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1.
Paternity and paternal care in the polygynandrous Smith's longspur   总被引:4,自引:0,他引:4  
In species where females copulate with more than one male during a single breeding attempt, males risk investing in offspring that are not their own. In the polygynandrous Smith's longspur (Calcarius pictus), females copulate sequentially with one to three males for each clutch of eggs and most of these males later assist in feeding the young. Using multilocus DNA profiling, we determined that there was mixed paternity in >75% of broods (n=31) but that few offspring (<1% of 114 nestlings) were sired by males outside the polygynandrous group. Male feeding rate increased significantly with the number of young sired, with males siring four nestlings feeding the brood at double the frequency of males siring only a single nestling. However, male Smith's longspurs appear to show a graded adjustment of paternal care in response to paternity only when other males are available to compensate for reduced care: feeding rate did not vary in relation to paternity when only one male provisioned young at the nest. There was no evidence that males could recognise their own offspring within a brood and feed them preferentially. The number of offspring sired by each male was significantly correlated with the number of days spent copulating with the attending female: on average, a male sired one offspring for every 2 days of copulatory access. If males use their access to females to estimate paternity (and thereby decide on their subsequent level of parental investment), a positive relationship is expected between the amount of female access and the subsequent feeding rate to the nestlings. Nonetheless, male feeding effort was only weakly correlated with female access and more study is needed to determine how males estimate their paternity in a brood. Received: 1 June 1997 / Accepted after revision: 1 April 1998  相似文献   

2.
Emlen and Oring (1977) suggested that monogamy in birds is maintained because of the need for strict biparental care. A corollary of their suggestion is that paternal care should decrease under conditions of high food abundance. An alternative is that paternal care would increase if males take advantage of the higher food abundance by trying to reduce the length of the nestling feeding period. We tested these two ideas using yellow warblers (Dendroica petechia) by providing some pairs with supplemental food, thereby reducing the importance of biparental care. However, the extra food did not decrease paternal effort, nor did it increase it (Fig. 2). Early in the nestling period experimental females brooded more but visited their nestlings less than did control females, but later, when brooding times decreased, experimental females fed their nestlings more than did control females (Fig. 3). There were no significant differences in nestling survival (Fig. 5), but nestlings in the control treatment were larger and heavier up to 6 days old (Fig. 6). The main effect of supplemental food was on maternal, not paternal behaviour. Models of biparental care assume interdependence between the parental effort of both parents. In this species, however, males and females provide for their brood independently from each other.  相似文献   

3.
The extent to which male birds in polygynous species with biparental care assist in nestling feeding often varies considerably between nests of different mating status. Both how much polygynous males assist and how they divide their effort between nests may have a profound effect on the evolution of mating systems. In this study we investigated how males in the facultatively polygynous European starling Sturnus vulgaris invested in their different nests. The amount of male assistance affected the quality of the offspring. Polygynous males invested as much as monogamous males, but divided their effort asymmetrically between nests, predominantly feeding nestlings of first-mated (primary) females. Although females partly compensated for loss of male assistance, total feeding frequency was lower at primary females’ nests than at monogamous females nests. Secondary females received even less assistance with nestling rearing, and the extent to which males assisted decreased with the length of the interval between the hatching of the primary and secondary clutches. These results are contrasted with those from a Belgian populations of starlings with a much more protracted breeding season and thus greater opportunities for males to attract additional mates during the nestling rearing period. The results show that both the “defence of male parental investment model” and the “asynchronous settlement model” have explanatory power, but that their validity depends on the potential length of the breeding season. Received: 21 July 1995/Accepted after revision: 13 July 1996  相似文献   

4.
In sequentially polyandrous bird species, where females mate with different males in succession during a single breeding season, sperm stored by females can occasionally lead to extrapair fertilisations (EPFs) in clutches cared for by the second and subsequent males. Thus, we predicted that in red phalaropes (Phalaropus fulicarius) – a sex-role-reversed, sequentially polyandrous, arctic breeding shorebird – EPFs would occur more frequently in clutches laid later in the breeding season. We used multilocus DNA profiling to examine the frequency and timing of EPFs in a population of red phalaropes breeding in the Canadian high arctic. Using a technique to determine parentage without maternal DNA, we inferred that 6 of 70 chicks in 18 broods resulted from EPFs – one extrapair chick in each of 6 broods. These results were supported by a further analysis using microsatellite DNA. As predicted, broods containing EPFs hatched from clutches laid significantly later in the season than did broods containing no EPFs. The difference in median hatch dates between broods with and without EPFs was 9.0 days, or 38% of the entire egg-laying period in that season. For the whole breeding season, we estimated that 6.5% of chicks were sired by extrapair males, which is similar to extrapair paternity estimates for other sex-role-reversed birds, but relatively low compared to the majority of socially monogamous species studied so far. Received: 24 August 1998 / Received in revised form: 18 January 1999 / Accepted: 24 January 1999  相似文献   

