Reproductive Value Hypothesis Research Articles

Parental investment does not directly affect reproductive success in the saffron finch

In tropical species, the study of parental care and the description of the intraspecific variation of parental care remain relatively understudied, especially when compared to the vast works dedicated to species from the Northern Hemisphere. In Colombia, the saffron finch Sicalis flaveola, is a species with a wide geographical distribution, and despite its abundance in open habitats and urban environments, little is known about its reproductive ecology. As a small‐bodied, short‐lived passerine, we postulated that the saffron finch should behave according to the ‘reproductive value hypothesis', investing in the current brood at the expense of future survival. Consequently, we predicted: 1) that parental investment would be associated with brood size and 2) parental investment would be positively associated with nestling growth rate and reproductive success (defined as the number of nestlings which reached fledging age). In 2018, two reproductive peaks of S. flaveola flaveola were documented in the Meléndez campus of Universidad del Valle, Cali. Direct observations and video cameras (> 1700 h of recording) were used to monitor the nests from 38 different breeding pairs. We found that feeding visits and the number of regurgitation events were positively related to brood size. In an experiment of simulated nest predation, 85% of breeding pairs responded to the stimulus and parents who exhibited highly responsive behaviours (50%) raised nestlings with a higher growth rate. We also found that egg surface area positively affected the number of incubation bouts per hour. Whilst no relationship was found between overall parental investment and reproductive success, our results appear to show that the intensity of parental investment during reproduction was modulated by brood size. Our findings suggest that there are multiple ecological factors that influence reproductive success in the saffron finch, and reinforce the need for longer term studies of tropical passerines.

Environmental unpredictability shapes glucocorticoid regulation across populations of tree swallows

The ability to respond appropriately to challenges is an important contributor to fitness. Variation in the regulation of glucocorticoid hormones, which mediate the phenotypic response to challenges, can therefore influence the ability to persist in a given environment. We compared stress responsiveness in four populations of tree swallows (Tachycineta bicolor) breeding under different environmental conditions to evaluate support for different selective pressures in driving the evolution of glucocorticoid regulation. In accordance with the environmental unpredictability hypothesis, stronger stress responses were seen in more unpredictable environments. Contrary to the reproductive value hypothesis, the stress response was not lower in populations engaging in more valuable reproductive attempts. Populations with stronger stress responses also had stronger negative feedback, which supports a “mitigating” rather than a “magnifying” effect of negative feedback on stress responses. These results suggest that combining a robust stress response with strong negative feedback may be important for persisting in unpredictable or rapidly changing environments.

Higher maternal care and tolerance in more experienced giraffe mothers

Maternal investment and maternal care provided by mammalian females can change during their ontogeny. Differences may be related to the age and/or experience (parity) of the female. Several hypotheses have been postulated to explain changes in the rate of maternal care of females during their lifetime. The residual reproductive value hypothesis supposes a higher rate of maternal care in older and more experienced females, in contrast the targeted reproductive effort hypothesis predicts lower levels of maternal care in older and/or more experienced females. To test these hypotheses we investigated nursing bout frequency and time devoted to nursing as predictors of the rate of maternal care, and rate of successful nursing bouts as a predictor of maternal investment, in captive giraffe (22 females, 47 calves in four zoos). We also considered the high rate of allonursing (nursing of non-filial calves) which appeared in all herds. The nursing and allonursing bout frequency as well as the total time devoted to nursing and allonursing increased with increasing parity and age of the female, thus supporting the residual reproductive value hypothesis. In addition, maternal experience of individual females in terms of parity rather than age was responsible for variation in maternal behaviour. This suggests that variation depends on individual experiences.

Childlessness and investment in nieces, nephews, aunts and uncles in Finland.

Kin selection theory predicts that individuals may increase their inclusive fitness by investing in their genetically related kin. In addition, according to the reproductive value hypothesis, individuals may increase their fitness more by investing in their kin in descending rather than ascending order. The present study uses the Generational Transmissions in Finland data collected in 2012 (n ¼ 601 women) and analyses whether childless younger women invest more in their kin than younger women with children. The study finds that childless women are more likely than mothers to invest in their nieces and nephews but not their aunts and uncles. Thus the results are in line with the reproductive value prediction.

