Testosterone effects on avian basal metabolic rate and aerobic performance : facts and artefacts

We examined the effects of cage size and testosterone (T) levels on basal and peak metabolic rates (BMR and PMR, respectively) and on pectoral and leg muscle masses of male house sparrows (Passer domesticus). Birds were housed either in small birdcages or in flight aviaries for at least 2 weeks prior to the initial metabolic evaluations. They were then implanted with either empty or T-filled silastic capsules and remeasured 5–6 weeks later. Birds treated with single T implants achieved breeding levels (4–6 ng/mL) and one group given double implants reached 10 ng/mL. There was no effect of T on BMR or PMR in any group studied, but there was an effect of caging. Caged birds showed significant reductions in PMR over the course of captivity, whereas PMR in aviary-housed birds were indistinguishable from their free-living counterparts. Testosterone treatment significantly increased leg muscle mass in caged birds, but had no effect on muscle mass in aviary-housed sparrows. We conclude that testosterone has no direct effect on sparrow metabolic rate or muscle mass, but may interact with cage conditions to produce indirect changes to these variables.

Camera traps : the research paparazzi

The use of cameras to monitor wildlife is commonplace; however, little is known of the effectiveness of different camera technologies for the detection of mammals. We compared the detection success of three different camera systems, a passive infrared (IR) system, an active IR and a constant video camera, alongside a trapping grid of Elliott and cage traps to determine their effectiveness at detecting mammals at multiple locations in the Otways National Park, Victoria, Australia (n = 160 events; 40 ± 23 [SD] events per night). Species detected and detection rates differed between methods (χ2 = 57.95, df = 2, p < 0.0001). Only house mice (Mus musculus) were detected by camera and traditional trapping techniques. Camera systems alone detected foxes (Vulpes vulpes) and a koala (Phascolarctos cinereus), while traditional traps captured bush rats (Rattus fuscipes), agile antechinus (Antechinus agilis) and a brush-tailed possum (Trichosurus vulpecula) which were not detected by the camera systems. Assuming that the video camera detected all mammals at the camera trap, the passive IR system detected almost all mammals detected by the video and it detected significantly more species than the active IR system. The choice of method will ultimately depend on the species of interest, logistics and the study site, and may substantially influence the results of a study.

Traceability and discrimination among differently farmed fish : a case study on Australian murray cod

The development of traceability methods to distinguish between farmed and wild-caught fish and seafood is becoming increasingly important. However, very little is known about how to distinguish fish originating from different farms. The present study addresses this issue by attempting to discriminate among intensively farmed freshwater Murray cod originating from different farms (indoor recirculating, outdoor floating cage, and flow through systems) in different geographical areas, using a combination of morphological, chemical, and isotopic analyses. The results show that stable isotopes are the most informative variables. In particular, δ13C and/or δ15N clearly linked fish to a specific commercial diet, while δ18O linked fish to a specific water source. Thus, the combination of these isotopes can distinguish among fish originating from different farms. On the contrary, fatty acid and tissue proximate compositions and morphological parameters, which are useful in distinguishing between farmed and wild fish, are less informative in discriminating among fish originating from different farms.

Effects of dietary astaxanthin concentration and feeding period on the skin pigmentation of Australian snapper Pagrus auratus (Bloch & Schneider, 1801)

