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71.
72.
Intraflock variation in the speed of escape-flight response on attack by an avian predator 总被引:7,自引:2,他引:5
The benefits of flocking to prey species, whether through collective
vigilance,dilution of risk, or predator confusion, depend on flock members
respondingin a coordinated way to attack. We videotaped sparrowhawks
attackingredshank flocks to determine if there were differences in thetiming
of escape flights between flock members and the factorsthat might affect any
differences. Sparrowhawks are surpriseshort-chase predators, so variation in
the time taken to takeflight on attack is likely to be a good index of
predation risk.Most birds in a flock flew within 0.25 s of the first bird
flying,and all birds were flying within 0.7 s. Redshanks that werevigilant,
that were closest to the approaching raptor, and thatwere close to their
neighbors took flight earliest within aflock. Birds in larger flocks took
longer, on average, to takeflight, measured from the time that the first bird
in the flockflew. Most birds took flight immediately after near neighbors
tookoff, but later flying birds were more likely to fly immediatelyafter
more distant neighbors took flight. This result, alongwith the result that
increased nearest neighbor distance increasedflight delay, suggests that most
redshanks flew in responseto conspecifics flying. The results strongly
suggest that thereis significant individual variation in predation risk
withinflocks so that individuals within a flock will vary in benefitsthat
they gain from flocking. 相似文献
73.
Low and annually variable migratory connectivity in a long‐distance migrant: Whinchats Saxicola rubetra may show a bet‐hedging strategy
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Emma Blackburn Malcolm Burgess Benedictus Freeman Alice Risely Arin Izang Sam Ivande Chris Hewson Will Cresswell 《Ibis》2017,159(4):902-918
The spatial scale of non‐breeding areas used by long‐distance migrant animals can vary from specific, relatively small non‐breeding areas for each independent breeding population (high connectivity) to a distribution over a large non‐breeding area with mixing of breeding populations (low connectivity). Measuring variation in the degree of connectivity and how it arises is crucial to predict how migratory animals can respond to global habitat and climate change because low connectivity is likely to be an adaptation to environmental uncertainty. Here, we assess whether use of non‐breeding areas in a long‐distance migrant may be stochastic by measuring the degree of connectivity, and whether it is annually variable. Twenty‐nine wintering Whinchats tagged with geolocators over 2 years within 40 km2 in central Nigeria were found to be breeding over 2.55 million km2 (26% of the land area of Europe), without an asymptote being approached in the relationship between area and sample size. Ranges differed in size between years by 1.51 million km2 and only 15% of the total breeding range across both years overlapped (8% overlap between years when only first‐year birds were considered), well above the range size difference and below the proportion of overlap that would be predicted from two equivalent groups breeding at random locations within the observed range. Mean distance between breeding locations (i.e. migratory spread) differed significantly between years (604 ± 18 km in 2013 and 869 ± 33 km in 2014). The results showed very low and variable connectivity that was reasonably robust to the errors and assumptions inherent in the use of geolocators, but with the caveat of having only ranges of 2 years to compare, and the sensitivity of range to the breeding locations of a small number of individuals. However, if representative, the results suggest the scope for between‐year variation (cohort effects) to determine migrant distribution on a large scale. Furthermore, for species with similarly low connectivity, we would predict breeding population trends to reflect average conditions across large non‐breeding areas: thus, as large areas of Africa become subject to habitat loss, migrant populations throughout Europe will decline. 相似文献
74.
Cresswell Will; Holt S.; Reid J. M.; Whitfield D. P.; Mellanby R. J. 《Behavioral ecology》2003,14(1):97-102
The high energetic demands of incubation in birds may be animportant ecological factor limiting the evolution of life-historytraits, such as clutch size. In biparental species, however,the demands of incubation may not be a major constraint becausethere may always be sufficient feeding time available for theoff-duty bird to regain energy used during an incubation bout.We investigated whether the energetic demands of incubationconstrain optimum incubation bout length in a biparental incubatorby decreasing the energetic demands of incubation. We put aninsulated cup around the lining of semipalmated sandpiper nestsso that the rate of cooling of eggs was reduced by 21%. Semipalmatedsandpipers responded by increasing their mean incubation boutlength of around 11.1 h by about 10%. Bout lengths in unmanipulatednatural nests became longer as hatch approached (incubationstage), and this was independent of weather. Bout lengths mayhave decreased with increasing rainfall and were independentof time of day. The results suggest that bout length in semipalmatedsandpipers is constrained by their cumulative energetic expenditureduring an incubation bout, and this is determined partly bythe high costs of steady-state incubation. The results alsosuggest that the incubating bird determines the bout lengthrather than the returning bird. Semipalmated sandpipersmay havemaximized incubation bout length to minimize changeovers duringincubation because these probably increasepredation risk. Selectionto minimize the frequency of changeover may then be a factorcontributing to the evolution ofbiparental care and life-historytraits in semipalmated sandpipers. 相似文献
75.
