Termite Digestibility and Water and Energy Contents Determine the Water Economy Index of Numbats (Myrmecobius fasciatus) and Other Myrmecophages

Implications of heat exchange for a free-living endangered marsupial determined by non-invasive thermal imaging

We used thermal imagining and heat balance modelling to examine the thermal ecology of wild mammals, using the diurnal marsupial numbat (Myrmecobius fasciatus) as a model. Body surface temperature was measured using infra-red thermography at environmental wet and dry bulb temperatures of 11.7-29°C and 16.4-49.3°C, respectively; surface temperature varied for different body parts and with environmental temperature. Radiative and convective heat exchange varied markedly with environmental conditions and for various body surfaces reflecting their shapes, surface areas and projected areas. Both the anterior and posterior dorsolateral body areas functioned as thermal windows. Numbats in the shade had lower rates of solar radiative heat gain but non-solar avenues for radiative heat gain were substantial. Radiative gain was higher for black and lower for white stripes, but overall, the stripes had no thermal role. Total heat gain was generally positive (<4 to >20 W) and often greatly exceeded metabolic heat production (3-6 W). Our heat balance model indicates that high environmental heat loads limit foraging in open areas to as little as 10 min and that climate change may extend periods of inactivity, with implications for future conservation and management. We conclude that non-invasive thermal imaging is informative for modelling heat balance of free-living mammals.

Digesta retention time and recovery rates of ants and termites in Chinese pangolins (Manis pentadactyla)

Pangolins are myrmecophagous mammals whose biology and ecology remain poorly studied. Termite mandibles and ant head capsules are the two primary remains found in pangolin feces. Determining the retention time of insect cuticles is important for understanding the digestive physiology of pangolins, while determining the recovery rate of termites and ants in feces is required to estimate the number of these prey items that are consumed by pangolins. In this study, the authors conducted feeding trials with captive Chinese pangolins (Manis pentadactyla). Sixty grams of the fungus-growing termite Odontotermes formosanus (18,816 individuals) and 15-20 g of the yellow crazy ant Anoplolepis gracilipes (14,400-19,200 individuals) were fed to each pangolin. After feeding, pangolin feces were collected daily for 1 week. The authors also assessed the accuracy of using chromium (III) oxide powder (Cr₂ O₃ ) as a proxy for determining gut passage time, as has been done in previous studies. The results showed that remaining termite mandibles and ant head capsules in feces peaked at 66 and 90 hr after feeding and their recovery rates were 0.35 ± 0.10 and 0.65 ± 0.04, respectively. In both feeding trials, the retention time of Cr₂ O₃ was much shorter than that of the termite mandibles and ant head capsules, indicating that Cr₂ O₃ is not an appropriate indicator for estimating food retention time of myrmecophagous animals. Our results revealed that the ant head capsules were preserved better in feces compared with the termite mandibles, suggesting that termites may be considerably underestimated in the feces of wild pangolins.

Ant-termite interactions: an important but under-explored ecological linkage

Animal interactions play an important role in understanding ecological processes. The nature and intensity of these interactions can shape the impacts of organisms on their environment. Because ants and termites, with their high biomass and range of ecological functions, have considerable effects on their environment, the interaction between them is important for ecosystem processes. Although the manner in which ants and termites interact is becoming increasingly well studied, there has been no synthesis to date of the available literature. Here we review and synthesise all existing literature on ant-termite interactions. We infer that ant predation on termites is the most important, most widespread, and most studied type of interaction. Predatory ant species can regulate termite populations and subsequently slow down the decomposition of wood, litter and soil organic matter. As a consequence they also affect plant growth and distribution, nutrient cycling and nutrient availability. Although some ant species are specialised termite predators, there is probably a high level of opportunistic predation by generalist ant species, and hence their impact on ecosystem processes that termites are known to provide varies at the species level. The most fruitful future research direction will be to evaluate the impact of ant-termite predation on broader ecosystem processes. To do this it will be necessary to quantify the efficacy both of particular ant species and of ant communities as a whole in regulating termite populations in different biomes. We envisage that this work will require a combination of methods, including DNA barcoding of ant gut contents along with field observations and exclusion experiments. Such a combined approach is necessary for assessing how this interaction influences entire ecosystems.

Comparison of two faecal analysis techniques to assess Formosan pangolin Manis pentadactyla pentadactyla diet

The diet of myrmecophagous mammals is usually studied by investigating the chitinous remains of termites and ants obtained from stomachs, guts, and faeces; however, this process is time and labour intensive. Moreover, faeces of obligate myrmecophagous mammals contain other materials such as soil, sand, rocks, and plant matter, which hinder the accurate and efficient identification of faeces’ contents; this makes estimating the biomass of each prey species difficult. This study tested non-filtering and filtering faecal analysis procedures and compared their identification accuracy and efficiency in the analysis of Formosan pangolin Manis pentadactyla pentadactyla faeces. In the non-filtering procedure, 1 g of dried faeces was distributed over an area greater than 360 cm2 to be able to see most ant capsules and termite mandibles. In the filtering procedure, 0.5 cm3 of filtered chitinous remains of termites and ants was spread over a 45 cm2 area to obtain a high resolution of the diet composition. The filtering procedure can sieve out insect remains from the debris, which facilitates further identification of the insect chitin. Using the two proposed faecal analysis procedures, the prey species composition and the number of prey remains could be obtained. Our results provide a quantitative method to evaluate the diversity of wild pangolin’s diets for determining their ecological requirements and developing in-situ and ex-situ conservation plans.

