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1. Replicated radiations in the South American marsh pitcher plants ( Heliamphora ) lead to convergent carnivorous trap morphologies

   https://doi.org/10.1002/ajb2.16230  

   Liu, Sukuan ; Smith, Stacey D. ( October 2023 , American Journal of Botany)

   The evolution of carnivorous pitcher traps across multiple angiosperm lineages represents a classic example of morphological convergence. Nevertheless, no comparative study to‐date has examined pitcher evolution from a quantitative morphometric perspective.

   In the present study, we used comparative morphometric approaches to quantify the shape space occupied byHeliamphorapitchers and to trace evolutionary trajectories through this space to examine patterns of divergence and convergence within the genus. We also investigated pitcher development, and, how the packing of pitchers is affected by crowding, a common condition in their natural environments.

   Our results showed thatHeliamphorapitchers have diverged along three main axes in morphospace: (1) pitcher curvature; (2) nectar spoon elaboration; and (3) pitcher stoutness. Both curvature and stoutness are correlated with pitcher size, suggesting structural constraints in pitcher morphological evolution. Among the four traits (curvature, spoon elaboration, stoutness, and size), all but curvature lacked phylogenetic signal and showed marked convergence across the phylogeny. We also observed tighter packing of pitchers in crowded conditions, and this effect was most pronounced in curved, slender pitchers.

   Overall, our study demonstrates that diversification and convergent evolution of carnivory‐related traits extends to finer evolutionary timescales, reinforcing the notion that ecological specialization may not necessarily be an evolutionary dead end.

    

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2. Conspicuous coloration of toxin‐resistant predators implicates additional trophic interactions in a predator–prey arms race

   https://doi.org/10.1111/mec.16772  

   Hague, Michael T. J. ; Miller, Lauren E. ; Stokes, Amber N. ; Feldman, Chris R. ; Brodie, Jr, Edmund D. ; Brodie, III, Edmund D. ( November 2022 , Molecular Ecology)

   Antagonistic coevolution between natural enemies can produce highly exaggerated traits, such as prey toxins and predator resistance. This reciprocal process of adaptation and counter‐adaptation may also open doors to other evolutionary novelties not directly involved in the phenotypic interface of coevolution. We tested the hypothesis that predator–prey coevolution coincided with the evolution of conspicuous coloration on resistant predators that retain prey toxins. In western North America, common garter snakes (Thamnophis sirtalis) have evolved extreme resistance to tetrodotoxin (TTX) in the coevolutionary arms race with their deadly prey, Pacific newts (Tarichaspp.). TTX‐resistant snakes can retain large amounts of ingested TTX, which could serve as a deterrent against the snakes' own predators if TTX toxicity and resistance are coupled with a conspicuous warning signal. We evaluated whether arms race escalation covaries with bright red coloration in snake populations across the geographic mosaic of coevolution. Snake colour variation departs from the neutral expectations of population genetic structure and covaries with escalating clines of newt TTX and snake resistance at two coevolutionary hotspots. In the Pacific Northwest, bright red coloration fits an expected pattern of an aposematic warning to avian predators: TTX‐resistant snakes that consume highly toxic newts also have relatively large, reddish‐orange dorsal blotches. Snake coloration also seems to have evolved with the arms race in California, but overall patterns are less intuitively consistent with aposematism. These results suggest that interactions with additional trophic levels can generate novel traits as a cascading consequence of arms race coevolution across the geographic mosaic.

    

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3. Diatom β‐diversity in streams increases with spatial scale and decreases with nutrient enrichment across regional to sub‐continental scales

   https://doi.org/10.1111/jbi.13517  

   Leboucher, Thibault ; Budnick, William R. ; Passy, Sophia I. ; Boutry, Sébastien ; Jamoneau, Aurélien ; Soininen, Janne ; Vyverman, Wim ; Tison‐Rosebery, Juliette ( February 2019 , Journal of Biogeography)

   To quantify the relative contributions of local community assembly processes versus γ‐diversity to β‐diversity, and to assess how spatial scale and anthropogenic disturbance (i.e. nutrient enrichment) interact to dictate which driver dominates.

   France and the United States.

   1993–2011.

   Freshwater stream diatoms.

   β‐diversity along a nutrient enrichment gradient was examined across multiple spatial scales. β‐diversity was estimated using multi‐site Sørensen dissimilarity. We assessed the relative importance of specialists versus generalists using Friedley coefficient, and the contribution of local community assembly versus γ‐diversity to β‐diversity across spatial scales, with a null model. Finally, we estimated the response of β‐diversity to environmental and spatial factors by testing the correlations between community, environmental and geographical distance matrices with partial Mantel tests.