Parental Risk-Taking Behaviour and Nest Defence During the Nestling Rearing Stage in Northern House WrensTroglodytes aedon

Abstract Risk-taking behaviour of short lived nesting birds is often explained in relation to the reproductive value of offspring (the reproductive value hypothesis) and the harm that the absence of parental care can cause to nestlings (risk of harm-to-offspring hypothesis). The reproductive value hypothesis predicts that the risk assumed by adults should increases with nestling age, whereas the risk of harm-to-offspring hypothesis predicts the opposite pattern. We assessed the risk-taking behaviour of nesting males and females Northern House Wrens, Troglodytes aedon, faced with a predation threat (plastic owl model) when rearing 3–4 and 10–12 days old nestlings. We used the time elapsed until parents first entered the nest-box as a measure of risk-taking behaviour and alarm calling rate as a proxy of nest defence. Females resumed sooner parental activities when exposed to the model when nestlings were young, supporting the risk of harm-to-offspring hypothesis. In contrast, the time lasted to resume paren...

Dissecting the mechanisms underlying old male mating advantage in a butterfly

Selection is expected to maximize an individual’s own genetic reward regardless of the potential fitness consequences for its sexual partners, which may cause sexual conflict. Although performance in holometabolous insects typically diminishes with age, old male mating advantage has been documented in a few species. Whether this pattern arises from female preference for older males based on, e.g., pheromone blends (intersexual selection), or from increased eagerness to mate in older compared to younger males is currently debated. We explore the mechanistic basis of old male mating advantage, using a series of experiments including behavioral as well as manipulative approaches, in the tropical butterfly Bicyclus anynana. Consistent with the residual reproductive value hypothesis, old male mating advantage was associated with a greater eagerness to mate, evidenced by a two times higher flying and courting activity in older than in younger males. In contrast, we found only limited support for a contribution of female preference for older males based on pheromone composition, although male sex pheromones clearly do play a role in mating success. Our results suggest that male behavior may play a primary role in old male mating advantage, and that pheromones are likely of secondary importance only. Male mating success was related to higher overall pheromone titers rather than variation in a single component. A dominant importance of male behavior in determining mating success may result in sexual conflict.

Old male mating advantage results from sexual conflict in a butterfly

Accumulating evidence suggests that sexual conflict is all pervasive, although cooperation is evidently needed in sexually reproducing organisms. While male mating success is typically positively associated with resource-holding potential, old male mating success prevails in some organisms despite old males being in greatly reduced condition. We tested whether this counterintuitive pattern is the outcome of (1) sexual conflict or (2) female preference for older males in the tropical butterfly Bicyclus anynana. Our results support the first hypothesis as females that mated with older compared to younger males showed reduced hatching success of eggs and higher remating propensity, and tended to show shorter refractory periods. Thus, females apparently try to compensate for reduced fitness arising from mating with older (low-quality) males by being more willing to remate, especially with young and/or virgin (high-quality) males. As mating with older males negatively affects female fitness, old males may acquire a mating advantage by being more aggressive and persistent during courtship, in line with the residual reproductive value hypothesis. Thus, males increase their own reproductive success at the expense of their female partners, such that the ‘cooperation–conflict balance’ between the sexes seems to be shifted towards conflict in B. anynana.

Life History of Brachyrhaphis parismina: Variation Within and Among Populations

Poeciliids provide a model system for comparative studies of life-history variation because of the relatively large number of species and the diversity of environments they occupy. Brachyrhaphis parismina is a narrow-bodied poeciliid that occupies rivers and streams in the eastern lowlands of Costa Rica. Detailed life-history information on species in the narrow-bodied clade of the genus Brachyrhaphis is lacking compared to the many studies on the round-bodied species of the genus. We test for variation in life history among five populations of Brachyrhaphis parismina, and for patterns of allometry associated with the reproductive value hypothesis among individuals. Life-history traits exhibited little variation among populations in contrast to variation observed among populations of round-bodied congeners. Furthermore, within locations females exhibit isometric patterns of reproductive allocation with female body size, thus life history varies little over a female's lifetime. This pattern is inconsistent with that expected from the reproductive value hypothesis. Variation among and within populations in this species may be constrained by the high flow environment they occupy.

Sex differences in biparental care as offspring develop: a field study of convict cichlids (Amatitlania siquia)

Parental investment theory states that parents should contribute more to older offspring. Differences between the sexes also influence how each parent contributes to offspring in biparental species. Here, we examined a naturally occurring population of biparental convict cichlids in Costa Rica to determine how each parent cared for offspring during two distinct offspring development stages. Consistent with the predictions of the reproductive value hypothesis, we hypothesized that the levels of parental contribution would be relative to the value that each parent places on a brood. We predicted that female parents would contribute more than male parents because female convict cichlids have lower future reproductive success than males. Additionally, we predicted that both parents should contribute more to older offspring, either due to the young’s increased susceptibility to predation (i.e., the vulnerability hypothesis) or because of the longer period of time parents have been interacting with older offspring (i.e., feedback hypotheses). This increase in investment by males should coincide with a change in the coordination of care between parents. Detailed observations of parental pairs in their natural habitat supported these predictions. Females contributed more to broods than males and were relatively unaffected by offspring age while males spent significantly more time with older, free-swimming fry. Additionally, males tended to leave younger offspring more than females did, and were more likely to do so consecutively with younger offspring. This suggests that the coordination of duties between parents changes as parental investment changes. Overall, these data support both the reproductive value and the vulnerability hypotheses, but not necessarily the feedback hypothesis.

