Male age mediates reproductive investment and response to paternity assurance

Theory predicts that male response to reduced paternity will depend on male state and interactions between the sexes. If there is little chance of reproducing again, then males should invest heavily in current offspring, regardless of their share in paternity. We tested this by manipulating male age and paternity assurance in the burying beetle Nicrophorus vespilloides. We found older males invested more in both mating effort and parental effort than younger males. Furthermore, male age, a component of male state, mediated male response to perceived paternity. Older males provided more prenatal care, whereas younger males provided less prenatal care, when perceived paternity was low. Adjustments in male care, however, did not influence selection acting indirectly on parents, through offspring performance. This is because females adjusted their care in response to the age of their partner, providing less care when paired with older males than younger males. As a result offspring, performance did not differ between treatments. Our study shows, for the first time, that a male state variable is an important modifier of paternity–parental care trade-offs and highlights the importance of social interactions between males and females during care in determining male response to perceived paternity.     

Male parental care, female reproductive success, and extrapair paternity

Birds differ considerably in the degree of male parental care,and it has been suggested that interspecific variation in extrapairpaternity is determined by the relative importance of benefitsto females from male parental care and good genes from extrapairsires. I estimated the relationship between extrapair paternityand the importance of male parental care for female reproductivesuccess mainly based on male removal studies, using a comparativeapproach. The reduction in female reproductive success causedby the absence of a male mate was positively correlated withthe male contribution to feeding offspring. The frequency ofextrapair paternity was negatively related to the reductionin female reproductive success caused by the absence of a mate.This was also the case when potentially confounding variablessuch as developmental mode of offspring and sexual dichromatismwere considered. A high frequency of extrapair paternity occursparticularly in bird species in which males play a minor rolein offspring provisioning and in which attractive males providerelatively little parental care. Bird species with frequentextrapair paternity thus appear to be those in which directfitness benefits from male care are small, females can readilycompensate for the absence of male care, and indirect fitnessbenefits from extrapair sires are important.     

Aphid reproductive investment in response to mortality risks

Background  

Aphids are striking in their prodigious reproductive capacity and reliance on microbial endosymbionts, which provision their hosts with necessary amino acids and provide protection against parasites and heat stress. Perhaps as a result of this bacterial dependence, aphids have limited immune function that may leave them vulnerable to bacterial pathogens. An alternative, non-immunological response that may be available to infected aphids is to increase reproduction, thereby ameliorating fitness loss from infection. Such a response would reduce the need to mount a potentially energetically costly immune response, and would parallel that of other hosts that alter life-history traits when there is a risk of infection. Here we examined whether pea aphids (Acyrthosiphon pisum) respond to immunological challenges by increasing reproduction. As a comparison to the response to the internal cue of risk elicited by immunological challenge, we also exposed pea aphids to an external cue of risk - the aphid alarm pheromone (E)-β-farnesene (EBF), which is released in the presence of predators. For each challenge, we also examined whether the presence of symbionts modified the host response, as maintaining host fitness in the face of challenge would benefit both the host and its dependent bacteria.     

Male reproductive investment and queen mating-frequency in fungus-growing ants

Sperm number and male accessory gland compounds are often importantdeterminants of male mating success but have been little studiedin social insects. This is because mating in social insectsis often difficult to manipulate experimentally, and first evidencefor an explicit influence of accessory gland secretions on malemating success in social insects was obtained only recently.Here we perform a comparative analysis of male sexual organsacross 11 species of attine fungus-growing ants, representingboth genera with single- and multiple-queen mating. We foundthat the general morphology of the male sexual organs was verysimilar across all species, but the relative sizes of the accessoryglands and the sperm-containing accessory testes vary significantlyacross species. Small testes and large accessory glands characterizespecies with singly mated queens, whereas the opposite is foundin species with multiply mated queens. However, in the socialparasite Acromyrmex insinuator, in which queens have secondarilyreverted to single mating, males have accessory gland characteristicsreminiscent of the lower attine ants, but without having significantlyreduced their investment in sperm production. We hypothesizethat the main function of accessory gland compounds in attineants is to monopolize male paternity in similar ways as knownfrom other social insects. This would imply that the evolutionof polyandry in the terminal clade of the fungus-growing ants(the leafcutter ants) has resulted in selection for decreasedinvestment by males in accessory gland secretions and increasedinvestment in sperm number, in response to sperm competitionfor sperm storage.     

