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1.
Michler SP Nicolaus M Ubels R van der Velde M Komdeur J Both C Tinbergen JM 《Behavioral ecology and sociobiology》2011,65(10):1975-1986
An individual’s decision to disperse from the natal habitat can affect its future fitness prospects. Especially in species
with sex-biased dispersal, we expect the cost–benefit balance for dispersal to vary according to the social environment (e.g.,
local sex ratio and density). However, little is known about the social factors affecting dispersal decisions and about the
temporal and spatial patterns of the dispersal process. In our study, we investigated experimentally the effects of the social
environment on post-fledging dispersal of juvenile great tits by simultaneously manipulating the density and sex ratio of
fledglings within forest plots. We expected young females in the post-fledging period mainly to compete for resources related
to food and, as they are subordinate to males, we predicted higher female dispersal from male-biased plots. Juvenile males
compete for vacant territories already in late summer and autumn; thus, we predicted increased male dispersal from high density
and male-biased plots. We found that juvenile females had a higher probability to leave male-biased plots and had dispersed
further from male-biased plots in the later post-fledging phase when juvenile males start to become territorial and more aggressive.
Juvenile males were least likely to leave male-biased plots and had smallest dispersal distances from female-biased plots
early after fledging. The results suggest that the social environment differentially affected the costs and benefits of philopatry
for male and female juveniles. The local sex ratio of individuals is thus an important social trait to be considered for understanding
sex-specific dispersal processes. 相似文献
2.
Kjell Einar Erikstad Jan Ove Bustnes Svein-Håkon Lorentsen Tone Kristin Reiertsen 《Behavioral ecology and sociobiology》2009,63(6):931-938
In birds, there is ample evidence that the mother can manipulate the sex of the young and produce more of the sex, which gives
the highest fitness return. This has previously been documented in gulls, Laridae. Gulls are sexually size dimorphic with
males larger than females, and there is good evidence that parents in poor body condition switch their investment to the smallest
sex. In the present study, we examined the primary sex ratio and the survival of male and female chicks of lesser black-backed
gull (Larus fuscus fuscus) in relation to their blood levels of organochlorines (OCs), perfluorinated compounds (PFCs) and polybrominated diphenyl
ethers (BDE-47). We show that females with high levels of OCs (but not PFCs and BDE-47) are likely to skew their sex ratio
at hatching towards female offspring. Few females had very high levels of OCs, and the many females with low levels of OCs
overproduced sons resulting in a male skew at hatching (59%). The survival of female offspring was lower than the survival
of male offspring, causing an even stronger male skew in sex ratio (71%). There is evidence to conclude that circulating levels
of OCs in the blood of females may have detrimental effect on the sex allocation strategy and could be of serious threat to
the population.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
3.
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
4.
Luc A. Wauters Simon A. de Crombrugghe Nadia Nour Erik Matthysen 《Behavioral ecology and sociobiology》1995,37(3):189-193
In polygynous roe deer Capreolus capreolus, males are only slightly heavier than females and the overall sex ratio at birth is close to unity. We studied offspring sex ratio and litter size (range 1–4, n = 74) of culled females, in utero, which provided an opportunity to examine responses of sex ratio to maternal condition. Male embryos were heavier than their sisters, and male fawns (9 months old) heavier than female fawns, suggesting a higher growth rate in males. There was no evidence for differential mortality between the sexes from birth to 9 months old. Heavier adult females produced larger embryos than lighter, or primiparous females. The overall sex ratio of embryos did not differ from unity, but adult does had more male embryos (55%) than primiparous does (32%), and the proportion of male embryos in a litter increased with the mother's body mass. Litter size also tended to increase with maternal age and body mass. We argue that this pattern reflects adaptive variation in offspring sex ratio. 相似文献
5.
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
6.
Mark R. Forbes Dean G. McCurdy Keiko Lui Selma I. Mautner J. Sherman Boates 《Behavioral ecology and sociobiology》2006,60(1):87-95
Potential rates of reproduction (PRR) differ between the sexes of many animal species. Adult sex ratios together with PRR
are expected to determine the operational sex ratio (OSR) defined as the ratio of fertilizable females to sexually active
males at any given time. OSR is expected to determine the degree to which one sex competes for another—the limiting sex. We
explored the potential for mate limitation in an intertidal amphipod, Corophium volutator (Pallas). Males have higher PRR than females, but males may be limiting because of extreme female-biased sex ratios observed
in this species. Consistent with this idea, late season females were less likely to be ovigerous and had smaller size-specific
clutches, both of which were associated with seasonal declines in availability of males of reproductive size. Seasonal changes
in ovigery could not be explained by seasonal changes across sites in other factors (e.g., female body size or phenology of
breeding). Smaller females were less likely to become ovigerous later in the season at three of four sites. Seasonal reductions
in clutch size also occurred among small females expected to be reproducing for their first time. In complimentary laboratory
experiments, reduced likelihood of ovigery and reduced fecundity occurred when the number of receptive females was increased
relative to availability of a reproductively active male. Our results suggest male mate limitation can occur seasonally in
this species and that male limitation is regionally widespread and may affect recruitment. 相似文献
7.
