Strategic female reproductive investment in response to male attractiveness in birds

Life-history theory predicts that individuals should adjust their reproductive effort according to the expected fitness returns on investment. Because sexually selected male traits should provide honest information about male genetic or phenotypic quality, females may invest more when paired with attractive males. However, there is substantial disagreement in the literature whether such differential allocation is a general pattern. Using a comparative meta-regression approach, we show that female birds generally invest more into reproduction when paired with attractive males, both in terms of egg size and number as well as food provisioning. However, whereas females of species with bi-parental care tend to primarily increase the number of eggs when paired with attractive males, females of species with female-only care produce larger, but not more, eggs. These patterns may reflect adaptive differences in female allocation strategies arising from variation in the signal content of sexually selected male traits between systems of parental care. In contrast to reproductive effort, female allocation of immune-stimulants, anti-oxidants and androgens to the egg yolk was not consistently increased when mated to attractive males, which probably reflects the context-dependent costs and benefits of those yolk compounds to females and offspring.     

Habitat quality and reproductive investment in aphids

ABSTRACT.

• 1 Genetically identical vetch aphids, Megoura viciae (Buckton), showed a weak but significant positive relationship between reproductive investment (number of ovarioles) and weight, here used as an indicator of habitat quality.
• 2 Apterae reared on poor quality plants showed the same range in numbers (twelve to twenty-two) but on average fewer ovarioles than those reared on high quality plants.
• 3 The variability in ovariole number was determined prior to birth.
• 4 Under constant conditions the age of a mother does not affect the range of ovariole numbers or the proportion of her offspring in each ovariole class.
• 5 Apterae reared on poor quality host plants gave birth to proportionately fewer offspring with a high ovariole number than apterae reared on high quality plants.
• 6 Winged individuals gave birth to proportionately more offspring with a high number of ovarioles than apterae.
• 7 The control and ecological significance of the intramorph variation in reproductive tactics shown by many species of aphids is discussed in the light of these results.

     

Condition and reproductive investment in the western mosquitofish (Gambusia affinis): little evidence for condition‐dependent sex‐biased investment

In sexually reproducing species, resources may theoretically be distributed with bias to the production of male or female offspring in response to the condition of the mother, commonly recognized as sex allocation. Using a recently characterized sex‐specific molecular marker, we tested for maternal sex allocation (i.e. maternal primary sex ratio bias and sex‐specific offspring investment) in captive laboratory‐bred western mosquitofish (Gambusia affinis) at early stages of offspring development. We found no statistical evidence to support sex allocation in G. affinis, based on maternal condition. In addition, we found little evidence for correlations between maternal condition and investment in the condition (mass) of individual offspring (of one sex or the other), although we did find that larger mothers tended to have higher fecundity.     

Sex-biased terminal investment in offspring induced by maternal immune challenge in the house wren (Troglodytes aedon)

The reproductive costs associated with the upregulation of immunity have been well-documented and constitute a fundamental trade-off between reproduction and self-maintenance. However, recent experimental work suggests that parents may increase their reproductive effort following immunostimulation as a form of terminal parental investment as prospects for future reproduction decline. We tested the trade-off and terminal investment hypotheses in a wild population of house wrens (Troglodytes aedon) by challenging the immune system of breeding females with lipopolysaccharide, a potent but non-lethal antigen. Immunized females showed no evidence of reproductive costs; instead, they produced offspring of higher phenotypic quality, but in a sex-specific manner. Relative to control offspring, sons of immunized females had increased body mass and their sisters exhibited higher cutaneous immune responsiveness to phytohaemagglutinin injection, constituting an adaptive strategy of sex-biased allocation by immune-challenged females to enhance the reproductive value of their offspring. Thus, our results are consistent with the terminal investment hypothesis, and suggest that maternal immunization can induce pronounced transgenerational effects on offspring phenotypes.     

Age-specific resource investment strategies: evidence from female Richardson's ground squirrels (Spermophilus richardsonii)

To avoid a possible cost to their future survival and/or reproduction, individuals must balance their somatic and reproductive investments. The van Noordwijk and De Jong model of resource investment predicts that investments into reproduction and soma can vary among individuals of a population based on the variation in the total amount of energy that individuals acquire. With principal components analysis (PCA), we created two axes of life history for female Richardson's ground squirrels Spermophilus richardsonii : an index of total energy investment (PC1) and an index of investment tactic (PC2). Using these indices, we examined patterns of resource allocation to reproductive and somatic investments. Because yearling female Richardson's ground squirrels complete growth to adult size during pregnancy and early lactation, their somatic needs exceed those of older, fully grown females. Therefore, we predicted that yearlings would show more evidence of a tradeoff between reproductive and somatic investments compared with older females. Both yearling and older females invested four to five times more mass into their litters than into their own body mass. With increasing total investment, yearling females increased investment in both reproduction and themselves, whereas older females invested relatively more in reproduction than themselves. Regardless of age, females that emerged heavier from hibernation invested fewer resources into themselves and more into their litters. Variation in total energy investment and investment tactic indices was similar for yearling and older females. Contrary to our prediction, however, yearling females showed positive associations between reproductive and somatic investments, whereas older females exhibited showed no significant association between reproductive and somatic investments.     

