The tailless gecko gets the worm: prey type alters the effects of caudal autotomy on prey capture and subjugation kinematics

Prey capture and subjugation are complex behaviors affected by many factors including physiological and behavioral traits of both the predator and the prey. The western banded gecko (Coleonyx variegatus) is a small generalist predator that consumes both evasive prey items, such as spiders, wasps, and orthopterans, and non-evasive prey items, including larvae, pupae, and isopterans. When consuming certain prey (e.g., scorpions), banded geckos will capture and then rapidly oscillate, or shake, their head and anterior part of their body. Banded geckos also have large, active tails that can account for over 20% of their body weight and can be voluntarily severed through the process of caudal autotomy. However, how autotomy influences prey capture behavior in geckos is poorly understood. Using high-speed 3D videography, we studied the effects of both prey type (mealworms and crickets) and tail autotomy on prey capture and subjugation performance in banded geckos. Performance metrics included maximum velocity and distance of prey capture, as well as velocity and frequency of post-capture shaking. Maximum velocity and distance of prey capture were lower for mealworms than crickets regardless of tail state. However, after autotomy, maximum velocity increased for strikes on mealworms but significantly decreased for crickets. After capture, geckos always shook mealworms, but never crickets. The frequency of shaking mealworms decreased after autotomy and additional qualitative differences were observed. Our results highlight the complex and interactive effects of prey type and caudal autotomy on prey capture biomechanics.

Ecology, sexual dimorphism, and jumping evolution in anurans

Sexual dimorphism (SD) is a common feature of animals, and selection for sexually dimorphic traits may affect both functional morphological traits and organismal performance. Trait evolution through natural selection can also vary across environments. However, whether the evolution of organismal performance is distinct between the sexes is rarely tested in a phylogenetic comparative context. Anurans commonly exhibit sexual size dimorphism, which may affect jumping performance given the effects of body size on locomotion. They also live in a wide variety of microhabitats. Yet the relationships among dimorphism, performance, and ecology remain underexamined in anurans. Here, we explore relationships between microhabitat use, body size, and jumping performance in males and females to determine the drivers of dimorphic patterns in jumping performance. Using methods for predicting jumping performance through anatomical measurements, we describe how fecundity selection and natural selection associated with body size and microhabitat have likely shaped female jumping performance. We found that the magnitude of sexual size dimorphism (where females are about 14% larger than males) was much lower than dimorphism in muscle volume, where females had 42% more muscle than males (after accounting for body size). Despite these sometimes-large averages, phylogenetic t-tests failed to show the statistical significance of SD for any variable, indicating sexually dimorphic species tend to be closely related. While SD of jumping performance did not vary among microhabitats, we found female jumping velocity and energy differed across microhabitats. Overall, our findings indicate that differences in sex-specific reproductive roles, size, jumping-related morphology, and performance are all important determinants in how selection has led to the incredible ecophenotypic diversity of anurans.

Morphological Correlates of Locomotion in the Aquatic and the Terrestrial Phases of Pleurodeles waltl Newts from Southwestern Iberia

Animals capable of moving in different environments might face conflicting selection on morphology, thus posing trade-offs on the relationships between morphology and locomotor performance in each of these environments. Moreover, given the distinct ecological roles of the sexes, these relationships can be sexually dimorphic. In this article, I studied the relationships between morphological traits and locomotor performance in male and female semiaquatic Pleurodeles waltl newts in their aquatic and their terrestrial stages. Morphology was sexually dimorphic: males have proportionally longer limbs and tails, as well as a better body condition (only in the aquatic phase), whereas females were larger and had greater body mass in both phases. Nonetheless, these morphological differences did not translate into sexual divergence in locomotor performance in either stage. This finding suggests other functions for the morphological traits measured, among which only SVL showed a positive relationship with locomotor performance in both stages, whereas the effect of SMI was negative only in the terrestrial stage, and that of tail length was positive only in the aquatic stage. In any case, the morphological correlates of terrestrial and aquatic locomotion did not conflict, which suggests no trade-off between both locomotory modes in the newts studied.

High predation risk decimates survival during the reproduction season

Predators attack conspicuous prey phenotypes that are present in the environment. Male display behavior of conspicuous nuptial coloration becomes risky in the presence of a predator, and adult males face higher predation risk. High predation risk in one sex will lead to low survival and sex ratio bias in adult cohorts, unless the increased predation risk is compensated by higher escape rate.Here, we tested the hypothesis that sand lizards (Lacerta agilis) have sex-specific predation risk and escape rate. We expected the differences to manifest in changes in sex ratio with age, differences in frequency of tail autotomy, and in sex-specific survival rate.We developed a statistical model to estimate predation risk and escape rate, combining the observed sex ratio and frequency of tail autotomy with likelihood-based survival rate. Using Bayesian framework, we estimated the model parameters. We projected the date of the tail autotomy events from growth rates derived from capture-recapture data measurements.We found statistically stable sex ratio in age groups, equal frequency of tail regenerates between sexes, and similar survival rate. Predation risk is similar between sexes, and escape rate increases survival by about 5%. We found low survival rate and a low number of tail autotomy events in females during months when sand lizards mate and lay eggs, indicating high predator pressure throughout reproduction. Our data show that gravid females fail to escape predation.The risks of reproduction season in an ectotherm are a convolution of morphological changes (conspicuous coloration in males and body allometry changes in gravid females), behavior (nuptial displays), and environmental conditions which challenge lizard thermal performance. Performance of endotherm predators in cold spring months endangers gravid females more than displaying males in bright nuptial coloration.

