Many Australians who work outdoors (notably, farmers and graziers) routinely kill venomous snakes. We argue that this attitude is misguided and dangerous. Despite their fearsome reputation, venomous Australian snakes pose little risk to human health (snakes kill an average of less than three people per year in Australia). Also, snakes confer a substantial benefit by consuming agricultural pests such as rodents. We estimate the magnitude of that benefit with data on snake diets, feeding rates and abundances. The most valuable rodent-controllers are Brownsnakes (genus Pseudonaja), which are rodent-specialists as adults and are abundant in agroecosystems across much of Australia. We calculate that a free-living adult Eastern Brownsnake consumes at least 50 mice per year (probably twice that number), and that population densities of Brownsnakes in agricultural areas can exceed 100 per km(2). Thus, Brownsnakes remove thousands of mice per square kilometre of farmland per year. That offtake plausibly reduces rodent densities because Brownsnakes take all age classes and both sexes of rodents by hunting in burrows. Tolerating Brownsnakes also would benefit the environment (e.g. less reliance on toxic chemicals) and the health of humans and domestic pets (fewer rodent-mediated diseases) and counter-intuitively, might reduce rates of snakebite (because many bites occur when a snake is attacked). In summary, a societal policy of coexisting with highly venomous snakes would confer multiple benefits to Australian farmers.

If an animal’s size, age and/or sex influence its vulnerability to an invasive species, the arrival of such an invader can cause rapid changes in the population demography of an affected species. We studied free-ranging varanid lizards (Yellow-spotted monitors, Varanus panoptes) at a site in tropical Australia during the influx of fatally toxic cane toads, Rhinella marina. Mortality was inferred from shifts in population structure, as well as the survival rates (time to death) of 107 radio-tracked lizards. Of 57 deaths whose cause was unambiguous, 32 were due to fatal poisoning by ingesting a cane toad; the other 25 lizards were consumed by pythons. Size and age structure shifted between years, such that the population post-invasion was dominated by smaller, younger lizards, and by females rather than males. Radiotelemetric monitoring confirmed that survival rates were reduced more in males than in females in the post-toad year, with males most at risk late in the dry-season, when food was scarce and females were nesting rather than foraging. Pythons disproportionately consumed larger female lizards during the nesting season. Toad-induced poisoning of adult male varanids (which are larger and bolder than females) likely produced a population that was more resilient to toad impact, but less easily surveyed by conventional techniques.

The transition from terrestrial to aquatic life by hydrophiine elapid snakes modified targets of natural selection and likely affected sexual selection also. Thus, the shift to marine life also might have affected sexual dimorphism. Our measurements of 419 preserved specimens of six species of aipysurine snakes (genera Emydocephalus and Aipysurus) revealed sexual dimorphism in mean adult snout–vent length (SVL), body width relative to SVL, lengths and widths of heads and tails relative to SVL, and eye diameter relative to head length. Females averaged larger than males in all taxa, and generally were wider-bodied with shorter and wider tails and smaller eyes. For other traits, sexual dimorphism varied among species: for example, relative head length ranged from male-biased to female-biased, and head shape (width relative to length) was highly dimorphic only in A. laevis. The transition to marine life may have eliminated male–male combat (reducing selection for large males) and favoured visual rather than pheromone-based mate-searching (favouring larger eyes in males). Variation in head-size dimorphism may reflect intersexual niche partitioning, with different taxa following different trajectories. Repeated evolutionary transitions from terrestrial to aquatic life in snakes provide a powerful opportunity to explore selective forces on sexually dimorphic traits.

Invasive species offer insights into rapid adaptations in novel environments. The iconic cane toad ( Rhinella marina ) is an excellent model for studying rapid adaptation during invasion. Previous research using the mitochondrial NADH dehydrogenase 3 ( ND3 ) gene in the Hawai’ian and Australian invasive populations found a single haplotype, indicating an extreme genetic bottleneck following introduction. Nuclear genetic diversity also exhibited reductions across the genome in these two populations. Here, we investigated the mitochondrial genome diversity of cane toads across this invasion trajectory. We created the first reference mitochondrial genome of the cane toad with long-read sequencing and constructed a phylogeny of Anura full mitochondrial genomes. We used transcriptomic data of 125 individuals from the native (French Guiana) and introduced (Hawai’i and Australia) ranges to construct nearly-complete mitochondrial genomes for population genomics analyses. As expected, the cane toad belongs to family Bufonidae, distinct from genus Bufo . In agreement with previous investigations of these populations, we identified genetic bottlenecks in both Hawai’ian and Australian introduced populations, alongside evidence of population expansion in the invasive ranges. Although mitochondrial genetic diversity in introduced populations was reduced, our results revealed that it had been underestimated: we identified 45 mitochondrial haplotypes in Hawai’ian and Australian samples, none of which were found in the native range. Additionally, we identified two distinct groups of haplotypes from the native range, separated by a minimum of 110 base pairs (0.6%). These findings enhance our understanding of Anura phylogenetics and how invasion has shaped the genetic landscape of this species.

