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

Many classic tests of ecological theory have involved populations and communities maintained for many generations in the laboratory under tightly controlled conditions. In spite of this, such “bottle experiments” now play only a minor role within the larger field of ecology, and their relevance to natural populations and communities is regarded with suspicion by many field ecologists. Here, we compare and critique several recent bottle experiments, which were designed to test open questions in ecological theory that could never feasibly be addressed in natural communities. Judging from this set of experiments, we suspect that it will be difficult to relate the qualitative results of bottle experiments to natural populations and communities. What we learn from these experiments depends heavily on the relationship between theoretical models and experimental design. If the demography of organisms is completely under experimental control, bottle experiments can teach us about the possible range of population dynamics, but not about what regulates dynamics in natural populations. Furthermore, if experimental results are not linked to a mechanistic model, we can support or refute broad generalizations, but there is no direct way to relate bottle experiments to natural communities. Consequently, we argue that the most informative bottle experiments must incorporate both mechanistic models and unmanipulated demography; such bottle experiments can generate new ideas and future directions for both empirical and theoretical research.

Olfactory imprinting is a specialized form of unconditioned learning in which olfactory information is acquired and then used in some specific behavioral context later in life. One of the hallmarks of olfactory imprinting is that it tends to be linked to a sensitive period of development. This prerequisite thus distinguishes olfactory imprinting from other types of odor learning in which only conditioned exposure to an odor stimulus is required for learning to occur. Most investigations designed to explore the mechanisms underlying olfactory imprinting have focused on mammalian species, concentrating on synaptic events at the level of the main and accessory olfactory bulbs.¹ Recent integrative studies with salmon^2,3 and rabbits,⁴ however, provide compelling evidence that highly specific imprinted odor memories may also be retained in the periphery, i.e., at the level of the olfactory epithelium proper. These results suggest that populations of olfactory receptor neurons may be selectively tuned to respond to odor molecules present during a hormonally linked sensitive period. A potential key to the mechanism of how these peripheral odor memories become established draws on the unique ability of olfactory receptor neurons to turn over throughout an organism's life span.⁵ How hormonal and environmental factors work together to influence olfactory neurogenesis is currently only sketchily understood,⁶ but ultimately may provide important new insights not only for basic science but for salmon conservation as well.

Phylogenetic systematics, as espoused in a recent book review by Harry W. Greene published in this journal, promotes the idea that paraphyly obscures the recognition of phylogenetic relationships and other aspects of organismic biology. I argue here that this viewpoint is not only without merit (what, in fact, do derived taxa tell us about paraphyletic taxa?), but that insistence on holophyly in itself may obscure ready appreciation of phylogenetic relationships. It has been recognized and accepted for the better part of this century that taxonomic groups at all levels may be derived from within other taxonomic groups, resulting in paraphyly. This phenomenon is becoming more and more evident as cladistic analyses of molecular and morphological data are more penetrating, and many well-defined taxa, including sponges, are now seen as probably paraphyletic. Computer-based cladistic analysis, integrating both molecular and morphological characters, is a powerful and increasingly essential approach for sorting out and establishing both sister-group and paraphyletic relationships. Paraphyletic taxa should be recognized as such for the fascinating perspective they provide in unraveling evolutionary patterns.

Animals are equipped with a variety of sensory systems that allow them to extract information from the environments they inhabit. The ability to detect the chemical environment is probably the most ancient sense. The sense of smell can provide important details about the habitat because chemical signals emitted by both beneficial and potentially harmful sources can be detected and appropriate behavior initiated without relying upon input from other sensory modalities. Even though olfactory communication can be slow compared to other sensory modalities such as vision and sound, it is sometimes very reliable and stable (e.g. trail or territory marking) and in other circumstances may be much more ephemeral (e.g. odors released only during specific periods of the day or night). Thus, olfactory cues can be manipulated over time and spatial scales that other sensory modalities cannot, and this is perhaps why we find an abundance of olfactory communication in the animal world. For adult moths, olfactory signals are a vital source of information that modulate many aspects of their behavior. In these animals, an appreciation of the features of odors coupled with behavioral experimentation has enhanced our understanding of the neurobiology of olfactory processing.

Propagation of a modified form of the cellular prion protein is thought to be the primary cause of the transmissible spongiform encephalopathies, which include kuru, Creutzfeldt-Jakob disease (CJD), scrapie, and bovine spongiform encephalopathy (BSE). These highly unusual neurological maladies seem to arise spontaneously at extremely low rates. In addition, these diseases can be transmitted directly, in which case the incubation period is remarkably constant. The challenge is to understand these crucial features of prion diseases, without invoking the action of any viral agent. A simple model is developed in which the onset and progression of spongiform encephalopathies are explained by the kinetics of prion aggregate formation. Interestingly, ordered aggregations of proteins such as occurs in prion diseases are also associated with other neurological disorders such as Alzheimer's disease. Thus, insights developed about prion aggregation may have wide significance. © 1998 Wiley-Liss, Inc.

There is great interest in the invention of multicellularity because it is one of the major transitions during the course of early evolution.¹ Most of the emphasis has been on why it occurred. For instance, recently Gerhart and Kirschner² have argued that a multicellular organism has gained the advantage of a unicellular ancestor because it can more effectively shield itself from the vagaries of the environment by producing its own internal environment. In broader terms, this is Dawkins'³ argument that a competitively effective way of carrying the genes from one generation to the next is by building a complex soma that safely sees to it that the germ plasm survives. © 1998 Wiley-Liss, Inc.

Ecotoxicology is a new discipline that supposedly melds the fields of ecology and toxicology. Yet as today's scientists grapple with wide-ranging environmental degradation, the field of ecotoxicology often seems an ineffectual, naïve and confused science, far from a seamless merger of two well-established and respected disciplines. We set out to examine the current state of ecotoxicology, paying special attention to some of the major simplifications and misunderstandings that underlie its weaknesses. By exposing major areas of needed improvement, we hope to point the way towards giving ecotoxicology a more prominent voice in the analysis of pressing contemporary environmental problems.