Influence of inflorescence size on sexual expression and female reproductive success in a monoecious species

Sex allocation theory forecasts that larger plant size may modify the balance in fitness gain in both genders, leading to uneven optimal male and female allocation. This reasoning can be applied to flowers and inflorescences, because the increase in flower or inflorescence size can differentially benefit different gender functions, and thus favour preferential allocation to specific floral structures. We investigated how inflorescence size influenced sexual expression and female reproductive success in the monoecious Tussilago farfara, by measuring patterns of biomass, and N and P allocation. Inflorescences of T.?farfara showed broad variation in sex expression and, according to expectations, allocation to different sexual structures showed an allometric pattern. Unexpectedly, two studied populations had a contrasting pattern of sex allocation with an increase in inflorescence size. In a shaded site, larger inflorescences were female-biased and had disproportionately more allocation to attraction structures; while in an open site, larger inflorescences were male-biased. Female reproductive success was higher in larger, showier inflorescences. Surprisingly, male flowers positively influenced female reproductive success. These allometric patterns were not easily interpretable as a result of pollen limitation when na?vely assuming an unequivocal relationship between structure and function for the inflorescence structures. In this and other Asteraceae, where inflorescences are the pollination unit, both male and female flowers can play a role in pollinator attraction.     

Computing expected reproductive success of female Atlantic salmon as a function of salmon size

A method is described for determining the expected reproductive success (gonadal mass of a returning fish times the probability of surviving to return) and expected fecundity of salmonids as a function of smolt size. Application of the method requires data relating (i) return weight and smolt size; (ii) probability of survival and smolt size; (iii) probability of return after one or two sea winters and smolt size; and (iv) gonads and return weight. Although there exists no published data set that contains all of this information, it is possible to piece together enough information from published sources on female Atlantic salmon to demonstrate the feasibility of the method, with the goal of encouraging the publication of datasets that will allow meaningful calculations for a single river. Thus, one should not expect general predictions about Atlantic salmon, but once local conditions are taken into account, it will be possible to predict the relationships between smolt size and expected fecundity or expected reproductive success.     

Effects of floral display size on male and female reproductive success in Mimulus ringens

Background and Aims

The number of flowers blooming simultaneously on a plant may have profound consequences for reproductive success. Large floral displays often attract more pollinator visits, increasing outcross pollen receipt. However, pollinators frequently probe more flowers in sequence on large displays, potentially increasing self-pollination and reducing pollen export per flower. To better understand how floral display size influences male and female fitness, we manipulated display phenotypes and then used paternity analysis to quantify siring success and selfing rates.

Methods

To facilitate unambiguous assignment of paternity, we established four replicate (cloned) arrays of Mimulus ringens, each consisting of genets with unique combinations of homozygous marker genotypes. In each array, we trimmed displays to two, four, eight or 16 flowers. When fruits ripened, we counted the number of seeds per fruit and assigned paternity to 1935 progeny.

Key Results

Siring success per flower declined sharply with increasing display size, while female success per flower did not vary with display. The rate of self-fertilization increased for large floral displays, but siring losses due to geitonogamous pollen discounting were much greater than siring gains through increased self-fertilization. As display size increased, each additional seed sired through geitonogamous self-pollination was associated with a loss of 9·7 seeds sired through outcrossing.

Conclusions

Although total fitness increased with floral display size, the marginal return on each additional flower declined steadily as display size increased. Therefore, a plant could maximize fitness by producing small displays over a long flowering period, rather than large displays over a brief flowering period.     

Clutch size and malarial parasites in female great tits

life-history models predict an evolutionary trade-off in theallocation of resources to current versus future reproduction.This corresponds, at the physiological level, to a trade-offin the allocation of resources to current reproduction or tothe immune system, which will enhance survival and thereforefuture reproduction. For clutch size, life-history models predicta positive correlation between current investment in eggs andthe subsequent parasite load. In a population of great tits,we analyzed the correlation between natural clutch size of femalesand the subsequent prevalence of Plasmodium spp., a potentiallyharmful blood parasite. Females that showed, 14 days after hatchingof the nestlings, an infection with Plasmodium had a significantlylarger clutch (9.3 eggs ± 0.5 SE, n = 18) than uninfectedfemales (8.0 eggs ± 0.2 SE, n = 80), as predicted bythe allocation trade-off. Clutch size was positively correlatedwith the prevalence of Plasmodium, but brood size 14 days afterhatching was not. This suggests that females incur higher costsduring laying the clutch than during rearing nestlings. Infectionstatus of some females changed between years, and these changeswere significantly correlated with a change in clutch size aspredicted by the trade-off. The link between reproductive effortand parasitism may represent a possible mechanism by which thecost of egg production is mediated into future survival andmay thereby be an important selective force in the shaping ofclutch size     

