Diet and dietary selectivity of Cane Toads (Rhinella marina) in restoration sites: a case study in Far North Queensland,Australia

Cane Toads (Rhinella marina, formerly Bufo marinus) in restoration sites on the Atherton Tableland in NE Australia consumed invertebrates belonging to 11 different taxa with ants being the most abundant prey item. Principal component analyses showed that the composition of invertebrates in Cane Toad diet is largely a reflection of invertebrates found in pitfall and leaf litter samples suggesting that the species is an indiscriminant feeder. However, pitfall samples contained more Collembola and Isopoda than were found in Cane Toad stomachs. The Cane Toad may benefit from restoration management practices by utilizing food resources enhanced by mulching and providing microhabitats (e.g. rock piles, logs) as shelter. While further studies would be needed to test this practitioners working in areas where the Cane Toad is problematic may consider trade‐offs between attracting invertebrates and Cane Toads by monitoring provided microhabitat features.     

Wild Cane Toads (Rhinella marina) Expel Foreign Matter from the Coelom via the Urinary Bladder in Response to Internal Injury,Endoparasites and Disease

Dissections of >1,200 wild-caught cane toads (Rhinella marina) in tropical Australia confirm a laboratory report that anurans can expel foreign objects from the coelom by incorporating them into the urinary bladder. The foreign objects that we found inside bladders included a diverse array of items (e.g., grass seeds, twigs, insect prey, parasites), many of which may have entered the coelom via rupture of the gut wall. In some cases, the urinary bladder was fused to other organs including liver, fat bodies, ovaries, Bidder’s organs, lungs, mesentery, stomach wall, gall bladder, and the abdominal wall. Acanthocephalan parasites (of a range of developmental stages) were identified from the walls of the urinary bladders of three cane toads. This organ may play a significant role in destroying or excreting metazoan parasites, as well as inanimate objects.     

Carry‐over Effects of Size at Metamorphosis in Red‐eyed Treefrogs: Higher Survival but Slower Growth of Larger Metamorphs

Most animals have complex life histories, composed of a series of ecologically distinct stages, and the transitions between stages are often plastic. Anurans are models for research on complex life cycles. Many species exhibit plastic timing of and size at metamorphosis, due to both environmental constraints on larval growth and development and adaptive plastic responses to environmental variation. Models predicting optimal timing of metamorphosis balance cost/benefit ratios across stages, assuming that size affects growth and mortality rates in each stage. Much research has documented such effects in the larval period, but we lack an equal understanding of juvenile growth and mortality. Here, we examine how variation in size at metamorphosis in the Neotropical red‐eyed treefrog, Agalychnis callidryas, affects post‐metamorphic growth, foraging, and behavior in the lab as well as growth and survival in the field. Surprisingly, many individuals lost mass for weeks after metamorphosis. In the lab, larger metamorphs lost more mass following metamorphosis, ate similar amounts, had lower food conversion efficiencies, and grew more slowly after mass loss ceased than did smaller ones. In field cages larger metamorphs were more likely to survive than smaller ones; just one froglet died in the lab. Our data suggest that size‐specific differences in physiology and behavior influence these trends. Comparing across species and studies, large size at metamorphosis generally confers higher survival; size effects on growth rates vary substantially among species, in both magnitude and direction, but may be stronger in the tropics.     

Patterns of Genetic Variability in Island Populations of the Cane Toad (Rhinella marina) from the Mouth of the Amazon

The Amazonian coast has several unique geological characteristics resulting from the interaction between drainage pattern of the Amazon River and the Atlantic Ocean. It is one of the most extensive and sedimentologically dynamic regions of the world, with a large number of continental islands mostly formed less than 10,000 years ago. The natural distribution of the cane toad (Rhinella marina), one of the world’s most successful invasive species, in this complex Amazonian system provides an intriguing model for the investigation of the effects of isolation or the combined effects of isolation and habitat dynamic changes on patterns of genetic variability and population differentiation. We used nine fast-evolving microsatellite loci to contrast patterns of genetic variability in six coastal (three mainlands and three islands) populations of the cane toad near the mouth of the Amazon River. Results from Bayesian multilocus clustering approach and Discriminant Analyses of Principal Component were congruent in showing that each island population was genetically differentiated from the mainland populations. All F_ST values obtained from all pairwise comparisons were significant, ranging from 0.048 to 0.186. Estimates of both recent and historical gene flow were not significantly different from zero across all population pairs, except the two mainland populations inhabiting continuous habitats. Patterns of population differentiation, with a high level of population substructure and absence/restricted gene flow, suggested that island populations of R. marina are likely isolated since the Holocene sea-level rise. However, considering the similar levels of genetic variability found in both island and mainland populations, it is reliable to assume that they were also isolated for longer periods. Given the genetic uniqueness of each cane toad population, together with the high natural vulnerability of the coastal regions and intense human pressures, we suggest that these populations should be treated as discrete units for conservation management purposes.     

