Digest: Life history evolution in Darwin's dream ponds*

Can variation in sex‐specific parental investment lead to sexual dimorphism in immune response? Keller et al. (2018) measured immune cell parameters, expression of candidate genes, and composition of buccal microbiota in mouthbrooding cichlid species from Lake Tanganyika that show either maternal or biparental care. They found that maternal mouthbrooding species have increased sexual dimorphism in immune parameters, while biparental mouthbrooders exhibit an upregulated adaptive immune response, suggesting resource allocation shifts between parental investment and the immune system.     

Digest: Sexual selection and evolution of cognition in seed beetles*

Sexual selection is hypothesized to be a driver of the evolution of cognitive ability. Baur et al. manipulated the strength of sexual selection in seed beetles subjected to enforced mating systems over 35 generations, and then quantified cognitive ability in males and females. Stronger sexual selection led to increased cognitive ability in males, but not females, when each performed a task requiring spatial orientation. Standing genetic variation, presumably maintained by balancing selection, is thought to have facilitated this rapid, sex‐specific evolution.     

Digest: Microhabitat use and developmental timing shape anuran limb evolution*

Do frog limb shapes reflect microhabitat use against the backdrop of shared ancestry, body size variation, and developmental constraints? Stepanova and Womack found that when phylogeny and body size are controlled, microhabitat use is a key factor in explaining anuran limb evolution. The shape of distal limb elements in anuran limbs also evolves at a higher rate than proximal elements, suggesting that a relaxation of developmental constraints in distal elements may be shared across tetrapod limb development.     

Digest: Floral evolution through the lens of the community context*

How do emergent properties of natural plant communities affect floral evolution? In this issue, Eisen et al. explored this question by studying selection on floral traits in natural communities of Clarkia species. They found that two community properties, namely congeneric species richness and floral density (of conspecifics and heterospecifics), influenced the patterns of selection, although not through the expected means of pollinator-mediated selection. Instead, the authors suggest that additional factors like competition and facilitation between plants are responsible. The results support the hypothesis that, beside pollinators, other factors of the community context can also determine floral evolution.     

Digest: The evolution of sexual imprinting as an assortative mating mechanism*

In this issue, Yeh et al. (2018) investigated whether sexual imprinting could act as an assortative mating mechanism, reducing hybridization and increasing premating isolation. While they indeed find that imprinting leads to assortative mating and reduced hybridization, the strength at which imprinting evolves is usually intermediate, because it is counterbalanced by the costs of imprinting and the benefits of adaptive hybridization. Thus, while sexual imprinting can act as an assortative mating mechanism, it is often not the sole element of female mate choice.     

Digest: Female‐limited X chromosome evolution in Drosophila melanogaster*

Sexual dimorphism can cause sexual antagonism of phenotypic traits. Lund‐Hansen and colleagues (2020) investigated female‐limited X chromosome evolution in Drosophila melanogaster using forced matrilineal inheritance. Body size and developmental time evolved toward their female optima, but reproductive fitness and locomotion remained unchanged. These findings imply that some sexually antagonized loci may be distributed across the genome and that some phenotypes may have already reached their female optima in nature.     

Digest: The role of intra- and interspecific behavior in habitat use evolution*

Cycloramphus and Zachaenus Neotropical frogs breed in rocky streams (saxicolous breeding) or in terrestrial environments. In their recent work, de Sá et al. investigate shifts between these habitats and the impact that these shifts have on body size and sexual size dimorphism (SSD). The researchers found that terrestrial breeding evolved on three occasions. Additionally, there was an association between habitat and SSD, with decreases in male body size correlating with shifts toward terrestrial breeding.     

Digest: Differentiating Fisherian sexual selection dynamics between haploids and diploids*

Female mate preference for males displaying costly traits is a puzzling phenomenon found in nature. Fisher was the first to propose a formal model describing this paradoxical system of sexual selection. Despite the many models constructed from his theory, much remains unknown about its mechanics, especially in different genetic settings. Through simulations, Veller et al. compared population dynamics between haploids and diploids and found that Fisherian sexual selection acts differently on diploids compared to haploids due to linkage mechanisms.     

Digest: Disentangled bank: Less diverse urban environments modify the shape and magnitude of natural selection*

Urbanization provides a natural experiment for biologists to test how anthropogenic environmental change affects evolution in real time and frames predictions for anticipated evolutionary outcomes worldwide. Start et al. ( 2018 ) found that changes in species interactions (herbivore abundance and avian predation) along urbanization gradients predictably alter the shape and magnitude of natural selection on gall size (a defensive trait), suggesting that rapid global environmental change can alter species interactions, which may have foreseeable evolutionary consequences.     

Digest: Structuring interactions in Streptomyces*

For bacteria growing in colonies, spatial structure can allow maintenance of costly traits such as the production of antibiotics. Using spatially structured environments, Westhoff et al. examined the benefits of streptomycin production for the bacterium Streptomyces griseus in competition with a streptomycin-susceptible strain. Streptomyces griseus outcompeted susceptible competitors, but the benefit of its antibiotic decreased as competitor resistance to streptomycin increased. Spatial structure also increased the ability of S. griseus to invade susceptible competitor populations from low starting densities. These results demonstrate that spatially structured environments can both provide and amplify benefits of antibiotics to antibiotic-producing bacteria on a microbial scale.     

Digest: Ecology and signal structure drive the evolution of synchronous displays in fiddler crabs*

Behaviors are often influenced by both ecology and genetics. Perez et al. tested whether display patterns and the ecology of different species of fiddler crabs influence synchronous waving and whether this a phylogenetic phenomenon. They found that there was no phylogenetic signal in wave display synchronicity, and suggested that signal structure, microhabitat complexity, and different mating systems might instead be the cause. These results support the non-phylogenetic nature of synchronicity that can be observed across animal taxa.     

Digest: Ecomorphological convergence across the Atlantic*

Did the remarkable helicopter damselflies (family Pseudostigmatidae) evolve their unique feeding and oviposition behaviors independently on two continents? In this issue, Toussaint et al. use molecular phylogenetic approaches to provide convincing evidence that these “forest giants” are in fact an example of ecomorphological convergence across the Atlantic Ocean.     

Digest: Insights into diatoms diversity patterns*

Biological diversity is not equally distributed across the Tree of Life, and the causes are not yet well defined. Nakov et al. investigate this by exploring the reasons behind diatoms’ uneven species richness across different environments. Simple traits are not enough to fully understand the variation in diatoms’ species richness. Therefore, investigating the role of habitat may improve our understanding of biodiversity patterns.     

Digest: Local adaptation at close quarters*

Although the theory of how gene flow and genetic drift interact with local adaptation is well understood, few empirical studies have examined this process. Hämälä et al. (2018) present evidence that adaptive divergence between populations of Arabidopsis lyrata can persist in the face of relatively high levels of gene flow and drift. Maintaining divergence despite gene flow and drift has important implications for understanding adaptive responses of populations in response to human‐driven environmental change.