Desiccation Risk Drives the Spatial Ecology of an Invasive Anuran (Rhinella marina) in the Australian Semi-Desert

Some invasive species flourish in places that impose challenges very different from those faced in their native geographic ranges. Cane toads (Rhinella marina) are native to tropical and subtropical habitats of South and Central America, but have colonised extremely arid regions over the course of their Australian invasion. We radio-tracked 44 adult cane toads at a semi-arid invasion front to investigate how this invasive anuran has managed to expand its geographic range into arid areas that lie outside of its native climatic niche. As predicted from their low physiological control over rates of evaporative water loss, toads selected diurnal shelter sites that were consistently cooler and damper (and thus, conferred lower water loss rates) than nearby random sites. Desiccation risk also had a profound influence on rates of daily movement. Under wet conditions, toads that were far from water moved further between shelter sites than did conspecifics that remained close to water, presumably in an attempt to reach permanent water sources. However, this relationship was reversed under dry conditions, such that only toads that were close to permanent water bodies made substantial daily movements. Toads that were far from water bodies also travelled along straighter paths than did conspecifics that generally remained close to water. Thus, behavioural flexibility—in particular, an ability to exploit spatial and temporal heterogeneity in the availability of moist conditions—has allowed this invasive anuran to successfully colonize arid habitats in Australia. This finding illustrates that risk assessment protocols need to recognise that under some circumstances an introduced species may be able to thrive in conditions far removed from any that it experiences in its native range

Mistaken identity may explain why male sea snakes (Aipysurus laevis, Elapidae, Hydrophiinae) “attack” scuba divers

Scuba-divers on tropical coral-reefs often report unprovoked “attacks” by highly venomous Olive sea snakes (Aipysurus laevis). Snakes swim directly towards divers, sometimes wrapping coils around the diver’s limbs and biting. Based on a focal animal observation study of free-ranging Olive sea snakes in the southern Great Barrier Reef, we suggest that these “attacks” are misdirected courtship responses. Approaches to divers were most common during the breeding season (winter) and were by males rather than by female snakes. Males also made repeated approaches, spent more time with the diver, and exhibited behaviours (such as coiling around a limb) also seen during courtship. Agitated rapid approaches by males, easily interpreted as “attacks”, often occurred after a courting male lost contact with a female he was pursuing, after interactions between rival males, or when a diver tried to flee from a male. These patterns suggest that “attacks” by sea snakes on humans result from mistaken identity during sexual interactions. Rapid approaches by females occurred when they were being chased by males. Divers that flee from snakes may inadvertently mimic the responses of female snakes to courtship, encouraging males to give chase. To prevent escalation of encounters, divers should keep still and avoid retaliation

A phylogenetic analysis of variation in reproductive mode within an Australian lizard (Saiphos equalis, Scincidae)

Saiphos equalis, a semi-fossorial scincid lizard from south-eastern Australia, is one of only three reptile species world-wide that are known to display geographic variation in reproductive mode. Uniquely, Saiphos equalis includes populations with three reproductive modes: oviparous with long (15-day) incubation periods; oviparous with short (5-day) incubation periods; and viviparous (0-day incubation periods). No Saipho populations show \u27normal\u27 scincid oviparity (\u3e30-day incubation period). We used mitochondrial nucleotide sequences (ND2 and cytochrome b) to reconstruct relationships among populations from throughout the species\u27 distribution in New South Wales, Australia. Under the phylogenetic species concept, phylogenetic analyses are consistent with the oviparous and viviparous populations of S. equalis being conspecific. Phylogenetic analyses suggest that the long incubation period oviparous lineage is the sister group to all other populations; and that the viviparous populations belong to a cluster of weakly supported clades basal to the short-incubation-period oviparous clade. These clades correspond to variation in reproductive mode and geographic location. © 2001 The Linnean Society of London

Habitat Selection in a Rocky Landscape: Experimentally Decoupling the Influence of Retreat Site Attributes from That of Landscape Features

Organisms selecting retreat sites may evaluate not only the quality of the specific shelter, but also the proximity of that site to resources in the surrounding area. Distinguishing between habitat selection at these two spatial scales is complicated by co-variation among microhabitat factors (i.e., the attributes of individual retreat sites often correlate with their proximity to landscape features). Disentangling this co-variation may facilitate the restoration or conservation of threatened systems. To experimentally examine the role of landscape attributes in determining retreat-site quality for saxicolous ectotherms, we deployed 198 identical artificial rocks in open (sun-exposed) sites on sandstone outcrops in southeastern Australia, and recorded faunal usage of those retreat sites over the next 29 months. Several landscape-scale attributes were associated with occupancy of experimental rocks, but different features were important for different species. For example, endangered broad-headed snakes (Hoplocephalus bungaroides) preferred retreat sites close to cliff edges, flat rock spiders (Hemicloea major) preferred small outcrops, and velvet geckos (Oedura lesueurii) preferred rocks close to the cliff edge with higher-than-average sun exposure. Standardized retreat sites can provide robust experimental data on the effects of landscape-scale attributes on retreat site selection, revealing interspecific divergences among sympatric taxa that use similar habitats

