Tropics Of North-eastern Australia Research Articles

In-field carbon dioxide removal via weathering of crushed basalt applied to acidic tropical agricultural soil

Enhanced weathering (EW) of silicate rocks such as basalt provides a potential carbon dioxide removal (CDR) technology for combatting climate change. Modelling and mesocosm studies suggest significant CDR via EW but there are few field studies. This study aimed to directly measure in-field CDR via EW of basalt applied to sugarcane on acidic (pH 5.8, 0–0.25 m) Ultisol in tropical northeastern Australia, where weathering potential is high. Coarsely crushed basalt produced as a byproduct of gravel manufacture (<5 mm) was applied annually from 2018 to 2022 at 0 or 50 t ha−1 a−1, incorporated into the soil in 2018 but not in subsequent years. Measurements in 2022 show increased soil pH and extractable Mg and Si at 0–0.25 m depth, indicating significant weathering of the basalt, but showed no increase in crop yield. Soil inorganic carbon content and bicarbonate (HCO3−) flux to deep drainage (1.25 m depth) were measured to quantify CDR in the 2022–2023 wet season (i.e. one year). Soil inorganic carbon was below detection limits. Mean HCO3− flux was 3.15 kmol ha−1 a−1 (±0.40) in the basalt-treated plots and 2.56 kmol ha−1 a−1 (±0.18) in the untreated plots but the difference (0.59 kmol ha−1 a−1 or 0.026 t CO2 ha−1 a−1) was not significant (p = 0.082). Most weathering of the basalt was attributed to acids stronger than carbonic acid. These were, in decreasing order of contribution, surface-bound protons (inherent soil acidity), nitric acid (from nitrification), organic acids, and acids associated with cation uptake by plants. These results indicate in-field CDR via EW of basalt is low where soil and regolith pH is well below the pKa1 of 6.4 for H2CO3. However, increased soil pH, and the consumption of strong acids by weathering will eventually lead to reduced CO2 emission from soil or evasion from rivers, with continued basalt addition.

The Black-winged Monarch (Monarcha frater): Geographic variation, taxonomy, a "new" population, and an enduring mystery in migration

The Black-winged Monarch (Monarcha frater) inhabits low-mid elevation forests across New Guinea and far north-eastern Australia. Of its four recognized subspecies, M. f. canescens is migratory, breeding in tropical north-eastern Australia from approximately November–March. The non-breeding range of M. f. canescens, apart from some individuals overwintering in Australia, has been unknown for >100 years. Data from 194 New Guinean and Australian specimens and a literature review have not solved this mystery; the narrow latitudinal range of the intratropical migration may inhibit use of GPS loggers in resolving the migration route. Field work in central and western parts of southern New Guinea is needed. Specimen data, however, revealed an essentially overlooked population in north-western New Guinea east of the Bird's Head Peninsula phenotypically indistinguishable from nominate M. f. frater of that Peninsula. Future genomic analysis of the complex will be largely done from toepad skin because frozen tissue samples for DNA analysis exist only of four individuals of what we suggest should be elevated to species rank as M. periophthalmicus. We discuss how genomic analysis might distinguish among alternative taxonomic hypotheses of one, two or three species. We suggest English names for what we consider to be three diagnosable taxa worth recognizing at species rank in this group: Arfak Monarch corresponding to M. frater (Bird's Head Peninsula and the “new” population of north-western New Guinea); Pearly Monarch for M. canescens (Australia and still unknown non-breeding range), and Masked Monarch for M. periophthalmicus (including kunupi, elsewhere in New Guinea).

Reply to the comment by Dougherty, A.J. on “Relative sea-level records preserved in Holocene beach-ridge strandplains – An example from tropical northeastern Australia” by Brooke, B.P., Huang, Z., Nicholas, W.A., Oliver, T.S.N., Tamura, T., Woodroffe, C.D., Nichol, S.L.

The approach and results of our 2019 paper (Brooke et al., 2019) have been criticised by Dougherty (2022). We examined the sensitivity of a tropical, coarse sand strandplain to changes in relative sea level as expressed through beach-ridge morphology and the elevation of beach berms preserved in the succession of cyclone-generated beach ridges at Cowley Beach, Queensland, Australia. Rather than presenting a new sea-level curve for this region as suggested by Dougherty, our 2019 study of the Cowley Beach strandplain revealed that when compared with the modelled Holocene relative sea-level record and sea-level indicator data for north-eastern Queensland, the strandplain morphology and stratigraphy provide a first-order representation of sea-level position. Importantly, Dougherty (2022) has overlooked the processes involved in the formation of beach ridges at this site and the spatial coverage of our analysis of the strandplain morphology. Both these factors are fundamental to the approach and conclusions of our 2019 paper. We reiterate here that the Cowley Beach strandplain morphology and succession of beach-berm deposits have elevation patterns that match well the broad trend in the regional relative sea-level model for the past 7 ka. We highlight those key beach-ridge formative processes and data limitations neglected in the Dougherty Comment. Finally, we note the challenges and opportunities for further research into the sedimentary records preserved in this distinctive type of tropical strandplain.

