The Consequences of Speed: Studies of Cavitation During the Mantis Shrimp Strike and the Control of Rapid Deceleration During Toad Landing

There are consequences of moving quickly in this world. Here we investigate how two very different species, mantis shrimp (Odontodactylus scyllarus) and cane toads (Bufo marinus), negotiate forces that result from moving rapidly in different environments. To study the mechanical principles and fluid dynamics of ultrafast power-amplified systems, we built Ninjabot, a physical model of the extremely fast mantis shrimp. While mantis shrimp produce damaging cavitation upon impact with their prey, they do not cavitate during the forward portion of their strike despite extreme speeds. In order to study cavitation onset in non-linear flows common during the mantis shrimp strike, we used Ninjabot to produce strikes of varying kinematics and measured cavitation presence or absence. We found that in rotating and accelerating biological conditions, cavitation inception is best explained only by maximum linear velocity. Thus, studies of cavitation onset in biological conditions only need to focus on maximum velocity. On land, moving quickly requires avoiding or preparing for impact with other objects, often the ground. Within anurans (frogs and toads), a group well known for jumping, cane toads are known to perform particularly controlled landings in which the forelimbs are used to decelerate and balance the body after impact as the hind limbs are lowered to the ground. Here I explore whether and how toads modulate landing preparation depending on hopping and landing conditions and what this can tell us about how they utilize sensory information to help them perform controlled landings. We found that toads modulate three components of impact preparation to specific hop conditions: 1) They position the forelimbs to hit the ground first by protracting and abducting the humeri, 2) They prepare and brace for impact by extending the elbows and activating underlying musculature to stiffen the joint and 3) they control torques during the landing by retracting the hind limbs and rotating the forelimbs to align with the impact angle. By perturbing landing conditions we found that toads tune these components to specific landing conditions with a combination of passive and active control and toads do so by primarily relying on non-visual sensory feedback

Endocrinology of osmoregulation and thermoregulation of Australian desert tetrapods: A historical perspective.

Many Australian tetrapods inhabit desert environments characterised by low productivity, unpredictable rainfall, high temperatures and high incident solar radiation. Maintaining a homeostatic milieu intérieur by osmoregulation and thermoregulation are two physiological challenges faced by tetrapods in deserts, and the endocrine system plays an important role in regulating these processes. There is a considerable body of work examining the osmoregulatory role of antidiuretic hormones for Australian amphibians, reptiles and mammals, with particular contributions concerning their role and function for wild, free-living animals in arid environments. The osmoregulatory role of the natriuretic peptide system has received some attention, while the role of adrenal corticosteroids has been more thoroughly investigated for reptiles and marsupials. The endocrinology of thermoregulation has not received similar attention. Reptiles are best-studied, with research examining the influence of arginine vasotocin and melatonin on body temperature, the role of prostaglandins in heart rate hysteresis and the effect of melanocyte-stimulating hormone on skin reflectivity. Australian mammals have been under-utilised in studies examining the regulation, development and evolution of endothermy, and there is little information concerning the endocrinology of thermoregulation for desert species. There is a paucity of data concerning the endocrinology of osmoregulation and thermoregulation for Australian desert birds. Studies of Australian desert fauna have made substantial contributions to endocrinology, but there is considerable scope for further research. A co-ordinated approach to examine arid-habitat adaptations of the endocrine system in an environmental and evolutionary context would be of particular value

Phenotypic evolution in the invasive cane toad (Rhinella marina): adaptations for dispersal

Phenotypic evolution in the invasive cane toad (Rhinella marina): adaptations for dispersal Abstract Invasive species provide a rare opportunity to study how organisms adapt when colonising novel environments. Despite the negative ecological impacts caused by the introduction of alien species, biological invasions act as natural experiments that we can exploit for ecological and evolutionary research. This is particularly true for introductions with precise geographic and historical records, such as the cane toad (Rhinella marina) introduction to Australia. Arguably the most successful invasive anuran worldwide, the cane toad was first introduced to the Hawai’ian Islands in 1932, and subsequently to northeastern Queensland in 1935. Over the past 82 years, R. marina has spread rapidly and at an accelerating pace throughout northern and eastern Australia, causing massive ecological disturbances in its wake. This acceleration of dispersal capability is a well-documented phenomenon in invasive organisms that can occur via a combination of natural selection, and spatial sorting. Although the increasing rate of cane toad dispersal has been extensively researched, my thesis aims to address questions about the evolutionary changes that have taken place throughout the process. Namely, what morphological, behavioural, or physiological shifts in cane toad phenotypes are associated with increased dispersal ability? I began by taking gross morphological measurements from toads across a transect through their northern Australian range that included long-colonised and invasion-front populations. Additional populations from a prior invasion (Hawai’i), and the native range (French Guiana) were later added to compare the morphology of individuals from the source populations. I focused on the components of each limb (hand, radioulna, humerus [forelimb]; femur, tibiofibula, foot [hindlimb]), as limb morphology is strongly linked to locomotor ability, but also collected data on mass, snout-vent length, head width, and parotoid gland shape. A subset of Australian individuals were collected from the edges of the range, representing the oldest and newest toad populations to be used in a common-garden breeding experiment. These individuals, and their resulting offspring were held in captivity and subjected to a series of performance trials. A separate group of individuals from invasion-front and range-core populations was used for Computerised X-ray Tomography (CT) scanning for precise geometric morphometric comparison of skeletal structure. Captive breeding of cane toads from the invasion-front (in Western Australia) and long-colonised areas (in Queensland) allowed me to control for the influence of rearing environment on common-garden F1 individuals. This also enabled analyses on heritability of morphology and performance traits by comparing offspring to their parents, and siblings to each other. Common-garden F1 offspring were raised over a period of 27 months, and measured repeatedly throughout ontogeny. Performance trials consisted of climbing trials (where toads would have to escape from a mesh tube by climbing vertically) and anti-predator raceway trials (where toads were encouraged to hop down a raceway by prodding). These trials were conducted on wild and captive toads. Within this thesis I document reproductive differences between invasion-front and long-colonised populations, significant geographic variation in locomotor performance, regional changes to skeletal structure, shifts in sexual dimorphism with time since colonisation, and heritability of behavioural and morphological traits; and I demonstrate that these changes have arisen via the rapid evolution of a high-dispersal phenotype during the invasion process

