Search

Migratory animals exhibit traits that allow them to exploit seasonally variable habitats. In environments where migration is no longer beneficial, such as oceanic islands, migration-association traits may be selected against or be under relaxed selection. Monarch butterflies are best known for their continent-scale migration in North America but have repeatedly become established as nonmigrants in the tropical Americas and on Atlantic and Pacific Islands. These replicated nonmigratory populations provide natural laboratories for understanding the rate of evolution of migration-associated traits. We measured >6,000 museum specimens of monarch butterflies collected from 1856 to the present as well as contemporary wild-caught monarchs from around the world. We determined 1) how wing morphology varies across the monarch's global range, 2) whether initial long-distance founders were particularly suited for migration, and 3) whether recently established nonmigrants show evidence for contemporary phenotypic evolution. We further reared >1,000 monarchs from six populations around the world under controlled conditions and measured migration-associated traits. Historical specimens show that 1) initial founders are well suited for long-distance movement and 2) loss of seasonal migration is associated with reductions in forewing size and elongation. Monarch butterflies raised in a common garden from four derived nonmigratory populations exhibit genetically based reductions in forewing size, consistent with a previous study. Our findings provide a compelling example of how migration-associated traits may be favored during the early stages of range expansion, and also the rate of reductions in those same traits upon loss of migration.

Insect populations including butterflies are declining worldwide, and they are becoming an urgent conservation priority in many regions. Understanding which butterfly species migrate is critical to planning for their conservation, because management actions for migrants need to be coordinated across time and space. Yet, while migration appears to be widespread among butterflies, its prevalence, as well as its taxonomic and geographic distribution are poorly understood. The study of insect migration is hampered by their small size and the difficulty of tracking individuals over long distances. Here we review the literature on migration in butterflies, one of the best-known insect groups. We find that nearly 600 butterfly species show evidence of migratory movements. Indeed, the rate of 'discovery' of migratory movements in butterflies suggests that many more species might in fact be migratory. Butterfly migration occurs across all families, in tropical as well as temperate taxa; Nymphalidae has more migratory species than any other family (275 species), and Pieridae has the highest proportion of migrants (13%; 133 species). Some 13 lines of evidence have been used to ascribe migration status in the literature, but only a single line of evidence is available for 92% of the migratory species identified, with four or more lines of evidence available for only 10 species - all from the Pieridae and Nymphalidae. Migratory butterflies occur worldwide, although the geographic distribution of migration in butterflies is poorly resolved, with most data so far coming from Europe, USA, and Australia. Migration is much more widespread in butterflies than previously realised - extending far beyond the well-known examples of the monarch Danaus plexippus and the painted lady Vanessa cardui - and actions to conserve butterflies and insects in general must account for the spatial dependencies introduced by migratory movements.

Monarch butterfly wing morphology varies substantially throughout their global range, both between resident and migratory populations and also within the migratory North American population. Here, we use a dataset comprising more than 1800 North American individuals collected between 1878-2017 to characterize the factors shaping continent-wide patterns of wing morphological variation. North American overwintering butterflies have forewings that are approximately 4.4% larger than those collected in summer breeding areas. Monarchs overwintering in Mexico have forewings that are approximately 1.8% larger than monarchs overwintering in California, conducive to the idea that migration distance is positively correlated with wing area. We find evidence for a latitudinal cline within North America, such that butterflies collected at higher latitudes have significantly larger and more elongated forewings. We also find a significant increase of approximately 4.9% in forewing area between 1878-2017, but no difference through time in wing elongation. This result is corroborated by a reanalysis of a recently published dataset of more than 600 butterflies from Mexican overwintering sites. We discuss possible reasons for this increase in wing size through time, including northward shifts in the monarch’s breeding range and changes in relative abundance of milkweed hosts, and present experimental data addressing the influence of larval host plant on adult wing morphology. Our analysis suggests that (1) migration is indeed an important selective force for monarch wing morphology; (2) wing size has increased through time in North America; (3) factors such as host plant identity must be considered to fully understand monarch wing morphological variation.