Reproductive success in a socially polymorphic spider: social individuals experience depressed reproductive success in isolation

1. Correlated individual differences in behaviour across ecological contexts, or behavioural syndromes, can theoretically constrain individuals' ability to optimally adjust their behaviour for specific contexts. 2. Female Anelosimus studiosus exhibit a unique behavioural polymorphism: ‘social’ females are tolerant of conspecifics and aggregate in multi‐female colonies, while ‘solitary’ females aggressively defend their singleton webs from intrusion by adult female conspecifics. Previous work found that social females are also less aggressive toward prey and are more fearful of predators. 3. In this study we quantify potential fitness consequences of these correlated behaviours by examining the potential and realised fecundities of the two phenotypes in naturally occurring colonies, and by quantifying their ability to rear offspring as singleton individuals. 4. There were no differences in the fecundities of laboratory‐reared females between the phenotypes, nor were there differences in field‐collected brooding females from naturally occurring solitary and social nests. 5. Brooding females from solitary and social colonies that were isolated in new nests for the growing season were both capable of rearing their broods; however, females from solitary nests had significantly greater success. 6. These results suggest a fitness consequence to the reduced‐aggression syndrome of social females that may represent a general impediment to the evolution of sociality in spiders.     

Lifetime reproductive success in female Japanese macaques

Lifetime reproductive success, measured by the number of offspring surviving to age five, varied from 0 to 10 in a group of 33 provisioned female Japanese macaques. Of the three contributors to reproductive success, the number of reproductive years, fecundity per year and survivorship of offspring to reproductive age, the first accounted for two-thirds of the variation. Fecundity per year and survivorship were negatively correlated, indicating reproductive costs of reducing interbirth interval. No other demographic measure used, nor the behavioral measure 'dominance rank', significantly correlated with lifetime reproductive success or its components. Age-specific changes in fecundity and infant survival were not found for this sample, neither could cessation of reproduction, even in very old females, be demonstrated.     

Sexual selection in a hermaphroditic plant through female reproductive success

Sexual selection is well accepted as a mechanism of shaping traits in animals. However, whether and how floral traits are sexually selected in hermaphroditic plants remains less clear. Here, we use Passiflora incarnata to address how floral traits that affect pollination success are selected via female function. We manipulated the ecological context by limiting pollination and adding resources to expand the phenotypic distribution and alter the intensity of sexual selection. Total sexual selection favoured lower style deflexion because of its impact on pollen receipt and subsequent seed number. However, total selection on style deflexion was not significant, indicating additional selection on style deflexion through routes other than mating. Limited pollination and enhanced resources were expected to alter the distribution of pollen deposition and seed production and therefore intensify the Bateman gradient – the relationship between pollen receipt and seed production. Indeed, the Bateman gradient was strongest when pollination was limited, suggesting potential for sexual selection to influence floral trait evolution under these conditions. Overall, we found floral traits may be shaped by sexual selection through female reproductive success in this hermaphroditic plant. These results support manipulations to enhance the variance in mating as a mechanism to understand patterns of sexual selection.     

Clutch size and breeding success in relation to nest-box size in Tengmalm's owl Aegolius funereus

Clutch size and breeding success was related to nest-box size in 215 nests of Tengmalm's owl in the Kauhava region, western Finland in 1966–82. In vole peak years, but not in other years, mean clutch size was positively correlated with the bottom area of the nest-box, increasing on average by 0.005 eggs cm⁻². In successful nests there were fewer nestlings in small and medium-sized than in large boxes. Breeding was most successful in thick-walled boxes with a small entrance diameter. The optimal box for Tengmalm's owl has the following dimensions: bottom area 20 × 20 cm, entrance diameter 8 cm, and wall thickness at least 3 cm.
Hypotheses suggested to explain the "area effect" based on breeding data of hole-nesting passerines do not hold good for Tengmalm's owl. Since there were more stored prey animals in medium-sized and large boxes than in small boxes, I suggest that the "area effect" is related to food availability, which may determine how sensitive the species is to different bottom areas of the boxes, at least in areas with cyclic food (e.g. northern Europe).     

