H. V. Danks

Dehydration in dormant insects

Many of the mechanisms used by active insects to maintain water balance are not available to dormant individuals. Physiological and biochemical mechanisms of dehydration tolerance and resistance in dormant insects and some other invertebrates are reviewed, as well as linkages of dehydration with energy use and metabolism, with cold hardiness, and with diapause. Many dormant insects combine several striking adaptations to maintain water balance that-in addition to habitat choice-may include especially reduction of body water content, decreased cuticular permeability, absorption of water vapour, and tolerance of low body water levels. Many such features require energy and hence that metabolism, albeit much reduced, continues during dormancy. Four types of progressively dehydrated states are recognized: water is managed internally by solute or ion transport; relatively high concentrations of solutes modify the behaviour of water in solutions; still higher concentrations of certain carbohydrates lead to plasticized rubbers or glasses with very slow molecular kinetics; and anhydrobiosis eliminates metabolism.

Importance of insects in environmental impact assessment

Insects are particularly suited for use in environmental impact assessment (e.i.a.) because of their high species diversity, ubiquitous occurrence, and importance in the functioning of natural ecosystems. Examples are given of the use of insects in the predictive phase of e.i.a., in the monitoring and assessment phase, and in the much rarer instance of an e.i.a. that includes both of these phases. The importance of working at the species level to understanding the results of e.i.a. is emphasized.

Arctic arthropods : a review of systematics and ecology with particular reference to the North American fauna

from the valuable perspective of a researcher who has spent winters as well as summers in eastern Beringia. Alhugb eastern Siberian data are utilized, emphasis is on the late Pleistocene and early Holocene prehistory of interior Alaska. While there is some discussion of West’s own work in the Tangle Lakes region of central Alaska, the monograph is not, even incidentally, a site reprt. The ultimate objective is “a contribution toward a comprehmsive Wry on the poopling of Beringia and the New World” @. 163). As such it invites the attention of moat Americanist archaealogists as well as northern specialists. Chapter One is an excellent synthesis of contemporary environments in northcastcrn Siberia and Alaska, one which I suspect will contribute to a number of lectures in the next few years. Chapter Two reconstructs Beringia between 25 OOO and 8OOO B.C. as a unique, now-extinct, cold ry steppe tundra capable of supporting a diverse fauna including many large herbivores. The serious reader will have to integrate this familiar reconstruction with the various views expressed in the recently published Paleoecology of Beringia (Academic Press, 1982), a work unavailable to West. Chapter Three introduces the hem of the book, the Beringians. Although the author appears reluctant to provide a full-face characterization, these are eventually revealed to be terrestrial arctic hunters adapted to the exploitation of large herbivores of the arctic steppe Beringian biome. The hallmark of their technology is sharp-edged parallel-sided flakes (blades, more commonly microblades) struck from specially prepared cores or microcores. Some regional variation is noted in Beringian tool inventories with varying emphasis on retouched flake tools, burins, and large lenticular bifaces which are thought to have functioned as knives. Blsdes and microblacks, while often broken, are seldom shaped or retouched. Absence of obvious stone weapon tips leads to the plausible inference that seldom-preserved tools of antler, bone, and ivory were significant. The Beringians are reasonably viewed as a late Pleistocene eastern extension of a widespread Eurasian Upper Paleolithic technology. A close historical relationship between eastern Siberian and Alaskan final Pleistocene techdogies is indicated. The term “Dyuktai culture” includes most pertinent Siberian assemblages, and the term “ D e d i culture” most (not all) Alaskan Beringian assemblages. More technological diversity is seen in Siberia than in Alaska and a key role is postulated (plausibly but on minimal evidence) for the nowdmwned heartiand of central Beringia. The coming of man to eastern Beringia is seen as late, perhaps not much earlier than 11 000 years ago. Candidates for an earlier human presence in far northwestern North America are dismissed. One major exception is made to the simple formula that northern core and blade technology equals Beringian. Quite reasonably excluded is the Araic Small Tool tradition which appeand on the NndrasandcosstsofarcticAmericPbetween4000and5000yearsago. Core and blade technology is thus basic to the concept of a Beringian tradition. The author presents a rough form cntegorization (misleadingly termed a formal claesification) of cores. As is true of other illustrations in this book, the core drawings are so reduced in size that they almost require study under magnification. Nineteen pages of tables provide a summary of over 165 microblade sites (ca. 137 from eastern Beringia and 28 from western Beringia) known up to 1980 with references, dating, inventory description, and comments. Any specialist can find something to complain about in tabulations of this kind. I merely note that more detailed published dtscriptions than those utilized here are available for sites on the Alaska P e h u l a , Anangula Island, and the southwest Yukon Territory of Canada. Also, some unlikely candiites (for example, Tuktu in Anaktuvuk Pass) are incorporated in the Beringian tradition by mechanical equation of earky microblades with this entity. Tukh~ is later explained @. 226) as a contact phenomenon between relict Beringians and Northern Archaic (West terms them “Boreal Archaic”) users of sidenotched projectile points, but since the Tuktu inventory is dominated by Northern Archaic f m s its inclusion in the Fkringian tradition on the basis of the presence of a microblade industry seems dubious taxonomic procedure. About 30 pages are devoted to a general discussion of the author’s work in the Tangle Lakes. Twenty Beringian tradition sites are known here, but none is described in detail. Those interested in using this material for comparative purposes will be frustrated by failure to provide. site provenience for the majority of the illustrated specimens and confused by the transposition of most text references to Figures 14 and 15, an unfortunate editorial l pse. There are also 15 figures of diagnostic artifact8 fromother Beringian sites. Unfommte.ly, references to Figures 29 and 30 have also been transposed. REVIEWS

