Many organisms exhibit diverse anti-predator tactics, influenced by genetics and prior experience. In ectothermic taxa, offspring phenotypes are often sensitive to developmental temperatures. If the effectiveness of alternative anti-predator responses depends on thermally sensitive traits, then the temperatures experienced during embryonic life should also affect how offspring respond to an approaching predator. We incubated 16 clutches of Swedish grass snakes (Natrix natrix) at a range of developmental temperatures, and scored body size, colour pattern, locomotor performance and anti-predator responses of 213 hatchlings from those clutches. A hatchling snake’s size and locomotor abilities were affected by its clutch of origin, its developmental temperature, and by an interaction between these two factors. Anti-predator tactics were strongly linked to locomotor ability, such that slower snakes tended to rely upon aggressive displays rather than flight. Incubation temperatures that generated slow (and thus aggressive) snakes also modified the colour of the snake’s nuchal spot. Temperatures in the low to medium range generated mostly cream, white and orange spots, whereas medium to high temperatures generated more yellow spots. Incubation effects, and gene X environment interactions, thus may generate complex correlations between morphology, locomotor ability, and anti-predator tactics.

Understanding the interacting outcomes of selection and historical contingency in shaping adaptive evolution remains a challenge in evolutionary biology. While selection can produce convergent outcomes when species occupy similar environments, the unique history of each species can also influence evolutionary trajectories and result in different phenotypic end points. The question is to what extent historical contingency places species on different adaptive pathways and, in turn, the extent to which we can predict evolutionary outcomes. Among lizards there are several distantly related genera that have independently evolved an elaborate extendible dewlap for territorial communication. We conducted a detailed morphological study and employed new phylogenetic comparative methods to investigate the evolution of the underlying hyoid that powers the extension of the dewlap. This analysis showed that there appear to have been multiple phenotypic pathways for evolving a functionally convergent dewlap. The biomechanical complexity that underlies this morphological structure implies that adaptation should have been constrained to a narrow phenotypic pathway. However, multiple adaptive solutions have been possible in apparent response to a common selection pressure. Thus, the phenotypic outcome that subsequently evolved in different genera seems to have been contingent on the history of the group in question. This blurs the distinction between convergent and historically contingent adaptation and suggests that adaptive phenotypic diversity can evolve without the need for divergent natural selection.

Adaptations that enhance fitness in one situation can become liabilities if circumstances change. In tropical Australia, native snake species are vulnerable to the invasion of toxic cane toads. Death adders (Acanthophis praelongus) are ambush foragers that (i) attract vertebrate prey by caudal luring and (ii) handle anuran prey by killing the frog then waiting until the frog's chemical defences degrade before ingesting it. These tactics render death adders vulnerable to toxic cane toads (Bufo marinus), because toads elicit caudal luring more effectively than do native frogs, and are more readily attracted to the lure. Moreover, the strategy of delaying ingestion of a toad after the strike does not prevent fatal poisoning, because toad toxins (unlike those of native frogs) do not degrade shortly after the prey dies. In our laboratory and field trials, half of the death adders died after ingesting a toad, showing that the specialized predatory behaviours death adders use to capture and process prey render them vulnerable to this novel prey type. The toads' strong response to caudal luring also renders them less fit than native anurans (which largely ignored the lure): all toads bitten by adders died. Together, these results illustrate the dissonance in behavioural adaptations that can arise following the arrival of invasive species, and reveal the strong selection that occurs when mutually naive species first interact.

If pheromonal communication systems of invasive species differ from those of native biota, it may be possible to control the invader by exploiting that difference. When injured, the larvae of cane toads, Bufo marinus, an invasive species of major concern in tropical Australia, produce species-specific chemical cues that alert conspecific tadpoles to danger. Repeated exposure to the alarm chemical reduces tadpole survival rates and body sizes at metamorphosis and, thus, could help control toad populations. To evaluate the feasibility of this approach, we need to know how the intensity of toad tadpole response to the alarm chemical is affected by factors such as water temperature, time of day, larval stage and feeding history, geographic origin of the tadpoles, and habituation. Information on these topics may enable us to optimize deployment, so that tadpoles encounter pheromone at the times and places that confer maximum effect. In our studies, tadpole density, nutritional state, larval stage, and geographic origin had little effect on the intensity of the alarm response, but tadpoles reacted most strongly in higher water temperatures and during daylight hours. Repeated, once-daily exposure to pheromone did not induce habituation, but repeated exposure at 15-min interva