Los grillos constituyen animales excelentes en estudios de agresividad y comportamiento sexual porque son muy activos y muy fáciles de mantener en el laboratorio. Se han utilizado particularmente en el estudio del sonido en el comportamiento.Nuestro propósito en este ejercicio será analizar la agresividad, la territorialidad y el galanteo en grillos; el papel del sonido en estas actividades y el grado de organización social presente en estos animales.

Monarch butterflies are best known from their migratory North American range, although many resident, year-round breeding populations are established throughout the world. Here, we evaluate two non-exclusive hypotheses for the loss of migration in resident monarch populations: (1) absence of cues that trigger migration; and (2) loss of sensory, neural or physiological systems required for migration. To evaluate the first hypothesis, we exposed resident monarchs from Queensland, Australia to decreasing larval photoperiod and observed reproductive development in resulting females to assess their propensity to show reduced reproductive development, a precursor for long-distance migration. To address the second hypothesis, we measured antennal circadian clock gene expression, a crucial element of the monarch's ability to orientate directionally, in a resident and a migratory population. We found that Australian resident monarchs show reduced reproductive development in response to decreasing photoperiod, consistent with the 'loss of cues' hypothesis. We found no differences in antennal clock gene expression between migratory and resident populations, inconsistent with the 'loss of mechanism' hypothesis. Together, these data indicate that even after hundreds of generations of non-migration, monarchs retain two crucial elements of their migratory repertoire: developmental plasticity associated with decreasing photoperiod and antennal circadian rhythms necessary for directional orientation.

We examined the distribution of butterflies over the mostly arid and semi-arid continent of Australia and analyzed the proportion of migrant species and species diversity with respect to an array of climatic and geographic variables. On a continent-wide scale, latitude explained virtually no variance in either proportion of migrants (r2=0.01) or species diversity (r2=0.03) in Australian butterflies. These results are in marked contrast to those for temperate-zone birds from three continents where latitude explained between 82 and 98% of the variance in frequency of migrants and also accounted for much of the variance in bird species diversity. In eastern Australia where rainfall regimes are similar to those in temperate Europe and North and South America, latitude explains 78% of the variance in frequency of butterfly migrants. In both eastern and central Australia, latitude also accounts for relatively high proportions of the variance in species diversity. Rainfall patterns and especially soil moisture are negatively associated with migration frequency in Australian butterfly faunas, both alone and in combination with other climate variables. Where moisture levels are relatively high, as in eastern Australia, measures of temperature are associated with migration frequency, a result consistent with findings for temperate-zone birds, suggesting latitude is a surrogate for temperature. The ultimate causes of migration in temperate-zone birds and Australian butterflies are the uneven temporal, and in Australia also spatial, distribution of resources. Uneven distribution is brought about primarily by temperature in temperate regions and by erratic rainfall over much of arid Australia. As a key determinant of productivity, especially in the tropics and subtropics, aridity is likely to be an important determinant of the global distributions of migrants.