The elements of seasonal adaptations in insects

The many components of seasonal adaptations in insects are reviewed, especially from the viewpoint of aspects that must be studied in order to understand the structure and purposes of the adaptations. Component responses include dispersal, habitat selection, habitat modification, resistance to cold, dryness, and food limitation, trade-offs, diapause, modifications of developmental rate, sensitivity to environmental signals, life-cycle patterns including multiple alternatives in one species, and types of variation in phenology and development. Spatial, temporal, and resource elements of the environment are also reviewed, as are environmental signals, supporting the conclusion that further understanding of all of these seasonal responses requires detailed simultaneous study of the natural environments that drive the patterns of response.

Seasonal Adaptations in Arctic Insects

Abstract Many insect species live in the arctic and show a wide range of adaptations to its extreme severity and seasonality. Long, cold winters are met, for example, by cold hardiness and choice of protected sites. Cold hardiness includes both widespread tolerance to freezing and extreme supercooling ability, as well as unusual responses in a few species, such as lack of typical cryoprotectants. Adaptations to short, cool summers include activity at low temperatures, selection of warm habitats and microhabitats, melanism and hairiness coupled with basking behaviour, and prolonged or abbreviated life cycles. Diapause ensures that many species emerge early in summer, with brief synchronized reproduction that maximizes the time for offspring development before winter returns. Some species overwinter in sites that thaw earliest in spring, even if they are relatively exposed in winter. Other adaptations respond to year-to-year variability: for example, prolonged diapause can provide insurance against unsuitable summers. All of these adaptations are co-ordinated. For example, cold hardiness relies on physiological and biochemical adaptations but also on habitat choice and timing. Because the adaptations are complex, predicted climatic warming probably will have unexpected effects. In particular, an increase in temperature that increases summer cloud when sea ice melts would likely reduce temperatures for insect development and activity, because sunshine provides critical warmth to insects and their microhabitats. Changes in moisture will also be important. Moreover, responses differ among species, depending especially on their microhabitats. The complexity of the responses of insects to arctic conditions reinforces the need for research that is sufficiently detailed.

Winter Habitats and Ecological Adaptations for Winter Survival

In most insect species, ecological or behavioral means of avoiding low winter temperatures are more conspicuous than biochemical and other adjustments to withstand the low temperatures. In practice, many adaptations combine to permit winter survival, notably the timing of the lifecycle, including the overwintering stage, and diapause and correlated changes in food storage. This chapter emphasizes habitat choices made by overwintering insects and temperature conditions in those winter habitats.

