Gregory P Brown

The cane toad (Rhinella marina) has undergone rapid evolution during its invasion of tropical Australia. Toads from invasion front populations (in Western Australia) have been reported to exhibit a stronger baseline phagocytic immune response than do conspecifics from range core populations (in Queensland). To explore this difference, we injected wild-caught toads from both areas with the experimental antigen lipopolysaccharide (LPS, to mimic bacterial infection) and measured whole-blood phagocytosis. Because the hypothalamic-pituitary-adrenal axis is stimulated by infection (and may influence immune responses), we measured glucocorticoid response through urinary corticosterone levels. Relative to injection of a control (phosphate-buffered saline), LPS injection increased both phagocytosis and the proportion of neutrophils in the blood. However, responses were similar in toads from both populations. This null result may reflect the ubiquity of bacterial risks across the toad's i...

Immune responsiveness, the ability of an organism to effectively respond immunologically following antigenic exposure, is an essential component of life history, as organisms require effective immune functionality in order to grow, survive and reproduce. However, immune status is also associated with concomitant trade-offs in these physiological functions. Herein we demonstrate the validation of phytohaemagglutinin (PHA) injection in saltwater crocodiles, Crocodylus porosus, to assess cellular immune responsiveness. Following injection of 2 mg mL–1 PHA into the hind toe webbing, we observed a peak swelling response 12 h after injection, with PHA inducing increased thickness compared with webs injected with phosphate-buffered saline (PBS) (F5,518 = 145.13, P < 0.001). Subsequent injections increased responsiveness relative to the primary injection response (F5,290 = 2.92, P = 0.029), suggesting that PHA exposure induced immunological memory, a tenet of acquired immunity. Histologi...

Dispersal biology at an invasion front differs from that of populations within the range core, because novel evolutionary and ecological processes come into play in the nonequilibrium conditions at expanding range edges. In a world where species' range limits are changing rapidly, we need to understand how individuals disperse at an invasion front. We analyzed an extensive dataset from radio-tracking invasive cane toads (Rhinella marina) over the first 8 y since they arrived at a site in tropical Australia. Movement patterns of toads in the invasion vanguard differed from those of individuals in the same area postcoloniza-tion. Our model discriminated encamped versus dispersive phases within each toad's movements and demonstrated that pioneer toads spent longer periods in dispersive mode and displayed longer , more directed movements while they were in dispersive mode. These analyses predict that overall displacement per year is more than twice as far for toads at the invasion front compared with those tracked a few years later at the same site. Studies on established populations (or even those a few years postestablish-ment) thus may massively underestimate dispersal rates at the leading edge of an expanding population. This, in turn, will cause us to underpredict the rates at which invasive organisms move into new territory and at which native taxa can expand into newly available habitat under climate change. hierarchical Bayes | shift | spatial sorting | relocation data | hidden states M any populations are shifting their range edges in response to climate change (1, 2) and other anthropogenic stressors (3, 4), and invasive species are spreading rapidly worldwide (5, 6). We need to predict rates of range shift to manage these changes, but (despite sophisticated theory on the processes underlying range shift), models routinely underestimate the rate of spread (7) because they underestimate the frequency of long-distance dispersal. Not only are rare long-distance dispersal events difficult to document (8, 9), but populations in the spreading vanguard are subject to powerful ecological and evolutionary forces not experienced by conspecifics within the range core. On the expanding range edge, individuals mate assorta-tively by dispersal ability ("spatial sorting") (10, 11); deleterious mutations can surf to fixation (12, 13), and parasites and pathogens may get left behind (14, 15). These differences could all affect dispersal rates and mean that to predict rates of range shift, we need to actually measure dispersal at the invasion front. Understanding the differences in dispersal rates at and behind an invasion front also may clarify the roles of plasticity, evolution , and ecology. For example, covariation of dispersal rates with conspecific or pathogen density implies a role for plasticity (e.g., density-dependent dispersal) or ecology (the effect of parasites and pathogens) rather than evolutionary processes in driving dispersal-rate variation. In contrast, higher dispersal rates at the invasion front versus further back in the range core, un-correlated with ecological factors, would suggest an underlying signal of ongoing spatial sorting. There are two ways that we could measure such a shift: by comparing populations (invasion front versus postinvasion) through space or by comparing those populations in the same area, through time. Neither approach is ideal: the former is confounded through space (local landscape features may change dispersal rates), whereas the latter is confounded through time (differences in weather among years may change dispersal rates). The second potential complication is easier to quantify (and thus, to control for), so we measured dispersal rates at a single site, from the first arrival of an invasive species until several years later. To analyze movements across a heterogeneous landscape, we need new methods as well as new data. On the analytical front, we need to acknowledge differences among individuals (16, 17) as well as an individual's ability to switch from one behavioral mode to another (18-20) (Fig. 1). In the present paper, we develop a hierarchical Bayesian model to analyze animal dispersal at both individual and population levels and apply it to an extensive radio-tracking dataset on the movements of invasive cane toads (Rhinella marina) as they first arrived at our study site in tropical Australia, and over the subsequent 8 y. Cane toads are large, toxic American amphibians that were brought to Australia in 1935 to control insect pests, and have been spreading ever since. The rate of toad invasion has accelerated dramatically during the toads' Australian expansion across northern Aus-tralia, partly due to rapid evolutionary shifts in dispersal and population growth rates (21-23). Here, we investigate whether the toads that first arrived at our field site (pioneers) were more dispersive than postinvasion toads tracked in the same area. Results Toads in the invasion vanguard showed strikingly different patterns of movement than did conspecifics that we tracked at the same site a few years postinvasion. Fig. 2 compares the two groups of toads with respect to the movement parameters that most influence long-term displacement rate (SI Appendix, Fig. S19), the aspect that is most obviously critical to the rate of range expansion and that has evolved rapidly upwards during the toads' Australian invasion (24). Although the tendency to switch from encamped to dispersive mode was similar between populations (Fig. 2A), pioneer toads remained for longer in dispersive mode (Fig. 2B) and consequently spent a larger proportion of time in dispersive mode. They also showed higher directionality (Fig. 2C) and longer daily displacement (Fig. 2D) when in dispersive mode than did postinvasion toads. The coefficient of variation of movement distances (an estimate of "tail fatness," important for invasion speed) (25, 26) was similar in dispersive-mode pioneer versus postinvasion toads.

