Host-seeking behaviour by Australian ticks (Acari: Ixodidae) with differing host specificities

Ticks generally detach from their hosts into sites where they are later exposed to host species which may or may not be suitable for infestation. The question of how four species of ixodid ticks, with differing specificities, behave towards such potential host species was examined. Observations of the generalists,Aponomma hydrosauri andAmblyomma limbatum and the specialists,Aponomma fimbriatum andAponomma concolor, showed that the generalists were attracted to a wider range of potential host species than the specialists and that the larval stages of all tick species, regardless of specificity, contacted more potential host species than the adults. The interspecific differences may be attributed to reliance on different sets of host cues, while the intraspecific differences may reflect the developmental state of the sensory system.     

Circadian rhythms of locomotor activity and temperature selection in sleepy lizards, <Emphasis Type="Italic">Tiliqua rugosa</Emphasis>

This study examined whether the daily rhythms of locomotor activity and behavioural thermoregulation that have previously been observed in Australian sleepy lizards (Tiliqua rugosa) under field conditions are true circadian rhythms that persist in constant darkness (DD) and whether these rhythms show similar characteristics. Lizards held on laboratory thermal gradients in the Australian spring under the prevailing 12-hour light : dark (LD) cycle for 14 days displayed robust daily rhythms of behavioural thermoregulation and locomotor activity. In the 13-day period of DD that followed LD, most lizards exhibited free-running circadian rhythms of locomotor activity and behavioural thermoregulation. The predominant activity pattern displayed in LD was unimodal and this was retained in DD. While mean levels of skin temperature and locomotor activity were found to decrease from LD to DD, activity duration remained unchanged. The present results demonstrate for the first time that this species’ daily rhythm of locomotor activity is an endogenous circadian rhythm. Our results also demonstrate a close correlation between the circadian activity and thermoregulatory rhythms in this species indicating that the two rhythms are controlled by the same master oscillator(s). Future examination of seasonal aspects of these rhythms, may, however, cause this hypothesis to be modified.     

Prolonged Decay of Evoked Inhibitory Postsynaptic Currents in Hippocampal Neurons Is Not Shaped by Asynchronous Release

During evoked release, several quanta of neurotransmitter are synchronously released in several GABA-ergic synapses. Assuming that not more than one vesicle is released at each release site, the decay of miniature and evoked IPSC (mIPSC and eIPSC, respectively) should coincide. In this study, we found that in a considerable part of the cultured hippocampal neurons eIPSC decayed more slowly than mIPSC did. We investigated the mechanisms underlying this difference using conventional electrophysiological approaches, deconvolution, simulations, and nonstationary noise analysis. Our results indicate that asynchronous release of synaptic vesicles cannot explain the prolonged decay of the GABA-ergic IPSC. We suggest that some interaction between the quanta at the pre- and/or post-synaptic level should result in a slower decay of the eIPSC in comparison with that of mIPSC.     

Extranuptial nectaries in flowers: ants increase the reproductive success of the ant‐plant Miconia tococa (Melastomataceae)

• Although the production of extranuptial nectar is a common strategy of indirect defence against herbivores among tropical plants, the presence of extranuptial nectaries in reproductive structures is rare, especially in ant‐plants. This is because the presence of ants in reproductive organs can generate conflicts between the partners, as ants can inhibit the activity of pollinators or even castrate their host plants. Here we evaluate the hypothesis that the ant‐plant Miconia tococa produces nectar in its petals which attracts ants and affects fruit set.
• Floral buds were analysed using anatomical and histochemical techniques. The frequency and behaviour of floral visitors were recorded in field observations. Finally, an ant exclusion experiment was conducted to evaluate the effect of ant presence on fruit production.
• The petals of M. tococa have a secretory epidermis that produces sugary compounds. Nectar production occurred during the floral bud stage and attracted 17 species of non‐obligate ants (i.e. have a facultative association with ant‐plants). Ants foraged only on floral buds, and thus did not affect the activity of pollinators in the neighbouring open flowers. The presence of ants in the inflorescences increased fruit production by 15%.
• To our knowledge, the production of extranuptial nectar in the reproductive structures of a myrmecophyte is very rare, with few records in the literature. Although studies show conflicts between the partners in the ant–plant interaction, ants that forage on M. tococa floral buds protect the plant against floral herbivores without affecting bee pollination.