Comment on “Relative sea-level records preserved in Holocene beach-ridge strandplains – An example from tropical northeastern Australia” by Brooke, B.P., Huang, Z., Nicholas, W.A., Oliver, T.S.N., Tamura, T., Woodroffe, C.D., Nichol, S.L

Refined records of Holocene sea level and coastal evolution are needed to forecast changes in the Anthropocene. Beach ridge strandplains and other prograded barriers preserve an exceptional (and relatively untapped) archive of past sea level within their stratigraphy. Extracting these records using high-resolution geophysics can unearth sea-level indicators with the potential to resolve small fluctuations over large spatial- and temporal-scales. Brooke et al. (2019) construct a sea-level curve from Cowley strandplain and performs interesting modelling/analyses; but does so based on the beach ridge topography. Unfortunately, this methodological approach contradicts a long-held understanding that it is not appropriate to use ridge morphology or sediment analysis from cores/augers/pits to indicate sea level. This sets a misleading precedent if perpetuated in future research and does so at a critical time when extracting sea-level reconstructions from prograded barriers is becoming more established. While the Brooke et al. (2019) curve appears to correlate with data from this region, it is not precisely clear how it was constructed. Particularly perplexing is the most recent half of the curve, starting with the peculiar location of the modern analogue below mean sea level. Simply adjusting the existing curve to zero on the y-axis removes it from the tenuous correlation. This comment paper uses the geophysical and topographic data published in Brooke et al. (2019), as well as the protocol referenced, to construct relative sea-level curves. The results accentuate the difference between the reconstructions from the berm stratigraphy and the ridge morphology. Furthermore, despite the nature of this analysis utilizing a derivative dataset, the berm heights demonstrate remarkable correlation with the modelled sea-level curve for the region as well as the more traditional sea-level indicators. Ultimately, this glimpse provides insight on the possible extent of information that lies buried not just at Cowley and the 30+ prograded barriers around Australia, but at 300+ sites worldwide.

New ages of the world's largest-ever marsupial: Diprotodon optatum from Pleistocene Australia

The extinction of large-bodied terrestrial ‘megafauna’ during earlier phases of the Quaternary had a significant impact on the transforming structure of ecosystems. However, the causes of such losses remains difficult to determine in part because of a paucity of reliable geochronological information about the taxa involved. This is especially true for continents such as Australia where the majority of extinct species have never been dated using radiometric and/or luminescence methods. Here we add new understanding about the geochronology of the world's largest-ever marsupial, the giant wombat-like Diprotodon optatum, an iconic member of the large herbivore guild of Pleistocene Australia. We present 28 new direct U-series ages (dentine) and 10 luminescence ages (sediments) for D. optatum fossils from three sites in tropical north and subtropical eastern Australia. The luminescence ages lie close to saturation for the tropical northern site of Floraville and therefore indicate minimum ages, and sediments from Gowrie Creek in the Darling Downs were mixed and can only be stated as a likely age range. Nevertheless the results assist in our broader understanding of the timing of persistence of the species. Our results demonstrate that the species roamed the northern tropics at least until the mid-Pleistocene (ca. 420 ka). They likely remained widespread during Marine Isotope Stage 5 (ca. 110 ka) and were abundant on the Darling Downs of eastern Australia. The youngest of the new ages that we report (ca. 60 ka) are from Neds Gully on the Darling Downs, a catchment previously considered by some to contain among the last survivors of the now-extinct megafauna. The new dated record demonstrates that deposits of varying ages occur within the catchment. Consequently, existing species lists that treat Neds Gully as a single faunal assemblage are likely significantly time-averaged and overinflated in terms of palaeo-diversity.