Competition among larval anurans can occur via interference as well as via a reduction in per-capita food supply. Previous research on intraspecific interference competition in cane toad (Rhinella marina) tadpoles found conflicting results, with one study detecting strong effects on tadpoles and another detecting no effects on metamorphs. A capacity to recover from competitive suppression by the time of metamorphosis might explain those contrasting impacts. In a laboratory experiment, we found that nine days of exposure to intraspecific interference competition strongly reduced tadpole growth and development, especially when the competing tadpoles were young (early-stage) individuals. Those competitive effects disappeared by the time of metamorphosis, with no significant effect of competition on metamorph body condition, size, larval period or survival. Temporal changes in the impact of competition were not related to tadpole density or to variation in water quality. The ability of larval cane toads to recover from intraspecific interference competition may enhance the invasive success of this species, because size at metamorphosis is a significant predictor of future fitness. Our study also demonstrates a cautionary tale: conclusions about the existence and strength of competitive interactions among anuran larvae may depend on which developmental stages are measured.

The availability of prey varies through time and space, forcing predators to modify the times, places and ways in which they forage. Although studied most intensively in mammalian and avian predators, seasonal shifts in predation tactics are widespread in ectotherms also. In tropical rainforests of north-eastern Australia, scrub pythons (Simalia amethistina) congregate below the emergent trees used as communal rookeries by metallic starlings (Aplonis metallica) for four months per year, but the snakes move more widely through the landscape during the remaining 8 months. Radio-tracking of 23 pythons confirmed that the availability of nestling starlings (that often fall from the rookery trees) induces pythons to shift from ambush predation to active foraging, increases spatial concentration of pythons, reduces home-range size and decreases daily distances moved. Pythons that utilized the starling colonies preyed almost exclusively on starlings during the nesting period, whereas those from the broader environment consumed a more diverse assemblage of prey. The ability to flexibly modify foraging tactics and spatial ecology in response to ephemeral concentrations of prey may be critical for many apex predators.

Abstract Within a population of apex predators, differences among individuals can influence both their ecological impact and their vulnerability to threatening processes. Our field studies on a large monitor lizard (Varanus panoptes) in the Australian wet–dry tropics show that diets shift seasonally and depend upon a lizard’s sex and body size. Individuals that had previously been recorded to consume frogs were most at risk following biological invasion by toxic cane toads (Rhinella marina), as were individuals with broad diets during the wet season. As a result, mortality of those individual predators likely reduced predation pressure on other taxa (invertebrates and reptiles) that were frequently consumed by the same lizards that ate frogs, but with less benefit for taxa (e.g., rodents) that were consumed by non‐anuran‐eating individuals within the predator population. In particular, individuals killed by cane toads often had consumed agamid lizards, a group whose abundance has been reported to increase due to toad‐induced mortality of V. panoptes. To understand the vulnerability of apex predators, or the ecological consequences of their extirpation, we need to incorporate the role of variation among individuals in critical ecological traits.

As technological advancements enhance our ability to study population genetics, we must understand how the intrinsic properties of our datasets influence the decisions we make when designing experiments. Filtering parameter thresholds, such as call rate and minimum minor allele frequency (MAF), are known to affect inferences of population structure in reduced representation sequencing (RRS) studies. However, it is unclear to what extent the impacts of these parameter choices vary across datasets. Here, we reviewed literature on filtering choices and levels of genetic differentiation across RRS studies on wild populations to highlight the diverse approaches that have been used. Next, we hypothesized that choices in filtering thresholds would have the greatest impact when analyzing datasets with low levels of genetic differentiation between populations. To test this hypothesis, we produced seven simulated RRS datasets with varying levels of population structure, and analyzed them using four different combinations of call rate and MAF. We performed the same analysis on two empirical RRS datasets (low or high population structure). Our simulated and empirical results suggest that the effects of filtering choices indeed vary based on inherent levels of differentiation: specifically, choosing stringent filtering choices was important to detect distinct populations that were slightly differentiated, but not those that were highly differentiated. As a result, experimental design and analysis choices need to consider attributes of each specific dataset. Based on our literature review and analyses, we recommend testing a range of filtering parameter choices, and presenting all results with clear justification for ultimate filtering decisions used in downstream analyses.

