Steel wheels: The Age of Migration 5.0

As with all previous editions, the fifth edition offers substantial updates and developments. The addition of de Haas as a third author in this edition has had noticeable impacts on the shape and content of the book. The Age of Migration does not simply report on or contribute to the field of migration studies; it has done more than any other book to define that field.     

A landmark in the landscape of migration studies

The Age of Migration continues to play an important role in defining migration studies as a multidisciplinary field. It is primarily a textbook, although it is also used by established researchers and professionals. The book does a formidable job in providing a foundation of knowledge, albeit in a form that makes it most suited as a sourcebook to be read and digested over time. The authors seek to motivate readers with reference to the dramas of immigration in current events and politics; appeal to intellectual curiosity as a motivation for studying migration is not as well developed in the text.     

Faster migration in autumn than in spring: seasonal migration patterns and non‐breeding distribution of Icelandic whimbrels Numenius phaeopus islandicus

Migration is fundamental in the life of many birds and entails significant energetic and time investments. Given the importance of arrival time in the breeding area and the relatively short period available to reproduce (particularly at high latitudes), it is expected that birds reduce spring migration duration to a greater extent than autumn migration, assuming that pressure to arrive into the wintering area might be relaxed. This has previously been shown for several avian groups, but recent evidence from four tracked Icelandic whimbrels Numenius phaeopus islandicus, a long distance migratory wader, suggests that this subspecies tends to migrate faster in autumn than in spring. Here, we 1) investigate differences in seasonal migration duration, migration speed and ground speed of whimbrels using 56 migrations from 19 individuals tracked with geolocators and 2) map the migration routes, wintering and stopover areas for this population. Tracking methods only provide temporal information on the migration period between departure and arrival. However, migration starts with the fuelling that takes place ahead of departure. Here we estimate the period of first fuelling using published fuel deposition rates and thus explore migration speed using tracking data. We found that migration duration was shorter in autumn than in spring. Migration speed was higher in autumn, with all individuals undertaking a direct flight to the wintering areas, while in spring most made a stopover. Wind patterns could drive whimbrels to stop in spring, but be more favourable during autumn migration and allow a direct flight. Additionally, the stopover might allow the appraisal of weather conditions closer to the breeding areas and/or improve body condition in order to arrive at the breeding sites with reserves.     

How selective migration enables socioeconomic mobility

ABSTRACT

Jennifer Lee and Min Zhou’s new book, The Asian American Achievement Paradox, revives Asian American scholarship from a period of relative stagnation and elevates the discussion from the morass of cultural essentialism. Its major contributions are to extensively articulate: (1) how much cultural explanations are actually class-based explanations and (2) how selective migration creates the conditions that promote social mobility. This book resolves empirical paradoxes in the scholarship and engages broader debates on race, immigration and inequality.     

Diffuse, short and slow migration among Blue Tits

The knowledge of migration systems in long-distance regular migrants is in many cases extensive. Our understanding of the migratory characteristics of partial migrants, on the other hand, is far more rudimentary. We investigated migratory characteristics of partially migratory Blue Tits Cyanistes caeruleus using ringing recoveries of Swedish birds, to answer questions about geographic migration patterns, age-specific migrations, migration speeds and synchrony of movements. Median migration distance of Swedish Blue Tits was 82 km, with a main autumn direction in the sector between S and W (large directional scatter). Northerly and southerly populations did not differ in migration directions or distances, suggesting chain migration to be the general pattern. A larger proportion of adult Blue Tits remained near the breeding grounds during winter than was the case for juveniles. Some of the migrating birds (17%) seemed not to return in spring but stayed to breed closer to the winter area. Swedish Blue Tits show an exceptionally slow migration speed (median 13 km/day), among the slowest speeds recorded for any migrant bird. The Blue Tit represents an extreme case of diffuse, short and slow bird migration.     