The local resource enhancement (LRE) model predicts that in cooperatively breeding species, sex ratios will be biased in favor
of the more helpful sex. In this study, we assess the assumptions underlying the LRE model in a population of cooperatively
breeding wild dogs (Lycaon pictus) in Northern Botswana monitored over a 15-year period. In this population, litter size and pup survival to 1 year are strongly
affected by pack size and the breeding female’s age, but adult males have a stronger and more linear effect on females’ reproductive
performance than do adult females. This asymmetry in the benefits derived from male and female helpers is reflected in male-biased
sex ratios in litters at the time pups emerge from the den. Sex ratio biases are most pronounced in the litters of the youngest
mothers who live in significantly smaller packs than older females. The presence of potential rivals for the dominant female’s
position depresses pup production at the time of emergence, suggesting that competition among females for breeding positions
may also contribute to the selective forces affecting birth sex ratios. 相似文献
8.
M. S. Mooring A. A. McKenzie Benjamin L. Hart 《Behavioral ecology and sociobiology》1996,38(4):259-266
The lesser mouse lemur (Microcebus murinus) is a prosimian primate which presents evidence of sex ratio bias of offspring that agrees with the direction of bias predicted
by the local resource competition model for facultative sex ratio adjustment. That is, females overproduced sons when grouped
prior to mating, whereas isolated females exhibited the opposite tendency. In this solitary species, social communication
relies heavily on urinary chemical signals. To test the hypothesis that sex biases induced by social factors may be linked
to urinary cues, isolated females were exposed (n = 76) or not (control group, n = 16) to urinary cues from other reproductively active females from the beginning of the breeding season (induced by long
photoperiod) until oestrus. During that period, females were either continuously (n = 17) or partially (n = 59) exposed to chemosignal stimulation. Females in oestrus were placed in contact with a breeding male and subsequently
isolated until they gave birth. All females entered oestrus but the timing of oestrus was significantly delayed by 1 week
in urine-exposed females. A general depressive effect of long-term urine exposure on fecundity was demonstrated, involving
fewer impregnations, higher abortion frequency and smaller litter sizes. Among females giving birth (n = 55) to a total of 129 young, a significant positive correlation was found between sex ratio bias towards males and the
duration of urine exposure. However, the shift in sex ratio at birth depended on the duration of urine stimulation during
a sensitive period extending from the beginning of the long photoperiod until the beginning of the follicular phase. In the
absence of urinary cues during the sensitive period, females significantly overproduced daughters (32% males of 53 newborn).
As urine exposure increased during the sensitive phase, the proportion of males in litters increased from 54% males (n = 50) in partially urine-exposed females to a significant bias towards males (69.2% of 26 newborn) in totally exposed females.
The biased sex ratio in response to chemical cues did not show consistent relationships with maternal body weight, parity
or litter size. Although the intrinsic mechanisms involved in sex-biased conceptions are not known, chemical cues could interact
with the photoperiodic control of gonadotropin secretions.
Received: 14 January 1995/Accepted after revision: 26 November 1995 相似文献
9.
