CHOLESTEROL AS AN EVOLUTIONARY RESPONSE TO LIVING WITH OXYGEN

Although often considered in a negative light, cholesterol is an essential molecule with unusually diverse functions. Cholesterol and related sterols (ergosterol in yeast, phytosterols in plants) is considered a hallmark of eukaryotes, and may even have triggered the evolution of multicellular organisms. Synthesis of cholesterol is an extremely oxygen‐intensive process and requires sufficient terrestrial oxygen to proceed. In turn, several lines of evidence support the argument that cholesterol evolved at least in part as an adaptation to the hazards of oxygen. This evolutionary perspective usefully informs medical research on cholesterol to address health‐related issues, as illustrated by examples drawn from three prominent human diseases: cataracts, heart disease, and cancer.     

QUANTITATIVE GENETIC APPROACHES TO EVOLUTIONARY CONSTRAINT: HOW USEFUL?

The study of evolutionary constraint is an active and important area, and genetic correlations and quantitative genetic techniques more generally have been the dominant approach to constraint. Here, I argue that genetic correlations are not very useful for studying constraint, review recent alternative approaches, and briefly discuss the state of our knowledge of the evolutionary importance of constraints caused by genetic variance and covariance.     

EMOTIONS IN THE FIELD: WHAT ARE WE TALKING ABOUT?

In the anthropology of emotion, rival approaches – cultural relativism and a universalism based on common humanity or shared experience – imply different forms of engagement in the field. This article, a sceptical appraisal, suggests that ethnographers commonly fail to build the diversity of emotional practice into their accounts and have therefore provided a flawed basis for theorizing and comparison. With reference to two Indonesian cases – Nias and Java – I suggest that the domain of emotion is diversely bounded cross-culturally and is inconsistently constructed in particular contexts. This has critical implications for fieldwork methodology, cross-cultural comparison, and theories of human development.     

TETRODOTOXIN RESISTANCE IN GARTER SNAKES: AN EVOLUTIONARY RESPONSE OF PREDATORS TO DANGEROUS PREY

The use of the “arms race” analogy as a conceptualization of evolutionary predator-prey interactions has been criticized because of the lack of evidence that predators can and do adapt to increased antipredator ability of prey. We present evidence that the garter snake Thamnophis sirtalis has evolved resistance to tetrodotoxin (TTX) in response to the toxicity of the newt Taricha granulosa on which the snake feeds. A bioassay (locomotor performance before and after injection of TTX) was used to obtain repeated measures of resistance for individual snakes. We studied interpopulation and interspecific variation by comparing resistance in Thamnophis sirtalis from populations occurring sympatrically and allopatrically with Taricha granulosa, and in Thamnophis ordinoides (which does not feed on the newt) occurring sympatrically with Taricha granulosa. We also examined intrapopulation variation in TTX resistance using snakes from a population known to feed on Taricha granulosa. Resistance differed significantly among individuals and litters; repeatability and heritability estimates of the assay were significantly different from zero, demonstrating the potential for response to selection. The population of Thamnophis sirtalis that occurs with Taricha granulosa exhibited levels of resistance much greater than either of the other groups. These results suggest that the predator-prey arms race analogy may be applicable to this system.     

Tyrosyl Radicals in Dehaloperoxidase: HOW NATURE DEALS WITH EVOLVING AN OXYGEN-BINDING GLOBIN TO A BIOLOGICALLY RELEVANT PEROXIDASE*

Dehaloperoxidase (DHP) from Amphitrite ornata, having been shown to catalyze the hydrogen peroxide-dependent oxidation of trihalophenols to dihaloquinones, is the first oxygen binding globin that possesses a biologically relevant peroxidase activity. The catalytically competent species in DHP appears to be Compound ES, a reactive intermediate that contains both a ferryl heme and a tyrosyl radical. By simulating the EPR spectra of DHP activated by H₂O₂, Thompson et al. (Thompson, M. K., Franzen, S., Ghiladi, R. A., Reeder, B. J., and Svistunenko, D. A. (2010) J. Am. Chem. Soc. 132, 17501–17510) proposed that two different radicals, depending on the pH, are formed, one located on either Tyr-34 or Tyr-28 and the other on Tyr-38. To provide additional support for these simulation-based assignments and to deduce the role(s) that tyrosyl radicals play in DHP, stopped-flow UV-visible and rapid-freeze-quench EPR spectroscopic methods were employed to study radical formation in DHP when three tyrosine residues, Tyr-28, Tyr-34, and Tyr-38, were replaced either individually or in combination with phenylalanines. The results indicate that radicals form on all three tyrosines in DHP. Evidence for the formation of DHP Compound I in several tyrosine mutants was obtained. Variants that formed Compound I showed an increase in the catalytic rate for substrate oxidation but also an increase in heme bleaching, suggesting that the tyrosines are necessary for protecting the enzyme from oxidizing itself. This protective role of tyrosines is likely an evolutionary adaptation allowing DHP to avoid self-inflicted damage in the oxidative environment.     

LABORATORY EXPERIMENTS ON SPECIATION: WHAT HAVE WE LEARNED IN 40 YEARS?

We integrate experimental studies attempting to duplicate all or part of the speciation process under controlled laboratory conditions and ask what general conclusions can be made concerning the major models of speciation. Strong support is found for the evolution of reproductive isolation via pleiotropy and/or genetic hitchhiking with or without allopatry. Little or no support is found for the bottleneck and reinforcement models of speciation. We conclude that the role of geographical separation in generating allopatry (i.e., zero gene flow induced by spatial isolation) has been overemphasized in the past, whereas its role in generating diminished gene flow in combination with strong, discontinuous, and multifarious divergent selection, has been largely unappreciated.     