Costing reproduction: effects of mating opportunity on mating success in male Bicyclus anynana butterflies

It is frequently assumed that males have an almost unlimited reproductive capacity, while access to receptive females is typically limiting. Consequently, sexual selection is expected to favor vigorous courtship behavior in males. If such behavior is associated with non-trivial costs, ample current mating opportunities should be accompanied by a reduction in future mating vigor. To test this hypothesis, three treatments differing in sex ratio were established using the tropical butterfly Bicyclus anynana: 50 males each were housed either with 0, 25, or 50 females. Mating trials involving the competition among males from each treatment for a single virgin female were carried out on days 3, 9, and 15 after allocation to treatments. While there was no difference on day 3, prior mating opportunity clearly reduced mating success on days 9 and 15, being lowest if identical numbers of males and females were housed together. This finding suggests accumulating costs associated with high courtship and/or mating activity. Further, older males were more active and initiated copulation earlier than the younger ones, consistent with the residual reproductive value hypothesis. We found no evidence for a survival or fertility cost of mating.

Changing costs of reproduction: age-based differences in reproductive allocation and escape performance in a livebearing fish

The reproductive value hypothesis predicts that if residual reproductive value declines as a female ages, then young females should allocate less of available energy to current fecundity and more to future reproduction; whereas, older females should allocate more of available energy to current fecundity and less to future reproduction (i.e. survival). We test the prediction that older female Gambusia affinis exhibit higher levels of allocation to reproduction (i.e. fecundity) and consequently experience greater decline in escape performance (survival cost) during pregnancy compared to young females. Old females had relatively larger clutch wet masses and clutch wet mass increased more during pregnancy compared to young females. Correspondingly, old females exhibit a significant decline in escape velocity over the course of pregnancy; whereas young females show no change in escape velocity throughout pregnancy. Old females have higher escape velocities early in pregnancy and their performance only declines to about the level of performance of young females by the end of pregnancy. Thus, although old females exhibit a greater decline in performance they are better able to ameliorate the cost of decreased performance.

Nest defence in the meadow pipit Anthus pratensis: the influence of renesting potential

The reproductive value hypothesis predicts that the level of nest defence is determined by the expected chance of offspring to survive until reproduction, and by the reproductive potential of the parents. Rates of survival from one breeding season to the next are low in small passerines, and their residual reproductive potential strongly declines as the current breeding season terminates. Therefore, we can expect that parents which have only one breeding attempt per season should defend their nests more intensively than parents with a possibility to renest. We studied nest defence in populations of meadow pipit (Anthus pratensis) breeding in Norway and the Czech Republic, differing in renesting potential. To simulate the threat from a predator, we placed a stuffed stoat (Mustela erminea) first 5 m and then 1 m away from a nest with nestlings. Parents increased or kept nest defence constant when the stoat approached their nests in Norway and, during a breeding season shortened by severe weather, in the Czech Republic (when renesting potential was limited). Parents decreased nest defence when the stoat approached the nest during “normal” breeding seasons in the Czech Republic (when renesting was common). These findings give support to the reproductive value hypothesis.

Intermittent breeding as a cost of site fidelity

Intermittent breeding (skipping a breeding season) can be the result of an adaptive decision by a focal individual, trading current reproductive success in favour of future reproductive success (residual reproductive value hypothesis). In contrast, an individual can also be forced by conspecifics to abandon the familiar breeding site and refrain from breeding due to lack of suitable alternative breeding sites or mates (competition hypothesis). I studied intermittent breeding in the territorial and site-faithful Eurasian oystercatcher Haematopus ostralegus, using a dataset covering 20 years. Intermittent breeding (in total 86 cases) occurred among breeders that formerly bred in high- as well as low-quality territories. The main factor associated with intermittent breeding in high-quality sites was death of a mate, while in low quality sites divorce was the most prominent factor. In 93% of the cases birds were forced to cease breeding due to pressure from conspecifics consistent with the competition hypothesis. There was no association between intermittent breeding and promotion to a territory of better quality. Instead, oystercatchers returned to breeding habitat of similar quality and at a very close distance (median distance 128 m) from the previous breeding location. Breeding absences lasted on average 2.4 years, with a maximum of 9 years, and the quality of the territory obtained after the absence varied with the duration of it. Birds who re-bred in a high-quality territory acquired this on average faster than those that re-bred in a low-quality territory, indicating that birds in high-quality sites are better competitors.