To broaden perspectives and stimulate research on migration, I survey the bird species that breed in the northern hemisphere and migrate to the southern hemisphere and species that migrate within the southern hemisphere, comparing routes, seasonal patterns and life histories. Differences in the area and latitudinal extent of land masses on the two sides of the Equator influence patterns of bird migration. In contrast to birds breeding in the northern hemisphere, no land or freshwater birds breeding in the southern hemisphere migrate between continents and only a very few cross the Equator. Furthermore, except for shorebirds, few northern intercontinental migrants reach the southern hemisphere in regions south of the equatorial forest belt, because most encounter, and are filtered out by, suitable habitats en route. Australasia is an extreme case because only 10 land or freshwater migrants from the northern hemisphere regularly occur there (most are uncommon or rare) compared with 42 in Africa and 28 in South America, and no Australasian breeders enter Asia beyond Wallace’s Line. Historical geographical and oceanic barriers may be an additional factor limiting migration to Australasia. There are generally no or only slight differences in frequencies of austral migrants within foraging guilds or families across southern continents. Exceptions are rallids, with more migrants in Africa, and cuckoos and nectarivores, with more Old World than New World migrants. Austral migrations are of shorter distances than most of those of the northern hemisphere, and they appear to vary more with respect to routes and patterns. Breeding and non-breeding ranges frequently overlap. Partial migration is common, but there is no evidence that it differs in frequency from that in northern regions. Because climate is generally milder and drier in the southern hemisphere, rainfall is a more important influence on migration than in the north especially in some nomadic birds, but temperature also predicts migration frequency and pathways for many species. These patterns are similar across southern continents, but each continent has its own characteristics. Southern hemisphere migrants seem to display ecophysiologies and orientation mechanisms similar to those found in northern hemisphere species, but very few southern species have been studied. I argue that the variation present among southern hemisphere migrations provides exceptional opportunities to understand the evolution and ecology of migration systems. In order to take advantage of these systems, we need to focus on variation in movement behaviour, on associated syndromes of traits, and on the particular features of natural selection and ecology setting thresholds that lead to the diverse migration patterns observed.

We outline a general scheme for migration that applies across taxa, incorporates the several varieties of migration, and includes all levels of biological organization, from genes to populations. The scheme links the environment, pathways, traits, and genes, and highlights the selective forces that shape and maintain migratory adaptation. We endorse an individual-based behavioral definition of migration that allows an objective distinction between migration and other forms of movement. We recognize migration as an adaptation to resources that fluctuate spatiotemporally either seasonally or less predictably, and note that it is often preemptive. Migration plays a central role in the spatial dynamics of mobile populations, and is largely distinct in both form and function from the within-population mixing arising from postnatal dispersal and from the interpatch movements characteristic of metapopulations. We call for more interaction between biologists studying different taxa and different forms of movement, and between behaviorists and population ecologists.

Evolutionary change results from selection acting on genetic variation. For migration to be successful, many different aspects of an animal’s physiology and behaviour need to function in a co-coordinated way. Changes in one migratory trait are therefore likely to be accompanied by changes in other migratory and life-history traits. At present, we have some knowledge of the pressures that operate at the various stages of migration, but we know very little about the extent of genetic variation in various aspects of the migratory syndrome. As a consequence, our ability to predict which species is capable of what kind of evolutionary change, and at which rate, is limited. Here, we review how our evolutionary understanding of migration may benefit from taking a quantitative-genetic approach and present a framework for studying the causes of phenotypic variation. We review past research, that has mainly studied single migratory traits in captive birds, and discuss how this work could be extended to study genetic variation in the wild and to account for genetic correlations and correlated selection. In the future, reaction-norm approaches may become very important, as they allow the study of genetic and environmental effects on phenotypic expression within a single framework, as well as of their interactions. We advocate making more use of repeated measurements on single individuals to study the causes of among-individual variation in the wild, as they are easier to obtain than data on relatives and can provide valuable information for identifying and selecting traits. This approach will be particularly informative if it involves systematic testing of individuals under different environmental conditions. We propose extending this research agenda by using optimality models to predict levels of variation and covariation among traits and constraints. This may help us to select traits in which we might expect genetic variation, and to identify the most informative environmental axes. We also recommend an expansion of the passerine model, as this model does not apply to birds, like geese, where cultural transmission of spatio-temporal information is an important determinant of migration patterns and their variation. [KEYWORDS: Individual variation ; Migration ; Migratory syndrome ; Migratory traits ; Quantitative genetics]

