Whole-body mechanics and kinematics of terrestrial locomotion in the Elegant-crested Tinamou Eudromia elegans

Whereas humans and certain birds experience an abrupt change in locomotor dynamics when shifting from walks to runs, a smooth walk–run transition characterizes many ground-dwelling birds. This study defines the biomechanical distinction between walks and runs in the Elegant-crested Tinamou Eudromia elegans using ground reaction forces. Three birds were filmed at 250 Hz from a lateral view as they moved over a force plate built into a trackway. Centre of mass mechanics and kinematic variables were analysed in 81 steady-speed trials that represented a speed range from 0.66 to 2.78 m/s. E. elegans undergoes two speed-related changes in locomotor mechanics. The first is a shift from walking strides that utilize vaulting mechanics to low-speed runs that exhibit bouncing mechanics; this transition occurs at Froude numbers between 0.4 and 0.6. Such low-speed runs exhibit duty factors exceeding 0.5 and, hence, lack an aerial phase between steps. The second transition, from grounded running to aerial running, occurs when duty factors decrease below 0.5. Grounded running in birds may enhance vision by stabilizing visual stimuli over the retina. The eventual incorporation of an aerial phase during running enables increased locomotor speeds primarily through longer stride lengths.     

Why do host‐deprived seed beetles ‘dump’ their eggs?

Abstract.  If host seeds are absent, females of the seed beetle Callosobruchus maculatus sometimes 'dump' eggs on unsuitable substrates, which causes complete larval mortality and decreases female lifespan. To understand the possible function of this behaviour, the present study examines genetic variation in dumping behaviour between and within populations. When deprived of hosts, females from an African population are much more prone to dump eggs than Asian females, most of which dump no eggs over their lifetimes. Egg dumping therefore cannot be explained as a simple, species-wide constraint imposed by the accumulation of mature oocytes. A transfer experiment tested the hypothesis that dumping eggs improves a female's ability to exploit the subsequent availability of seeds, perhaps by preventing a disruption of oocyte maturation. Contrary to prediction, the number of eggs laid after females are transferred to seeds is inversely related to the number dumped during deprivation. Two bidirectional selection experiments revealed heritable variation in egg-dumping behaviour within the African population. Deprived females from the dumper line dump more than twice as many eggs as do females from the nondumper line. Pre-adult development time is significantly longer in the nondumper line, which suggests that trade-offs with other fitness components could maintain variation in egg-laying behaviour within populations. The divergent responses to host availability by African and Asian females may represent a pleiotropic effect of similarly divergent responses to host quality.     

Groundwater change forecasts widespread forest dieback across an extensive floodplain system

1. Regulation of rivers for human demands has led to extensive forest dieback on many floodplains. If these important ecosystems are to be maintained under future drier climates, we need accurate tools for predicting forest dieback. In the absence of spatially explicit flooding histories for many floodplains, changes in groundwater conditions may be a good indicator of water availability and, therefore, an important environmental indicator. 2. Eucalyptus camaldulensis forests of Australia are an acute example of forest dieback, with 70% of the Victorian Murray River floodplain dying back. We quantified the relationship between forest dieback and ground water across this extensive floodplain (c. 100 000 ha of forest over 1500 km of river length). 3. A combination of extensive ground surveys, remotely sensed data and modelling methods was used to predict forest dieback at the time of the survey and in the past. This approach provides a valuable tool for accurately monitoring forest condition over large spatial scales. Forest dieback was estimated to have increased from 45 to 70% of the floodplain between 1990 and 2006. 4. Accurate groundwater data (depth and salinity) over a 20‐year period were obtained for 289 bores and summarised using nonlinear regression. Groundwater depth and salinity were strong predictors of stand condition. This suggests that changes in groundwater conditions could be used to signal areas vulnerable to forest dieback and prioritise the limited water available for managed flooding. 5. In the upper Murray, where ground water is predominantly fresh (<15 mS cm^?2), dieback increased with increasing groundwater depth. In contrast, the condition of stands in the lower Murray improved with increases in groundwater depth due its high salinity (>30 mS cm^?2). These regional differences in response of the same tree species to groundwater conditions show that our understanding of the drivers of forest dieback is best achieved at spatial and temporal scales representative of the problem.     