Novel approaches to control invasive species are urgently needed. Cane toads (Bufo marinus) are large, highly toxic anurans that are spreading rapidly through tropical Australia. Injured toad larvae produce an alarm pheromone that elicits rapid avoidance by conspecifics but not by frog larvae. Experiments in outdoor ponds show that repeated exposure to the pheromone reduced toad tadpole survival rates (by > 50%) and body mass at metamorphosis (by 20%). The alarm pheromone did not induce tadpoles to seek shelter, but accelerated ontogenetic differentiation. Perhaps reflecting mortality of weaker individuals during larval life, growth rates post-metamorphosis were higher in animals emerging from the pheromone exposure treatment than from the control treatment. Nonetheless, body size differentials established at metamorphosis persisted through the first 8 days of post-metamorphic life. We will need substantial additional research before evaluating whether the alarm pheromone provides a way to reduce cane toad recruitment in nature, but our field trials are encouraging in this respect.

Novel approaches to control invasive species are urgently needed. Cane toads (Bufo marinus) are large, highly toxic anurans that are spreading rapidly through tropical Australia. Injured toad larvae produce an alarm pheromone that elicits rapid avoidance by conspecifics but not by frog larvae. Experiments in outdoor ponds show that repeated exposure to the pheromone reduced toad tadpole survival rates (by >50%) and body mass at metamorphosis (by 20%). The alarm pheromone did not induce tadpoles to seek shelter, but accelerated ontogenetic differentiation. Perhaps reflecting mortality of weaker individuals during larval life, growth rates post-metamorphosis were higher in animals emerging from the pheromone exposure treatment than from the control treatment. Nonetheless, body size differentials established at metamorphosis persisted through the first 8 days of post-metamorphic life. We will need substantial additional research before evaluating whether the alarm pheromone provides a way to reduce cane toad recruitment in nature, but our field trials are encouraging in this respect.

In previous work, we have shown that tadpoles of invasive cane toads (Bufo marinus) strongly avoid scent cues from crushed conspecific tadpoles. Thus, identifying the identity of the chemical involved may provide novel approaches to toad control, by manipulating the behaviour of toad tadpoles. A first step in the search for that chemical is to see whether toad tadpoles are similarly repelled by chemical cues from crushed tadpoles of other species. Our experimental trials with four native Australian frogs (three hylids, one myobatrachid) show that toads do not respond to chemical cues from these taxa. Hence, the specific chemicals that induce avoidance cannot be generic ones (e.g. body fluids, tissue fragments) but instead, must reflect some underlying chemical divergence in body composition between the tadpoles of cane toads versus the other anurans that we have tested.

Many ambush foraging predators possess specialized structures and behaviours that plausibly function to attract prey, but this hypothesis has rarely been subject to direct empirical tests. If luring evolved to attract specific prey types then we predict that it will be manifested only if that prey type is present, and only by predators of the size class that feed on that prey type. Also, luring should induce closer approach by prey; and aspects of the behaviour (e. g. frequency of movement of the lure) should have been. ne tuned by selection to induce maximal response from prey. We describe a novel luring system: small- and medium-sized ( but not metamorph and large) cane toads, Chaunus marinus, wave the long middle toe of the hind-foot up and down in an obvious display. In keeping with the functional hypothesis, toe waving is elicited by moving edible-sized objects such as crickets or metamorphic toads. Metamorphic toads are attracted to this stimulus, and trials with a mechanical model show that both the colour and the vibrational frequency of the toe correspond closely with those most effective at attracting smaller conspecifics towards the lure. The independent evolution of visual luring systems in many animal lineages provides a powerful opportunity for robust empirical tests of adaptive hypotheses about signal design.

