 2005. Communicating about danger: urgency alarm calling in a bird. Animal Behaviour 70: 365-373 . (doi: 10.1016/j.anbehav.2004.10.017) We studied the meaning of alarm calls given by scrubwrens, Sericornis frontalis , to predatory birds in flight, and found a remarkably precise system of communication. Scrubwrens provide information about the distance of the predator, and therefore the urgency of escape, by giving higher-pitched calls including more notes when predatory pied currawongs, Strepera graculina , fly closer. Furthermore, listeners respond appropriately to playback of these alarm calls: single note alarms provoke vigilance, while multi-note alarms cause birds to flee immediately to cover. Scrubwrens therefore communicate about the degree of danger posed by a predator, and others use this information sensibly to avoid predators. This work complements previous work showing that the type of alarm call can identify the type of predator (vervet monkeys, Seyfarth et al . 1980, Science 210: 801-803; chickens, Evans et al. 1993, Animal Behaviour 46: 23-38), and provides explicit support for the idea that bird alarm calls can specifically signal the degree of danger (Templeton et al. 2005, Science 308: 1934-1937).
Although defence against herbivores is often argued to be the main action of plant secondary metabolites (PSMs), very few examples have demonstrated that intraspecific variation in PSM concentrations influences foraging by wild vertebrate herbivores. Experiments with captive animals often indicate that PSM concentrations influence how much herbivores eat from individual plants, but these experiments do not replicate the subtle tradeoffs in diet selection faced by wild animals, which must avoid predators and extremes of weather, interact with conspecifics, and achieve a balanced, nutritious diet, while avoiding intoxication by PSMs. We characterized the foliar chemistry of every tree from two Eucalyptus species available to a population of koalas ( Phascolarctos cinereus ) and considered rates of tree visitation over a ten-year period. We show that visitation rate was most strongly influenced by tree size, but that koalas also visited trees less frequently if the foliage contained either high concentrations of deterrent PSMs known as formylated phloroglucinol compounds, or low concentrations of nitrogen. Consequently, plant chemistry restricts the use of trees by this herbivore, and thus limits the food available to koalas and potentially influences koala populations. Links to Media stories about this research ABC Science News ABC News online Physics and Technology News Faculty of 1000: evaluations for Moore BD & Foley WJ Nature 2005 May 26 435 (7041) :488-90
The koala is the quintessential specialist herbivore, feeding almost exclusively on Eucalyptus foliage. Consequently, the limitations imposed on the koala's diet by plant defences indicate the extent to which evolutionary adaptations allow mammalian herbivores to circumvent such defences. We tested whether a recently discovered group of plant secondary metabolites, the formylated phloroglucinol compounds (FPCs), deters koalas from feeding on some eucalypt foliage. We found that captive koalas ate less foliage in a single night from trees with high FPC concentrations. Individual trees also differ in the types of FPCs they possess, but for a given eucalypt species, most FPCs were similarly effective deterrents. Two closely related and sympatric eucalypt species could be clearly separated by the amounts that koalas ate from each, however this difference could not be explained by total FPC concentrations alone. We suggest that in this case, the presence of a distinct type of FPC deters koala herbivory on the less palatable species, and may have facilitated the evolutionary divergence of these species. We conclude that plant defences are likely to play an important role in determining the distribution and abundance of koalas. Links to Media Stories about this research German Science News Iran Daily http://www.rsc.org/chemistryworld/news/CW00504N021a.htm
Sexual advertisement is often costly - being brightly coloured or engaging in conspicuous and prolonged displays increases exposure to predators and raises energetic costs. If some males are of better quality than others, however, they should pay a smaller cost for a given level of investment in advertising. This has lead to the widely stated claim that more attractive males will live for longer than the average male. This, however, is not inevitable. The short-term mating gains from 'excessive' investment into advertising may more than compensate for any reduction in longevity. In a collaborative ARC funded project (John Hunt & Rob Brooks, U.N.S.W.; Michael Jennions, A.N.U.) we experimentally manipulated male quality. We reared crickets from hatching on either a high, medium or low protein diet. Females reared on the high protein diet lived longer than those on the low protein diet, while males reared on the high protein diet died soonest. The effect of diet on male longevity appears to be related to the earlier onset of advertisement calling and more calls being produced per night by males fed a high protein diet. In field studies we have shown that male call rate is a major determinant of male attractiveness. So high quality males (i.e. those that can accumulate more resources) by calling sooner and more incessantly may increase their mating success to such an extent that it can compensate for their reduced lifespan. Story in Science :
The Australian fossil record shows that the ancestral Gondwanan rainforest which existed 25 million years ago was mostly replaced over the next 15 million years by the present-day 'sclerophyll' flora dominated by eucalypts and acacias. This change coincided with a cooling, drying climate and the advent of fire. This paper describes how we have used DNA sequence data to compare the patterns and timing of speciation (and extinction) in eucalypts, casuarinas, banksias and legumes. We found that each group speciated rapidly during this period, but only in the drier areas. These similarities across several different lineages suggest that climatic change and ecological factors drove the evolution of the flora, and further support a close link between climate change and evolutionary response.
