Clyde Hamilton Wild

The effect of stress and stress hormones on dynamic colour-change in a sexually dichromatic Australian frog.

Rapid colour changes in vertebrates have fascinated biologists for centuries, herein we demonstrate dynamic colour change in an anuran amphibian, the stony creek frog (Litoria wilcoxii), which turns from brown to bright (lemon) yellow during amplexus. We show this by comparing the colour of baseline (unpaired males) and amplecting (paired) males. We also investigate the possible role of stress and stress hormones on this colour change. Frogs were subjected to four different levels of stressors (handling, toe-clipping, saline injection and adrenocorticotropic hormone [ACTH] injection) and the colour change was measured using digital photography. A comparison of baseline colour and stress hormone (corticosterone) levels was also conducted to give further insight to this topic. From the images, the Red Blue Green (RGB) colour values were calculated, and a principal components analysis (PCA) was used to create a single colour metric (the major axis) as an index of colour in the visible spectrum. A moderate stressor (toe-clipping) led to a significant change in colour (within 10 min) similar to that of amplecting males. Surprisingly, neither a mild stressor (handling and saline injection) nor the maximum stressor (handling and ACTH injection) led to a lightening response. This study confirms that the dynamic male colour change in this species in response to medium stressors adds new knowledge to the understanding of the functional mechanisms of dynamic colour change in amphibians.

Relationships between anopheline mosquitoes and topography in West Timor and Java, Indonesia

BackgroundMalaria is a serious health issue in Indonesia. Mosquito control is one aspect of an integrated malaria management programme. To focus resources on priority areas, information is needed about the vectors and their habitats. This research aimed to identify the relationship between anopheline mosquitoes and topography in West Timor and Java.MethodsStudy areas were selected in three topographic types in West Timor and Java. These were: coastal plain, hilly (rice field) and highland. Adult mosquitoes were captured landing on humans identified to species level and counted.ResultsEleven species were recorded, four of which were significant for malaria transmission: Anopheles aconitus, Anopheles barbirostris, Anopheles subpictus and Anopheles sundaicus. Each species occupied different topographies, but only five were significantly associated: Anopheles annularis, Anopheles vagus and Anopheles subpictus (Java only) with hilly rice fields; Anopheles barbirostris, Anopheles maculatus and Anopheles subpictus (West Timor only) with coastal areas.ConclusionInformation on significant malaria vectors associated with specific topography is useful for planning the mosquito control aspect of malaria management.

Distribution and population genetics of the threatened freshwater crayfish genus Tenuibranchiurus (Decapoda : Parastacidae)

Very high rates of extinction are recorded in freshwater ecosystems, with coastally distributed species threatened by urban development, pollution and climate change. One example, the world’s second smallest freshwater crayfish (genus Tenuibranchiurus), inhabits coastal swamps in central-eastern Australia. Although only one species is described (Tenuibranchiurus glypticus), it was expected that populations isolated through habitat fragmentation would be highly divergent. The aims of this study were to determine if populations of Tenuibranchiurus are genetically distinct, and if ancient divergence, as indicated in other species in the region, was evident. Tenuibranchiurus were collected at seven sites, extending the known geographical distribution ∼260 km south to Wooli, New South Wales. Analysis of two mitochondrial DNA gene regions indicated two highly divergent clades, with numerous additional subclades. Both clades and subclades were strongly congruent with geographical location, and were estimated to have diverged from each other during the Miocene or Pliocene era. Little sharing of haplotypes between subpopulations was evident, indicating negligible gene flow, and genetic differentiation between subclades possibly indicates distinct species. The coastal distribution of Tenuibranchiurus, severe habitat fragmentation and clear differences between subclades suggest that they should be recognised as evolutionarily significant units, and be treated as such if conservation and management initiatives are warranted.