5.
For males of socially polygynous avian species like the spotless starling, there may exist a trade-off between investing in paternal care and controlling several nests. To determine how the intensity of paternal care affects reproductive success per brood sired or expressed as the total number of young raised in all nests controlled by the same male, it is necessary to manipulate paternal care. Testosterone (T) has been shown to depress the tendency for males to care for their young, and induces them to acquire more mates. The effects of paternal care on reproductive success were studied by treating certain male starlings with exogenous T and others with the antiandrogen cyproterone acetate (CA), and comparing the parental behavior of T- and CA-males throughout the breeding season with that of controls. CA-males fed their chicks more during the first week after hatching than T-males, with controls feeding at intermediate rates, both on a per nest basis and as total effort for all nests controlled by the same male. Paternal feeding rates during the first week of chick life had a significant positive effect on the number of fledged young. The hormone treatment significantly affected the number of chicks raised per nest, CA-males having a higher breeding success per nest than T-males, and controls showing intermediate levels of success. There was no significant effect of treatment on total reproductive success attained by males throughout the season. In the polygonous spotless starling, the intensity of paternal care of young affects reproductive success per nest positively but not on a seasonal basis. Received: 6 February 1999 / Received in revised form: 30 June 1999 / Accepted: 11 July 1999  相似文献   

6.
A recent hypothesis suggests that birds’ blue-green egg colors may be a sexually selected signal of female (and potentially nestling) quality that males use to make parental investment decisions. While there is some empirical support for this idea, both theory and observations question its validity. To test this hypothesis experimentally, we examined the influence of egg color on male American robin Turdus migratorius behavior by replacing natural clutches with four artificial eggs that were all either pale or vividly colored, close to the extremes in natural egg coloration. At the end of the incubation period, three unrelated nestlings were fostered into each experimental nest, and parental provisioning behavior was monitored when nestlings were 3, 6, and 9 days old. Male provisioning rate for 3-day-old nestlings was significantly higher in the vivid egg treatment compared to both the pale egg treatment and untreated controls, but there was no effect of egg color on paternal behavior at the older nestling stages. Male feeding rate at unmanipulated nests was only weakly positively related to natural egg color (chroma) when nestlings were 3 days old. These results suggest that blue-green egg color may act as a post-mating signal of female quality or investment in this species, but our findings do not exclude the possibility that egg color pigmentation also serves other adaptive functions.  相似文献   

7.
In western bluebirds (Sialia mexicana), most pairs remain together for life and share equally in post-hatching parental care. We removed resident males of socially monogamous pairs during laying and after clutch completion to examine chick-feeding rules used by replacement males and current and future fitness consequences of paternal care. Replacement males were not infanticidal and 7 (47%) fed nestlings. Feeding replacement males and the females they joined fed at rates similar to controls. Females without a feeding replacement male compensated by feeding more themselves so that overall feeding rates were not compromised, but they reduced their brooding time. Unlike assisted females, unassisted females exhibited reduced nesting success and their 14-day-old chicks weighed less than controls. Field metabolic rates of unassisted females were 17% higher than those of control females, but the difference was not statistically significant. Older females were better able to raise young without the male's help than were yearling females. Female condition was not affected by male provisioning and unassisted females were as likely to survive to the next breeding season as assisted females. We found no future benefits of provisioning by replacement males; those that fed were no more likely to breed with the female on her subsequent attempt than were males that did not feed, and subsequent clutch sizes were not reduced for females rearing young without the male's help. These experiments suggest that male parental care increases nesting success in western bluebirds and that replacement males use an all-or-none rule to determine whether or not to feed chicks: if they are present during the fertile period they feed at typical rates; if they are not, they usually do not feed at all. Because chick-feeding by males is tied to opportunity for paternity, influences success in the current nest, and does not affect the male's future breeding success, it appears to be parental rather than mating effort. Received: 8 May 1998 / Accepted after revision: 23 July 1998  相似文献   