Juvenile Survival in a Population of Neotropical Migrant Birds 总被引:4,自引:0,他引:4
Angela D. Anders Donald C. Dearborn John Faaborg & Frank R. Thompson Iii 《Conservation biology》1997,11(3):698-707
Determination of population productivity of Neotropical migrant birds and assessment of breeding habitat quality have been based on population densities and nesting success. Data on juvenile survival improve our estimates of population productivity, provide information on factors during the post-fledging period that affect this productivity and, with comparative data, enable us to better assess breeding habitat quality. We present the first estimate of post-fledging juvenile survival in a population of Neotropical migrant birds. We studied post-fledging survival in a population of Wood Thrush ( Hylocichla mustelina) in southern Missouri, (U.S.) an area hypothesized to contain source populations. Nesting success during our study period was 0.266, and individual survival within the nest was 0.245. Post-fledging survival during the first 8 weeks after fledging was 0.423. Survival varied significantly between post-fledging weekly age classes, with survival of weeks 1, 2, 3, and 4 through 8 being 0.716, 0.930, 0.637, and 1.00, respectively. Probability of predation after fledging was 0.506. Probability of mortality by other causes was 0.071. Probability of predation varied by weekly age class and may have been related to behaviors occurring at different developmental stages. Post-fledging survival was not correlated with nestling mass and did not change throughout the course of the breeding season. Analysis of the source/sink status of the population based on our estimates of nesting success and post-fledging survival indicates that young were being produced below replacement levels during our study period. Large-scale management decisions should take into account potential fluctuations in the productivity of Neotropical migrant populations over time. Data on post-fledging juvenile survival are needed from other populations of Neotropical migrant birds to more accurately assess differential productivity between populations and better assess breeding habitat quality. 相似文献
10.
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
11.
Within a family there are conflicts of interest between parents and offspring, and between male and female parents, over the
supply of parental care. The observed pattern of parental care is the outcome of negotiations within the family, and may be
influenced by environmental factors such as food abundance. We experimentally increased food supply to ten Tengmalm’s owl
(Aegolius funereus) nests from hatching to fledging, mimicking natural cached prey. Ten un-supplemented nests served as controls. Parents and
offspring were fitted with radio-tags. Food provisioning by parents was measured both in the (1) mid- and (2) late nestling
stage and in the (3) early and (4) late post-fledging stage. In response to food supplementation, both males and females reduced
food provisioning, but the effect was more pronounced in females. Females generally contributed much less to food provisioning
than males, and food supplementation increased the difference between the sexes. Mass loss during the brooding stage was substantially
lower for supplemented than for control females. Food supplementation did not improve offspring survival, and had no effect
on body measurements of nestlings. In conclusion, parents of both sexes used the increased food supply to reduce the costs
of caring for their current offspring, but females responded more strongly than males. 相似文献
12.
Anita Aisenberg Carmen Viera Fernando G. Costa 《Behavioral ecology and sociobiology》2007,62(1):29-35
Sexual selection theory predicts that a higher investment in offspring will turn females into the selective sex, while males
will compete for accessing and courting them. However, there are exceptions to the rule. When males present a high reproductive
investment, sex roles can reverse from typical patterns, turning males into the choosy sex, while females locate males and
initiate courtship. In many spiders, males are smaller than females, wandering in search of sedentary females and maximizing
the number of copulations. In the present study, we present findings on the sand-dwelling wolf spider, Allocosa brasiliensis, evidencing a reversal in typical courtship roles reported for the first time in spiders. Males were bigger than females.
Females located males and initiated courtship. Copulation always occurred in male burrows and took place mainly in long burrows.
Males donated their burrows to the females after copulation, closing the entrance before leaving with female cooperation from
inside. Males would provide females with a secure place for ovipositing, being exposed to predation and diminishing their
future mating possibilities until constructing a new burrow. The cost of vacating the burrow and losing the refuge in an unpredictable
habitat, such as sand dunes, would explain the courtship roles reversal in this spider species. Results turn A. brasiliensis as a promising model for discussing the determinants of sex roles and the pressures that drive their evolution and maintenance.
Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users. 相似文献
13.
Protandrous hermaphrodites are predicted to change sex from male to female when relative reproductive fitness of females surpasses
that of males. How size at sex transition varies with population, mating group and individual parameters was investigated
for five populations of the protandrous hermaphrodite slipper snail, Crepidula fornicata. The populations varied for density, size distribution, average mating group size and sex ratio. Size at sex-change was correlated
with the population sex ratio. Comparisons of multiple hypotheses revealed that variables predicting the sex of a snail vary
among positions in the mating group. The variables included body size, the relative size of the snail sitting atop the focal
snail and population density. Our data support the conclusions that size at sex-change (and by inference, the size at which
one sex has relatively greater fitness) is not fixed for these hermaphrodites and that individual size, social conditions
and population differences all influence variation in relative fitness. 相似文献
14.