Although widespread, the large Hydrophiinae sea snake Hydrophis major is poorly known ecologically. We dissected 119 preserved specimens in museum collections to quantify body sizes and proportions, sexual dimorphism, reproductive biology and diet. The sexes mature at similar snout–vent lengths (SVLs, about 75 cm) and attain similar maximum sizes (females 123 cm vs. males 122 cm SVL), but females in our sample exhibited larger mean sizes than did males (means 98.8 vs. 93.1 cm SVL). The adult sex ratio in museum specimens was highly female-biased (64:30), and the high proportion of reproductive females during the austral summer suggests annual reproduction. At the same SVL, females had shorter tails and wider bodies than did males, but sex differences in other body proportions (e.g. tail shape, head dimensions, eye diameter) were minimal. Skin rugosity increased with SVL, was greater in males than females and was greater on the dorsal than the ventral surface of the body. Litter size averaged 4.9 offspring (range 2–10) and increased with maternal body size. Neonates were approximately 33 cm SVL. The only prey items found inside dissected snakes (and also, recorded as prey in free-ranging snakes in our New Caledonia field studies) were catfish (Plotosus lineatus), whereas previous studies have suggested a more diverse diet. Although H. major resembles its terrestrial relatives in some respects, other characteristics (such as scale rugosity, low proportion of juveniles in collections, frequent production of small litters of large offspring) may reflect adaptation to marine habitats.

AbstractAttempts to cull an invasive species often create a paradoxical situation, whereby the consequent reduction in invader densities frees the survivors from intraspecific competition—and hence, increases the viability of those survivors. Our laboratory experiments with invasive cane toads (Rhinella marina) show that this backfire effect can occur with pheromone‐baited trapping. Eliminating most of the tadpoles from a tank accelerates metamorphosis of the survivors and increases the size (and thus quality) of those metamorphs. Thus, trapping is likely to reduce recruitment only if the program catches all, or almost all, of the tadpoles in a waterbody. In contrast, toad control using the suppression pheromone, either alone or alongside trapping, causes similar rates of mortality as via trapping alone, but the survivors exhibit smaller mass at metamorphosis and a longer, not shorter, larval period. Thus, the combination of pheromone‐based suppression and trapping can reduce effective recruitment of cane toads more successfully than can either method when used alone.

The human brain integrates diverse cognitive processes into a coherent whole, shifting fluidly as a function of changing environmental demands. Despite recent progress, the neurobiological mechanisms responsible for this dynamic system-level integration remain poorly understood. Here, we used multi-task fMRI data from the Human Connectome Project to examine the spatiotemporal architecture of cognition in the human brain. By investigating the spatial, dynamic and molecular signatures of system-wide neural activity across a range of cognitive tasks, we show that large-scale neuronal activity converges onto a low dimensional manifold that facilitates the dynamic execution of diverse task states. Flow within this attractor space is associated with dissociable cognitive functions, and with unique patterns of network-level topology and information processing complexity. The axes of the low-dimensional neurocognitive architecture align with regional differences in the density of neuromodulatory receptors, which in turn relate to distinct signatures of network controllability estimated from the structural connectome. These results advance our understanding of functional brain organization by emphasizing the interface between low dimensional neural activity, network topology, neuromodulatory systems and cognitive function. One Sentence Summary A diverse set of neuromodulators facilitates the formation of a dynamic, low-dimensional integrative core in the brain that is recruited by diverse cognitive demands

In ?Behavioral Thermoregulation by Turtle Embryos,? published in Proceedings of the National Academy of Sciences [4] in April, 2011, Wei-Guo Du, Bo Zhao, Ye Chen, and Richard Shine report that turtle embryos can move towards warmer temperatures within the egg [5] when presented with a small, 0.8 degrees Celsius gradient. This behavioral thermoregulation may benefit the embryo?s fitness by accelerating the rate of development enough to decrease the incubation period by up to four and a half days. Embryos are generally thought to have little control over their surroundings. This study revealed that embryos may be able to control their developmental environment by modifying their behavior.

Squamate embryos require weeks of high temperature to complete development, with the result that cool climatic areas are dominated by viviparous taxa (in which gravid females can sun-bask to keep embryos warm) rather than oviparous taxa (which rely on warm soil to incubate their eggs). How, then, can some oviparous taxa reproduce successfully in cool climates - especially late in summer, when soil temperatures are falling? Near the northern limit of their distribution (in Sweden), sand lizards (Lacerta agilis) shift tactics seasonally, such that the eggs in late clutches complete development more quickly (when incubated at a standard temperature) than do those of early clutches. That acceleration is achieved by a reduction in egg size and by an increase in the duration of uterine retention of eggs (especially, after cool weather). Our results clarify the ability of oviparous reptiles to reproduce successfully in cool climates and suggest a novel advantage to reptilian viviparity in such conditions: by maintaining high body temperatures, viviparous females may escape the need to reduce offspring size in late-season litters.