Research on the ecological impacts of invasive organisms typically looks only for negative impacts, ignoring the possibility that the wider community might see benefits in some of these effects. To truly understand the impact of invasive species, we need to look as broadly as possible, and incorporate studies on a diversity of variables. The spread of the South American cane toad (Bufo marinus) through tropical Australia is widely viewed as an ecological catastrophe, but anecdotal reports suggest that the invasion of toads may reduce the numbers of mosquitoes (and thus, potentially, the risk they pose to human health). We conducted experiments to determine whether the presence of toad tadpoles affects survival rates, adult body sizes and/or rates of oviposition of four species of disease-carrying mosquitoes. In the laboratory, the presence of toad tadpoles significantly reduced the sizes of adult mosquitoes at emergence, and also reduced survival rates of the larvae of one mosquito species. In field trials, mosquitoes were less likely to oviposit in waterbodies containing toad tadpoles. Accordingly, these data suggest (but do not prove) that toad invasion may reduce mosquito abundance. More generally, any overall evaluation of the impact of an invasive species needs to consider possible benefits (e.g. to human health) as well as negative effects (e.g. to native species). Both types of information are essential to inform community decisions about the management of feral taxa such as the cane toad in Australia.

Spawning sites are a critical and often scarce resource for aquatic-breeding amphibians, including invasive species such as the cane toad (Bufo marinus). If toads select spawning sites based on habitat characteristics, we can potentially manipulate those characteristics to either enhance or reduce their suitability as breeding sites. We surveyed 25 spawning sites used by cane toads, and 25 adjacent unused sites, in an area of tropical Australia recently invaded by these feral anurans. Water chemistry (pH, conductivity, salinity, turbidity) was virtually identical between the two sets of waterbodies, but habitat characteristics were very different. Toads selectively oviposited in shallow pools with gradual rather than steep slopes, and with open (unvegetated) gradually sloping muddy banks. They avoided flowing water, and pools with steep surrounds. In these respects, cane toads broadly resemble previously studied toad species in other parts of the world, as well as conspecifics within their natural range in South America.

Larvae of many anuran taxa display strong behavioural responses to chemical cues, including alarm signals from injured conspecific tadpoles. We exposed tadpoles and metamorphs from an Australian population of the invasive cane toad (Chaunus [Bufo] marinus) to a range of chemical stimuli and quantified their responses both in the laboratory and in the field. Filtered fluids containing scent cues from crushed conspecifics elicited strong avoidance from tadpoles, whereas other cues (e.g. scent of food, of native-range fish or urodele predators, and thermal stimuli) did not. Apparent aggregation of tadpoles in response to scent cues proved to be an artifact of tank design, and was an indirect consequence of avoidance of those cues. Field trials confirmed that free-ranging toad tadpoles and metamorphs avoided chemical cues from crushed conspecifics, suggesting that the chemicals inducing this response might provide an opportunity to develop targeted control methods for this invasive species.

We conducted a quantitative and qualitative chemical analysis of cane toad bufadienolides-the cardioactive steroids that are believed to be the principal cane toad toxins. We found complex shifts in toxin composition through toad ontogeny: (1) eggs contain at least 28 dominant bufadienolides, 17 of which are not detected in any other ontogenetic stage; (2) tadpoles present a simpler chemical profile with two to eight dominant bufadienolides; and (3) toxin diversity decreases during tadpole life but increases again after metamorphosis (larger metamorph/juvenile toads display five major bufadienolides). Total bufadienolide concentrations are highest in eggs (2.64 +/- 0.56 mu mol/mg), decreasing during tadpole life stages (0.084 +/- 0.060 mu mol/mg) before rising again after metamorphosis (2.35 +/- 0.45 mu mol/mg). These variations in total bufadienolide levels correlate with toxicity to Australian frog species. For example, consumption of cane toad eggs killed tadpoles of two Australian frog species (Limnodynastes convexiusculus and Litoria rothii), whereas no tadpoles died after consuming late-stage cane toad tadpoles or small metamorphs. The high toxicity of toad eggs reflects components in the egg itself, not the surrounding jelly coat. Our results suggest a dramatic ontogenetic shift in the danger that toads pose to native predators, reflecting rapid changes in the types and amounts of toxins during toad development.