8.
Determinants of male mating success in the red bishop (Euplectes orix)   总被引:4,自引:0,他引:4  
We studied sexual selection in the red bishop, Euplectes orix, a colonial, polygynous weaverbird widely distributed over sub-Saharan Africa. Male reproductive success measured in terms of the number of nests accepted by females and the number of eggs and nestlings in all the nests on a male's territory varied considerably. The standardized variance (variance/mean2) in male reproductive success ranged from 0.505 to 1.737 in different years, indicating a high potential for sexual selection in this species. An analysis of genetic parentage for 432 nestlings by non-radioactive, multilocus DNA fingerprinting confirmed that male reproductive success (number of young sired on the territory) in this species can be reliably estimated by the measures introduced above. In all 4 study years there was a strong positive correlation between male mating success and the total number of nests that males built in their territories. The number of nests built can be partitioned into the number of weeks a male held a territory and his nest-building performance. Both factors exert a significant positive effect on male mating success and in combination explained between 53.3 and 86.3% of the variation in male reproductive success. Male morphological characters were found to be of no importance. Males that established a territory in the following season built more nests and held their territories for longer than males that did not establish a territory in the following season, suggesting that these measures might be indicators of male condition and quality. Male nest-building performance (number of nests built per week) seems to be unrelated to male condition or quality. Received: 8 January 1999 / Received in revised form: 7 June 1999 / Accepted: 13 June 1999  相似文献   

9.
Summary To determine the effects of male mating status on female fitness, we compared the reproductive success, survival, and future fecundity of female Savannah sparrows (Passerculus sandwichensis) mated to monogamous vs. polygynous males in a 5-year study on Kent Island, New Brunswick, Canada. The proportion of males with more than one mate varied from 15 to 43% between years and sites. Polygynous and monogamous males fledged young of equal size in every year of the study. Females who shared paternal care with other females laid as many eggs per clutch and clutches per season as monogamously mated females. In most years polygynously mated females showed no delay in laying a second clutch, and they suffered no reduction in fecundity the following year. Recruitment of a female's offspring into the breeding population was generally independent of her mating status. Fitness costs of being mated to a polygynous male were only apparent in one year of the study, during which females mated to polygynous males had higher over-winter mortality than those mated to monogamous males. That same year, young raised by polygynous males were only one-third as likely to survive to reproductive maturity (as inferred by returns) as those raised by monogamous males. A male's mating status had no effect on his own survivorship. A male's mating status did not necessarily reflect his contributions to raising nestlings, which may partially explain why monogamously and polygynously mated females had equal fitness. At 35 nests the proportion of food deliveries brought by individual males varied from 0 to 75%; on average, males brought fewer than 30% of all food deliveries. Yet parental care by polygynous males was no less than that of monogamous males, at least at the nests of their primary females. Secondary females tended to receive less male assistance during the nestling stage, but their reproductive success was indistinguishable from that of primary females. Females feeding young without male assistance made as many food deliveries/h as did pairs in which males brought at least 30% of all food deliveries. Unassisted females did not suffer diminished fledging success or produce smaller fledglings. The benefits of polygyny for male Savannah sparrows are clear: polygynous males recruit more surviving offspring into the breeding population than monogamous males. The fitness of females, on the other hand, appears to be unaffected by whether their mate was monogamous or polygynous except in occasional years. Polygyny may be maintained in this population by the constraints of a female-biased sex ratio, the inability of females to predict a male's paternal care based on his morphology or behavior, the poor correlation between a male's mating status and his assistance at the nest, and inconsistent natural selection against mating with a polygynous male. Correspondence to: N.T. Wheelwright  相似文献   

10.
We investigated sexual conflict over parental care in blue-headed vireos (Vireo solitarius) and documented the first example of unvarying unisexual brood desertion in passerines. Females at all nests (N = 24) that were monitored closely near fledgling, deserted their broods on or near the day of fledging leaving males alone to complete parental care of young. No males deserted. This observational evidence was confirmed with radiotracking of females (2004, 2007) and both pair members (2008). Radiotracked females began visiting distant males 1–4 days before young left the nest, subsequently paired with males 355–802 m away, and laid first eggs in new nests less than 5 days after deserting. In contrast, females suffering nest predation did not desert and renested with the same male. We suggest equal parental care (nest building, incubation, feeding) in the sexes, genetic monogamy, and an adult sex ratio biased towards males has led to female control of brood desertion in this species. Unisexual desertion may be more important in altricial birds than generally realized and we discuss prerequisites to predict its occurrence. One is genetic monogamy, which may be a female tactic that reduces the likelihood of males evolving counter-adaptations to female desertion.  相似文献   

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