Diversity and integration of life-cycle controls in insects

An ecological view of insect life cycles provides a broad context for the polymorphism and polyphenism that characterize many such life cycles. Selective forces are diverse; consequently, adaptations that budget time represent trade-offs among different objectives. Many different patterns of trade-offs in time and energetic resources, for example between duration of development and size, size and fecundity, and fecundity and longevity, appear in different species. Moreover, these various components interact more widely. In addition, many environmental factors are available for use in the proximate control of development. Therefore, temporal control can be achieved in many different ways.

How aquatic insects live in cold climates

In cold climates most aquatic habitats are frozen for many months. Nevertheless, even in such regions the conditions in different types of habitat, in different parts of one habitat, and from one year to the next can vary considerably; some water bodies even allow winter growth. Winter cold and ice provide challenges for aquatic insects, but so do high spring flows, short, cool summers, and unpredictable conditions. General adaptations to cope with these constraints, depending on species and habitat, include the use of widely available foods, increased food range, prolonged development (including development lasting more than one year per generation), programmed life cycles with diapause and other responses to environmental cues (often enforcing strict univoltinism), and staggered development. Winter conditions may be anticipated not only by diapause and related responses but also by movement for the winter to terrestrial habitats, to less severe aquatic habitats, or to different parts of the same habitat, and by construction of shelters. Winter itself is met by various types of cold hardiness, including tolerance of freezing in at least some species, especially chironomid midges, and supercooling even when surrounded by ice in others. Special cocoons provide protection in some species. A few species move during winter or resist anoxia beneath ice. Spring challenges of high flows and ice scour may be withstood or avoided by wintering in less severe habitats, penetrating the substrate, or delaying activity until after peak flow. However, where possible species emerge early in the spring to compensate for the shortness of the summer season, a trait enhanced (at least in some lentic habitats) by choosing overwintering sites that warm up first in spring. Relatively low summer temperatures are offset by development at low temperatures, by selection of warm habitats and microhabitats, and in adults by thermoregulation and modified mating activity. Notwithstanding the many abiotic constraints in cold climates, aquatic communities are relatively diverse, though dominated by taxa that combine traits such as cold adaptation with use of the habitats and foods that are most widely available and most favourable. Consequently, except in the most severe habitats, food chains and community structure are complex even at high latitudes and elevations, including many links between aquatic and terrestrial habitats. Despite the complex involvement of aquatic insects in these cold-climate ecosystems, we know relatively little about the physiological and biochemical basis of their cold hardiness and its relationship to habitat conditions, especially compared with information about terrestrial species from the same regions.

Variations in mitochondrial DNA and gene transcription in freezing-tolerant larvae of Eurosta solidaginis (Diptera: Tephritidae) and Gynaephora groenlandica (Lepidoptera: Lymantriidae)

Respiration, mitochondrial (mt)DNA content, and mitochondrial‐specific RNA expression in fat body cells from active and cold‐adapted larvae of the goldenrod gall fly, Eurosta solidaginis, and the Arctic woolly bear caterpillar, Gynaephora groenlandica, were compared. Reduced amounts of mtDNA were observed in cold‐adapted larvae of both E. solidaginis and G. groenlandica collected in fall or winter, compared with summer‐collected larvae. mtDNA increased to levels similar to those of summer‐collected larvae after incubation at 10 °C or 15 °C for 5 h. Mitochondrial‐specific RNAs (COI and 16S) were observed in fat body cells of both active and cold‐adapted E. solidaginis larvae. Our results suggest that mitochondrial proteins required for respiration may be restored rapidly from stable RNAs present in overwintering larvae.

Insect life-cycle polymorphism: Current ideas and future prospects

Polymorphisms are important components of insect life cycles and interact with responses to the environment. The forces selecting these adaptations can be estimated, through ecological correlations and mathematical modelling, especially from the ways in which different species budget time, space, and energy.