Effect of ontogenetic increases in body size on burst swimming performance in tadpoles of the striped marsh frog, Limnodynastes peronii

The effect of ontogenetic increases in total length on burst swimming performance was investigated in tadpoles of the striped marsh frog (Limnodynastes peronii) over the total-length range of 1.5-4 cm and Gosner developmental stages 25-38. The burst swimming performance of tadpoles at 10 degrees and 24 degrees C was determined by videotaping startle responses with a highspeed video camera at 200 Hz and analysing the sequences frame by frame. Maximum swimming velocity (U-max) and acceleration (A(max)) increased with total length (L) at a rate that was proportionally greater than the increase in total length (i.e., positive allometry; exponents >1) and was described by the allometric equations U-max = 0.061L(1.34) and A(max) =1.15L(1.11) at 10 degrees C and U-max = 0.114L(1.34) and A(max) = 1.54L(1.11) at 24 degrees C. Stride length increased with a total-length exponent of approximately 1 bur was unaffected by temperature. Tail-beat frequency was not affected by total length and increased from 7.8 +/- 0.2 Hz at 10 degrees C to 21.7 +/- 0.7 Hz at 24 degrees C. Developmental stage did not significantly influence the relationship between total length and U-max or A(max). Furthermore, temperature and the associated changes in water viscosity did not affect the relationship between total length and burst swimming performance. At their U-max, Reynolds numbers ranged from approximately 1,500 in the smaller tadpoles up to 50,000 for the larger animals at 24 degrees C We suggest the positive allometry of U-max in larval L. peronii was due in part to the increases in tail width (TW) with total length (TW= -1.36(1.66)), possibly reflecting the increasing importance of burst swimming performance to survival during larval development

Geographic variation in thermal sensitivity of jumping performance in the frog Limnodynastes peronii

I compared the thermal sensitivity of jumping performance of five populations of the striped marsh frog (Limnodynastes peronii) over a wide geographic range extending from the cool-temperate south to the tropical north of Australia. Maximum jumping performance of adult E peronii was assessed for each population at eight temperatures between 5degreesC and 32degreesC using a custom-designed force platform. From force recordings for each individual jump, maximum jumping force (F-max) and acceleration (A(max)) and maximum power output (P-max), take-off velocity (U-max), jump distance (D-J) and contact time on the platform (T-C) were calculated. The body mass of adult E peronii varied over their geographic range, from approximately 5 g for the lowland tropical population to more than 22 g for the cool-temperate populations. The thermal sensitivity of jumping performance varied over their geographic range, with the populations from the cooler climates generally performing better than those from the warmer climate populations at the cooler temperatures, and vice versa at the higher temperatures. However, not all parameters of jumping performance underwent parallel changes in thermal sensitivity amongst the populations of L. peronii. Only minor differences in the shape of the thermal sensitivity curves for F-max and A(max) were detected amongst the populations, while the thermal sensitivities of U-max, D-J and P-max all displayed considerable variation amongst the populations. The optimal temperatures for U-max, D-J and P-max were generally lower in the cool-temperate populations than in the tropical populations of L. peronii. To determine whether this geographic variation was due to genetic variation, or merely reflected phenotypic plasticity, I also compared the thermal sensitivity of jumping performance between metamorph L. peronii from two different populations raised under identical conditions in the laboratory. The maximum jumping distance of the metamorph L. peronii was assessed at seven temperatures between 8degreesC and 35degreesC for the two latitudinally extreme populations (i.e. lowland tropical Proserpine and cool-temperate Gippsland populations). Like adult L. peronii, the metamorphs from the cool-temperate population jumped further than those from the lowland tropical population at the lower temperatures, although no differences were detected at the higher temperatures. Thus, geographic variation in thermal sensitivity of jumping performance in L. peronii probably has a genetic component, and the different populations appear to have undergone genetic adaptation of their thermal sensitivity to the varied thermal environments

Improving sneaky-sex in a low oxygen environment: reproductive and physiological responses of male mosquito fish to chronic hypoxia

