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Mating with another species (hybridization) is often maladaptive. Consequently, females typically avoid heterospecifics as mates. Contrary to these expectations, female spadefoot toads were more likely to choose heterospecific males when exposed to environmental conditions that favor hybridization. Indeed, those females with phenotypic characteristics for which hybridization is most favorable were most likely to switch from choosing conspecifics to heterospecifics. Moreover, environmentally dependent mate choice has evolved only in populations and species that risk engaging in, and can potentially benefit from, hybridization. Thus, when the benefits of mate choice vary, females may radically alter their mate selection in response to their own phenotype and their environment, even to the point of choosing males of other species.

Raising The Tone Some bats, dolphins and rodents are notable among vertebrates in being able to produce and detect ultrasonic frequencies. Now for the first time an amphibian can be added to that select list. The spectacular bird-like sounds made by a type of Chinese torrent frog were known to edge into the ultrasonic range: now these frogs are shown to use ultrasonics as a form of communication. The males do at least, during competition for territory. Frogs are a long way, evolutionarily speaking, from the other known users of ultrasonics so this ability seems to have evolved independently several times. It is possible, too, that many other species are chatting away in the ultrasonic waveband, but that nobody has looked for them. Among vertebrates, only microchiropteran bats, cetaceans and some rodents are known to produce and detect ultrasounds (frequencies greater than 20 kHz) for the purpose of communication and/or echolocation, suggesting that this capacity might be restricted to mammals 1 , 2 . Amphibians, reptiles and most birds generally have limited hearing capacity, with the ability to detect and produce sounds below ∼12 kHz. Here we report evidence of ultrasonic communication in an amphibian, the concave-eared torrent frog ( Amolops tormotus ) from Huangshan Hot Springs, China. Males of A. tormotus produce diverse bird-like melodic calls with pronounced frequency modulations that often contain spectral energy in the ultrasonic range 3 , 4 . To determine whether A. tormotus communicates using ultrasound to avoid masking by the wideband background noise of local fast-flowing streams, or whether the ultrasound is simply a by-product of the sound-production mechanism, we conducted acoustic playback experiments in the frogs' natural habitat. We found that the audible as well as the ultrasonic components of an A. tormotus call can evoke male vocal responses. Electrophysiological recordings from the auditory midbrain confirmed the ultrasonic hearing capacity of these frogs and that of a sympatric species facing similar environmental constraints. This extraordinary upward extension into the ultrasonic range of both the harmonic content of the advertisement calls and the frog's hearing sensitivity is likely to have co-evolved in response to the intense, predominantly low-frequency ambient noise from local streams. Because amphibians are a distinct evolutionary lineage from microchiropterans and cetaceans (which have evolved ultrasonic hearing to minimize congestion in the frequency bands used for sound communication 5 and to increase hunting efficacy in darkness 2 ), ultrasonic perception in these animals represents a new example of independent evolution.

Variation in behavior, morphology and life history traits of larval anurans across predator gradients, and consequences of that variation, have been abundantly studied. Yet the functional link between morphology and burst-swimming speed is largely unknown. We conducted experiments with two divergent species of anurans, Scaphiopus holbrookii and Rana sphenocephala, to examine how behavior and morphology influence predator vulnerability, and whether tadpole shape is related to burst-swimming performance. Scaphiopus holbrookii, a species that typically uses ephemeral pools, was more active, exhibited slower burst speeds, and was more susceptible to predation than R. sphenocephala, a species associated with more permanent aquatic sites. Our analysis of morphology and burst speed defined a shared axis of shape variation associated with burst-swimming speed regardless of species. Tadpoles with a deeper tail fin and muscle and a smaller body produced faster speeds. The nature and breadth of the morphology-speed relationship suggests it may represent a generalized ecomorphological paradigm for larval anurans.