Sex ratios,mating behavior and sexual size dimorphism of the northern water snake,Nerodia sipedon 总被引:4,自引:0,他引:4
Patrick J. Weatherhead Frances E. Barry Gregory P. Brown Mark R. L. Forbes 《Behavioral ecology and sociobiology》1995,36(5):301-311
Competition among males to mate is generally associated with male-biased size dimorphism. In this study we examine mating behavior in the northern water snake (Nerodia sipedon), a species in which males are much smaller than females despite substantial competition among males to mate. Competition among males was a consequence of a male-biased operational sex ratio due to slightly higher female mortality from a birth sex ratio of 1 : 1, and, in 1 year, more synchronous and longer mating activity by males. Approximately one-third of both males and females appeared not to mate in a given year. Larger males were generally more likely to attempt mating, but size did not explain the variance in the number of aggregations in which individual males participated. Within aggregations, males that were successful at achieving intromission were larger than unsuccessful males in 1 of 2 years. Variation in condition (mass relative to length) and relative tail length were not generally useful predictors of either mating effort or success in males. Because large size was often advantageous to males, sexual size dimorphism appeared not to be a consequence of sexual selection favoring smaller males. Because sexual dimorphism was evident at birth, and both males and females matured sexually at about 4 years, sexual dimorphism was not simply a consequence of one sex growing at the maximum rate for longer. Female fecundity increased with size, and sex differences in size-fecundity relations may underly the pattern of sexual size dimorphism. However, because multiple mating by females is common, sperm competition is likely to be important in determining male reproductive success. Therefore, allocation of energy to sperm rather than growth may also prove to be an important influence on male growth rates and sexual size dimorphism. 相似文献
15.
The operational sex ratio (OSR) may influence the intensity of competition for mates and mate choice and is therefore thought
to be a major factor predicting the intensity and direction of sexual selection. We studied the opportunity for sexual selection,
i.e., the variance in male reproductive success and the direction and intensity of sexual selection on male body mass in bank
vole (Clethrionomys glareolus) enclosure populations with experimentally manipulated sex ratios. The opportunity for sexual selection was high among male-biased
OSRs and decreased towards female-biased OSRs. Paradoxically, selection for large male body mass was strongest in female-biased
OSRs and also considerable at intermediate OSRs, whereas at male-biased OSRs, only a weak relationship between male size and
reproductive success was found. Litters in male-biased OSRs were more likely to be sired by multiple males than litters in
female-biased OSRs. Our results suggest that the intensity and direction of sexual selection in males differs among different
OSRs. Although the direction of sexual selection on male body mass was opposite than predicted, large body mass can be favored
by sexual selection. Naturally varying OSRs may therefore contribute to maintain variation in male sexually selected traits. 相似文献
16.
Burney J. Le Bœuf Richard Condit Joanne Reiter 《Behavioral ecology and sociobiology》1989,25(2):109-117
Summary Data on northern elephant seals, Mirounga angustirostris, bearing on sex ratio theory were collected at Año Nuevo, California, and other Californian and Mexican Islands, during the period 1967 to 1988. The mass of males exceeded that of females by 7–8% at birth and at weaning. The sex ratio was biased to males at birth (51.2%) and was near unity at weaning (49.6% males). The sex ratio did not vary as a function of maternal age or maternal mass except in 6-year-old females, who produced significantly more males. Although sons cost more to rear in energetic terms than daughters, and mothers were more successful weaning the latter, the sex of the pup reared exerted no significant effect on the mother's reproductive performance the following year or on her subsequent survival. These data suggest that parents invest equally in sons and daughters when investment is measured in terms of future reproduction (Fisher 1930) and provide no support for the theory of adaptive shifts in sex ratio (Trivers and Willard 1973). The small sex difference in mass due to maternal effort reflects the fact that females fast during lactation and all energy transferred is from limited body stores. Because of these circumstances, selection for superior condition at the end of the period of parental investment may act more strongly on pups, who have the opportunity to steal milk, than on their mothers. 相似文献
17.
We evaluated the influences of several ecological, biological, and methodological factors on post-fledging survival of a shortgrass prairie bird, the Lark Bunting (Calamospiza melanocorys). We estimated daily post-fledging survival (n = 206, 82 broods) using radiotelemetry and color bands to track fledglings. Daily survival probabilities were best explained by drought intensity, time in season (quadratic trend), ages < or = 3 d post-fledging, and rank given drought intensity. Drought intensity had a strong negative effect on survival. Rank was an important predictor of fledgling survival only during the severe drought of 2002 when the smallest fledglings had lower survival. Recently fledged young (ages < or = 3 d post-fledging) undergoing the transition from nest to surrounding habitat experienced markedly lower survival, demonstrating the vulnerable nature of this time period. Survival was greater in mid and late season than early season, corresponding to our assumptions of food availability. Neither mark type nor sex of attending parent influenced survival. The model-averaged product of the 22-d survival calculated using mean rank and median value of time in season was 0.360 +/- 0.08 in 2001 and 0.276 +/- 0.08 in 2002. Survival estimates that account for age, condition of young, ecological conditions, and other factors are important for parameterization of realistic population models. Biologists using population growth models to elucidate mechanisms of population declines should attempt to estimate species-specific of post-fledging survival rather than use generalized estimates. 相似文献
18.