Few studies have examined the adaptive significance of reversible acclimation responses. The aerobic performance and mating behaviour of the sexually coercive male eastern mosquito fish ( Gambusia holbrooki) offers an excellent model system for testing the benefits of reversible acclimation responses to mating success. We exposed male mosquito fish to normoxic or hypoxic conditions for 4 weeks and tested their maximum sustained swimming performance and their ability to obtain coercive matings under both normoxic and hypoxic conditions. We predicted that hypoxia-acclimated males would possess greater swimming and mating performance in hypoxic conditions than normoxic-acclimated males, and vice versa when tested in normoxia. Supporting our predictions, we found the sustained swimming performance of male mosquito fish was greater in a hypoxic environment following long-term exposure to low partial pressures of oxygen. However, the benefits of acclimation responses to mating performance were dependent on whether they were tested in the presence or absence of male-male competition. In a non-competitive environment, male mosquito fish acclimated to hypoxic conditions spent a greater amount of time following females and obtained more copulations than normoxic-acclimated males when tested in low partial pressures of oxygen. When males were competed against each other for copulations, we found no influence of long-term exposure to different partial pressures of oxygen on mating behaviour. Thus, despite improvements in the aerobic capacity of male mosquito fish following long-term acclimation to hypoxic conditions, these benefits did not always manifest themselves in improved mating performance. This study represents one of the first experimental tests of the benefits of reversible acclimation responses, and indicates that the ecological significance of physiological plasticity may be more complicated than previously imagined

Trade-offs between speed and endurance in the frog Xenopus laevis: a multi-level approach

One of the most interesting trade-offs within the vertebrate locomotor system is that between speed and endurance capacity. However, few studies have demonstrated a conflict between whole-animal speed and endurance within a vertebrate species. We investigated the existence of trade-offs between speed and endurance capacity at both the whole-muscle and whole-animal levels in post-metamorphs of the frog Xenopus laevis. The burst-swimming performance of 55 frogs was assessed using a high-speed digital camera, and their endurance capacity was measured in a constant-velocity swimming flume. The work-loop technique was used to assess maximum power production of whole peroneus muscles at a cycle frequency of 6 Hz, while fatigue-resistance was determined by recording the decrease in force and net power production during a set of continuous cycles at 2 Hz. We found no significant correlations between measures of burst swimming performance and endurance capacity, suggesting that there is no trade-off between these two measures of whole-animal performance. In contrast, there was a significant negative correlation between peak instantaneous power output of the muscles at 6 Hz and the fatigue-resistance of force production at 2 Hz (other correlations between power and fatigue were negative but non-significant). Thus, our data support the suggestion that a physiological conflict between maximum power output and fatigue resistance exists at the level of vertebrate muscles. The apparent incongruence between whole-muscle and whole-animal performance warrants further detailed investigation and may be related to factors influencing both whole-muscle and whole-animal performance measures

Allometric scaling relationships of jumping performance in the striped marsh frog Limnodynastes peronii

We constructed a force platform to investigate the scaling relationships of the detailed dynamics of jumping performance in striped marsh frogs (Limnodynastes peronii). Data were used to test between two alternative models that describe the scaling of anuran jumping performance; Hill's model, which predicts mass-independence of jump distance, and Marsh's model, which predicts that jump distance increases as M-0.2, where M is body mass. From the force platform, scaling relationships were calculated for maximum jumping force (F-max), acceleration, take-off velocity (U-max), mass- specific jumping power (P-max), total jumping distance (D-J) and total contact time for 75 L. peronii weighing between 2.9 and 38.4 g. F-max was positively correlated with body mass and was described by the equation F-max=0.16M(0.61), while P-max decreased significantly with body mass and was described by the equation P-max=347M(-0.46). Both D-J and U-max were mass- independent over the post-metamorph size range, and thus more closely resembled Hill's model for the scaling of locomotion. We also examined the scaling relationships of jumping performance in metamorph L. peronii by recording the maximum jump distance of 39 animals weighing between 0.19 and 0.58 g. In contrast to the post-metamorphic L. peronii, D-J and U-max were highly dependent on body mass in metamorphs and were described by the equations D-J=38M(0.53) and U-max=1.82M(0.23), respectively. Neither model for the scaling of anuran jumping performance resembled data from metamorph L. peronii. Although the hindlimbs of post-metamorphic L. peronii scaled geometrically (body mass exponent approximately 0.33), the hindlimbs of metamorphs showed greater proportional increases with body mass (mass exponents of 0.41-0.42)

Cameras, competition and creativity: assessing 1st year ecology in the field

The great outdoors is the laboratory for most studies in ecology. This article reports on the use of cameras, competition and creativity as novel ways to assess learning during a one-day field trip for a large (~600 students) introductory biology/ecology course. Among the assessment activities, students find and photograph examples of various types of ecological interactions, create a dichotomous plant key in the lab and apply it in the field, and evaluate the potential impact of various environmental change scenarios on ecosystems. The activities and accompanying assessment foster higher order thinking (such as application, evaluation and synthesis) and better retention of knowledge because students create their own context for concepts and content, which have traditionally been learned by rote approaches. This article provides practical advice on how to implement this type of assessment