A single-factor experiment was conducted to investigate the effects of dietary astaxanthin concentration on the skin colour of snapper. Snapper (mean weight=129 g) were held in white cages and fed one of seven dietary levels of unesterified astaxanthin (0, 13, 26, 39, 52, 65 or 78 mg astaxanthin kg⁻¹) for 63 days. Treatments comprised four replicate cages, each containing five fish. The skin colour of all fish was quantified using the CIE L^*, a^*, b^* colour scale after 21, 42 and 63 days. In addition, total carotenoid concentrations of the skin of two fish cage−1 were determined after 63 days. Supplementing diets with astaxanthin strongly affected redness (a^*) and yellowness (b^*) values of the skin at all sampling times. After 21 days, the a^* values increased linearly as the dietary astaxanthin concentration was increased before a plateau was attained between 39 and 78 mg kg⁻¹. The b^* values similarly increased above basal levels in all astaxanthin diets. By 42 days, a^* and b^* values increased in magnitude while a plateau remained between 39 and 78 mg kg⁻¹. After 63 days, there were no further increases in measured colour values, suggesting that maximum pigmentation was imparted in the skin of snapper fed diets >39 mg kg⁻¹ after 42 days. Similarly, there were no differences in total carotenoid concentrations of the skin of snapper fed diets >39 mg kg⁻¹ after 63 days. The plateaus that occurred in a^* and b^* values, while still increasing in magnitude between 21 and 42 days, indicate that the rate of astaxanthin deposition in snapper is limited and astaxanthin in diets containing >39 mg astaxanthin kg⁻¹ is not efficiently utilized. Astaxanthin retention after 63 days was greatest from the 13 mg kg⁻¹ diet; however, skin pigmentation was not adequate. An astaxanthin concentration of 39 mg kg⁻¹ provided the second greatest retention in the skin while obtaining maximum pigmentation. To efficiently maximize skin pigmentation, snapper growers should commence feeding diets containing a minimum of 39 mg unesterified astaxanthin kg⁻¹ at least 42 days before sale.

Changes in skin colour and cortisol response of Australian snapper Pagrus auratus (Bloch & Schneider, 1801) to different background colours

A two-factor experiment was carried out to investigate the change in skin colour and plasma cortisol response of cultured Australian snapper Pagrus auratus to a change in background colour. Snapper (mean weight=437 g) were held in black or white tanks and fed diets containing 39 mg unesterified astaxanthin kg⁻¹ for 49 days before being transferred from white tanks to black cages (WB) or black tanks to white cages (BW). Skin colour values [L^* (lightness), a^* (redness) and b^* (yellowness)] of all snapper were measured at stocking (t=0 days) and from cages of fish randomly assigned to each sampling time at 0.25, 0.5, 1, 2, 3, 5 and 7 days. Plasma cortisol was measured in anaesthetized snapper following colour measurements at 0, 1 and 7 days. Fish from additional black-to-black (BB) and white-to-white (WW) control treatments were also sampled for colour and cortisol at those times. Rapid changes occurred in skin lightness (L^* values) after altering background colour with maximum change in L^* values for BW and WB treatments occurring within 1 day. Skin redness (a*) of BW snapper continued to steadily decrease over the 7 days (a*=7.93 × e^{−0.051 × time}). Plasma cortisol concentrations were highest at stocking when fish were held at greater densities and were not affected by cage colour. The results of this study suggest that transferring dark coloured snapper to white cages for 1 day is sufficient to affect the greatest benefit in terms of producing light coloured fish while minimizing the reduction in favourable red skin colouration.

