Insights into the adaptive significance of vertical pupil shape in snakes

Pupil shape in vertebrates ranges from circular to vertical, with multiple phylogenetic shifts in this trait. Our analyses challenge the widely held view that the vertical pupil evolved as an adaptation to enhance night vision. On functional grounds, a variable‐aperture vertical pupil (i) allows a nocturnal species to have a sensitive retina for night vision but avoid dazzle by day by adjusting pupil closure, and (ii) increases visual acuity by day, because a narrow vertical pupil can project a sharper image onto the retina in the horizontal plane. Detection of horizontal movement may be critical for predators that wait in ambush for moving prey, suggesting that foraging mode (ambush predation) as well as polyphasic activity may favour the evolution of vertical pupil shape. Camouflage (disruption of the circular outline of the eye) also may be beneficial for ambush predators. A comparative analysis in snakes reveals significant functional links between pupil shape and foraging mode, as well as between pupil shape and diel timing of activity. Similar associations between ambush predation and vertically slit pupils occur in lizards and mammals also, suggesting that foraging mode has exerted major selective forces on visual systems in vertebrates.     

Native Australian frogs avoid the scent of invasive cane toads

Invasive species can affect the ecosystems they colonize by modifying the behaviour of native taxa; for example, avoidance of chemical cues from the invader may modify habitat use (shelter site selection) by native species. In laboratory trials, we show that metamorphs of most (but not all) native frog species on a tropical Australian floodplain avoid the scent of invasive cane toads (Bufo marinus Linnaeus 1758). Cane toads also avoid conspecific scent. This response might reduce vulnerability of metamorph frogs and toads to larger predatory toads. However, similar avoidance of one type of pungency control (garlic), and the presence of this avoidance behaviour in frogs at the toad invasion front (and hence, with no prior exposure to toads), suggest that this may not be an evolved toad‐specific response. Instead, our data support the simpler hypothesis that the metamorph anurans tend to avoid shelter sites that contain strong and unfamiliar scents. Temporal and spatial differences in activity of frogs versus toads, plus the abundance of suitable retreat sites during the wet season (the primary time of frog activity), suggest that avoiding toad scent will have only a minor impact on the behaviour of native frogs. However, this behavioural impact may be important when environmental conditions bring toads and frogs into closer contact.     

Ecological impacts of invading species: Do parasites of the cane toad imperil Australian frogs?

Parasite transfer to native fauna is a potentially catastrophic impact of invasive species. Introduced cane toads in Australia frequently host the nematode lungworm Rhabdias pseudosphaerocephala, which reduces viability of metamorph toads. If native frogs are vulnerable to this South American parasite, cane toad invasion may affect native species via this route; but if the native taxa are not vulnerable, we may be able to exploit the parasites for managing toads. Our laboratory experiments show that infective larvae can penetrate the body of all seven species of Australian frogs (five hylids: Cyclorana longipes, Litoria caerulea, Litoria dahlii, Litoria nasuta, Litoria rothii, one myobatrachid: Opisthodon ornatus, and one limnodynastid: Limnodynastes convexiusculus) we tested, but most did not host the adult worms at the end of the trials, and none showed major impairment of growth, survival or locomotor performance. One native tree‐frog (L. caerulea) retained high infection levels with few ill effects, suggesting that we might be able to use this taxon as a reservoir species to build up local parasite densities for toad management. However, the interspecific variation in lungworm retention suggests that generalizations about parasite effects on native frogs will be elusive.     

Evolutionary and biogeographical history of an ancient and global group of arachnids (Arachnida: Opiliones: Cyphophthalmi) with a new taxonomic arrangement