Ornithologists, and especially northern hemisphere ornithologists, have traditionally thought of migration as an annual return movement of populations between regular breeding and non-breeding grounds. Problems arise because selection does not ordinarily act on populations and because organisms of many taxa (including birds) are clearly migrants, but fail to undertake movements of the kind described. There are also extensive return movements that are not migratory. I propose that it is more useful to think of migration as a syndrome of behavioral and other traits that function together within individuals, and that such a syndrome provides a common ground across taxa from aphids to albatrosses. Large-scale return movements of populations are one outcome of the syndrome. Similar behavioral and physiological traits serve both to define migration and to provide a test for it. I use two insect (Hemipteran) examples to illustrate migratory syndromes and to demonstrate that, in many migrants, behavior and physiology correlate with life history and morphological traits to form syndromes at two levels. I then compare the two Hemipterans with migration in birds, butterflies, and fish to assess the question of whether there are migratory syndromes in common between these diverse migrants. Syndromes are more similar at the level of behavior than when morphology and life history traits are included. Recognizing syndromes leads to important evolutionary questions concerning migration strategies, trade-offs, the maintenance of genetic variance and the responses of migratory syndromes to both similar and different selective regimes.

Soapberry bugs are worldwide seed predators of plants in the family Sapindaceae. Australian sapinds are diverse and widespread, consisting of about 200 native trees and shrubs. This flora also includes two introduced environmental weeds, plus cultivated lychee (Litchi chinensis Sonn.), longan (Dimocarpus longan Lour.) and rambutan (Nephelium lappaceum L.). Accordingly, Australian soapberry bugs may be significant in ecology, conservation and agriculture. Here we provide the first account of their ecology. We find five species of Leptocoris Hahn in Australia, and list sapinds that do and do not serve as reproductive hosts. From museum and field records we map the continental distributions of the insects and primary hosts. Frequency of occupation varies among host species, and the number of hosts varies among the insects. In addition, differences in body size and beak length are related to host use. For example, the long-beaked Leptocoris tagalicus Burmeister is highly polyphagous in eastern rainforests, where it occurs on at least 10 native and non-native hosts. It aggregates on hosts with immature fruit and commences feeding before fruits dehisce. Most of its continental range, however, matches that of a single dryland tree, Atalaya hemiglauca F. Muell., which has comparatively unprotected seeds. The taxon includes a smaller and shorter-beaked form that is closely associated with Atalaya, and appears to be taxonomically distinct. The other widespread soapberry bug is the endemic Leptocoris mitellatus Bergroth. It too is short-beaked, and colonises hosts phenologically later than L. tagalicus, as seeds become more accessible in open capsules. Continentally its distribution is more southerly and corresponds mainly to that of Alectryon oleifolius Desf. Among all host species, the non-native environmental weeds Cardiospermum L. and Koelreuteria Laxm. are most consistently attacked, principally by L. tagalicus. These recent host shifts have biocontrol implications. In contrast, the sapinds planted as fruit crops appear to be less frequently used at present and mainly by the longer-beaked species.

The increased demographic performance of biological invaders may often depend on their escape from specifically adapted enemies. Here we report that native taxa in colonized regions may swiftly evolve to exploit such emancipated exotic species because of selection caused by invaders. A native Australian true bug has expanded it host range to include a vine imported from tropical America that has become a serious environmental weed. Based on field comparisons and historical museum specimens, we show that over the past 30-40 years, seed feeding soapberry bugs have evolved 5-10% longer mouthparts, better suited to attack the forest-invading balloon vines, which have large fruits. Laboratory experiments show that these differences are genetically based, and result in a near-doubling of the rate at which seeds are attacked. Thus a native biota that initially permits invasion may rapidly respond in ways that ultimately facilitate control.

The standard model for the migration of the monarch butterfly in western North America has hitherto been movement in the autumn to overwintering sites in coastal California, followed by a return inland by most individuals in the spring. This model is based largely on observational and limited tagging and recovery data. In this paper we test the model by plotting many years of museum and collection records on a monthly basis on a map of the region. Our plots suggest a movement of Oregon, Washington and other north-western populations of summer butterflies to California in the autumn, but movement of more north-easterly populations (e.g. from Idaho and Montana) along two pathways through Nevada, Utah and Arizona to Mexico. The more westerly of these two pathways may follow the Colorado River south as indicated by museum records and seasonal temperature data. The eastern pathway may enter northern Utah along the western scarp of the Wasatch Mountains and run south through Utah and Arizona. Further analysis of distributions suggests that monarch butterflies in the American West occur primarily along rivers, and there are observations indicating that autumn migrants often follow riparian corridors. More data are needed to test our new model; we suggest the nature of the data required. (c) 2005 The Linnean Society of London.

