Integrative Biology: Issues, News, and Reviews最新文献

Humans have become such a dominant factor on the planet that they have shaped the evolution of many organisms. In some cases, the evolutionary response of the organisms in turn has profound implications for human and environmental health. Nowhere is this more apparent than in the case of bacteria and their evolutionary response to antibiotics, heavy metals and pesticides. This review examines bacterial responses to human-mediated selection on antibiotic and heavy metal resistances and pesticide degradation ability. Although there are differences in the fine details concerning the mechanisms, genetics, origins and selective pressures of these traits, taken as whole, their evolutionary paths are very similar to each other. However, those features which distinguish resistance traits are likely to be important for implementing intervention schemes to reduce the spread of antibiotic resistances and exploiting bacterial traits for bioremediation.

The U.S. Endangered Species Act establishes categories for endangered and threatened species but provides no criteria for deciding when a species should be listed, delisted, or downlisted. As a result, listing and recovery actions for marine mammals are widely inconsistent. In most cases, Endangered Species Act listing and recovery actions have been done without the benefit of high-quality population assessments and have been based on arbitrary, nonquantitative criteria. A new approach to determining classification criteria for marine mammals is presented, with the North Pacific humpback whale as a test case. The key idea underlying this approach is an attempt to incorporate biological uncertainty explicitly in the definition of threatened and endangered. I sketch the essential ingredients of this new approach and its motivation and use this discussion to illuminate the challenges we face in pursuing conservation in an uncertain and data-poor world.

Lyme disease and gypsy moth outbreaks plague many temperate oak forests. Over the past decade, we have developed models and hypotheses designed to allow us to predict irruptions of both gypsy moths and the tick vector of Lyme disease. We have documented a web of connections involving mast production by oak trees, population responses by white-footed mice, habitat selection by white-tailed deer, and population dynamics of both tick parasites and defoliating insects. In patchy landscapes typical of the northeastern U.S., dispersal by mice, deer, and attached ticks between oak and nonoak forests creates dynamics that would not be predictable by focusing on a single patch type. We would not have uncovered these interactions without adopting a research approach that comprised: (1) the inclusion of diverse taxa of animals, plants, and microbes; (2) the integration of individual, population, community, and ecosystem levels of organization; (3) the incorporation of more than one patch type in a heterogeneous landscape; and (4) a combination of long-term monitoring and manipulative field experiments.

Self-organizing behavior is one of the most remarkable properties of regulative animal embryos. The reorganization of disarranged embryonic primordia to form an approximation of the “correct” structure by any number of abnormal pathways constitutes a form of goal-directed behavior. One might suppose that such anatomical “goals” are specified by genetic programs evolved through mutation and natural selection to produce useful structures. However, one might also ask the following questions: how can genes direct morphogenesis without specifying the pathways to be followed? How can genetic systems have evolved to specify the organization of the never-before-assembled structures reproducibly generated by abnormal tissue combinations? Experiments have shown that the layered structures generated in such experiments belong to the category of “inherently precise” machines, in which a specific pattern is generated with great precision by the constant repetition of a simple local behavior throughout the pattern-forming system. The organization characteristic of the chordate body plan—the “goal” of early development—also arises by very different developmental pathways in the various members of the phylum. Yet divergent evolution can hardly have altered the mechanisms governing gastrulation and neurulation while holding the end results essentially constant. Evidence suggests that the striking differences in these pathways may be understood less as fundamental alterations of morphogenetic mechanisms than as the physical consequences arising from heterochrony—differences in the times at which a shared set of underlying cellular changes are initiated.

Human beings have a natural interest in their origins. We are vertebrates, within the craniates, within the chordates. Fossils indicate how the chordates separated, in early Palaeozoic times or before, from their latest common ancestor with the echinoderms. The most primitive known fossil chordates retained a calcitic skeleton of echinoderm type (calcichordates) and some of these, the mitrates, were like giant calcite-plated tunicate tadpoles, consisting of a head and a tail with no trunk region. Some mitrates are themselves craniates in the broad sense and represent the ancestral group (stem group) from which extant craniates descended. In this paper, we describe such a stem-craniate mitrate, and reconstruct, from the shared characteristics of the extant craniates supplemented by evidence from fossils, the latest common ancestor of extant craniates which we call “animal x”. (In most respects animal x would resemble a hagfish, but its larva would filter-feed like a lamprey larva.) We then list the changes involved in transforming a mitrate into animal x and describe the probable changes in development in early embryos that converted a mitrate into animal x. During this transition, our ancestors took to swimming forwards rather than crawling rearwards, lost the calcitic skeleton, and acquired the trunk region, the notochordal region to the head, kidneys, and neural-crest cartilage. An important developmental mechanism involved was forward extension of the notochord, caused by anteriorly directed convergent extension movements.