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1.
In polygynous and sexually dimorphic mammals, parents may be expected to bias their investment towards sons because variation in reproductive success is usually higher among males than among females. Moreover, male reproductive success often depends on adult body size, which, in turn, may depend on the level of parental investment. We therefore predicted that in the grey seal (Halichoerus grypus), a polygynous and sexually dimorphic phocid seal, females should invest more in individual sons than in individual daughters. We found that male pups were born heavier than female pups, but that the growth rates and suckling behaviour were similar for the two sexes. The growth rates and the birth weights were not correlated for the pups of either sex. Mothers did not behave differentially towards offspring of the two sexes, except that mothers of male pups spent more time in visual contact with their pups. Male and female pups had similar activity levels and begged at similar rates. We argue that reports of equal expenditure on the two sexes can be accepted as evidence of equal investment, provided that three assumptions are fulfilled. First, parental care must be costly to the parent. Second, energy expenditure must be the most important component of parental investment. Third, there must be no negative correlation between maternal body condition and the ratio of sons to daughters produced. We argue that these assumptions are met in our study, and that our results provide evidence of equal maternal investment in the sexes in grey seals. 相似文献
2.
We investigated the effects of population fluctuation on the offspring’s sex allocation by a weakly polygynous mouse, Apodemus argenteus, for 3 years. In acorn-poor seasons, heavier mothers invested more in sons, and lighter mothers invested more in daughters.
In acorn-rich seasons, heavier mothers invested more in daughters, and lighter mothers invested more in sons. Maternal body
condition and litter size affected the sex allocation. Furthermore, there was a maternal investment trade-off between a son’s
birth mass and the number of daughters. Based upon the effect of population fluctuation on the lifetime reproductive success
of each sex, we proposed the new “safe bet hypothesis”. This hypothesis predicts that frequent and unpredictable change in
female distribution, which is often caused by abrupt fall in food condition, favors female-biased maternal investment to offspring
by polygynous mammals and is applicable to many small mammals inhabiting in unstable environments. 相似文献
3.
Summary In polygynous mammals, it may be adaptive for mothers to invest more in sons and/or to adjust the sex ratio of offspring in relation to body condition. Calving patterns were examined over an 8-year period (1982–1989) for a population of Bison bison in which barren females are not selectively culled. From these data, we tested predictions of the sex ratio adjustment hypothesis as well as two assumptions: (1) that offspring weight at the end of the period of parental investment (PI) is correlated with later condition, and (2) that maternal and offspring condition during the period of PI are correlated. In contrast to predictions, there was little evidence that mothers in better condition bear more sons. Short- and long-term measures of maternal condition (previous reproductive status, age, dominance status, pre-pubertal body weight, age at first reproduction, birth date, and the duration of the mother's own suckling period) were little related to offspring sex ratio, although the last calves of old females were nearly always female. Similarly, there was little evidence for sex-biased PI. Weights at about 7 months of age were greater for males than females; males also had somewhat later birth dates, suggesting either longer gestation or later conception. However, maternal reproductive costs, as measured by subsequent fecundity, weight loss, and interbirth intervals, did not vary with calf sex. Both assumptions of the model received some support. However, while maternal condition was correlated with offspring condition, there may be sex differences in investment patterns. Mothers appear better able to influence the condition of daughters than of sons. This sex difference may negate any benefit from male-biased investment. 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.
