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1. Distinguishing between active plasticity due to thermal acclimation and passive plasticity due to Q 10 effects: Why methodology matters

   https://doi.org/10.1111/1365-2435.13534  

   Havird, Justin C. ; Neuwald, Jennifer L. ; Shah, Alisha A. ; Mauro, Alexander ; Marshall, Craig A. ; Ghalambor, Cameron K. ; Fox, ed., Charles ( March 2020 , Functional Ecology)

   Characterizing thermal acclimation is a common goal of eco‐physiological studies and has important implications for models of climate change and environmental adaptation. However, quantifying thermal acclimation in biological rate processes is not straightforward because many rates increase with temperature due to the acute effect of thermodynamics on molecular interactions. Disentangling such passive plastic responses from active acclimation responses is critical for describing patterns of thermal acclimation.

   Here, we reviewed published studies and distinguished between different study designs measuring the acute (i.e. passive) and acclimated (i.e. active) effects of temperature on metabolic rate. We then developed a method to quantify and classify acclimation responses by comparing acute and acclimatedQ₁₀values. Finally, we applied this method using meta‐analysis to characterize thermal acclimation in metabolic rates of ectothermic animals.

   We reviewed 258 studies measuring thermal effects on metabolic rates, and found that a majority of these studies (74%) did not allow for quantifying the independent effects of acclimation. Such studies were more common when testing aquatic taxa and continue to be published even in recent years.

   A meta‐analysis of 96 studies where acclimation could be quantified (using 1,072Q₁₀values) revealed that ‘partial compensation’ was the most common acclimation response (i.e. acclimation tended to offset the passive change in metabolic rate due to acute temperature changes). However, ‘no acclimation’ and ‘inverse compensation’, in which acclimation further augmented the acute change in metabolic rate, were also common.

   Acclimation responses differed among taxa, habitats and with experimental design. Amphibians and other terrestrial taxa tended to show weak acclimation responses, whereas fishes and other aquatic taxa tended to show stronger compensatory responses. Increasing how long the animal was allowed to adjust to a new test temperature increased the acclimation response, but body size did not. Acclimation responses were also stronger with longer acclimation durations.

   Collectively, these results highlight the importance of using the appropriate experimental design to investigate and estimate thermal acclimation of biological rates. To facilitate and guide future studies of thermal acclimation, we end with some suggestions for designing and interpreting experiments.

   A freePlain Language Summarycan be found within the Supporting Information of this article.

    

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2. Hunters versus hunted: New perspectives on the energetic costs of survival at the top of the food chain

   https://doi.org/10.1111/1365-2435.13649  

   Williams, Terrie M. ; Peter‐Heide Jørgensen, Mads ; Pagano, Anthony M. ; Bryce, Caleb M. ; Crocker, ed., Daniel ( October 2020 , Functional Ecology)

   Global biotic and abiotic threats, particularly from pervasive human activities, are progressively pushing large, apex carnivorous mammals into the functional role of mesopredator. Hunters are now becoming the hunted. Despite marked impacts on these animals and the ecosystems in which they live, little is known about the physiological repercussions of this role downgrading from ultimate to penultimate predator.

   Here we examine how such ecological role reversals alter the physiological processes associated with energy expenditure, and ultimately the cost of survival during peak performance.

   Taxonomic group, preferred habitat and domestication affected the capacity of the oxygen pathway to support high levels of aerobic performance by carnivorous mammals. Fear responses associated with anthropogenic threats also impacted aerobic performance.

   Allometric trends for three energetic metrics [maximum oxygen consumption, field metabolic rates (FMRs) and the cost per stride or stroke], showed distinct trends in aerobic capacity for different evolutionary lineages of mammalian predators. Cursorial canids that chase down prey demonstrated the highest relative maximum oxygen consumption rates (10–25 times resting levels) and FMRs, while ambush predators (i.e. felids) and diving marine mammals had aerobic capacities that were similar to or lower than sedentary domestic mammals of comparable size.

   The maximum energetic cost of performance for apex predators depended on whether the animals were hunters or the hunted. Escape responses were exceptionally costly for marine (narwhalMonodon monoceros) and terrestrial (mountain lionPuma concolor) locomotor specialists, as well as semi‐aquatic (polar bearUrsus maritimus) species; all showed a nearly two‐fold increase in peak energy expenditure when avoiding threats.

   As the duration and frequency of threats to wild species continue to grow, cumulative energetic costs are becoming more apparent. In view of this, attention to the energy demands of apex predators will provide vital predictive power to anticipate mismatches between a species' functional design and human‐induced pressures, and allow for the development of conservation strategies based on how species are built to survive.

   A freePlain Language Summarycan be found within the Supporting Information of this article.