Brought to Australia in 1935 to control agricultural pests (from French Guiana, via Martinique, Barbados, Jamaica, Puerto Rico and Hawai'i), repeated stepwise translocations of small numbers of founders enabled the cane toad (Rhinella marina) to escape many parasites and pathogens from its native range. However, the infective organisms that survived the journey continue to affect the dynamics of the toad in its new environment. In Australia, the native-range lungworm Rhabdias pseudosphaerocephala decreases its host's cardiac capacity, as well as growth and survival, but not rate of dispersal. The lungworm is most prevalent in long-colonised areas within the toads' Australian range, and absent from the invasion front. Several parasites and pathogens of Australian taxa have host-shifted to cane toads in Australia; for example, invasion-front toads are susceptible to spinal arthritis caused by the soil bacterium, Ochrobactrum anthropi. The pentastome Raillietiella frenata has host-shifted to toads and may thereby expand its Australian range due to the continued range expansion of the invasive toads. Spill-over and spill-back of parasites may be detrimental to other host species; however, toads may also reduce parasite loads in native taxa by acting as terminal hosts. We review the impact of the toad's parasites and pathogens on the invasive anuran's biology in Australia, as well as collateral effects of toad-borne parasites and pathogens on other host species in Australia. Both novel and co-evolved pathogens and parasites may have played significant roles in shaping the rapid evolution of immune system responses in cane toads within their invaded range.

In Australia, large native predators are fatally poisoned when they ingest invasive cane toads ( Rhinella marina ). As a result, the spread of cane toads has caused catastrophic population declines in these predators. Immediately prior to the arrival of toads at a floodplain in the Kimberley region, we induced conditioned taste aversion in free-ranging varanid lizards ( Varanus panoptes ), by offering them small cane toads. By the end of the 18-month study, only one of 31 untrained lizards had survived longer than 110 days, compared to more than half (nine of 16) of trained lizards; the maximum known survival of a trained lizard in the presence of toads was 482 days. In situ aversion training (releasing small toads in advance of the main invasion front) offers a logistically simple and feasible way to buffer the impact of invasive toads on apex predators.

Biological invasions can induce rapid evolutionary change. As cane toads (Rhinella marina) have spread across tropical Australia over an 80-year period, their rate of invasion has increased from around 15 to 60 km per annum. Toads at the invasion front disperse much faster and further than conspecifics from range-core areas, and their offspring inherit that rapid dispersal rate. We investigated morphological changes that have accompanied this dramatic acceleration, by conducting three-dimensional morphometric analyses of toads from both range-core and invasion-front populations. Morphology of heads, limbs, pectoral girdles and pelvic girdles differed significantly between toads from the two areas, ranging from 0.5% to 16.5% difference in mean bone dimensions between populations, with invasion-front toads exhibiting wider forelimbs, narrower hindlimbs and more compact skulls. Those changes plausibly reflect an increased reliance on bounding (multiple short hops in quick succession) rather than separate large leaps. Within an 80-year period, invasive cane toads have converted the basic anuran body plan - which evolved for occasional large leaps to evade predators - into a morphotype better-suited to sustained long-distance travel.

Phenotypic plasticity can enhance a species' ability to persist in a new and stressful environment, so that reaction norms are expected to evolve as organisms encounter novel environments. Biological invasions provide a robust system to investigate such changes. We measured the rates of early growth and development in tadpoles of invasive cane toads (Rhinella marina) in Australia, from a range of locations and at different larval densities. Populations in long-colonized areas have had the opportunity to adapt to local conditions, whereas at the expanding range edge, the invader is likely to encounter challenges that are both novel and unpredictable. We thus expected invasion-vanguard populations to exhibit less phenotypic plasticity than range-core populations. Compared to clutches from long-colonized areas, clutches from the invasion front were indeed less plastic (i.e. rates of larval growth and development were less sensitive to density). In contrast, those rates were highly variable in clutches from the invasion front, even among siblings from the same clutch under standard conditions. Clutches with highly variable rates of growth and development under constant conditions had lower phenotypic plasticity, suggesting a trade-off between these two strategies. Although these results reveal a strong pattern, further investigation is needed to determine whether these different developmental strategies are adaptive (i.e. adaptive phenotypic plasticity vs. bet-hedging) or instead are driven by geographic variation in genetic quality or parental effects.