Stress and immunity at the invasion front: a comparison across cane toad (Rhinella marina) populations

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.     

The Effects of Snake Predation on Metamorphosis of Western Toads,Bufo boreas (Amphibia,Bufonidae)

For some anuran species, synchronous metamorphosis may function as an antipredator adaptation by swamping predators during the period of transformation. We examined the levels of synchrony of emergence from the water of metamorphosing western toads (Bufo boreas) in the presence and absence of a live snake predator, the common garter snake (Thamnophis sirtalis) in a laboratory experiment. To compare between the treatments, we measured the time to emergence from the water, the number of metamorphs emerging together, and the level of aggregation (before and during emergence) of the toads in each treatment. There was a difference between the treatments when all three factors were considered. We attributed these differences to a behavioral response in which B. boreas emerged sooner in the presence of the predator, regardless of whether individual toads had reached the point at which they were physically better suited to the terrestrial environment than the larval environment.     

The accelerating anuran: evolution of locomotor performance in cane toads (Rhinella marina,Bufonidae) at an invasion front

As is common in biological invasions, the rate at which cane toads (Rhinella marina) have spread across tropical Australia has accelerated through time. Individuals at the invasion front travel further than range-core conspecifics and exhibit distinctive morphologies that may facilitate rapid dispersal. However, the links between these morphological changes and locomotor performance have not been clearly documented. We used raceway trials and high-speed videography to document locomotor traits (e.g. hop distances, heights, velocities, and angles of take-off and landing) of toads from range-core and invasion-front populations. Locomotor performance varied geographically, and this variation in performance was linked to morphological features that have evolved during the toads'' Australian invasion. Geographical variation in morphology and locomotor ability was evident not only in wild-caught animals, but also in individuals that had been raised under standardized conditions in captivity. Our data thus support the hypothesis that the cane toad''s invasion across Australia has generated rapid evolutionary shifts in dispersal-relevant performance traits, and that these differences in performance are linked to concurrent shifts in morphological traits.     

中华蟾蜍体重及脏器大小对禁食和重喂食处理的响应

两栖动物的体重和内脏器官大小可随环境条件而变化,具有表型可塑性,但实验例证较少,尤其缺乏与可变的食物可利用性有关的研究。本研究以捕自安徽省定远县县郊的雌、雄中华蟾蜍(Bufo gargarizans)为研究对象,测定了自由取食组、禁食1周组、禁食2周组、重喂食1周组和重喂食2周组其体重、内脏器官湿重和干重的变化情况。1)中华蟾蜍的体重、胴体湿重和干重均无明显的性别(P0.05)和组间(P0.05)差异。2)雌蟾胃的湿重、干重和大肠湿重高于雄蟾(P0.05),其他内脏器官(小肠、胸腺、心、肝、肺、脂肪体、脾和肾)的湿重和干重均无性别差异(P0.05);雄蟾上述指标均无组间差异(P0.05);雌蟾的胃湿重和大肠湿重均无组间差异(P0.05),但胃干重自由取食组高于重喂食1周组(P0.05)。禁食2周组的小肠湿重下降,低于自由取食组、重喂食1周和2周组(P0.05)。3)禁食1周组的心湿重高于重喂食2周组(P0.05)。结果表明,中华蟾蜍在整体水平不受短期禁食和重喂食处理的影响,器官水平可能主要依赖适度饥饿而导致的心肌功能的提升和消化道的可塑性来应对变化的食物条件。     

Morphological differentiation among populations of Rhinella marina (Amphibia: Anura) in western Mexico

Conspecific populations inhabiting different environments may exhibit morphological differences, potentially reflecting differential local adaptation. In anuran amphibians, morphology of the pelvis and hindlimbs may often experience strong selection due to effects on locomotion. In this study, we used the cane toad Rhinella marina to test the hypothesis that populations experiencing a higher abundance of predators should suffer higher mortality rates and exhibit morphological traits associated with enhanced locomotor performance (narrower pelvis and head, longer pelvis and hindlimbs, shorter presacral vertebral column). We investigated inter-population variation in survival rate, abundance of predators, and body shape across five populations in rivers in western Mexico. We conducted (1) mark-recapture experiments to calculate survival rates, (2) linear transects with point counts to estimate abundance of predatory spiders, snakes, and birds, and (3) geometric morphometric analyses to investigate body shape variation. We found significant differences among populations in survival rates, abundance of predators, and body shape. However, these three variables were not necessarily inter-related. Increased predator abundance did not result in decreased survival rates, suggesting other causes of mortality affect these populations. While some morphological differences supported our predictions (trend for longer pelvis, shorter presacral vertebral column, and narrower head in sites with increased abundance of spiders and snakes), other aspects of morphology did not. We discuss alternative explanations for the lack of clear associations between predation, survival, and morphology.     