Short- and long-term effects of an extreme case of autotomy: does "tail" loss and subsequent constipation decrease the locomotor performance of male and female scorpions?

In many taxa, individuals voluntarily detach a body part as a form to increase their chances of escaping predation. This defense mechanism, known as autotomy, has several consequences, such as changes in locomotor performance that may affect fitness. Scorpions of the genus Ananteris autotomize the "tail", which in fact corresponds to the last abdominal segments. After autotomy, individuals lose nearly 25% of their body mass and the last portion of the digestive tract, including the anus, which prevents defecation and leads to constipation, because regeneration does not occur. Here, we experimentally investigated the short- and long-term effects of tail loss on the locomotor performance of Ananteris balzani. In a short-term experiment, the maximum running speed (MRS) of males and females did not change after autotomy. Moreover, the relative mass of the lost tail did not affect the change in MRS after autotomy. In a long-term experiment, autotomy had a negative effect on the MRS of males, but not of females. Autotomized over-fed individuals suffered from severe constipation but were not slower than autotomized normally fed individuals. In conclusion, tail loss has no immediate effect on the locomotor performance of scorpions. The long-term decrease in the locomotor performance of autotomized males may impair mate searching. However, because death by constipation takes several months, males have a long time to find mates and reproduce. Thus, the prolonged period between autotomy and death by constipation is crucial for understanding the evolution of one of the most extreme cases of autotomy in nature.

Linking ecomechanical models and functional traits to understand phenotypic diversity

Physical principles and laws determine the set of possible organismal phenotypes. Constraints arising from development, the environment, and evolutionary history then yield workable, integrated phenotypes. We propose a theoretical and practical framework that considers the role of changing environments. This 'ecomechanical approach' integrates functional organismal traits with the ecological variables. This approach informs our ability to predict species shifts in survival and distribution and provides critical insights into phenotypic diversity. We outline how to use the ecomechanical paradigm using drag-induced bending in trees as an example. Our approach can be incorporated into existing research and help build interdisciplinary bridges. Finally, we identify key factors needed for mass data collection, analysis, and the dissemination of models relevant to this framework.

The dendrite arbor of Purkinje cells is altered following to tail regeneration in the leopard gecko

Purkinje cells of the cerebellum have a complex arborized arrangement of dendrites and are amongst the most distinctive cell types of the nervous system. Although the neuromorphology of Purkinje cells has been well described for some mammals and teleost fish, for most vertebrates less is known. Here we used a modified Golgi-Cox method to investigate the neuromorphology of Purkinje cells from the lizard Eublepharis macularius, the leopard gecko. Using Sholl and Branch Structure Analyses, we sought to investigate whether the neuromorphology of gecko Purkinje cells was altered is response to tail loss and regeneration. Tail loss is an evolved mechanism commonly used by geckos to escape predation. Loss of the tail represents a significant and sudden change in body length and mass, which is only partially recovered as the tail is regenerated. We predicted that tail loss and regeneration would induce a quantifiable change in Purkinje cell dendrite arborization. Post hoc comparisons of Sholl analyses data showed that geckos with regenerated tails have significant changes in dendrite diameter and the number of dendrite intersections in regions corresponding to the position of parallel fiber synapses. We propose that the neuromorphological alterations observed in gecko Purkinje cells represent a compensatory response to tail regrowth, and perhaps a role in motor learning.

Foot anatomy, walking energetics, and the evolution of human bipedalism

Interspecies differences in locomotor efficiency have been extensively researched, but within-species variation in the metabolic cost of walking and its underlying causes have received much less attention. This is somewhat surprising given the importance of walking energetics to natural selection, and the fact that the mechanical efficiency of striding bipedalism in modern humans is thought to be related in some part to the unique morphology of the human foot. Previous studies of human running have linked specific anatomical traits in the foot to variations in locomotor energetics to provide insight into form-function relationships in human evolution. However, such studies are relatively rare, particularly for walking. In this study, relationships between a range of functional musculoskeletal traits in the human lower limb and the energetics of walking over compliant and noncompliant substrates are examined, with particular focus on the lower limb and foot. Twenty-nine young, healthy individuals walked across three surfaces-a noncompliant laboratory floor, and compliant 6 cm and 13 cm thick foams-at self-selected speeds while oxygen consumption was measured, from which the metabolic cost of transport was calculated. Lower limb lengths, calcaneus lengths, foot shape indices, and maximum isometric plantarflexion torques were also measured and subsequently tested for relationships with metabolic cost over these surfaces using linear regression. It was found that metabolic cost varied considerably between individuals within and across substrate types, but this variation was not statistically related to or explained by variations in musculoskeletal parameters considered to be adaptively important to efficient bipedal locomotion. This therefore provides no supportive evidence that variations in these gross anatomical parameters confer significant advantages to the efficiency of walking, and therefore suggest caution in the use of similar metrics to infer differences in walking energetics in closely related fossil species.

