Greater Lifetime Reproductive Success Research Articles

Older mothers produce more successful daughters

Annual reproductive success and senescence patterns vary substantially among individuals in the wild. However, it is still seldom considered that senescence may not only affect an individual but also affect age-specific reproductive success in its offspring, generating transgenerational reproductive senescence. We used long-term data from wild yellow-bellied marmots (Marmota flaviventer) living in two different elevational environments to quantify age-specific reproductive success of daughters born to mothers differing in age. Contrary to prediction, daughters born to older mothers had greater annual reproductive success on average than daughters born to younger mothers, and this translated into greater lifetime reproductive success. However, in the favorable lower elevation environment, daughters born to older mothers also had greater age-specific decreases in annual reproductive success. In the harsher higher elevation environment on the other hand, daughters born to older mothers tended to die before reaching ages at which such senescent decreases could be observed. Our study highlights the importance of incorporating environment-specific transgenerational parent age effects on adult offspring age-specific life-history traits to fully understand the substantial variation observed in senescence patterns in wild populations.

Polyandry and fitness in female horned flour beetles, Gnatocerus cornutus

Although polyandry is common, it is often unclear why females mate with multiple males, because although polyandry may provide females with direct or indirect fitness benefits, it can also be costly. Our understanding of polyandry is also restricted by the relative paucity of studies that disentangle the fitness effects of mating more than once with a single male and mating with multiple males. Here we investigated potential benefits and costs of polyandry in the horned beetle, Gnatocerus cornutus , while controlling for the number of matings. We found that female life span was independent of mating frequency, indicating that mating itself is not very costly. However, females that mated more than once laid more eggs and had greater lifetime reproductive success than singly mated females. Because the magnitude of these effects was similar in monandrous and polyandrous females, this improved fertility was due to multiple mating itself, rather than mating with multiple males. However, although polyandrous females produced more attractive sons, these males tended to have smaller mandibles and so may fare less well in male–male competition. These results indicate that polyandry is relatively cost free, at least in the laboratory, and has direct and indirect benefits to female fitness. However, because the attractive sons produced by polyandrous females may fight less well, the indirect benefits of polyandry will depend on the intensity of male–male competition and how free females are to exert mate choice. Where competition between males is intense, polyandry benefits via son attractiveness may be reduced and perhaps even carry costs to female fitness.

Breeding performance and survival in the peregrine falcon Falco peregrinus support an age‐related competence improvement hypothesis mediated via an age threshold

We studied the effects of age on breeding performance and survival probability in a peregrine falcon population, using data from a long term monitoring programme (carried out over 16 yr), in which we were able to identify individual birds. We compared the breeding performance and survival of yearling breeders, first‐time adult breeders and adult breeders. We found significant differences in breeding performance but not in survival. Yearling breeders had lower breeding success than older individuals but the breeding performance of inexperienced adults did not differ from that of experienced adults. We did not find changes in terminal breeding success since peregrines in their last year of life sustained the performance levels shown in previous years although with increasing variability. We found no evidence that attempting to breed affected survival probability in any age group. We argue that differences in breeding performance are related to age, not to breeding experience, and that there is an age threshold, coincident with the development of adult plumage, after which breeding performance is not affected either by age or experience. Peregrines that start breeding as yearlings are likely to have greater lifetime reproductive success than birds entering the breeding pool as adults. Consequently, such birds may represent a set of high quality individuals. Our results support the age‐related competence improvement hypothesis as being the relevant explanation for the increase in breeding performance with age.

Facial morphology predicts male fitness and rank but not survival in Second World War Finnish soldiers

We investigated fitness, military rank and survival of facial phenotypes in large-scale warfare using 795 Finnish soldiers who fought in the Winter War (1939–1940). We measured facial width-to-height ratio—a trait known to predict aggressive behaviour in males—and assessed whether facial morphology could predict survival, lifetime reproductive success (LRS) and social status. We found no difference in survival along the phenotypic gradient, however, wider-faced individuals had greater LRS, but achieved a lower military rank.