Birth sex ratios in toque macaques and other mammals: integrating the effects of maternal condition and competition 总被引:2,自引:0,他引:2
Wolfgang P. J. Dittus 《Behavioral ecology and sociobiology》1998,44(3):149-160
Mammalian life histories suggest that maternal body condition and social dominance (a measure of resource-holding potential)
influence the physical and social development of offspring, and thereby their reproductive success. Predictably, a mother
should produce that sex of offspring which contributes most to her fitness (as measured by the number of her grandchildren)
and that she is best able to raise within the constraints imposed by her condition, social rank, and environment. Such combined
effects were investigated by monitoring variations in body condition (weight) and behavior of female toque macaques, Macaca sinica of Sri Lanka, in a changing forest environment over 18 years. Maternal rank, by itself, had no influence on offspring sex,
but did affect maternal body condition. The combined effects of rank and condition indicated the following: mothers in robust
condition bore more sons, whereas those in moderate condition bore more daughters, but both effects were expressed most strongly
among mothers of high rank. Where the consequences of low rank were felt most acutely, as shown by poor condition, mothers
underproduced daughters. Environmental quality directly influenced rank and condition interactions, and thus sex ratios. These
relationships, and data from other mammals suggest an empirically and theoretically consistent pattern of sex allocation in
mammals. New predictions integrate effects, proposed by Trivers and Willard, that are rooted in male mate competition, which
is universal among polygynous mammals, with those of local resource competition (and/or female reproductive competition),
which are not universal and differ in intensity between the socioecologies and local environments of different species.
Received: 30 May 1998 / Accepted after revision: 29 August 1998 相似文献
6.
Fritz Trillmich 《Behavioral ecology and sociobiology》1986,19(3):157-164
Summary Maternal investment and sex-allocation were measured in a large, sexually dimorphic mammal, the Galapagos fur seal (Arctocephalus galapagoensis). The sex ratio at birth was 1.06. Males were always heavier than females and, at least initially, grew faster. Growth was variable from year to year suggesting energetic constraints on maternal investment. Sucking time conrrelated with milk intake. Mothers suckled yearling and 2-year-old sons more than daughters of the same age. Age at weaning appeared to be the same in both sexes or even slightly greater in males. No sex differences was found in mortality prior to weaning or in post-weaning dispersal. Birth rates of females with yearlings or 2-year-olds were significantly lower than those of females with no dependent young. Mothers invested more in sons than in daughters until weaning. It is unlikely that higher post-weaning investment in daughters balances the higher pre-weaning investment in sons. Data on sex ratio at birth, different growth rates, and weaning age of the sexes are typical of otariid seals as a group. The results of this study fit Maynard Smith's (1980) model of the evolution of sex allocation better than Fisher's (1930). 相似文献
7.
Studies of the otariids (fur seals and sea lions), a highly sexually dimorphic group, have provided conflicting evidence of
differential maternal expenditure in male and female offspring and, thus, suggestions that they conform to predictions of
investment theory are equivocal. Since the mid-1970s, a diversity of research on Antarctic fur seals (Arctocephalus gazella) including studies of their reproductive ecology, lactation energetics, and foraging behaviour have been conducted at Bird
Island, South Georgia that have resulted in one of the more complete and diverse data sets for any species of otariid. These
long-term data were reviewed to determine whether there was any evidence to support that differential maternal expenditure
occurred in Antarctic fur seals. Most of the data examined were collected during five consecutive austral summers from 1988
through 1992 and included years in which local food resources were abundant and scarce. We were unable to detect differences
in the sex ratios of pups at birth or sex-biased differences in growth rates estimated from serial data, the number of foraging
trips made, the duration of attendance ashore, diving behaviour, suckling behaviour, or milk consumption in any year and in
the duration of foraging trips or age at weaning in 2 of 3 years. In addition, we found no evidence of greater reproductive
costs between mothers with sons or daughters relative to their reproductive performance the following year. In contrast, sex-biased
differences were only found in the duration of foraging trips in 1990, the age at weaning in 1988, and consistently in growth
rates estimated from cross-sectional data. We suggest that differential maternal expenditure does not occur in Antarctic fur
seals because male pups probably do not gain greater benefit from additional maternal expenditure than female pups. After
weaning, males experience a period of rapid juvenile growth over 3–4 years during which time body mass nearly trebles. This
growth will almost certainly be dependent upon available food resources then rather than on any maternal expenditure received
over the first 4 months of life and, thus, the assumptions of the Trivers and Willard hypothesis are probably invalid for
Antarctic fur seals.
