GRADUAL VERSUS PUNCTUATED EQUILIBRIUM EVOLUTION IN THE TURKANA BASIN MOLLUSCS: EVOLUTIONARY EVENTS OR BIOLOGICAL INVASIONS?

A running controversy in evolutionary thought was Eldredge and Gould's punctuated equilibrium model, which proposes long periods of morphological stasis interspersed with rapid bursts of dramatic evolutionary change. One of the earliest and most iconic pieces of research in support of punctuated equilibrium is the work of Williamson on the Plio-Pleistocene molluscs of the Turkana Basin. Williamson claimed to have found firm evidence for three episodes of rapid evolutionary change separated by long periods of stasis in a high-resolution sequence. Most of the discussions following this report centered on the topics of (eco)phenotype versus genotype and the possible presence of preservational and temporal artifacts. The debate proved inconclusive, leaving Williamson's reports as one of the empirical foundations of the paradigm of punctuated equilibrium. Here we conclusively show Williamson's original interpretations to be highly flawed. The supposed rapid bursts of punctuated evolutionary change represent artifacts resulting from the invasion of extrabasinal faunal elements in the Turkana palaeolakes during wet phases well known from elsewhere in Africa.     

EXPLAINING MUTUALISM VARIATION: A NEW EVOLUTIONARY PARADOX?

The paradox of mutualism is typically framed as the persistence of interspecific cooperation, despite the potential advantages of cheating. Thus, mutualism research has tended to focus on stabilizing mechanisms that prevent the invasion of low‐quality partners. These mechanisms alone cannot explain the persistence of variation for partner quality observed in nature, leaving a large gap in our understanding of how mutualisms evolve. Studying partner quality variation is necessary for applying genetically explicit models to predict evolution in natural populations, a necessary step for understanding the origins of mutualisms as well as their ongoing dynamics. An evolutionary genetic approach, which is focused on naturally occurring mutualist variation, can potentially synthesize the currently disconnected fields of mutualism evolution and coevolutionary genetics. We outline explanations for the maintenance of genetic variation for mutualism and suggest approaches necessary to address them.     

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.     

GLOBAL BIOETHICS: UTOPIA OR REALITY?

This article discusses what 'global bioethics' means today and what features make bioethical research 'global'. The article provides a historical view of the development of the field of 'bioethics', from medical ethics to the wider study of bioethics in a global context. It critically examines the particular problems that 'global bioethics' research faces across cultural and political borders and suggests some solutions on how to move towards a more balanced and culturally less biased dialogue in the issues of bioethics. The main thesis is that we need to bring global and local aspects closer together, when looking for international guidelines, by paying more attention to particular cultures and local economic and social circumstances in reaching a shared understanding of the main values and principles of bioethics, and in building 'biodemocracy'.     

SURROGATE MOTHERING:EXPLOITATION OR EMPOWERMENT?

The morality of surrogate mothering is analyzed from a "consequentialist" framework which attempts to separate those consequences that invariably accompany a given act from those that accompany it only in particular circumstances. Critics of surrogacy argue that it transfers the burden and risk of pregnancy onto another woman, separates sex and reproduction, and separates reproduction and childrearing; none of these acts is necessarily wrong, either morally or for women's or society's basic interests. While surrogate mothering can be rendered immoral if women are coerced into the practice or become victims of subordinating or penalizing contracts, it has the potential to empower women and increase their status in society by providing a job that is less risky and more enjoyable than other jobs women are forced to take and by achieving greater social recognition for reproductive labor.     

LIFE-HISTORY TRAITS: ADAPTATIONS OR EFFECTS?

Summary

Kemp, A. C. 1985. Life-history traits: adaptations or effects? Ostrich 56:147-150.

Attention is drawn to the epigeneticist viewpoint concerning life-history traits, whereby differences between organisms are considered as effects of, among other things, scaling relationships. The recent papers of Western &; Ssemakula (1982) and Calder (1983) have shown the extent to which variation in life-history traits of endotherms can be explained by scaling, mainly to body size, brain size and body temperature. Collection of comparative data and the search for scaling relationships in birds is encouraged.     