An animal's foraging decisions are the outcome of the relative importance of the risk of starvation and predation. Fat deposition insures against periods of food shortage but it also carries a cost in terms of mass dependent predation risk due to reduced escape probability and extended exposure time. Accordingly, birds have been observed to show a unimodal foraging pattern with foraging concentrated at the end of the day under conditions of predictable food resources and high predation risk. We tested this hypothesis in a tropical granivorous finch, the rock firefinch Lagonosticta sanguinodorsalis , in an outdoor aviary experiment during which food was provided ad lib and the risk of predation was varied by providing food either adjacent to, or 5 m away from cover. Rock firefinches showed a bimodal foraging pattern regardless of the risk of predation at which they fed. The results suggest that predation is relatively unimportant in shaping their daily feeding pattern despite mass gain during the day being similar to temperate birds. Foraging patterns closely follow diurnal temperature variation and this is suggested to be the main determinant of the observed bimodal pattern. 相似文献
76.
W. Cresswell J. A. Clark R. Macleod 《Proceedings. Biological sciences / The Royal Society》2009,276(1672):3553-3560
Climate change within the UK will affect winter starvation risk because higher temperatures reduce energy budgets and are likely to increase the quality of the foraging environment. Mass regulation in birds is a consequence of the starvation–predation risk trade-off: decreasing starvation risk because of climate change should decrease mass, but this will be countered by the effects of predation risk, because high predation risk has a negative effect on mass when foraging conditions are poor and a positive effect on mass when foraging conditions are good. We tested whether mass regulation in great tits (Parus major) across the UK was related to temporal changes in starvation risk (winter temperature 1995–2005) and spatial changes in predation risk (sparrowhawk Accipiter nisus abundance). As predicted, great tits carried less mass during later, warmer, winters, demonstrating that starvation risk overall has decreased. Also, the effects of predation risk interacted with the effects of temperature (as an index of foraging conditions), so that in colder winters higher sparrowhawk abundance led to lower mass, whereas in warmer, later, winters higher sparrowhawk abundance led to higher mass. Mass regulation in a small bird species may therefore provide an index of how environmental change is affecting the foraging environment. 相似文献
77.
Viperin is an evolutionarily conserved interferon-inducible protein that
localizes to the endoplasmic reticulum (ER) and inhibits a number of DNA and
RNA viruses. In this study, we report that viperin specifically localizes to
the cytoplasmic face of the ER and that an amphipathic α-helix at its N
terminus is necessary for the ER localization of viperin and sufficient to
promote ER localization of a reporter protein, dsRed. Overexpression of intact
viperin but not the amphipathic α-helix fused to dsRed induced
crystalloid ER. Consistent with other proteins that induce crystalloid ER,
viperin self-associates, and it does so independently of the amphipathic
α-helix. Viperin expression also affected the transport of soluble but
not membrane-associated proteins. Expression of intact viperin or an
N-terminal α-helix-dsRed fusion protein significantly reduced secretion
of soluble alkaline phosphatase and reduced its rate of ER-to-Golgi
trafficking. Similarly, viperin expression inhibited bulk protein secretion
and secretion of endogenous α1-antitrypsin and serum albumin
from HepG2 cells. Converting hydrophobic residues in the N-terminal
α-helix to acidic residues partially or completely restored normal
transport of soluble alkaline phosphatase, suggesting that the extended
amphipathic nature of the N-terminal α-helical domain is essential for
inhibiting protein secretion.Type I interferons are the first line of defense against viral infections.
