Turnover of passerine birds on islands in the Aegean Sea (Greece)

Aim We wish to determine the effect of migratory status on turnover rates in island birds. Because turnover is influenced by factors other than migratory status, we also considered the influence of body size and physical characteristics of the islands inhabited on the probabilities of extinction and immigration. Location The Mediterranean islands of Delos, Astypalea, Paros, Naxos and Lesvos in the Aegean Sea, Greece. Methods The passerine birds of these islands were surveyed between 1954 and 1961 by G.E. Watson, and were resurveyed between 1988 and 1992. The effects of migratory status and body size on the probabilities of extinction and immigration were examined by G‐tests of linear trend in proportion, and analysis of variance, respectively. A combined analysis of migratory status, body size and physical characteristics of the islands was carried out using logistic regressions of the probabilities of extinction and immigration on these factors. Results Species number on each island changed little between surveys, with no island's species number changing by more than one species. Twelve population extinctions and 11 immigrations were recorded. The smallest island, Delos (6 km²), had the highest annualized relative turnover rate (1.08), while the four larger islands (96–1614 km²) had lower and mutually similar rates (0.21–0.27). Populations on higher elevation islands were less likely to go extinct. There is no evidence for an effect of body size on the probabilities of extinction or immigration. Migratory status affected extinction and immigration probabilities differently: migratory species were more likely to immigrate, but less likely to go extinct. Main conclusions The position of the Aegean islands along a major north–south flyway may account for the observed effects of migratory status. The annual passage of large numbers of migrants may, via the rescue effect, decrease the chances of extinction, while at the same time increasing the chances of colonization of unoccupied islands. The likelihood of both extinction and immigration involves a complex interaction between life‐history traits and island characteristics. The effects of migratory status will depend not only on consideration of vagility, vulnerability and stochasticity identified by previous authors, but also upon the location of the islands in relationship to migratory pathways.     

Regulation of adult neural precursor cell migration

Adult neural precursor cells (NPCs) are predominantly located in the subventricular zone (SVZ) of the lateral ventricles or in the subgranular zone of the dentate gyrus. These NPCs produce neuroblasts that normally migrate and integrate into the olfactory bulb and hippocampus, respectively. Following CNS damage due to disease or injury, NPCs can also migrate to the site of damage. Enhancement of NPC migration to sites of neural damage may increase their potential for repair but requires an understanding of processes that regulate basal and injury-induced migration so we can harness this potential. This review highlights the extrinsic factors and major intrinsic signalling pathways that regulate endogenous basal NPC migration to the olfactory bulb and the role of inflammatory mediators and chemokines in disease and injury-induced NPC migration.     

Stochastic dynamics of magnetosomes and a mechanism of biological orientation in the geomagnetic field

The rotations of nanoscopic magnetic particles, magnetosomes, embedded into the cytoskeleton are considered. Under the influence of thermal disturbances, a great number of magnetosomes are shown to move chaotically between two stable equilibrium positions, in which their magnetic moments are neither parallel nor antiparallel to the static Earth's magnetic field (MF). The random rotations attain the value of order of a radian. The rate of the transitions and the probability of magnetosomes to be in the different states depend on the MF direction with respect to an averaged magnetosome's orientation. This effect explains the ability of migratory animals to orient themselves faultlessly in long term passages in the absence of the direct visibility of optical reference points. The sensitivity to deviation from an "ideal" orientation is estimated to be 2-4 degrees. Possible involvement of the stochastic dynamics of magnetosomes in biological magnetic navigation is discussed.     

Size and accumulation of fuel reserves at stopover predict nocturnal restlessness in a migratory bird

Early arrival at the breeding site positively affects the breeding success of migratory birds. During migration, birds spend most of their time at stopovers. Therefore, determining which factors shape stopover duration is essential to our understanding of avian migration. Because the main purpose of stopover is to accumulate fat as fuel for the next flight bout, fuel reserves at arrival and the accumulation of fuel are both expected to affect stopover departure decisions. Here, we determined whether fuel reserves and fuel accumulation predict a bird''s motivation to depart, as quantified by nocturnal migratory restlessness (Zugunruhe), using northern wheatears (Oenanthe oenanthe) that were captured and temporarily contained at spring stopover. We found that fuel reserves at capture were positively correlated with Zugunruhe, and negatively correlated with fuel accumulation. This indicates that fat birds were motivated to depart, whereas lean birds were set on staying and accumulating fuel. Moreover, the change in fuel reserves was positively correlated with the concurrent change in Zugunruhe, providing the first empirical evidence for a direct link between fuel accumulation and Zugunruhe during stopover. Our study indicates that, together with innate rhythms and weather, the size and accumulation of fuel reserves shape stopover duration, and hence overall migration time.     

