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1.
Early family life is characterized by a close interaction between parents and their offspring. This needs to be disentangled when studying the ontogeny and evolution of a given behavior—e.g. via cross-fostering. But cross-fostering may change the expression of parent and offspring behaviors as they may respond to the novel environment. Furthermore, parent and offspring traits are potentially co-adjusted and cross-fostering may, therefore, introduce a costly mismatch. To study such consequences of cross-fostering, we created an experimental group (EG) of broods raised by foster parents from day 3 onwards and a control group of broods raised by their biological parents throughout. We tested offspring begging intensity in all broods and the provisioning of the EG-parents only, both on day 3 just before cross-fostering and then again on day 5. Costs were estimated in terms of growth and survival (offspring costs) and mass of a second clutch (parental costs). Offspring begging intensity varied with age, but this change was neither affected by cross-fostering per se nor by small-scale differences in parental provisioning between biological and foster parents. Similarly, the change in parental provisioning with offspring age among the EG-parents was not affected by the difference in begging between biological and foster nestlings. This lack in behavioral plasticity in response to cross-fostering did not entail costs to neither of the parties. Our results suggest a rather predetermined pattern of behavioral expression, which may be shaped by limits and costs to plasticity and/or an (apparent) lack of costs of a behavioral mismatch. 相似文献
2.
Mathias Kölliker 《Behavioral ecology and sociobiology》2007,61(9):1489-1497
The evolution of parental care and family group formation critically depends on offspring survival benefits and parental fecundity
costs of care under given ecological conditions. Investigations of the functional significance of care in insect species that
exhibit facultative parental care have been relatively rare but may be of particular interest for better understanding of
benefit and cost schedules at an early evolutionary stage. In this study, aspects of benefits and costs of care were addressed
in the sub-social European earwig (Forficula auricularia; Dermaptera: Forficulidae) by manipulating the presence of tending mothers and brood size in a fully crossed experimental
design. Larvae growing in broods tended by their mother or of reduced size showed a higher survival probability than larvae
growing in untended or large broods, as predicted if maternal care is beneficial and shaped by a trade-off between number
and quality of offspring. Analysis of patterns of food consumption and developmental time further suggested that the benefit
of maternal attendance is mediated by the maternal provisioning of food, while the quality–quantity trade-off seemed to be
driven by sibling rivalry. Further, tending mothers delayed the production of a second clutch, indicating a potential cost
of care in terms of lifetime fecundity. This study experimentally shows benefits and potential costs of maternal care and
family group formation in the European earwig. More detailed behavioural experiments will be required to fully understand
how behavioural interactions among family members mediate these reproductive outcomes. 相似文献
3.
Parents adjust care in response to weather conditions and egg dehydration in a Neotropical glassfrog
Jesse R. J. Delia Aurelio Ramírez-Bautista Kyle Summers 《Behavioral ecology and sociobiology》2013,67(4):557-569
Parental hydration of terrestrially developing eggs has evolved repeatedly among frogs and is thought to buffer embryos from environmental variation. While many anurans offer relevant opportunities to study parental care, research on how parents respond to environmental variation and offspring conditions are lacking. In this study, we investigated the interrelationships of weather, embryo hydration demands, and parental provisioning in a wild population of the glassfrog Hyalinobatrachium (‘Centrolenella’) fleischmanni in Oaxaca, Mexico. We determined whether males modify parental behavior in response to changes in weather conditions that effect embryo dehydration, how variation in both weather and parental hydration affect egg water balance and embryonic mortality, and whether parental provisioning is related to the hydration levels of egg clutches. We found that male H. fleischmanni compensate for environmental variation in offspring conditions by adjusting the frequency of parental care in response to both weather and egg dehydration. Using a male removal experiment, we examined the function of paternal care and made comparisons with previous research, finding that both the adaptive value of parental care and flexibility in parental behavior are impacted by spatial and temporal conditions. We present observations that indicate a direct conflict between providing parental care and multiple matings. In summary, this research demonstrates that the variable frequency of paternal care in H. fleischmanni is a response to the fluctuating nature of the climate and resulting hydration requirements of embryos in combination with the allocation of effort to parental care versus mating activity. 相似文献
4.