Crabs lend a helping claw - Backwell, P., Jennions, M., (2004) "Coalition among male fiddler crabs", Nature, Vol 430, pp 417. Although it has long been predicted by theorists, there is no compelling evidence from studies of animal territoriality to show that a resident will strategically help a neighbour to defend its territory against an intruder. Patricia Backwell and Michael Jennions have, however, recently shown that territory-owning male fiddler crabs will assist a neighbour to defend his territory against an intruder. This cooperation supports the prediction that animals may sometimes find it less costly to assist a familiar neighbour than to renegotiate boundaries with a new, and possibly stronger, neighbour. Pat and Michael found that males only assisted their neighbours in certain contexts. Specifically, a male helped his neighbour when this was most likely to have a beneficial effect. In crabs, body size equals strength so larger crabs tend to win fights. In 94% of cases where assistance was provided, the resident being challenged was smaller than the intruder. This was only true in 51% of cases when no assistance was given. Males therefore provided assistance when their neighbour was more likely to lose his territory. In addition, the male that helped was generally larger than the intruder and therefore more likely to defeat the intruder than was his neighbour. So the circumstances under which assistance was provided give the impression that crabs make judicious decision about the relative strength of the three participants. In reality, it is likely that the crabs use very simple 'rules of thumb' to determine when to intervene in a fight between a neighbour and an intruder. That this form of cooperation between territorial rivals occurs in an invertebrate, but has still not been reported in birds or mammals, suggests that territorial coalitions depend more on appropriate circumstances than on advanced cognitive skills. This work was carried out in tropical Darwin, where the A.N.U. has a research station ( N.A.R.U.) that is now the base for BoZo's fiddler crab research. Links to media stories about this research: Story on ABC Science News: Story on ABC Robyn Williams' Science Show:  How cross-species comparative methods benefit conservation biology - Fisher, D., Owens, I., (2004) "The comparative method in conservation biology", Trends in Ecology and Evolution, Vol 19, Issue 7, pp 391-398.
The phylogenetic comparative method is a way of finding correlates of a particular trait across many species. It has revolutionised evolutionary biology in the past decade, but can it also help solve key problems in conservation, such as prioritising endangered species research, predicting invasions and understanding species responses to climate change? We suggest that this method is helping us to understand broad-scale mechanisms in conservation, but that its ability to predict susceptibility of individual species to threats is limited. For example, it can tell us that Australian marsupials in areas of more intense pastoralism have suffered more population and species extinctions, but it won't reveal exactly what made a particular species disappear. Links to media stories about this research: Story on ABC Science News:  Cuckoos versus hosts: Australian fairy-wrens have the last laugh - Langmore, NE , Hunt, S & Kilner, RM (2003) Escalation of a coevolutionary arms race through host rejection of brood parasitic young. Nature , 422, 157-160.
