Knowledge of the investment rules adopted by breeders and non-breeders, and the factors that affect them, is essential to
understanding cooperative breeding as part of a life-history tactic. Although the factors that affect relative contributions
to care of young have been studied in some cooperative bird species, there is little data on mammals, making coherent generalisations
within mammals and across taxa difficult. In this study, we investigate individual contributions to pup escorting, a strong
predictor of offspring provisioning, in the banded mongoose (Mungos mungo), a cooperatively breeding mammal in which reproductive skew is low. Contributions by those under a year old (which virtually
never breed) increased with age and body weight but were generally low. Among older age classes (yearlings and adults), individuals
that had not bred in the current litter generally contributed less to escorting than those that had bred (with the exception
of yearling males). In addition, females that did not breed reduced their investment if they were heavy presumably because
such females are more likely to breed in the following event and benefit from saving resources for this. The generally greater
contributions by breeders in banded mongooses contrast with the recent findings in meerkats (Suricata suricatta), another obligatorily cooperative mongoose with similar group size but wherein reproductive skew is high. Our results suggest
that relative contributions by breeders vs non-breeders are not dependent on group size but on the ratio of breeders to carers
and the probability that non-breeders will breed in the near future. 相似文献
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
The striking diversity of avian eggshell colour has long fascinated biologists. Recently, it has been proposed that the blue-green colour of some eggs may function as a post-mating sexually selected signal of female phenotypic quality to their mates to induce higher allocation of paternal care. It has been suggested that maternally deposited yolk carotenoids may be the specific aspect of reproductive quality that the female is signalling via eggshell colour. We use the known properties of the thrush visual system (Turdus sp.) to calculate photon capture for the four single cone photoreceptors, and the principal member of the double cone class for eggs in clutches of two introduced European thrush species (Turdus merula and Turdus philomelos) in New Zealand. We show that differences in the avian-perceived colours of individual eggs are not consistently correlated with different measures of maternal investment in the egg. Given the growing extent of the knowledge between maternal quality, parental investment and eggshell pigmentation across avian taxa, we encourage the use of avian perceptual modelling for testing alternative non-signalling explanations for the structural and physiological basis of these relationships. 相似文献
Reproduction in opportunistically breeding bird species has traditionally been considered non-seasonal with individuals taking
advantage of favourable environmental conditions as they arise. However, some studies imply that this opportunistic breeding
may be superimposed on an underlying seasonality, which has effects on the readiness to breed when conditions are favourable.
The zebra finch (Taeniopygia guttata) is the classic opportunistic breeder and widely used as such in studies. In a series of laboratory-based breeding experiments,
we found evidence to suggest that there are seasonal differences in maternal reproductive investment in the zebra finch even
when photoperiod, temperature, relative humidity and diet were held constant. Females showed highly significant seasonal differences
in clutch size and egg mass with laying order. Clutch size showed a spring/summer peak typical of multi-brooded species in
the wild. There was also a significant increase in egg mass with laying order in all seasons except winter. This variation
in breeding parameters with season may allow females to adjust investment depending on the potential fitness returns from
a given reproductive attempt. These findings also raise a warning about interpreting results of multiple zebra finch breeding
experiments that have been carried out in different seasons. 相似文献
In insects, large ejaculate and associated materials, including spermatophores, appear to have evolved via sexual selection acting on males to either delay female remating or to increase the rate of egg-laying. It is also possible, however, that females use nutrients transferred during mating to increase their lifetime fecundity. If so, male ejaculate size may also have evolved under natural selection as a form of paternal investment. In Lepidoptera, males with a greater number of prior matings tend to produce smaller spermatophores. However, the reported effects of male mating history on female fecundity vary widely among species. We therefore performed a meta-analysis using data from 29 studies of 25 species. Overall, the reproductive output of females mated to virgin males was significantly higher than that of females mated to sexually experienced males (Hedges d=0.33, P<0.01). A sample size of around 145 females per male mating type is required to detect an effect of this size with 80% statistical power at =0.05 (two-tailed). There was no difference in mean effect size between butterflies/skippers and moths. After controlling for any effect of taxonomic group, however, the mean effect size for polyandrous species was significantly greater than that for monandrous species (Hedges d=0.45 vs 0.25, P=0.01). We then discuss possible reasons why male mating history, presumably acting through its effect on spermatophore size, might have a stronger effect in polyandrous than monandrous species.Communicated by A. Cockburn 相似文献
Objective: Statistics indicate that employees commuting or traveling as part of their work are overrepresented in workplace injury and death. Despite this, many organizations are unaware of the factors within their organizations that are likely to influence potential reductions in work-related road traffic injury.
Methods: This article presents a multilevel conceptual framework that identifies health investment as the central feature in reducing work-related road traffic injury. Within this framework, we explore factors operating at the individual driver, workgroup supervisor, and organizational senior management levels that create a mutually reinforcing system of safety.
Results: The health investment framework identifies key factors at the senior manager, supervisor, and driver levels to cultivating a safe working environment. These factors are high-performance workplace systems, leader–member exchange and autonomy, trust and empowerment, respectively. The framework demonstrates the important interactions between these factors and how they create a self-sustaining organizational safety system.
Conclusions: The framework aims to provide insight into the future development of interventions that are strategically aligned with the organization and target elements that facilitate and enhance driver safety and ultimately reduce work-related road traffic injury and death. 相似文献
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
The behaviour of a male bird towards a potential mate and her clutch may depend both on his expected paternity and on the
likelihood that she will produce a replacement clutch if he commits infanticide. In this study we evaluate the choices made
by replacement male European starlings Sturnus vulgaris. By removing males before and during laying, we induced other males, mainly neighbours, to mate with the reproductively active
females. When the original male was removed before laying, a new male adopted the subsequent clutch in 14 out of 15 cases.
When ten females were widowed during their laying period, replacement males never adopted their clutches. The paternity of
replacement males was a function of when they replaced the former male. When replacement occurred more than 3 days before
egglaying, the new male fathered nearly all offspring; when it occurred the day before laying, the new male still fathered
more than every second young. When the original male was removed during his mate’s laying period, in five out of ten cases
a replacement male committed infanticide by throwing out the eggs, but this only occurred in one out of 15 cases when removal
took place before laying. The evidence for infanticide actually being committed by the replacement male was circumstantial.
Four out of six of the females affected by apparent infanticide produced replacement clutches in which the male presumably
had higher paternity than in the original clutch. In all cases, the male adopted the replacement clutch. In five cases when
the original male was removed during laying, the neighbours neither adopted the brood nor committed infanticide, although
they sometimes were seen courting the widowed female and copulating with her. These cases occurred later during laying than
those were males comitted infanticide. The time from infanticide to the laying of the replacement clutch tended to increase
as infanticide was committed later in the laying sequence. We conclude that strategies of potential replacement males are
influenced by their expected paternity in the current brood and the probability that the female will produce an early replacement
clutch.
Received: 10 March 1995 / Accepted after revision: 28 October 1995 相似文献