Acyl migration during deacylation of phospholipids rich in docosahexaenoic acid (DHA): an enzymatic approach for evidence and study

Non-enzymatic acyl migration could be counter-productive for the preparation of structured phospholipids with docosahexaenoic acid (DHA) at a designated position. Therefore enzymatic approaches have been developed to investigate acyl migration. First, acyl migration from sn-2 to sn-1 position has been set into relief by a three step enzymatic method using a typo-selective lipase, a phospholipase A2 and a non-selective lipase. The effect of reaction temperature on acyl migration from sn-2 to sn-1 was monitored: lowering the reaction temperature from 40 to 30°C allowed a reduction of DHA migration rate of 40%. Secondly, acyl migration from sn-1 to sn-2 position was negligible. This last result was obtained through the study of structured phosphatidylcholine selective deacylation using a phospholipase A2.     

Restricted distribution and limited gene flow in the model ciliate Tetrahymena thermophila

The biogeography of microbial eukaryotes has long been debated, but few phylogeographic data have been available to assess whether protists tend to have ubiquitous or endemic distributions. We addressed this issue in the ciliate Tetrahymena thermophila, a highly successful model system in cell and molecular biology. We found that this species has a distribution that is restricted to the Eastern United States, with high diversity in the northeast and low diversity across the rest of its distribution. We find high levels of population subdivision, low rates of migration and significant isolation by distance, supporting the moderate endemicity model of protist biogeography. This restricted gene flow may be a result of small population size, which would reduce the probability of migration events, or the inability to establish after migration. This work lays the foundation for T. thermophila to become a valuable model system for studying population biology.     

Counterintuitive migration patterns by Atlantic salmon Salmo salar smolts in a large lake

What little is known about the seaward migration of Salmo salar smolt migration through standing waters indicates that it is both slow and results in high mortality rates, compared with riverine migration. This may be partly because smolts in lakes need to swim more actively and require more complex directional cues than they do in rivers. In this telemetry study of smolt migration through Loch Lomond, S. salar smolts made repeated movements in directions away from the outflowing river, which considerably increased migration time.     

Independent evolution of migration on the South American landscape in a long-distance temperate-tropical migratory bird, Swainson's flycatcher (Myiarchus swainsoni)

Aim To understand the evolution of long‐distance temperate–tropical migration in a South American bird, Swainson's flycatcher (Myiarchus swainsoni). Methods A total of 842 base pairs of the mitochondrial DNA genes ATPase 8 and 6 were sequenced from forty‐nine individuals of the M. swainsoni complex from most of its range. Analyses measured the phylogenetic signal in the data, and tools of population genetics, phylogeography and phylogeny were used to interpret the evolution of the bird and its migration on the South American landscape. Results Migratory populations in the M. swainsoni complex are not each other's closest relatives. The migratory subspecies M. s. swainsoni, which breeds in south‐eastern South America, is not closely related to the rest of the complex. The remaining migratory populations of the subspecies M. s. ferocior and two intergrade populations are extremely closely related to non‐migratory populations with which they form a well‐supported clade despite substantial morphological differentiation from each other. Within this clade of migrants and non‐migrants, net divergence across 4000 km of lowland South America is zero and most diversity is distributed among individuals not populations. Mismatch analyses and significant values of Tajima's D and Fu's Fs suggest the clade has undergone a very recent range expansion. Migration and the shifts of breeding distribution that accompanied its evolution evolved twice within what has recently been considered the polytypic species M. swainsoni. Furthermore, these shifts of range probably occurred at very different times as parts of different southward ‘pulses’ of humid, Amazonian taxa. Main conclusions Evolution of temperate‐tropical migration in the M. swainsoni complex has been spatio‐temporally layered on the South American landscape. The analysis cautions that the historical biogeography underlying a single present‐day migration system need not have been driven by a single set of environmental factors operating at one time. We suggest directions for further study of ecology and demography in zones of apparent contact between various migratory and non‐migratory populations.     