Thermal limit of Euastacus sulcatus (Decapoda: Parastacidae), a freshwater crayfish from the highlands of central eastern Australia

Increased temperature as a potentially threatening process, and the need to investigate the thermal tolerance of the ‘highland-rainforest’ Euastacus were first identified 20 years ago; however, the thermal repertoire of Euastacus has still not been explored. Euastacus is the largest of Australia’s 10 freshwater crayfish genera with 52 species, and includes many of the largest, slowest-growing and longest-lived species (some >35 years) in the World. Several species have distributions consistent with being ‘climate refugees’, namely, being closely associated with cool, damp conditions and restricted to isolated mountain-top refuges. The present study investigated the critical thermal limit of a well known abundant species, Euastacus sulcatus, from central eastern Australia. Thermal limit was assessed using chronic, ongoing exposure to steadily increasing temperature, with the breakdown of physiological function tested by righting response. Distress was clearly evident in the crayfish at ~23°C (e.g. sluggish, lack of aggression), and the test criterion was met at ~27°C, with animals effectively incapacitated and unable to right themselves. Field water temperatures rarely exceed 21°C; however, any increases in environmental temperature may expose this species to temperatures where physiological stress may become problematic.

Long-term frequent prescribed fire decreases surface soil carbon and nitrogen pools in a wet sclerophyll forest of southeast Queensland, Australia.

Prescribed fire is one of the most widely-used management tools for reducing fuel loads in managed forests. However the long-term effects of repeated prescribed fires on soil carbon (C) and nitrogen (N) pools are poorly understood. This study aimed to investigate how different fire frequency regimes influence C and N pools in the surface soils (0-10 cm). A prescribed fire field experiment in a wet sclerophyll forest established in 1972 in southeast Queensland was used in this study. The fire frequency regimes included long unburnt (NB), burnt every 2 years (2yrB) and burnt every 4 years (4yrB), with four replications. Compared with the NB treatment, the 2yrB treatment lowered soil total C by 44%, total N by 54%, HCl hydrolysable C and N by 48% and 59%, KMnO4 oxidizable C by 81%, microbial biomass C and N by 42% and 33%, cumulative CO2-C by 28%, NaOCl-non-oxidizable C and N by 41% and 51%, and charcoal-C by 17%, respectively. The 4yrB and NB treatments showed no significant differences for these soil C and N pools. All soil labile, biologically active and recalcitrant and total C and N pools were correlated positively with each other and with soil moisture content, but negatively correlated with soil pH. The C:N ratios of different C and N pools were greater in the burned treatments than in the NB treatments. This study has highlighted that the prescribed burning at four year interval is a more sustainable management practice for this subtropical forest ecosystem.

Soil carbon and nitrogen dynamics in the first year following herbicide and scalping in a revegetation trial in south-east Queensland, Australia

During revegetation, the maintenance of soil carbon (C) pools and nitrogen (N) availability is considered essential for soil fertility and this study aimed to evaluate contrasting methods of site preparation (herbicide and scalping) with respect to the effects on soil organic matter (SOM) during the critical early establishment phase. Soil total C (TC), total N (TN), hot-water extractable organic C (HWEOC), hot-water extractable total N (HWETN), microbial biomass C and N (MBC and MBN), total inorganic N (TIN) and potentially mineralizable N (PMN) were measured over 53 weeks. MBC and MBN were the only variables affected by herbicide application. Scalping caused an immediate reduction in all variables, and the values remained low without any sign of recovery for the period of the study. The impact of scalping on HWETN and TIN lasted 22 weeks and stabilised afterwards. MBC and MBN were affected by both herbicide and scalping after initial treatment application and remained lower than control during the period of the study but did not decrease over time. While scalping had an inevitable impact on all soil properties that were measured, that impact did not worsen over time, and actually improved plant growth (unpublished data) while reducing site establishment costs. Therefore, it provides a useful alternative for weed control in revegetation projects where it is applied only once at site establishment and where SOM would be expected to recover as canopy closure is obtained and nutrient cycling through litterfall commences.