Feeding of the Cymatiid Gastropod, Argobuccinum argus, in Relation to the Structure of the Proboscis and Secretions of the Proboscis Gland

Several gastropod families belonging to the superfamily Tonnaceaare known to bore into the calcareous shells of echinoids andbivalves, but little work has been done on the family Cymatiidae.New observations show that the cymatiid, Argobuccinum argus,which feeds on the tubicolous polychaete, Gunnarea capensis,possesses large proboscis glands which secrete 0.4 to 0.5N H₂SO₄;further, the secretion dissolves greater amounts of pure CaCO₃than does O.47N H₂SO₄, alone. A toxin is also present, whichabolishes responses to light and touch in several invertebrates. The proboscis is atypically pleurembolic, having a permanentproboscis sheath. Retraction is due to the muscles ot the probosciswall, and the contracted proboscis is not inverted. Unlike othermesogastropods, the Tonnacea have three pairs ofglands associatedwith the foregut: proboscis glands, true salivary glands, anda small, partly paired gland of unknown function immediatelyposterior to the buccal mass. It is concluded that because of an abundance of readily availablefood in the form of Gunnarea, A. argus does not drillinto animalsprotected by a calcareous shell. The presence of a CaCO₃ dissolvingmechanism indicates that the Cymatiidae ingeneral may be ableto employ this method of feeding.     

Contrasts between dystrophic and clearwater lakes in the long‐term effects of acidification on cladoceran assemblages

1. Most studies on zooplankton responses to acidification have focused on clearwater lakes with a dramatic acidification history. The role of dissolved organic carbon (DOC) in moderating zooplankton responses to acidification in naturally acidic, dystrophic lakes is less well understood and is partially impeded by a lack of baseline data. 2. Cladocera leave identifiable remains preserved in lake sediments that can be used to provide information on pre‐industrial species assemblages and their responses to environmental stressors such as acidification. Therefore, we used palaeolimnological approaches to track cladoceran assemblage responses to acidification since c.1850 (inferred from sedimentary diatom assemblages) in three acidified lakes in Kejimkujik National Park (Nova Scotia, Canada) that differ markedly in DOC content. These include two highly dystrophic lakes (Kejimkujik and Pebbleogittch lakes), and one clearwater lake (Beaverskin Lake). 3. In dystrophic Pebbleogittch Lake, an increase in the acid‐tolerant, jelly‐clad, pelagic taxon Holopedium glacialis occurred coincident with diatom‐inferred pH (DI‐pH) declines, but no other notable cladoceran assemblage shifts occurred. Similarly, Cladocera assemblages did not appear to respond to lakewater acidification in dystrophic Kejimkujik Lake. 4. In contrast, in the clearwater Beaverskin Lake, several observed shifts in cladoceran assemblage corresponded to DI‐pH declines, including an increase in the proportion of littoral taxa and an increase in Hill’s N2 species diversity. This may indicate increased water clarity as a result of acidification‐related decreases in DOC, which may have enhanced growth of emergent aquatic macrophytes and improved visibility for planktivorous fish, leading to increased predation on pelagic taxa. Species shifts within the littoral assemblage of Beaverskin Lake may reflect the differing tolerances of littoral taxa to low pH and aluminium toxicity. 5. Overall, our results suggest that cladoceran assemblages in naturally acidic, dystrophic lakes may be resilient against additional pH declines related to industrial emissions of acidifying agents, as dystrophic lakes are less vulnerable to increased aluminium toxicity and acidification‐induced increases in water clarity and often have a pre‐industrial cladoceran assemblage already adapted to acidic conditions.     

Effects of historical forest contraction on the phylogeographic structure of Australo‐Papuan populations of the red‐legged pademelon (Macropodidae: Thylogale stigmatica)

Geographic patterns of genetic variation are strongly influenced by historical changes in species habitats. Whether such patterns are common to co‐distributed taxa may depend on the extent to which species vary in ecology and vagility. We investigated whether broad‐scale phylogeographic patterns common to a number of small‐bodied vertebrate and invertebrate species in eastern Australian forests were reflected in the population genetic structure of an Australo‐Papuan forest marsupial, the red‐legged pademelon (Macropodidae: Thylogale stigmatica). Strong genetic structuring of mtDNA haplotypes indicated the persistence of T. stigmatica populations across eastern Australia and southern New Guinea in Pleistocene refugial areas consistent with those inferred from studies of smaller, poorly dispersing species. However, there was limited divergence of haplotypes across two known historical barriers in the northeastern Wet Tropics (Black Mountain Barrier) and coastal mideastern Queensland (Burdekin Gap) regions. Lack of divergence across these barriers may reflect post‐glacial recolonization of forests from a large, central refugium in the Wet Tropics. Additionally, genetic structure is not consistent with the present delimitation of subspecies T. s. wilcoxi and T. s. stigmatica across the Burdekin Gap. Instead, the genetic division occurs further to the south in mideastern Queensland. Thus, while larger‐bodied marsupials such as T. stigmatica did persist in Pleistocene refugia common to a number of other forest‐restricted species, species‐specific local extinction and recolonization events have resulted in cryptic patterns of genetic variation. Our study demonstrates the importance of understanding individualistic responses to historical climate change in order to adequately conserve genetic diversity and the evolutionary potential of species.     