Background: Emerging global positioning system (GPS) technologies can clarify movement patterns of free-ranging animals in far more detail than has been possible with previous methods. We conducted long-term (mean, 65 days; maximum, 221 days) GPS radio-tracking of 41 northern bluetongue lizards (Tiliqua scincoides intermedia) and 8 centralian bluetongue lizards (T. multifasciata) at two study sites in northwestern Australia, close to the border between Western Australia and the Northern Territory. Results: Individuals of both species spent long periods within small and distinctive habitat patches, interspersed with longer directional relocations from one patch to the next. Our sampling showed that these patches of core activity differed significantly from the surrounding landscape in several respects. The patches provided relatively shaded, cool, and damp conditions, with higher grass and more leaf-litter cover. The location of these patches in the landscape is probably determined by drainage patterns, soil moisture-holding ability, and stochastic recruitment of shade trees. Conclusions: These scattered patches provide a critically important habitat for lizards (and probably, other taxa) within this hot dry landscape. Future conservation and management strategies need to prioritize the retention of such sites, at a spatial scale that allows animals to move between them.

Effects of perturbations to wildlife often are measured by changes in rates of encounter with animals during standardised surveys, such as along roads. Previous work has predicted that the invasion of toxic cane toads (Rhinella marina) through the Australian tropics will cause massive mortality of anuran-eating snakes, and influence abundances of other native species. We surveyed three adjacent road transects for nocturnal snakes and lizards, beginning shortly before toads arrived at this site near Darwin, in the Northern Territory. In the wet-seasons of four successive years, we conducted surveys on 591 nights; on 302 of these nights, all three transects were surveyed. We recorded 8,880 live cane toads and 3,365 live reptiles. Toad numbers increased over time on all three transects but encounters with 13 species of native reptiles varied inconsistently. Eight of the 13 species of native reptile showed no significant change in encounter rates following the arrival of toads. Of the five species that did change in encounter rates, only one taxon (the bluetongue skink, Tiliqua scincoides intermedia) declined across all three transects. Encounter rates of the other four species often increased on at least one transect but decreased on at least one other. Thus, either the impact of cane toads on counts of reptiles differed between nearby sites, or (more likely) other factors had more influence on reptile numbers. A consistent decrease in reptile numbers on the busiest road over the study period suggests that local snake populations were affected more by road-kill than by invasive toads. Without spatial replication, this decrease could have been interpreted as an impact of toad invasion.