THE ACCUMULATION OF ELECTROLYTES : II. SUGGESTIONS AS TO THE NATURE OF ACCUMULATION IN VALONIA

It is suggested that K enters chiefly as KOH, whose thermodynamic potential (proportional to the ionic activity product (a _K) (a _OH)) is greater outside than within. As this difference is maintained by the production of acid in the cell K continues to enter, and reaches a greater concentration inside than outside. KOH combines with a weak organic acid which is exchanged for HCl entering from the sea water (or its anion is exchanged for Cl^-), so that KCl accumulates in the sap. Na enters more slowly and its internal concentration remains below that of K. The facts indicate that penetration is chiefly in molecular form. As the system is not in equilibrium the suggestion is not susceptible of thermodynamic proof but it is useful in predicting the behavior of K, Na, and NH₄.     

DEVELOPMENTAL CONSEQUENCES OF AN EVOLUTIONARY CHANGE IN EGG SIZE: AN EXPERIMENTAL TEST

Larvae of two species of sea urchins (Strongylocentrotus droebachiensis and S. purpuratus) differ in initial form and in the rate of development. To determine whether these differences are attributable to the large interspecific difference in egg size, we experimentally reduced egg size by isolating blastomeres from embryos. The rate of development of feeding larvae derived from isolated blastomeres was quantified using a novel morphometric method. If the differences early in the life histories of these two species are due strictly to differences in egg size, then experimental reduction of the size of S. droebachiensis eggs should yield an initial larval form and rate of development similar to that of S. purpuratus. Our experimental manipulations of egg size produced three clear results: 1) smaller eggs yielded larvae that were smaller and had simpler body forms, 2) smaller eggs resulted in slower development through the early feeding larval stages, and 3) effects of egg size were restricted to early larval stages. Larvae from experimentally reduced eggs of the larger species had rates of development similar to those of the smaller species. Thus, cytoplasmic volumes of the eggs, not genetic differences expressed during development, account for differences in larval form and the rate of form change. This is the first definitive demonstration of the causal relationship between egg size (parental investment per offspring) and life-history characteristics in marine benthic invertebrates. Because larval form influences feeding capability, the epigenetic effects of egg size on larval form are likely to have important functional consequences. Adaptive evolution of egg size may be constrained by the developmental relationships between egg size and larval form: evolutionary changes in egg size alone can result in concerted changes in larval form and function; likewise evolutionary changes in larval form and function can be achieved through changes in egg size. These findings may have broader implications for other taxa in which larval morphology and, consequently, performance may be influenced by changes in egg size.     

THE ISSUE OF ANTIBIOTIC USE IN THE LIVESTOCK INDUSTRY: WHAT HAVE WE LEARNED?

It is generally believed that it is better to use medicinal products as therapeutics to treat disease situations, using high doses for short periods of time, rather than as prophylactics, when low doses are fed continuously. It is therefore the continuous use of low levels of medicinal products as growth promoters in farm animals that has been brought into question, as it is thought that this may increase the risk of development of bacterial resistance to antibiotics used as therapeutic drugs to treat disease in humans.     

CLEAVAGE PATTERNS AND MESENTOBLAST FORMATION IN THE GASTROPODA: AN EVOLUTIONARY PERSPECTIVE

The larger gastropod taxa are characterized by distinctive cleavage patterns. The cell stage at which the mesentoblast is formed appears to be crucial. In none of the taxa is it formed earlier than the 24- and not later than the 63-cell stage. A heterochronic shift from late to early mesentoblast formation appears to coincide with successive steps in gastropod evolution. Comparison of the early cleavage patterns appears to be a powerful method for investigating the evolutionary relations between major gastropod taxa.     

A DEVELOPMENTAL ANALYSIS OF AN EVOLUTIONARY TREND: DIGITAL REDUCTION IN AMPHIBIANS

In this study, we integrate information from phylogeny, comparative ontogeny, and experimental embryology in an attempt to elucidate the mechanisms controlling evolutionary trends towards digital reduction and loss observed in amphibians. Frogs and salamanders that have lost phalanges and even whole toes have done so in a very ordered manner, i.e., certain skeletal elements are lost prior to others. This pattern of morphological diversity is described and trends elucidated. It is concluded that the process is characterized by striking intraordinal convergences coupled with substantial differences between the trends observed in frogs as compared to urodeles. We argue that this pattern is essentially a reflection of the differences in the ontogenies of the two orders. Similarly, the convergences within urodeles and within anurans can be explained as the result of regulation of developmental parameters in a resilient developmental program. We further explore this hypothesis by experimentally perturbing the number of cells in the embryonic limb primordium to show that reduction in the number of mesenchymal cells secondarily affects the developmental process of pattern formation causing a rearrangement of the skeletal morphology of the foot. The same experimental manipulation has different effects in frogs as compared to salamanders. However, in both cases, the experimentally generated morphologies tend to parallel the phenotypes and trends observed in nature. Our conclusion is that most of the patterns of diversity in the digital morphology of amphibians can be explained as a reflection of developmental properties. In general, we present a methodology that attempts to empirically address the issue of identifying developmental constraint in morphological evolution.