Pair bonding and "the widow effect" in female prairie voles.

We conducted field and laboratory experiments with the well-studied monogamous prairie vole, Microtus ochrogaster, to distinguish among three hypotheses for the failure of females that lose their mates to bond with a new male ("the widow effect"). The reproductive value hypothesis predicts that males prefer young to older females because they potentially have a longer reproductive lifespan. The mate rejection hypothesis predicts that females will prevent repairing by aggressively deterring males that might harm their current offspring. The misdirected paternal care hypothesis assumes that females will mate during postpartum estrus and thus will be pregnant and/or nursing young throughout the breeding season; males will avoid pairing with older females to avoid providing care to unrelated offspring and/or because of a delay to the next breeding opportunity. Males associated and bred more with older than young females, allowing us to reject the reproductive value hypothesis. Our results were consistent with the male rejection hypothesis in that females were aggressive toward unfamiliar males. Our results were most consistent with the misdirected paternal care hypothesis in that once females started breeding, they continued to become pregnant and nurse young throughout the study period. Thus, our findings suggest that the potential of misdirected paternal care and delayed mating opportunity in conjunction with the aggressive behavior of females toward unfamiliar males are likely explanations for the lack of repairing for widow females.

Pair bonding and ?the widow effect? in female prairie voles

We conducted field and laboratory experiments with the well-studied monogamous prairie vole, Microtus ochrogaster, to distinguish among three hypotheses for the failure of females that lose their mates to bond with a new male (“the widow effect”). The reproductive value hypothesis predicts that males prefer young to older females because they potentially have a longer reproductive lifespan. The mate rejection hypothesis predicts that females will prevent repairing by aggressively deterring males that might harm their current offspring. The misdirected paternal care hypothesis assumes that females will mate during postpartum estrus and thus will be pregnant and/or nursing young throughout the breeding season; males will avoid pairing with older females to avoid providing care to unrelated offspring and/or because of a delay to the next breeding opportunity. Males associated and bred more with older than young females, allowing us to reject the reproductive value hypothesis. Our results were consistent with the male rejection hypothesis in that females were aggressive toward unfamiliar males. Our results were most consistent with the misdirected paternal care hypothesis in that once females started breeding, they continued to become pregnant and nurse young throughout the study period. Thus, our findings suggest that the potential of misdirected paternal care and delayed mating opportunity in conjunction with the aggressive behavior of females toward unfamiliar males are likely explanations for the lack of repairing for widow females.

Importance of competition for food and nest-sites in aggressive behaviour of Collared Flycatcher Ficedula albicollis

Capsule Using an experimental approach, this study disentangles effects of two important sources on the elicitation of aggressive interspecific behaviour. Aims To investigate experimentally whether competition for nest cavities and/or food can explain aggressive behaviour between competing species. Methods The Collared Flycatcher's Ficedula albicollis responses to mounts of Great Tit Parus major (nest-site and food competitor), Chaffinch Fringilla coelebs (food competitor) and Dunnock Prunella modularis (control species) were tested. Trials were performed near flycatchers' nests during nest building, incubation and care of nestlings. Results The intensity of dive attacks and frequency of contact attacks showed that the aggression of Collared Flycatchers decreased in the direction: Great Tit > Chaffinch > Dunnock. The difference in aggressiveness was greater between Great Tit and Chaffinch than between Chaffinch and Dunnock. Aggression directed toward Great Tits increased from the nest building to the incubation stage and then decreased markedly in the nestling stage. Males were more aggressive than females. Conclusion These results suggest that competition for nest-sites, and to a lesser extent for food, may be of an interference nature and that the reproductive value hypothesis can only partly explain differences in the Collared Flycatcher's defensive behaviour found between sexes and stages of the breeding cycle.

Aging and improving reproductive success in horses: declining residual reproductive value or just older and wiser?

In many mammalian species, female success in raising offspring improves as they age. The residual reproductive value hypothesis predicts that each individual offspring will be more valuable to the mother as she ages because there is less conflict between the current and potential future offspring. Therefore, as mothers age, their investment into individual offspring should increase. Empirical evidence for an influence of declining residual reproductive value on maternal investment is unconvincing. Older mothers may not invest more, but may be more successful due to greater experience, allowing them to target their investment more appropriately (targeted reproductive effort hypothesis). Most studies do not preclude either hypothesis. Mare age significantly influenced maternal investment in feral horses living on the North Island of New Zealand. Older mares, that were more successful at raising foals, were more protective for the first 20 days of life, but less diligent thereafter. Total maternal input by older mothers did not seem to be any greater, but was better targeted at the most critical period for foal survival and a similar pattern was observed in mares that had lost a foal in the previous year. In addition, older mothers were more likely to foal in consecutive years, supporting the hypothesis that they are investing less than younger mares in individual offspring. Therefore, older mothers seem to become more successful by targeting their investment better due to experience, not by investing more in their offspring.

