Nonlethally assessing elasmobranch ontogenetic shifts in energetics

Body condition is an important proxy for the overall health and energetic status of fishes. The classically used Fulton's condition factor requires length and mass measurements, but mass can be difficult to obtain in large species. Girth measurements can replace mass for wild pelagic sharks. However, girth-calculated condition has not been validated against Fulton's condition factor intraspecifically, across ontogeny or reproduction, or in a controlled setting. We used the epaulette shark (Hemiscyllium ocellatum), because they are amenable to captive reproduction, to track fine-scale body condition changes across life stages, oviparous reproduction and between condition indices. We measured four girths, total length and mass of 16 captive epaulette sharks across 1 year and tracked female reproduction daily. We also collected length and mass data from an additional 72 wild-caught sharks and 155 sharks from five previous studies and two public aquaria to examine the relationship between length and mass for this species. Even though data were derived from a variety of sources, a predictable length–mass relationship (R2 = 0.990) was achievable, indicating that combining data from a variety of sources could help overcome knowledge gaps regarding basic life history characteristics. We also found that condition factor decreased during early life stages, then increased again into adulthood, with predictable changes across the female reproductive cycle. Finally, we determined that both Fulton's and girth condition analyses were comparable. Outcomes from this study uniquely provide body condition changes across the complete life history, including fine-scale female reproductive stages, and validate the use of girths as a nonlethal whole-organism energetic assessment for fishes

Testing the Persistence of Phenotypic Plasticity After Incubation in the Western Fence Lizard, Sceloporus Occidentalis

Hypothesis: Phenotypic variation in traits induced by different incubation temperatures does not persist into the lifetime of young lizards, and therefore contributes little to variation in long-term fitness. Organism: Western fence lizard (Sceloporus occidentalis). Methods: Split-clutch laboratory incubation experiment including eggs from two different populations under two different incubation regimes, measurement of morphological traits at hatching, and tracking of morphology and temperature preference behaviour for 7 weeks after hatching. Results: Several morphological traits, including body mass, hindlimb length, inter-limb length, and tail length, initially differed between the two incubation treatments, but only the difference in tail length persisted to age 7 weeks. Thermal preference was relatively conserved, with juveniles showing no difference in mean selected body temperatures across treatments; however, warm-incubated lizards thermoregulated more precisely than their cool-incubated counterparts. Conclusion: Studies of incubation effects can reveal changes in animal phenotypes post-hatching, but if these effects do not persist, they may not be subject to natural selection and consequently be of little ecological relevance

Do the relationships between hindlimb anatomy and sprint speed variation differ between sexes in Anolis lizards?

The ability of an animal to run fast has important consequences on its survival capacity and overall fitness. Previous studies have documented how variation in the morphology of the limbs is related to variation in locomotor performance. Although these studies have suggested direct relations between sprint speed and hindlimb morphology, few quantitative data exist. Consequently, it remains unclear whether selection acts in limb segment lengths, overall muscle mass or muscle architecture (e.g. muscle fiber length and cross-sectional area). Here, we investigate whether muscle architecture (mass, fiber length and physiological cross-sectional area), hindlimb segment dimensions, or both, explain variation in sprint speed across 14 species of Anolis lizards. Moreover, we test whether similar relationships exist between morphology and performance for both sexes, which may not be the case given the known differences in locomotor behavior and habitat use. Our results show that the main driver of sprint speed is the variation in femur length for both males and females. Our results further show sexual dimorphism in the traits studied and, moreover, show differences in the traits that predict maximal sprint speed in males and females. For example, snout vent length and overall muscle mass are also good predictors of sprint speed in males, whereas no relationships between muscle mass and sprint speed was observed in females. Only a few significant relationships were found between muscle architecture (fiber length, cross-sectional area) and sprint speed in male anoles, suggesting that overall muscles size, rather than muscle architecture, appears to be under selection

Developmental plasticity affects sexual size dimorphism in an anole lizard

This is the peer reviewed version of the following article: Bonneaud, C., Marnocha, E., Herrel, A., Vanhooydonck, B., Irschick, D. J., Smith, T. B. (2015), Developmental plasticity affects sexual size dimorphism in an anole lizard. Functional Ecology, which has been published in final form at 10.1111/1365-2435.12468. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving: http://olabout.wiley.com/WileyCDA/Section/id-820227.html#termsSummary While developmental plasticity has been shown to contribute to sexual size dimorphism (SSD) in laboratory studies, its role in shaping SSD variation in wild vertebrate populations is unclear. Here we use a field study and a laboratory experiment to show that resource availability influences the degree of SSD among insular populations of Anolis sagrei lizards in the Bahamas. Total amounts of food biomass explained variation in male, but not female, body size on six Bahamian islands, giving rise to significant differences in SSD. Laboratory experiments on a captive colony of A. sagrei confirmed that variation in SSD was mediated by the effects of prey biomass on developmental plasticity in males, but not females. Indeed, males grew faster and attained larger sizes as adults under high-food treatments than under restricted diets, whereas adult females retained similar body sizes under both conditions. Our results indicate that the amount of food available can influence intersexual variation in body size within a vertebrate species. Sex-specific developmental plasticity may be favoured if it allows individuals to take advantage of varying levels of food opportunities offered by different habitats, by reducing competition between the sexes. As such, plasticity in response to food availability may have played a role in the invasion success of A. sagrei. This study adds to our growing understanding of the effect of resource availability in shaping SSD in reptiles and lends further support to the condition-dependent hypothesis, according to which the larger sex should display greater plasticity in growth in response to environmental conditions.Marie Curie Reintegration GrantUnited States Environmental Protection AgencyUCLA Department of Ecology and Evolutionary BiologyFund for Scientific Research (FWO-Vl), BelgiumNational Science Foundatio