Finish with a sprint: Evidence for time‐selected last leg of migration in a long‐distance migratory songbird

Under time‐selected migration, birds should choose a strategy for outcompeting rivals over securing access to prime resources at the final destination. Thus, migration can be viewed as a race among individuals where winners are arriving first when conditions are suitable. The sprint migration hypothesis predicts that individuals shift from maximum sustained speed to a final burst of sprint to shorten the transition from migration to breeding (Alerstam, 2006). In this study, we test the hypothesis of a final sprint migration in a long‐distance Afro‐Palearctic migrant, the collared flycatcher Ficedula albicollis, during autumn and spring, and compare migration strategies between the seasons. In both seasons, collared flycatchers evidently exhibited sprint migration by increasing their overall speed over the last leg of migration after the Sahara crossing. This phenomenon was more pronounced in spring, contributing to overall faster spring migration and possibly highlighting higher importance for early arrival at the breeding grounds. In both seasons and particularly in spring, late departing individuals flew at a faster rate, partially being able to catch up with their early departing conspecifics. Differential fueling strategies may play an important role in determining migration speed, especially during the early stages of the migration, and might explain the observed differences in migration speeds between late and early departing individuals. Our findings suggest competition for early arrival at the breeding and at the nonbreeding destinations alike. Sprint migration might be an appropriate strategy to gain advantage over conspecifics and settle in prime territories as well as to cope with the increasingly earlier springs at high latitudes.     

Crispld2 is required for neural crest cell migration and cell viability during zebrafish craniofacial development

The CAP superfamily member, CRISPLD2, has previously been shown to be associated with nonsyndromic cleft lip and palate (NSCLP) in human populations and to be essential for normal craniofacial development in the zebrafish. Additionally, in rodent models, CRISPLD2 has been shown to play a role in normal lung and kidney development. However, the specific role of CRISPLD2 during these developmental processes has yet to be determined. In this study, it was demonstrated that Crispld2 protein localizes to the orofacial region of the zebrafish embryo and knockdown of crispld2 resulted in abnormal migration of neural crest cells (NCCs) during both early and late time points. An increase in cell death after crispld2 knockdown as well as an increase in apoptotic marker genes was also shown. This data suggests that Crispld2 modulates the migration, differentiation, and/or survival of NCCs during early craniofacial development. These results indicate an important role for Crispld2 in NCC migration during craniofacial development and suggests involvement of Crispld2 in cell viability during formation of the orofacies. genesis 53:660–667, 2015. © 2015 Wiley Periodicals, Inc.     

Glacial survival does not matter: RAPD phylogeography of Nordic Saxifraga oppositifolia

The arctic-alpine Saxifraga oppositifolia has recently been suggested to have survived the last glaciation in high-arctic refugia, based on a finding of more genetic (RFLP) variation in Svalbard compared with more southern areas. To elucidate the migration history of this allogamous species, we analysed 18 populations from Norway, Svalbard and Novaya Zemlya using random amplified polymorphic DNAs (RAPDs). There was no more RAPD variation in the high Arctic than further south. In an analysis of molecular variance (AMOV A), most of the RAPD variation was found within populations (64%). There was less intrapopulational variation in Svalbard (65%) than in northern Norway (78%) and southern Norway (86%), suggesting that there is more inbreeding towards the north, probably because of lower pollinator activity. Twenty-eight per cent of the RAPD variation was found among populations within these geographical regions, and only 9% was found among the regions. In PCO and UPGMA analyses, plants and populations of different geographical origins were to a large extent intermingled. There was, however, a distinct, south-north clinal geographical structuring of the RAPD variation both in the PCO analysis and in a spatial autocorrelation (Mantel) analysis. These results suggest that there has been extensive gene flow among more or less continuously distributed populations of S. oppositifolia during the Weichselian, and that the extant Nordic populations were established after massive, centripetal immigration from these genetically variable, periglacial populations. The postglacial period may not have been sufficiently long for the subsequently isolated populations of this long-lived, allogamous perennial to diverge. Given the high levels of migration inferred from this study, genetic differentiation of glacial survivor populations, if any existed, would most likely have been swamped in the postglacial period. Thus, our molecular data support recent conclusions based on palaeobotanical and biogeographical data that the glacial survival hypothesis is superfluous.     

The study of bird migrations – some future perspectives

Capsule Routes and destinations have been unveiled but modern techniques offer the chance to explore much more.