PERSPECTIVE: MODELS OF SPECIATION: WHAT HAVE WE LEARNED IN 40 YEARS?

Theoretical studies of speciation have been dominated by numerical simulations aiming to demonstrate that speciation in a certain scenario may occur. What is needed now is a shift in focus to identifying more general rules and patterns in the dynamics of speciation. The crucial step in achieving this goal is the development of simple and general dynamical models that can be studied not only numerically but analytically as well. I review some of the existing analytical results on speciation. I first show why the classical theories of speciation by peak shifts across adaptive valleys driven by random genetic drift run into trouble (and into what kind of trouble). Then I describe the Bateson-Dobzhansky-Muller (BDM) model of speciation that does not require overcoming selection. I describe exactly how the probability of speciation, the average waiting time to speciation, and the average duration of speciation depend on the mutation and migration rates, population size, and selection for local adaptation. The BDM model postulates a rather specific genetic architecture of reproductive isolation. I then show exactly why the genetic architecture required by the BDM model should be common in general. Next I consider the multilocus generalizations of the BDM model again concentrating on the qualitative characteristics of speciation such as the average waiting time to speciation and the average duration of speciation. Finally, I consider two models of sympatric speciation in which the conditions for sympatric speciation were found analytically. A number of important conclusions have emerged from analytical studies. Unless the population size is small and the adaptive valley is shallow, the waiting time to a stochastic transition between the adaptive peaks is extremely long. However, if transition does happen, it is very quick. Speciation can occur by mutation and random drift alone with no contribution from selection as different populations accumulate incompatible genes. The importance of mutations and drift in speciation is augmented by the general structure of adaptive landscapes. Speciation can be understood as the divergence along nearly neutral networks and holey adaptive landscapes (driven by mutation, drift, and selection for adaptation to a local biotic and/or abiotic environment) accompanied by the accumulation of reproductive isolation as a by-product. The waiting time to speciation driven by mutation and drift is typically very long. Selection for local adaptation (either acting directly on the loci underlying reproductive isolation via their pleiotropic effects or acting indirectly via establishing a genetic barrier to gene flow) can significantly decrease the waiting time to speciation. In the parapatric case the average actual duration of speciation is much shorter than the average waiting time to speciation. Speciation is expected to be triggered by changes in the environment. Once genetic changes underlying speciation start, they go to completion very rapidly. Sympatric speciation is possible if disruptive selection and/or assortativeness in mating are strong enough. Sympatric speciation is promoted if costs of being choosy are small (or absent) and if linkage between the loci experiencing disruptive selection and those controlling assortative mating is strong.     

EVOLUTIONARY RESPONSES TO ENVIRONMENTAL CHANGES: HOW DOES COMPETITION AFFECT ADAPTATION?

The role and importance of ecological interactions for evolutionary responses to environmental changes is to large extent unknown. Here it is shown that interspecific competition may slow down rates of adaptation substantially and fundamentally change patterns of adaptation to long-term environmental changes. In the model investigated here, species compete for resources distributed along an ecological niche space. Environmental change is represented by a slowly moving resource maximum and evolutionary responses of single species are compared with responses of coalitions of two and three competing species. In scenarios with two and three species, species that are favored by increasing resource availability increase in equilibrium population size whereas disfavored species decline in size. Increased competition makes it less favorable for individuals of a disfavored species to occupy a niche close to the maximum and reduces the selection pressure for tracking the moving resource distribution. Individual-based simulations and an analysis using adaptive dynamics show that the combination of weaker selection pressure and reduced population size reduces the evolutionary rate of the disfavored species considerably. If the resource landscape moves stochastically, weak evolutionary responses cause large fluctuations in population size and thereby large extinction risk for competing species, whereas a single species subject to the same environmental variability may track the resource maximum closely and maintain a much more stable population size. Other studies have shown that competitive interactions may amplify changes in mean population sizes due to environmental changes and thereby increase extinction risks. This study accentuates the harmful role of competitive interactions by illustrating that they may also decrease rates of adaptation. The slowdown in evolutionary rates caused by competition may also contribute to explain low rates of morphological change in spite of large environmental fluctuations found in fossil records.     