Morph-ratio variation, population size and female reproductive success in distylous Pulmonaria officinalis (Boraginaceae)

Theory predicts that morph ratios in heterostylous populations are governed by negative frequency-dependent selection typically resulting in equal morph ratios at equilibrium. Previous work on the distylous perennial herb Pulmonaria officinalis, however, showed asymmetric mating between floral morphs and a weak self-incompatibility system, with the long-styled morph (L-morph) producing significantly higher seed set following intramorph crosses and even selfing than the short-styled morph (S-morph), two aspects thought to affect female fecundity and morph-ratio variation. Here, we evaluated morph ratios and population size of all known P. officinalis populations in the northern part of Belgium. Morph ratios deviated significantly from 1:1 (range 0.09-1 L-morph frequency, mean = 0.58). Relative fecundity of the S-morph (i.e. mean seed set of the S-morph/mean seed set of the L-morph) was on average 0.73, was positively related to the frequency of the L-morph, and reached 1 (similar levels of female fecundity) at an average L-morph frequency of 0.66 in the population. As some small populations had the S-morph in majority, our results suggest that local morph ratios are influenced both by the relative fecundity of L- and S-morph individuals and by stochastic processes in small populations.     

Lifetime reproductive success in reproductively suppressed female voles

A population of the grey red-backed vole, Clethrionomys rufocanus bedfordiae, was investigated on a 1 ha control grid and a 1 ha grid on which the voles were fed within a 2.1 ha outdoor enclosure in Hokkaido, Japan by live trapping from 1984 to 1986, for testing the Reproductive Suppression Model of Wasser and Barash (1983)-females can optimize their lifetime reproductive success by suppressing reproduction when future conditions for the survival of offspring are likely to be sufficiently better than present ones as to exceed the costs of the suppression itself. Age at the first pregnancy more varied in a higher density population on the experimental grid and females could be classified into the early and the late reproductive type in two generations (A: females born from February to June 1985; B: females born from September to November 1985). Lifetime reproductive success (the number of pregnancies, the number of successful litters, and the number of offspring) was not different between the early and the late reproducing females. The late reproducing females lived for longer periods than the early reproducing females, so that the loss by delayed start of reproduction was compensated for by a longer life span. Life span was not different between offspring of the early and the late reproducing females. These facts supported the Reproductive Suppression Model.     

Determinants of reproductive success in dominant female meerkats

1. In cooperative societies with high reproductive skew, selection on females is likely to operate principally through variation in the probability of acquiring dominant status and variation in reproductive success while dominant. Despite this, few studies of cooperative societies have investigated the factors that influence which females become dominant, and/or their reproductive output while in the dominant position. 2. Here we use long-term data from a wild meerkats population to describe variation in the breeding success of dominant female meerkats Suricata suricatta and investigate its causes. 3. Female meerkats compete intensely for breeding positions, and the probability of acquiring the breeding role depends upon a female's age in relation to competitors and her weight, both at the time of dominance acquisition and early in life. 4. Once dominant, individual differences in breeding success depend principally on the duration of dominance tenure. Females remain for longer in the dominant position if they are heavier than their competitors at the start of dominance, and if the number of adult female competitors at the start is low. 5. Female breeding success is also affected by variation in fecundity and pup survival, both of which increase with group size. After controlling for these effects, female body weight has a positive influence on breeding rate and litter size, while the number of adult female competitors reduces litter survival. 6. These findings suggest that selection for body weight and competitive ability will be high in female meerkats, which may moderate their investment in cooperative activities. We suggest that similar consequences of competition may occur among females in other cooperative societies where the benefits of attaining dominance status are high.     

Lifetime reproductive success of female mountain gorillas

Studies of lifetime reproductive success (LRS) are important for understanding population dynamics and life history strategies, yet relatively little information is available for long-lived species. This study provides a preliminary assessment of LRS among female mountain gorillas in the Virunga volcanoes region. Adult females produced an average of 3.6 ± 2.1 surviving offspring during their lifetime, which indicates a growing population that contrasts with most other great apes. The standardized variance in LRS (variance/mean(2) = 0.34) was lower than many other mammals and birds. When we excluded the most apparent source of environmental variability (poaching), the average LRS increased to 4.3 ± 1.8 and the standardized variance dropped in half. Adult lifespan was a greater source of variance in LRS than fertility or offspring survival. Females with higher LRS had significantly longer adult lifespans and higher dominance ranks. Results for LRS were similar to another standard fitness measurement, the individually estimated finite rate of increase (λ(ind) ), but λ(ind) showed diminishing benefits for greater longevity.     

