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One of the world's richest deltas has been radically replumbed, its ecosystem is collapsing, and Californians are realizing their water supply is tapped out. Despite decades of efforts—and some positive trends—solutions may not be any closer. Downstream, the San Francisco Bay looks good by comparison.
The field of ecotoxicology uses biomarkers to assess the health of populations of sentinel organisms and to determine risk associated with environmental chemicals. The tools of modern biology are being used to develop promising new suites of biomarkers that must be rigorously tested and validated within a comprehensive mechanistic understanding of how toxic chemicals in the environment influence basic physiology and behavior. The zebrafish is a well-established laboratory model organism with a well-equipped molecular toolbox for basic biology and biomedicine with logical applications in ecotoxicology. As a model organism for ecotoxicology, the zebrafish can be used to develop mechanistic models of gene-environment interactions that will provide a foundation for the development of genomic resources in other fish species. Integration of mechanistic molecular data from multiple fish species will lead to the development of integrated dynamic models that will enable better diagnosis and treatment of environmental disease and improved ecological risk assessments.
Wildlife species have been recognized as sentinels of environmental health for decades. In fact, ecological data on various wildlife populations provided the impetus for banning some organochlorine pesticides over the last few decades. Alligators are important sentinels of ecosystem health in the wetlands of the southeastern United States. Over the last 15 years, a series of studies have demonstrated that environmental exposure to a complex mixture of contaminants from agricultural and municipal activities alters the development and functioning of alligators' reproductive and endocrine systems. Further studies of basic developmental and reproductive endocrinology in alligators and exposure studies performed under controlled laboratory conditions support the role of contaminants as causal agents of abnormalities in gonadal steroidogenesis and in reproductive tract development. These studies offer potential insight into environmentally induced defects reported in other wildlife and human populations exposed to a wide array of endocrine-disruptive contaminants.
Androgens are hormones produced by the gonads and other endocrine organs of vertebrates. Testosterone, along with its metabolite dihydrotestosterone, is critical for the differentiation of the fetal male reproductive tract from an indifferent state, for the development of male traits during puberty, and for the maintenance of reproductive function in mature animals. The androgen signaling pathway is highly conserved in the reproductive system of all vertebrates from fish to humans; therefore, environmental chemicals have the potential to induce adverse effects in any vertebrate species. There are synthetic androgens present in the environment, and several pesticides and toxic substances display antiandrogenic activity. For example, exposure to mixtures of antiandrogens during sexual differentiation results in cumulative adverse effects in male rat offspring. Continued characterization of the role of androgens in reproductive and other systems is warranted to enable better understanding of the potential adverse effects of chemical disruption of androgen signaling.
Feminization of the male roach, Rutilus rutilus, a freshwater, group-spawning fish, is widespread in English rivers; among the causative agents are natural and synthetic steroidal estrogens and chemicals that mimic estrogens. In feminized male roach, concentrations of the egg-yolk protein vitellogenin are elevated, sex steroid hormone dynamics are altered, and gonad development is disrupted (most notably, a female reproductive duct or developing eggs [oocytes] are present in the testis). In some English rivers containing high levels of estrogens, all male roach sampled have been feminized to varying degrees. In the more severely affected males, individuals produce low-quality sperm with a reduced capability for fertilization. Laboratory studies have shown that the environmental estrogens responsible for inducing gonadal feminization in roach can also alter reproductive behavior, disrupting normal breeding dynamics (parentage) in the zebrafish, another group-spawning fish. Together these findings indicate that feminization of wild roach may result in adverse population-level effects, but this hypothesis has yet to be fully addressed.
Several nuclear receptors have recently been identified as mediators of endocrine disruption as well as steroid hormone receptors. The ubiquitous environmental contaminant tributyltin chloride (TBT) is a ligand for retinoid X receptor (RXR) in rock shell at the nanomolar level, and it acts as a ligand for both the RXR and the peroxisome proliferator-activated receptor γin the frog Xenopus laevis and in humans. TBT, which induces imposex in marine snails and promotes adipogenesis in X. laevis and in mice, is an example of an environmental endocrine disrupter that promotes adverse effects, from the snail to mammals, through common signaling. In addition, juvenile hormone agonists used as pesticides showed endocrine-disruptive effects on parthenogenic Daphnia magna, lowering rates of reproduction, and inducing 100% male offspring. In this article, we focus on commonality in signaling through nuclear receptors and newly found endocrine disruption in D. magna.
Although the geomorphic and ecological importance of large wood in streams and rivers is well recognized, most studies consider only dead wood in channels. However, we have observed that living parts of trees are often found within active channels and that this “livewood” shares functions with both instream dead wood and live riparian trees, while also providing some functions unique to living woody material within a channel. We describe the mechanisms that produce livewood and illustrate its characteristics and influences on riparian and stream ecosystems with examples from Europe, North America, and New Zealand. We hypothesize that, compared with dead wood in channels, livewood (a) persists longer because of greater stability and greater resistance to decay, and (b) imparts greater structural complexity (with associated hydraulic roughness and retentiveness). The phenomenon of livewood implies that a broader range of tree species and sizes than previously considered may contribute functionally important wood to channels. We encourage the study of livewood in a range of forest-stream ecosystems to test our hypotheses and further our understanding of how forests interact with rivers and streams.
Faculty from numerous science disciplines have used concept inventories to focus their efforts on a few core concepts and ways of thinking in introductory courses. These inventories also help faculty recognize students' misconceptions and faulty reasoning from the onset of a course and track gains in understanding as the course progresses. The biology concept inventories that several groups of biologists and educators are now working on will add significantly to the few that have already been published. This article introduces biology faculty to concept inventories, including what they are and how they are developed and used. In addition, I propose next steps, which would lead to faculty development workshops based on the use of concept inventories, student-active teaching, and scientific teaching in introductory biology courses. These workshops could be offered through professional biological societies and coordinated by societies' educators working together on common goals and strategies.