Spinal arthritis in invasive cane toads is linked to rate of dispersal as well as to latitude

Initial research on the spread of cane toads (Rhinella marina) through tropical Australia reported a high incidence of spinal arthritis (spondylosis) in toads at the invasion front (where toads disperse rapidly), but not in areas colonized earlier (where toads are more sedentary). The idea that spondylosis was a cost of rapid dispersal was challenged by wider spatial sampling which linked rates of spondylosis to hot (tropical) climates rather than to dispersal rates. Here, the authors of these competing interpretations collaborate to reinterpret the data. Our reanalysis supports both previous hypotheses; rates of spondylosis are higher in populations established by fast-dispersing toads, and are higher in tropical than in temperate environments; they are also higher in larger toads. The functional reason for climatic effects is unclear, but might involve effects on the soil-living bacteria involved in the induction of spondylosis; and/or may reflect higher movement (as opposed to dispersal) or more pronounced dry-season aggregation rates of toads in tropical conditions

The Physiological Basis of Geographic Variation in Rates of Embryonic Development within a Widespread Lizard Species

The duration of embryonic development (e.g., egg incubation period) is a critical life‐history variable because it affects both the amount of time that an embryo is exposed to conditions within the nest and the seasonal timing of hatching. Variation in incubation periods among oviparous reptiles might result from variation in either the amount of embryogenesis completed before laying or the subsequent developmental rates of embryos. Selection on incubation duration could change either of those traits. We examined embryonic development of fence lizards (Sceloporus undulatus) from three populations (Indiana, Mississippi, and Florida) that occur at different latitudes and therefore experience different temperatures and season lengths. These data reveal countergradient variation: at identical temperatures in the laboratory, incubation periods were shorter for lizards from cooler areas. This variation was not related to stage at oviposition; eggs of all populations were laid at similar developmental stages. Instead, embryonic development proceeded more rapidly in cooler‐climate populations, compensating for the delayed development caused by lower incubation temperatures in the field. The accelerated development appears to occur via an increase in heart mass (and, thus, stroke volume) in one population and an increase in heart rate in the other. Hence, superficially similar adaptations of embryonic developmental rate to local conditions may be generated by dissimilar proximate mechanisms

Hinode Calibration for Precise Image Co-alignment between SOT and XRT (November 2006 -- April 2007)

To understand the physical mechanisms for activity and heating in the solar atmosphere, the magnetic coupling from the photosphere to the corona is an important piece of information from the Hinode observations, and therefore precise positional alignment is required among the data acquired by different telescopes. The Hinode spacecraft and its onboard telescopes were developed to allow us to investigate magnetic coupling with co-alignment accuracy better than 1 arcsec. Using the Mercury transit observed on 8 November 2006 and co-alignment measurements regularly performed on a weekly basis, we have determined the information necessary for precise image co-alignment and have confirmed that co-alignment better than 1 arcsec can be realized between Solar Optical Telescope (SOT) and X-Ray Telescope (XRT) with our baseline co-alignment method. This paper presents results from the calibration for precise co-alignment of CCD images from SOT and XRT.Comment: 8 pages, 9 figures, accepted for publication in PASJ (Hinode Special issue

Observations of Sunspot Oscillations in G band and Ca II H line with Solar Optical Telescope on Hinode

Exploiting high-resolution observations made by the Solar Optical Telescope onboard Hinode, we investigate the spatial distribution of power spectral density of oscillatory signal in and around NOAA active region 10935. The G-band data show that in the umbra the oscillatory power is suppressed in all frequency ranges. On the other hand, in Ca II H intensity maps oscillations in the umbra, so-called umbral flashes, are clearly seen with the power peaking around 5.5 mHz. The Ca II H power distribution shows the enhanced elements with the spatial scale of the umbral flashes over most of the umbra but there is a region with suppressed power at the center of the umbra. The origin and property of this node-like feature remain unexplained.Comment: 7 pages, 8 figures, accepted for publication in PASJ (Hinode Special Issue