Diurnal sheltering preferences and associated conservation management for the endangered sandhill dunnart, Sminthopsis psammophila.

Dasyurids are small mammals that can conserve energy and water by using shelters that insulate against extreme conditions, prevent predation, and facilitate torpor. To quantify the diurnal sheltering requirements of a poorly known, endangered dasyurid, the sandhill dunnart, Sminthopsis psammophila, we radiotracked 40 individuals in the Western Australian Great Victoria Desert between 2015 and 2019. We assessed the effect of habitat class (broad habitat features), plot-level (the area surrounding each shelter), and shelter characteristics (e.g., daily temperature ranges), on shelter selection and sheltering habitat preferences. Two hundred and eleven diurnal shelters (mean of 5 ± 3 shelters per individual) were located on 363 shelter days (the number of days each shelter was used), within mature vegetation (mean seral age of 32 ± 12 years postfire). Burrows were used on 77% of shelter days and were typically concealed under mature spinifex, Triodia spp., with stable temperature ranges and northern aspects facing the sun. While many burrows were reused (n = 40 across 175 shelter days), spinifex hummock shelters typically were used for one shelter day and were not insulative against extreme temperatures. However, shallow scrapes within Lepidobolus deserti hummock shelters had thermal advantages and log shelters retained heat and were selected on cooler days. Sminthopsis psammophila requires long-unburned sheltering habitat with mature vegetation. Summer fires in the Great Victoria Desert can be extensive and destroy large areas of land, rendering them a key threat to the species. We conclude that the survey and conservation of S. psammophila requires attention to long-unburned, dense lower stratum swale, sand plain, and dune slope habitats, and the tendency of S. psammophila to burrow allows the species to survive within the extreme conditions of its desert environment.

Increased muscular volume and cuticular specialisations enhance jump velocity in solitarious compared with gregarious desert locusts, Schistocerca gregaria.

The desert locust, Schistocerca gregaria, shows a strong phenotypic plasticity. It can develop, depending upon population density, into either a solitarious or gregarious phase that differs in many aspects of behaviour, physiology and morphology. Prominent amongst these differences is that solitarious locusts have proportionately longer hind femora than gregarious locusts. The hind femora contain the muscles and energy-storing cuticular structures that propel powerful jumps using a catapult-like mechanism. We show that solitarious locusts jump on average 23% faster and 27% further than gregarious locusts, and attribute this improved performance to three sources: first, a 17.5% increase in the relative volume of their hind femur, and hence muscle volume; second, a 24.3% decrease in the stiffness of the energy-storing semi-lunar processes of the distal femur; and third, a 4.5% decrease in the stiffness of the tendon of the extensor tibiae muscle. These differences mean that solitarious locusts can generate more power and store more energy in preparation for a jump than can gregarious locusts. This improved performance comes at a cost: solitarious locusts expend nearly twice the energy of gregarious locusts during a single jump and the muscular co-contraction that energises the cuticular springs takes twice as long. There is thus a trade-off between achieving maximum jump velocity in the solitarious phase against the ability to engage jumping rapidly and repeatedly in the gregarious phase.

Strategic sperm allocation under parasitic sex-ratio distortion.

Parasitic sex-ratio distorters are a major selective force in the evolution of host mating behaviour and mate choice. Here, we investigate sperm limitation in the amphipod Gammarus duebeni and the impact of the microsporidian sex-ratio distorter Nosema granulosis on sperm allocation strategies. We show that males become sperm limited after three consecutive matings and provide uninfected, high fecundity, females with more sperm than infected females. We show that sperm limitation leads to a decrease in female productivity. The outcome of sex-ratio distortion has been shown theoretically to be sensitive to the mating limits of males. Our results indicate that strategic sperm allocation under male rarity will have a greater impact on infected females and has the potential to regulate spread of parasitic feminisers in host populations.