Size delays female senescence in a medium sized marsupial: The effects of maternal traits on annual fecundity in the northern brown bandicoot (Isoodon macrourus)

The degree to which females allocate resources between current reproduction, future fecundity and survival is a central theme in life history theory. We investigated two hypotheses proposed to explain patterns of reproductive investment, terminal investment and senescence, by examining the effects of maternal traits (age and maternal mass) on annual fecundity in female northern brown bandicoots, Isoodon macrourus (Marsupialia: Peramelidae). We found that annual fecundity in females declined in their final year of reproduction, indicating reproductive senescence. Maternal mass significantly influenced the rate of senescence and, in turn, a female's lifetime reproductive output. Mass had little effect on fecundity in 1st and 2nd year females, but a positive relationship with fecundity in 3rd year females. This meant that heavy, 3rd year females did not suffer the decline in fecundity shown in light 3rd year females. For 1st year females, mass and leg length increased between their first and second reproductive seasons, indicating a temporary shift, from the allocation of resources to reproduction, to increasing condition or structural size post their first breeding event. There were no net changes to body mass in subsequent years. We suggest that this year of post‐reproductive growth has important consequences for senescent effects on reproduction. Overall, results provided support for the effects of senescence on annual fecundity. Our findings were not consistent with the terminal investment hypothesis; reproductive output did not increase in females' final reproductive season despite a rapid decline in survival. However, this notion cannot be entirely dismissed; other measures of reproductive performance not examined here (e.g. offspring mass) may have provided an indication that females did increase their effort at the end of their lifespan. This study highlights the difficulty of measuring reproductive costs and the importance of understanding the combined effects of specific characteristics of an individual when interpreting reproductive strategies in iteroparous organisms.     

Tree size and its relationship with flowering phenology and reproductive output in Wild Nutmeg trees

Reproductive strategies, sexual selection, and their relationship with the phenotype of individuals are topics widely studied in animals, but this information is less abundant for plants. Variability in flowering phenology among individuals has direct impact on their fitness, but how reproductive phenology is affected by the size of the individuals needs further study. We quantified the flowering intensity, length, and reproductive synchronization of two sympatric dioecious Wild Nutmeg tree species (Virola, Myristicaceae) in the Brazilian Atlantic forest, and analyzed its relationships with tree size. Two distinct strategies in flowering timing and intensity were found between species (annual versus biennial flowering), and among individuals in the annual flowering species (extended versus peak flowering). Only for the annual flowering species the reproductive output is related to tree size and large trees present proportionally higher flower coverage, and lower synchronization than smaller ones. Flowering is massive and highly synchronized in the biennial species. Sex ratios are not different from 1:1 in the two species, and in the two segregated reproductive subgroups in the biennial flowering species. The biennial flowering at individual level is a novelty among reproductive patterns in plants, separating the population in two reproductive subgroups. A proportional increase in the reproductive output with size exists only for the annual flowering species. A biennial flowering can allow resource storage favouring massive flowering for all the individuals diluting their relationship with size.     

Resource allocation in ascidians: reproductive investment vs. other life-history traits

Abstract. To determine patterns of resource allocation among ascidians, we studied 16 colonial and solitary species. We measured investment in reproductive vs. structural material (tunic) both in terms of weight and caloric content, as well as fecundity and degree of larval complexity in the colonial species. Measurements in weight and caloric content were highly correlated in the species studied. A wide range of investment in reproduction was found. Tunic production was related to the growth form of the species, stolonic and solitary species investing less in tunic than massive species, but no significant relationship was found between investment in tunic production vs. reproduction. In colonial species we found that in species with small zooid size, the reproductive investment per zooid was significantly higher. There was a significant negative relationship between investment in reproduction and fecundity. We also found a significant relationship between reproductive investment and larval complexity. The overall trend was that species with low fecundity had large complex larvae and invested the most energy in reproduction.     

