School of Biomedical Sciences - Research Publications
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ItemInsect Antennal Morphology: The Evolution of Diverse Solutions to Odorant Perception(Yale University, 2018-12-01)Chemical communication involves the production, transmission, and perception of odors. Most adult insects rely on chemical signals and cues to locate food resources, oviposition sites or reproductive partners and, consequently, numerous odors provide a vital source of information. Insects detect these odors with receptors mostly located on the antennae, and the diverse shapes and sizes of these antennae (and sensilla) are both astonishing and puzzling: what selective pressures are responsible for these different solutions to the same problem - to perceive signals and cues? This review describes the selection pressures derived from chemical communication that are responsible for shaping the diversity of insect antennal morphology. In particular, we highlight new technologies and techniques that offer exciting opportunities for addressing this surprisingly neglected and yet crucial component of chemical communication.
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ItemAntennal asymmetry is not associated with social behaviour in Australian Hymenoptera(WILEY, 2019-08)Abstract Lateralisation of biological form and function are well known for vertebrates and are being increasingly documented among invertebrates in recent years. Behavioural lateralisation in insects, together with asymmetrical distributions of antennal sensilla, has been linked to the communication challenges faced by social, but not solitary, insects. Recent evidence on patterns of asymmetry in insects outside of the Hymenoptera suggests that this explanation for antennal sensilla asymmetry may not be phylogenetically constrained. We explore this possibility by examining the distribution of antennal sensilla in three species of ants (Formicidae), the meat ant Iridomyrmex purpureus (Dolichoderinae), the green tree ant Oecophylla smaragdina (Formicinae) and the shield ant Meranoplus sp. (Myrmicinae) in which colony organisation is eusocial, and two species of nomiine bees, Mellitidia tomentifera and Reepenia bituberculata (Halictidae: Nomiinae), where colony organisation is not eusocial. Our results demonstrate that while there are differences in the left–right asymmetry of antennal sensilla basiconica in workers of the formicine ant I. purpureus, there is no consistent sensilla asymmetry across the five species. We find a negative correlation between antennal sensilla density and body size in R. bituberculata, which was not apparent in the other species. Our results contradict the suggestion that asymmetrical distribution of antennal sensilla is associated with the evolution of eusocial behaviour.
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ItemThe eyes have it: dim-light activity is associated with the morphology of eyes but not antennae across insect orders(OXFORD UNIV PRESS, 2021-10)Abstract The perception of cues and signals in visual, olfactory and auditory modalities underpins all animal interactions and provides crucial fitness-related information. Sensory organ morphology is under strong selection to optimize detection of salient cues and signals in a given signalling environment, the most well-studied example being selection on eye design in different photic environments. Many dim-light active species have larger compound eyes relative to body size, but little is known about differences in non-visual sensory organ morphology between diurnal and dim-light active insects. Here, we compare the micromorphology of the compound eyes (visual receptors) and antennae (olfactory and mechanical receptors) in representative pairs of day active and dim-light active species spanning multiple taxonomic orders of insects. We find that dim-light activity is associated with larger compound eye ommatidia and larger overall eye surface area across taxonomic orders but find no evidence that morphological adaptations that enhance the sensitivity of the eye in dim-light active insects are accompanied by morphological traits of the antennae that may increase sensitivity to olfactory, chemical or physical stimuli. This suggests that the ecology and natural history of species is a stronger driver of sensory organ morphology than is selection for complementary investment between sensory modalities.
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ItemNeurochemical System of the Retina Involved in the Control of Movement(FRONTIERS MEDIA SA, 2017-07-05)Recent studies have revealed that the retina may exert control over deep brain function and may be importantly involved in the etiology, progression, and treatment of disorders such as Parkinson's disease (PD). While such a concept is uncharted territory and even less is known about the mechanism by which this might be achieved, this study was undertaken to determine how retinal dopamine (DA), serotonin (5-HT), and melatonin (MEL) neurotransmitter systems might be involved in the control of movement in their own right. To explore these further, intravitreal (IVIT) injections of DA, 5-HT, and MEL were made 0.5 or 3 h prior to testing horizontal and vertical movement in the open field as well as assessment on three motor tests used routinely to evaluate movement as a preclinical model of PD. The doses of DA (2 µl of 25 and 75 µg/µl), 5-HT (2 µl of 5 and 15 µg/µl), and MEL (2 µl of 5 µg/µl) were chosen because of previous work demonstrating an anatomically precise effect of these transmitters after they were injected directly into the brain. The postinjection times of testing were also chosen on the basis of previous intracerebral and IVIT work intimating the importance of the circadian cycle in determining the efficacy of such effects. 0.5 h after IVIT injection of DA at the 25 and 75 µg/µl doses, significant inhibition of motor function was observed. While IVIT injection of 10 or 30 µg of 5-HT also inhibited motor performance, this was significantly less than that seen with DA. In fact, IVIT injection increases motor performance compared to vehicle injection on some parameters. The IVIT injection of 10 µg of MEL facilitated motor function on many parameters compared to DA, 5-HT, and vehicle injection. When rats were tested 3 h after IVIT injection, the inhibition of vertical movement was also observed compared to controls. The present results illustrate that specific retinal neurotransmitter systems participate in the normal control of bodily motor function. The possible involvement of these systems in movement disorders such as PD is the subject of ongoing research.
