Allometric power scaling, ontogenetic growth, and phenotypic plasticity represent three fundamental developmental features for every living organism. To analyze these three features of an organism at the interface between development and evolution, researchers must understand their underlying genetic bases. We have developed a general framework for deciphering the genetic machinery that guides allometric scaling, ontogenetic growth, and environment-dependent plasticity in biological organisms. This approach constitutes a step toward creating a unified view of evolutionary biology and developmental biology (“evo-devo”).

Ecological processes of insular tropical stream drainages are not well understood. Furthermore, it is not yet clear how the concepts and paradigms derived from studies of continental stream ecosystems in the temperate zone can be effectively applied to understanding and managing tropical island watersheds. The articles in this special section describe important aspects of how tropical stream ecosystems are structured and how these systems function and change over time in response to natural processes and human activities.

Streams throughout the tropics have been altered by water diversion, channel modification, introduced species, and water quality degradation. The Hawaiian Islands, with watersheds ranging from the relatively pristine to the highly degraded, offer an opportunity to examine the impacts of human disturbance on native stream communities. For example, urbanization is often accompanied by stream-channel modification and reduced canopy cover, resulting in higher water temperatures and greater fluctuations in daily temperature. Even in relatively pristine watersheds, stream diversions can result in decreased flow velocity and water depth, reducing habitat availability. Dewatering of stream reaches can also inhibit downstream dispersal of larvae and upstream migration of juveniles and adults of native species. Many nonnative aquatic species are better adapted than native species to degraded habitats; once established in these habitats, they can cause further reduction in native populations through competition, predation, and the introduction of parasites or diseases. Understanding the relationship between habitat alteration and aquatic community structure is critical for developing sound management strategies.

The global spread of parasites threatens native animals even in the most isolated of all habitats on Earth. In the Hawaiian archipelago, the five native species of stream fishes are infected with several species of alien parasites introduced through human activities. These exotic parasites have been shown to present greater disease threats to their Hawaiian fish hosts than do parasites that have colonized native fish by natural means. By studying the biological characteristics and mechanisms of transmission of parasite colonists, researchers can enhance understanding of the parasites' global dispersal.

The combination of human population growth, increased water usage, and limited groundwater resources often leads to extensive damming of rivers and streams on tropical islands. Ecological effects of dams on tropical islands can be dramatic, because the vast majority of native stream faunas (fishes, shrimps, and snails) migrate between freshwater and saltwater during their lives. Dams and associated water withdrawals have been shown to extirpate native faunas from upstream reaches and increase mortality of downstream-drifting larvae. A better understanding of the effects of dams and the behavior of tropical island stream faunas is providing insights into how managers can mitigate the negative effects of existing dams and develop alternatives to dam construction while still providing freshwater for human use. We review the ecological effects of dams on tropical island streams, explore means to mitigate some of these effects, describe alternatives to dam construction, and recommend research priorities.

Running water habitats develop in concert with the age of hotspot volcanic islands. This study tracks the geologic and hydrologic processes involved in this development for the Society Islands, French Polynesia. Over a period of about 6 million years, these islands have rafted northwest on the Pacific Plate and eroded from high islands with many stream systems to atolls with no running water. Black flies that require running water for their immature stages have undergone a species radiation into a wide array of running water habitats on Tahiti. From there, black flies appear to have dispersed to older islands farther west. The reduction of running water habitat with the island's increasing age has had consequences for the biogeography of these insects. The habitat generalist species are the most widespread. Species with dependence on cascades cannot colonize islands where cascade habitats have eroded away.

An ongoing survey of macroinvertebrates inhabiting the relatively unstudied freshwater habitats on 14 small Caribbean islands was initiated in 1991. These collections have yielded almost 200 species; when these species are combined with collections previously made by other researchers, a total of at least 328 freshwater macroinvertebrates are now known from these islands. The dominant taxa on the islands include several species of snails, shrimps, mayflies, dragonflies, damselflies, beetles, and other insects. Many of these species have fairly widespread distributions across the islands. Most stream species are associated with leaf packs, and most pond species are associated with aquatic macrophytes. As is typical of tropical island systems, the macroinvertebrate faunas of these islands are sparse, most likely because of their oceanic origin, their small size, and the frequent disturbances to their freshwater environments.

The island nation of Madagascar, an international conservation priority, is now also recognized as a global hotspot for freshwater biodiversity. Three emerging characteristics of Madagascar's threatened freshwater biota deserve increased attention from the scientific and conservation communities. First, species richness is not low, as was once assumed for both the freshwater fishes and the invertebrates. Second, many species are restricted to a specific region or even to single river basins. Often these species are also limited to streams or rivers draining primary forest habitat. Finally, many of the island's freshwater fishes are basal taxa, having diverged earlier than any other extant members of their clade. As such, these taxa assume disproportional phylogenetic importance. In the face of ongoing environmental threats, links among microendemism, forest stream specialization, and basal phylogenetic position highlight the importance and vulnerability of these species and provide a powerful incentive for immediate conservation action.

Biological stoichiometry is the study of the balance of energy and multiple chemical elements in biological systems. A key idea in biological stoichiometry is the growth rate hypothesis, which states that variation in the carbon:nitrogen:phosphorus stoichiometry of living things is associated with growth rate because of the elevated demands for phosphorus-rich ribosomal RNA, a requirement for rapid growth. In this article, we synthesize studies in the cancer literature to test the growth rate hypothesis; consistent with its predictions, rapidly growing tumors have elevated ribosome content, key oncogenes are closely affiliated with regulation of ribosome biogenesis, and tumor development has physiological impacts on patient phosphate metabolism. We also describe a new eco-evolutionary model of tumor dynamics that incorporates stoichiometric mechanisms. Since biological stoichiometry is fundamental in its approach, other areas of biology in which multiple key resources are involved in generating important tradeoffs may also benefit from the new tools provided by stoichiometric theory.

Encouraged by improvements in the quality of science education since the 1960s, cognitive researchers are testing and applying theory-based research on learning in science classrooms. To introduce faculty to research on cognition and learning, I focus on metacognition: the awareness of one's own thinking, or “knowing what we know.” I analyze two ecology texts and describe several active-learning strategies in the context of metacognitive theory. Information about pedagogy and its theoretical underpinnings may well help faculty improve their teaching practices.