Height, Relationship Satisfaction, Jealousy, and Mate Retention

Male height is associated with high mate value. In particular, tall men are perceived as more attractive, dominant and of a higher status than shorter rivals, resulting in a greater lifetime reproductive success. Female infidelity and relationship dissolution may therefore present a greater risk to short men. It was predicted that tall men would report greater relationship satisfaction and lower jealousy and mate retention behavior than short men. Ninety eight heterosexual men in a current romantic relationship completed a questionnaire. Both linear and quadratic relationships were found between male height and relationship satisfaction, cognitive and behavioral jealousy. Tall men reported greater relationship satisfaction and lower levels of cognitive or behavioral jealousy than short men. In addition, linear and quadratic relationships were found between male height and a number of mate retention behaviors. Tall and short men engaged in different mate retention behaviors. These findings are consistent with previous research conducted in this area detailing the greater attractiveness of tall men.

Interspecific competition influences reproduction in spotted hyenas

AbstractInterspecific competition among carnivores is an important determinant of predator population dynamics, and it may also affect lower trophic levels. Whereas considerable research has focused on effects of interspecific competition on threatened carnivore populations, here we examine the effects of interspecific competition on the most abundant large carnivore in Africa, the spotted hyena Crocuta crocuta. Specifically, we compared two populations of spotted hyenas to examine the sources of variation in fitness, including effects of competition with lions Panthera leo. Hyenas living in Amboseli National Park and the Masai Mara National Reserve, Kenya, were monitored from 2003 to 2005 and 1988 to 1992, respectively. Females reproduced at significantly higher rates in Amboseli, due to shorter lactation periods, though neither juvenile survival nor litter size differed between populations. Differences in reproduction were estimated to result in 24% greater lifetime reproductive success among Amboseli than among Mara females. We then tested alternative ecological hypotheses to explain these differences in fitness measures between populations. We found little support for hypotheses suggesting that population differences were due to variation in prey availability or dispersion, or to intraspecific competition either within or between hyena groups. Our results were most consistent with the hypothesis that population differences were due to variation in interspecific competition with lions. Hyenas in Amboseli lived at lower lion density, enjoyed higher rates of food intake despite less abundant prey, and scavenged more food from lions than did Mara hyenas. Our results indicate that competition with lions operated primarily via food competition, rather than direct killing, to generate the fitness differences.

Delayed Breeding Affects Lifetime Reproductive Success Differently in Male and Female Green Woodhoopoes

In cooperatively breeding species, many individuals only start breeding long after reaching physiological maturity [1], and this delay is expected to reduce lifetime reproductive success (LRS) [1-3]. Although many studies have investigated how nonbreeding helpers might mitigate the assumed cost of delayed breeding (reviewed in [3]), few have directly quantified the cost itself [4, 5] (but see [6, 7]). Moreover, although life-history tradeoffs frequently influence the sexes in profoundly different ways [8, 9], it has been generally assumed that males and females are similarly affected by a delayed start to breeding [7]. Here, we use 24 years of data to investigate the sex-specific cost of delayed breeding in the cooperatively breeding green woodhoopoe (Phoeniculus purpureus) and show that age at first breeding is related to LRS differently in males and females. As is traditionally expected, males that started to breed earlier in life had greater LRS than those that started later. However, females showed the opposite pattern: Those individuals that started to breed later in life actually had greater LRS than those that started earlier. In both sexes, the association between age at first breeding and LRS was driven by differences in breeding-career length, rather than per-season productivity. We hypothesize that the high mortality rate of young female breeders, and thus their short breeding careers, is related to a reduced ability to deal with the high physiological costs of reproduction in this species. These results demonstrate the importance of considering sex-specific reproductive costs when estimating the payoffs of life-history decisions and bring into question the long-held assumption that delayed breeding is necessarily costly.