The significance of the interferon pathway is illustrated by the
susceptibility of interferon signaling mutants to infection and by viral
mechanisms that counteract this pathway
(1,
2). Although many genes are
induced upon interferon stimulation, very few of these genes have been
functionally characterized. Viperin is highly induced by both Type I and II
interferons and has a broad range of antiviral activity, inhibiting DNA
viruses, notably human cytomegalovirus
(3); RNA viruses such as
influenza, hepatitis C virus
(HCV),2 and
alphaviruses
(4-6);
and retroviruses such as human immunodeficiency virus
(7). Upon expression, viperin
localizes to the endoplasmic reticulum (ER), where it interacts with
farnesyl-diphosphate synthase, an enzyme involved in lipid biosynthesis. This
interaction appears to result in the disruption of lipid raft microdomains and
prevention of influenza virus from budding from the plasma membrane
(4).Although recent studies have explored the antiviral functions of viperin,
the general biochemical properties of this protein remain largely undefined.
Viperin is highly conserved across both mammals and lower vertebrates and
shares homology with the MoaA family of “radical
S-adenosylmethionine” enzymes that bind Fe-S clusters
(3,
8). In addition to a putative
Fe-S cluster-binding domain, viperin has a 42-amino acid residue N-terminal
amphipathic α-helix, and similar domains in other proteins have been
shown to bind membranes and induce membrane curvature
(9,
10).In this study, we examined the role of the viperin N-terminal
α-helical domain in both cellular localization and ER membrane
morphology and analyzed the biochemical properties of viperin. We discovered
that viperin forms dimers and induces a tightly ordered, visually striking
array of ER membranes, known as crystalloid
ER(11-13),
upon overexpression. In addition, viperin expression impedes the secretion of
a variety of soluble proteins. Although the N-terminal amphipathic
α-helix is not sufficient to induce crystalloid ER formation, it is both
necessary and sufficient to mediate ER localization and to inhibit protein
secretion. 相似文献
78.
1.?How group size affects predator attack and success rate, and so prey vulnerability, is important in determining the nonlethal consequences of predation risk on animal populations and communities. Theory predicts that both predator attack success rate and the dilution effect decline exponentially with group size and that selection generates optimal group sizes at a 'risk threshold' above which antipredation benefits are outweighed by costs, such as those owing to higher attack rates. 2.?We examined whether flock size risk thresholds for attack rate, success rate or dilution differed, and therefore whether the strength of selection for group size differed for these three factors, using a system of redshank Tringa totanus flocks being hunted by Eurasian sparrowhawks Accipiter nisus. We also asked which of the three thresholds, on their own or in combination, predicted the most commonly observed group size. 3.?Mean redshank flock size increased with a very gradual quadratic function (i.e. approximately linearly) with population size, although at a rate half that possible; when population size was not limiting, individuals almost always avoided flocks of less than 30 and birds were frequently in flocks up to at least 80. Sparrowhawk attack rate showed a quadratic relationship with flock size and peaked at 55 redshanks. Sparrowhawk attack success rate, however, declined exponentially, becoming less steep at flock sizes of about 40 and remaining uniformly low (a 95% decrease) by 70. Combined with dilution, individual risk of death per attack decreased by 95% when group size reached 30 (20 for the dilution effect alone). 4.?Redshanks most commonly formed group sizes that gained the maximum individual predation risk reduction. They also commonly formed group sizes far above any further substantial advantages from the dilution effect or from reducing attack rate, but that continued to reduce predation risk by lowering attack success rate. Individuals did not always form the largest groups possible which we suggest is because individual variation in risk-taking subdivides the population. This places a constraint on the ability of individuals to compensate for predation risk and will have a variety of important effects on animal populations. 相似文献
79.
HLA-DR molecules are heterodimeric transmembrane glycoproteins that associate intracellularly with a polypeptide known as the invariant (I) chain. Shortly before expression of the HLA-DR αβ dimer on the cell surface, however the I chain is removed from the intracellular αβI complex by a mechanism thought to involve proteolysis . In this report, we show that treatment of purified αβI with the cysteine proteinase cathepsin B results in the specific proteolysis of the HLA-DR-associated I chain in vitro. As a consequence of this, the I chain is removed and free αβ dimers are released from αβI. Although αβI fails to bind an immunogenic peptide, the released αβ dimers acquire the ability to bind the peptide after proteolysis of the I chain. These results suggest that the I chain inhibits immunogenic peptide binding to αβI early during intracellular transport and demonstrate that proteolysis is likely to be the in vivo mechanism of I chain removal. 相似文献
80.
Anika I Tsuchida Michiel Beekhuizen Marieke C ‘t Hart Timothy RDJ Radstake Wouter JA Dhert Daniel BF Saris Gerjo JVM van Osch Laura B Creemers 《Arthritis research & therapy》2014,16(5)