Are behavioural responses to predation cues linked across life cycle stages?

1. Prey organisms can perceive cues to predation hazard and adopt low‐risk behaviours to increase survival. Animals with complex life cycles, such as insects, can exhibit such anti‐predatory behaviours in multiple life stages. 2. Cues to predation risk may induce ovipositing females to choose habitats with low predation risk. Cues to predation risk may also induce larvae to adopt facultative behaviours that reduce risk of predation. 3. One hypothesis postulates that anti‐predation behaviours across adult and larval stages may be negatively associated because selection for effective anti‐predator behaviour in one stage leads to reduced selection for avoidance of predators in other stages. An alternative hypothesis suggests that selection by predation favours multi‐component defences, with both avoidance of oviposition and facultative adoption of low‐risk behaviours by larvae. 4. Laboratory and field experiments were used to determine whether defensive responses of adult and larval mosquitoes are positively or negatively associated. The study tested effects of waterborne cues from predatory Toxorhynchites theobaldi on oviposition choices and larval behaviours of three of its common prey: Culex mollis, Limatus durhamii and Aedes albopictus. 5. Culex mollis shows strong anti‐predator responses in both life stages, consistent with the hypothesis of a multi‐component behavioural defence. The other two species showed no detectable responses to waterborne predator cues in either adult or larval stages. Larvae of these unresponsive species were significantly more vulnerable to this predator than was C. mollis. 6. For these mosquitoes, species appear either to have been selected for multi‐component defences against predation or to act in ways that could be called predator‐naïve.     

Nutrient uptake in streams draining agricultural catchments of the midwestern United States

1. Agriculture is a major contributor of non‐point source pollution to surface waters in the midwestern United States, resulting in eutrophication of freshwater aquatic ecosystems and development of hypoxia in the Gulf of Mexico. Agriculturally influenced streams are diverse in morphology and have variable nutrient concentrations. Understanding how nutrients are transformed and retained within agricultural streams may aid in mitigating increased nutrient export to downstream ecosystems. 2. We studied six agriculturally influenced streams in Indiana and Michigan to develop a more comprehensive understanding of the factors controlling nutrient retention and export in agricultural streams using nutrient addition and isotopic tracer studies. 3. Metrics of nutrient uptake indicated that nitrate uptake was saturated in these streams whereas ammonium and phosphorus uptake increased with higher concentrations. Phosphorus uptake was likely approaching saturation as evidenced by decreasing uptake velocities with concentration; ammonium uptake velocity also declined with concentration, though not significantly. 4. Higher whole‐stream uptake rates of phosphorus and ammonium were associated with the observed presence of stream autotrophs (e.g. algae and macrophytes). However, there was no significant relationship between measures of nutrient uptake and stream metabolism. Water‐column nutrient concentrations were positively correlated with gross primary production but not community respiration. 5. Overall, nutrient uptake and metabolism were affected by nutrient concentrations in these agriculturally influenced streams. Biological uptake of ammonium and phosphorus was not saturated, although nitrate uptake did appear to be saturated in these ecosystems. Biological activity in agriculturally influenced streams is higher relative to more pristine streams and this increased biological activity likely influences nutrient retention and transport to downstream ecosystems.     

New microsatellite loci for Carcharhinid sharks (Carcharhinus tilstoni and C. sorrah) and their cross‐amplification in other shark species

Twelve microsatellite DNA markers were isolated in the spot‐tail shark (Carcharhinus sorrah) and nine were isolated in Australian black‐tip shark (Carcharhinus tilstoni). These loci plus 18 others developed for sharks from the genera Negaprion, Ginglymostoma, Carcharodon and Isurus were tested for amplification success on four species of Carcharhinus (including C. sorrah and C. tilstoni) and four other species representing three diverse families. Cross‐amplification was most common within families. Five loci were subsequently tested for polymorphism on 50 C. sorrah and 60 C. tilstoni. The number of alleles per locus was two to 24 and the average heterozygosity was 0.54 (range 0.16–0.87) for C. sorrah and 0.64 (range 0.44–0.78) for C. tilstoni. These loci may be useful tools for genetic analyses of the Carcharhinidae.