In many organisms reproductive success is strongly dependent on several breeding site characteristics, which often vary in space and time. Although we have a good understanding of how ovipositing organisms respond to single factors, we still have little information about how they respond under more complex natural conditions. We examined the oviposition behavior of a tree-hole breeding frog, Phrynobatrachus guineensis, with respect to abiotic and biotic oviposition site characteristics, including desiccation risk and the presence of conspecific offspring using both observation and experiments. Based on daily monitoring data, compiled from 69 natural oviposition sites during a complete reproductive season, we developed oviposition site-selection models. A model based on water presence, sediment depth and maximal possible water depth showed the best predictive performance and was transferable to the subsequent season. Field observations and experiments revealed that frogs could estimate water-holding capacity of sites and timed oviposition with respect to future water presence. Despite the negative effects on larval growth and the availability of sites without conspecifics, data suggest that ovipositing individuals are attracted to conspecific offspring because they serve as a cue for low predation risk. Our results imply that a site's potential for being used at least once for oviposition was determined by abiotic factors, whereas the relative use of breeding sites was determined by a response to conspecifics. Our study demonstrates the importance of including multiple biotic and abiotic factors in the analysis of oviposition site-selection.

Anuran reproduction is influenced by various biotic and abiotic factors, of which temperature and rainfall are the best studied. Here we examine the relationship between multiple abiotic environmental variables -- specifically, air and water temperature, rainfall, barometric pressure, relative humidity and wind velocity -- and the calling activity of five species (Rana sylvatica, Pseudacris crucifer, Bufo americanus, Rana clamitans, and Rana catesbeiana) in an anuran community in New Brunswick, Canada. Acoustical and environmental data were sampled hourly for 4 months during the breeding season in 1997. Logistic regression analyses indicated that each species responded to a unique combination of meteorological variables, even when calling concurrently. Calling in the spring breeding species, R. sylvatica, P. crucifer, and B. americanus, was most associated with the time of day (i.e., they called primarily at night), while calling in the summer breeding species, R. clamitans and R. catesbeiana, was associated primarily with high water temperature. Species with short breeding periods (i.e., explosive breeders; R. sylvatica, B. americanus) responded to fewer environmental variables than did species with prolonged breeding periods (P. crucifer, R. clamitans, R. catesbeiana). Prolonged breeding species responded differently to climatic variables throughout the breeding season: during the latter half of their calling periods, the time of day and a variable that predicts rain, i.e., barometric pressure, became more important, and water temperature became less important.

I examined the long-term consequences of a trade-off between predation risk and resource acquisition for the garden skink (Lampropholis guichenoti) by rearing hatchlings to maturity in outdoor enclosures covered with snake predator scent (mimicking high predator densities) or control scent (mimicking low predator densities). Open areas provided optimal foraging and basking sites but were covered with scent, whereas retreat sites provided suboptimal foraging and basking opportunities and were not scented. During the initial six months of the experiment, lizards reared in enclosures covered with scent from a natural predator became active later in the day, showed reduced mobility, and selected \"safer\" substrate microhabitats than did lizards raised in enclosures covered with control scent. These behavioral shifts reduced opportunities to forage and bask for lizards in the predator-scented enclosures. During the study, however, lizards from predator-scented enclosures became gradually less responsive to snake chemical cues, and after one year there were no differences in the activity patterns and substrate microhabitat use of lizards in both treatments. This pattern of behavior is paralleled by variation in growth rates of lizards. Throughout the study, lizards exposed to predator scent were lighter and shorter than were lizards exposed to control scent. However, this result reflects differential rates of growth by lizards only during the first six months of the experiment. Nevertheless, lizards that grew slowly early in life, as a consequence of predator avoidance, attained smaller body sizes at maturity and produced lighter clutch masses and offspring. Thus, predator avoidance tactics employed early in a lizard's life can impose long-term fitness costs.

There is growing recognition of the need to incorporate information on movement behavior in landscape-scale studies of dispersal. One way to do this is by using indirect indices of dispersal (e.g., genetic differentiation) to test predictions derived from direct data on movement behavior. Mark-recapture studies documented upstream-biased movement in the salamander Gyrinophilus porphyriticus (Plethodontidae). Based on this information, we hypothesized that gene flow in G. porphyriticus is affected by the slope of the stream. Specifically, because the energy required for upstream dispersal is positively related to slope, we predicted gene flow to be negatively related to change in elevation between sampling sites. Using amplified DNA fragment length polymorphisms among tissue samples from paired sites in nine streams in the Hubbard Brook Watershed, New Hampshire, USA, we found that genetic distances between downstream and upstream sites were positively related to change in elevation over standardized 1-km distances. This pattern of isolation by slope elucidates controls on population connectivity in stream networks and underscores the potential for specific behaviors to affect the genetic structure of species at the landscape scale. More broadly, our results show the value of combining direct data on movement behavior and indirect indices to assess patterns and consequences of dispersal in spatially complex ecosystems.

