So far in this course we have dealt entirely with the evolution of characters that are controlled by simple Mendelian inheritance at a single locus. There are notes on the course website about gametic disequilibrium and how allele frequencies change at two loci simultaneously, but we didn’t discuss them. In every example we’ve considered we’ve imagined that we could understand something about evolution by examining the evolution of a single gene. That’s the domain of classical population genetics. For the next few weeks we’re going to be exploring a field that’s actually older than classical population genetics, although the approach we’ll be taking to it involves the use of population genetic machinery. If you know a little about the history of evolutionary biology, you may know that after the rediscovery of Mendel’s work in 1900 there was a heated debate between the “biometricians” (e.g., Galton and Pearson) and the “Mendelians” (e.g., de Vries, Correns, Bateson, and Morgan). Biometricians asserted that the really important variation in evolution didn’t follow Mendelian rules. Height, weight, skin color, and similar traits seemed to

Human biochemical genetics

The evidentiary basis of the currently accepted classification of living amphibians is discussed and shown not to warrant the degree of authority conferred on it by use and tradition. A new taxonomy of living amphibians is proposed to correct the deficiencies of the old one. This new taxonomy is based on the largest phylogenetic analysis of living Amphibia so far accomplished. We combined the comparative anatomical character evidence of Haas (2003) with DNA sequences from the mitochondrial transcription unit H1 (12S and 16S ribosomal RNA and tRNAValine genes, ≈ 2,400 bp of mitochondrial sequences) and the nuclear genes histone H3, rhodopsin, tyrosinase, and seven in absentia, and the large ribosomal subunit 28S (≈ 2,300 bp of nuclear sequences; ca. 1.8 million base pairs; x = 3.7 kb/terminal). The dataset includes 532 terminals sampled from 522 species representative of the global diversity of amphibians as well as seven of the closest living relatives of amphibians for outgroup comparisons. The...

https://bioone.org/journals/Bulletin-of-the-American-Museum-of-Natural-History/volume-2006/issue-297/0003-0090(2006)297[0001:TATOL]2.0.CO;2/THE-AMPHIBIAN-TREE-OF-LIFE/10.1206/0003-0090(2006)297[0001:TATOL]2.0.CO;2.pdf

The amphibian tree of life

Geckos have evolved one of the most versatile and effective adhesives known. The mechanism of dry adhesion in the millions of setae on the toes of geckos has been the focus of scientific study for over a century. We provide the first direct experimental evidence for dry adhesion of gecko setae by van der Waals forces, and reject the use of mechanisms relying on high surface polarity, including capillary adhesion. The toes of live Tokay geckos were highly hydrophobic, and adhered equally well to strongly hydrophobic and strongly hydrophilic, polarizable surfaces. Adhesion of a single isolated gecko seta was equally effective on the hydrophobic and hydrophilic surfaces of a microelectro-mechanical systems force sensor. A van der Waals mechanism implies that the remarkable adhesive properties of gecko setae are merely a result of the size and shape of the tips, and are not strongly affected by surface chemistry. Theory predicts greater adhesive forces simply from subdividing setae to increase surface density, and suggests a possible design principle underlying the repeated, convergent evolution of dry adhesive microstructures in gecko, anoles, skinks, and insects. Estimates using a standard adhesion model and our measured forces come remarkably close to predicting the tip size of Tokay gecko seta. We verified the dependence on size and not surface type by using physical models of setal tips nanofabricated from two different materials. Both artificial setal tips stuck as predicted and provide a path to manufacturing the first dry, adhesive microstructures.

/pdf/evidence-for-van-der-waals-adhesion-in-gecko-setae-4esa9k0pl1.pdf

Evidence for van der Waals adhesion in gecko setae

Synopsis. Selection can be measured in natural populations by the changes it causes in the means, variances and covariances of phenotypic characters. Furthermore the force of selection can be measured in conventional statistical terms that also play a key role in theoreticai equations for evolutionary change. The problem of measuring selection on morphological traits is simplified by breaking the task into two parts: measurement of the effects of morphological variation on performance and measurement of the effects of performance on fitness. The first part can be pursued in the laboratory but the second part is best accomplished in the field. The approach is illustrated with a hypothetical analysis of selection acting on the complex trophic morphology of snakes.