Field trials of chemical suppression of embryonic cane toads (Rhinella marina) by older conspecifics

1. Laboratory experiments have shown that the viability of embryos of the invasive cane toad (Rhinella marina) can be reduced by exposure to chemical cues from older conspecific larvae. These effects (very strong in laboratory trials) may offer an exciting new approach to controlling this problematic invasive species in Australia. However, the degree to which the method works in natural environments has yet to be assessed.
2. Our experiments in the laboratory and in seminatural outdoor waterbodies show that chemical cues from tadpoles do indeed suppress the growth, development, and survival of conspecific larvae that are exposed as embryos and do so in a dose‐dependent manner; higher tadpole densities cause greater suppression of embryos.
3. In seminatural outdoor waterbodies, suppressor‐exposed tadpoles were less than half as likely to survive to metamorphosis as were controls, and were much smaller when they did so and hence, less likely to survive the metamorph stage. Additionally, female cane toads were less likely to oviposit in a waterbody containing free‐ranging (but not cage‐enclosed) tadpoles, suggesting that the presence of tadpoles (rather than the chemical cues they produce) may discourage oviposition.
4. Broadly, our results suggest that the suppression effect documented in laboratory studies does indeed occur in the field also, and hence that we may be able to translate that approach to develop new and more effective ways to reduce rates of recruitment of peri‐urban populations of cane toads in their invasive range.

     

Hydric balance and locomotor performance of an anuran (Rhinella marina) invading the Australian arid zone

Invasive species often encounter environmental conditions well outside those found in their native geographic ranges, and thus provide ideal model systems with which to explore responses to novel abiotic challenges. Within Australia, the invasive cane toad Rhinella marina has colonized areas that are considerably more arid than those found within its native range. Has the colonization of these novel environments been accompanied by shifts in physiology and/or locomotor performance? We measured rates of evaporative water loss, water gain, and effects of desiccation on locomotor performance of cane toads from two invasion fronts: one mesic (the wet‐dry tropics) and one arid (the semi‐desert). The two populations diverged substantially. Contrary to intuition (but consistent with intra‐specific comparisons between other toad populations from mesic vs arid areas), rates of evaporative water loss were lower (not higher) in toads from the mesic population. However, arid‐zone toads gained water more rapidly through their ventral surfaces, and rates of water loss and gain were highly correlated within individual toads from the arid‐zone population. Rates of water exchange in laboratory‐acclimated toads from the semi‐arid zone did not differ from those of free‐ranging conspecifics from the same population, suggesting that divergences between mesic and semi‐arid toads reflect genetic changes that have occurred during the species’ Australian invasion. Mesic and semi‐arid toads showed similar locomotor performance (endurance, distance per hop) when fully hydrated, but locomotor performance declined much more rapidly with desiccation in the mesic toads. Thus, within the short (decades‐long) timespan of the cane toad's Australian invasion, there has been substantial population divergence in the ability to withstand desiccating conditions. If we are to accurately predict the distributions (and hence impacts) of invading organisms, we will need to include adaptation potential in risk assessment schemes.     

Ability of Young Women to Recall Past Body Size and Age at Menarche

Objective: The ability of young women (n = 132, average age 17 years) to recall body size and age at menarche was examined. The use of body silhouettes to assist women in recalling their body size at menarche and to represent their current body size was also evaluated. Research Methods and Procedures: Subjects, who previously participated in a cohort study, were asked to recall height and weight at the time of menarche, to select body silhouettes that best reflected their body shape at the time of menarche and their current body shape, and to recall age at menarche. Two sets of body silhouettes were developed, one representative of an adult body shape and another representative of an adolescent body shape. Results: Pearson correlation coefficients between the adult and adolescent body figures and actual body mass index (BMI; kg/m²) at the time of menarche were not significantly different (r = 0.82 for adult figures vs. r = 0.72 for adolescent figures, p > 0.05). The correlation between actual BMI at the time of menarche and body silhouette (r = 0.77, all subjects) was similar to the correlation between actual and recalled BMI at the time of menarche (r = 0.83) as well as the correlation between current BMI and current body silhouette (r = 0.75). Recalled and actual ages at menarche were highly correlated (r = 0.83). Discussion: The recall of body shape was considered to be a less precise measure of body size than asking about height and weight, but use of body silhouettes may offer advantages in certain situations.     