Population dynamics of the infaunal bivalve, Soletellina alba

The population dynamics of the infaunal bivalve Soletellina alba was investigated at three sites situated within close proximity to the mouth of the Hopkins River estuary. The initial study design was planned to examine the importance of winter flooding to the persistence of this bivalve mollusc within the Hopkins estuary, since mass mortalities have been observed during previous years coincident with periods of winter flooding. Unfortunately, the climatic conditions experienced during this study were atypical compared to the long-term average, so detailed sampling was limited to two, unanticipated, non-flood years rather than two, highly anticipated, flood years. This hampered my ability to conduct complete tests of the importance of winter flooding. Patterns of river discharge and the frequency and duration of mouth opening and closing differed greatly from that expected. Unexpectedly, periods of mouth closure were not always associated with periods of minimal river discharge; low salinities were another unexpected result during an extended period of mouth closure during 1998. As expected, salinities varied considerably with increasing water depth when the estuary mouth was open. Mouth closure lead to salinities becoming more uniform between water depths but hypoxic and anoxic conditions became evident via stratification in the water column at 1 m below the Australian Height Datum (AHD). Other than trends associated with increased water depth, significant variation was not evident between measurements of salinity taken from three sites within close proximity of the estuary mouth (approximately 500 m), or during changes in tide. The most pertinent anomaly was the absence of winter flooding. The distribution and abundance of juvenile and adult S. alba was variable across all Dates, Sites and Channel elevations (i.e. water depths) sampled during this study. An experimental test comparing the recruitment of juveniles at different channel elevations and in sediments of varying particle size was conducted during an exceptionally successful period of recruitment during 1999. The results of these tests showed that recruitment was greatest at the shallowest channel elevation used, and there was little evidence that sediment particle size influenced recruitment. In contrast to 1999, recruitment during 1997 or 1998 was extremely poor. Growth rates were monitored using tagged individuals held in caged and uncaged plots, which revealed that growth was highly variable among individuals, but not between Sites. These tests also revealed that growth was negligible during the colder, winter months, and that the fastest growing individuals were capable of growing 0.2 mm/day. Mixed results were obtained for tests of potential cage artifacts and the influence of handling. Caging and differing amounts of handling did not appear to influence growth, but there was evidence that cages and handling influenced bivalve condition and number of mortalities. These direct tests appeared to be the most appropriate method for determining growth rates of this species, since attempts to analyse length-frequency data were made difficult by the apparent convergence of cohorts, and shell aging is difficult due to the thin, fragile nature of the shell. As expected, mass mortalities were observed during the flood of 1996, but not during the two non-flood years of 1997 and 1998. There were, however, some considerable declines in abundances at some channel elevations during the two non-flood years. However, these declines were attributable to the complete disappearance of individuals, rather than the sudden presence of numerous, recently dead individuals that typify observed declines during winter flooding. The complete disappearance of individuals suggest that S. alba may be capable of post-settlement emigration, or that they were consumed by an unknown predator. Salinity tolerance tests showed that bivalves exposed to low salinities (≤6 ppt), exhibited poorer condition and took longer to re-burrow into sediments than those exposed to greater salinities (≥14 ppt), while death of bivalves exposed to salinities ≤1 ppt occurred after 8 days of exposure. These tests provide evidence that low salinities are probably the principal cause of mass mortalities during winter flooding, although the interaction between salinity, temperature and turbidity also deserve consideration. The results of this study indicate that certain aspects of winter flooding, especially salinity, are responsible for the mass mortalities of S. alba rather than the result of a short-lived life history. I hypothesise that the survival of very young juveniles (between 0.5 and 1 mm shell length) and rapid growth rates are important features of the life history of S. alba that explain its successful persistence within the Hopkins River estuary. The rapid rates of growth suggest that it may be possible for juveniles that survive winter flooding to grow, reach sexual maturity, and reproduce before the onset of the next flood event. Unfortunately, the increased survivorship of juveniles during periods of winter flooding was not demonstrated by this study because of the absence of winter flooding and also relatively poor recruitment. It is highly likely that this species is capable of completing it entire life cycle within the estuary since the absence of other nearby populations, together with periods of mouth closure, are likely to greatly limit the potential contribution made by larvae entering from the surrounding marine environment. This study has added considerably to our knowledge of how infauna cope with life in the intermittently closing estuaries that typify semi-arid coastlines in the Southern Hemisphere.

Factors influencing skin colour in cultured Australian snapper Pagrus auratus

Sea cage production of Australian snapper has been largely constrained during the past decade by abnormal skin pigmentation which has negatively impacted marketability. The research described in this study identified dietary, environmental and harvesting techniques to successfully alter skin colour to potentially improve the viability of snapper aquaculture in Australia.