Is There Adaptive Value to Reproductive Termination in Japanese Macaques? A Test of Maternal Investment Hypotheses

Evolutionary biologists often argue that menopause evolved in the human female as the result of selection for a postreproductive phase of life, during which increased maternal investment in existing progeny could lead to enhanced survivorship of descendents. Adaptive theories relating menopause to enhanced maternal investment are known as the mother (first-generation) and grandmother (second-generation-offspring) hypotheses. Although menopause—universal midlife termination of reproduction—has not been documented in primates other than humans, some researchers have argued that postreproductive alloprimates also have a positive impact on the survivorship of first and second generation progeny. We tested the maternal investment hypotheses in Japanese macaques by comparing the survivorship of offspring, final infants, and great-offspring of females that terminated reproduction before death with females that continued to reproduce until death. SURVIVAL analyses revealed no significant difference in the survivorship of descendents of postreproductive and reproductive females, though final infants of postreproductive females were 13% more likely to survive than final infants of females that reproduced until death were. We also explored possible differences between these two groups of females, other than survivorship of progeny. We found no difference in dominance rank, matrilineal affiliation, body weight, infant sex ratio, age at first birth, fecundity rate or lifetime reproductive success. However, postreproductive females are significantly longer-lived than reproductive females and as a result experienced more years of reproduction and produced more infants in total. Apart from final infants, offspring survival is marginally lower in postreproductive females. Since offspring survival is not significantly enhanced in postreproductive females, the greater number of infants produced did not translate into greater lifetime reproductive success. Our findings fail to support the maternal investment hypotheses and instead suggest that reproductive termination in this population of Japanese macaques is most closely associated with enhanced longevity and its repercussions.

Influence of helping and breeding experience on reproductive performance in the Seychelles warbler: a translocation experiment

Reproductive success of the cooperative breeding Seychelles warbler (Acrocephalus sechellensis) increases with age. This age effect is not due to differential survival or increased reproductive effort, but to accumulated helping and breeding experience. In their first year of breeding, reproductive performance of inexperienced warblers with neither helping nor breeding experience was significantly lower than that of warblers of the same age with either previous helping or breeding experience. Reproductive performance was the same for primiparae with helping experience and for birds with breeding experience. Female primiparae with helping experience or breeding experience built better nests and spent more time incubating than inexperienced females, which led to increased hatching success. Male primiparae with helping experience or males with breeding experience guarded the clutch better than inexperienced males, which led to reduced egg predation. Even-aged warblers with different previous experiences were transferred to unoccupied islands, where birds started breeding immediately in high-quality territories. The experiment showed that birds with helping experience produced their first fledgling as fast as experienced breeders, and significantly faster than inexperienced birds. Breeding performance did not improve further with experience after the first successful breeding attempt. Only birds with previous breeding experience who paired with inexperienced birds, were likely to change mate. The other pair combinations remained stable. Thus, primiparous birds with helping experience have greater lifetime reproductive success than inexperienced primiparae of the same age. This experiment shows that helping behavior has not only been selected for in the context of promoting an individual's indirect fitness, but also in the context of gaining helping experience which translates into improved reproductive success when a helper becomes a breeder.

Life history costs and consequences of rapid reproductive maturation in female rhesus macaques

Life history theory suggests that reproduction at one point in time involves costs in terms of energy, reduced survival, or probability of reproduction at a future point in time. ln long-lived iteroparous organisms, initiating reproduction at a relatively young age may exact a cost in terms of reduced survivorship, but an early age of first reproduction could be beneficial if it lengthens the breeding lifespan. Data collected over 30 years from one population of rhesus macaques, Macaca mulatta, were analyzed to determine the fertility and survivorship costs of initiating reproduction at a relatively young age. Low population density and high social status increased the chances of accelerating age at first parturition, but high dominance rank was not associated with greater lifetime reproductive success. Rapid reproductive maturation neither reduced short-term survivorship nor decreased lifespan. Fertility costs arose if young females reared a male, but not female, offspring. The fitness consequences of rapid reproductive maturation depend upon longevity, with age at death having a significantly greater impact on lifetime reproductive success than age at first parturition.