Received: 10 July 1996 / Accepted after revision: 3 March 1997 相似文献
8.
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
9.
It has been argued that female mammals should terminate expensive forms of infant care earlier as habitat quality declines.
More recently it has been shown that among a variety of mammalian species, early termination of care is also associated with
highly favourable conditions. In this paper we present data on maternal investment decisions among baboons (Papio cynocephalus ursinus) inhabiting the Drakensberg Mountains of South Africa, and compare these with data from East African baboon studies. Mothers
in the mountain habitat face a set of environmental conditions where the problem of resource allocation to offspring is expected
to be particularly acute. We begin by using the model of Altmann (1980) of maternal time budgets to demonstrate that mountain
baboon mothers experience greater perturbations to their activity budgets while suckling than do mothers in other populations.
They also provide consistently greater levels of care to their infants and do so in the absence of any form of overt conflict
over access to the nipple. Although this investment results in a relative lengthening of the interbirth interval (IBI), it
is accompanied by relatively higher infant survival. We argue that factors that influence the maternal strategy adopted by
mountain baboons include slow infant growth rates and a lack of predation in the habitat which influences probability of offspring
survival beyond the immediate postnatal period. We suggest that both “care-dependent” sources of mortality (e.g. female reproductive
condition, the amount of milk transferred to offspring) as well as “care independent” sources of mortality (e.g. predation,
infectious disease) should be considered in studies of parental investment.
Received: 26 May 1997 / Accepted after revision: 9 August 1997 相似文献
10.
R. S. Sikes 《Behavioral ecology and sociobiology》1996,38(5):303-310
The Trivers-Willard hypothesis of sex-biased maternal investment in response to fluctuations in resource availability has
provided a theoretical foundation for research on maternal investment for more than two decades. Their hypothesis holds that
mothers in poor condition as a result of poor resource availability should bias parental investment towards offspring with
the highest probability of reproducing. In the polygynous mating system of mammals where males compete for breeding access
to females, the hypothesis predicts investment favoring females. Although data from many systems have supported this hypothesis,
other systems do not follow the predicted patterns and have resulted in various alternative hypotheses. The present research
was designed to test whether differences in body condition of young reared by nutritionally stressed dams relative to young
reared by unstressed dams were maintained into adulthood, one of the fundamental assumptions underlying the Trivers-Willard
hypothesis. Post-weaning growth in eastern woodrats (Neotoma floridana) and northern grasshopper mice (Onychomys leucogaster) was examined relative to maternal nutritional plane. Individuals from undernourished dams were lighter than their unrestricted
counterparts at weaning but no difference was evident by the time they had reached adult size. Failure to maintain body condition
differences into adulthood violates one of the assumptions essential for application of the Trivers-Willard hypothesis of
maternal investment patterns. Although the Trivers-Willard model proposed that natural selection favors differential investment
in the sexes over the entire course of parental investment, evidence from this and other studies suggests that the Trivers-Willard
hypothesis might not be appropriate to address maternal investment questions in postnatally malnourished dams, but instead
should be restricted to systems concerned with prenatal maternal condition or resource availability.
Received: 22 February 1995/Accepted after revision: 30 December 1995 相似文献
11.