A comparison of the effectiveness of camera trapping and live trapping for sampling terrestrial small-mammal communities

Context. There is an increasing reliance on the use of camera-trap technologies for surveys of medium to large terrestrial mammals. Camera trapping may, however, also have significant applications for broad-scale surveys of small mammals.
Aims. The present study aims to compare results from camera-trapping surveys to those of the more traditional live trapping techniques. Specifically, it aims to test the effectiveness of the techniques for detecting species, and the cost effectiveness of both approaches.
Methods. Surveys were conducted across 36 sites in the Grampians National Park, Victoria, Australia, between April and July 2009. At each site, independent surveys were conducted for small mammals by using a combination of Elliot and cage trapping, then camera trapping. Results for the two different approaches were compared for both their ability to generate small-mammal presence data and their cost effectiveness.
Key results. Camera-trapping surveys of 36 sites in the Grampians National Park compared favourably with those of live trapping surveys. Similar species were detected across the sites, and camera trapping was a considerably more cost effective than live trapping.
Conclusions. Camera-trapping surveys of small terrestrial mammals may provide a new and cost-effective technique for surveying terrestrial small mammals. This is particularly the case when presence data are the main requirement of the survey, with no requirement to capture and tag animals.
Implications. Given the cost-effective nature of camera trapping, there is potential to use this approach to increase the level of replication and spatial coverage of small-mammal surveys. Improving the replication and spatial coverage of studies has the potential to significantly increase the scope of research questions that can be asked, thus providing the potential to improve wildlife management.

The male germ unit of Rhododendron : quantitative cytology, three-dimensional reconstruction, isolation and detection using fluorescent probes

The sperm cells of Rhododendron laetum and R. macgregoriae differentiate within the pollen tube about 24 h after germination in vitro. Threedimensional reconstruction shows that the sperm cells are paired together, and both have extensions that link with the tube nucleus, forming a male germ unit. Quantitative analysis shows that the sperm cells in each pair differ significantly in surface area, but not in cell volume nor in numbers of mitochondria or plastids. When isolated from pollen tubes by osmotic shock, the sperm cells became ellipsoidal and surrounded by their own plasma membrane, while a proportion remained in pairs linked by the inner tube plasma membrane. Both generative and sperm cells are visualized in pollen tube preparations by immunofluorescence with anti-tubulin and anti-actin monoclonal antibodies (MAbs) combined with H33258 fluorescence of the nuclei. Video-image processing shows the presence of an axial microtubule cage in the generative cells, and some microtubules are present in the cytoplasmic extensions that clasp the tube nucleus. Following sperm cell division, the extensive phragmoplast between the sperm nuclei is partitioned by the plasma membranes.

Coping with defeat : acute glucocorticoid and forebrain responses to social defeat vary with defeat episode behaviour

Individuals vary in the way in which they cope with stressful situations. It has been suggested that ‘active’ coping behaviour, characterised by aggression and territorial control, is more effective in moderating the stress associated with social defeat than ‘passive’ coping behaviour, as characterised by immobility, decreased reactivity, and low aggression. We used the rodent ‘resident/intruder’ paradigm to determine whether individual differences in coping behaviour modulate the acute adrenocortical response to social defeat. During the 10 min conflict episode, behaviours displayed by the intruder were recorded and subsequently scored. Intruders that engaged in large numbers of fights and/or frequently used physical structures to block the resident's approach (a behaviour referred to as ‘guarding’), displayed smaller corticosterone responses to defeat than other intruders. Corticosterone responses to defeat were unrelated to a measure of coping style preferences (defensive burying test) obtained prior to the defeat encounter. We further chose to investigate the neurobiological basis of this observation by comparing the patterns of defeat-induced neuronal activation in the forebrains of intruders that displayed high versus low numbers of defensive behaviours during the defeat episode. The results of this analysis indicated that ‘low fight’ and ‘low guard’ intruders, i.e. those that achieved a fight or a guard score below the 20th percentile, had significantly higher numbers of Fos-positive neurons in forebrain regions such as the medial prefrontal cortex and the amygdala than did control animals exposed to an empty resident's cage. In summary, the present data suggest that ‘active’ coping behaviour is associated with both a smaller adrenocortical response and a lower level of ‘neural activation’ following social defeat. This outcome differs from that of earlier studies, a difference that we suggest is due to the fact that the present study is the first to assess coping on the basis of behaviour actually displayed during the conflict interaction.

