Organisms have gravity: taking an organism-centered approach in experimental biology.

When you take the time to observe another organism, there is a sort of gravity that can take hold, a mixture of curiosity and connection that expands and strengthens the more you interact with that organism. Yet, in research, a connection with one's study organism can, at times, feel countercultural. Study organisms are sometimes viewed more as tools to conveniently study biological questions.

Amphibians Exhibit Extremely High Hydric Costs of Respiration.

Terrestrial environments pose many challenges to organisms, but perhaps one of the greatest is the need to breathe while maintaining water balance. Breathing air requires thin, moist respiratory surfaces, and thus the conditions necessary for gas exchange are also responsible for high rates of water loss that lead to desiccation. Across the diversity of terrestrial life, water loss acts as a universal cost of gas exchange and thus imposes limits on respiration.

Habitat and Respiratory Strategy Effects on Hypoxia Performance in Anuran Tadpoles.

A critical component of animal conservation in a changing world is an understanding of the physiological resilience of animals to different conditions. In many aquatic animals, hypoxia (low environmental oxygen levels) is a regular occurrence, but the likelihood and severity of hypoxia vary across habitats. Fast-flowing, stream-like habitats are never hypoxic, so long as flow is maintained.

Convergent Anuran Middle Ear Loss Lacks a Universal, Adaptive Explanation.

Introduction: Shared selection pressures often explain convergent trait loss, yet anurans (frogs and toads) have lost their middle ears at least 38 times with no obvious shared selection pressures unifying "earless" taxa. Anuran tympanic middle ear loss is especially perplexing because acoustic communication is dominant within Anura and tympanic middle ears enhance airborne hearing in most tetrapods.

Methods: Here, we use phylogenetic comparative methods to examine whether particular geographic ranges, microhabitats, activity patterns, or aspects of acoustic communication are associated with anuran tympanic middle ear loss.

Developmental Plasticity in Anurans: Meta-analysis Reveals Effects of Larval Environments on Size at Metamorphosis And Timing of Metamorphosis.

Many anuran amphibians (frogs and toads) rely on aquatic habitats during their larval stage. The quality of this environment can significantly impact lifetime fitness and population dynamics. Over 450 studies have been published on environmental impacts on anuran developmental plasticity, yet we lack a synthesis of these effects across different environments.

The continued importance of comparative auditory research to modern scientific discovery.

A rich history of comparative research in the auditory field has afforded a synthetic view of sound information processing by ears and brains. Some organisms have proven to be powerful models for human hearing due to fundamental similarities (e.g.

Ocular lens morphology is influenced by ecology and metamorphosis in frogs and toads.

The shape and relative size of an ocular lens affect the focal length of the eye, with consequences for visual acuity and sensitivity. Lenses are typically spherical in aquatic animals with camera-type eyes and axially flattened in terrestrial species to facilitate vision in optical media with different refractive indices. Frogs and toads (Amphibia: Anura) are ecologically diverse, with many species shifting from aquatic to terrestrial ecologies during metamorphosis.

Evolutionary rates and shape variation along the anuran vertebral column with attention to phylogeny, body size, and ecology.

The vertebral column is critical to a vertebrate species' flexibility and skeletal support, making vertebrae a clear target for selection. Anurans (frogs and toads) have a unique, truncated vertebral column that appears constrained to provide axial rigidity for efficient jumping. However, no study has examined how presacral vertebrae shape varies among anuran species at the macroevolutionary scale nor how intrinsic (developmental and phylogenetic) and extrinsic (ecological) factors may have influenced vertebrae shape evolution.

The mechanics of air breathing in African clawed frog tadpoles, Xenopus laevis (Anura: Pipidae).

Frog larvae (tadpoles) undergo many physiological, morphological and behavioral transformations throughout development before metamorphosing into their adult form. The surface tension of water prevents small tadpoles from breaching the surface to breathe air (including those of Xenopus laevis), forcing them to acquire air using a form of breathing called bubble sucking. With growth, tadpoles typically make a behavioral/biomechanical transition from bubble sucking to breaching.

Peripheral Auditory System Divergence Does Not Explain Species Differences in Call Preference.

Receiver sensory systems have long been cited as an important source of variation in mate preferences that could lead to signal diversification and behavioral isolation between lineages, with a general assumption that animals prefer the most conspicuous signals. The matched filter hypothesis posits that tuning of the frog peripheral auditory system matches dominant frequencies in advertisement calls used to attract mates. However, little work has characterized species with frequency modulation in their calls.

Unraveling the heritage of lost traits.

We synthesize ontogenetic work spanning the past century that show evolutionarily lost structures are rarely entirely absent from earlier developmental stages. We discuss morphological and genetic insights from developmental studies reveal about the evolution of trait loss and regain.

Whispers from vestigial nubbins: Arrested development provokes trait loss in toads.

Despite the use of acoustic communication, many species of toads (family Bufonidae) have lost parts of the tympanic middle ear, representing at least 12 independent evolutionary occurrences of trait loss. The comparative development of the tympanic middle ear in toads is poorly understood. Here, we compared middle ear development among two pairs of closely related toad species in the genera Atelopus and Rhinella that have (eared) or lack (earless) middle ear structures.

Two-hundred million years of anuran body-size evolution in relation to geography, ecology and life history.