Receivers Limit the Prevalence of Deception in Humans: Evidence from Diving Behaviour in Soccer Players

Deception remains a hotly debated topic in evolutionary and behavioural research. Our understanding of what impedes or facilitates the use and detection of deceptive signals in humans is still largely limited to studies of verbal deception under laboratory conditions. Recent theoretical models of non-human behaviour have suggested that the potential outcome for deceivers and the ability of receivers to discriminate signals can effectively maintain their honesty. In this paper, we empirically test these predictions in a real-world case of human deception, simulation in soccer. In support of theoretical predictions in signalling theory, we show that cost-free deceit by soccer players decreases as the potential outcome for the signaller becomes more costly. We further show that the ability of receivers (referees) to detect deceptive signals may limit the prevalence of deception by soccer players. Our study provides empirical support to recent theoretical models in signalling theory, and identifies conditions that may facilitate human deception and hinder its detection

Urban Physiology: City Ants Possess High Heat Tolerance

Urbanization has caused regional increases in temperature that exceed those measured on a global scale, leading to urban heat islands as much as 12°C hotter than their surroundings. Optimality models predict ectotherms in urban areas should tolerate heat better and cold worse than ectotherms in rural areas. We tested these predications by measuring heat and cold tolerances of leaf-cutter ants from South America's largest city (São Paulo, Brazil). Specifically, we compared thermal tolerances of ants from inside and outside of the city. Knock-down resistance and chill-coma recovery were used as indicators of heat and cold tolerances, respectively. Ants from within the city took 20% longer to lose mobility at 42°C than ants from outside the city. Interestingly, greater heat tolerance came at no obvious expense of cold tolerance; hence, our observations only partially support current theory. Our results indicate that thermal tolerances of some organisms can respond to rapid changes in climate. Predictive models should account for acclimatory and evolutionary responses during climate change

Modeling the two-dimensional accuracy of soccer kicks

In many sports, athletes perform motor tasks that simultaneously require both speed and accuracy for success, such as kicking a ball. Because of the biomechanical trade-off between speed and accuracy, athletes must balance these competing demands. Modelling the optimal compromise between speed and accuracy requires one to quantifyhow task speed affects the dispersion around a target, a level of experimental detail not previously addressed. Using soccer penalties as a system, we measured two-dimensional kicking error over a range of speeds, target heights, and kicking techniques. Twenty experienced soccer players executed a total of 8466 kicks at two targets (high and low). Players kicked with the side of their foot or the instep at ball speeds ranging from 40% to 100% of their maximum. The inaccuracy of kicks was measured in horizontal and vertical dimensions. For both horizontal and vertical inaccuracy, variance increased as a power function of speed, whose parameter values depended on the combination of kicking technique and target height. Kicking precision was greater when aiming at a low target compared to a high target. Side-foot kicks were more accurate than instep kicks. The centre of the dispersion of shots shifted as a function of speed. An analysis of the covariance between horizontal and vertical error revealed right-footed kickers tended to miss below and to the left of the target or above and to the right, while left-footed kickers tended along the reflected axis. Our analysis provides relationships needed to model the optimal strategy for penalty kickers

Running faster causes disaster: trade-offs between speed, manoeuvrability and motor control when running around corners in northern quolls (Dasyurus hallucatus)

Movement speed is fundamental to all animal behaviour, yet no general framework exists for understanding why animals move at the speeds they do. Even during fitness-defining behaviours like running away from predators, an animal should select a speed that balances the benefits of high speed against the increased probability of mistakes. In this study, we explored this idea by quantifying trade-offs between speed, manoeuvrability and motor control in wild northern quolls (Dasyurus hallucatus) - a medium-sized carnivorous marsupial native to northern Australia. First, we quantified how running speed affected the probability of crashes when rounding corners of 45, 90 and 135 deg. We found that the faster an individual approached a turn, the higher the probability that they would crash, and these risks were greater when negotiating tighter turns. To avoid crashes, quolls modulated their running speed when they moved through turns of varying angles. Average speed for quolls when sprinting along a straight path was around 4.5 m s-1 but this decreased linearly to speeds of around 1.5 m s-1 when running through 135 deg turns. Finally, we explored how an individual's morphology affects their manoeuvrability. We found that individuals with larger relative foot sizes were more manoeuvrable than individuals with smaller relative foot sizes. Thus, movement speed, even during extreme situations like escaping predation, should be based on a compromise between high speed, manoeuvrability and motor control. We advocate that optimal - rather than maximal - performance capabilities underlie fitnessdefining behaviours such as escaping predators and capturing prey