Background: Individual movement is critical to organismal fitness and also influences broader population processes such as demographic stochasticity and gene flow. Climatic change and habitat fragmentation render the drivers of individual movement especially critical to understand. Rates of movement of free-ranging animals through the landscape are influenced both by intrinsic attributes of an organism (e.g., size, body condition, age), and by external forces (e.g., weather, predation risk). Statistical modelling can clarify the relative importance of those processes, because externally-imposed pressures should generate synchronous displacements among individuals within a population, whereas intrinsic factors should generate consistency through time within each individual. External and intrinsic factors may vary in importance at different time scales.

1. Disentangling the effects of prey limitation (bottom-up) and predation (top-down) processes on natural populations is difficult, but the perturbations introduced by an invasive species can provide pseudo-experimental evidence on this issue. 2. In tropical Australia, keelbacks (Tropidonophis mairii) and slatey-grey snakes (Stegonotus cucullatus) experience little direct cost or benefit from the arrival of toxic invasive cane toads (Rhinella marina), because they rarely eat toads and if they do, are relatively resistant to the toads' toxins. Nonetheless, these snakes could be affected indirectly by toad-induced decreases in the availability of prey (native frogs) and/or by fatal poisoning of the snakes' predators (large varanid lizards). The former (bottom-up) effect predicts decreases in snake body condition , feeding and growth rates after toads arrive, whereas the latter (top-down) effect predicts increases in survival. 3. Our mark-recapture studies on these snakes in tropical Australia (for 7 years before and 7 years after toad arrival) reveal bottom-up effects both on an anurophagous dietary specialist (keelbacks) and a generalist feeder (slatey-grey snakes). 4. Top-down effects of toad arrival were seen in keelbacks but not in slatey-grey snakes, perhaps reflecting the latter's larger body size. 5. Indirect effects coinciding with the timing of toad invasion thus were mediated through changes in food supply for both native species and in rates of predation for one species.

Habitat disturbance and the spread of invasive organisms are major threats to biodiversity, but the interactions between these two factors remain poorly understood in many systems. Grazing activities may facilitate the spread of invasive cane toads (Rhinella marina) through tropical Australia by providing year-round access to otherwise-seasonal resources. We quantified the cane toad's use of cowpats (feces piles) in the field, and conducted experimental trials to assess the potential role of cowpats as sources of prey, water, and warmth for toads. Our field surveys show that cane toads are found on or near cowpats more often than expected by chance. Field-enclosure experiments show that cowpats facilitate toad feeding by providing access to dung beetles. Cowpats also offer moist surfaces that can reduce dehydration rates of toads and are warmer than other nearby substrates. Livestock grazing is the primary form of land use over vast areas of Australia, and pastoral activities may have contributed substantially to the cane toad's successful invasion of that continent.

1. In biological invasions, rates of range expansion tend to accelerate through time. What kind of benefits to more rapidly dispersing organisms might impose natural selection for faster rates of dispersal, and hence the evolution of range-edge acceleration? We can answer that question by comparing fitness-relevant ecological traits of individuals at the invasion front compared with conspecifics in the same area a few years post-invasion. 2. In tropical Australia, the rate of invasion by cane toads (Rhinella marina) has increased substantially over recent decades, due to shifts in heritable traits. Our data on field-collected cane toads at a recently invaded site in the Australian wet-dry tropics span a 5-year period beginning with toad arrival. 3. Compared with conspecifics that we monitored in the same sites post-invasion, toads in the invasion vanguard exhibited higher feeding rates, larger energy stores, better body condition and faster growth. 4. Three processes may have contributed to this pattern: (i) higher prey availability at the front (perhaps due to reduced competition from conspecifics); (ii) the lack of viability-reducing parasites and pathogens in invasion-front toads; and (iii) distinctive (active, fast-growing) phenotypes of the invasion-front toads. 5. Nutritional benefits to individuals in the invasion vanguard (whether because of higher prey availability, or lower pathogen levels) thus may have conferred a selective advantage to accelerated dispersal in this system.