The effect of social defeat on tyrosine hydroxylase phosphorylation in the rat brain and adrenal gland

Tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis, is regulated acutely by protein phosphorylation and chronically by protein synthesis. No studies have systematically investigated the phosphorylation of these sites in vivo in response to stressors. We specifically investigated the phosphorylation of TH occurring within the first 24 h in response to the social defeat stress in the rat adrenal, the locus coeruleus, substantia nigra and ventral tegmental area. Five groups were investigated; home cage control (HCC), two groups that underwent social defeat (SD+) which were sacrificed either 10 min or 24 h after the end of the protocol and two groups that were put into the cage without the resident being present (SD−) which were sacrificed at time points identical to the SD+. We found at 10 min there were significant increases in serine 40 and 31 phosphorylation levels in the locus coeruleus in SD+ compared to HCC and increases in serine 40 phosphorylation levels in the substantia nigra in SD+ compared to SD−. We found at 24 h there were significant increases in serine 19 phosphorylation levels in the ventral tegmental area in SD+ compared to HCC and decreases in serine 40 phosphorylation levels in the adrenal in SD+ compared to SD−. These findings suggest that the regulation of TH phosphorylation in different catecholamine-producing cells varies considerably and is dependent on both the nature of the stressor and the time at which the response is analysed.

Repeated social defeat selectively increases ΔFosB expression and histone H3 acetylation in the infralimbic medial prefrontal cortex

Exposure to social stress has been linked to the development and maintenance of mood-related psychopathology; however, the underlying neurobiological changes remain uncertain. In this study, we examined numbers of ΔFosB-immunoreactive cells in the forebrains of rats subjected to 12 episodes of social defeat. This was achieved using the social conflict model whereby animals are introduced into the home cage of older males (“residents”) trained to attack and defeat all such “intruders”; importantly, controls were treated identically except that the resident was absent. Our results indicated that the only region in which ΔFosB-positive cells were found in significantly higher numbers in intruders than in controls was the infralimbic medial prefrontal cortex (mPFC). This same effect was not apparent using another psychological stressor, noise stress. Cells of the infralimbic mPFC also displayed evidence of chromatin remodeling. We found that exposure to repeated episodes of social defeat increased numbers of cells immunoreactive for histone H3 acetylation, but not for histone H3 phosphoacetylation, in the infralimbic mPFC. Collectively, these findings highlight the importance of the infralimbic mPFC in responding to social stress—a finding that provides insight into the possible neurobiological alterations associated with stress-induced psychiatric illness.

Strain differences in coping behaviour, novelty seeking behaviour, and susceptibility to socially conditioned fear : a comparison between Wistar and Sprague Dawley rats

The aim of the current study was to generate socially conditioned fear in two different strains of rat (Wistar, W and Sprague Dawley, SD) using social conflict, in order to investigate whether the magnitude of the conditioned fear responses in each strain was related to behaviour exhibited prior to or during fear induction (i.e. social conflict). On day one of the study, all intruders were assessed for exploratory activity in a novel environment. Twenty four hours following the novel environment test the locomotor activity of the intruders was assessed, while they underwent a single familiarisation exposure to the arena in which the conflict was subsequently to occur in. Twenty-four hours following familiarisation, intruders underwent either a 10 min social conflict or sham conflict session. One day later we examined the response of the intruders when they were returned to the vacant resident's cage. Upon return to the conflict context, we examined the intruder's ultrasonic distress vocalisations and the extent to which locomotor activity was inhibited. We found that W rats displayed significantly more immobility (i.e. conditioned fear) upon return to context than did SD rats (p < 0.05). Importantly, we observed that the differences in the two strains behaviour upon return to context appeared to be related to their quite different patterns of coping behaviour. The results of the current study indicate that preclinical between-strain comparisons potentially have much to offer in regard to understanding the basis of resilience to social stress.