Mechanisms of competition between tadpoles of Australian frogs (Litoria spp.) and invasive cane toads (Rhinella marina)

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Phylogeny and biogeography of the Rhinella marina species complex (Amphibia,Bufonidae) revisited: implications for Neotropical diversification hypotheses

Vallinoto, M., Sequeira, F., Sodré, D., Bernardi, J. A. R., Sampaio, I. & Schneider, H. (2009). Phylogeny and biogeography of the Rhinella marina species complex (Amphibia, Bufonidae) revisited: implications for Neotropical diversification hypotheses. —Zoologica Scripta, 39, 128–140. A number of distinct hypotheses have been proposed to account for the origin of the considerable biological diversity found in the Neotropics, which is still a matter of intense debate. Here, we conducted a phylogenetic analysis of the Rhinella marina complex, a group of species widely distributed in Central and South America, combining published data with new sequences of three mtDNA genes (12S, 16S and cyt b) in order to clarify the evolutionary relationships and biogeographical history of the group. We included eight of the ten currently recognized R. marina group species and several outgroups. Maximum parsimony, maximum likelihood, and Bayesian inference analyses produced similar topologies, with two well‐supported main clades, each characterized by a deep subdivision. One of these major clades includes the samples of R. marina from Central America and Ecuador (west of the Andes), whereas the other comprises the remaining species of the group and samples of R. marina from the Amazon basin and other areas east of the Andes. A Bayesian coalescent‐based method (BEAST) dated the divergence between the two major clades, and between the Central American and Ecuadorian clades to the Miocene, matching the timing of other Central‐South American faunal divergences. Taken together, the results highlight the importance of Tertiary events such as the Pebas/marine incursions into the Amazon basin and Andean uplift for the diversification and historical biogeography of R. marina, making such taxa paraphyletic, and provide new perspectives on the debate on its species status.     

The role of biotic and abiotic cues in stimulating aggregation by larval cane toads (Rhinella marina)

Tadpoles of the cane toad (Rhinella marina) form dense aggregations in the field, but the proximate cues eliciting this behavior are not well understood. We sampled water‐bodies in the Northern Territory of Australia, finding that the density of cane toad tadpoles increased with increasing temperature. Furthermore, we conducted laboratory experiments to explore the roles of biotic factors (attraction to conspecifics; chemical cues from an injured conspecific; food) and spatially heterogeneous abiotic factors (light levels, water depth, physical structure) to identify the cues that induce tadpole aggregation. Annulus and binary choice trials demonstrated weak but significant attraction between conspecifics. Tadpoles decreased swimming speeds, but did not increase grouping in response to cues from an injured conspecific. Larvae aggregated in response to abiotic cues (high levels of illumination and proximity to physical structures) and were strongly attracted to feeding conspecifics. Overall, aggregation by cane toad tadpoles is likely driven by weak social attraction coupled with a shared preference for specific abiotic features, creating loose aggregations that are then reinforced by movement toward feeding conspecifics.     

Pectoral girdle movements and the role of the glenohumeral joint during landing in the toad, Rhinella marina (Linnaeus, 1758)

Compared to anurans from other families, landings of toads (Bufonidae) during saltation appear well coordinated and the initial landing impact is absorbed exclusively by the forelimbs. Although the forelimbs and particularly the pectoral girdle have been suggested to be important for shock absorption, the functional roles of its various elements have not been evaluated in detail. This study addresses open questions regarding the kinematics of the forelimbs during landing in Rhinella marina using X-ray reconstruction of moving morphology and scientific rotoscoping. The kinematic analysis clearly showed that in addition to motions in the shoulder and elbow joints, substantial movements of the pectoral girdle in toto as well as of its elements relative to each other do occur during landing. The pectoral girdle showed first and foremost rotations about its latero-lateral axis as well as dorso-ventral translations relative to the spine. Our results quantify the extent of flexion and extension in the suprascapula-scapular synchondrosis during landing. Forelimb kinematics in R. marina differed from that of other anurans in starting elbow extension relatively early during the landing process, which likely prevents the chest from contacting the ground. Furthermore, the animal regains an upright and ready-to-hop-again position quickly and the recovery phase is short compared to other anurans. Humeral kinematics and anatomy confirm that the glenohumeral interlocking mechanism guides the humerus during the initial landing phase. Cranio-ventral ridges on the humeral head and the paraglenoid cartilage interlock in anteverted and slightly retroverted humeral positions. This occurs at the beginning of the landing. When interlocked, adduction/abduction as well as long-axis rotation of the humerus are restricted. During the course of landing, the humerus retroverts and is gradually freed from interlocking restrictions due to a smoother relief at the caudal aspect of the humeral head.     