多年生龙胆属植物个体大小与花期资源分配研究

于各物种花中前期对青藏高原东部高寒草甸6种多年生龙胆属植物花期的繁殖分配和性分配进行分析,结果表明:(1)多年生龙胆属植物的植株个体越大,繁殖投入越高,繁殖分配越低;(2)随着植物个体的增大,对雌性、雄性和吸引结构的投入都在增加,这可保证资源的充分利用,不会因为单一部分的增加而造成资源的浪费;(3)6种龙胆属植物中,有4种其性分配结果与性别分配(SDS)的理论预测一致,即大个体更偏向雌性器官的资源投入,但麻花艽(Gentiana atraminea)和达乌里秦艽(Gentiana dahurica)的性分配与个体大小则没有表现出负相关,可能与其本身具有的雌雄异熟———雄性先熟特点有关;(4)资源在雌雄功能间的分配没有表现出权衡关系,可能是由于植物必须在许多不同生活史性状之间进行资源分配,而不是两两之间非此即彼.     

Learning enhances female control over reproductive investment in the Japanese quail

The adaptive significance of learning is supported by studies showing its positive effects on mating behaviour, but they rarely go beyond fertilization success. Here we studied how learning contributes to qualitative reproductive investment, by testing the hypothesis that mating in the context that predicts male appearance has positive effects on female reproductive investment compared with unsignalled mating. Using Japanese quail (Coturnix japonica), we found that effects of mating in the context predicting mating opportunity depend on female body condition and receptivity, while the outcome of unexpected mating depends on male behaviour. In particular, among females mated with the familiar male in the context predicting that he will appear, female condition positively affected the number of fertilized eggs and egg mass and more receptive females tended to produce more sons. Additionally, conditioned females laid heavier eggs for daughters than for sons. In contrast, in females that were mated unexpectedly and with a novel male, the number of fertilized eggs was highly dependent on male behaviour and was negatively related to maternal body condition. Egg mass was not related to body condition, and there were no indications of sex allocation. This is, to our knowledge, the first study demonstrating how female body condition and behaviour interact with the context of mating in shaping maternal reproductive investment.     

Maternal investment and reproductive success in Chinese water deer

Among cervids, maternal investment, estimated as the amount of resources and care allocated to the offspring, was expected to be related to species body size. Therefore, maternal investment in a herd of captive Chinese water deer Hydropotes inermis, a relatively small species of cervid, was investigated over 3 years. Except during the lactation period, reproductive females spent about 2-fold more time resting than feeding. During lactation, the amount of time spent feeding increased highly (25.3 min/h during lactation vs 17.3 min/h during the gestation period). Females spent less than 30% of time in communal behaviours with offspring. They did not reject alien fawns during this care period. Frequency and duration of suckling events decreased exponentially from the second week onwards. More than 10% of suckling bouts were non-filial. Prenatal investment leads to a mean litter mass (about 12% of maternal mass) higher than in most cervid species. Postnatal investment in fawns represents a daily mass gain of ca. 85 g/d during the first 2 weeks, without any sexual difference. Female production, timing and synchrony of births and survival of fawns characterized reproductive success. Seventy percent of mature females gave birth, with a mean of 1.9 offspring per female. The sex ratio was even. Births were synchronous, 80% of births occurring in 25 days. In this herd, 0.74 fawn per female was successfully weaned and 0.56 fawn per female survived through their first year. Based on these results we conclude that reproductive strategy of Chinese water deer was efficient and characterized by mother-offspring relationships typical of hiders and high levels of pre- and postnatal investments. This strategy seems typical of small species of cervids without marked sexual dimorphism.[Current Zoology 55(2):102-110,2009].     

Male genotype influences female reproductive investment in Drosophila melanogaster

In many species, males can influence the amount of resources their mates invest in reproduction. Two favoured hypotheses for this observation are that females assess male quality during courtship or copulation and alter their investment in offspring accordingly, or that males manipulate females to invest heavily in offspring produced soon after mating. Here, we examined whether there is genetic variation for males to influence female short-term reproductive investment in Drosophila melanogaster, a species with strong sexual selection and substantial sexual conflict. We measured the fecundity and egg size of females mated to males from multiple isofemale lines collected from populations around the globe. Although these traits were not strongly influenced by the male's population of origin, we found that 22 per cent of the variation in female short-term reproductive investment was attributable to the genotype of her mate. This is the first direct evidence that male D. melanogaster vary genetically in their proximate influence on female fecundity, egg size and overall reproductive investment.     