Brood sex ratio is dependent on female mating status in polygynous great reed warblers 总被引:2,自引:0,他引:2
Isao Nishiumi 《Behavioral ecology and sociobiology》1998,44(1):9-14
Females capable of adjusting the sex ratio of their offspring should be more fit than females lacking such an ability. In
polygynous birds where breeding success in males is more strongly influenced by body size and/or attractiveness than in females,
females might produce more sons when predicting good conditions or when mating with attractive males. Polygynous great reed
warbler, Acrocephalusarundinaceus, males direct most of their feeding effort to the primary (first-hatching) nest and in these nests increase their feeding
effort in relation to the brood sex ratio (proportion of sons). Therefore, with the expectation of well-nourished sons, we
would predict that females which start breeding first within harems might produce more sons than those which start breeding
later, and in anticipation of sons with good genes, that females mated to polygynous males might produce more sons than females
mated to monogamous males. I took blood samples from hatchlings and determined the sex using DNA markers. The sex ratio of
primary (monogamous and polygynous primary) broods is more male-biased (mean 0.58 males, n = 50) than that of secondary (polygynous secondary and tertiary) broods (mean 0.46, n = 25). Moreover, in the secondary broods with the largest clutch (five eggs), in which offspring are most likely to suffer
food shortage, the sex ratio was distinctively female biased (mean 0.33, n = 10). In the primary broods, sex ratio was correlated to harem size. The results suggest that great reed warbler females
modify the brood sex ratio to produce both well-nourished sons and sons with good genes, but the former effect is probably
stronger than the latter factor.
Received: 11 March 1998 / Accepted after revision: 23 May 1998 相似文献
19.
Birth sex ratios were examined for ringtailed lemurs (Lemur catta) at the Duke University Primate Center. This population provides a long-term database of births under a variety of demographic
and management conditions, including two semi-freeranging groups between which males transfer freely and females defend stable
territorial boundaries. We examined three hypotheses usually considered in studies of primate sex ratio bias. The Trivers-Willard
hypothesis predicts that dominant females produce males, local resource competition at the population level (LRC-population)
predicts that the dispersing sex (males) will be overproduced in dense populations, and local resource competition among individuals
(LRC-individual) predicts that dominant females overproduce the philopatric sex (females). We also examined a fourth hypothesis,
local resource enhancement (LRE), which is usually subsumed under LRC-individual in studies of primate sex ratio evolution.
LRE predicts that under certain conditions, females will produce the sex that provides later cooperative benefits, such as
alliance support for within- or between-group competition. Our data provide support for LRE: females overproduce daughters
given prospects of new group formation, either through group fission or threatened expulsion of young mothers. Behavioral
data from Duke and also wild populations show that daughters serve mothers as important allies in this context and LRE effects
also have been documented in other mammals that experience similar group histories. Nonsignificant trends in the data supported
the LRC-population hypothesis, and we suggest that LRC interacts with LRE to explain offspring sex ratios in ringtailed lemurs.
Received: 27 August 1999 / Received in revised form: 6 March 2000 / Accepted: 18 March 2000 相似文献
20.
Facultative sex ratio manipulation in American kestrels 总被引:10,自引:0,他引:10
Summary For animals that are sexually dimorphic in size, the larger sex is expected to be more costly to raise to independence. Manipulating offspring sex ratios may thus be one means by which parents can fine-tune their reproductive effort to resource availability. Parents in poor physical condition or during poor food years should produce more of the cheaper (smaller) sex. We examined the sex ratios of 259 broods of American kestrels (Falco sparverius) between 1988 and 1990 in relation to food abundance (small mammals) and various attributes to the parents. The proportion of males at hatching increased as the food supply declined, and both male and female parents in poor physical condition were more likely to have male-biased broods than those in good condition. The mortality of eggs and young did not appear to be responsible for the biased sex ratios. The sex ratio was independent of the laying date; however, it was correlated with female body size. Small females produced more sons, perhaps because small size is more detrimental for females than males.
Offprint requests to: G.R. Bortolotti 相似文献