Black and Gold Aposematic Ants
In 1927, entomologist Alexander Nicholson first proposed that widespread mimicry across species, known as ‘mimetic complexes’, existed in Australian invertebrates. Such complexes have been widely recorded in wasps and in some butterfly species, but have previously not been studied in ants. Pekár et al. studied Australian ants and the insects that mimic them, finding that more than 140 arthropod species, including 126 ant species, 7 spider species, 3 true bug species, one wasp, and one treehopper, use varying gold and black dorsal colouration to warn off predators. Some of these ant-like mimics also employed other defences, such as unpalatable chemicals or spines. Using colouration to deter would-be predators, known as ‘aposematism’, is a well-known defence strategy that either warns of actual toxicity or mimics the ‘advertising’ of unpalatable or toxic species. Warning signals and mimicry are likely to have evolved alongside toxicity or lack of palatability. Consequently, the more apparent the warning or the better the mimicry, the more distasteful the species should be to predators. Predators of the look-alike species were found to avoid preying on the black and gold ants or mimics if given a choice. The study used next-generation sequencing to examine the faeces or stomach contents of natural predators of the ants or ant-mimics in the wild to determine whether they consumed the black and gold species. Predators studied included 553 spiders, 50 skinks, and 48 birds. Black and gold ‘mimicking’ insects were also offered as prey to a lizard and two spider species (one ant-specialist and one ant-averse); all but one – the ant-specialist predator – preferred to eat the offering that was not black and gold. The finding adds to the small number of sizable cross-order complexes on record. Furthermore, this cross-order mimicry complex contains more species than those known among Australian fish or millipedes, although still fewer than the complex recognised in mutillid wasps.
Iron And Acid Link To Whale Strandings
Tasmania has an unfortunate history of toothed whale strandings, with some 680 mass stranding events over 200 years. But why? Environmental factors from oceanography to winds, to seismic activity and sonar disruption have been implicated. Now, Nash et al. believe that iron-rich dust blowing into southern waters and increasing algal blooms could cause acid poisoning that alters whales’ navigational ability. Pseudo-nitzschia is a planktonic organism known to respond to increased marine nutrient concentrations with a resultant algal bloom. Recent studies conducted on iron fertilisation in the Southern Ocean revealed that increased iron stimulated Pseudo-nitzschia growth. Although once thought to be non-toxic, it is now recognised that algal blooms of this diatomic organism create domoic acid (DA). DA is a neurotoxin that can cause amnesic shellfish poisoning in humans and neurological dysfunction in sea lions and fur seals, specifically hippocampic lesions that potentially disrupt spatial orientation. Furthermore, DA is known to transfer through marine food webs to cetaceans, having been found in the faeces of humpback whales and blue whales. The team analysed the frequency of whale strandings in Tasmania from 1965, cross correlating strandings with dust activity using Dust Storm Index records from the Australian Bureau of Meteorology and with ocean chlorophyll levels as proxy for phytoplanktonic growth. They found that most strandings occurred during summer, when chlorophyll concentrations were also at their highest (from November to February). Dust activity was also increased at that time. The strong correlations support the hypothesis of a causative link between increased DA from iron-rich dust events and mass whale strandings, although more robust multidisciplinary research is required, including post mortem testing of stranded cetaceans for the presence of DA and bio-monitoring to confirm algal blooms of Pseudo-nitzschia whenever mass stranding events occur.