Early reproductive investment,senescence and lifetime reproductive success in female Asian elephants

The evolutionary theory of senescence posits that as the probability of extrinsic mortality increases with age, selection should favour early‐life over late‐life reproduction. Studies on natural vertebrate populations show early reproduction may impair later‐life performance, but the consequences for lifetime fitness have rarely been determined, and little is known of whether similar patterns apply to mammals which typically live for several decades. We used a longitudinal dataset on Asian elephants (Elephas maximus) to investigate associations between early‐life reproduction and female age‐specific survival, fecundity and offspring survival to independence, as well as lifetime breeding success (lifetime number of calves produced). Females showed low fecundity following sexual maturity, followed by a rapid increase to a peak at age 19 and a subsequent decline. High early life reproductive output (before the peak of performance) was positively associated with subsequent age‐specific fecundity and offspring survival, but significantly impaired a female's own later‐life survival. Despite the negative effects of early reproduction on late‐life survival, early reproduction is under positive selection through a positive association with lifetime breeding success. Our results suggest a trade‐off between early reproduction and later survival which is maintained by strong selection for high early fecundity, and thus support the prediction from life history theory that high investment in reproductive success in early life is favoured by selection through lifetime fitness despite costs to later‐life survival. That maternal survival in elephants depends on previous reproductive investment also has implications for the success of (semi‐)captive breeding programmes of this endangered species.     

Group size and composition influence male and female reproductive success in black howler monkeys (Alouatta pigra)

It has been argued that grouping patterns might influence the reproductive performance of individuals. Increasing group size results in greater travel costs and competition over depletable food resources, which could lead to reduced individual reproductive success. However, in groups with an increasing number of males, female reproductive success is predicted to augment because larger male groups might better protect immatures from infanticidal attacks. In contrast, male reproductive success is predicted to decrease with number of males in a group because fertilization cannot be shared between males. In this paper, we test these predictions on the Mesoamerican black howler monkey (Alouatta pigra) with data on group size and composition for 120 groups from eight populations of black howler monkeys existing in eight protected forests in Mexico and Guatemala. Male and female reproductive success were calculated as a deviation of the observed number of infants (or immatures) from the expected number of infants (or immatures), relative to the number of males and females in a group. Results indicate that both male and female reproductive success decreased with group size. Male reproductive success decreased with an increasing number of males in a group and with increasing proportion of males relative to females in a group. Decreased female reproductive success was associated with increasing number of females in a group, and female reproductive success had a tendency to increase with increasing number of males in a group. These results suggest that in black howler monkeys, living in larger groups might negatively affect the reproductive success of each member. Our findings are similar to those reported for a population of a sister species, Alouatta palliata, living in larger groups.     

Effects of population size, seed predation and plant size on male and female reproductive success in Vincetoxicum hirundinaria (Asclepiadaceae)

Here we present the results of a study on the effects of population size, seed predation, and plant size on male and female reproductive success in ten Vincetoxicum hirundinaria populations in southwestern Finland. We investigated male reproductive success by recording pollinia removal, and studying pollen quality and quantity. Pod and seed production, and the number of ovules per ovary were counted to estimate female reproductive success. Both pollen quality and pollinia removal were higher in small V. hirundinaria populations compared to large populations. In contrast, the quantity of pollen was higher in large populations than in small populations. Pod initiation was higher in large populations. However, large populations had higher abortion rates and proportionally fewer intact pods. Plant size did not affect male reproductive success whereas pod and seed production correlated positively with plant size, although only in large populations. Population size had no clear impact on seed predation intensities. Variation was, however, observed among populations. Larger plant individuals suffered from an increased risk of being attacked only in two populations. This correlation was not clearly attributed to plant population size. The results of this study suggest that reproductive success in V. hirundinaria may be highly variable and this variation is to some extent explained by population size. Further, population size affected male and female reproductive success differently.     

Determinants of reproductive success in female Columbian ground squirrels

Summary We studied the reproductive success of female Columbian ground squirrels (Spermophilus columbianus) in southwestern Alberta for nine years. We defined reproductive success as the number of offspring surviving their first hibernation, classified as yearlings. The number of weaned juveniles explained one third of the variance in number of yearlings at emergence from their first hibernation the following spring, and much of the variance in individual reproductive success originated after weaning. Weight of adult females at emergence from hibernation was correlated with annual reproductive success. The mother's survival beyond weaning and the subsequent winter's snow accumulation had positive effects on annual reproductive success, whereas population density and summer temperature had negative effects. We found no effects on annual reproductive success of date of litter emergence, weight at emergence as a yearling, presence or absence of adult kin, distance from the natal site, location within the study area, winter temperature or summer precipitation. Age of first breeding did not affect lifetime reproductive success, which ranged from 0 to 19 yearlings produced over a lifetime. The greatest source of variation in lifetime reproductive success for females surviving to breeding age was offspring survival, followed by reproductive lifespan.