   β‐diversity generally increased with spatial scale but the rate of increase depended on nutrient enrichment level. β‐diversity decreased significantly with increasing nutrient enrichment level due to the loss of specialist species. Local assembly was an important driver of β‐diversity especially under low nutrient enrichment. Significant partial Mantel correlations were observed between diatom β‐diversity and pure environmental distances under these conditions, highlighting the role of species sorting in local assembly processes. Conversely, in heavily enriched sites, only spatial distances were significantly correlated with β‐diversity, which indicated a substantial role of dispersal processes.

   Nutrient concentration mediated the expected increase in β‐diversity with spatial scales. Across spatial scales, β‐diversity was more influenced by local assembly processes rather than by γ‐diversity. Nutrient enrichment was associated with an overall decline in diatom β‐diversity and a shift in assembly processes from species sorting to dispersal, notably due to the elimination of some specialists and their subsequent replacement by generalists.

    

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4. Differential survival and dispersal of avian feather mites with contrasting host specificities

   https://doi.org/10.1111/een.13176  

   Matthews, Alix E. ; Barnett, Cody J. ; Boves, Than J. ( June 2022 , Ecological Entomology)

   Host specificity is a fundamental life history trait of symbionts and exists on a broad continuum from symbionts that are specific to one or a few hosts (host specialists), to those associated with multiple different host species (host generalists). However, the biological mechanisms underlying the complexity and wide variation in symbiont host specificity are poorly understood from both the symbiont and host perspectives across many symbiotic systems.

   Feather mites are common avian symbionts that vary in their host specificity from extreme host generalists to host specialists, even among species within the same genus.

   Here, we measured and compared survival probability and rate of dispersal to determine how these traits differ between two species of feather mites in the same genus: one host generalist associated with 17 host species (Amerodectes ischyros) and one host specialist with only one known host (A. protonotaria).

   We initially predicted that the host generalist would live longer and disperse more rapidly but discovered that while the host generalist mite survived longer, the host specialist mite dispersed more quickly.

   The differing environmental and ecological conditions in which the hosts of these mites are associated may explain the survival and dispersal patterns we uncovered, as differential microclimates may have led to different selective pressures on each species of mite. We also noted mite behavioural observations and suggest experiments to extend our understanding of feather mite ecology and evolution.

    

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5. Latitudinal variation in plant defence against herbivory in a marine foundation species does not follow a linear pattern: The importance of resource availability

   https://doi.org/10.1111/geb.13217  

   Hernán, Gema ; Ortega, María J. ; Henderson, Jeremy ; Alós, Josep ; Boyer, Katharyn ; Cimon, Stephanie ; Combes, Vincent ; Cusson, Mathieu ; Hereu, Clara M. ; Hessing‐Lewis, Margot ; et al ( November 2020 , Global Ecology and Biogeography)

   Studies on latitudinal patterns in plant defence have traditionally overlooked the potential effect that resource availability may have in shaping plant defence. Likewise, latitudinal patterns of tolerance traits have rarely been studied, yet they can be a critical component of plant defence. Therefore, the aim of our study was to examine latitudinal variation in the production of tolerance and resistance traits against herbivory along a latitudinal range and a natural gradient of resource availability from upwelling conditions.

   North America (Canada, USA, Mexico).

   Summer months of 2015.

   The seagrassZostera marina.

   We conducted experiments simulating macroherbivore (e.g., bird, fish) damage on the seagrassZ. marinaat 10 sites across the Eastern Pacific coast (Canada–Mexico) and Quebec and analysed several traits related to resistance and tolerance strategies against herbivory. In addition, we examined the effects of potential seagrass changes in defence strategies by performing a series of feeding experiments with mesoherbivores in a subset of sites.

   We found that eelgrass resistance defences did not follow a linear latitudinal pattern but rather followed a bell‐shaped curve which correlated with bottom‐up control. In sites with higher nutrient availability, plants allocated resources to tolerance strategies and had lower resistance traits. Furthermore, seagrasses did not respond linearly to increased herbivory pressure; while they tolerated moderate levels of herbivory, they underwent a significant reduction in tolerance and resistance under high herbivory levels, which also made them more susceptible to consumers in feeding experiments.

   Our results highlight the importance that nutrient availability has in shaping latitudinal patterns of plant defence against herbivory and show how these defences may not respond linearly to increased herbivory pressure in seagrasses.

    

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