Growth, maturation and reproductive investment in Arctic charr

Size and rates of growth in a cohort of 1 + Arctic charr housed in standard conditions were tracked over 12 months (December to December) and mature and immature males and females compared retrospectively. In both sexes, maturing fish were larger than non-maturing ones. In males, this size differential was the result of differences in growth in winter and early spring, but not in the remainder of the study period. In females, size differentials resulted mainly from growth rate differences immediately prior to breeding. In females but not in males, gonadosomatic index was predicted by growth rates in the months leading up to maturation, and among the females that matured, faster growing fish produced more eggs. Lipid reserves in July were correlated negatively with growth during the previous 7 months and, in females only, lipid reserves were significantly lower in maturing fish than in non-maturing fish, indicating that mobilization of lipid energy reserves in maturing fish had commenced by this time. Variation in investment in gonadal tissue, measured as gonadosomatic index, was not explained by variation in July lipid reserves for either males or females. However, July lipid reserves were negatively correlated with egg number, so females investing more in ova exhibited greater depletion of lipid reserves. These results are discussed in the context of the relationship between body condition and the onset of maturation in salmonids, relative investment in reproduction and sexual differences in the cost of reproduction.     

Reproductive strategy of the ghost shrimp Callichirus major (Crustacea: Axiidea: Callianassidae) from the southwestern Atlantic: sexual maturity of females,fecundity, egg features,and reproductive output

Reproduction and reproductive investment of females is an intriguing feature in axiidean shrimps. They have a cryptic behavior and great ecological importance in sediment turnover, and recycling of organic material and nutrient. Herein, we describe different aspects of the reproductive biology (size at sexual maturity of females, fecundity, egg characteristics, and reproductive output [RO]) of the ghost shrimp Callichirus major from the southeastern coast of Brazil. Females reached sexual maturity at sizes ≥11.85?mm dorsal oval length. Fecundity increased significantly with female size and varied between 1455 and 9931 eggs (average 4564 eggs). Individual egg volume almost doubled during embryogenesis, and average egg water content increased during the incubation period from 75.0 to 93.3%. The egg mass comprised on average 13.2% of the dry body weight of females. This relatively high RO value is probably compensatory to the relatively low number of ovigerous females in axiidean populations. The few published data on RO values suggest that female investment in reproduction of axiidean shrimps is somewhat higher than in other decapods. The high investment in egg production reflects most likely an effort to maximize the viability of the progeny. Studies with additional congeneric species will clarify whether there is a tendency of axiidean shrimps to have RO values at the upper end of the range reported for decapods.     

Evidence for Sex-Biased Behavioral Maternal Investment in the Gray Mouse Lemur (Microcebus murinus)

To study sex-differential allocation of maternal behavior in Microcebus murinus, I recorded behavioral patterns on 21 litters from parturition to the weaning period. After a pregnancy of 61.5 ± 0.9 days, females may produce from one to four young per litter. Litters were weaned in 40 days by mothers. Behavioral observations at the beginning of the nocturnal activity period demonstrated that close contacts between mothers and infants were more frequent in multiparous mothers than in primiparous ones (p < .01). Time in close contact with offspring aged >15 days old compared to contacts with neonates is significantly lower only in single-sex litters and is more marked for all-female litters (p < .01). Mother's approaches toward mixed litters or all-male litters were always significantly greater than approaches toward all-female litters (p = .04). However, mother's approaches within mixed sex litters were not biased toward either sex (p = .7). Males in a litter may be interpreted as a stimulator of maternal behavior. Similarly, using retrieving tests of 15-min duration, a significant maternal preference for male neonates is evident. Latency to first retrieval is significantly shorter in multiparous females than in primiparous ones (p < .05) independent of size and sex ratio of the litter. For multiparous females only, male neonates were chosen first for retrieval more often than females (p < .05). Finally, the calls of young played a stimulator effect on maternal retrieving (p < .001). Accordingly multiparous mothers exhibit more interest in their young, which appears to be biased toward male neonates.     

Implication of life history strategies for prenatal investment in cetaceans

Prenatal investment directly determines the size at birth and fetus growth rate, which affects neonatal survival and growth and potentially affects maternal fitness. This study explored the associated prenatal life history traits of cetaceans. Using multivariate analysis and ANCOVA, baleen whales and toothed cetaceans had distinct energy patterns, with two exceptions including beaked whales and eusocial cetaceans. Baleen whales are characterized by fast prenatal growth, which suggests high prenatal energetics, and utilize the capital breeder tactic. Toothed cetaceans, except for beaked whales, utilize income breeder energetics, which yields relatively slow prenatal growth. However, eusocial cetaceans have especially slow prenatal growth, suggesting very low prenatal energetic effort with social compensation. Although beaked whales are behaviorally income breeders, both discriminant analysis and ANCOVA showed that they are energetically similar to baleen whales, utilizing capital energetics. ANCOVA further revealed that beaked whales have comparatively large calf size, suggesting high prenatal investment. Because all cetaceans wean their calves at comparable size, high prenatal investment may further suggest reduced cost of lactation, which may be behaviorally and energetically adaptive to their specific deep‐dive‐feeding niche.     

