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A number of studies have focused on the form and function of intracranial movements in lizards (cranial kinesis), but rarely has the anatomy and potential movement of individual joints been evaluated. Frazetta (1983) suggested that cranial kinesis is an adaptation for precise and simultaneous contact of upper and lower jaws during prey capture. According to Schwenk (2000), cranial kinesis should therefore be restricted to lizards employing jaw-prehension (Scleroglossa) and absent in lingual feeders (Iguania). Limited functional observations are consistent with this hypothesis. We studied the microscopic anatomy of the kinetic joints in iguanian and scleroglossan lizards and found that all five intracranial joints we examined were capable of movement in scleroglossan lizards, but only two of five joints showed potential for kinesis in iguanian species. Although more species need to be sampled, these data offer preliminary support to the Frazzetta and Schwenk hypotheses.

Predator-prey evolutionary arms races are rarer than supposed owing to asymmetry in the strength of selection, and the sensitivity of selection patterns to population dynamics and adaptive trade-offs. Two factors predator dietary specialization and dangerous prey are believed to increase the likelihood of an arms race by promoting balance and reciprocity in predator-prey selection. We present evidence suggesting that horned lizards (Phrynosoma) and their prey of harvester ants (Pogonomyrmex) are involved in such a race: the lizards are ant-specialists that favor Pogonomyrmex species endowed with formidable defensive weapons, including an exceptionally venomous sting and a powerful bite weapons believed to have evolved in response to horned lizard predation. Indeed, one commonly eaten prey species, Pogonmyrmex maricopa, possesses the most toxic venom of any invertebrate known. Nevertheless, horned lizards consume dozens of these noxious ants daily without harm, capturing them with the soft tissues of the tongue and swallowing them directly with neither biting nor chewing. High speed films of horned lizards feeding, gross and microscopic anatomy of the mouth and pharynx, and stomach content analyses of wild specimens show that horned lizards incapacitate prey immediately upon capture by binding them with mucus secreted by long papillae within the pharynx. Comparative studies of closely related lizards demonstrate that morphological and behavioral components of mucusbinding are uniquely derived in Phrynosoma, suggesting an adaptive response to the ants weaponry consistent with a predatorprey arms race.

As organisms transition between different environments, they must do more than simply move through that transition and those environments. Changes in the environment must be detected via the senses. The types of sensory information and the mechanisms of collecting that information may also change as an individual moves through different environments. We use tongue-flicking in northern water snakes, Nerodia sipedon, to examine the mechanics of sensory behavior as snakes move from terrestrial to aquatic habitats. A combination of high-speed video and mesocosm experiment revealed that water snakes will alter the mechanics of tongue-flicking in the context of their environment. Tongue-flicks on land are distinctive, with multiple oscillations, large protrusion distance, and high velocities. Comparatively, tongue-flicks under water are much shorter events, with reduced protrusion and fewer oscillations. At the surface of the water, in the presence of potential anuran prey, water snakes will tap the tips of the tongue on the surface of the water, without undergoing the full oscillations observed on land or underwater. We attribute the differences in the aerial and underwater tongue-flicks to trade-offs in the physical and chemical properties of the environment. The surface tapping behavior we observed is likely snakes altering their behavior to maximize the encounter and collection of frog-specific chemical cues, which are known to travel on the water's surface. Given the ecological transitions and distinctive biogeographical patterns rooted in water snake ecology, there are likely more examples of changing sensory mechanics to be discovered upon further investigation., (© The Author(s) 2022. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology.)

Hybridization and introgression are recognized as an important source of variation that influence adaptive processes; both phenomena are frequent in the genus Daphnia, a keystone zooplankton taxon in freshwater ecosystems that comprises several species complexes. To investigate genome-wide consequences of introgression between species, we provide here the first high-quality genome assembly for a member of the Daphnia longispina species complex, Daphnia galeata. We further resequenced 49 whole genomes of three species of the complex and their interspecific hybrids both from genotypes sampled in the water column and from single resting eggs extracted from sediment cores. Populations from habitats with diverse ecological conditions offered an opportunity to study the dynamics of hybridization linked to ecological changes and revealed a high prevalence of hybrids. Using phylogenetic and population genomic approaches, we provide first insights into the intra- and interspecific genome-wide variability in this species complex and identify regions of high divergence. Finally, we assess the length of ancestry tracts in hybrids to characterize introgression patterns across the genome. Our analyses uncover a complex history of hybridization and introgression reflecting multiple generations of hybridization and backcrossing in the Daphnia longispina species complex. Overall, this study and the new resources presented here pave the way for a better understanding of ancient and contemporary gene flow in the species complex and facilitate future studies on resting egg banks accumulating in lake sediment., (© The Author(s) 2021. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.)

A renaissance in organismal biology has been sparked by recent conceptual, theoretical, methodological, and computational advances in the life sciences, along with an unprecedented interdisciplinary integration with Mathematics, Engineering, and the physical sciences. Despite a decades-long trend toward reductionist approaches to biological problems, it is increasingly recognized that whole organisms play a central role in organizing and interpreting information from across the biological spectrum. Organisms represent the nexus where sub- and supra-organismal processes meet, and it is the performance of organisms within the environment that provides the material for natural selection. Here, we identify five "grand challenges" for future research in organismal biology. It is intended that these challenges will spark further discussion in the broader community and identify future research priorities, opportunities, and directions, which will ultimately help to guide the allocation of support for and training in organismal biology.

Three coexisting Daphnia species belonging to the D. longispina group (D. galeata, D. hyalina, and D. cucullata) form species-hybrid complexes by producing interspecific hybrids in several lakes in Germany and The Netherlands. To evaluate the genetic consequences of interspecific hybridization, I studied the patterns of mitochondrial DNA (mtDNA) sequence variation. The directionality of interspecific hybridization and divergence of hybrids from parental species was tested, using the DNA sequences of a segment of mtDNA. Via the polymerase chain reaction, it was possible to investigate single animals and even single resting eggs. A species-specific marker was established, using restriction patterns of amplified cytochrome b segments. mtDNA genotypes of hybrids revealed unidirectional mitochondrial gene flow for two hybrids, which were investigated by using multiple clones. No evidence for introgression of mtDNA was found. On the basis of a phylogenetic analysis, the species exhibit considerable distinctness, whereas differences between clones within species and between hybrids and maternal species tend to be very low. These results indicate a recent origin of hybrids and suggest that the radiation of the D. longispina group occurred > 5 Mya.