Lyndon Alexander Jordan James Edward Herbert-Read Ashley J. W. Ward 《Behavioral ecology and sociobiology》2013,67(3):449-455
When the costs of parental care do not scale with the number of offspring being cared for, inclusion of non-descendant young into broods can be advantageous, leading to systems of alloparental care. However, if the cost of care scales with the number of offspring, selection may act against misdirected parental care. The spiny chromis, Acanthochromis polyacanthus, is a marine fish with extended biparental care, and broods that increase in size over the care period strongly suggest that alloparental care occurs in this species. However, A. polyacanthus parents directly provision their offspring by producing ectodermal mucus for their fry to feed on. The costs of such provisioning may scale with brood size, potentially increasing the costs of parental care. Using wild A. polyacanthus pairs, we tested whether foreign offspring are accepted into established broods, and measured how brood defence effort and mucal feeding scale with brood size. We found that A. polyacanthus discriminate between their own and foreign young, vigorously expelling experimentally introduced foreign offspring. Although defensive effort did not scale with brood size, mucal feeding was strongly dependent on brood size, and this increasing cost of care likely acts as the primary selective force on parental discrimination and rejection of foreign fry in A. polyacanthus. 相似文献
5.
Selection should favor flexibility in reproductive tactics when the combination of sexual traits and reproductive behaviors that achieve the highest fitness differs between males within a population. Understanding the functional significance of variation in male reproductive tactics can provide insight into their evolution. Male house finches (Carpodacus mexicanus) in a Montana population display continuous variation in parental tactics: males with more elaborated (redder) plumage color provide little or no parental care compared to less elaborated (dull) males. Here, we first determined whether elevation of prolactin (a pituitary hormone) was related to variation in male parental tactics and, second, we used the relationship between prolactin levels and parental behavior to investigate why redder males avoid a high investment in parental care. We found that prolactin elevation was closely associated with paternal care. In addition, males with redder plumage color had low prolactin levels, whereas dull males, which provision twice as frequently, had high levels of prolactin. We also found that male condition was unrelated to plumage color but negatively related to prolactin levels. These results suggest that the low provisioning of redder males was not due to physiological constraints, but instead reflected a tactic to avoid the costs associated with parental care. The condition benefits accrued by redder males may explain their higher post-breeding survival compared to dull males. Moreover, dull males were previously shown to have higher pairing success than redder males, suggesting that the relationship between male plumage color and parental care may reflect individually optimized parental tactics.Communicated by H. Kokko 相似文献
6.
Giuseppe Boncoraglio Roberta Martinelli Nicola Saino 《Behavioral ecology and sociobiology》2008,62(5):729-738
In diverse taxa, offspring solicit parental care using complex displays, which may evolve as reliable signals of condition
or as mechanisms to manipulate parental investment. Differential sex allocation may therefore result from adaptive parental
decisions or sex-related variation in competitive ability or because of sex-related asymmetries in kin selection. Under normal
food provisioning, female barn swallow (Hirundo rustica) nestlings begged more loudly but did not receive more food than male nestlings. After food deprivation, begging call loudness
of males but not females increased. Begging loudness positively predicted the number of feedings received by the nestlings,
and males gained more mass than females after food deprivation. Male nestlings are more severely affected by chronic food
reduction and may therefore accrue a larger benefit compared to females by increasing their food intake under short-term conditions
of food scarcity. These results suggest that either females do not increase begging intensity to favour male broodmates which
are more vulnerable to prolonged food stress, or that males prevail in scramble competition despite being similar in size
to females. 相似文献
7.
