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61.
Apostolos Kapranas P. Pacheco L. D. Forster J. G. Morse R. F. Luck 《Behavioral ecology and sociobiology》2008,62(6):901-912
We examined whether several facultatively gregarious encyrtid (Hymenoptera: Encyrtidae) endoparasitoids of brown soft scale,
Coccus hesperidum L., manifest precise sex allocation under field conditions. Metaphycus luteolus (Timberlake), Metaphycus angustifrons (Compere), Metaphycus stanleyi (Compere), and Microterys nietneri (Motshulsky) evince brood sex ratios that are female-biased and extremely precise (low variance in the number of sons per
host). Typically, this sex allocation pattern is attributed to extreme local mate competition (LMC) in which only one foundress
exploits a patch of hosts and mating occurs mostly between her offspring. However, such a pattern of sex allocation was not
detected for Metaphycus helvolus (Compere). Also, a large proportion of the broods in all five species contained only daughters; thus, an excess of male-only
broods was expected if unmated females (i.e., females that can produce only sons) contribute offspring before mating. All-male
broods were rare in our samples. This finding coupled with the life history characteristics of these wasps, such as the exploitation
of aggregated hosts and the long life span and mobility of males, suggest that nonlocal mating is frequent. Our empirical
work suggests that it is advantageous to allocate precise sex ratios in cases in which mating opportunities for males are
not restricted to their natal host and/or when multiple foundresses exploit large patches of hosts. Limited theoretical work
also supports this prediction but more detailed studies of this taxon’s mating structure and other life history characteristics
are necessary to understand their sex allocation decisions. 相似文献
62.
Amy C. Dolan Michael T. Murphy Lucas J. Redmond Debbie Duffield 《Behavioral ecology and sociobiology》2009,63(10):1527-1537
Sex allocation theory predicts that if variance in reproductive success differs between the sexes, females who are able to
produce high-quality young should bias offspring sex ratio towards the sex with the higher potential reproductive success.
We tested the hypothesis that high-quality (i.e., heavy) female eastern kingbirds (Tyrannus tyrannus) that bred early in the breeding season would produce male-biased clutches. A significant opportunity for sexual selection
also exists in this socially monogamous but cryptically polygamous species, and we predicted that successful extra-pair (EP)
sires would be associated with an excess of male offspring. Although population brood sex ratio did not differ from parity,
it increased significantly with female body mass and declined with female breeding date, but was independent of the morphology
and display (song) behavior (correlates of reproductive success) of social males and EP sires. Male offspring were significantly
heavier than female offspring at fledging. Moreover, the probability that male offspring were resighted in subsequent years
declined with breeding date, and was greater in replacement clutches, but lower when clutch size was large. Probability of
resighting female offspring varied annually, but was independent of all other variables. Given that variance in reproductive
success of male kingbirds is much greater than that of females, and that male offspring are more expensive to produce and
have a higher probability of recruitment if fledged early in the season, our results support predictions of sex allocation
theory: high-quality (heavy) females breeding when conditions were optimal for male recruitment produced an excess of sons. 相似文献
63.
Do males and females differ in the feeding of large and small siblings? An experiment with the bluethroat 总被引:3,自引:0,他引:3
Per T. Smiseth Trond Amundsen Lars T. T. Hansen 《Behavioral ecology and sociobiology》1998,42(5):321-328
Males and females have been reported to differ in their feeding of large and small siblings in several species of birds.
According to recent hypotheses, this phenomenon may be related to a sexual conflict over avian hatching patterns. We designed
an experiment to test for the existence of such a sex difference by manipulating nestling size hierarchies of the bluethroat
(Luscinia s. svecica) in two directions; half the broods were “asynchronized” to yield large size-differences within broods and the other half
were “synchronized” to yield small size-differences. In all broods, nestlings were categorized as being either large or small
according to body mass. We recorded male and female food distribution by video early (day 4 after hatching) and late (day
8) in the nestling period. Males and females did not differ in their distribution of food among different-sized nestlings.
With large size-differences, both males and females fed large nestlings nearly twice as often as small ones. In contrast,
when the size-differences were small, food was more evenly distributed among nestlings. Early in the nestling period, males
fed more nestlings during each feeding visit than did females. Our finding that male and female bluethroats do not differ
in the feeding of large and small siblings is in contrast to most previous studies. Variation in costs and benefits to males
and females from feeding different-sized nestlings, and restrictions to parental choice due to nestling interactions, may
explain interspecific variation.
Received: 27 June 1997 / Accepted after revision: 26 January 1998 相似文献
64.