Many invading species have brought devastating parasites and diseases to their new homes, thereby imperiling native taxa. Potentially, though, invaders might have the opposite effect. If they take up parasites that otherwise would infect native taxa, but those parasites fail to develop in the invader, the introduced species might reduce parasite burdens of the native fauna. Similarly, earlier exposure to the other taxon's parasites might 'prime' an anuran's immune system such that it is then able to reject subsequent infection by its own parasite species. Field surveys suggest that lungworm counts in native Australian frogs decrease after the arrival of invasive cane toads (Rhinella marina), and laboratory studies confirm that native lungworm larvae enter, but do not survive in, the toads. In laboratory trials, we confirmed that the presence of anurans (either frogs or toads) in an experimental arena reduced uptake rates of lungworm larvae by anurans that were later added to the same arena. However, experimental exposure to lungworms from native frogs did not enhance a toad's ability to reject subsequent infection by its own lungworm species.

In an ecosystem under simultaneous threat from multiple alien species, one invader may buffer the impact of another. Our surveys on a remote floodplain in the Kimberley region of north western Australia show that invasive chinee apple trees (Ziziphus mauritiana) provide critical refuge habitat for native rodents (pale field rats, Rattus tunneyi). Feral horses (Equus caballus) have trampled most of the remaining floodplain, but are excluded from the area around each chinee apple tree by thorny foliage. Although chinee apple trees constituted <10% of trees along our transects, they represented >50% of trees that harboured rat burrows. The mean number of burrows under each chinee apple tree was twice as high as under most other tree species, and we trapped more than seven times as many rats under chinee apple trees as under other types of trees. The extensive burrow systems under chinee apple trees contained female as well as male rats, whereas we only captured males around the smaller burrow systems under other tree species. Our data suggest that this invasive tree plays a critical role in the persistence of pale field rat populations in this degraded ecosystem, and that managers should maintain these trees (despite their alien origins) at least until feral horses have been removed.

Translocation of native-range parasites to control invasive species is effective only if the parasite substantially impairs either the viability or dispersal rate of the invasive host. Lungworms (Rhabdias pseudosphaerocephala) of cane toads (Rhinella marina) were introduced to Australia from the toad's native range, along with the toads, and have been suggested as a potential biocontrol of invasive toads due to various negative impacts on toad viability. We conducted two radio-telemetry studies on a tropical floodplain to specifically assess the parasite's impact on toad dispersal. First, a retrospective correlative analysis of data from field-collected animals showed that toads infected with lungworms moved farther, not less, than uninfected conspecifics. Second, an experimental study (comparing movements of experimentally infected toads vs. uninfected controls) showed that lungworms did not modify rates of toad dispersal. In addition, experimental infection with lungworms did not elicit an immune response substantial enough to influence dispersal behaviour. Thus, we conclude that increasing lungworm densities at the invasion front as an attempt at biocontrol would not slow down the spread of cane toads.

1. The ability to disperse along a consistent compass heading strongly affects the rate and efficiency of an animal's displacement, and thus is under selection at the expanding edge of a biological invasion. 2. We used radiotelemetry to assess whether the dispersal direction of cane toads (Rhinella marina) changed as a function of time since invasion, by comparing (i) toads at a single site monitored annually for 10 years subsequent to toad arrival; (ii) toads collected from sites across the species' invaded range in Australia, and radiotracked at a common site; and (iii) the offspring of those transported toads that were reared in captivity under common-garden conditions. 3. The first of these data sets showed non-random directionality, indicating strong spatial sorting operating on this trait: toads moved in a north-westerly direction for the first 6 years post-invasion, but in random directions thereafter. Despite the evidence for trait sorting, no consistent directionality was seen in toads relocated from populations with different invasion histories nor in their offspring. Why do we see no evolutionary shifts? 4. Dispersal directionality of the offspring was not correlated with that of their parents, arguing against a genetic basis to this behavioural trait. Thus, while an expanding invasion front creates an evolutionary pressure for animals to move in a specific direction, evolution of this trait has not occurred in this system because directionality is not heritable. 5. The observed north-westerly movements of toads at the invasion front were due to simple density differentials: in the first few years, most toads arriving at our study site originated from earlier-colonized (and hence denser) populations to the southeast .

