What can population genetics tell us about dispersal and biogeographic history of coral-reef fishes?

Abstract Coral-reef fishes, like many other marine organisms, generally possess a benthic adult stage and pelagic larval stage. What can population genetics studies tell us about the demographic, evolutionary and biogeographic consequences of this life cycle? Ten studies of geographical patterns of intraspecific genetic differentiation in reef fishes have been published. These studies have included 2t > species/species complexes (14 in the family Pomacentridae, the remaining 12 in 9 different families) and have been about equally divided between the tropical Pacific and the tropical western Atlantic. A survey of these studies shows the following: (i) the existence of the pelagic larval stage appears to have led to high levels of gene flow even among populations separated by thousands of kilometres of open ocean; (ii) an apparent pattern of increased gene flow among populations connected by intermediate 'stepping stones’; (iii) very tentative evidence for a relationship between length of pelagic larval life and gene flow; (iv) no clear relationship between egg type (pelagic rs non-pelagic) and gene flow; and (v) suggestive evidence that damselfishes (family Pomacentridae) may have more restricted dispersal (less gene flow) than other reef fishes. The application of current and future molecular tools has the strong potential to clarify some of these relationships, particularly by using relatively neutral genetic markers. Additionally, discoveries of DNA markers having very high rates of mutation may allow tracking of demographically relevant levels of larval dispersal. Molecular tools are becoming especially valuable in uncovering the biogeographic and phylogenetic history of reef fishes. The one molecular study to date has suggested that at least some speciation events may have occurred during the climate changes and sea-level regressions associated with Pleistocene glacial episodes. Molecular tools need to be used to further explore the means by which high species diversity can be generated in the face of the apparently high gene flow observed in most coral-reef fishes.     

What does Drosophila genetics tell us about speciation?

Studies of hybrid inviability, sterility and 'speciation genes' in Drosophila have given insight into the genetic changes that result in reproductive isolation. Here, I survey some extraordinary and important advances in Drosophila speciation research. However, 'reproductive isolation' is not the same as 'speciation', and this Drosophila work has resulted in a lopsided view of speciation. In particular, Drosophila are not always well-suited to investigating ecological and other selection-driven primary causes of speciation in nature. Recent advances have made use of far less tractable, but more charismatic organisms, such as flowering plants, vertebrates and larger insects. Work with these organisms has complemented Drosophila studies of hybrid unfitness to provide a more complete understanding of speciation.     

What can DNA tell us about biological invasions?

It is often hoped that population genetics can answer questions about the demographic and geographic dynamics of recent biological invasions. Conversely, invasions with well-known histories are sometimes billed as opportunities to test methods of population genetic inference. In both cases, underappreciated limitations constrain the usefulness of genetic methods. The most significant is that human-caused invasions have occurred on historical timescales that are orders of magnitude smaller than the timescales of mutation and genetic drift for most multicellular organisms. Analyses based on the neutral theory of molecular evolution cannot resolve such rapid dynamics. Invasion histories cannot be reconstructed in the same way as biogeographic changes occurring over millenia. Analyses assuming equilibrium between mutation, drift, gene flow, and selection will rarely be applicable, and even methods designed for explicitly non-equilibrium questions often require longer timescales than the few generations of most invasions of current concern. We identified only a few population genetic questions that are tractable over such short timescales. These include comparison of alternative hypotheses for the geographic origin of an invasion, testing for bottlenecks, and hybridization between native and invasive species. When proposing population genetic analysis of a biological invasion, we recommend that biologists ask (i) whether the questions to be addressed will materially affect management practice or policy, and (ii) whether the proposed analyses can really be expected to address important population genetic questions. Despite our own enthusiasm for population genetic research, we conclude that genetic analysis of biological invasions is justified only under exceptional circumstances.     

What can dolphins tell us about primate evolution?

Fifty-five million years ago, a furry, hoofed mammal about the size of a dog ventured into the shallow brackish remnant of the Tethys Sea and set its descendants on a path that would lead to their complete abandonment of the land. These early ancestors of cetaceans (dolphins, porpoises, and whales) thereafter set on an evolutionary course that is arguably the most unusual of any mammal that ever lived. Primates and cetaceans, because of their adaptation to exclusively different physical environments, have had essentially nothing to do with each other throughout their evolution as distinct orders. In fact, the closest phylogenetic relatives of cetaceans are even-toed ungulates.     

What can mathematical modeling tell us about hybrid invasions?

Compared to the vast theoretical literature on the dynamics of single species invasions, relatively few models have dealt with the emergence of invasive hybrids. Here, we review the variety of modeling approaches that have been used to study the dynamics of hybridization, outlining the underlying assumptions and highlighting their advantages and disadvantages. We summarize the predicted outcomes for the persistence for the native species and the resulting genetic composition of the native–exotic–hybrid complex under a variety of model scenarios. We highlight promising future directions for theoretical investigation and its integration with experimental studies.     

What else can green monkeys tell us about AIDS?