1. Introduced plant species modify the environment and alter ecological interactions in communities, often to the detriment of native fauna, but the causes driving negative effects on fauna are rarely examined. We used native Australian scincid lizards Carlia munda and Carlia pectoralis and the introduced weed rubber vine Cryptostegia grandiflora as a model system to determine the possible underlying mechanisms driving habitat selection by native fauna in an environment invaded by weeds. 2. Lizards were allowed to select between rubber vine and native eucalypt leaf litter in semi-natural enclosures. To determine the mechanisms of habitat preference, we examined differences in temperature, prey (arthropod) availability and composition, and leaf shape of naturally occurring rubber vine and native vegetation. 3. Lizards discriminated between leaf litter types: 85% of Carlia pectoralis and 80% of Carlia munda chose native leaf litter over rubber vine, clearly indicating a preference for native habitat. 4. In the field, rubber vine leaf litter was cooler at the surface than native leaf litter, and during peak lizard activity was below the temperature range of Carlia. Rubber vine also contained significantly fewer arthropod taxa and a significantly different composition of arthropod taxa, with fewer preferred prey items of Carlia than native vegetation. 5. Finally, rubber vine leaves were significantly shorter than native leaves and the lizards themselves. The shape of rubber vine leaves was different from that of the lizards, potentially making the lizards more obvious on rubber vine litter. This may increase the susceptibility of the lizards to detection by predators. 6. Synthesis and applications. In comparison with native habitat, rubber vine provided a suboptimal environment for litter-dwelling lizards because of the lower ambient temperatures, reduced availability of prey and a reduction in camouflage from predators (dissimilar leaf and lizard shapes). Our study has identified three possible mechanisms by which an introduced plant species can alter the availability of resources in an environment, making it less attractive to native fauna. Our results highlight the importance of understanding how alien plants alter the environment and further emphasize the critical need for management of plants that replace native habitat with a suboptimal environment.

Many animals respond behaviourally to the infective stages of parasites, but the efficacy of such responses in reducing risk of parasitism often is not established. It was found that tadpoles of Rana clamitans Latr., 1801 (green frogs) and R. sylvatica LeConte, 1825 (wood frogs) increased their activity when exposed to live infective stages (cercariae) of the trematode Echinostoma trivolvis Rudolphi, 1809. The susceptibility to parasitism for green frog tadpoles subjected to three different treatments was compared. Tadpoles were housed at 20 °C and allowed to respond to cercariae, held at 6-8 °C and showing reduced behavioural responses, or anesthetized and showing no responses. Low levels of parasitism were found for tadpoles that responded behaviourally to cercariae;; such responses are expected to occur under normal field conditions in the absence of factors suppressing activity of tadpoles. We also demonstrate that infectivity of E. trivolvis cercariae to non-responding (anesthetized) wood frog tadpoles was higher at warm than at cool temperatures. Thus, lowered parasitism at warm temperatures in the first experiment likely resulted from host behavioural responses and not from low infectivity of cercariae. These results have implications for observing effects of environmental factors on susceptibility to parasitism where susceptibility is thought or known to be mediated by host behaviour.

We examined how autotomy-induced shifts in behavior of a diurnal lizard (Lampropholis guichenoti) and two natural snake predators influence the outcome of predatory interactions. During staged encounters in seminatural enclosures, we estimated the consumption order of lizards with recently autotomised tails (\"tailless\") and intact tails (\"tailed\"). Tail loss increased a lizard's chances of being consumed first by a diurnal snake (Demansia psammophis), but not by a nocturnal species (Rhinoplocephalus nigrescens). We presented snakes with an inert tailed lizard vs. tailless lizard, scoring which was consumed first. Neither predator actively selected tailless prey. We quantified variation in the behavior of tailed and tailless lizards that determines the outcome of predator-prey interactions. Tailless lizards were not easier to detect visually or via chemoreception than were tailed lizards. Instead, the higher consumption rate of tailless lizards by the diurnal snake probably reflects reduced locomotor performance, and their tendency to flee sooner from approaching predators (thereby eliciting attack by this snake). In contrast, tail presence or absence did not determine a lizard's chances of detection by the nocturnal snake. Thus, tail loss can induce shifts in behavior of lizards, affecting their later chances of being consumed by some predators, but not by others.