At an invasion front, energetic and physiological trade-offs may differ from those at the range-core as a result of selection for enhanced dispersal, combined with a low density of conspecifics (which reduces pathogen transmission and competition for food). We measured traits related to energy stores and immunity in wild cane toads (Rhinella marina) across a 750-km transect from their invasion front in tropical Australia, back into sites colonized 21 years earlier. Several traits were found to vary with population age; some linearly and others in a curvilinear manner. The relative size of spleens and fat bodies was highest in the oldest and newest populations, where rates of lungworm infection were lowest. Toads from older populations produced more corticosterone in response to a standardized stressor, and had higher lymphocyte counts (but lower basophil counts). The amount of skin swelling elicited by phytohaemagglutinin injection did not vary geographically, although recruitment of leukocytes to the injected tissue was higher in toads from long-colonized areas. Because this was a field-based study, we cannot differentiate the effects of population age, toad density or pathogen pressure on our measures of stress and immune responses, nor can we distinguish whether the causation involves hard-wired adaptive processes or phenotypically plastic responses. Nonetheless, our data demonstrate substantial variation in immune systems among toads at varying distances from an invasion front, showing that a biological invasion imposes strong pressures on physiological systems of the invader.

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, Ochro-bactrum 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. Crown

Although widespread declines in anuran populations have attracted considerable concern, the stochastic demographics of these animals make it difficult to detect consistent trends against a background of spatial and temporal variation. To identify long-term trends, we need datasets gathered over long time periods, especially from tropical areas where anuran biodiversity is highest. We conducted road surveys of four anurans in the Australian wet-dry tropics on 4637 nights over a 16-year period. Our surveys spanned the arrival of invasive cane toads (Rhinella marina), allowing us to assess the invader's impact on native anuran populations. Our counts demonstrate abrupt and asynchronous shifts in abundance and species composition from one year to the next, not clearly linked to rainfall patterns. Typically, periods of decline in numbers of a species were limited to 1-2 years and were followed by 1-to 2-year periods of increase. No taxa showed consistent declines over time, although trajectories for some species showed significant perturbations coincident with the arrival of toads. None of the four focal frog species was less common at the end of the study than at the beginning, and three of the species reached peak abundances after toad arrival. Survey counts of cane toads increased rapidly during the initial stage of invasion but have subsequently declined and fluctuated. Distinguishing consistent declines versus stochastic fluctuations in anuran populations requires extensive time-series analysis, coupled with an understanding of the shifts expected under local climatic conditions. This is especially pertinent when assessing impacts of specific perturbations such as invasive species.

In midsummer 2002-2003, intense wildfires raged through the Brindabella Range of southeastern Australia, including sites where we have studied the ecology of scincid lizards (especially Bassiana duperreyi) for decades. Data-loggers measured the thermal regimes experienced by eggs during these fires (revealing lethally high temperatures in nests under logs in the forest but minimal effect in nests under rocks in clearings). Eggs from forest-clearing nests hatched successfully. Reproductive output of lizards in one area was reduced in the years post-fire (perhaps because of inadequate food [insect] abundance to fuel female reproduction) but soon recovered. The fires reduced vegetation density and thus increased the availability of sun-exposed rocks that serve as potential nest sites. However, the magnitude and duration of these effects differed among sites. Five years after these intense fires, canopy openness (and thus, sunlight penetration to create thermally suitable nest sites) was indistinguishable from pre-fire conditions. Our data reveal strong spatial hetero-geneity both in the immediate effects of fire on lizard reproduction and in longer-term post-fire changes in habitat quality. Surprisingly, these intense wildfires had only transitory and local effects on nest-site availability for the heliothermic lizards that we study, but impacts likely were more severe on sympatric taxa that depend upon moist cool microhabitats.

What level of immunocompetence should an animal maintain while undertaking long-distance dispersal? Immune function (surveillance and response) might be down-regulated during prolonged physical exertion due to energy depletion, and/or to avoid autoimmune reactions arising from damaged tissue. On the other hand, heightened immune vigilance might be favored if the organism encounters novel pathogens as it enters novel environments. We assessed the links between immune defense and long-distance movement in a population of invasive cane toads (Rhinella marina) in Australia. Toads were radio-tracked for seven days to measure their activity levels and were then captured and subjected to a suite of immune assays. Toads that moved further showed decreased bacteria-killing ability in their plasma and decreased phagocytic activity in their whole blood, but a heightened skin-swelling response to phytohemagglutinin. Baseline and post-stress corticosterone levels were unrelated to distance moved. Thus, long-distance movement in cane toads is associated with a dampened response in some systems and enhanced response in another. This pattern suggests that sustained activity is accompanied by trade-offs among immune components rather than an overall down or up-regulation. The finding that high mobility is accompanied by modification of the immune system has important implications for animal invasions.

