More Like this

1. How venom pore placement may influence puncture performance in snake fangs

   https://doi.org/10.1242/jeb.245666  

   Crofts, Stephanie B. ; Anderson, Philip S. ( September 2023 , Journal of Experimental Biology)

   When designing experimental studies, it is important to understand the biological context of the question being asked. For example, many biological puncture experiments embed the puncture tool to a standardized depth based on a percentage of the total tool length, to compare the performance between tools. However, this may not always be biologically relevant to the question being asked. To understand how definitions of penetration depth may influence comparative results, we performed puncture experiments on a series of venomous snake fangs using the venom pore location as a functionally relevant depth standard. After exploring variation in pore placement across snake phylogeny, we compared the work expended during puncture experiments across a set of snake fangs using various depth standards: puncture initiation, penetration to a series of depths defined by the venom pore and penetration to 15% of fang length. Contrary to our hypothesis, we found almost no pattern in pore placement between clades, dietary groups or venom toxicity. Rank correlation statistics of our experimental energetics results showed no difference in the broad comparison of fangs when different puncture depth standards were used. However, pairwise comparisons between fangs showed major shifts in significance patterns between the different depth standards used. These results imply that the interpretation of experimental puncture data will heavily depend upon which depth standard is used during the experiments. Our results illustrate the importance of understanding the biological context of the question being addressed when designing comparative experiments.

    

   more » « less
2. High variation in handling times confers 35‐year stability to predator feeding rates despite community change

   https://doi.org/10.1002/ecy.3954  

   Novak, Mark ( January 2023 , Ecology)

   Historical resurveys of ecological communities are important for placing the structure of modern ecosystems in context. Rarely, however, are snapshot surveys alone sufficient for providing direct insight into the rates of the ecological processes underlying community functioning, either now or in the past. In this study, I used a statistically reasoned observational approach to estimate the feeding rates of a New Zealand intertidal predator,Haustrum haustorium, using diet surveys performed at several sites by Robert Paine in 1968–1969 and by me in 2004. Comparisons between time periods reveal a remarkable consistency in the predator's prey‐specific feeding rates, which contrasts with the changes I observed in prey abundances, the predator's body‐size distribution, and the prey's proportional contributions to the predator's apparent diet. Although these and additional changes in the predator's per‐capita attack rates seem to show adaptive changes in its prey preferences, they do not. Rather, feeding‐rate stability is an inherently statistical consequence of the predator's high among‐prey variation in handling times which determine the length of time that feeding events will remain detectable to observers performing diet surveys. Though understudied, similarly high among‐prey variation in handling (or digestion) times is evident in many predator species throughout the animal kingdom. The resultant disconnect between a predator's apparent diet and its actual feeding rates suggests that much of the temporal, biogeographic, and seemingly context‐dependent variation that is often perceived in community structure, predator diets, and food‐web topology may be of less functional consequence than assumed. Qualitative changes in ecological pattern need not represent qualitative changes in ecological process.

    

   more » « less
3. Gradual and Discrete Ontogenetic Shifts in Rattlesnake Venom Composition and Assessment of Hormonal and Ecological Correlates

   https://doi.org/10.3390/toxins12100659  

   Schonour, Richard B. ; Huff, Emma M. ; Holding, Matthew L. ; Claunch, Natalie M. ; Ellsworth, Schyler A. ; Hogan, Michael P. ; Wray, Kenneth ; McGivern, James ; Margres, Mark J. ; Colston, Timothy J. ; et al ( October 2020 , Toxins)

   null (Ed.)

   Ontogenetic shifts in venom occur in many snakes but establishing their nature as gradual or discrete processes required additional study. We profiled shifts in venom expression from the neonate to adult sizes of two rattlesnake species, the eastern diamondback and the timber rattlesnake. We used serial sampling and venom chromatographic profiling to test if ontogenetic change occurs gradually or discretely. We found evidence for gradual shifts in overall venom composition in six of eight snakes, which sometimes spanned more than two years. Most chromatographic peaks shift gradually, but one quarter shift in a discrete fashion. Analysis of published diet data showed gradual shifts in overall diet composition across the range of body sizes attained by our eight study animals, while the shifts in abundance of different prey classes varied in form from gradual to discrete. Testosterone concentrations were correlated with the change in venom protein composition, but the relationship is not strong enough to suggest causation. Venom research employing simple juvenile versus adult size thresholds may be failing to account for continuous variation in venom composition lifespan. Our results imply that venom shifts represent adaptive matches to dietary shifts and highlight venom for studies of alternative gene regulatory mechanisms. 

