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Abstract Dispersal strategies are critical life history traits influencing bio-geographical, ecological, and evolutionary patterns and processes, including range expansion and contractions, abiotic and biotic interactions, and rates of speciation. Yet, dispersal strategies are challenging to study because they are complex suites of morphological, physiological, and behavioral traits. Thus, our understanding of how and why dispersal strategies evolve remains incomplete. Wing dimorphisms have evolved repeatedly within nearly every major insect order and are characterized by the co-occurrence of fully winged dispersing and short- or wingless non-dispersing morphs within species or populations, making them ideal model systems for studying the evolution of alternative dispersal strategies. Forty years ago, Derek Roff proposed that wing dimorphisms are a threshold trait that evolves as an intermediate step on the trajectory toward complete loss of flight, driven by the high physiological and life history costs of dispersal. Here, we synthesize recent mechanistic studies of wing-morph determination along with new phylogenetic reconstructions of wing dimorphism in the well-developed model Gryllus field crickets to update and refine our evolutionary hypotheses and identify critical areas for future inquiry. 

Abstract The field crickets, Gryllus pennsylvanicus and Gryllus firmus, share a well-studied hybrid zone in the eastern United States and are a key study system in speciation research. We report the genome assembly for each species using PacBio HiFi long-read sequencing data. We assembled the sequenced reads for G. pennsylvanicus into 2,924 scaffolds totaling 2.1 Gb and for G. firmus into 3,010 scaffolds totaling 2.0 Gb. Using a reference-based protocol, we achieved chromosome-level assemblies comprising 15 chromosomes for each species (totaling 1.86 and 1.84 Gb, respectively). The assemblies were nearly complete, with scaffold N50s of 115.64 and 119.52 Mb, respectively, and Benchmarking Universal Single-Copy Orthologs completeness score of 97%. We characterized structural variants (SVs) between the two species using both genome assemblies and HiFi sequencing data. The longest SV found was a potential inversion spanning 10.12 Mb along the X chromosome; this inversion may represent a key component of divergence between the two species. Both reference genomes will be essential resources for ongoing studies of the evolution of reproductive isolation and comparative studies across field crickets. 

ABSTRACT Stability selection is the process by which species are lost from a community due to a structural susceptibility to extinction. Stability selection is non‐adaptive because it does not lead to the evolution of traits that increase individual fitness. However, stability selection could still drive evolutionary change because the stability of populations is linked to heritable traits. Here we demonstrate both phenomena with a live predator–prey system. We show that the stability properties of a predator–prey pair vary with prey genetics, indicating the potential for differential extinction to influence the genotypic makeup of populations. Second, we show that the loss of unstable predator–prey pairs in subpopulations from the overall population can lead to trait evolution in the aggregate population, providing empirical support for the stability selection mechanism. Our results indicate that community‐level processes such as predator–prey interactions can generate eco‐evolutionary change at the population scale. 

Abstract Predator and prey traits are important determinants of the outcomes of trophic interactions. In turn, the outcomes of trophic interactions shape predator and prey trait evolution. How species' traits respond to selection from trophic interactions depends crucially on whether and how heritable species' traits are and their genetic correlations. Of the many traits influencing the outcomes of trophic interactions, body size and movement traits have emerged as key traits. Yet, how these traits shape and are shaped by trophic interactions is unclear, as few studies have simultaneously measured the impacts of these traits on the outcomes of trophic interactions, their heritability, and their correlations within the same system.We used outcrossed lines of the ciliate protistParamecium caudatumfrom natural populations to examine variation in morphology and movement behaviour, the heritability of that variation, and its effects onParameciumsusceptibility to predation by the copepodMacrocyclops albidus.We found that theParameciumlines exhibited heritable variation in body size and movement traits. In contrast to expectations from allometric relationships, body size and movement speed showed little covariance among clonal lines. The proportion ofParameciumconsumed by copepods was positively associated withParameciumbody size and velocity but with an interaction such that greater velocities led to greater predation risk for large body‐sized paramecia but did not alter predation risk for smaller paramecia. The proportion of paramecia consumed was not related to copepod body size. These patterns of predation risk and heritable trait variation in paramecia suggest that copepod predation may act as a selective force operating independently on movement and body size and generating the strongest selection against large, high‐velocity paramecia.Our results illustrate how ecology and genetics can shape potential natural selection on prey traits through the outcomes of trophic interactions. Further simultaneous measures of predation outcomes, traits, and their quantitative genetics will provide insights into the evolutionary ecology of species interactions and their eco‐evolutionary consequences. Read the freePlain Language Summaryfor this article on the Journal blog. 