Pekka Pamilo 《Behavioral ecology and sociobiology》1990,27(1):31-36
Summary Sex allocation theory is developed for polygynous eusocial Hymenoptera in which nests recruit their own daughters as new reproductive queens. Such restricted dispersal of females leads to the expectation of male-biased investment ratios. The expectation depends on the parameter q telling what proportion of the total contribution in the gene pool by all new queens is due to those dispersing. Under queen control the expected sex allocation, expressed as the proportion of resources invested in males, is IM =1/(1 + q). Under worker control, IM depends on the relatedness of old queens, on the number of males they have mated with, and on the proportion of males produced by workers. With single mating and no worker reproduction, the approximate predictions for IM are 1/(1 + q) when the nests have many highly related queens, 1/(1 + 2 q) when the old queens are as related as average worker nest mates, and 1/(1 + 3q) when the old queens are not related to each other at all. The observed investment ratios in polygynous ants would, on average, match values of the parameter q between 0.4 and 0.5. Values of q have not been estimated in nature. If q is smaller than 0.4, which may well be true, the observed sex allocation in polygynous ants is in fact more female-biased than predicted by the theory. This indicates that the female bias found in monogynous ants may not be exceptional and could be due to factors other than worker control of sex allocation. Because the value of q is likely to vary among species, testing the predictions of the theory requires thorough single-species studies. 相似文献
12.
Summary The suckling behaviour of 130 freeranging elephant calves aged between birth and 4.5 years old was examined in Amboseli National Park, Kenya. Analyses of frequencies of suckling and durations of suckling bouts showed that males attempted to suckle more often, were more successful at their attempts, and as a result were estimated to have a higher milk intake than did female calves. Mothers were equally tolerant of their sons' and daughters' demands to suckle at young ages, but were less tolerant of their older sons' demands. The growth rates of males based on hind footprint length were faster than those of females from birth onwards. During drought years with low food availability, male calf survivorship in the first year was lower than that of female calves. During wet years, there was little difference between sexes in survivorship. It appeared that during dry years mothers were unable to sustain milk production at a level that met the metabolic requirements of their sons, and as result male calves were more likely to die. Females with a surviving son tended to have a longer interbirth interval than did females with a surviving daughter. We suggest that greater early maternal investment in male calves occurs because, in the highly-competitive polygynous mating system of elephants, size in adult male elephants is an important factor in mating success. 相似文献
13.
I. Nishiumi Satoshi Yamagishi Hiromi Maekawa Chikashi Shimoda 《Behavioral ecology and sociobiology》1996,39(4):211-217
In many polygynous animals, parents invest more heavily in individual sons than in daughters. However, it is unclear if these
differences in investment are a consequence of sex differences in the demand of offspring related to sexual size dimorphism
or a consequence of parental manipulation. Here, we report on parental food delivery frequency in relation to brood size and
brood sex ratio in a wild population of polygynous great reed warblers Acrocephalus arundinaceus. We used the polymorphic microsatellite loci on the Z chromosome to sex chicks. We found that paternal feeding frequency
(times/h per nest) increased not with brood size, but with the proportion of males in the brood, although the demand per nest
was more closely related to brood size than to brood sex ratio. Additionally, the increase in rate of paternal feeding frequency
in relation to the brood sex ratio was much higher than the increase in rate of nestling food demands. Maternal feeding frequency
was independent of both brood size and brood sex ratio. These results strongly suggest that fathers preferentially invest
in their sons. We propose that parents can afford sex-biased parental care in animals in which food provisioning is enough
for all offspring to survive.
Received: 22 January 1996/Accepted after revision: 30 June 1996 相似文献
14.
Proximal mechanisms underlying a faster growth rate in male compared to female California sea lion pups were investigated.
Males are significantly larger at birth than females. Specifically, we asked if differential maternal investment contributed
to enhanced male growth via: (1) larger mothers having disproportionately more male pups, (2) more time and energy put into
foraging by mothers of male pups, and (3) greater milk production in mothers of male pups. We also considered four aspects
of differential energy utilization and acquisition by male and female pups: (1) male pups attempting to save energy for growth
by changes in behavior, (2) longer suckling bouts with mother and more sneak suckling of non-filial females by male pups,
(3) lower maintenance costs in males via a lowered resting metabolic rate, and (4) increased assimilation efficiency in males.