Subject Category: Biology (whole organism) Subject Areas: ecology/health and disease and epidemiology/immunology Like most ectothermic vertebrates, keelback snakes (Tropidonophis mairii) do not exhibit parental care. Thus, offspring must possess an immune system capable of dealing with challenges such as pathogens, without assistance from an attendant parent. We know very little about immune system characteristics of neonatal reptiles, including the magnitude of heritability and other maternal influences. To identify sources of variation in circulating white blood cell (WBC) concentrations and differentials, we examined blood smears from 246 hatchling snakes and their field-caught mothers. WBC concentrations were lower in hatchlings than in adults, and hatchlings had more basophils and fewer azurophils than adults. A hatchling keelback's WBC differential was also influenced by its sex and body size. Although hatchling WBC measures exhibited negligible heritability, they were strongly influenced by maternal body size and parasite infection (but not by maternal body condition, relative clutch mass or time in captivity). Larger mothers produced offspring with more azurophils and fewer lymphocytes. The mechanisms and consequences of WBC variation are currently unknown, but if these maternal effects enhance offspring fitness, the impact of maternal body size on reproductive success may be greater than expected simply from allometric increases in the numbers and sizes of progeny.

At the edge of a biological invasion, evolutionary processes (spatial sorting, natural selection) often drive increases in dispersal. Although numerous traits influence an individual's displacement (e.g. speed, stamina), one of the most important is path straightness. A straight (i.e. highly correlated) path strongly enhances overall dispersal rate relative to time and energetic cost. Thus, we predict that, if path straightness has a genetic basis, organisms in the invasion vanguard will exhibit straighter paths than those following behind. Our studies on invasive cane toads (Rhinella marina) in tropical Australia clearly support this prediction. Radio-tracking of field-collected toads at a single site showed that path straightness steadily decreased over the first 10 years post-invasion. Consistent with an evolved (genetic) basis to that behavioural shift, path straight-ness of toads reared under common garden conditions varied according to the location of their parents' origin. Offspring produced by toads from the invasion vanguard followed straighter paths than did those produced by parents from long-established populations. At the individual level, offspring exhibited similar path straightness to their parents. The dramatic acceleration of the cane toad invasion through tropical Australia has been driven, in part, by the evolution of a behavioural tendency towards dispersing in a straight line.

Invasive species often exhibit rapid evolutionary changes, and can provide powerful insights into the selective forces shaping phenotypic traits that influence dispersal rates and/or sexual interactions. Invasions also may modify sexual dimorphism. We measured relative lengths of forelimbs and hindlimbs of more than 3000 field-caught adult cane toads (Rhinella marina) from 67 sites in Hawai'i and Australia (1-80 years post-colonization), along with 489 captive-bred individuals from multiple Australian sites raised in a 'common garden' (to examine heritability and reduce environmental influences on morphology). As cane toads spread from east to west across Australia, the ancestral condition (long limbs, especially in males) was modified. Limb length relative to body size was first reduced (perhaps owing to natural selection on locomotor ability), but then increased again (perhaps owing to spatial sorting) in the invasion vanguard. In contrast, the sex disparity in relative limb length has progressively decreased during the toads' Australian invasion. Offspring reared in a common environment exhibited similar geographical divergences in morphology as did wild-caught animals, suggesting a genetic basis to the changes. Limb dimensions showed significant heritability (2-17%), consistent with the possibility of an evolved response. Cane toad populations thus have undergone a major shift in sexual dimorphism in relative limb lengths during their brief (81 years) spread through tropical Australia.

Like most ectothermic vertebrates, keelback snakes (Tropidonophis mairii) do not exhibit parental care. Thus, offspring must possess an immune system capable of dealing with challenges such as pathogens, without assistance from an attendant parent. We know very little about immune system characteristics of neonatal reptiles, including the magnitude of heritability and other maternal influences. To identify sources of variation in circulating white blood cell (WBC) concentrations and differentials, we examined blood smears from 246 hatchling snakes and their field-caught mothers. WBC concentrations were lower in hatchlings than in adults, and hatchlings had more basophils and fewer azurophils than adults. A hatchling keelback&#39;s WBC differential was also influenced by its sex and body size. Although hatchling WBC measures exhibited negligible heritability, they were strongly influenced by maternal body size and parasite infection (but not by maternal body condition, relative clutc...