Detailed observations on interactions between parasites and prospective hosts during the infection process can clarify (1) the routes by which parasites enter the host and (2) the ability of prospective hosts to detect, avoid, or resist potential parasites. Such information can clarify determinants of host vulnerability. Infective larvae of the nematode Rhabdias pseudosphaerocephala entered the bodies of their anuran host the Cane Toad (Rhinella marina, formerly Bufo marinus) primarily through the orbit (i.e., by crawling over the surface of the toad's eye) rather than by burrowing through the skin (believed to be the usual route of infection for rhabditid parasites). In our experimental infections, metamorph Cane Toads detected infective R. pseudosphaerocephala larvae but did not avoid them, nor did they manage to restrict rates of infective larvae penetration by using behavioral means (the toads kicked at infective larvae but failed to dislodge them). Rhabdias pseudosphaerocephala cause damage to their toad host during the process of host entry and throughout the ensuing infection. Despite the high cost of infection and the low cost of avoidance, metamorph Cane Toads seem to lack effective parasite avoidance strategies.

Temperature has a major influence on the rate of embryonic development in ectothermic organisms. While incubation experiments unambiguously show that constant high temperature accelerates development and shortens embryonic life, studies on the effect of fluctuating temperatures have generated contradictory results. Grass snakes (Natrix natrix) occur at latitudes and altitudes that are unusually cool for an oviparous reptile. In these cool climates females typically lay their eggs in heat-generating anthropogenic microhabitats that provide either a highly fluctuating (compost piles) or a relatively constant (manure heaps) thermal nesting environment. A laboratory experiment with fluctuating and constant incubation temperatures mimicking those recorded in such nests in the field showed that this nest-site dichotomy influences the development of the embryos, and the morphology and locomotor performance of the hatchlings. The incubation period increased at fluctuating temperatures and the fact that the rate of embryonic development showed a decelerating pattern with temperature suggests that periods of low temperature had a relatively larger influence on average development than periods of high temperature. Our study demonstrates how a dichotomy in the nesting environments available to female grass snakes in cool climates can affect variation in the duration of the incubation period and offspring phenotypes in ways that may have consequences for fitness.

Thermally-induced scale asymmetries in reptiles are often considered to be indicative of underlying osteological deformities that incur fitness costs. However, this typically rests on subjective plausibility arguments and anecdotal reports about links between deformities and fitness, as well as between superficial asymmetries and deeper deformities rather than on empirical data. To shed light on these issues, we used a combination of Xrays of museum specimens and locomotor performance trials of hatchlings grass snakes (Natrix natrix) incubated in the laboratory at either 25 degrees C or 31 degrees C. We found that 30% of the museum specimens with asymmetrical ventral scales also had a rib duplication on one side of the underlying vertebrae associated with a scale asymmetry. In some cases, there was also a second extra rib on the opposite side of the vertebrae. However, although there was a statistically significant association between asymmetric ventral scales and rib duplication, a relatively weak correlation coefficient (r(s) = 0.35) indicated that scale asymmetries are not a very strong predictor of rib duplication. In the performance trials, scale asymmetries had a significant effect on terrestrial but not aquatic locomotor ability of the hatchlings, and the magnitude of this effect depended on the temperature regimes that they experienced as embryos during incubation. Although both asymmetrical and normal snakes incubated at the higher temperature had more stamina than their respective counterparts incubated at the lower temperature, asymmetrical hatchlings overall became exhausted much sooner than normal snakes across the two treatments.