Our study showed that there are no differences in the size of females or length of foraging trips for mothers of male and
female pups. Male pups received more milk from their mothers, but the difference was no longer significant when the larger
body size of males was considered. There were no differences in either the activity budgets or suckling behavior of male and
female pups. Male pups, however, did have lower resting metabolic rates than females. We conclude that enhanced male perinatal
growth is a consequence of a larger size at birth, proportionally more milk from mothers to support the greater demands of
larger body size, and lower maintenance costs due to a lower resting metabolic rate.
Received: 28 April 1995/Accepted after revision: 25 July 1995 相似文献
15.
A number of models have been proposed to provide adaptive explanations of sex-ratio variation in mammals. Two models have been applied commonly to primates and ungulates with varying success—the Trivers-Willard (TW) hypothesis, and the local resource competition (LRC) hypothesis. For polygynous, sexually dimorphic mammals, where males are larger and disperse more readily, these models predict opposite outcomes of sex-ratio adjustment within the same environmental context (high-resource years: TW—more sons; LRC—more daughters). However, many of the predictions of these two models can vary depending on factors influencing resource availability, such as environmental stochasticity, resource predictability, and population density. The New Zealand fur seal (Arctocephalus forsteri) is a polygynous mammal showing marked sexual dimorphism (larger males), with higher variation in male reproductive success expected. We provide clear evidence of male-biased sex ratios from a large sample of A. forsteri pups captured around South Island, New Zealand during 1996/1998, even after accounting for a sex bias in capture probability. The extent of the bias depended upon year and, in 1998, strong climatic perturbations (El Niño/Southern Oscillation, ENSO) probably reduced food availability. Significant male-biased sex ratios were found in all years; however, there was a significant decline in the male bias in 1998. There was no relationship between sex ratio and population density. We suggest that the sex-ratio bias resulted from the production of relatively more male pups. Under the density-independent scenario, the strong male bias in A. forsteri sex ratios is support for the TW model within an environment of high resource predictability. We suggest that some plasticity in the determination of pup sex among years is a mechanism by which A. forsteri females in New Zealand, and perhaps other otariid seals, can maximise fitness benefits when living in regions of high, yet apparently predictable, environmental variability. We also suggest that much of the inconsistency in the reported sex ratios for otariid seals results from the complex interaction of population density and environmental stochasticity influencing relative food availability over time. 相似文献
16.
Jason H. Peterson Bernard D. Roitberg J. H. Peterson 《Behavioral ecology and sociobiology》2006,59(5):589-596
Fisher's theoretical prediction of equal investment in each sex for a panmictic population (The genetical theory of natural selection. Clarendon, Oxford, 1930) can be altered by a number of factors. For example, the sex ratio theory predicts variation in
equal investment in each sex when the maternal fitness gains from increased investment differ between sexes. Changing sex
allocation because of changing payoffs may result from different ecological situations, such as foraging conditions. We investigated
the impact of foraging travel cost on relative investment in sons vs daughters. Field studies were carried out with the central-place-foraging
leafcutter bee Megachile rotundata (Fabricius), which has smaller males than females. Therefore, less investment is required to produce a viable son compared
with a daughter. We found that with increased flight distance to resources, females produced a greater proportion of sons.
Females also invested fewer resources in individual sons and daughters and produced fewer offspring with increased flight
distance. 相似文献
17.
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
18.
High-ranking females bias their investment in favour of male calves in captive Ammotragus lervia 总被引:1,自引:0,他引:1
Jorge Cassinello 《Behavioral ecology and sociobiology》1996,38(6):417-424
Calf suckling behaviour is a valid measure of maternal investment in the Saharan arrui, Ammotragus lervia sahariensis, since this variable is strongly correlated with the inter-birth interval. High-ranking females allocate their resources
preferentially towards their sons, as the average suckling rate is significantly higher in male calves than in female calves
during their 1st month of life, when maternal investment reaches the highest values of the whole lactation period. However,
average suckling-bout duration shows no sex differences. Some maternal behaviours, such as sniffing and licking, are strongly
correlated with suckling events. Only during the calves’ 1st week is the mother responsible for maintaining proximity; but
from the following week on the calves are mainly responsible for maintaining it. In addition, when the calves are 1 month
old, high-ranking females tend to maintain a stronger link with their male calves. Female calves spend more time with their
mothers than male calves during their 1st month of life, if the mother’s rank is lower than 60%; otherwise, the opposite occurs,
male calves being close to their mothers for longer, even from their 1st week of life. Finally, the higher the maternal rank
the higher the proportion of male calves delivered.
