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1. Body condition helps to explain metabolic rate variation in wolf spiders

   https://doi.org/10.1111/een.12741  

   Uiterwaal, Stella F. ; DeLong, John P. ( April 2019 , Ecological Entomology)

   1. Metabolism is the fundamental process that powers life. Understanding what drives metabolism is therefore critical to our understanding of the ecology and behaviour of organisms in nature.

   2. Metabolic rate generally scales with body size according to a power law. However, considerable unexplained variation in metabolic rate remains after accounting for body mass with scaling functions.

   3. We measured resting metabolic rates (oxygen consumption) of 227 field‐caught wolf spiders. Then, we tested for effects of body mass, species, and body condition on metabolic rate.

   4. Metabolic rate scales with body mass to the 0.85 power in these wolf spiders, and there are metabolic rate differences between species. After accounting for these factors, residual variation in metabolic rate is related to spider body condition (abdomen:cephalothorax ratio). Spiders with better body condition consume more oxygen.

   5. These results indicate that recent foraging history is an important determinant of metabolic rate, suggesting that although body mass and taxonomic identity are important, other factors can provide helpful insights into metabolic rate variation in ecological communities.

    

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2. Sympatry leads to reduced body condition in chickadees that occasionally hybridize

   https://doi.org/10.1002/ece3.8756  

   Grabenstein, Kathryn C. ; Otter, Ken A. ; Burg, Theresa M. ; Taylor, Scott A. ( April 2022 , Ecology and Evolution)

   Both abiotic and biotic drivers influence species distributions. Abiotic drivers such as climate have received considerable attention, even though biotic drivers such as hybridization often interact with abiotic drivers. We sought to explore the (1) costs of co‐occurrence for ecologically similar species that hybridize and (2) associations between ecological factors and condition to understand how abiotic and biotic factors influence species distributions. For two closely related and ecologically similar songbirds, black‐capped and mountain chickadees, we characterized body condition, as a proxy for fitness, using a 1358‐individual range‐wide dataset. We compared body condition in sympatry and allopatry with several abiotic and biotic factors using species‐specific generalized linear mixed models. We generated genomic data for a subset of 217 individuals to determine the extent of hybridization‐driven admixture in our dataset. Within this data subset, we found that ~11% of the chickadees had hybrid ancestry, and all hybrid individuals had typical black‐capped chickadee plumage. In the full dataset, we found that birds of both species, independent of demographic and abiotic factors, had significantly lower body condition when occurring in sympatry than birds in allopatry. This could be driven by either the inclusion of cryptic, likely poor condition, hybrids in our full dataset, competitive interactions in sympatry, or range edge effects. We are currently unable to discriminate between these mechanisms. Our findings have implications for mountain chickadees in particular, which will encounter more black‐capped chickadees as black‐capped chickadee ranges shift upslope and could lead to local declines in mountain chickadee populations.

    

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3. The relationship of body condition, superoxide dismutase, and superoxide with sperm performance

   https://doi.org/10.1093/beheco/arz086  

   Friesen, Christopher R. ; de Graaf, Simon P. ; Olsson, Mats ; Quinn, ed., John ( June 2019 , Behavioral Ecology)

   Sperm competition theory predicts a negative correlation between somatic investment and traits that aid in pre- and postcopulatory sexual selection. Sperm performance is critical for postcopulatory success but sperm are susceptible to damage by free radicals such as superoxide radicals generated during mitochondrial respiration (mtSOx). Males can ameliorate damage to spermatozoa by investing in the production of antioxidants, like superoxide dismutase (SOD), which may act as a mechanistic link to pre- and postcopulatory trade-offs. Some male Australian, color-polymorphic painted dragon lizards (Ctenophorus pictus) possess a yellow throat patch (bib) that females prefer over nonbibbed males and are also more likely to win male–male contests indicating that males with bibs may be better at monopolizing females. We tested whether the sperm performance in nonbibbed males was superior to that of bibbed males. We show that overall sperm performance was not different between the bib-morphs, however, higher mtSOx levels were negatively correlated with sperm performance in bibbed males, but not of nonbibbed males. Blood cell mtSOx levels are negatively correlated with SOD activity in the plasma in all males early in the breeding season but SOD was lower in bibbed males. Nonbibbed males maintain a positive correlation between body condition and SOD activity over time while bibbed males do not. Together, these data suggest physiological associations between body condition, SOD activity, and sperm performance are linked to the expression of a yellow gular patch, which may be related to intrinsic differences in the metabolism of bibbed versus nonbibbed males.

    

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4. Energy-twisted boundary condition and response in one-dimensional quantum many-body systems

   https://doi.org/10.1103/PhysRevB.106.155128  

   Nakai, Ryota ; Guo, Taozhi ; Ryu, Shinsei ( October 2022 , Physical Review B)
5. Body condition indices are better surrogates for lean mass and water content than for body fat content in an insect

   https://doi.org/10.1111/jzo.12909  

   Stahlschmidt, Z. R. ; Chang, E. ( June 2021 , Journal of Zoology)

   Ecologists and evolutionary biologists often use body condition indices (BCIs) to approximate an animal’s energetic state, which is important because energy (typically, lipid) reserves influence an animal’s investment into fitness‐related traits. A BCI’s utility is typically assessed by examining its ability to predict standardized fat content (fat mass in fresh mass after correcting for body size) across a population. Less frequently, a BCI is assessed as a response variable by comparing its sensitivity to a particular treatment or factor (e.g. food availability or age) relative to that of standardized fat content. We assessed five common BCIs (or equivalent) with these two approaches in the wing‐dimorphic sand field cricket (Gryllus firmusScudder 1902). All of the BCI methods significantly predicted standardized fat content in both sexes and wing morphs where the scaled mass index and Que ́telet’s index explained the most and least amount of variation, respectively. The BCIs and fat content were also similarly affected by adult age. However, BCIs were universally better proxies for lean mass and water content than for fat content. The relationships between BCIs and standardized lean mass and water content were stronger than those between BCIs and standardized fat content, and the effect sizes of age on BCIs were closer to that of lean mass relative to that of fat content. Thus, although BCIs reasonably predicted energy (fat) stores inG. firmus, they may be more indicative of lean mass or water content in insects. If BCIs are surrogates for protein and water storage, they may still approximate the storage of resources that fuel fitness‐related traits. Yet, future work is required to understand which body components (e.g. fat, protein or water) are most tightly linked to fitness, and whether traditional BCIs explain variation in fitness‐related body components across animal taxa.

    

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