Populations of snakes and other reptiles are declining worldwide. Habitat loss and degradation is thought to be a significant factor in these declines, so to improve management strategies it is important to increase our understanding of reptilian habitat requirements. Modern agriculture is abandoning the tradition of gathering compost and manure in large heaps. Consequently these unusually warm environments are disappearing from the landscape. This may imperil populations of grass snakes (Natrix natrix) that rely on these anthropogenic heat sources to incubate their eggs. We conducted a relocation experiment to examine if eggs can develop successfully in other more natural environments that grass snakes potentially could utilize in the absence of manure heaps and compost piles. We found that hatching success was high (71 %) when we placed eggs in manure heaps and non-existent (0 %) when we placed them in potential ‘natural’ nests. Placement in compost piles resulted in intermediate (43 %) hatching success. Eggs in manure heaps hatched earlier than eggs in compost piles and thermal data from the nests showed that temperatures were higher and more stable in manure heaps than in compost piles and potential ‘natural’ nests. Jointly these results suggest that manure heaps generally provide a better nesting habitat than compost piles, attributable to thermal differences between the environments. Our findings facilitate improvement of current management strategies and have implications for conservation of oviparous reptiles in general.

Phenotypic traits of hatchling reptiles are strongly influenced by incubation regimes (e.g. of temperature and moisture), suggesting that maternal choice of suitable nest-sites should be under intense selection. Our laboratory incubation of 209 eggs (17 clutches) from wild-caught Swedish grass snakes (Natrix natrix) showed that scale abnormalities (half-scales on one side of the body, often reflecting lateral asymmetry in the number of ribs) occurred more frequently if eggs were incubated under cooler conditions. Especially at low incubation temperatures, individuals with scale asymmetries took longer to hatch than did symmetric conspecifics, were smaller in body length at hatching and were slower in trials of locomotor speed. Anti-predator tactics also covaried with scale asymmetry. These patterns suggest that individuals with asymmetric scales should have lower fitness and hence should rarely survive to adulthood in the wild. We tested this prediction by examining 201 field-collected snakes from museum collections. As predicted, scale asymmetries were seen primarily in small snakes, and rarely in larger animals. We interpret these data to suggest that scale asymmetries in this species offer an index of developmental instability and that fitness disadvantages to disrupted embryogenesis impose selection against suboptimal nest-site choice by females.

P>1. A lack of warm nest-sites prevents oviparous reptile species from reproducing in cool climates; such areas are dominated by viviparous species because sun-seeking pregnant females can maintain high temperatures for their developing offspring. 2. Our field and laboratory studies show that one oviparous species (the grass snake, Natrix natrix) escapes this cold-climate constraint (and hence, extends much further north in Europe than do other oviparous taxa) by ovipositing in a thermally distinctive man-made microhabitat (manure heaps on farms). 3. In the field, temperatures inside manure heaps averaged 30 center dot 7 degrees C, much higher than compost heaps (20 center dot 6 degrees C) or potential natural nest-sites under logs and rocks (15 center dot 5 degrees C). 4. In the laboratory, higher incubation temperatures not only hastened hatching, but also increased hatching success and modified the body sizes, colours, and locomotor abilities of hatchlings. Incubation temperatures typical of manure heaps (rather than alternative nest-sites) resulted in larger, faster offspring that hatched earlier in the season. 5. Thus, anthropogenic activities have generated potential nest-sites offering thermal regimes not naturally available in the region; and grass snakes have exploited that opportunity to escape the thermal limits that restrict geographic distributions of other oviparous reptile taxa.

There are few longtime studies on the effects on aphids of being tended by ants. The aim of this study is to investigate how the presence of ants influences settling decisions by colonizing aphids and the post-settlement growth and survival of aphid colonies. We conducted a field experiment using the facultative myrmecophile Aphis fabae and the ant Lasius niger. The experiment relied on natural aphid colonization of potted plants of scentless mayweed Tripleurospermum perforatum placed outdoors. Ants occurred naturally at the field site and had access to half of the pots and were prevented from accessing the remainder. The presence of winged, dispersing aphids, the growth and survival of establishing aphid colonies, and the presence of parasitoids were measured in relation to presence or absence of ants, over a period of five weeks. The presence of ants did not significantly influence the pattern of initial host plant colonization or the initial colony growth, but ant-tended aphids were subject to higher parasitism by hymenopteran parasitoids. The net result over the experimental period was that the presence of ants decreased aphid colony productivity, measured as the number of winged summer migrants produced from the colonized host plants. This implies that aphids do not always benefit from the presence of ants, but under some conditions rather pay a cost in the form of reduced dispersal.