We investigated the adaptive significance of behavioural thermoregulation in univoltine populations of the grasshopper Melanoplus sanguinipes along an altitudinal gradient in California using laboratory tests of animals raised under different temperatures. Trials consisted of continuous body temperature measurements with semi-implanted microprobes in a test arena, and observation and simultaneous recording of behavioural responses. These responses included mobility, basking and orientation of the body axes (aspect angle) towards a radiation source. Mobility and basking are determined by the altitudinal origin of the parental generation and not by the temperature treatments. With increasing altitude, individuals tend increasingly to raise body temperatures via mobility and increased basking. In contrast, body orientation towards the radiation source is influenced by the temperature treatments but not by the altitude of origin. Individuals experiencing higher temperatures during rearing show a lower tendency to lateral flanking. We conclude that body orientation responses are not adapted locally. In contrast other components of the behavioural syndrome that increase body temperature, such as mobility and basking, are adaptive in response to local selection pressure. The thermoregulatory syndrome of these grasshoppers is an important contribution to life-history adaptations that appropriately match season lengths.

With respect to its avian migrants, Australo-Papua is a largely self-contained region. Only some 30 species of shorebird and 10 species of land bird migrate from Asia to Australo-Papua to winter. Possible factors precluding migration of Asian birds include long over-water distances and lack of suitable habitats in Australia or New Guinea. Whether evolved within the region or descended from Asian relatives, Australasian species all confine their migratory movements east of Wallace's Line. The most likely factors restricting migration to the region are climate and habitat. The open forests and arid habitats of Australasia are absent from south-east Asia, so there is little, if any, selection promoting extra-regional migration. The arid or semi-arid but otherwise mild climates of much of Australia favour partial migration and widely varying movement patterns and pathways, although with an underlying north to south component. Movements also occur between mainland Australia and New Guinea and Tasmania. The restriction of migration within Australo-Papua and the high variability of migratory pathways have important implications for the ecology and evolution of the Australasian avifauna.

The colonization of an introduced plant by s bugsin Florida hasres ulted in the rapid evolution of a distinctive "host race." Differences in the synchrony and persistence of local seed crops may have favored interracial differentiation in sight/life history tactics. To advance previous work, we quantiÞed seed availability in individual native and introduced host plants. We tested the prediction that the new hostOs relatively discrete period of annual seed production has selected for a higher frequency of a short-winged, sightless morph with a briefer generation time. Contrary to that prediction, short-winged bugs were not more common in the derived race, but further investigation revealed the unexpected presence of a long-winged morph, that like the short-winged, lacks sight muscle and exhibits the same rapid life cycle advantages. Consistent with prediction, the derived race, descended from volant long-winged colonists, shows an abundance of this "cryptic" sightless morph. In total, four sight/life history morphs were discovered, including two additional long-winged types that either histolyze or retain sight muscle. The morphs differed in life history traits both within and between host races. Morph frequency may be insuenced by evolution in correlated characters: we found that beak length, which has rapidly evolved to be shorter on the smaller fruits of the introduced host, is discontinuously distributed between sight morphs, being greater in long- winged bugs. This study shows complex, unpredicted evolutionary relations between a mobility character, a trophic character, and the life history.

