Stevan James Arnold

Oregon State University | OSU · Department of Integrative Biology

An examination of courtship in salamanders helps resolve the puzzling problem of long-term evolutionary stasis in behavior. To address the companion issues of stasis and diversification, we summarize and synthesize courtship observations in Rhyacotriton and 13 genera of plethodontids. We use a modular analysis of courtship to identify conservative,...

abstract: Models of the Fisher‐Lande process (FLP) have been used successfully to explore many aspects of evolution by sexual selection. Despite this success, quantitative tests of these models using data from sexual radiations are rare. Consequently, we do not know whether realistic versions of the FLP can account for the extent and the rate of ev...

The evolutionary trajectories of complex traits are constrained by levels of genetic variation as well as genetic correlations among traits. As the ultimate source of all genetic variation is mutation, the distribution of mutations entering populations profoundly affects standing variation and genetic correlations. Here we use an individual-based s...

I explore the proposition that evolutionary biology is currently in the midst of its greatest period of synthesis. This period, which I call the Ongoing Synthesis, began in 1963 and continues at the present time. I use analysis of citations, conduct, and content to compare the Ongoing Synthesis to widely recognized periods of synthesis in the ninet...

We lack a comprehensive understanding of evolutionary pattern and process because short-term and long-term data have rarely been combined into a single analytical framework. Here we test alternative models of phenotypic evolution using a dataset of unprecedented size and temporal span (over 8,000 data points). The data are body-size measurements ta...

The adoption of a multivariate perspective of selection implies the existence of multivariate adaptive peaks and pervasive correlational selection that promotes coadaptation between traits. However, to test for the ubiquity of correlational selection in nature, we must first have a sense of how well can we estimate multivariate nonlinear selection...

Ecologists and evolutionary biologists are well aware that natural and sexual selection do not operate on traits in isolation, but instead act on combinations of traits. This long-recognized and pervasive phenomenon is known as multivariate selection, or—in the particular case where it favours correlations between interacting traits—correlational s...

Timothy Richard Halliday, 73, a zoologist, conservationist and artist, died on 10th April 2019, after a long illness caused by lymphoma, in Oxford, England. Tim Halliday was one of the fathers of the study of sexual selection and a leading light in amphibian conservation; he was also a talented illustrator and will be sorely missed by his family, f...

With the advent of next-generation sequencing approaches, the search for individual loci underlying local adaptation has become a major enterprise in evolutionary biology. One promising method to identify such loci is to examine genome-wide patterns of differentiation, using an FST-outlier approach. The effects of pleiotropy and epistasis on this a...

Traits that interact to perform an ecologically relevant function are expected to be under multivariate non-linear selection. Using the lower jaw morphology as a biomechanical model, we test the hypothesis that lower jaw bones of lizards are subjected to stabilizing and correlational selection, associated with mechanical advantage and maximum bite...

This essay describes my experiences as a graduate student in the Department of Zoology and in the Museum of Zoology at the University of Michigan from 1966-1972. During those years I metamorphosed from an undergraduate to a scientist capable of designing, executing, and publishing research projects. I also learned how to conduct experiments and sta...

Genetic variation plays a fundamental role in all models of evolution. For phenotypes composed of multiple quantitative traits, genetic variation is best quantified as additive genetic variances and covariances, as these values determine the rate and trajectory of evolution. Additive genetic variances and covariances are often summarized convenient...

This revised version of the figure was supposed to have been published with the manuscript but was overlooked by the editorial office.

Rapid evolution is a hallmark of proteins involved in reproduction. The protein courtship pheromones in plethodontid salamanders are classic examples of such rapidly evolving reproductive proteins, with male pheromones likely coevolving with female receptors to improve reproductive success. Over the past 66 million years of plethodontid evolution,...

Although many examples of behavioral homology have been documented in the vertebrate literature, these examples are skewed towards short timescales. In this article we report the case of complex behavior used by salamanders in sperm transfer that is at least 123–153 million years old. Rhyacotriton is an ancient salamander lineage with distant relat...

Comparative studies of salamander courtship have shed light on questions of broad biological and practical importance, such as the evolution of complex behaviors, molecular and behavioral foundations of prezygotic barriers, and the implementation of captive breeding programs. Unfortunately, most observations of courtship in plethodontid salamanders...