Gut content analysis to distinguish between seed feeding and mycophagy of a biphyllid beetle larva found on Acacia melanoxylon

In a search for potential biocontrol agents for Acacia melanoxylon R. Br. (Mimosaceae), larvae of the beetle Diplocoelus dilataticollis Lea (Coleoptera; Biphyllidae) were found within damaged seeds of A. melanoxylon. The gut contents of larvae and adults were examined to determine whether their diet included seeds, in apparent contradiction to the known mycophagous diet of members of this family of beetles. Calcofluor M2R White, a plant cell-wall staining optical brightener was used to differentiate between plant cell fragments and fungal tissue in the gut content smears. Gut contents of adults of a known seed predator of A. melanoxylon, a weevil of the genus Melanterius, were examined in the same way to provide a benchmark. The gut contents of D. dilataticollis differed from those of Melanterius sp. Fungal structures and microbes were found in the gut of D. dilataticollis, in contrast to plant cell fragments found in the gut of the weevil and from scrapes made directly from seeds. We conclude that larvae of D. dilataticollis feed primarily on fungi associated with damaged seed and therefore may not be the proximate cause of seed damage.

A novel genus and cryptic species harboured within the monotypic freshwater crayfish genus Tenuibranchiurus Riek, 1951 (Decapoda: Parastacidae)

Identifying species groups is an important yet difficult task, with there being no single accepted definition as to what constitutes a species, nor a set of criteria by which they should be delineated. Employing the General Lineage Concept somewhat circumvents these issues, as this concept allows multiple concordant lines of evidence to be used as support for species delimitation, where a species is defined as any independently evolving lineage. Genetically diverse groups have previously been identified within the monotypic parastacid genus Tenuibranchiurus Riek, 1951, but no further investigation of this diversity has previously been undertaken. Analysis of two mitochondrial DNA gene regions has previously identified two highly divergent groups within this taxon, representing populations from Queensland (Qld) and New South Wales (NSW), respectively. Additional testing within this study of both mitochondrial and nuclear DNA through species discovery analyses identified genetically diverse groups within these regions, which were further supported by lineage validation methods. The degree of genetic differentiation between Qld and NSW populations supports the recognition of two genera; with Qld retaining the original genus name Tenuibranchiurus, and NSW designated as Gen. nov. until a formal description is completed. Concordance between the species discovery and lineage validation methods supports the presence of six species within Tenuibranchiurus and two within Gen. nov. The recognition of additional species removes the monotypy of the genus, and the methods used can improve species identification within groups of organisms with taxonomic problems and cryptic diversity.

Mosquito Longevity, Vector Capacity, and Malaria Incidence in West Timor and Central Java, Indonesia

The aim of this paper was to relate anopheline mosquito longevity to malaria incidence in two areas in Indonesia: West Timor and Central Java. We estimated the physiological age of females captured landing on humans or resting inside and outside buildings. The estimate was based on the state of the ovaries and was used to estimate longevity. The results showed that there were large differences between the two areas surveyed. In West Timor the longevity of the anophelines ranged from 13 to 23 days, sufficient for completing the intrinsic incubation cycle and for malaria transmission, whereas in Central Java the longevity was only 3 days, insufficient both for incubation and for transmission. We concluded that the West Timor study area had a greater risk of malaria transmission than that of Central Java and this was supported by village survey data that showed greater malaria incidence in West Timor than in Central Java.

Physiological and biochemical responses to elevated temperature in a threatened freshwater crayfish, Euastacus sulcatus (Decapoda: Parastacidae)

Projected elevations in environmental temperature are expected to have a detrimental effect on organisms with distributions that are already restricted to high-altitude refugia, especially where dispersal is compromised due to population isolation by unsuitable intervening habitats. The present study was carried out on such an organism, namely Euastacus sulcatus, to determine: (1) the temperature at which thermal stress occurs under laboratory conditions; and (2) whether thermal stress is already occurring naturally in contemporary field-acclimatised individuals. The laboratory data provided evidence that biochemical and physiological stress occurred in E. sulcatus at 22.5°C or higher. In the field, oxidative stress was characterised by an increase in the oxidised redox state of glutathione within a low-altitude population accompanied by significantly elevated protein carbonyls and lipid peroxidation. The data confirmed that potential thermal stress was present in E. sulcatus residing at the lower end of its altitudinal distribution, indicating that this threatened species is already challenged within localised populations in their natural environment. Together, these results reveal that future increases in environmental temperature are not only likely to result in increased baseline levels of stress in E. sulcatus, but also forecast further restriction in the altitudinal distribution of the species in a warming climate.