Opposing selective pressures on hatching asynchrony: egg viability, brood reduction, and nestling growth 总被引:6,自引:0,他引:6
J. Viñuela 《Behavioral ecology and sociobiology》2000,48(5):333-343
At least 19 hypotheses have been proposed to explain the evolutionary significance of avian hatching asynchrony, and hatching
patterns have been suggested to be the result of several simultaneous selective pressures. Hatching asynchrony was experimentally
modified in the black kite Milvus migrans by manipulating the onset of incubation during the laying period. Delayed onset of incubation reduced egg viability of first-laid
eggs, especially when ambient temperature during the laying period was high. Brood reduction (nestling mortality by starvation
or siblicide) was more commonly observed in asynchronous nests. The growth rate was slower in synchronous broods, probably
due to stronger sibling rivalry in broods with high size symmetry. Last-hatched chicks in synchronous broods fledged at a
small size/mass, while in control broods, hatching order affected growth rates, but not final size. Brood reduction, variable
growth rates, and the ability to face long periods of food scarcity are probably mechanisms to adjust productivity to stochastic
food availability in a highly opportunistic predator. The natural pattern of hatching asynchrony may be the consequence of
opposing selective forces. Extreme hatching synchrony is associated with slow growth rates, small final size of last-hatched
chicks, and low viability of first-laid eggs, while extreme hatching asynchrony is associated with high mortality rates. Females
seem to facultatively manipulate the degree of hatching asynchrony according to those pressures, because hatching asynchrony
of control clutches was positively correlated with temperature during laying, and negatively correlated with the rate of rabbit
consumption.
Received: 25 October 1999 / Revised: 30 May 2000 / Accepted: 25 June 2000 相似文献
65.
Parental condition, brood sex ratio and differential young survival: an experimental study in gulls (Larus fuscus) 总被引:6,自引:6,他引:0
R. G. Nager P. Monaghan D. C. Houston M. Genovart 《Behavioral ecology and sociobiology》2000,48(6):452-457
Empirical evidence is growing that the offspring sex ratio in birds can be biased in relation to the body condition of parents
during breeding. The sex ratio bias may come about because (1) the actual production of the two sexes may be skewed and/or
(2) there may be a sex bias in early nestling mortality contingent on parental condition. By manipulating parental condition
and giving them a control brood to rear, thereby eliminating effects operating via the eggs, we examined the extent to which
parental condition influences the post-hatching survival of male and female lesser black-backed gulls, Larus fuscus. We found that the pre-fledging survival of male chicks was strongly reduced in all-male broods reared by parents in poor
condition. Pre-fledging survival of female chicks was, however, unaffected by parental condition or brood sex composition.
Thus, independently of any production biases, sex differences in nestling mortality alone can bias the offspring sex ratio
at fledging in relation to the prevailing rearing conditions. In other studies on gulls we have, however, also shown that
females in poor condition at laying preferentially produce female eggs. Clearly a bias in fledging sex ratio can occur within
the same species due to a combination of differential production and differential post-laying mortality; the latter can involve
a differential effect of poor egg quality on male and female offspring, differential effects of brood sex composition on their
survival and a difference in the capacity of parents to rear males and females. All of these processes need to be taken into
account in attempting to understand offspring sex ratios.
Received: 15 February 2000 / Revised: 7 August 2000 / Accepted: 26 August 2000 相似文献
66.
Brood sex ratios, female harem status and resources for nestling provisioning in the great reed warbler (Acrocephalus arundinaceus) 总被引:4,自引:0,他引:4
H. Westerdahl Staffan Bensch Bengt Hansson Dennis Hasselquist Torbjörn von Schantz 《Behavioral ecology and sociobiology》2000,47(5):312-318
The theory of parental investment and brood sex ratio manipulation predicts that parents should invest in the more costly
sex during conditions when resources are abundant. In the polygynous great reed warbler, Acrocephalus arundinaceus, females of primary harem status have more resources for nestling provisioning than secondary females, because polygynous
males predominantly assist the primary female whereas the secondary female has to feed her young alone. Sons weigh significantly
more than daughters, and are hence likely to be the more costly sex. In the present study, we measured the brood sex ratio
when the chicks were 9 days old, i.e. the fledging sex ratio. As expected from theory, we found that female great reed warblers
of primary status had a higher proportion of sons in their broods than females of lower (secondary) harem status. This pattern
is in accordance with the results from two other species of marsh-nesting polygynous birds, the oriental reed warbler, Acrocephalus orientalis, and the yellow-headed blackbird Xanthocephalus xanthocephalus. As in the oriental reed warbler, we found that great reed warbler males increased their share of parental care as the proportion
of sons in the brood increased. We did not find any difference in fitness of sons and daughters raised in primary and secondary
nests. The occurrence of adaptive sex ratio manipulations in birds has been questioned, and it is therefore important that
three studies of polygynous bird species, including our own, have demonstrated the same pattern of a male-biased offspring
sex ratio in primary compared with secondary nests.
Received: 1 June 1999 / Received in revised form: 10 January 2000 / Accepted: 12 February 2000 相似文献
67.