Large numbers of adults of certain species of butterfly flying in an apparently 'purposeful' manner are often noted by entomologists and the general public. Occasionally, these are recorded in the literature. Using these records we summarise information regarding the direction of movement in Australian butterflies and test whether there are consistent patterns that could account for known seasonal shifts in geographical range. The data were analysed using contingency tables and directionality statistics. Vanessa itea, Vanessa kershawi, Danaus plexippus, Danaus chrysippus and Badamia exclamationis flew predominately south in the spring-summer and north in the autumn-winter. Tirumala hamata has a strong southern component to its flight in spring but, as in Euploea core, appears non-directional in the autumn. For many supposedly known migratory species, the number of literature records are few, particularly in one season (mainly autumn). Thus, for Appias paulina, four of seven records were south in the spring-summer, as were six of nine records for Catopsilia pomona, and three of five for Zizina labradus. For Belenois java, flight records were only available for the spring and these showed geographical differences; predominantly north-west in northern Australia (Queensland) and south-west in southern Australia (Victoria, New South Wales). There were too few records for Papilio demoleus in the literature (four only) to draw any conclusions. Major exceptions to the seasonal trend of south in the spring and north in the autumn were Junonia villida, which showed a predominant north-westward direction in both seasons, and Eurema smilax, with a predominant southern or western flight in both seasons. We discuss these species specific trends in migration direction in relation to seasonal shifts in suitable habitat conditions, possible cues used in orientation and in timing changes in direction.

With reciprocal rearing experiments, we tested the hypothesis that adaptive differences in host-use traits among soapberry bug populations have a genetic basis. These experiments were conducted with two host races from Florida, an ‘ancestral-type’ one on a native host plant species and a ‘derived’ one on a recently introduced plant species (colonized mainly post-1950), on whose seed crops this insect depends for growth and reproduction. Compared to the native host species, the introduced host produces larger seed crops over a much briefer annual period. Its seeds are also significantly higher in lipids and lower in nitrogen. The bug populations exhibit greater juvenile survivorship on their ‘home’ hosts; that is, the derived population survives better on seeds of the introduced host than does its ancestral-type counterpart, and vice versa. Regardless of the rearing host, populations from the introduced host lay much smaller eggs, and fecundity measures show a more complex pattern than does survivorship: the ancestral-type population produces eggs at the same rate on each host, while the derived population is less fecund on the native host and exhibits enhanced fecundity on the introduced host. These results indicate that the population differences are evolved rather than host-induced. They appear to be adaptive responses to host differences in the spatial and temporal distribution of seed availability and nutritional quality, and show that increased performance on the alien host has evolved with surprising speed and magnitude, with concomitant reductions in performance on the original host.

In this study we used reciprocal rearing experiments to test the hypothesis that there is a genetic basis for the adaptive differences in host-use traits among host-associated soapberry bug populations (described in Carroll and Boyd 1992). These experiments were conducted on two host races from Florida, in which differences in beak length and development were found between natural populations on a native host plant species and those on a recently introduced plant species (colonized mainly post-1950). Performance was generally superior on the host species from which each lab population originated (i.e., on the "Home" host species): in analysis of variance, there was significant population-by-host interaction for size, development time, and growth rate. These results indicate that the population differences in nature are evolved rather than host induced. Increased performance on the introduced host was accompanied by reduced performance on the native host, a pattern that could theoretically promote further differentiation between the host races.

Insects display much variation in life histories mediated by juvenile hormone. We focus on the contribution of JH to variations in migratory life histories. In many migrants such as the large milkweed bug and the monarch butterfly, JH directly influences migratory flight and the relation between flight and reproduction (oogenesis-flight syndrome). In the true armyworm, JH regulates interactions among female calling, pheromone production, ovarian development, and migration with varying blends of structurally related forms of JH and JH acid. A role for JH also occurs in wing polymorphisms. Aphids regulate wing production via JH-mediated maternal effects; and in crickets, JH esterase modulates the JH influence on wing form. In addition, JH is implicated in wing muscle histolysis. The comprehensive Fairbairn model for JH regulation of wing polymorphisms in flight behavior predicts that JH action will depend on the mode of genetic control, whether single locus or polygenic. Our own studies of the soapberry bug, Jadera haematoloma, reveal a four-morph wing polymorphism in a species rapidly evolving on a new host plant. There are long- and short-winged forms, and the long-winged form displays three degrees of flight muscle histolysis. The polymorphism is subject to both genetic and environmental variations that are mediated by JH. Application of methoprene increases the frequency of the short-winged forms, but there is both within- and between-population genetic variation and genotype by environment interaction (plasticity) in the response to JH. Arch. Insect Biochem. Physiol. 35:359–373, 1997. © 1997 Wiley-Liss, Inc.