Masquerade is associated with polyphagy and larval overwintering in Lepidoptera

Masquerading animals benefit from the difficulty that predators have in differentiating them from the inedible objects, such as twigs, that they resemble. The function of masquerade has been demonstrated, but how it interacts with the life history of organisms has not yet been studied. Here, we report the use of comparative analyses to test hypotheses linking masquerade to life‐history parameters. We constructed a phylogenetic tree of the British species of the lepidoptera families Geometridae and Drepanidae, and compiled life history and coloration data from the literature. We found that masquerade is associated with the exploitation of a greater diversity of host plants whether measured by the number of families or genera. We found a positive relationship between body size and polyphagy among masquerading species, and no relationship among cryptic species. Among those species predominantly found on woody host plants, masquerading species are more likely to overwinter as larvae while cryptic species mostly overwinter as pupae. Polyphenism was associated with multivoltinism in masquerading species but not cryptic species. Taken together, our results show that masquerade must be viewed as a strategy distinct to crypsis and hence may provide insights into the evolution of both defensive strategies. Our study further demonstrates the utility of broad‐scale between‐species comparisons in studying associations between diverse life‐history parameters and sensory aspects of predator‐prey interactions. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 90–103.     

Spatial and temporal variation in population trends in a long‐distance migratory bird

Aim Over the past three decades, evidence has been growing that many Afro‐Palaearctic migratory bird populations have suffered sustained and severe declines. As causes of these declines exist across both the breeding and non‐breeding season, identifying potential drivers of population change is complex. In order to explore the roles of changes in regional and local environmental conditions on population change, we examine spatial and temporal variation in population trajectories of one of Europe’s most abundant Afro‐Palaearctic summer migrants, the willow warbler, Phylloscopus trochilus. Location Britain and Ireland. Methods We use national survey data from Britain and Ireland (BBS: BTO/RSPB/JNCC Breeding Bird Survey and CBS: BWI/NPWS/Heritage Council Countryside Breeding Survey) from 1994 to 2006 to model the spatial and temporal variation in willow warbler population trends. Results Across Britain and Ireland, population trends follow a gradient from sharp declines in the south and east of England to shallow declines and/or slight increases in parts of north and west England, across Scotland and Ireland. Decreasing the spatial scale of analysis reveals variation in both the rate and spatial extent of population change within central England and the majority of Scotland. The rates of population change also vary temporally; declines in the south of England are shallower now than at the start of the time series, whereas populations further north in Britain have undergone periods of increase and decline. Main conclusion These patterns suggest that regional‐scale drivers, such as changing climatic conditions, and local‐scale processes, such as habitat change, are interacting to produce spatially variable population trends. We discuss the potential mechanisms underlying these interactions and the challenges in addressing such changes at scales relevant to migratory species.     

Impact of migratory snow geese on nitrogen and phosphorus dynamics in a freshwater reservoir

1. We examined impacts of nutrient loading, particularly of nitrogen and phosphorus, from greater snow geese (Chen caerulescens atlantica) on a reservoir in south‐eastern Pennsylvania, U.S.A. Approximately 100 000 geese use the reservoir for 2–6 weeks prior to their spring migration northward. 2. We estimated the magnitude of nutrient loading by geese during their presence and compared that to surface input and output rates. We also conducted nutrient limitation bioassay experiments to examine patterns of algal nutrient limitation upstream and downstream of the reservoir. 3. During their presence from 1 February to 27 March 2001, snow geese contributed 85–93% of the phosphorus and 33–44% of the nitrogen loaded to the reservoir. Both nutrients were exported from the reservoir slowly rather than as a quick pulse. Consequently, phosphorus concentrations in the outflow were higher than in the inflow from February to the end of July. However, nitrogen concentrations were consistently lower in the outflow than the inflow. 4. Nutrient limitation bioassays conducted in June and July indicated that primary production in the outflow was limited by nitrogen whereas the inflow was co‐limited by nitrogen and phosphorus. Further downstream from the reservoir, primary production was consistently phosphorus limited. Therefore, nitrogen limitation persisted long after the geese had left, but was relatively localised.     

飞蝗及沙漠蝗信息素概述

飞蝗和沙漠蝗自古以来就是重要的农业害虫,这与其生物学特性是密不可分的.信息素对飞蝗和沙漠蝗生物学特征的调节起到了非常重要的作用.到目前为止,沙漠蝗Schistocerca gregaria和飞蝗Locusta migratoria 的研究较为深入,本文对其主要成果进行了综述,以此作为以后飞蝗和沙漠蝗信息素进一步研究的参...     

飞蝗复眼生理和结构上的节律变化

采用细胞内记录和光镜方法研究了飞蝗(Locusta migratoria)夜间和日间在暗适应和明适应状态下小网膜细胞角敏感度以及晶锥和小网膜细胞之间区域结构上的变化.结果表明小网膜细胞角敏感度的变化不仅仅由于晶锥周围主色素细胞色素颗粒的移动,而且也由于小眼感杆束结构上的节律变化.