Regulatory Mechanisms of Reproductive Effort in Plants 1. Plasticity in Reproductive Energy Allocation and Propagule Output of Helianthus annuus L. (Compositae) Cultivated at Varying Densities and Nitrogen Levels

Abstract Plasticity in growth, reproductive energy allocation (RA), and reproductive output were investigated in Helianthus annuus L. cultivar. Russia (Compositae) grown under varying densities and soil nitrogen levels. The role and behaviour of pollinators in seed production was also examined.
Exceedingly marked plastic responses were detected in individual biomass, the patterns of resource allocation to total reproductive structures (RA) and also to propagules, fecundity, reproductive outputs, and propagule size and weight under changing densities and soil nitrogen levels. Plants cultivated at higher densities exhibited proportionately lower individual biomass, lower RA, lower fecundity, lower seed output, and smaller seed size in response to increasing density and decreasing soil nitrogen levels. However, differences due to different N-levels were not as great as those to changing density.
One of the most significant findings was that seed production under limited resource availability, i.e., lack of ample solar radiation and soil nutrients, due to strong interference at higher density plots, is exceedingly costlty , This was most clearly demonstrated by a very sharp increase in relative energy partitioning to a single propagule in response to the increased density and decreasing nitrogen levels, the relative energy cost to a single achcne (R_A) increasing from one to twenty-fourfold. Reproduction was also affected by pollinator-limitations, and seed size showed a marked position effect.     

Aphids do not attend to leaf colour as visual signal, but to the handicap of reproductive investment

The evolution of visual warning signals is well known in animals but has received scant attention in plants. The coevolutionary hypothesis is the most influential hypothesis on warning signals in plants proposing that red and yellow leaf colours in autumn signal defensive strength to herbivores. So far, evidence in support of the hypothesis, which assumes a coevolutionary origin of autumnal leaf colours, is correlative and open to alternative explanations. We therefore tested the coevolutionary hypothesis experimentally by colouring the leaves either red or green of same-aged mountain ash (Sorbus aucuparia) individuals. We monitored the response of winged aphids to leaf colour using insect glue on branches with natural and artificial leaf colours in each individual. In contrast to the prediction of the coevolutionary hypothesis, aphid numbers did not differ between the individuals with artificial green or artificial red leaves. Likewise, at the within-plant level, aphids did not colonize branches with natural green leaves preferentially. However, we suggest that plants emitted warning signals because aphids colonized the hosts non-randomly. We found a strong positive correlation between aphid numbers and fruit production, suggesting an allocation trade-off between investment in plant defence and reproduction. Our study demonstrates that aphids use warning signals or cues in host selection, probably volatiles, but that they did not use leaf colour.     

Parasitism of maternal investment selects for increased clutch size and brood reduction in a host

The allocation of resources to young that will ultimately beleft to die appears counterintuitive. Yet obligate brood reductionhas evolved in a number of species, despite the waste of reproductiveinvestment this may incur. Here we test whether brood parasitismcould be one factor leading to the evolution of obligate broodreduction because surplus eggs in the nest during incubationoffer some protection from the costs of parasitism. Surpluseggs could benefit females in two ways. First, additional eggsmay protect against the direct costs of parasitism by facilitatingrecognition and removal of parasitic eggs with greater accuracy.Second, additional eggs may protect against the indirect costsof parasitism as parasites often damage or remove host eggswhen entering the host nest; surplus eggs may be an essentialinsurance strategy against this damage. We test these possibilitiesin the Montezuma Oropendola (Psarocolius Montezuma), a speciesexperiencing high levels of parasitism by Giant Cowbirds (Scaphiduraoryzivora) throughout their range. Overall rejection rates ofcowbird eggs were high (72%), and experimental addition of parasiticeggs to empty, one-, and two-egg nests demonstrated that recognitionsuccess was unaffected by the presence of additional host eggsfor comparison. However, the value of surplus eggs when oneegg was removed or damaged by a parasite was high; 31.6% ofsuccessful two-egg clutches lost a single egg during incubationand would have failed to produce a chick without a second egg.This was directly attributable to parasitism in at least 33%of all cases. Therefore, despite highly developed host defensesagainst direct costs of parasitism (recognition and removalof parasitic eggs), the associated indirect costs (egg damageand removal) could play an important role in selection for aclutch size that results in more chicks than can be raised.