Comparative studies of salamander courtship have shed light on questions of broad biological and practical importance, such as the evolution of complex behaviors, molecular and behavioral foundations of prezygotic barriers, and the implementation of captive breeding programs. Unfortunately, most observations of courtship in plethodontid salamanders...

Pheromones are a diverse class of biological molecules that play critical roles in mediating social and sexual behaviours. In many systems, pheromones exist in complex mixtures, with the precise composition and ratios of the different components essential for bioactivity. The interactive effects of complex pheromone mixtures, however, have been min...

Predation pressure has often been postulated as a major selective force for the evolution of life histories, with high predation (particularly on small sizes) resulting in a fast-living strategy characterized by fast growth, early maturation, and short lifespan. However, due to the difficulty of assessing actual predation pressure in the wild, evid...

New theoretical and conceptual frameworks are required for evolutionary biology to capitalize on the wealth of data now becoming available from the study of genomes, phenotypes, and organisms - including humans - in their natural environments.

Training to sustain evolutionary biology. (DOCX)

An example of the enormous phylogenetic trees that soon will represent the norm in phylogenetic analyses. This is the consensus tree of the maximum likelihood phylogenies for 55,473 species of seed plants with the location of significant shifts in species diversification rates marked in red across the tree. Adapted from [4]. (TIF)

The Phenomobile, a remote sensing field buggy, and the Blimp, for remotely imaging an entire field. The Phenomobile integrates a variety of remote sensing technologies for measuring phenotypic variables on many plants simultaneously. The buggy straddles a plot and collects measurements of plant temperature, stress, chemistry, color, size and shape,...

Infrastructure needs and opportunities in evolutionary biology. (DOCX)

Long-term sperm storage may contribute to postcopulatory sexual selection because it enhances the commingling of sperm from different males within the female reproductive tract, which is the prerequisite for sperm competition. Long-term sperm storage and multiple paternity has been documented in snakes, but the identity of the last potential father...

Theoretical and empirical results demonstrate that the G-matrix, which summarizes additive genetic variances and covariances of quantitative traits, changes over time. Such evolution and fluctuation of the G-matrix could potentially have wide-ranging effects on phenotypic evolution. Nevertheless, no studies have yet addressed G-matrix stability and...

G-protein-coupled receptors are responsible for binding to chemosensory cues and initiating responses in vertebrate olfactory neurons. We investigated the genetic diversity and expression of one family of G-protein-coupled receptors in a terrestrial caudate amphibian (the red-legged salamander, Plethodon shermani). We used degenerate RT-PCR to isol...

Comparative evaluations of population dynamics in species with temporal and spatial variation in life-history traits are rare because they require long-term demographic time series from multiple populations. We present such an analysis using demographic data collected during the interval 1978-1996 for six populations of western terrestrial garter s...

Cytokines of the gp130 family are fundamental regulators of immune responses and signal through multimeric receptors to initiate intracellular second-messenger cascades. Here, we provide the first characterization of two full-length gp130 cytokine receptors from the cDNA of the red-legged salamander (Plethodon shermani). The first, gp130 (2745 bp),...

Multiple cues, across multiple sensory modalities, are involved in mate choice in a wide range of animal taxa. This multiplicity leads to the prediction that, in adaptive radiations, sexual isolation results from divergence in multiple dimensions. However, difficulties in directly measuring preferences and detecting multiple effects limit our abili...

Sexual communication in plethodontid salamanders is mediated by a proteinaceous pheromone that a male delivers to a female during courtship, boosting her receptivity. The pheromone consists of three proteins from three unrelated protein families. These proteins are among a small group of pheromones known to affect female receptivity in vertebrates....

The G-matrix occupies an important position in evolutionary biology both as a summary of the inheritance of quantitative traits and as an ingredient in predicting how those traits will respond to selection and drift. Consequently, the stability of G has an important bearing on the accuracy of predicted evolutionary trajectories. Furthermore, G shou...

This spreadsheet calculates the Krzanowski statistics discussed in Barker et al. 2010.

Courtship behavior in salamanders of the family Plethodontidae can last more than an hour. During courtship, males use stereotyped behaviors to repeatedly deliver a variety of proteinaceous pheromones to the female. These pheromones are produced and released from a specialized gland on the male's chin (the mental gland). Several pheromone component...