Ringing of birds unveiled many mysteries of avian migrations, notably routes and destinations. However, there is still much to be explored by the use of ringing and other marks. Satellite tracking, geolocation and global positioning systems, and even electronic tags may enable much more detailed insights into the migration patterns of individual birds and populations. But also a more elaborated colour-marking approach is recommended. Moreover, particular chemical and molecular markers appear to be very useful in the study of bird migration by delineating the origin of birds and connectivity between breeding and non-breeding grounds. Co-ordinated, collaborative, standardized and large-scale migration networks provide another elaborate tool to study differential migration and patterns of migratory timing and fuelling. Although our understanding of bird migration has gained much from captive studies about the internal mechanisms in the control of bird migration, we still lack knowledge about external factors, such as food availability, weather, competitors, parasites or diseases. Such data are also required to refine theoretical models of migration strategies. Future migration research must aim at much more comparative research and a more integrative approach at various spatial and temporal scales, and link various subdisciplines. It must also consider that migration is only one part of the life of a migrating species. Thus, linking migration and breeding is another future challenge, both for basic science and for effective protection of migratory birds.     

Contradictions and Complexities—Current Perspectives on Pacific Islander Mobilities

From the first movements of people towards the Pacific Islands millennia ago to recent transnational migration in a globalised world, translocal mobility has been a central aspect of the social lives, cultures and histories of many Pacific Islanders. While Oceania has always been an area of migration as well as cultural and economic exchange, current transnational Pacific movements are deeply embedded in a twentieth- and twenty-first-century global phenomenon, which Castles and Miller [2009. The Age of Migration. International Population Movements in the Modern World. Houndsmill: MacMillan Press. (1993 1st edition)] have called the ‘age of migration’. This essay gives an overview of Pacific Islander migration and its patterns and motives as presented in previous studies. It shows how useful cultural categories can be for a deeper understanding of notions of moving and staying, two pluralistic and not contradictorily perceived concepts for Pacific Islanders that are crucial in transnational migration. With its focus on transnational migration and the challenges experienced by Fijians in the UK and Japan, and Micronesian Chuukese in Guam, Hawai'i, and the US mainland, this introduction concludes by analysing how the case studies presented in this special issue contribute to and complement current anthropological perspectives on Pacific Islanders’ multiple and complex forms of transnationalism.     

Unique neuronal tracers show migration and differentiation of SVZ progenitors in organotypic slices

Continual neurogenesis in the subventricular zone (SVZ) of postnatal and adult mammalian forebrain has been well documented, but the mechanisms underlying cell migration and differentiation in this region are poorly understood. We have developed novel in vivo and in vitro methods to investigate these processes. Using stereotaxic injections of a variety of tracers/tracker [Cholera Toxin β subunit (CTb‐), Fluorogold (FG), and Cell Tracker Green (CTG)], we could efficiently label SVZ cells. Over several days, labeled cells migrate along the rostral migratory stream (RMS) to their final differentiation site in the olfactory bulb (OB). The compatibility of these tracers/trackers with immunohistochemistry allows for cell labeling with multiple dyes (e.g., CTb and CTG) and/or specific cell antigens. To investigate the dynamics of migration we labeled SVZ progenitor cells with small injections of CTG and monitored the movements of individual cells in fresh parasagittal brain slices over several hours using time‐lapse confocal microscopy. Our observations suggest that tangential cell migration along the RMS occurs more rapidly than radial cell migration into the OB granule cell layer. To investigate migration over longer time periods, we developed an in vitro organotypic slice in which labeled SVZ progenitors migrate along the RMS and differentiate within the OB. The phenotypic characteristics of these cells in vitro were equivalent to those observed in vivo. Taken together, these methods provide useful tools investigating cell migration and differentiation in a preparation that maintains the anatomical organization of the RMS. © 2001 John Wiley & Sons, Inc. J Neurobiol 49: 326–338, 2001     