In avian species whose chicks show facultative siblicide, attacks increase with food deprivation. In species that show obligate siblicide, this causal relationship is not expected, but no test has been made. When we composed artificial pairs of young brown boobies, Sula leucogaster (an obligately siblicidal species), and supplied variable amounts of food to the older nestlings in each pair, food ingestion was related to the most intense form of attack, pushes, which can cause death by expelling the broodmate from the nest. The less food an older nestling ingested, the more time it spent active and the greater its rate and absolute frequency of pushes, and the more often it expelled its nestmate. Hence, deficient food provision to older nestlings could precipitate siblicidal expulsion of broodmates. Younger nestmates were aggressive too, and the more they were pushed and expelled, the more they pecked. Aggression of senior brown-booby broodmates may be flexible and food sensitive in order to optimize the timing of siblicide or to make siblicide weakly facultative.Communicated by R. Gibson 相似文献
68.
Intraspecific brood parasitism in the moorhen: parentage and parasite-host relationships determined by DNA fingerprinting 总被引:6,自引:0,他引:6
Parasitic female moorhens (Gallinula chloropus) lay from one to six eggs in the nests of conspecific neighbours. DNA fingerprinting was used to show that parasitic eggs
could be correctly identified when they appeared in addition to or outside the host’s laying sequence. Moorhen hosts accept
all parasitic eggs laid after the 2nd day of their laying period. To understand why moorhen hosts tolerate parasitic eggs,
we tested two hypotheses. (1) The quasi-parasitism hypothesis: females lay their eggs in the evening when the host males are normally in attendance at the nest, so host males may allow
parasitic females to lay in their nests in exchange for fertilizing their eggs. However, DNA fingerprinting showed that all
the parasitic eggs were sired by the parasites’ mates. Parasitic moorhens frequently continue laying a clutch in their own
nest, without a break in the laying sequence after a parasitic laying bout. The eggs laid by brood parasites in their own
nests were also sired by their own mates. Therefore this hypothesis was rejected. (2) The kin selection hypothesis: if one or both members of the host pair are close relatives of the parasite, the costs of rearing parasitic chicks will
be to some degree offset by inclusive fitness benefits. We examined the genetic relationships between parasites and their
hosts using DNA fingerprinting and genealogical data. Natal philopatry by both sexes was relatively common in this population,
and the probability that a neighbour of either sex was a first-order relative (parent-offspring) was calculated as 0.18. Although
first-order relatives were not preferentially chosen as hosts over individuals that were not first-order relatives, even through
random host selection there is almost a one-in-five chance that brood parasites in this population are closely related to
their hosts. This may facilitate host tolerance of parasitic eggs. Other hypotheses are also discussed.
Received: 3 February 1995/Accepted after revision: 27 August 1995 相似文献
69.
G.?Lichtenstein Donald?C.?DearbornEmail author 《Behavioral ecology and sociobiology》2004,56(4):352-359
Because brood parasitic nestlings are usually unrelated to their nestmates and to the provisioning adult, they are free from indirect costs of begging. Consequently, they are predicted to beg more intensely than host nestlings, and some models predict they will beg at an invariantly high level, regardless of short-term need. Previous work has shown intense begging by parasitic cowbirds, but short-term need was not controlled. In this study, we manipulated short-term need and measured begging intensity in two species pairs of host and parasitic nestlings: shiny cowbirds (Molothrus bonariensis) parasitizing larger hosts than themselves (rufous-bellied thrushes, Turdus rufiventris), and brown-headed cowbirds (M. ater) parasitizing smaller hosts than themselves (yellow warblers, Dendroica petechia). All four species increased their begging intensity with short-term need, though the change was much less pronounced between food-deprived and control treatments than between control and hand-feeding treatments. Shiny cowbirds begged more intensely than rufous-bellied thrushes following each treatment. In contrast, brown-headed cowbirds did not beg significantly more intensely than yellow warblers under any of the treatments. Intense begging by both species of parasites was as effective as host begging in stimulating the adults to make provisioning visits, but shiny cowbirds were less successful at acquiring food from adult thrushes. A wide array of factors may underlie the apparent differences in the begging behavior and success of brown-headed and shiny cowbirds, including relative size, experience, and local risk of nest predation. Our experiments clearly demonstrate, however, that these two species of parasitic cowbirds adjust their begging intensity based on short-term need.Communicated by H. Kokko 相似文献
70.
Pollen is the sole source of protein for honey bees, most importantly used to rear young. Honey bees are adept at regulating
pollen stores in the colonies based on the needs of the colony. Mechanisms for regulation of pollen foraging in honey bee
are complex and remain controversial. In this study, we used a novel approach to test the two competing hypothesis of pollen
foraging regulation. We manipulated nurse bee biosynthesis of brood food using a protease inhibitor that interferes with midgut
protein digestion, significantly decreasing the amount of protein extractable from hypopharyngeal glands. Experimental colonies
were given equal amounts of protease inhibitor-treated and untreated pollen. Colonies receiving protease inhibitor treatment
had significantly lower hypopharyngeal gland protein content than controls. There was no significant difference in the ratio
of pollen to nonpollen foragers between the treatments. Pollen load weights were also not significantly different between
treatments. Our results supported the pollen foraging effort predictions generated from the direct independent effects of
pollen on the regulation of pollen foraging and did not support the prediction that nurse bees regulate pollen foraging through
amount of hypopharyngeal gland protein biosynthesis. 相似文献