CLINAL DISTRIBUTION OF A CHROMOSOMAL REARRANGEMENT: A PRECURSOR TO CHROMOSOMAL SPECIATION?

Geographically structured genetic variants provide an effective means to assess sources of natural selection and mechanisms of adaptation to local environments. Correlated selection pressures along environmental gradients favor subdivision of genomes through chromosomal rearrangement. This study examines populations of Drosophila americana to evaluate selection pressures affecting chromosomal forms distinguished by a centromeric fusion. Analyses of chromosomal polymorphism throughout the Mississippi River Valley in the central United States reveal the presence of a distinct latitudinal cline for the chromosomal rearrangement. The cline has a width of 623 km centered at 35.97 degrees N and displays a characteristic sigmoid shape consistent with a balance between selection and dispersal. Extreme low temperature during January, an indicator of winter severity, was identified as the environmental variable that most accurately predicts arrangement frequency. An intriguing relationship identified between the chromosomal cline and operational sex ratio indicates that these alternative arrangements of the X chromosome may influence sex-specific survival. A hypothesis for the cline is presented wherein variation associated with the alternative chromosome forms influences distinct overwintering strategies. The resulting subdivision within the genome embodies a transitory stage of a speciation process in which locally adapted gene complexes provide a foundation for species formation.     

DO GEOLOGICAL OR CLIMATIC PROCESSES DRIVE SPECIATION IN DYNAMIC ARCHIPELAGOS? THE TEMPO AND MODE OF DIVERSIFICATION IN SOUTHEAST ASIAN SHREWS

Geological and climatic processes potentially alter speciation rates by generating and modifying barriers to dispersal. In Southeast Asia, two processes have substantially altered the distribution of land. Volcanic uplift produced many new islands during the Miocene–Pliocene and repeated sea level fluctuations during the Pleistocene resulted in intermittent land connections among islands. Each process represents a potential driver of diversification. We use a phylogenetic analysis of a group of Southeast Asian shrews ( Crocidura ) to examine geographic and temporal processes of diversification. In general, diversification has taken place in allopatry following the colonization of new areas. Sulawesi provides an exception, where we cannot reject within-island speciation for a clade of eight sympatric and syntopic species. We find only weak support for temporally declining diversification rates, implying that neither volcanic uplift nor sea level fluctuations had a strong effect on diversification rates. We suggest that dynamic archipelagos continually offer new opportunities for allopatric diversification, thereby sustaining high speciation rates over long periods of time, or Southeast Asian shrews represent an immature radiation on a density-dependent trajectory that has yet to fill geographic and ecological space.     

LOSS OF EVOLUTIONARY RESISTANCE BY THE OLIGOCHAETE LIMNODRILUS HOFFMEISTERI TO A TOXIC SUBSTANCE—COST OR GENE FLOW?

The oligochaete Limnodrilus hoffmeisteri at Foundry Cove (FC), New York evolved genetic resistance to cadmium (Cd) and lost resistance after contaminated sediments were removed by dredging. Selection (on survival time in dissolved Cd) was used to generate tolerance to evaluate fitness cost, the commonplace expectation for evolutionary reversal. The hypothesis that gene flow from neighboring populations could "swamp" resistance was addressed by 16S rDNA sequences. In disagreement with the cost hypothesis, selected-Cd tolerant worms and controls showed no difference in total fecundity or growth rate in environments. Highly-Cd-tolerant worms of the FC-selected population grew rapidly at different temperatures and showed no growth impairment in the presence of Cd, indicating metabolically efficient resistance. Genetic structure at FC was consistent with invasion of genotypes from an adjacent population in the time since dredging. Applying selection to lines from FC and a reference site, demonstrated a more rapid increase in Cd tolerance in FC-origin lines, indicating standing allelic variation for resistance at FC (despite phenotypic erosion). The selection experiment supports the view that resistance is simply controlled—probably by one allele of large effect. Whether such rapid "readaptation" could occur naturally is an important question for understanding broad effects of pollutants.     