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ItemPolychromatic Light Exposure as a Therapeutic in the Treatment and Management of Parkinson's Disease: A Controlled Exploratory Trial(FRONTIERS MEDIA SA, 2018-09-19)Parkinson's disease (PD) is a disorder characterized by loss of dopamine (DA) in the nigro-striatal dopamine (NSD) system with the primary symptoms of bradykinaesia, rigidity, tremor, and altered gate. Secondary symptoms including depression, insomnia, involuntary movement, and psychiatric side effects are also commonly observed. While the treatment focus for the past 50 years has been aimed at replacing deficient DA, to relieve the primary symptoms, more recent studies have suggested that the circadian system plays a critical role in the etiology and treatment of this disorder. Several case studies and open label trials have implemented bright light therapy (BT) in an attempt to repair sleep, depression and even the primary motor symptoms of this disorder, however controlled studies are yet to be fully implemented. In this controlled trial, patients that had been maintained on BT daily for 4 months to 5 years previously were assigned to one of three groups: continued polychromatic light, continued with red light or discontinued polychromatic light for a 2 week period. The Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDSUPDRS), The Parkinson's Disease Questionnaire (PDQ-39), The Beck Depression Inventory II, The Beck Anxiety Inventory, The Epworth Sleep Scale (ESS) and a global rating scale were used to assess patients prior to and at 1 and 2 weeks after commencing the trial. Patients continuing polychromatic BT showed significant improvement on the MDSUPDRS Rating Scale (12 points; p = 0.028), the PDQ-39 (10 points; p = 0.011), ESS (4 points; p = 0.013), and numerous motor and secondary symptoms on a global rating scale. Performance on standardized motor tests also incrementally improved in this group while those exposed to red light and those that discontinued BT treatment deteriorated. These results demonstrate that strategically applied polychromatic light was beneficial in reducing many primary motor and secondary symptoms of PD. Further work investigating the role of light in mitigating PD symptoms and involvement of the circadian system will provide further advances in the treatment of PD. Clinical Trial Registration: http://www.anzctr.org.au, identifier ACTRN12617001309370.
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ItemLong-term captivity is associated with changes to sensory organ morphology in a critically endangered insect(WILEY, 2022-02)Abstract Captive breeding programmes are key to many threatened species reintroduction strategies but could potentially be associated with adaptations to captivity that are maladaptive in their natural habitat. Despite the importance of sensory ecology to biological fitness, few studies explore sensory system adaptations to captivity. Captive environments are devoid of predators and provide ready access to food sources and potential mates, thus reducing the need for individuals to use signals and cues to identify and locate resources or detect potential threats. With reduced complexity of the signalling environment, relaxation of selective pressures may favour reduced investment in sensory organs in captivity. We test this prediction in an iconic critically endangered invertebrate, the Lord Howe Island stick insect Dryococelus australis, which was extirpated from the island in the 1920s/30s and rediscovered on a nearby volcanic stack, Ball's Pyramid, in 2001. Using historical specimens from these populations and specimens from the 8–10th and 14th generations of a long‐term conservation captive breeding programme, we examine differences in behaviourally relevant morphological traits of the compound eyes (visual organs) and antennae (olfactory organs). We find that captivity is associated with smaller compound eye size, smaller eye ommatidia and reduced density of antennal odour receptors. These morphological changes are indicative of reduced sensitivity to visual and olfactory signals and cues, and therefore are likely to have fitness implications when reintroducing a captive population into the wild. Synthesis and applications. We observe differences in sensory organ morphology between wild and captive‐bred populations of the critically endangered Lord Howe Island stick insect. Our results emphasise the importance of incorporating evolutionary biology and sensory ecology into conservation programme design: to minimise the potential for captive breeding environments to compromise sensory systems that support appropriate behaviours upon reintroduction of populations into a natural habitat.