   more » « less
4. A novel larval diet interacts with nutritional stress to modify juvenile behaviors and glucocorticoid responses

   https://doi.org/10.1002/ece3.7860  

   Ledón‐Rettig, Cristina C. ; Lagon, Sarah R. ( July 2021 , Ecology and Evolution)

   Developmental plasticity can allow the exploitation of alternative diets. While such flexibility during early life is often adaptive, it can leave a legacy in later life that alters the overall health and fitness of an individual. Species of the spadefoot toad genusSpeaare uniquely poised to address such carryover effects because their larvae can consume drastically different diets: their ancestral diet of detritus or a derived shrimp diet. Here, we useSpeabombifronsto assess the effects of developmental plasticity in response to larval diet type and nutritional stress on juvenile behaviors and stress axis reactivity. We find that, in an open‐field assay, juveniles fed shrimp as larvae have longer latencies to move, avoid prey items more often, and have poorer prey‐capture abilities. While juveniles fed shrimp as larvae are more exploratory, this effect disappears if they also experienced a temporary nutritional stressor during early life. The larval shrimp diet additionally impairs juvenile jumping performance. Finally, larvae that were fed shrimp under normal nutritional conditions produce juveniles with higher overall glucocorticoid levels, and larvae that were fed shrimp and experienced a temporary nutritional stressor produce juveniles with higher stress‐induced glucocorticoid levels. Thus, while it has been demonstrated that consuming the novel, alternative diet can be adaptive for larvae in nature, doing so has marked effects on juvenile phenotypes that may recalibrate an individual's overall fitness. Given that organisms often utilize diverse diets in nature, our study underscores the importance of considering how diet type interacts with early‐life nutritional adversity to influence subsequent life stages.

    

   more » « less
5. Head shape predicts isotopic diet in anoles and day geckos

   https://doi.org/10.1111/1365-2435.14331  

   Figueira, Tyler J. ; Kennedy‐Gold, Stevie ; Piantoni, Carla ; Screen, Robyn M. ; Wright, Amber N. ( April 2023 , Functional Ecology)

   Trophic morphology affects resource acquisition; therefore, species differences in such traits may be informative for inferring resource use overlap and potential species interactions.

   In lizards, head size and shape determine the size and hardness of prey that can be consumed. Lizards with large differences in head morphology are expected to overlap less in prey use than lizards with more similar traits.

   Stable isotopes are increasingly being used to describe diet, yet how traditional functional traits affect isotopic diet is often not clear a priori.

   We measured head size, head shape, 𝛿¹⁵N, and 𝛿¹³C under controlled resource availability in an enclosure experiment using introduced lizards in Hawaiʻi to test whether functional traits predict isotopic diet.

   Brown anolesAnolis sagreihad the tallest and narrowest heads, the highest values of 𝛿¹³C, and the lowest values of 𝛿¹⁵N. Gold dust day geckosPhelsuma laticaudahad the shortest and widest heads, the lowest values of 𝛿¹³C, and the highest values of 𝛿¹⁵N. Green anolesAnolis carolinensiswere intermediate in both diet and morphology.

   As a result of isotopic diet overlap, green anoles have reduced competitor‐free resource space in the presence of both of the other lizard species.

   Head shape was the best predictor of diet and the only trait that explained variation within as well as among species. Head size was sexually dimorphic, and therefore the weaker diet correlations with this trait may be explained by sexual selection.

   Breadth in morphospace did not correlate with isotopic diet breadth, nor did the amount of overlap in morphospace predict the amount of overlap in isotopic diet space.

   While lizards were able to locally depress prey in experimental enclosures, no shifts in diet were detected in response to the presence of heterospecifics.

   The generality of head shape in predicting isotopic diet, and whether it does so independent of habitat use, warrants additional study. Head shape provides a potentially fruitful avenue for trait‐based approaches to studying ecology and evolution in lizards.

   Read the freePlain Language Summaryfor this article on the Journal blog.

    

   more » « less