Parental care is often characterized by complex behavioral interactions between offspring soliciting for food and parents providing food. During this interplay both behaviors, offspring begging and parental provisioning, can exert a selective pressure on the expression of the other. It has, therefore, been predicted that traits involved in this interplay may coevolve and ultimately become (genetically) correlated. Such covariation has—at least at the phenotypic level—been found in a number of cross-fostering studies, including evidence from the canary (Serinus canaria), our model species. However, a common challenge for these studies has been to establish a genetic covariation given the difficulty to disentangle the relative contribution of genetic and maternal effects, as the latter may act already before cross-fostering. We addressed this problem by studying within-individual covariation between begging (expressed at the nestling stage) and provisioning (expressed at the adult stage). In addition, we estimated the degree of heritability of these behaviors using parent-offspring regressions, as inheritance forms a prerequisite for any genetic correlation. Both traits showed a low to moderate non-significant heritability, similar to those previously reported in other bird species. However, offspring begging and parental provisioning did not covary at the intra-individual level. Thus, individuals begging intensively as nestlings were not necessarily individuals that provided more food as adults or vice versa. These findings provide important insights for our understanding of coadaptation, suggesting that factors other than genes such as maternal effects may play a role in adjusting offspring begging to the levels of parental provisioning. 相似文献
8.
Optimal investment theory is based on the assumption that the proximate constraint acting on parental investment is resource based. A trade-off between per offspring investment and total investment seems intuitive. Consequently, a parents investment strategy is expected to represent a trade-off between the benefits of investment for current offspring and the costs to future reproduction for parents. In this study, we provide clear evidence that the costs and benefits of maternal provisioning in the dung beetle Onthophagus taurus influence the amount of provisions provided by the mother. Horse dung is typically of a higher nutritional value than cow dung and females were shown to provide 20% less dung to offspring when provisioning with horse dung. By reducing their investment per offspring and exhibiting a clear preference to provision offspring with horse dung, females were able to produce significantly more offspring. Females provisioning with horse dung received greater fitness returns per unit of investment and experienced lower provisioning costs, in terms of the minimum amount of dung required to produce a surviving offspring, than females provisioning with cow dung. Females provisioning in soil of low moisture content were found to have higher tunneling costs than those provisioning in soil of high moisture content, while the fitness returns per unit of investment did not differ. We adopted a marginal value theorem (MVT) approach to calculate the theoretical optimal level of investment for each dung type and for each soil moisture. Predicted levels of provisioning were lower for horse dung than for cow dung and for moist soil than for dry soil. Therefore, the results of this study are in qualitative agreement with MVT predictions and provide empirical support for the proposal that females can adaptively adjust their level of investment in response to resource and/or habitat quality. However, the theoretically predicted optimal investment yielded a poor quantitative fit with our observed levels of investment, with females providing over twice the investment predicted by the MVT approach. We suggest that this difference may reflect either our inability in directly quantifying all the necessary costs and benefits of investment in O. taurus and/or the applicability of the underlying assumptions of MVT.Communicated by D. Gwynne 相似文献
9.
Sjouke A. Kingma Michelle L. Hall Anne Peters 《Behavioral ecology and sociobiology》2011,65(6):1203-1213
When fitness returns or production costs vary between male and female offspring, selection is expected to favor females that
adjust offspring sex ratio accordingly. However, to what extent vertebrates can do so is the subject of ongoing debate. Here,
we explore primary sex ratios in 125 broods of cooperatively breeding purple-crowned fairy-wrens Malurus coronatus. We expected that females might adjust offspring sex ratio because this passerine species experiences considerable variation
in social and environmental conditions. (1) However, although helpers substantially increase parental fitness, females (particularly
in pairs and small groups) did not overproduce philopatric males (helper-repayment hypothesis). (2) Sex-ratio adjustment based on competition among individuals (helper-competition hypothesis) did not conceal helper-repayment effects or drive sex allocation on its own: while high-quality territories can accommodate
more birds, brood sex ratios were independent of territory quality, alone or in interaction with group size. (3) Additionally,
males are larger than females and are possibly more costly to produce (costly sex hypothesis), and (4) female offspring may benefit more from long-term effects of favorable conditions early in life (Trivers–Willard hypothesis). Nonetheless, large seasonal variation in food abundance was not associated with a consistent skew in primary sex ratios.