Sex-dependent risk taking in the collared flycatcher, Ficedula albicollis, when exposed to a predator at the nestling stage

An increased mortality rate is a cost of parental care, and can be high during the provisioning phase of altricial nestlings. When a parent stops feeding the nestlings temporarily after seeing a predator, it can reduce its own predation risk, but the suspension of parental care may also reduce its offspring's chances of surviving. We modelled this situation by exposing a stuffed sparrowhawk near collared flycatcher nests and removing it when both parents had seen it. We measured the time (return time) between the removal and when each parent entered the nestbox. The parents' risk taking and the return time are assumed to be inversely related. We studied which brood variables the parents take into account when deciding how much risk they are willing to take during the provisioning period. Males took more risk for older and better-quality nestlings and earlier broods. The females' behaviour was opposite to that of the males: they took significantly less risk for older and better-quality offspring and visited the nestbox later for earlier broods. The males' behaviour supported the reproductive value hypothesis, that risk taking is related to brood value and survival chances, whereas the females' behaviour supported the harm to offspring hypothesis, that risk taking is related to the broods' vulnerability.

Variation in Parental Care with Offspring Age in the Greater Flamingo

Several studies have predicted how parental investment should change in relation to the age of offspring (Williams 1966, Winkler 1987). The Reproductive Value Hypothesis (RVH) states that parents should be prepared to invest more in older juveniles because they have a higher probability of surviving to breeding age. This may occur because older juveniles are closer to maturation and because the instantaneous rate of juvenile mortality generally decreases with increasing age (Clutton-Brock 1991). Increase in feeding effort with chick age has been documented for some species of colonial waterbirds. In Pigeon Guillemots (Cepphus columba) provisioning rates increased with chick age, only during the first part of the nestling period (Emms and Verbeek 1991). Feeding rates were not observed to vary with chick age in the closely related Black Guillemot (Cepphus grylle), but size of fish delivered to the nest increased with chick age (Cairns 1987). As chicks grow older they also have greater food requirements, and increased parental care might simply correspond to the higher energetics and nutritional demands of the offspring. Further evidence for increased parental care with increasing age of offspring comes from studies of brood defense. Brood defense has been reported to increase with nestling age in several passerine species (Andersson et al. 1980, Redondo and Carranza 1989, but see Knight and Temple 1986, Westmoreland 1989). However, the observed increase in parental care with offspring age can also be influenced by confounding variables such as parental age and or quality. Breeding success is known to increase with parental age in several bird species (Saether 1990) and this can be the result of increased experience with age. In addition, as parents grow older, their potential for future reproduction decreases. Thus the cost of reduced future reproductive success should decline with age and older parents should be selected to invest more in offspring compared to younger parents (Pugesek 1981). Therefore, it is important to control for parental age when considering variation in parental care with offspring age. Here, we analyze data from two years on the duration of feeding bouts by Greater Flamingo (Phoenicopterus ruber roseus) parents of known age and sex to their offspring. We show that only male parental care increases with offspring age. We discuss our results in relation to lifetime reproductive success and costs of reproduction.

Laying Date in the Coot: Effects of Age and Mate Choice

1. Laying date in coots advanced with the age of both the male and the female. 2. Individual females had different but rather constant laying dates. After controlling for these differences, the effect of female age on laying date remained, but that of male age disappeared. This implies that both early and late females advanced their laying date when becoming older. It also implies that male age has no direct effect on laying date, but that older males are better able to compete for earlylaying females. 3. Selective loss of late-breeding females from a cohort is a potential additional cause for a correlation between age and laying date. However, female survival rate was independent of laying date, thus refuting the selection hypothesis. 4. The data supported neither increased reproductive effort with age (residual reproductive value hypothesis), nor differential delay of reproduction between early and late females (delayed reproduction hypothesis) as additional explanations for the advancement of laying date with age. This advancement in the individual female is therefore considered to be due to increasing quality (maturation hypothesis). 5. The repeatability of laying date in females was 0-32, but the heritability, estimated with daughter-mother regression, was only 0-02. This indicates that the variation in laying date between individuals is predominantly environmental.