COMMENTARY: SCIENCE SCANDAL OR ETHICS SCANDAL? OLIVIERI REDUX

Dr. Nancy Olivieri has become an icon of research integrity for her insistence on publishing adverse data about a drug she was investigating. She has been celebrated world-wide as a hero of biomedical ethics for her bravery in disclosing potential dangers to research subjects, in the face of both drug company threats and coercive pressures from her hospital and university. Like so many other 'whistle-blowers' however, she now faces both personal vilification and disturbing accusations of scientific error. The case against Olivieri is assessed and found to be baseless.     

MANDATORY HIV TESTING IN PREGNANCY: IS THERE EVER A TIME?

Despite recent advances in ways to prevent transmission of HIV from a mother to her child during pregnancy, infants continue to be born and become infected with HIV, particularly in southern Africa where HIV prevalence is the highest in the world. In this region, emphasis has shifted from voluntary HIV counselling and testing to routine testing of women during pregnancy. There have also been proposals for mandatory testing. Could mandatory testing ever be an option, even in high‐prevalence settings? Many previous examinations of mandatory testing have dealt with it in the context of low HIV prevalence and a well‐resourced health care system. In this discussion, different assumptions are made. Within this context, where mandatory testing may be a strategy of last resort, the objections to it are reviewed. Special attention is paid in the discussion to the entrenched vulnerability of women in much of southern Africa and how this contributes to both HIV prevalence and ongoing challenges for preventing HIV transmission during pregnancy. While mandatory testing is ethically plausible, particularly when coupled with guaranteed access to treatment and care, the discussion argues that the moment to employ this strategy has not yet come. Many barriers remain for pregnant women in terms of access to testing, treatment and care, most acutely in the southern African setting, despite the presence of national and international human rights instruments aimed at empowering women and removing such barriers. While this situation persists, mandatory HIV testing during pregnancy cannot be justified.     

PERSPECTIVE: FROM MUTANTS TO MECHANISMS? ASSESSING THE CANDIDATE GENE PARADIGM IN EVOLUTIONARY BIOLOGY

The generation of mutants in model organisms by geneticists and developmental biologists over the last century has occasionally produced phenotypes that are startlingly reminiscent of those seen in other species. Such extreme mutations have generally been dismissed by evolutionary geneticists since the "modern synthesis" as irrelevant to adaptation and speciation. But only in recent years has information on the molecular bases of mutant phenotypes become widely available, and thus work on testing the relevance of such extreme mutations to the generation of phylogenetic diversity has just begun. Here we evaluate whether evolutionary mimics are, in fact, useful for pinpointing the genetic differences that distinguish morphological variants generated during evolution. Examples come from both plants and animals, and range from intraspecific to interordinal taxonomic ranges. The use of mutationally defined candidate genes to predict evolutionary mechanisms has so far been most fruitful in explaining intraspecific variants, where it has been effective in both plants and animals. In several cases these efforts were facilitated or supported by parallel results from quantitative trait loci studies, in which natural alleles controlling continuous variation in developmental model organisms were mapped to mutationally defined genes. However, despite these successes the approach's utility seems to rapidly decay as a function of phylogenetic distance. This suggests that the divergence of developmental genetic systems is great even in closely related organisms and may become intractable at larger distances. We discuss this result in the context of what it teaches us about development, the future prospects of the candidate gene approach, and the historical debate over process in micro- and macroevolution.