Thus, overall, our results did not support the main hypotheses of adaptive sex-ratio adjustment in M. coronatus. We discuss that long-term differential costs and benefits may be insufficient to drive evolution of primary sex-ratio manipulation
by M. coronatus females. More investigation is therefore needed to determine the general required sex differences in long-term fitness returns
for mechanisms of primary sex-ratio manipulation to evolve. 相似文献
10.
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
11.
Michelle Pellissier Scott 《Behavioral ecology and sociobiology》1990,26(1):31-39
Summary Parental behavior that has an impact on the increased survival of offspring, an important factor in the evolution of parental care, can include both guarding and provisioning. The effects of these two components of parental care can be separated and quantified in the burying beetle Nicrophorus orbicollis in which both male and female cooperate to rear young. Although in the absence of competition, reproductive success is reduced by the presence of the second parent in the brood chamber, two parents dramatically reduce the probability that conspecifics will usurp the resource, replace either the male or female, kill the newly hatched brood, and produce a replacement clutch. After the establishment of the burial chamber (but not before) beetles appear to assist their mates in driving off intrasexual competitors. Male assistance in burial does not account for very much of the variance in the speed in which the carcass can be concealed nor are two parents essential to guard against insect predators. There were no significant differences in the duration of parental care by males paired with virgin and non-virgin females suggesting that paternity of the brood for which the male provides care is not a factor determining the length of care. Since male and female reproductive success is limited in Nicrophorus by access to suitable carcasses, many of the typical asymmetries in the costs and benefits of parental care are lacking. However since sperm displacement is not complete, paternity of the replacement clutch, for which the male does not provide care, may be a factor encouraging male desertion before female desertion. Other factors important in the evolution of paternal care, especially the probability of additional reproductive opportunities, are discussed. 相似文献
12.
Smith Adam R. Wcislo William T. O'Donnell Sean 《Behavioral ecology and sociobiology》2003,54(1):14-21
Assured fitness returns models for the evolution of sociality emphasize the selective value of ensuring that offspring receive adequate parental care to reach maturity. If a member of a social group dies, it can accrue returns on investment in offspring through the efforts of surviving social partners. We provide evidence that in the mass-provisioning, facultatively social sweat bee Megalopta genalis, adult presence in the nest throughout brood development provides protection from ant predation. Nests with adults present were well protected, and brood in nests with adults removed suffered higher predation. Females in observation nests showed effective defensive behavior against experimentally introduced ants, and bees in natural nests repulsed naturally occurring ant raids. Megalopta nest architecture and behavior are such that the brood of several cooperating females can be defended with little additional cost relative to solitary nesting. The benefits of cooperative defense may favor group living in mass provisioning bees. Our observations and experiments suggest that parental care throughout brood development can be adaptive in mass provisioning species, supporting the predictions of assured fitness returns models. 相似文献
13.
Nina Wedell 《Behavioral ecology and sociobiology》2010,64(9):1385-1391
A cost of mating is common to both sexes but has predominantly been examined in females. In species where males provide resources
to females at copulation, male mating costs are expected to be high as nutrient provisioning enhancing female fecundity is
assumed to carry costs. In addition, males frequently court females prior to mating, which is known to carry survival costs
to both sexes. However, the magnitude and basis of variation in males’ mating costs remains largely unknown. Here, I examine
the effect of nutrient provisioning and courtship on male longevity across full-sib families in the paternally investing green-veined
white butterfly, Pieris napi. Copulating males suffered a survival cost as did courting males prevented from copulating, indicating the courtship component
of mating is costly. Male P. napi release aphrodisiacs during courtship to promote mating, indicating that these compounds may also be costly to produce. Contrary
to expectation, nutrient provisioning was not associated with reduced survival relative to males only allowed to court females,
although it is possible that this could be masked by the potentially elevated courtship rates of courting males relative to
mating males. Families differed in magnitude of reduced male survivorship, indicating a likely genetic basis to variation
in costs of courtship and copulation. Male weight was unrelated to longevity and mating success, whereas longevity strongly
influenced male mating success, indicating lifespan is an important male fitness trait in this species. 相似文献
14.