Relative sea-level records preserved in Holocene beach-ridge strandplains – An example from tropical northeastern Australia

Northeastern Queensland is a far-field site from ice caps formed during the Last Glacial. However, the region has experienced glacio-hydroisostatically driven coastal elevation change during the Holocene that generated a distinctive relative sea-level record. We tested whether this subtle vertical movement of the coast is recorded in the morphology and stratigraphy of the beach-ridge strandplain at Cowley Beach, which comprises a series of 36 prominent and several subdued or truncated beach ridges. Previous studies have shown that the strandplain records the long-term progradation of the coast, with the ridges comprising coarse-medium sand that was deposited during both fairweather (foreshore and berm facies) and tropical cyclone events (erosional unconformities; storm-surge deposits) over the past approximately 7 ka. We utilised a fine-scale digital elevation model of the strandplain to examine beach ridge morphology and to compare the elevation pattern with published Holocene sea-level data for the region. The overall elevation pattern of the strandplain surface is consistent with the regional sea-level history, that includes a highstand at around 6 ka BP generated by isostatic uplift, and the elevation of the berm facies matches well robust coral sea-level indicator data. We also modelled the strandplain topographic patterns that would result under stable and continually rising Holocene sea-levels. The frequencies of elevation classes across the strandplain are normally distributed when the strandplain is deposited during a period of stable sea level, and negatively skewed with a continually rising sea level, consistent with the expected patterns. The results indicate the sensitivity of the elevation of the top of the berm facies preserved in beach ridges to subtle changes in sea level (tens of cm over a thousand years). Our results further underline the utility of beach-ridge strandplains, a globally distributed coastal landform, for building relatively detailed regional records of sea level during the Holocene at sites currently lacking this information.

Trophic guild concept: factors affecting within‑guild consistency for tropical estuarine fish

The trophic guild concept has proved useful in distilling the diverse feeding inter-actions displayed by fish in temperate estuaries into a standardised subset that simplifies the application of trophic information to management. However, the high species richness displayed by tropical flora and fauna introduces the potential for feeding diversity within presumed guilds, potentially reducing the value of the standard guild concept. We evaluated within-guild consistency for a group of tropical estuarine fish species comprising a presumably coherent trophic zoobenthivore feeding guild (i.e. fish that feed primarily on zoobenthic prey) within 10 estuarine systems in tropical northeastern Australia. The zoobenthivore assemblage did not form a single coherent trophic group, rather the different components of the zoobenthivore guild responded to the broad spectrum of available prey in distinctly different ways. Some species displayed quite general diets while others fed principally on particular types of zoobenthic prey. The distinct prey specialisations often lead to different members of the presumed guild participating in different food chain pathways within the estuarine food web. As a result, substantial and important trophic differences would be masked if these disparate components were aggregated into a single trophic guild. While simplifications can be valuable, and often necessary, in data-poor situations, the complexity uncovered in this study emphasises that caution is required in applying a broad simplified scheme such as the guild concept to specific situations. Caution must be used when applying a guild approach that imports interpretation from other species and/or locations and should be explicitly recognised as an interim position until more specific data can be acquired.

Dugong dugon feeding in tropical Australian seagrass meadows: implications for conservation planning.

Dugongs (Dugong dugon) are listed as vulnerable to extinction due to rapid population reductions caused in part by loss of seagrass feeding meadows. Understanding dugong feeding behaviour in tropical Australia, where the majority of dugongs live, will assist conservation strategies. We examined whether feeding patterns in intertidal seagrass meadows in tropical north-eastern Australia were related to seagrass biomass, species composition and/or nitrogen content. The total biomass of each seagrass species removed by feeding dugongs was measured and compared to its relative availability. Nitrogen concentrations were also determined for each seagrass species present at the sites. Dugongs consumed seagrass species in proportion to their availability, with biomass being the primary determining factor. Species composition and/or nitrogen content influenced consumption to a lesser degree. Conservation plans focused on protecting high biomass intertidal seagrass meadows are likely to be most effective at ensuring the survival of dugong in tropical north-eastern Australia.

Declines of seagrasses in a tropical harbour, North Queensland, Australia, are not the result of a single event.

A recent paper inferred that all seagrass in Cairns Harbour, tropical north-eastern Australia, had undergone 'complete and catastrophic loss' as a result of tropical cyclone Yasi in 2011. While we agree with the concern expressed, we would like to correct the suggestion that the declines were the result of a single climatic event and that all seagrass in Cairns Harbour were lost. Recent survey data and trend analysis from an on-ground monitoring program show that seagrasses in Cairns Harbour do remain, albeit at low levels, and the decline in seagrasses occurred over several years with cyclone Yasi having little additional impact. We have conducted annual on-ground surveys of seagrass distribution and the above-ground meadow biomass in Cairns Harbour and Trinity Inlet since 2001. This has shown a declining trend in biomass since a peak in 2004 and in area since it peaked in 2007. In 2012, seagrass area and above-ground biomass were significantly below the long-term (12 year) average but seagrass was still present. Declines were associated with regional impacts on coastal seagrasses from multiple years of above-average rainfall and severe storm and cyclone activity, similar to other nearby seagrass areas, and not as a result of a single event.