Test of the Ecological Basis of Cooperative Breeding in Red-Cockaded Woodpeckers

-In many cooperatively breeding birds, the primary reason that helpers remain on the natal territory rather than disperse to breed independently may be to gain an advantage in competing for high-quality habitat. We hypothesized that cavities excavated in living pines, because they require much time to construct, are the critical determinant of habitat quality that has led to cooperative breeding in Red-cockaded Woodpeckers (Picoides borealis). These woodpeckers rarely colonize sites that lack existing cavities. To test our hypothesis we drilled cavities in 20 unoccupied sites. Eighteen were occupied subsequently, but none of 20 control sites were used. The manipulation added 12 new social units (breeding pairs or unpaired territorial males) to the population. New groups mostly comprised previous helpers and dispersing first-year birds. These results support our contention that variation in habitat quality dependent on the presence or absence of cavities is the ecological basis of group formation in Red-cockaded Woodpeckers. Cavity construction may be used to increase the number of groups in a population, and to prevent territory abandonment when bird-constructed cavities are lost. Received 3 October 1990, accepted 24 June 1991. COOPERATIVE breeding refers to a social system found in birds and mammals in which some reproductively mature individuals (helpers) assist others in raising young (Brown 1978, 1987, Emlen and Vehrencamp 1983, Emlen 1992). Understanding the evolution of cooperative breeding involves two interrelated but distinct issues (Emlen 1982a, b, 1992, Brown 1985, 1987, Ligon and Stacey 1989): (1) determining what leads individuals to remain with their natal groups or form groups rather than disperse to breed independently; and (2) determining why such individuals engage in helping behavior such as feeding young. Altruism evolved through kin selection is an accepted explanation of helping behavior (issue 2; Emlen and Wrege 1988,1989). In contrast, remaining in the natal group (issue 1) and thereby delaying reproduction and altering dispersal behavior generally is viewed as producing direct benefits to the individual under certain conditions (Emlen 1982a, Woolfenden and Fitzpatrick 1984, Brown 1985, 1987, Stacey and Ligon 1987). Emlen (1982a) outlined two conditions under which remaining with the natal group may result in greater lifetime reproductive success than early dispersal and breeding. One condition involves a harsh, unpredictable environment. In I Present address: RD1, Box 27, Spring Mills, Pennsylvania 16875, USA. poor years, inexperienced birds reproduce poorly, so that living with the natal group is favored over independent reproduction. This hypothesis may apply to species that inhabit the dry regions of Africa and Australia (Reyer 1980, Emlen 1981, 1982a, Clarke 1984). The second, perhaps more common condition has traditionally been termed habitat saturation, because it is thought to result from a shortage of vacancies in breeding habitat (Selander 1964, Brown 1969, Stacey 1979, Emlen 1982a). An apparent lack of unoccupied territories has been noted in many cooperative breeders (e.g. Selander 1964, Ridpath 1972, Woolfenden 1975, Ligon and Ligon 1978, Walters and Walters 1980, Zack and Ligon 1985, Koford et al. 1986), but not all (Rabenold 1985). In species to which the habitat-saturation hypothesis has been applied, helpers remain on their natal territory and compete for breeding vacancies on and in the immediate vicinity of the natal territory (stay-andforay, abbreviated SAF), rather than dispersing after fledging to wander in search of a breeding vacancy (depart-and-search, DAS; Brown 1987). Those practicing SAF appear to have an advantage in competing for positions in their vicinity over those practicing DAS (Zack and Rabenold 1989), perhaps because they can monitor the availability of those positions much more effectively. The demographic conditions under which SAF may be selected over DAS have been mod-

Blue TitParus caeruleussong in relation to survival, reproduction and biometry

A detailed analysis of singing performance of male Blue Tits is given, in relation to reproductive success and survival. Singing performance varied considerably between males and differences between males were probably retained from one year to the next. The lengths of 2 different song types were correlated but the size of the song repertoire was not correlated with song length. Two kinds of song features other than repertoire size, a measure of length and the rate at which the song slows down, seemed to reflect singing capacity. Males with longer songs survived better but there was no evidence that they had a greater lifetime reproductive success. Survival and reproductive success were not correlated with various measures of body size.