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Evolutionary correlations between chemical defense and protection by mutualist bodyguards have been long predicted, but tests of these patterns remain rare. We use a phylogenetic framework to test for evolutionary correlations indicative of trade-offs or synergisms between direct defense in the form of plant secondary metabolism and indirect defense in the form of leaf domatia, across 33 species in the wild grape genus, Vitis. We also performed a bioassay with a generalist herbivore to associate our chemical phenotypes with herbivore palatability. Finally, we tested whether defensive traits correlated with the average abiotic characteristics of each species’ contemporary range and whether these correlations were consistent with plant defense theory. We found a negative evolutionary correlation between domatia size and the diversity of secondary metabolites in Vitis leaf tissue across the genus, and also that leaves with a higher diversity and richness of secondary metabolites were less palatable to a generalist herbivore, consistent with a trade-off in chemical and mutualistic defense investment. Predictions from plant defense theory were not supported by associations between investment in defense phenotypes and abiotic variables. Our work demonstrates an evolutionary pattern indicative of a trade-off between indirect and direct defense strategies across the Vitis genus.

 

Rates of phenotypic evolution vary markedly across the tree of life, from the accelerated evolution apparent in adaptive radiations to the remarkable evolutionary stasis exhibited by so-called “living fossils.” Such rate variation has important consequences for large-scale evolutionary dynamics, generating vast disparities in phenotypic diversity across space, time, and taxa. Despite this, most methods for estimating trait evolution rates assume rates vary deterministically with respect to some variable of interest or change infrequently during a clade’s history. These assumptions may cause underfitting of trait evolution models and mislead hypothesis testing. Here, we develop a new trait evolution model that allows rates to vary gradually and stochastically across a clade. Further, we extend this model to accommodate generally decreasing or increasing rates over time, allowing for flexible modeling of “early/late bursts” of trait evolution. We implement a Bayesian method, termed “evolving rates” (evorates for short), to efficiently fit this model to comparative data. Through simulation, we demonstrate that evorates can reliably infer both how and in which lineages trait evolution rates varied during a clade’s history. We apply this method to body size evolution in cetaceans, recovering substantial support for an overall slowdown in body size evolution over time with recent bursts among some oceanic dolphins and relative stasis among beaked whales of the genus Mesoplodon. These results unify and expand on previous research, demonstrating the empirical utility of evorates. [cetacea; macroevolution; comparative methods; phenotypic diversity; disparity; early burst; late burst]

 

Linking interspecific interactions (e.g., mutualism, competition, predation, parasitism) to macroevolution (evolutionary change on deep timescales) is a key goal in biology. The role of species interactions in shaping macroevolutionary trajectories has been studied for centuries and remains a cutting-edge topic of current research. However, despite its deep historical roots, classic and current approaches to this topic are highly diverse. Here, we combine historical and contemporary perspectives on the study of ecological interactions in macroevolution, synthesizing ideas across eras to build a zoomed-out picture of the big questions at the nexus of ecology and macroevolution. We discuss the trajectory of this important and challenging field, dividing research into work done before the 1970s, research between 1970 and 2005, and work done since 2005. We argue that in response to long-standing questions in paleobiology, evidence accumulated to date has demonstrated that biotic interactions (including mutualism) can influence lineage diversification and trait evolution over macroevolutionary timescales, and we outline major open questions for future research in the field. 

Sexual and gender minorities face considerable inequities in society, including in science. In biology, course content provides opportunities to challenge harmful preconceptions about what is “natural” while avoiding the notion that anything found in nature is inherently good (the appeal-to-nature fallacy). We provide six principles for instructors to teach sex- and gender-related topics in postsecondary biology in a more inclusive and accurate manner: highlighting biological diversity early, presenting the social and historical context of science, using inclusive language, teaching the iterative process of science, presenting students with a diversity of role models, and developing a classroom culture of respect and inclusion. To illustrate these six principles, we review the many definitions of sex and demonstrate applying the principles to three example topics: sexual reproduction, sex determination or differentiation, and sexual selection. These principles provide a tangible starting place to create more scientifically accurate, engaging, and inclusive classrooms.

 

The seeds of many plant species produce mucilage on their surfaces that when wetted and dried, firmly adheres seeds to surfaces and substrates. Previous studies have demonstrated that seed anchorage to the ground can reduce seed predation, although only a few species have thus far been tested.

Here we investigated whether binding to the ground reduces seed removal by harvester antsPogonomyrmex subdentatus, an important granivore, for 53 species with mucilaginous seeds. We also explored functional traits that associate with seed removal risk to understand the ecological and evolutionary context of this granivory resistance trait.

Using a field cafeteria choice experiment, we compared harvester ant seed removal of wetted ground‐bound seeds to dry unbound control seeds for these 53 species. We developed a simple assay to score dislodgement force. We examined whether this force, seed mass and seed mucilage production explained the interspecific variation in protection that we observed in field seed removal. We integrated these experiments with a broad scale test of correlates of seed attachment using a previously published dataset of attachment potential of mucilaginous seeds for 432 species, examining correlations of attachment potential with 13 plant traits and the climate characteristics of the species' range.

Binding to the ground reduced seed removal in 42 of 53 species tested. The benefit increased with seed dislodgement force, which itself increased with mucilage production, but not with seed mass. In the larger dataset, shorter plant life span, higher temperature, more solar radiation, higher humidity, fewer wet days per year and higher seed density correlated positively with the odds of seed attachment. We also found that attachment potential showed a concave down quadratic relationship with latitude, peaking at roughly 30°. No strong evidence that any of the other six predictors correlated with attachment potential was found.

We demonstrate that protection from granivores is a widespread convergent function of seed mucilage and is associated with mucilage production. We highlight the need for increased mechanistic investigations into this common but poorly studied trait, particularly in relation to functional drivers of the broad patterns we found.

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