The use of the brown macroalgae, Sargassum flavicans, as a potential bioindicator of industrial nutrient enrichment

Nutrient bioindicators are increasingly being recognised as a diagnostic tool for nutrient enrichment of estuarine and marine ecosystems. Few studies, however, have focused on field translocation of bioindicator organisms to detect nutrient discharge from industrial waste. The brown macroalgae, Sargassum flavicans, was investigated as a potential bioindicator of nutrient-enriched industrial effluent originating from a nickel refinery in tropical north-eastern Australia. S. flavicans was translocated to a number of nutrient enriched creek and oceanic sites over two seasons and assessed for changes in stable isotope ratios of 15N and 13C within the plant tissue in comparison to reference sites. Nutrient uptake in macroalgae, translocated to the nutrient enriched sites adjacent to the refinery, increased 3–4-fold in δ15N, compared to reference sites. Using δ15N of translocated S. flavicans proved to be a successful method for monitoring time-integrated uptake of nitrogen, given the current lack of passive sampler technology for nutrient monitoring.

Late Quaternary terrestrial and marine environments for the Wet Tropics of Northeastern Australia, based on ODP Site 820

Late Quaternary terrestrial and marine environments for the Wet Tropics of Northeastern Australia, based on ODP Site 820

Australian Tropical and Subtropical Rain Forest Community Assembly: Phylogeny, Functional Biogeography, and Environmental Gradients

AbstractTo compare community assemblage patterns in tropical northeastern and subtropical central eastern Australia across selected gradients and scales, we tested the relationship of species traits with phylogenetic structure, and niche breadth. We considered phylogenetic relationships across current‐day species in assemblages in relation to rain forest species pool sizes, and trait values along gradients including elevation and latitude. Trait values were quantified across scales for seed size, leaf area, wood density and maximum height at maturity for 1137 species and 596 assemblages using trait gradient analysis (TGA). Local assemblages of subtropical species had narrower trait ranges, and higher niche breadth values than corresponding assemblages of tropical species. Leaf size and seed size increased at low latitudes, and community phylogenetic structure was most strongly correlated with seed traits in the subtropics, reflecting dispersal and re‐colonization processes. Elevation accounted for little of the variance in community phylogenetic structure or trait variation across local and regional scales. Stable moist forest areas retained many species from ancestral rain forest lineages across a range of temporally conserved habitats; species within assemblages were less related; and rain forest assemblages had higher functional diversity, but lower niche breadth. This suggests that on average, assemblages of species in stable areas had greater trait variation and narrower distributions. Historic and recent rain forest contraction and re‐expansion can result in recolonized areas that are dominated by species that are more related (phylogenetically) than by chance, have smaller, widely dispersed seeds, and greater niche breadth (broader distributions).

A 100 ka record of fluvial activity in the Fitzroy River Basin, tropical northeastern Australia

This study reports the nature and timing of Quaternary fluvial activity in the Fitzroy River basin, which drains a diverse 143,000 km 2 area in northeastern Queensland, before discharging into the Great Barrier Reef Marine Park. The catchment consists of an extensive array of channel and floodplain types that we show have undergone large-scale fluvial adjustment in-channel planform, geometry and sinuosity. Optically stimulated luminescence (OSL) dating of quartz sediments from fifteen (3–18 m) floodplain cores throughout the basin indicates several discrete phases of active bedload activity: at ∼105–85 ka in Marine Isotope Stage (MIS) 5, at ∼50–40 ka (MIS 3), and at ∼30–10 ka (MIS 3/2). The overall timing of late Quaternary fluvial activity correlates well with previous accounts from across Australia with rivers being primarily active during interstadials. Fluvial activity, however, does not appear to have been synchronous throughout the basin’s major sub-catchments. Fluvial activity throughout MIS 2 (i.e. across the Last Glacial Maximum) in the meandering channels of the Fitzroy correlates well with regional data in tropical northeastern Queensland, and casts new light on the river response to reduced rainfall and vegetation cover suggested by regional palaeoclimate indicators. Moreover, the absence of a strong Holocene signal is at odds with previous accounts from elsewhere throughout Australia. The latitudinal position of the Fitzroy across the Tropic of Capricorn places this catchment at a key location for elucidating the main hydrological drivers of Quaternary fluvial activity in northeastern Australia, and especially for determining tropical moisture sources feeding into the headwaters of Cooper Creek, a major river system of the continental interior.