    

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3. Mudskippers Modulate their Locomotor Kinematics when Moving on Deformable and Inclined Substrates

   https://doi.org/10.1093/icb/icac084  

   Naylor, Emily R. ; Kawano, Sandy M. ( June 2022 , Integrative and Comparative Biology)

   Many ecological factors influence animal movement, including properties of the media that they move on or through. Animals moving in terrestrial environments encounter conditions that can be challenging for generating propulsion and maintaining stability, such as inclines and deformable substrates that can cause slipping and sinking. In response, tetrapods tend to adopt a more crouched posture and lower their center of mass on inclines and increase the surface area of contact on deformable substrates, such as sand. Many amphibious fishes encounter the same challenges when moving on land, but how these finned animals modulate their locomotion with respect to different environmental conditions and how these modifications compare with those seen within tetrapods is relatively understudied. Mudskippers (Gobiidae: Oxudercinae) are a particularly noteworthy group of amphibious fishes in this context given that they navigate a wide range of environmental conditions, from flat mud to inclined mangrove trees. They use a unique form of terrestrial locomotion called “crutching,” where their pectoral fins synchronously lift and vault the front half of the body forward before landing on their pelvic fins, while the lower half of the body and tail are kept straight. However, recent work has shown that mudskippers modify some aspects of their locomotion when crutching on deformable surfaces, particularly those at an incline. For example, on inclined dry sand, mudskippers bent their bodies laterally and curled and extended their tails to potentially act as a secondary propulsor and/or anti-slip device. In order to gain a more comprehensive understanding of the functional diversity and context-dependency of mudskipper crutching, we compared their kinematics on different combinations of substrate types (solid, mud, and dry sand) and inclines (0°, 10°, and 20°). In addition to increasing lateral bending on deformable and inclined substrates, we found that mudskippers increased the relative contact time and contact area of their paired fins, while becoming more crouched, which are responses comparable to those seen in tetrapods and other amphibious fish. Mudskippers on these substrates also exhibited previously undocumented behaviors, such as extending and adpressing the distal portions of their pectoral fins more anteriorly, dorsoventrally bending their trunk, “belly-flopping” on sand, and “gripping” the mud substrate with their pectoral fin rays. Our study highlights potential compensatory mechanisms shared among vertebrates in terrestrial environments while also illustrating that locomotor flexibility and even novelty can emerge when animals are challenged with environmental variation.

    

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4. The contributions of individual traits to survival among terrestrial juvenile pond‐breeding salamanders

   https://doi.org/10.1111/1365-2435.13973  

   Messerman, Arianne F. ; Leal, Manuel ( December 2021 , Functional Ecology)

   Individual survival is influenced by interactions between local environmental conditions and an organism's morphological, behavioural and physiological traits. Studies examining the effects of individual phenotypes on survival under variable conditions are relatively rare among early transitional life stages, although the vital rates of these life stages can importantly influence population dynamics.

   We experimentally examined the effects of initial body mass, movement, standard metabolic rate (SMR) and respiratory surface area water loss (RSAWL) on survival in the transitional juvenile life stage of two biphasic amphibian species (Ambystoma maculatumandA. opacum) in a 7‐month mark–recapture study under semi‐natural conditions.

   Juveniles with a larger initial body mass, lower initial SMR and/or a lower tendency to change locations had a higher likelihood of known survival. In contrast, we found no significant effect of RSAWL on juvenile survival.

   The relationships between individual phenotypes and survival did not differ between species, but equivalent species‐specific survival rates may have been attributed to larger initial body sizes inA. maculatumand lower SMR inA. opacum.

   Our results illuminate the complex ways in which individual traits influence survival during the early transitional life stage of two ambystomatid species under varying abiotic conditions. More generally, our findings illustrate potential advantages of simultaneously examining multiple traits to evaluate survival.

   A freePlain Language Summarycan be found within the Supporting Information of this article.

    

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5. Periphytic algae decouple fungal activity from leaf litter decomposition via negative priming

   https://doi.org/10.1111/1365-2435.13235  

   Halvorson, Halvor M. ; Barry, Jacob R. ; Lodato, Matthew B. ; Findlay, Robert H. ; Francoeur, Steven N. ; Kuehn, Kevin A. ; Allen, ed., Daniel C. ( December 2018 , Functional Ecology)

   Well‐documented in terrestrial settings, priming effects describe stimulated heterotrophic microbial activity and decomposition of recalcitrant carbon by additions of labile carbon. In aquatic settings, algae produce labile exudates which may elicit priming during organic matter decomposition, yet the directions and mechanisms of aquatic priming effects remain poorly tested.

   We tested algal‐induced priming during decomposition of two leaf species of contrasting recalcitrance,Liriodendron tulipiferaandQuercus nigra, in experimental streams under light or dark conditions. We measured litter‐associated algal, bacterial, and fungal biomass and activity, stoichiometry, and litter decomposition rates over 43 days.

   Light increased algal biomass and production rates, in turn increasing bacterial abundance 141%–733% and fungal production rates 20%–157%. Incubations with a photosynthesis inhibitor established that algal activity directly stimulated fungal production rates in the short term.

   Algal‐stimulated fungal production rates on both leaf species were not coupled to long‐term increases in fungal biomass accrual or litter decomposition rates, which were 154%–157% and 164%–455% greater in the dark, respectively. The similar patterns on fast‐ vs. slow‐decomposingL. tulipiferaandQ. nigra, respectively, indicated that substrate recalcitrance may not mediate priming strength or direction.

   In this example of negative priming, periphytic algae decoupled fungal activity from decomposition, likely by providing labile carbon invested towards greater fungal growth and reproduction instead of recalcitrant carbon degradation. If common, algal‐induced negative priming could stimulate heterotrophy reliant on labile carbon yet suppress decomposition of recalcitrant carbon, modifying energy and nutrients available to upper trophic levels and enhancing organic carbon storage or export in well‐lit aquatic habitats.

   plain language summaryis available for this article.

    

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