Received: 18 April 1995/Accepted after revision: 11 February 1996 相似文献
19.
Karsten Seidelmann Karin Ulbrich Norbert Mielenz 《Behavioral ecology and sociobiology》2010,64(3):337-347
Trivers' and Willard's hypothesis that natural selection favors sex allocation in relation to maternal condition assumes iteropary.
Though this assumption is not met in most solitary Aculeata, the reproductive life span of semelparous females may be divided
into discrete successive cycles by the risk of open-cell parasitism. Females can avoid losing their investment to parasites
attacking the open cell only by limiting the provision time for each cell. The restriction of time available for the investment
in a single progeny irrespective of the condition of the female leads to de facto iteropary. Moreover, in Hymenoptera, there
are no costs for sex allocation due to the haplodiploid mode of sex determination. In sexually size dimorphic species, females
in poor condition are predicted to invest in the smaller sex and vice versa. The resulting prediction of a conditional sex
allocation in solitary Aculeata was tested in the Red Mason bee, Osmia rufa (Osmia bicornis), a stem or hole-nesting, polylectic, univoltine megachilid bee. Body size is a key component of condition in females of
nest-constructing solitary bees. Large females collect the same amount of pollen and nectar in a shorter time than small ones
and should suffer less from parasitism. We found that small females dealt with their handicap of a low provisioning performance
by shifting the sex ratio toward sons (the smaller sex) and by reducing the body size of daughters. Large females, however,
shifted their offspring sex ratio toward daughters, the sex that depends more on body size in its reproductive value. The
sex ratio in the population met the expected Fisherian sex ratio. Although females allocated their investment in the sexes
according to their body mass, the population-level investment was balanced. 相似文献
20.
Contradictory findings in studies of sex ratio variation in roe deer (Capreolus capreolus) 总被引:3,自引:0,他引:3
A. J. Mark Hewison Reidar Andersen Jean-Michel Gaillard John D. C. Linnell Daniel Delorme 《Behavioral ecology and sociobiology》1999,45(5):339-348
Patterns of sex ratio variation and maternal investment reported in the literature are often inconsistent. This could be
due to intra- and inter-specific variation in social systems, but may also be a result of the a posteriori nature of much
of this type of analysis or the testing of models which are inappropriate. Two recent papers reported directly opposed results
concerning variation in offspring sex ratios in relation to maternal condition in roe deer, interpreting the results as support
for the Trivers and Willard model and for the local resource competition hypothesis, respectively. In this paper, we present
data on offspring sex ratios and early juvenile body weight from two long-term studies of this species to test predictions
arising from these two models concerning sex biases in litter composition and maternal care. First, we observed no consistent
pattern of sex differences in an index of weaning weight or body weight at 1 month old in either population, indicating a
lack of sex bias in maternal care. However, in one population, higher maternal body weight was associated with higher juvenile
body weight of daughters, but not of sons. Secondly, we found a negative, but not statistically significant, relationship
between maternal body weight and litter sex ratio such that heavier females tended to produce more daughters and lighter females
to produce more sons. These results indicate that roe females which have additional investment potential available do not
invest it in sons, as predicted by the Trivers and Willard model. Our results may provide some support that roe deer are subject
to local resource competition acting at the level of the individual mother; however, the fact that particular trends in sex
ratio data can be explained in functional terms provides no indication that they are actually adaptive.
Received: 9 December 1997 / Accepted after revision: 11 November 1998 相似文献