Overlooked small and juvenile piscivores dominate shallow-water estuarine “refuges” in tropical Australia

A model was developed to estimate the relative impacts of different functional groups of piscivores on the shallow-water estuarine nursery assemblage of tropical north-eastern Australia. Data on variability in the occurrence, number and type of fish in the diet of different piscivores was combined with estimates of the abundance of each group. The model predicts that previously overlooked small and occasional or ‘minor’ piscivores, such as sillaginids, ambassids, sparids and small juvenile carangids, inflict mortality on new recruits to shallow-water nursery habitats that is orders of magnitude greater than that imparted by more conspicuous larger piscivores. Because of their high abundance, a shift in the diet of minor piscivores to prey on new recruits results in a massive increase in the consumption of fish prey by the piscivore assemblage as a whole. Even if the evidence that minor piscivores switch to target new recruits was rejected, the model shows that the highly abundant minor piscivores must still exert a significant proportion of predation mortality experienced by recruiting fishes. As a broad functional group, minor piscivores occur in most aquatic systems around the globe and are likely to play an important but largely overlooked role as predators that shape communities through predation on critical early life stages of other fishes.

Efficacy of exclusion fencing to protect ephemeral floodplain lagoon habitats from feral pigs (Sus scrofa)

Foraging by feral pigs can strongly affect wetland vegetation assemblages and so too wider ecological processes, although their effects on freshwater ecosystems have seldom been studied. We assessed the ecological effects of pig foraging in replicate fenced and unfenced ephemeral floodplain lagoons in tropical north-eastern Australia. Pig foraging activities in unfenced lagoons caused major changes to aquatic macrophyte communities and as a consequence, to the proportional amounts of open water and bare ground. The destruction of macrophyte communities and upheaval of wetland sediments significantly affected wetland turbidity, and caused prolonged anoxia and pH imbalances in the unfenced treatments. Whilst fencing of floodplain lagoons will protect against feral pig foraging activities, our repeated measures of many biological, physical and chemical parameters inferred that natural seasonal (i.e. temporal) effects had a greater influence on these variables than did pigs. To validate this observation requires measuring how these effects are influenced by the seemingly greater annual disturbance regime of variable flooding and drying in this tropical climate.

Sus scrofa: Population Structure, Reproduction and Condition in Tropical North-Eastern Australia

Three feral pig populations inhabiting contrasting environments along the north eastern coast of Australia have been investigated with respect to population structure, individual condition and reproduction. The population on Prince of Wales Island contains a large proportion of juvenile and sub-adult pigs but lacks pigs in the higher age classes. Individuals also breed at an earlier age than animals of the mainland populations. Pig populations on Cape York Peninsula show a larger proportion of older animals and feral pigs living in rainforest habitats show a low proportion of animals in very young and very old age classes. Pigs from the lowland rainforest population are in better condition than those of the other populations for most of the year, reflecting the availability of food all year round in this environment. Differences in the population structure of the three populations are discussed with respect to fecundity and several mortality factors such as predation and diseases/parasites.

Cyanobacterial composition of microbial mats from an Australian thermal spring: a polyphasic evaluation

Cyanobacterial composition of microbial mats from an alkaline thermal spring issuing at 43-71 degrees C from tropical north-eastern Australia are described using a polyphasic approach. Eight genera and 10 species from three cyanobacterial orders were identified based on morphological characters. These represented taxa previously known as thermophilic from other continents. Ultrastructural analysis of the tower mats revealed two filamentous morphotypes contributed the majority of the biomass. Both types had ultrastructural characteristics of the family Pseudanabaenaceae. DNA extracts were made from sections of the tentaculiform towers and the microbial community analysed by 16S cyanobacteria-specific PCR and denaturing-gradient gel electrophoresis. Five significant bands were identified and sequenced. Two bands clustered closely with Oscillatoria amphigranulata isolated from New Zealand hot springs; one unique phylotype had only moderate similarity to a range of Leptolyngbya species; and one phylotype was closely related to a number of Geitlerinema species. Generally the approaches yielded complementary information, however the results suggest that species designation based on morphological and ultrastructural criteria alone often fails to recognize their true phylogenetic position. Conversely some molecular techniques may fail to detect rare taxa suggesting that the widest possible suite of techniques be applied when conducting analyses of cyanobacterial diversity of natural populations. This is the first polyphasic evaluation of thermophilic cyanobacterial communities from the Australian continent.