Frog origins: inferences based on ancestral reconstructions of locomotor performance and anatomy

Frogs are the most species-rich and ecologically diverse group of amphibians and are characterized by a unique body plan including long legs, elongated ilia, and fused caudal vertebrae. Stem anurans such as Triadobatrachus or Czatkobatrachus have been suggested to have used jumping or hopping as part of their locomotor repertoire based on their anatomy. The earliest known true frog, Prosalirus bitis was suggested to have been a proficient jumper. However, data on jumping performance in frogs have never been used to attempt reconstruction of ancestral features at the base of the radiation. Here we provide data on jumping performance (forces and acceleration) in 20 species of extant frogs including representatives of most of the early radiating clades. We next use ancestral character value inferences to assess ancestral features. Our analyses suggest that frog ancestors were of small to medium size, had relatively short limbs, produced rather low jump forces, yet were capable of relatively high acceleration. Given the short limbs and low forces, the unique frog bauplan with a reduced vertebral column and a mobile ilio-sacral joint may not have been an adaptation for powerful jumping

Volume 2, Chapter 14-1: Amphibians: Anuran Adaptations

https://digitalcommons.mtu.edu/bryo-ecol-subchapters/1117/thumbnail.jp

Non-native Amphibian Pet Trade via Internet in Poland

Overharvesting and trade in amphibian populations is one of the causes of their global decline. Online trade not only encourages the exploitation of an increasing number of rare and endangered amphibian species from all over the world but also influences the spread of invasive species. The aim of our research was to investigate the amphibian pet trade conducted in online stores and portals in Poland and determine its potential impact on native species. Between November 2013 and October 2014, we regularly (on a monthly basis) checked sale offers on the websites of the 18 biggest pet shops in the country specialised in exotic animals, on a nationwide auction portal and on three exotic pet fan portals. During the study, we reported 486 offers of 112 amphibian species in online stores and on portals. Most of the offers involved one of the four families of amphibians: poison dart frogs (Dendrobatidae), tree frogs (Hylidae), true toads (Bufonidae) and true salamanders (Salamandridae). Our data show increased interest in amphibians as pets in Poland. At least half of the offered species are possible hosts for the chytrid fungus Batrachochytrium dendrobatidis. However, only one species, the American bullfrog Lithobates catesbeianus (Shaw, 1802), appears to be a potential invasive species. To summarise, the species offered in Poland that are characterised as threatened are predominantly those that are relatively easy to breed and that are popular as pets. Further studies are required to investigate the real threat to wild amphibian populations caused by the pet trade

Sympatric prey responses to lethal top-predator control: predator manipulation experiments

Introduction: Many prey species around the world are suffering declines due to a variety of interacting causes such as land use change, climate change, invasive species and novel disease. Recent studies on the ecological roles of top-predators have suggested that lethal top-predator control by humans (typically undertaken to protect livestock or managed game from predation) is an indirect additional cause of prey declines through trophic cascade effects. Such studies have prompted calls to prohibit lethal top-predator control with the expectation that doing so will result in widespread benefits for biodiversity at all trophic levels. However, applied experiments investigating in situ responses of prey populations to contemporary top-predator management practices are few and none have previously been conducted on the eclectic suite of native and exotic mammalian, reptilian, avian and amphibian predator and prey taxa we simultaneously assess. We conducted a series of landscape-scale, multi-year, manipulative experiments at nine sites spanning five ecosystem types across the Australian continental rangelands to investigate the responses of sympatric prey populations to contemporary poison-baiting programs intended to control top-predators (dingoes) for livestock protection. Results: Prey populations were almost always in similar or greater abundances in baited areas. Short-term prey responses to baiting were seldom apparent. Longer-term prey population trends fluctuated independently of baiting for every prey species at all sites, and divergence or convergence of prey population trends occurred rarely. Top-predator population trends fluctuated independently of baiting in all cases, and never did diverge or converge. Mesopredator population trends likewise fluctuated independently of baiting in almost all cases, but did diverge or converge in a few instances. Conclusions: These results demonstrate that Australian populations of prey fauna at lower trophic levels are typically unaffected by top-predator control because top-predator populations are not substantially affected by contemporary control practices, thus averting a trophic cascade. We conclude that alteration of current top-predator management practices is probably unnecessary for enhancing fauna recovery in the Australian rangelands. More generally, our results suggest that theoretical and observational studies advancing the idea that lethal control of top-predators induces trophic cascades may not be as universal as previously supposed