Tail Autotomy Alters Prey Capture Performance and Kinematics, but not Success, in Banded Geckos

Tails are versatile structures with diverse forms and functions across vertebrates. They are involved in almost all behaviors critical to survival including locomotion, feeding, and predator avoidance. Although the tail's role in locomotion and stability has been widely studied, its role in prey capture is relatively unknown. Lizards are an ideal system to examine the tail's impact on prey capture as most are capable of autotomizing, or dropping, their tail in response to predation and intraspecific competition. Tail autotomy can lower reproduction, decrease locomotor performance, impart instability during jumping, and decrease social status. Desert banded geckos (Coleonyx variegatus) frequently capture evasive prey in nature and appear to use their tail during strikes. However, it is unclear if these tail movements are important for the strike itself, or if they simply draw attention to that part of the body. We used high-speed 3D videography to quantify prey capture performance and kinematics of C. variegatus striking at crickets before and after total caudal autotomy. Trials were conducted within 2 h of autotomy and then repeatedly over a 2-week period. Overall, prey capture success was unaffected by caudal autotomy. However, maximum strike velocity decreased significantly after autotomy, highlighting the importance of the tail during prey capture. Strike kinematics were altered after autotomy in several ways, including geckos adopting a more sprawled posture. Maximum pectoral girdle and mid-back height were significantly lower during post-autotomy strikes, whereas maximum pelvic girdle height was unaffected. However, individual variation was considerable. This downward pitching of the body after tail loss suggests that the tail is necessary for counterbalancing the anterior portion of the body and resisting the rotational inertia incurred after pushing off with the hindlimbs. Utilizing autotomy to test tail function in prey capture can provide valuable insight into how the tail is used in terrestrial predation across a wide variety of species and ecological niches.

Walking kinematics in the polymorphic seed harvester ant Messor barbarus: influence of body size and load carriage

Ants are famous in the animal kingdom for their amazing load-carrying performance. Yet, the mechanisms that allow these insects to maintain their stability when carrying heavy loads have been poorly investigated. Here, we present a study of the kinematics of unloaded and loaded locomotion in the polymorphic seed-harvesting ant Messor barbarus In this species, large ants have larger heads relative to their size than small ants. Hence, their center of mass is shifted forward, and even more so when they are carrying a load in their mandibles. We tested the hypothesis that this could lead to large ants being less statically stable than small ants, thus explaining their lower load-carrying ability. We found that large ants were indeed less statically stable than small ants when walking unloaded, but they were nonetheless able to adjust their stepping pattern to partly compensate for this instability. When ants were walking loaded on the other hand, there was no evidence of different locomotor behaviors in individuals of different sizes. Loaded ants, whatever their size, move too slowly to maintain their balance through dynamic stability. Rather, they seem to do so by clinging to the ground with their hind legs during part of a stride. We show through a straightforward model that allometric relationships have a minor role in explaining the differences in load-carrying ability between large ants and small ants, and that a simple scale effect is sufficient to explain these differences.

Neuromuscular control of locomotion is altered by tail autotomy in geckos

Animal locomotion is driven by underlying axial and appendicular musculature. In order for locomotion to be effective, these muscles must be able to rapidly respond to changes in environmental and physiological demands. Although virtually unstudied, muscles must also respond to morphological changes, such as those that occur with tail autotomy in lizards. Tail autotomy in leopard geckos (Eublepharis macularius) results in a 25% loss of caudal mass and significant kinematic alterations to maintain stability. To elucidate how motor control of the locomotor muscles is modulated with these shifts, we used electromyography (EMG) to quantify patterns of in vivo muscle activity in fore- and hind limb muscles before and after autotomy. Forelimb muscles (biceps brachii and triceps brachii) exhibited no changes in motor recruitment, consistent with unaltered kinematics after autotomy. Amplitude of activity of propulsive muscles of the hind limbs (caudofemoralis and gastrocnemius) was significantly reduced and coincided with decreases in the propulsive phases of femur retraction and ankle extension, respectively. The puboischiotibialis did not exhibit these changes, despite significant reductions in femur depression and knee angle, suggesting that reduction in mass and vertical ground-reaction force by autotomy allows for the maintenance of a more sprawled and stable posture without increasing motor recruitment of the support muscles. These results highlight the significant neuromuscular shifts that occur to accommodate dramatic changes in body size and mass distribution, and illuminate the utility of tail autotomy as a system for studying the neuromuscular control of locomotion.