Mouritsen et al. (1) used a flight-simulator experiment and recapture data to examine two hypotheses: whether monarchs use true navigation or a vector-navigation strategy. In the flight-simulator experiment, flight directions of wild-captured, migratory butterflies were assessed near their capture location, and then ∼2,500 km west. The authors’ finding that monarchs flew southwest in both locations does not rule out true navigation because: (i) the experiment did not include reciprocal translocations and therefore lacked controls; (ii) experimental monarchs were moved to a location that an Ontario monarch would never traverse and where monarchs are only rarely found, and thus tell us little about monarchs following a normal migratory trajectory; …

Contemporary adaptation of plant feeding insects to introduced hosts provides clear cases of ecologically based population divergence. In most cases the mechanisms permitting rapid differentiation are not well known. Here we study morphological and genetic variation associated with recent shifts by the Australian soapberry bug Leptocoris tagalicus onto two naturalized Neotropical balloon vines, Cardiospermum halicacabum and C. grandiflorum that differ in time since introduction. Our results show that these vines have much larger fruits than the native hosts (Whitewood tree -Atalaya hemiglauca- and Woolly Rambutan -Alectryon tomentosus-) and that bugs living on them have evolved significantly longer beaks and new allometries. Genetic analyses of mitochondrial haplotypes and amplified fragment length polymorphic (AFLP) markers indicate that the lineage of bugs on the annual vine C. halicacabum, the older introduction, is intermediate between the two subspecies of L. tagalicus found on native hosts. Moreover, where the annual vine and Whitewood tree co-occur, the morphology and genomic composition of the bugs are similar to those occurring in allopatry. These results show that hybridization provided the genetic elements underlying the strongly differentiated 'Halicacabum bugs'. In contrast, the bugs feeding on the recently introduced perennial balloon vine (C. grandiflorum) showed no evidence of admixture, and are genetically indistinguishable from the nearby populations on a native host.

In this contribution we consider the biology of invading organisms after they have become established. Adaptive radiation over the long term has been a favorite subject in evolutionary biology. Examples have been Darwin's finches in the Galapagos and the honeycreepers and Droscphila of Hawaii. Hawaiian honeycreepers have evolved from a finch-like ancestor into guilds of seed eaters, nectar feeders, and combined nectar and insect feeders plus some species with unique beak structures. In the Hawaiian Drosophila sexual selection may have driven the extensive adaptive radiation and speciation in the group. The North American soapberry bug Jadera haemotoloma is an interesting model for post-invasion evolution in the short term. Some populations have moved onto introduced goldenrain trees Koelreuteria spp. and have evolved different stylet (mouthpart) lengths, as a function o f fruit size, and new host preferences, all within the last 50 years. These rapid responses are possible because of high additive genetic variances for these traits. Similarly, there has been rapid evolution of life history variation in American shad introduced from east coast to west coast rivers. We postulate that invaders most likely to integrate successfully are those in which high levels of additive genetic variation are expressed in traits most likely to be adaptive in the new environment. Copyright © 1996 Published by Elsevier Science Limited

Color markers in insects facilitate research in many areas, including developmental genetics and the study of sperm competition. Laboratory populations of the soapberry bug Jadera haematoloma contain two color variants, orange and lemon, in addition to the wild-type, red. Results of experimental crosses among these three types support a two-locus model with two alleles at each locus. The two loci interact epistatically such that individuals possessing two recessive genes at the second locus are lemon regardless of which genes are present at the first locus. The putative genotypes are red, R/– B/– ; orange, r/r B/– ; lemon, –/– b/b .