Each fall, millions of monarch butterflies across the northern US and Canada migrate up to 4,000km to overwinter in specific mountain peaks in central Mexico. To track monarchs precisely and study their navigation, a monarch tracker must obtain daily localization of the butterfly as it progresses on its three-month journey. And, the tracker must perform this task while having a weight in the tens of milligrams (mg) and measuring a few millimeters (mm) in size to avoid interfering with the monarch's flight. This paper proposes mSAIL, 8 × 8 × 2.6mm and 62mg embedded system for monarch migration tracking, constructed using 8 prior custom-designed ICs providing solar energy harvesting, an ultra-low power processor, light/temperature sensors, power management, and a wireless transceiver, all integrated and 3D stacked on a micro PCB with an 8 × 8mm printed antenna. The proposed system is designed to record and compress light and temperature data during the migration path while harvesting solar energy for energy autonomy, and wirelessly transmit the data at the overwintering site in Mexico, from which the daily location of the butterfly can be estimated using a deep learning-based localization algorithm. A two-day trial experiment of mSAIL attached to a live butterfly in an outdoor botanical garden demonstrates the feasibility of individual butterfly localization and tracking. 

Abstract Environmental heterogeneity in temperate latitudes is expected to maintain seasonally plastic life‐history strategies that include the tuning of morphologies and metabolism that support overwintering. For species that have expanded their ranges into tropical latitudes, it is unclear the extent to which the capacity for plasticity will be maintained or will erode with disuse. The migratory generations of the North American (NA) monarch butterflyDanaus plexippuslead distinctly different lives from their summer generation NA parents and their tropical descendants living in Costa Rica (CR). NA migratory monarchs postpone reproduction, travel thousands of kilometers south to overwinter in Mexico, and subsist on little food for months. Whether recently dispersed populations of monarchs such as those in Costa Rica, which are no longer subject to selection imposed by migration, retain ancestral seasonal plasticity is unclear. To investigate the differences in seasonal plasticity, we reared the NA and CR monarchs in summer and autumn in Illinois, USA, and measured the seasonal reaction norms for aspects of morphology and metabolism related to flight. NA monarchs were seasonally plastic in forewing and thorax size, increasing wing area and thorax to body mass ratio in autumn. While CR monarchs increased thorax mass in autumn, they did not increase the area of the forewing. NA monarchs maintained similar resting and maximal flight metabolic rates across seasons. However, CR monarchs had elevated metabolic rates in autumn. Our findings suggest that the recent expansion of monarchs into habitats that support year‐round breeding may be accompanied by (1) the loss of some aspects of morphological plasticity as well as (2) the underlying physiological mechanisms that maintain metabolic homeostasis in the face of temperature heterogeneity. 

Each fall, millions of monarch butterflies across the U.S. and Canada migrate up to 4,000 km to overwinter in the same cluster of mountaintops in central Mexico. In spring, these migrants mate and remigrate northwards to repopulate their northern breeding territory over 2-4 partially overlapping generations. Because each migrant monarch completes only part of this round trip and does not return to the overwintering site, this navigational task cannot be learned from the prior generation. The number of monarchs completing the journey has dramatically declined in the past decades, coincident with the decreased availability of their milkweed host plant. The U.S., Mexico, and Canada have invested tremendous resources into monarch conservation efforts, including enacting specific policy initiatives, public outreach programs, and habitat protection and restoration projects. The US invested over $11 million between 2015-2017 alone [1]. Developing a tracking technology for monarch can be a key in these efforts, providing, for instance, detailed understanding of habitat use during migratory flight and dependence on weather conditions. Furthermore, it can significantly benefit animal research, and agricultural and environmental science. 

Abstract Strict maternal transmission of mitochondrial DNA (mtDNA) is hypothesized to permit the accumulation of mitochondrial variants that are deleterious to males but not females, a phenomenon called mother’s curse. However, direct evidence that mtDNA mutations exhibit such sexually antagonistic fitness effects is sparse. Male-specific mutational effects can occur when the physiological requirements of the mitochondria differ between the sexes. Such male-specific effects could potentially occur if sex-specific cell types or tissues have energy requirements that are differentially impacted by mutations affecting energy metabolism. Here we summarize findings from a model mitochondrial–nuclear incompatibility in the fruit fly Drosophila that demonstrates sex-biased effects, but with deleterious effects that are generally larger in females. We present new results showing that the mitochondrial–nuclear incompatibility does negatively affect male fertility, but only when males are developed at high temperatures. The temperature-dependent male sterility can be partially rescued by diet, suggesting an energetic basis. Finally, we discuss fruitful paths forward in understanding the physiological scope for sex-specific effects of mitochondrial mutations in the context of the recent discovery that many aspects of metabolism are sexually dimorphic and downstream of sex-determination pathways in Drosophila. A key parameter of these models that remains to be quantified is the fraction of mitochondrial mutations with truly male-limited fitness effects across extrinsic and intrinsic environments. Given the energy demands of reproduction in females, only a small fraction of the mitochondrial mutational spectrum may have the potential to contribute to mother’s curse in natural populations.