盐城沿海海堤林带柳莺属(Phylloscopus)鸟类秋季迁徙规律

江苏盐城沿海具有广阔的平原与湿地滩涂,但缺少自然林地。经过多年的防风林建设,沿海海堤逐渐形成了特有的、南北走向的条带林生境,为迁徙鸟类提供了通道和停歇地,是研究鸟类迁徙规律的理想地点。柳莺属鸟类个体小,野外种类识别难,其迁徙规律缺乏深入研究。分别于2018年和2019年两个秋季,采用雾网法对盐城沿海海堤林带柳莺属鸟类的迁徙规律进行研究。结果表明：两个秋季共捕获柳莺属鸟类8种608只,其中极北柳莺（Phylloscopus borealis）、冕柳莺（P. coronatus）、淡脚柳莺（P. tenellipes）和黄眉柳莺（P. inornatus）的捕获数量分别为245只、131只、107只和94只,占捕获总数量的95%,是秋季迁徙期的优势种。对优势种柳莺日捕获率进行比较：2019年极北柳莺的日捕获率显著高于淡脚柳莺和黄眉柳莺（U test,P<0.05）。对捕获数量随时间变化进行分析,4种柳莺都以集中在短时间内快速通过的迁徙策略穿越盐城沿海海堤林带,符合秋季小型雀形目鸟类迁徙采取时间最小化假说。不同种类的柳莺在通过盐城沿海海堤林带的时间顺序上存在显著差异（K-W test,P<0.05）,2018年和2019年均以黄眉柳莺通过最晚。随着时间的推移,四种柳莺的脂肪度都逐渐下降。繁殖地纬度的差异可能是导致4种柳莺通过盐城沿海海堤林带时间差异的原因。盐城沿海海堤林带为柳莺属等雀形目小型鸟类的迁徙提供了非常理想的迁徙通道,应当加强海堤林带在鸟类迁徙和保护中的作用研究。     

The long arm of the Arab state

ABSTRACT

Under what conditions do authoritarian states exercise control over populations abroad? The securitization of cross-border mobility has been a common theme in examining immigration policies in the Global North. The securitization of emigration and diasporas in non-democratic contexts remains neglected; this is particularly true with regard to Arab states’ extraterritorial authoritarian practices. This article argues that authoritarian states develop a range of migration policies that are driven by the contradictory pressures of economic and political imperatives or, put differently, an illiberal paradox: if a state does not expect economic gains from cross-border mobility, it is more likely to securitize its emigration policy; otherwise, it is more likely to securitize its diaspora policy. The article illustrates this trade-off via a most-similar comparison of Algeria, Libya, Tunisia, and Morocco. Drawing on Arabic and non-Arabic primary and secondary sources, it sketches a novel area of research on migration and security.     

Mechanical and structural adaptations to migration in the flight feathers of a Palaearctic passerine

Current avian migration patterns in temperate regions have been developed during the glacial retreat and subsequent colonization of the ice‐free areas during the Holocene. This process resulted in a geographic gradient of greater seasonality as latitude increased that favoured migration‐related morphological and physiological (co)adaptations. Most evidence of avian morphological adaptations to migration comes from the analysis of variation in the length and shape of the wings, but the existence of intra‐feather structural adjustments has been greatly overlooked despite their potential to be under natural selection. To shed some light on this question, we used data from European robins Erithacus rubecula overwintering in Campo de Gibraltar (Southern Iberia), where sedentary robins coexist during winter with conspecifics showing a broad range of breeding origins and, hence, migration distances. We explicitly explored how wing length and shape, as well as several functional (bending stiffness), developmental (feather growth rate) and structural (size and complexity of feather components) characteristics of flight feathers, varied in relation to migration distance, which was estimated from the hydrogen stable isotope ratios of the summer‐produced tail feathers. Our results revealed that migration distance not only favoured longer and more concave wings, but also promoted primaries with a thicker dorsoventral rachis and shorter barb lengths, which, in turn, conferred more bending stiffness to these feathers. We suggest that these intra‐feather structural adjustments could be an additional, largely unnoticed, adaptation within the avian migratory syndrome that might have the potential to evolve relatively quickly to facilitate the occupation of seasonal environments.