Embryonic development times and the stage at which embryonic diapause occurs varied dramatically among 23 populations of the Melanoplus sanguinipes/ devastator species complex in California, USA. Grasshoppers were collected from a wide range of latitudes (32°57N to 41°20N) and altitudes (10m to 3031 m), spanning much of the variation in climatic conditions experienced by these insects in California. When reared in a “common garden” in the laboratory, total embryonic development times were positively correlated to the mean annual temperature of the habitat from which the grasshoppers were collected (varying from about 19 days to 32 days when reared at 27°C). These grasshoppers overwinter as diapausing eggs and the proportion of embryonic development completed prior to diapause was significantly higher in populations collected from cool habitats (>70%) than in populations collected from warm environments (

This paper applies the biological species concept to two ecologically distinct species of grasshopper, Melanoplus sanguinipes and M. devastator, by testing for reproductive isolation in the field in California. Two independent techniques for assessing gene flow between species were employed. Firstly, we examined male genitalic morphology in populations from the foothills of the Sierra Nevada where the two species are parapatric. Two genetically based genitalic traits that differed between allopatric populations of each species formed a cline in this zone. Males captured in the field from the region of parapatry resembled offspring from interspecific laboratory hybridizations. Secondly, we surveyed electrophoretic variation of populations from across California and used F statistics to estimate levels of gene flow within and between species. Results from both morphology and F statistics suggested that these grasshoppers are not reproductively isolated in nature but that gene flow between species is reduced relative to within-species. These field results were consistent with a laboratory study that showed partial but not complete hybrid egg inviability. Because the hybrid zone is centred along an ecological transition, this system offers an opportunity to investigate whether adaptive changes across the zone contribute to reduced gene flow between species.

Birds of North America . by Kenn Kaufman. Houghton Mifflin, New York, 2000. 384 pp. Paper, $20. ISBN 0-395-96464-4. The Sibley Guide to Birds . by David Allen Sibley. Knopf, New York, 2000. 544 pp. Paper, $35, C$53. ISBN 0-679-45122-6. North American Bird Guide . Pica (Helm Information), East Sussex, UK, 2000. 544 pp. Paper, £25. ISBN 1-873403-98-4. Collins Bird Guide . by Lars Svensson, Killian Mullarney, Dan Zetterström, and Peter J. Grant. Harper Collins, London, 1999. 399 pp. £24.99. ISBN 0-00-219728-6. Large format, 2000. £29.99. ISBN 0-00-710082-5. Paper, 2001. £16.99. ISBN 0-00-711332-3. Birds of Europe . Princeton University Press, Princeton, NJ, 2000. 400 pp. Paper, $29.95. ISBN 0-691-05054-6. These three books advance the state-of-the-art in bird guides. Those new to birdwatching will find Kaufman's digitally edited photographs and concise text an efficient introduction to North American birds. Sibley's annotated, detailed paintings of flying and perched birds cover sexual, age, and geographic variation, and his book has been enthusiastically received by birders. Svensson et al . combine a comprehensive text on the field identification of European birds and superb artwork in what is the finest field guide to date for any regional avifauna.

Unlike those in northeastern North America, wing-dimorphic populations of California Aquarius remigis (Say) may contain relatively high frequencies of the macropterous morph. Winged individuals breed in seasonal streams, and apterous individuals are frequent in permanent streams and pools. The latter also harbor macropterous individuals during the summer dry season and support some breeding by them. Macropterous waterstriders are also common in permanent high-altitude streams of the Sierra Nevada. In California, winged individuals also fly readily before the breeding period, but they histolyze flight muscles at the beginning of the reproductive period suggesting that selection for migratory behavior in A. remigis affects only flights before reproduction. Temporary streams lack many waterstrider predators and other waterstrider species. These streams, however, run the risk of drying during development of nymphs. Only individuals with flight ability can colonize these habitats effectively and also escape when streams dry out.