Vector activity and propagule size affect dispersal potential by vertebrates

Many small organisms in various life stages can be transported in the digestive system of larger vertebrates, a process known as endozoochory. Potential dispersal distances of these “propagules” are generally calculated after monitoring retrieval in experiments with resting vector animals. We argue that vectors in natural situations will be actively moving during effective transport rather than resting. We here test for the first time how physical activity of a vector animal might affect its dispersal efficiency. We compared digestive characteristics between swimming, wading (i.e. resting in water) and isolation (i.e. resting in a cage) mallards (Anas platyrhynchos). We fed plastic markers and aquatic gastropods, and monitored retrieval and survival of these propagules in the droppings over 24 h. Over a period of 5 h of swimming, mallards excreted 1.5 times more markers than when wading and 2.3 times more markers than isolation birds, the pattern being reversed over the subsequent period of monitoring where all birds were resting. Retention times of markers were shortened for approximately 1 h for swimming, and 0.5 h for wading birds. Shorter retention times imply higher survival of propagules at increased vector activity. However, digestive intensity measured directly by retrieval of snail shells was not a straightforward function of level of activity. Increased marker size had a negative effect on discharge rate. Our experiment indicates that previous estimates of propagule dispersal distances based on resting animals are overestimated, while propagule survival seems underestimated. These findings have implications for the dispersal of invasive species, meta-population structures and long distance colonization events.

Assessing effects of diel period, gear selectivity and predation on patterns of microhabitat use by fish in a mangrove dominated system in SE Australia

The relative value of temperate mangroves to fish, and the processes driving patterns of microhabitat use within this habitat, are unknown. There are 3 quickly identifiable microhabitats within temperate Australian mangroves: (1) forest (the area of mangroves with trees); (2) pneumatophores (the area directly seaward of the forest without trees but with pneumatophores [aerial roots]); and (3) channel (the area directly seaward of the pneumatophores without gross structural attributes such as trees or pneumatophores). Duplicate fyke and gill nets were both initially used to sample fish in the 3 microhabitats described above. Sampling took place across the seaward edge of mangroves on 10 sampling occasions (5 night and 5 day), in a large estuarine system in SE Australia. Fish assemblages (693 fish from 20 species and 15 families) varied significantly (p < 0.05) between the forest and the channel, and between diel periods for each gear (net type), but there was little difference in the assemblage structure of fish between forest–pneumatophore or pneumatophore–channel microhabitats. Juvenile lifestages (61% of all fish) and commercially important taxa (76%) were common. Abundance, biomass and species richness of fish were generally lower in the forest than the other microhabitats, but this pattern varied significantly (p < 0.05) between diel periods, among sampling occasions, and with water depth. Highly quantitative pop nets provided a preliminary assessment of whether differential gear selectivity caused patterns between microhabitats, but less rich fish assemblages were again recorded in forests than in pneumatophores. The importance of predation in structuring fish assemblages across microhabitats was assessed by measuring survival of juvenile fish tethered in 3 predation treatments (predator exclusion, cage control, and uncaged). Survival rates were high across the predator treatments and did not vary among microhabitats. The variation in fish assemblages across microhabitats within mangroves was not consistent with a model of mangrove structure providing a refuge for juvenile fish from predation, but instead could indicate differences in efficiency of gear types among microhabitats and/or other ‘edge effect’-driven processes such as the provision of food and/or shelter.