     

Endocytic adaptor protein intersectin 1 forms a complex with microtubule stabilizer STOP in neurons

Intersectin 1 (ITSN1) is a multidomain adaptor protein that functions in clathrin-mediated endocytosis and signal transduction. This protein is highly abundant in neurons and is implicated in Down syndrome, Alzheimer's disease and, possibly, other neurodegenerative disorders. Here we used an in vitro binding assay combined with MALDI-TOF mass spectrometry to identify novel binding partners of ITSN1. We found that the neuron-specific isoform of the stable tubule-only polypeptide (STOP) interacts with SH3A domain of ITSN1. STOP and ITSN1 were shown to form a complex in vivo and to partially co-localize in rat primary hippocampal neurons. As STOP is a microtubule-stabilizing protein that is required for several forms of synaptic plasticity in the hippocampus, identification of this interaction raises the possibility of ITSN1 participation in this process.     

Behavioral arousal in newborn infants and its association with termination of apnea

Arousal is an important protective mechanism that aids in the resolution of obstructive sleep apnea in adults and children, but its role in neonatal apnea has not been investigated. The primary aim of the present study was to determine the role of arousal in the termination of apnea in preterm infants. Videorecording was used to identify spontaneous behavioral arousal in a group of healthy full-term (n = 7) and preterm (n = 10) infants before and during polygraphic monitoring of cardiorespiratory variables and in a group of preterm infants with apnea (n = 10) during similar polygraphic monitoring. Spontaneous arousal rates (mean +/- SE) in full-term infants before and during polygraphic monitoring were 0.18 +/- 0.03 and 0.23 +/- 0.07 episodes/min, respectively. Corresponding values in nonapneic preterm infants were 0.24 +/- 0.03 and 0.24 +/- 0.02 episodes/min. In apneic preterm infants, mean spontaneous arousal rate during polygraphic recording was 0.26 +/- 0.02, but it was considerably higher during apneic sleep periods (0.59 +/- 0.17) than during nonapneic sleep periods (0.25 +/- 0.01). The frequency of occurrence of arousal was significantly higher (P less than 0.005) in long vs. short apnea, mixed vs. central apnea, and severe vs. mild apnea. Although a clear association between arousal and apneic resolution was observed in preterm infants, lack of arousal responses in a large number of apneic episodes suggests that behavioral arousal is not essential for the termination of apnea in these infants.     

Extrusion of calcium from a single isolated neuron of the snailHelix pomatia

Summary Simultaneous optical measurements of extra- and intracellular Ca²⁺ concentrations were carried out on isolated snail neurons injected iontophoretically with Ca²⁺. The fluorescent indicator Fura-2 was used to measure intracellular concentration of free Ca, and the absorbant indicator Antipyrylazo III to measure changes in extracellular calcium concentration in the microchamber containing the cell. The velocity of Ca²⁺ extrusion from a single cell has been shown to be in accordance with the level of free Ca in the neuronal cytoplasm. After an increase in intracellular free Ca by iontophoretic injection from a microeletrode to 0.2–0.5 m, the velocity of Ca²⁺ extrusion from the neuron was approximately 0.3–4.6 m/sec per cell volume. During caffeine-induced calcium-dependent calcium release of Ca²⁺ from intracellular stores a stimulation of calcium extrusion took place, reaching the velocity of 5.0 m/sec per cell volume.     

Melatonin rhythms in the Australian freshwater crocodile (Crocodylus johnstoni): a reptile lacking a pineal complex?

The vertebrate pineal gland is the primary source of melatonin, the rhythmic secretion of which is influenced by environmental light and temperature, thereby providing animals with information about seasonally changing photoperiod and thermoperiod. Although pineal glands are present in the majority of vertebrate species, a discrete organ is reported to be absent in the Crocodilia. However, if the melatonin rhythm is crucial to the survival of the organism, it would be expected that the rhythm would be present in crocodiles. In the present study, we measured blood plasma melatonin over a 30-h period in aestivating Australian freshwater crocodiles (Crocodylus johnstoni) in their natural habitat at the end of the dry season (November) and found no discernible melatonin rhythm. However, another group of captive-reared C. johnstoni, maintained under natural light and temperature cycles and sampled in the early dry season (June) showed a clear melatonin rhythm. These results suggest that there is either an extrapineal source of melatonin in this crocodile species or that there is melatonin producing tissue elsewhere which heretofore has not been discovered. Further studies are needed to determine why the melatonin rhythm is intermittently expressed and whether this may be related to seasonal changes in the expression of the rhythm linked to tropical environments.