Woylie Scats and Parasitic Stressors
Woylies (brush-tailed bettongs, Bettongia penicillata) were once widespread across much of Australia but are now critically endangered and exist in remnant populations in WA. It has been suggested that the effects of parasitic infections could be exacerbated by stress and may be an important contributing factor to this decline. Stephanie Hing and colleagues studied a captive population of adult woylies (nine females and six males) at Native Animal Rescue, Malaga, WA, where the animals had access to underground fungi, native forage, insects and year-round supplementary feeding of fruit and vegetables. They measured the concentration of faecal cortisol metabolites (FCM) as a non-invasive method of examining the relationship between stress physiology and season, sex, reproductive status and the presence of parasites. Stress levels were highest in autumn and winter, even though the woylies were supplementary fed; this may be associated with circadian rhythms, shortened day length, or increased metabolic demands. Female woylies had higher mean levels of FCM than males, regardless of their reproductive status, a pattern that has also been found in the bilby, koala and southern brown bandicoot, indicating that stress-induced inhibition of reproduction is at least not a major concern in woylies. A weak but significant relationship was found between high FCM and poor body condition when parasites were present. When animals were shedding oxyurid pinworm eggs, they also had higher mean FCM levels, possibly indicating increased stress from parasite infestation, although the relationship between stress physiology and multiple parasite infections was found to be complex, warranting further study.
SAVING LIVES WITH PLATYPUS MILK
An Australian breakthrough has introduced an unlikely hero in the global fight against antibiotic resistance: the platypus. Antimicrobial resistance occurs when bacteria build up a resistance to antibiotics and pass it on to the next generation, leading to persistent infections caused by resistant ‘superbugs’. In 2010, scientists discovered that platypus milk contained unique antibacterial properties. Now, a team of CSIRO researchers working with Deakin University has helped explain why platypus milk is so potent. The discovery was made by replicating a special protein contained in platypus milk in a laboratory setting. Platypuses express milk onto their belly for the young to suckle, leaving milk exposed and offspring susceptible to the perils of bacteria. Deakin University’s Dr Julie Sharp believes this is why platypus milk contains a protein with such unusual, antibacterial characteristics. Employing the marvels of molecular biology, the Synchrotron, and CSIRO’s state of the art Collaborative Crystallisation Centre (C3), the team successfully made the protein and then deciphered its structure. They found a never-before-seen 3D fold, which due to its ringlet-like formation, has been dubbed the ‘Shirley Temple’ fold in tribute to the former child-actor’s distinctive curls. Dr Janet Newman, CSIRO scientist and lead author on the research, said finding the new protein fold was pretty special. ‘We’ve identified this highly unusual protein as only existing in monotremes, but this discovery increases our knowledge of protein structures in general and will inform other drug discovery work performed at the Centre,’ she said. CSIRO and Deakin university are seeking collaborators to take the potentially life-saving platypus research to the next stage.
REDBACK SEX: CANNIBALISM BUT NOT ‘COERCION’
It has been known for some time that mature female redback spiders (Latrodectus hasseltii, right) cannibalise male partners during mating, but it has recently been discovered that males also engage in damaging mating tactics. Adult male redbacks mate with immature females (in their final juvenile instar), tearing the exoskeleton that covers the female’s reproductive tract in order to gain access to her newly developed, concealed genitalia. When males mate with mature females, prolonged vibratory courtship is typical, as males that attempt copulation early are killed by females before mating is complete (premature cannibalism). When males approach immature females, they engage in reduced courtship displays but are more likely to copulate twice, thus inseminating the females’ paired sperm-storage organs. The females store the sperm through their final moult and later produce fertilised eggs. At least one-third of immature females are mated this way in the field. Some researchers consider this behaviour coercive, because females do resist these matings (which cause haemolymph bleeding) and respond with elevated deterrent behaviours, such as rapidly raising and lowering their legs, hitting the male or the web near the male, or moving the rear legs and body while the male is mounted. However, coercion is said to occur only if the behaviour reduces overall female fitness. Luciana Baruffaldi and Maydianne Andrade set out to measure whether female fitness was reduced and found that immature-mating in females was either neutral or beneficial, as it meant they did not have to attract a male after moulting. Most immature-mated females did not produce sex pheromones as adults whereas unmated adult females produce sex pheromones that attract mates and trigger courtship. Some 17% of redback females die without mating. Those that do not mate as adults show reduced longevity, dying younger than mated females. Thus, Baruffaldi and Andrade found no reproductive cost for immature-mated females in terms of longevity, fertility or fecundity, and they therefore concluded that this male mating behaviour is not coercive.
Baruffaldi L, et al. 2017. Scientific Reports 7. DOI:10.1038/s41598-017-17524-6