The sight of a tiny host bird busily feeding an enormous cuckoo chick has puzzled naturalists for generations. Cuckoos lay their eggs in the nests of other birds and soon after hatching the cuckoo chick kills host young by throwing them out of the nest. Thus cuckoos impose a heavy cost on their hosts. Many host species have retaliated by evolving extremely fine egg discrimination abilities and rejecting any odd-looking eggs from their nests. This has led to an 'arms race' between cuckoos and hosts. Hosts evolve ever better means of detecting cuckoo eggs, and cuckoos evolve better and better means of fooling the host. However, if a cuckoo egg hatches, hosts fail to recognize the imposter even though it looks utterly unlike their own young and can be six times bigger than the adult hosts. Why has the arms race stopped short of hosts evolving recognition of cuckoo chicks? Recently, a study by Dr Naomi Langmore of the Australian National University, in collaboration with Dr Rebecca Kilner (Cambridge University) and Dr Sarah Hunt (Bristol University), revealed that the evolutionary arms race between cuckoos and hosts has escalated to a new stage in Australia. The Horsfield's bronze-cuckoo Chalcites basalis lays such a mimetic egg that it is never spotted and removed by hosts. However, roughly 40 % of host fairy-wren mothers have the last laugh. They abandon the nest, leaving the cuckoo chick to starve to death, while they renest. Cuckoo chicks are recognized partly because they are alone in the nest, and partly through their odd sounding begging calls. Links to media stories about this research: Story on National Geographic News: Story on ScienceWatch: Story on ABC Science News: Story in the Herald Sun:  Chemistry of Sexual Deception in an Orchid-Wasp Pollination System - Schiestl, F.P., Peakall , R., Mant, J.M., Ibarra, F., Schulz, C., Franke, S and Francke, W. (2003) The chemistry of sexual deception in an orchid-wasp pollination system. Science 302, 437-438.
Pollination by sexual deception of male pollinators is known only in orchids from Australia and Europe. These orchid flowers mimic the odour and appearance of female insects and pollination is achieved during mating attempts by the male. This pollination is sometimes known as "pseudocopulation" meaning false mating, although attempted mating is not necessary for pollination in all species, hence we use the more general term of "sexual deception". In Australia at least 100 species (perhaps has many as 300) in at least 9 orchid genera, are involved. Not only are male wasps of several kinds exploited, but also ants and sawflys. Although some orchids look remarkably like female wasps (see photos below) we have known for a long time that the floral odor (although not detectable to human noses), rather than appearance is most important. The exciting breakthrough we have described in our Science paper (Schiestl et al. 2003) is that a single compound, identical in the female and the orchid Chiloglottis trapeziformis , is sufficient to attract the male wasps. This single compound is unique, representing a new class of compounds previously unknown to science. This is also the first known case in orchids (and probably plants generally) where the orchids have evolved and copied an identical compound to that used by their pollinator as a sex pheromone. Links to media stories about this research: Science magazine commentary on this story: Science behind the news commentary on this story: This story featured as the lead story on the Science Show: Australian National University Media Release
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New species of Pacific Iguana discovered
Life-history change in disease-ravaged Tasmanian devil populations
Horsfield's bronze-cuckoos primarily parasitise fairy-wrens, but also exploit a range of other hosts including thornbills. Soon after hatching, the nestling cuckoo evicts the hosts' eggs from the nest. Despite never hearing the host chicks' begging calls, the cuckoo chicks accurately mimic the calls of two different hosts, superb fairy-wrens and buff-rumped thornbills. We tested whether (i) the cuckoos have two different races, each specializing on a different host and producing a begging call that mimics their favoured host, or (ii) the cuckoos are able to modify their begging calls after hatching, by cross-fostering cuckoo eggs from fairy-wren nests to thornbill nests. We found that upon hatching, all cuckoos produced a 'cheep cheep' fairy-wren begging call. However, those cuckoos that had been cross-fostered to thornbill nests modified their calls within a few days to imitate the long, rasping calls of thornbills. We suggest that plasticity in the development of host-specific traits after parasitism is likely to reduce selection for host race formation. 
Reduced Egg Investment Can Conceal Helper Effects in Cooperatively Breeding Birds
Fisher, D.O., M.C. Double, S.P. Blomberg, M.D. Jennions and A. Cockburn. 2006. Post-mating sexual selection increases lifetime fitness of polyandrous females in the wild. Nature 444: 89-92 (2nd November).
Communicating about danger 
How koalas make their food choices in the wild
Why koalas feed selectively on Eucalyptus.
Evolution of body size - Keogh, JS, IAW Scott, C Hayes. (2005). "Rapid and repeated origin of insular gigantism and dwarfism in Australian tiger snakes", Evolution, 59:226-233. 
Live hard and die young - Hunt, J., Brooks, R., Jennions, M., Smith, M. Bentsen, C., Bussiere, L . (2004) "High-quality male crickets invest heavily in sexual display but die young", Nature, 432: 1024-1027. 
Radiation of Australian plants - Mike Crisp, Lyn Cook and Dorothy Steane (2004) "Radiation of the Australian flora: what can comparisons of molecular phylogenies across multiple taxa tell us about the evolution of diversity in present-day communities?" Philosophical Transactions of the Royal Society London B. 359, 1551-1571 