Quantitative genetic models of sexual selection have generally failed to provide a direct connection to speciation and to explore the consequences of finite population size. The connection to speciation has been indirect because the models have treated only the evolution of male and female traits and have stopped short of modeling the evolution of...

The G-matrix summarizes the inheritance of multiple, phenotypic traits. The stability and evolution of this matrix are important issues because they affect our ability to predict how the phenotypic traits evolve by selection and drift. Despite the centrality of these issues, comparative, experimental, and analytical approaches to understanding the...

The use of regression analysis has been instrumental in allowing evolutionary biologists to estimate the strength and mode of natural selection. Although directional and correlational selection gradients are equal to their corresponding regression coefficients, quadratic regression coefficients must be doubled to estimate stabilizing/disruptive sel...

Pheromones are important chemical signals for many vertebrates, particularly during reproductive interactions. In the terrestrial salamander Plethodon shermani, a male delivers proteinaceous pheromones to the female as part of their ritualistic courtship behavior. These pheromones increase the female's receptivity to mating, as shown by a reduction...

Despite the many triumphs of comparative biology during the past few decades, the field has remained strangely divorced from evolutionary genetics. In particular, comparative methods have failed to incorporate multivariate process models of microevolution that include genetic constraint in the form of the G matrix. Here we explore the insights that...

Plethodontid (lungless) salamanders have evolved an unusual pheromone delivery system in which the male courtship pheromone is applied to the skin of the female, apparently diffusing through the mucosal-rich epithelia into her superficial capillary system. In Desmognathus ocoee, a plethodontid salamander that uses the diffusion mode of pheromone de...

Populations of the terrestrial garter snake (Thamnophis elegans) around Eagle Lake in California exhibit dramatic ecotypic differentiation in life history, colouration and morphology across distances as small as a few kilometres. We assayed the role of selection in ecotypic differentiation in T. elegans using F(ST)-Q(ST) analysis and identified sel...

The soluble members of the three-finger protein superfamily all share a relatively simple 'three-finger' structure, yet perform radically different functions. Plethodontid modulating factor (PMF), a pheromone protein produced by the lungless salamander, Plethodon shermani, is a new and unusual member of this group. It affects female receptivity whe...

Evolvability is a key characteristic of any evolving system, and the concept of evolvability serves as a unifying theme in a wide range of disciplines related to evolutionary theory. The field of quantitative genetics provides a framework for the exploration of evolvability with the promise to produce insights of global importance. With respect to...

Evolutionary theory predicts that differential reproductive effort and rate of reproductive senescence will evolve under different rates of external mortality. We examine the evolutionary divergence of age-specific reproduction in two life-history ecotypes of the western terrestrial garter snake, Thamnophis elegans. We test for the signature of rep...

We tested the ability of six quantitative genetic models to explain the evolution of phenotypic means using an extensive database compiled by Gingerich. Our approach differs from past efforts in that we use explicit models of evolutionary process, with parameters estimated from contemporary populations, to analyze a large sample of divergence data...

Vertebrate pheromones that affect female receptivity have been documented only in salamanders. These courtship pheromones have been investigated most intensively in plethodontid salamanders. The source of the plethodontid courtship pheromone is the male's submandibular (mental) gland, which produces a multiprotein secretion. In earlier work with ou...

In this article we explore the evolutionary history of a functional complex at the molecular level in plethodontid salamanders. The complex consists of a proteinaceous courtship pheromone, a pheromone-producing gland on the male's chin, and a set of behaviors for delivering the pheromone to the female. Long-term evolutionary stasis is the defining...

Identifying ecological factors associated with population genetic differentiation is important for understanding microevolutionary processes and guiding the management of threatened populations. We identified ecological correlates of several population genetic parameters for three interacting species (two garter snakes and an anuran) that occupy a...

Despite widespread belief that selection molds thermoregulatory behaviors, direct evidence for fitness effects is extremely rare. We studied the effect of developmental temperature on embryo mortality in a viviparous snake. Seventy-four female Thamnophis elegans were maintained at one of nine constant temperatures during pregnancy (21–33 C). The du...