Convergence of gut microbiomes in myrmecophagous mammals

Mammals have diversified into many dietary niches. Specialized myrmecophagous (ant- and termite-eating) placental mammals represent a textbook example of evolutionary convergence driven by extreme diet specialization. Armadillos, anteaters, aardvarks, pangolins and aardwolves thus provide a model system for understanding the potential role of gut microbiota in the convergent adaptation to myrmecophagy. Here, we expand upon previous mammalian gut microbiome studies by using high-throughput barcoded Illumina sequencing of the 16S rRNA gene to characterize the composition of gut microbiota in 15 species representing all placental myrmecophagous lineages and their close relatives from zoo- and field-collected samples. We confirm that both diet and phylogeny drive the evolution of mammalian gut microbiota, with cases of convergence in global composition, but also examples of phylogenetic inertia. Our results reveal specialized placental myrmecophages as a spectacular case of large-scale convergence in gut microbiome composition. Indeed, neighbour-net networks and beta-diversity plots based on UniFrac distances show significant clustering of myrmecophagous species (anteaters, aardvarks and aardwolves), even though they belong to phylogenetically distant lineages representing different orders. The aardwolf, which diverged from carnivorous hyenas only in the last 10 million years, experienced a convergent shift in the composition of its gut microbiome to become more similar to other myrmecophages. These results confirm diet adaptation to be a major driving factor of convergence in gut microbiome composition over evolutionary timescales. This study sets the scene for future metagenomic studies aiming at evaluating potential convergence in functional gene content in the microbiomes of specialized mammalian myrmecophages.

Eliminative behavior of captive numbats, Myrmecobius fasciatus (Mammalia; Marsupialia): pattern and identification of fecal deposits

This study examined the spatial defecation patterns of numbats within captivity and tested the efficacy of a food colorant as a fecal marker in this species. Rather than randomly distributing scats throughout their environment, the numbats aggregated their feces at specific sites forming latrines. It is unclear whether the strong inclination for latrine formation was due to this species' inherent behavior or is a direct result of captivity. Males were found to have a higher daily defecation rate, different defecation time, larger number of latrines, and greater number of scats per quadrant, as compared to females. In this study, the majority of scats were deposited along enclosure boundaries and for both sexes there was a higher probability of latrines being placed along enclosure fencing shared with a female neighbor. The high concentration of latrines along boundaries suggests that they may play a role in territorial defense. The results also indicated that captive numbats tend to choose defecation points away from food and refuge sites. Transit and total retention time of the marker through the GIT was ≤3 hr and between 24 and 27 hr, respectively. A marker dose of 3 gtts feed(-1)  × 2 feeds day(-1) was required to reach a steady and detectable state of marker output, which enabled accurate identification of individual samples during the breeding season. Reliable labeling was obtained using blue and red colored food dye, and there was no evidence that incorporation of the marker into the diet had any negative effects on food intake.

Digestibility of feeding regimes of the red-tailed phascogale (Phascogale calura) and the kultarr (Antechinomys laniger) in captivity

Digestibility was studied in the red-tailed phascogale (Phascogale calura) and the kultarr (Antechinomys laniger), small insectivorous/carnivorous marsupials, to determine their nutrient requirements in captivity. The marsupials were fed a range of insects, rat (Rattus rattus) and small carnivore food (Wombaroo). Digestibility experiments were conducted for a total of 12 days, which incorporated a five-day adjustment phase followed by a seven-day collection period. The apparent digestibility values for the phascogale and kultarr were above 81% for dry matter, energy, protein and lipids on all diets provided. No significant difference was found between phascogales and kultarrs on the same diet with respect to apparent digestibility of dry matter, energy, protein and lipids. The apparent absorption of minerals varied for each diet for the phascogale and kultarr. Maintenance energy requirements were determined to be 954 kJ kg0.75 day–1 for the red-tailed phascogale and 695 kJ kg0.75 day–1 for the kultarr. Presented here are the most comprehensive data on diet digestibility for dasyurids thus far.

Gross renal morphology of the numbat (Myrmecobius fasciatus) (Marsupialia:Myrmecobiidae)

There is a strong correlation between the structure of the mammalian kidney and its urinary concentrating ability. We examine here the kidney of an endangered termitivorous marsupial (Myrmecobius fasciatus) and use the measured kidney morphometrics to calculate maximal urinary concentration. The relative medullary area (1.34) of the kidney of M. fasciatus is typical of other dasyuromorph marsupials, as is its predicted maximal urinary concentration of 3617 mOsm kg–1 H2O, despite its historically semiarid/arid distribution. The termitivorous diet of M. fasciatus presumably provides it with sufficient water to limit selection for a high urinary concentrating capacity.

Effect of torpor on the water economy of an arid-zone marsupial, the stripe-faced dunnart (Sminthopsis macroura)

Metabolic rate and evaporative water loss (EWL) were measured for a small, arid-zone marsupial, the stripe-faced dunnart (Sminthopsis macroura), when normothermic and torpid. Metabolic rate increased linearly with decreasing ambient temperature (T(a)) for normothermic dunnarts, and calculated metabolic water production (MWP) ranged from 0.85+/-0.05 (T(a)=30 degrees C) to 3.13+/-0.22 mg H2O g(-1) h(-1) (T(a)=11 degrees C). Torpor at T(a)=11 and 16 degrees C reduced MWP to 24-36% of normothermic values. EWL increased with decreasing T(a), and ranged from 1.81+/-0.37 (T(a)=30 degrees C) to 5.26+/-0.86 mg H2O g(-1) h(-1) (T(a)=11 degrees C). Torpor significantly reduced absolute EWL to 23.5-42.3% of normothermic values, resulting in absolute water savings of 50-55 mg H2O h(-1). The relative water economy (EWL/MWP) of the dunnarts was unfavourable, remaining >1 at all T(a) investigated, and did not improve with torpor. Thus torpor in stripe-faced dunnarts results in absolute, but not relative, water savings.