Effects of Body Size and Food Ration on Over-winter Survival and Growth of Age-0 Atlantic cod, Gadus morhua

This study examined the effects of body size and food ration on over-winter survival of age-0 Atlantic cod. Cod were divided into two groups based on standard length (large=76.95±1.10 mm SL; small=57.65±1.02 mm SL; mean±1 SE) and wet weight (large=4.02± 0.21 g; small=1.52±0.09 g). Replicate tanks (n=2) of 10 large and 10 small cod were exposed to one of two food rations (0.25% and 1.0% body weight day^-1) for the entire experiment (December to June). Tanks were examined daily for mortalities and feeding was adjusted accordingly. The experiment was run under ambient light and seawater conditions. All but large age-0 cod exposed to the low food ration grew over the course of the experiment. The specific growth rate (SGR) of small cod was significantly higher (0.2425% wet weight day^-1) than that of the large fish (0.0443% wet weight day^-1). Food ration had no significant influence on SGR or over-winter survival. Significantly more of the large age-0 cod survived the winter (58.5% of those originally introduced) compared to the smaller fish (14%). Our results are consistent with those from studies of several other fish species, and are discussed in relation to the ecology of age-0 cod, and their potential use in aquaculture in Newfoundland.     

Desiccation risk drives the spatial ecology of an invasive anuran (Rhinella marina) in the Australian semi-desert

Some invasive species flourish in places that impose challenges very different from those faced in their native geographic ranges. Cane toads (Rhinella marina) are native to tropical and subtropical habitats of South and Central America, but have colonised extremely arid regions over the course of their Australian invasion. We radio-tracked 44 adult cane toads at a semi-arid invasion front to investigate how this invasive anuran has managed to expand its geographic range into arid areas that lie outside of its native climatic niche. As predicted from their low physiological control over rates of evaporative water loss, toads selected diurnal shelter sites that were consistently cooler and damper (and thus, conferred lower water loss rates) than nearby random sites. Desiccation risk also had a profound influence on rates of daily movement. Under wet conditions, toads that were far from water moved further between shelter sites than did conspecifics that remained close to water, presumably in an attempt to reach permanent water sources. However, this relationship was reversed under dry conditions, such that only toads that were close to permanent water bodies made substantial daily movements. Toads that were far from water bodies also travelled along straighter paths than did conspecifics that generally remained close to water. Thus, behavioural flexibility--in particular, an ability to exploit spatial and temporal heterogeneity in the availability of moist conditions--has allowed this invasive anuran to successfully colonize arid habitats in Australia. This finding illustrates that risk assessment protocols need to recognise that under some circumstances an introduced species may be able to thrive in conditions far removed from any that it experiences in its native range.     

A Quantitative Analysis of Growth and Size Regulation in Manduca sexta: The Physiological Basis of Variation in Size and Age at Metamorphosis

Body size and development time are important life history traits because they are often highly correlated with fitness. Although the developmental mechanisms that control growth have been well studied, the mechanisms that control how a species-characteristic body size is achieved remain poorly understood. In insects adult body size is determined by the number of larval molts, the size increment at each molt, and the mechanism that determines during which instar larval growth will stop. Adult insects do not grow, so the size at which a larva stops growing determines adult body size. Here we develop a quantitative understanding of the kinetics of growth throughout larval life of Manduca sexta, under different conditions of nutrition and temperature, and for genetic strains with different adult body sizes. We show that the generally accepted view that the size increment at each molt is constant (Dyar’s Rule) is systematically violated: there is actually a progressive increase in the size increment from instar to instar that is independent of temperature. In addition, the mass-specific growth rate declines throughout the growth phase in a temperature-dependent manner. We show that growth within an instar follows a truncated Gompertz trajectory. The critical weight, which determines when in an instar a molt will occur, and the threshold size, which determines which instar is the last, are different in genetic strains with different adult body sizes. Under nutrient and temperature stress Manduca has a variable number of larval instars and we show that this is due to the fact that more molts at smaller increments are taken before threshold size is reached. We test whether the new insight into the kinetics of growth and size determination are sufficient to explain body size and development time through a mathematical model that incorporates our quantitative findings.