Zair P. Burris 《Marine Biology》2011,158(2):381-390
Sea spiders are one of the few marine invertebrates whose males care exclusively for offspring. The costs of parental care,
however, have never been addressed for any species of pycnogonid. Costs may be significant for brooding sea spiders of Achelia simplissima, since males carry up to 12 egg masses simultaneously and actively aerate those eggs by moving their ovigerous legs back
and forth. This study explored four potential costs to males as a result of parental care: predation, dislodgment, movement
and feeding patterns, and frequency of epibionts. Brooding males were found to experience significantly higher frequencies
of predator attacks and epibionts, as well as a lower rate of movement compared with nonbrooding males. Interestingly, brooding
males were harder to dislodge than nonbrooding males and experienced no change in feeding frequency as a result of parental
care. This is the first study to provide evidence that parental care may be costly for male pycnogonids in terms of individual
survival and future reproductive success. 相似文献
15.
Andrea Romano Giuseppe Boncoraglio Diego Rubolini Nicola Saino 《Behavioral ecology and sociobiology》2013,67(5):851-859
In species with parental care, competition among siblings for access to limited parental resources is common. Sibling competition can be mediated by begging behaviour, a suite of different visual and acoustic displays by which offspring solicit parental care. These are mostly addressed to the parents upon food provisioning, but can also be performed in the absence of the attending parents. This so-called parent-absent begging (PAB) may function as an intrabrood communication signal and potentially affect intrabrood competition dynamics for access to food. We investigated the role of PAB in moulding sibling interactions and its effect on food intake among altricial barn swallow (Hirundo rustica) nestlings, both under normal and experimentally reduced food intake. Frequency of PAB increased after food deprivation. Nestlings that had performed PAB increased their begging intensity upon the subsequent parental feeding visit, while siblings reduced their own begging level, but only when they had not been food-deprived. As a consequence, nestlings which had performed PAB before parental arrival had larger chances of receiving food. However, nestlings did not benefit from displaying PAB when competing with food-deprived siblings. Our findings show that PAB reliably reflects need of food, indicating that a nestling will vigorously compete for the subsequent food item. By eavesdropping siblings' PAB displays, nestlings may optimally balance the costs of scrambling competition, the direct fitness gains of being fed and the indirect fitness costs of subtracting food to needy kin. However, large asymmetries in satiation between competitors may lead individual offspring to monopolize parental resources, irrespective of PAB displays. 相似文献
16.
Optimal parental investment usually differs depending on the sex of the offspring. However, parents in most organisms cannot
discriminate the sex of their young until those young are energetically independent. In a species with physical male–male
competition, males are often larger and usually develop sexual ornaments, so male offspring are often more costly to produce.
However, Onthophagus dung beetles (Coleoptera; Scarabaeidae) are highly dimorphic in secondary sexual characters, but sexually monomorphic in
body size, despite strong male–male competition for mates. We demonstrate that because parents provide all resources required
by their offspring before adulthood, O.
atripennis exhibits no sexual size dimorphism irrespective of sexual selection pressure favoring sexual dimorphism. By constructing
a graphic model with three fitness curves (for sons, daughters, and expected fitness return for parents), we demonstrate that
natural selection favors parents that provide both sons and daughters with the optimal amount of investment for sons, which
is far greater than that for daughters. This is because the cost of producing small sons, that are unable to compete for mates,
is far greater than the cost of producing daughters that are larger than necessary. This theoretical prediction can explain
sexual dimorphism without sexual size dimorphism, widely observed in species with crucial parental care such as dung beetles
and leaf-rolling beetles, and may provide an insight into the enigmatic relationship between sexual size dimorphism and sexual
dimorphism. 相似文献
17.
