Is dietary or microhabitat specialization associated with environmental heterogeneity in horned lizards (Phrynosoma)?

DNA-based networks reveal the ecological determinants of plant-herbivore interactions along environmental gradients

Understanding the ecological rules structuring the organization of species interactions is a prerequisite to predicting how ecosystems respond to environmental changes. While the ecological determinants of single networks have been documented, it remains unclear whether network ecological rules are conserved along spatial and environmental gradients. To address this gap, we reconstructed 48 plant-herbivore interaction networks along six elevation gradients in the Central European Alps in Switzerland, using DNA metabarcoding on orthoptera faeces. We developed hypotheses on the ecological mechanisms expected to structure interaction networks, based on plant phylogeny, plant abundance, leaf toughness, leaf nitrogen content and plant metabolomics. We show that plant phylogenetic relationships and species abundance have the greatest explanatory power regarding the structure of the ecological networks. Moreover, we found that leaf nitrogen content is a key determinant of interactions in warmer environments, while phenolic compounds and tannins are more important in colder environments, suggesting that determinants of species interactions can shift along environmental gradients. With this work, we propose an approach to study the mechanisms that structure the way species interact with each other between bioregions and ecosystems.

Cellular and whole-organism effects of prolonged versus acute heat stress in a montane, desert lizard

Global climate change involves both prolonged periods of higher-than-normal temperatures and short but extreme heat waves. Both types of temperature increases are likely to be detrimental to ectotherms, and even if such temperature increases do not cause mortality directly, compensating for such temperature increases will likely entail costs to organisms. We tested the effects of prolonged periods of higher-than-average temperatures and short-term, acute heat stress in wild populations of greater short-horned lizards (Phrynosoma hernandesi), a temperate, montane lizard of the Colorado Plateau, UT, USA. We transplanted one group of lizards from a high- to a low-elevation site, exposing them to a prolonged period of warmer temperatures. These lizards, exposed to prolonged periods of higher-than-average temperatures, experienced no change in sprint speed, endurance, or heat shock protein (HSP) production after treatment compared to baseline levels; however, they had lower water content after the transplant to a warmer climate compared to before the transplant. We exposed a second group of lizards to acute heat stress by exposing them to thermally stressful temperatures for 4 h. These lizards, exposed to a short period of acute heat stress, had no change in endurance, water content, or HSP production following acute heat stress; however, lizards exposed to acute heat stress had slower sprint speeds than control lizards. Our results demonstrate that both prolonged temperature increases and acute heat stress, each of which are predicted to occur with climate change, had different cellular and/or whole organismal-level effects on lizards.