Extreme positive allometry of animal adhesive pads and the size limits of adhesion-based climbing

Organismal functions are size-dependent whenever body surfaces supply body volumes. Larger organisms can develop strongly folded internal surfaces for enhanced diffusion, but in many cases areas cannot be folded so that their enlargement is constrained by anatomy, presenting a problem for larger animals. Here, we study the allometry of adhesive pad area in 225 climbing animal species, covering more than seven orders of magnitude in weight. Across all taxa, adhesive pad area showed extreme positive allometry and scaled with weight, implying a 200-fold increase of relative pad area from mites to geckos. However, allometric scaling coefficients for pad area systematically decreased with taxonomic level, and were close to isometry when evolutionary history was accounted for, indicating that the substantial anatomical changes required to achieve this increase in relative pad area are limited by phylogenetic constraints. Using a comparative phylogenetic approach, we found that the departure from isometry is almost exclusively caused by large differences in size-corrected pad area between arthropods and vertebrates. To mitigate the expected decrease of weight-specific adhesion within closely related taxa where pad area scaled close to isometry, data for several taxa suggest that the pads’ adhesive strength increased for larger animals. The combination of adjustments in relative pad area for distantly related taxa and changes in adhesive strength for closely related groups helps explain how climbing with adhesive pads has evolved in animals varying over seven orders of magnitude in body weight. Our results illustrate the size limits of adhesion-based climbing, with profound implications for large-scale bio-inspired adhesives.We are sincerely grateful to all our colleagues who readily shared published and unpublished data with us: Aaron M. Bauer, Jon Barnes, Niall Crawford, Thomas Endlein, Hanns Hagen Goetzke, Thomas E. Macrini, Anthony P. Russell & Joanna M. Smith. We also thank Casey Gilman, Dylan Briggs, Irina Showalter, Dan King and Mike Imburgia for their assistance with the collection of gecko toepad data. This study was supported by research grants from the UK Biotechnology and Biological Sciences Research Council (BB/I008667/1) to WF, the Human Frontier Science Programme (RGP0034/2012) to DI, AJC and WF, the Denman Baynes Senior Research Fellowship to DL and a Discovery Early Career Research Fellowship (DE120101503) to CJC.This is the author accepted manuscript. The final version is available from the National Academy of Sciences via http://dx.doi.org/ 10.1073/pnas.151945911

Bio-inspired geotechnical engineering: Principles, current work, opportunities and challenges

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Bio-inspired geotechnical engineering: principles, current work, opportunities and challenges

A broad diversity of biological organisms and systems interact with soil in ways that facilitate their growth and survival. These interactions are made possible by strategies that enable organisms to accomplish functions that can be analogous to those required in geotechnical engineering systems. Examples include anchorage in soft and weak ground, penetration into hard and stiff subsurface materials and movement in loose sand. Since the biological strategies have been ‘vetted’ by the process of natural selection, and the functions they accomplish are governed by the same physical laws in both the natural and engineered environments, they represent a unique source of principles and design ideas for addressing geotechnical challenges. Prior to implementation as engineering solutions, however, the differences in spatial and temporal scales and material properties between the biological environment and engineered system must be addressed. Current bio-inspired geotechnics research is addressing topics such as soil excavation and penetration, soil–structure interface shearing, load transfer between foundation and anchorage elements and soils, and mass and thermal transport, having gained inspiration from organisms such as worms, clams, ants, termites, fish, snakes and plant roots. This work highlights the potential benefits to both geotechnical engineering through new or improved solutions and biology through understanding of mechanisms as a result of cross-disciplinary interactions and collaborations

Measuring performance in nature: implications for studies of fitness within populations

SYNOPSIS. Significant relationships among morphology, behavior, performance and fitness have long served as bona fide evidence for the role of selection in shaping natural populations. Here, I discuss how studies of ecological performance, or how organisms perform in nature, provide an ecological context for such selection studies. Laboratory studies assume that the level of performance expressed under ‘‘optimal’ ’ conditions accurately reflects the level of performance used in nature, but I show here that this assumption is not always borne out. A review of how various factors affect ecological performance (ontogeny, microhabitat, and macrohabitat) show that animals often express very different levels of movement speed both among different tasks, and when comparing laboratory versus field performance. Thus, a failure to take this variation into account could lead to negative, or even misleading significant fitness-character correlations. While laboratory performance studies should continue to play a key role in studies of selection, recent technological (i.e., portable high-speed cameras) and methodological developments should enable researchers to measure performance in nature to high degrees of accuracy. Thus, I encourage researchers to measure performance both in the laboratory and in the field, and thus expand the traditional paradigm of morphology → performance → fitness to morphology → ecological performance → fitness