Although the development of an HIV vaccine may eventually provide a means of controlling AIDS in developed countries, more immediate and less sophisticated methods are going to have to be developed for use in the rural regions of Africa where AIDS may already have reached epidemic proportions. Evidence from several studies of wild primates suggests that plant secondary compounds may commonly act as control agents for a variety of different pathogens. Although studies of laboratory populations of green monkeys indicate that their resistance to AIDS is likely to be genetic, we argue that it may be worth screening some of the plants eaten by African primates in the hope of coming up with compounds that exhibit suitable anti-viral activity. Any compounds isolated in this way are likely to be much cheaper to manufacture than laboratory-produced drugs and may also have been already screened for unpleasant side-effects.     

What can animal aggression research tell us about human aggression?

Research on endocrinological correlates of aggression in laboratory animals is implicitly motivated by an expectation that the results of such studies may be applicable to human aggression as well. Research with a focus on the stimulus antecedents of aggression, its response characteristics, and its outcomes suggests a number of detailed correspondences between offensive aggression in laboratory rodents and human angry aggression. These include resource (including status and territory) competition as motives that are particularly elicited by conspecific challenge situations and, when the aggression is successful, outcomes of reduction of challenge and enhancement of resource control and status. Although the response characteristics of human aggression have been dramatically altered by human verbal, technological, and social advancements, there is some evidence for targeting of blows, similar to a well-established pattern for offensive aggression in many nonhuman mammals. Finally, for people as well as for nonhuman mammals, fear of defeat or punishment is a major factor inhibiting the expression of offensive aggression. While defensive aggression has been very little researched in people, it may represent a different phenomenon than angry aggression, again providing a parallel to the offense-defense distinction of laboratory rodent studies.     

What can Caenorhabditis elegans tell us about the nuclear envelope?

The nuclear envelope (NE) of the eukaryotic cell provides an essential barrier that separates the nuclear compartment from the cytoplasm. In addition, the NE is involved in essential functions such as nuclear stability, regulation of gene expression, centrosome separation and nuclear migration and positioning. In metazoa the NE breaks down and re-assembles around the segregated chromatids during each cell division. In this review we discuss the molecular constituents of the Caenorhabditis elegans NE and describe their role in post-mitotic NE re-formation, as well as the usefulness of C. elegans as an in vivo system for analyzing NE dynamics.     

What can epidemiology tell us about risks at low doses?

Puskin, J. S. What Can Epidemiology Tell Us about Risks at Low Doses? Radiat. Res. 169, 122-124 (2008). Limitations on statistical power preclude direct detection and quantification of radiogenic cancer risks at very low (environmental) levels of low-LET radiation through epidemiological studies. Given this limitation and our incomplete understanding of cellular processes leading to radiation carcinogenesis, an "effective threshold" in the dose range of interest for radiation protection cannot yet be ruled out. Ongoing epidemiological studies of chronically exposed individuals receiving very low daily doses of radiation can be used, however, together with radiobiological data, to critically test whether such a threshold is plausible.     

What can phylogenetics tell us about speciation in the Cape flora?

The spectacular diversity of the Cape flora has promoted wide speculation on the evolutionary processes behind its origins, but until recently these ideas could not be tested rigorously due to the almost complete absence of a fossil record for the region. Now, molecular phylogenetic approaches, combined with analyses of ecological and biogeographical information, offer the potential to test key hypotheses about speciation of so-called Cape clades of flowering plants. We outline the main theories and how they might be tested by phylogenetic approaches. One conclusion is that population level studies of particular species complexes are now needed to complement the growing volume of phylogenetic information for Cape clades and to provide better understanding of mechanisms of population divergence in the Cape. Another is that comparisons between Cape and non-Cape clades are needed to confirm whether speciation is indeed faster in the Cape region. An alternative possibility, that extinction rates are lower, should also be considered in these comparisons. By virtue of the ongoing, coordinated efforts by a global team of botanists, the Cape is now uniquely placed for exploring the origins and assembly of a regional assemblage or biome.     

What can Drosophila tell us about serpins,thrombosis and dementia?

The validity of the fruit-fly as a model of human disease has been confirmed in a striking way by Green and colleagues.1 They show that the mutations causing a necrotic disease phenotype in Drosophila, precisely mirror those resulting in a group of well-studied but perplexing diseases in the human. These diseases, ranging from thrombosis to dementia, arise from mutations causing a conformational instability of serpin protease inhibitors. The findings provide clues as to the unusual severity and variable onset of such conformational diseases and demonstrate the potential of Drosophila as a model for their future study.     

What can computed tomography and magnetic resonance imaging tell us about ventilation?

This review provides a summary of pulmonary functional imaging approaches for determining pulmonary ventilation, with a specific focus on multi-detector x-ray computed tomography and magnetic resonance imaging (MRI). We provide the important functional definitions of pulmonary ventilation typically used in medicine and physiology and discuss the fact that some of the imaging literature describes gas distribution abnormalities in pulmonary disease that may or may not be related to the physiological definition or clinical interpretation of ventilation. We also review the current state-of-the-field in terms of the key physiological questions yet unanswered related to ventilation and gas distribution in lung disease. Current and emerging imaging research methods are described, including their strengths and the challenges that remain to translate these methods to more wide-spread research and clinical use. We also examine how computed tomography and MRI might be used in the future to gain more insight into gas distribution and ventilation abnormalities in pulmonary disease.