We investigate the phylogeny, biogeography, time of origin and diversification, ancestral area reconstruction and large‐scale distributional patterns of an ancient group of arachnids, the harvestman suborder Cyphophthalmi. Analysis of molecular and morphological data allow us to propose a new classification system for the group; Pettalidae constitutes the infraorder Scopulophthalmi new clade , sister group to all other families, which are divided into the infraorders Sternophthalmi new clade and Boreophthalmi new clade . Sternophthalmi includes the families Troglosironidae, Ogoveidae, and Neogoveidae; Boreophthalmi includes Stylocellidae and Sironidae, the latter family of questionable monophyly. The internal resolution of each family is discussed and traced back to its geological time origin, as well as to its original landmass, using methods for estimating divergence times and ancestral area reconstruction. The origin of Cyphophthalmi can be traced back to the Carboniferous, whereas the diversification time of most families ranges between the Carboniferous and the Jurassic, with the exception of Troglosironidae, whose current diversity originates in the Cretaceous/Tertiary. Ancestral area reconstruction is ambiguous in most cases. Sternophthalmi is traced back to an ancestral land mass that contained New Caledonia and West Africa in the Permian, whereas the ancestral landmass for Neogoveidae included the south‐eastern USA and West Africa, dating back to the Triassic. For Pettalidae, most results include South Africa, or a combination of South Africa with the Australian plate of New Zealand or Sri Lanka, as the most likely ancestral landmass, back in the Jurassic. Stylocellidae is reconstructed to the Thai‐Malay Penisula during the Jurassic. Combination of the molecular and morphological data results in a hypothesis for all the cyphophthalmid genera, although the limited data available for some taxa represented only in the morphological partition negatively affects the phylogenetic reconstruction by decreasing nodal support in most clades. However, it resolves the position of many monotypic genera not available for molecular analysis, such as Iberosiro, Odontosiro, Speleosiro, Managotria or Marwe, although it does not place Shearogovea or Ankaratra within any existing family. The biogeographical data show a strong correlation between relatedness and formerly adjacent landmasses, and oceanic dispersal does not need to be postulated to explain disjunct distributions, especially when considering the time of divergence. The data also allow testing of the hypotheses of the supposed total submersion of New Zealand and New Caledonia, clearly falsifying submersion of the former, although the data cannot reject the latter. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 92–130.     

Morphological correlates of life‐history variation: is lizard clutch size related to the number of germinal beds in the ovary?

Clutch size varies widely in reptiles, both intraspecifically and interspecifically. The mechanisms that generate this variation have attracted detailed study, focusing primarily on ecological factors (e.g. food availability), trade‐offs with other traits (e.g. offspring size), and physical constraints (e.g. maternal body shape). Does ovarian morphology, specifically the number of germinal beds from which ova are produced, also correlate with clutch size? Our review of published data on 58 lizard species reveals that clutch size is correlated with the number of germinal beds per ovary (more fecund species have more germinal beds), and that phylogenetic changes in germinal beds have been consistently associated with concurrent phylogenetic changes in fecundity. These correlations imply a causal connection: either clutch size is constrained by ovarian morphology, and/or ovarian morphology evolves to allow adaptive shifts in clutch size. The latter hypothesis is more consistent with available data. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 94 , 81–88.     

Detection of phytoecdysteroids by gustatory sensilla on chelicerae of the brown dog tick Rhipicephalus sanguineus

Ecdysteroids are polyhydroxylated steroids that act as moulting hormones in arthropods and regulate several important life‐cycle processes. Phytoecdysteroids are ecdysteroid analogues produced by some plants that disrupt the growth and development of insects feeding on them, and can be perceived by the taste receptors of insects. The present study tested the hypothesis that the blood‐feeding tick Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae) is capable of detecting phytoecdysteroids. By recording from the chelicerae, six phytoecdysteroids are tested: α‐ecdysone, 20‐hydroxyecdysone, ponasterone A, makisterone A, inokosterone and pterosterone. In unfed ticks, makisterone A and pterosterone elicit frequencies of neural impulses higher than in a negative control (a KCl solution at 10^?3m ), with detection thresholds of 10^?6m and 10^?12m , respectively. The spike amplitudes of the responses to these compounds, and also for 20‐hydroxyecdysone and ponasterone A, are higher than in the control, indicating that a different neurone may be involved: perhaps a deterrent cell, as observed in insects. In fed ticks, only pterosterone at 10^?4m remains active. In behavioural attachment assays, no difference is observed between electrophysiologically active compounds and the negative control. These results show the capability of R. sanguineus ticks to detect phytoecdysteroids, although they do not clarify the role of ecdysteroids in tick biology, for which further studies are required.