Surprisingly, little is known about body-size evolution within the most diverse amphibian order, anurans (frogs and toads), despite known effects of body size on the physiological, ecological and life-history traits of animals more generally. Here, we examined anuran body-size evolution among 2,434 species with over 200 million years of shared evolutionary history. We found clade-specific evolutionary shifts to new body-size optima along with numerous independent transitions to gigantic and miniature body sizes, despite the upper limits of anuran body size remaining quite consistent throughout the fossil record.

Evolution of the Unique Anuran Pelvic and Hind limb Skeleton in Relation to Microhabitat, Locomotor Mode, and Jump Performance.

Anurans (frogs and toads) have a unique pelvic and hind limb skeleton among tetrapods. Although their distinct body plan is primarily associated with saltation, anuran species vary in their primary locomotor mode (e.g.

Anuran limbs reflect microhabitat and distal, later-developing bones are more evolutionarily labile.

Tetrapod limbs have been used as a model system to investigate how selective pressures and constraints shape morphological evolution. Anurans have had many independent transitions to various microhabitats, allowing us to dissect how these factors influence limb morphology. Furthermore, anurans provide a unique system to test the generality of developmental constraints proposed in mammals, namely that later-developing limb bones are under less constraint and show more variation.

Comment on "Amphibian fungal panzootic causes catastrophic and ongoing loss of biodiversity".

Scheele (Reports, 29 March 2019, p. 1459) bring needed attention to the effects of amphibian infectious disease. However, the data and methods implicating the disease chytridiomycosis in 501 amphibian species declines are deficient.

Invasive vegetation affects amphibian skin microbiota and body condition.

Invasive plants are major drivers of habitat modification and the scale of their impact is increasing globally as anthropogenic activities facilitate their spread. In California, an invasive plant genus of great concern is . leaves can alter soil chemistry and negatively affect underground macro- and microbial communities.

Larger Genomes Linked to Slower Development and Loss of Late-Developing Traits.

Genome size varies widely among organisms and is known to affect vertebrate development, morphology, and physiology. In amphibians, genome size is hypothesized to contribute to loss of late-forming structures, although this hypothesis has mainly been discussed in salamanders. Here we estimated genome size for 22 anuran species and combined this novel data set with existing genome size data for an additional 234 anuran species to determine whether larger genome size is associated with loss of a late-forming anuran sensory structure, the tympanic middle ear.

Prolonged middle ear development in Rhinella horribilis.

Despite the benefit of the tympanic middle ear to airborne hearing sensitivity, anurans range in how soon they develop functional middle ears after transitioning to life on land. Previous evidence suggested that bufonids had particularly slow middle ear developmental rates, but precise timelines have not yet been published for this family. Here, we provide the first age-verified middle ear development timeline for a true toad species (family Bufonidae).

Sensitive high-frequency hearing in earless and partially eared harlequin frogs ().

Harlequin frogs, genus , communicate at high frequencies despite most species lacking a complete tympanic middle ear that facilitates high-frequency hearing in most anurans and other tetrapods. Here, we tested whether are better at sensing high-frequency acoustic sound compared with other eared and earless species in the Bufonidae family, determined whether middle ear variation within affects hearing sensitivity and tested potential hearing mechanisms in We determined that at high frequencies (2000-4000 Hz), are 10-34 dB more sensitive than other earless bufonids but are relatively insensitive to mid-range frequencies (900-1500 Hz) compared with eared bufonids. Hearing among species is fairly consistent, evidence that the partial middle ears present in a subset of species do not convey a substantial hearing advantage.

Trait independence primes convergent trait loss.

The repeated, independent evolution of traits (convergent evolution) is often attributed to shared environmental selection pressures. However, developmental dependencies among traits can limit the phenotypic variation available to selection and bias evolutionary outcomes. Here, we determine how changes in developmentally correlated traits may impact convergent loss of the tympanic middle ear, a highly labile trait within toads that currently lack adaptive explanation.

Earless toads sense low frequencies but miss the high notes.

Sensory losses or reductions are frequently attributed to relaxed selection. However, anuran species have lost tympanic middle ears many times, despite anurans' use of acoustic communication and the benefit of middle ears for hearing airborne sound. Here we determine whether pre-existing alternative sensory pathways enable anurans lacking tympanic middle ears (termed earless anurans) to hear airborne sound as well as eared species or to better sense vibrations in the environment.

Better late than never: effective air-borne hearing of toads delayed by late maturation of the tympanic middle ear structures.

Most vertebrates have evolved a tympanic middle ear that enables effective hearing of airborne sound on land. Although inner ears develop during the tadpole stages of toads, tympanic middle ear structures are not complete until months after metamorphosis, potentially limiting the sensitivity of post-metamorphic juveniles to sounds in their environment. We tested the hearing of five species of toads to determine how delayed ear development impairs airborne auditory sensitivity.

The complex evolutionary history of the tympanic middle ear in frogs and toads (Anura).

Most anurans possess a tympanic middle ear (TME) that transmits sound waves to the inner ear; however, numerous species lack some or all TME components. To understand the evolution of these structures, we undertook a comprehensive assessment of their occurrence across anurans and performed ancestral character state reconstructions. Our analysis indicates that the TME was completely lost at least 38 independent times in Anura.

Morphology and putative function of the colon and cloaca of marine and freshwater snakes.

Among tetrapods, evidence for postrenal modification of the urine by the distal digestive tract (including the colon and cloaca) is highly variable. Birds and bladderless reptiles are of interest because the colon and cloaca represent the only sites from which water and ions can be reclaimed from the urine secreted by the kidney. For animals occupying desiccating environments (e.