L. E. Browning C. M. Young J. L. Savage D. J. F. Russell H. Barclay S. C. Griffith A. F. Russell 《Behavioral ecology and sociobiology》2012,66(12):1639-1649
Providing food to developing offspring is beneficial for offspring but costly for carers. Understanding patterns of provisioning thus yields important insights into how selection shapes (allo-) parental care strategies. Broadly, offspring development will be influenced by three components of provisioning (prey type, size and delivery rate). However, all three variables are rarely considered simultaneously, leading to suggestions that the results of many studies are misleading. Additionally, few studies have examined the provisioning strategies of breeders and non-breeding helpers in obligate cooperative breeders, wherein reproduction without help is typically unsuccessful. We investigated these components of provisioning in obligately cooperative chestnut-crowned babblers (Pomatostomus ruficeps). Prey type was associated with size, and delivery rate was the best predictor of the overall amount of food provided by carers. As broods aged, breeders and helpers similarly modified the relative proportion of different prey provided and increased both prey size and delivery rate. Breeding females contributed less prey than male breeders and adult helpers, and were the only carers to load-lighten by reducing their provisioning rates in the presence of additional carers. While our results suggest that breeders and helpers follow broadly comparable provisioning rules, they are also consistent with the idea that, in obligately cooperative species, breeding females benefit more from conserving resources for future reproduction than do helpers which have a low probability of breeding independently. 相似文献
18.
Parent–offspring conflict theory predicts the evolution of offspring solicitation signals that can influence the amount and/or
the duration of parental investment. Short-term effects of offspring solicitation signals on parental food provisioning have
been widely demonstrated, but persistent effects of offspring signals on the maintenance of parental care have been rarely
studied. Also, the relation between the amount of care provided to the brood and how it is distributed among individual offspring
within a brood is not well enough understood. Here, we investigated in the European earwig (Forficula auricularia) the effects of offspring condition-dependent chemical signals on the maintenance of maternal care among broods and the distribution
of maternal food within broods. Mothers were isolated from their brood for 3 days and continuously exposed to chemical signals
extracted from broods of experimentally manipulated nutritional state. After re-introducing mothers to their brood, a range
of maternal behaviours were quantified. We found that earwig mothers groomed their offspring significantly more after exposure
to chemical extract from high-food brood in comparison with mothers exposed to extract from low-food brood, which in turn
displayed significantly more aggressive behaviour. Furthermore, we manipulated offspring individual nutritional condition
within the brood to evaluate the effect of offspring state on the within-brood food distribution. Within broods, poorly fed
individuals received significantly more food than well-fed individuals, probably due to scramble competition. These results
show that earwig nymphs express multi-component condition-dependent signals and behaviours differentially affecting maternal
care provisioned to the brood and the distribution of care within broods. 相似文献
19.
Mark C. Mainwaring David Lucy Ian R. Hartley 《Behavioral ecology and sociobiology》2011,65(12):2261-2268
Family conflicts over parental care result in offspring attempting to exert control using solicitation behaviours, whilst
the parents are potentially able to retaliate through provisioning rules. However, the evolutionary interests of one parent
may not necessarily support the evolutionary interests of the other parent, and such conflicts of interest may be expressed
in how the two parents allocate the same form of parental care to individual offspring. Theory suggests that such parentally
biased favouritism is a universally predicted outcome of evolutionary conflicts of interest, and empirical evidence suggests
that parentally biased favouritism occurs in relation to offspring size and solicitation behaviours. However, unequivocal
empirical evidence of parentally biased favouritism in relation to offspring sex is absent, due to being strongly confounded
by sex differences in size and solicitation behaviours. Here, we present strong evidence for parentally biased favouritism
in relation to offspring sex in zebra finches (Taeniopygia guttata), independent of the effects of chick size and begging intensity. Mothers preferentially provisioned sons over daughters,
whilst fathers showed no bias, meaning that sons received more food than daughters. Parentally biased favouritism in relation
to offspring sex facilitates parental control over evolutionary conflicts of interest and is probably more widespread than
previously realised. 相似文献
20.
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