/pdf/morphology-performance-and-fitness-9qrmqlrsxg.pdf

Morphology, Performance and Fitness

Recent advances in integrative studies of locomotion have revealed several general principles. Energy storage and exchange mechanisms discovered in walking and running bipeds apply to multilegged locomotion and even to flying and swimming. Nonpropulsive lateral forces can be sizable, but they may benefit stability, maneuverability, or other criteria that become apparent in natural environments. Locomotor control systems combine rapid mechanical preflexes with multimodal sensory feedback and feedforward commands. Muscles have a surprising variety of functions in locomotion, serving as motors, brakes, springs, and struts. Integrative approaches reveal not only how each component within a locomotor system operates but how they function as a collective whole.

https://science.sciencemag.org/content/sci/288/5463/100.full.pdf

How Animals Move: An Integrative View

Superficially, anurans appear stereotyped in body shape, with short trunks and relatively long hindlimbs. This uniformity has been characterized by Inger (1967), who, borrowing from Gertrude Stein, wrote a frog is a frog is a frog. Because frogs preserve a generally similar body shape over a wide size range, they are an interesting group in which to study the relationship of locomotor function to body geometry and size. On land, jumping is the dominant locomotor mode of anurans. Previous studies of frog jumping (e.g., Wermel, 1934; Rand and Rand, 1966; Zug, 1972) have assumed that the principal function of this locomotor mode is to maximize distance between the animal and a potential predator, and have focused on the relationship between morphology and jump distance. There are, however, other parameters of jumping, such as quickness of movement (acceleration) that may be important and related to frog morphology. A correlated examination of allometry and locomotor behavior provides an approach for testing two alternative hypotheses of jump function: jump distance vs. quickness of movement.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1558-5646.1978.tb04598.x

Allometry and jumping in frogs: helping the twain to meet

Sticking ability in frogs was measured on a series of different substrates. Analysis of performance suggests that frogs use two sticking mechanisms: interlocking on rough surfaces and capillarity on smooth surfaces. There is a correlation between morphological specializations of the toe pad and sticking ability, but these morphological features are not unique to arboreal species. Terrestrial species that use leaves as resting sites during times of inactivity have many of the same morphological specializations and stick as well as the strictly arboreal species.

Toe pad morphology and mechanisms of sticking in frogs

The amphibian order Anura (frogs) is a major group whose origin appears related to the transformation of its locomotor system for saltation. However, the ilio-sacral articulation, a uniquely specialized part of the frog locomotor morphology, remains largely unstudied. Preliminary work reveals significant differences in the morphology of the ilio-sacral articulation among extant frogs and suggests that differences in types of articulation are correlated with different directional movements at the joint, with specific locomotor modes, and wim phylogenetic groupings.



SUMMARY

The morphology of the ilio-sacral articulation in frogs is correlated with different patterns of mobility at the joint and different locomotor behaviors. Overlain on diese basic differences in articulation among frogs is variation in other aspects of pelvic and vertebral morphology as well: muscle origin and insertion, urostyle fused or free, length and angle of the ilia, length of transverse processes of the pre-sacral vertebrae, and die articulation pattern of die presacral vertebrae. Obviously, the role of these additional morphologies must be established and integrated with the data on articular morphology before die form-function complex is completely understood. This paper is the first step towards that end, and work on other aspects of pelvic and vertebral morphology is underway.

The ilio‐sacral articulation in frogs: form and function

"Flying" frogs have evolved independently several times among anurans. In all cases flyers are distinguished from their nonflying arboreal relatives by a unique set of morphological features and behavioral postures. Using both live animal field tests and wind tunnel models, this study examines the importance of this characteristic morphology and limb position on five aerial performance variables: horizontal traveling distance, minimum glide speed, maximum time aloft, maneuverability, and stability. Comparison of relative performance between a model frog with a generalized nonflying morphology and limb position and a model frog with flying morphology and limb position reveals that the morphological and positional features associated with "flying" actually decrease horizontal traveling distance but improve maneuverability. This finding suggests that maneuverability rather than horizontal travel may be the key performance parameter in the evolution of "flying" frogs. More generally, this study illustrates that (1) derived morphological and postural features do not necessarily change a suite of performance variables in the same way, and (2) the performance consequences of postural shifts are a function of morphology. These findings indicate that the potential complexity of morphological and behavioral interactions in the evolution of new adaptive types is much greater than previously considered.

The interaction of behavioral and morphological change in the evolution of a novel locomotor type: "flying" frogs.

More than 95% of burrowing Anura dig hindfeet first into the soil, a pattern unique to frogs among terrestrial vertebrates. The postero-laterally placed hindlimbs and associated musculature of frogs are preadaptations for hindfeet digging. One fossorial, backwards burrower, Glyphoglossus molossus (Microhylidae), has morphological modifications of the hindlimb for positioning the spade-like metatarsal tubercle and for increasing the force of the lower leg during digging.



In contrast, in the headfirst burrower Hemisus marmoratus (Ranidae) there is extensive reorganization of the pectoral-cranial morphology compared to that: of a non-burrowing confamilial species. A model links the shifts in the pectoral morphology in Hemisus marmoratus to specific action patterns of headfirst: burrowing.



Finally, data on stomach contents, natural history and energy utilization of frog species are presented to demonstrate the interrelationships of distinct loco. motor patterns with specific feeding strategies.

Sharon B. Emerson

Papers

Allometry and jumping in frogs: helping the twain to meet

Toe pad morphology and mechanisms of sticking in frogs

The ilio‐sacral articulation in frogs: form and function

The interaction of behavioral and morphological change in the evolution of a novel locomotor type: "flying" frogs.

Burrowing in frogs