Trace metal uptake by the grass Melinis repens from roadside soils and sediments, tropical Australia

This study reports on trace metal uptake by the grass species Melinis repens, growing in roadside soils and sediments in tropical northeastern Australia. Median total Cu, Pb, Ni and Zn concentrations were significantly (P < 0.05) higher in road edge soils (Cu = 61.1 mg/kg, Pb = 97.3 mg/kg, Ni = 28.6 mg/kg, Zn = 729 mg/kg) than in background soils collected away from roads (Cu = 5.8 mg/kg, Pb = 11.2 mg/kg, Ni = 3.7 mg/kg, Zn = 21 mg/kg). Significantly (P < 0.05) elevated Zn values were recorded in the stems of the M. repens specimens growing on roadside soils (231.6 mg/kg dry weight of tissue) compared with those of grasses growing on background soils (40.8 mg/kg dry weight of tissue). Moreover, median Cu, Ni and Zn values in the roots of roadside grasses (Cu = 29.1 mg/kg, Ni = 2.73 mg/kg, Zn = 169 mg/kg) were significantly (P < 0.05) higher than their respective levels in the roots of background M. repens samples (Cu = 5.98 mg/kg, Ni = 0.70 mg/kg, Zn = 22 mg/kg). A greenhouse experiment showed that Cu and Zn in road sediments are labile and are available for uptake by M. repens. The studied roadside soils and sediments were leached with a diethylenetriaminepentaacetic acid–CaCl2–triethanolamine–HCl extraction solution, which proved to be a rudimentary indicator of Zn availability and uptake to the root tissue of M. repens. The results demonstrate that trace metals in roadside grasses have the potential to be directed up the food-chain as grasses are consumed by herbivores. In addition, bioavailable metal contaminants hosted by road sediments have the capacity to impact on ecosystems downstream of roads because these sediments are mobilised by road runoff waters from road surfaces into adjoining catchments.

Hydration Knowledge, Behaviours and Status of Staff at the Residential Camp of a Fly-in/Fly-out Minerals Extraction and Processing Operation in Tropical North-Eastern Australia

A study was conducted with staff at a fly-in/fly-out mine camp to determine the: hydration knowledge, perceptions and behaviours; hydration status and needs; and perceived taste of potable water. A structured questionnaire was used to survey the self-reported hydration behaviour, knowledge and perception of. The study of the hydration status and needs of day shift staff while at the residential camp comprised measurements at 1800 h and 0600 h of weight, urine specific gravity and fluid intake. Staff rated the perceived taste of bottled, filtered potable and unfiltered potable waters on a seven point visual analogue scale. The mean correct responses to the knowledge items surveyed (n=78) was 9.2 out of 12. Three-quarters (n=15) of the 20 responses to an open-ended question suggested improved water taste to increase water consumption. In the hydration status study (n=46), the mean urine specific gravities at 1800 h and 0600 h were both 1.022, and the median fluid intake and loss rates were both 2.1 ml.kg(-1).h(-1). Staff (n=105) rated unfiltered water (median 4.0) as tasting significantly worse than bottled (median 6.0) or filtered (median 6.0) waters (Friedman test, p<0.001). While dehydration knowledge appears adequate, the observed fluid intakes and specific gravities demonstrate that external factors such as perceived taste of water influence hydration behaviour.

VERY LOW ADDITIVE GENETIC VARIANCE AND EVOLUTIONARY POTENTIAL IN MULTIPLE POPULATIONS OF TWO RAINFORESTDROSOPHILASPECIES

Most quantitative traits are thought to exhibit high levels of genetic variance and evolutionary potential. However, this conclusion may be biased by a lack of studies on nonmodel organisms and may not generalize to restricted species. A recent study on a single, southern population of the rainforest-restricted Drosophila birchii failed to find significant additive genetic variance for the desiccation resistance trait; however, it is unclear whether this pattern extends to other D. birchii populations or to other rainforest species. Here we use an animal model design to show very low levels of additive genetic variance for desiccation resistance in multiple populations of two highly sensitive rainforest species of Drosophila from tropical northeastern Australia. In contrast, relatively high levels of genetic variance were found for morphological traits in all populations of the species tested. This indicates limited evolutionary potential for evolving increased desiccation resistance in these rainforest restricted species.