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.     

Male eastern bluebirds trade future ornamentation for current reproductive investment

Life-history theory proposes that organisms must trade-off investment in current and future reproduction. Production of ornamental display is an important component of reproductive effort that has rarely been considered in tests of allocation trade-offs. Male eastern bluebirds (Sialia sialis) display brilliant ultraviolet-blue plumage that is correlated with mate acquisition and male competitive ability. To investigate trade-offs between current reproductive effort and the future expression of a sexually selected ornament, we manipulated the parental effort of males by changing their brood sizes. We found that parents provisioned experimentally enlarged broods more often than reduced broods. As predicted by life-history theory, the change in parental effort had a significant effect on the relative plumage ornamentation of males in the subsequent year: males with reduced broods significantly increased in plumage brightness. Moreover, this change in plumage coloration had a direct effect on the timing of breeding in the following season: males that displayed brighter plumage in the year following the manipulation mated with females that initiated egg laying earlier in the season. These data indicate that male bluebirds must trade-off conserving energy for production of future ornamentation versus expending energy for current reproduction.     

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.     

Female age: Male preference and reproductive success in primates

A survey of the literature on male sexual preferences according to the age of the female partner supported the hypothesis that adult males should prefer older females of higher parity. Reproductive success was also surveyed by age and parity, and younger females of lower parity were universally found to have lower success than older females of higher parity. This appears to be true for either age or parity independently, as well as in combination. These findings are discussed and applied to human societies, where similar trends would be expected.     

Male reproductive success in a promiscuous mammal: behavioural estimates compared with genetic paternity

Molecular techniques have enabled behavioural ecologists to reassess mating systems from a genetic perspective. Studies of paternity frequently reveal that mating behaviour does not always reflect parentage, and may bring to light alternative mating tactics. Here we present a comparison of behavioural and genetic measures of male reproductive success in a mammalian mating system in which both sexes are highly promiscuous. Rather than having a stable harem social structure, Soay rams (Ovis aries) on the island of Hirta, St Kilda, UK usually consort with individual oestrous ewes sequentially. Not all matings occur between consort pairs, however, and ewes have been seen to mate with up to 10 different rams on the same day. Using locus-specific polymorphism at five protein and 10 microsatellite DNA loci, we determined paternity for 236 lambs born into three cohorts, and compared paternity with estimates of mating success derived from more than one census of rutting behaviour. The correlation between the number of ewes with which each ram was witnessed in consort and the number of paternities assigned was positive and statistically significant, and rams that were observed in consort with a ewe were 18 times more likely to have sired her offspring than other candidate rams. However, most lambs (73%) were not sired by a ram seen in consort with the oestrous mother. Many juveniles, yearlings and some adult rams were rarely seen in consort with ewes, yet were assigned a significant number of paternities. These results suggest that mating tactics differ between age groups, and that alternative mating strategies among adults that do not involve forming consorts with many females also confer mating success. For these reasons, census-based observations of consort associations between individuals cannot be used to accurately estimate individual male reproductive success in this population.     

Badge size, paternity assurance behaviours and paternity losses in male house sparrows

Male quality may influence both the outcome of sperm competition and female faithfulness. In male house sparrows Passer domesticus , the size of the black throat patch (badge) signals dominance and perhaps attractiveness. So far, however, no study has reported any significant relationships between badge size, paternity and paternity assurance behaviours in this species. We found that the time mates spent together at the nest was positively correlated with badge size. Furthermore, although paternity losses were influenced by both the time spent at the nest and within-pair copulation frequency, we found no relationship between copulation rate and badge size. It seems therefore that copulation frequency served as a paternity assurance behaviour, whereas the time mates stayed together at the nest may have reflected male attractiveness. Alternatively, females may have decided to stay with large-badged males because they were better able to protect them from harassment by strange males. We also found that paternity losses were related to male badge size; average-badged males cuckolded were more often than males with smaller or larger badges. We suggest that average-badged males suffered higher paternity losses because they had different time allocation strategies than other males.     

Fertility assurance through extrapair fertilizations and male paternity defense

Extrapair paternity has been observed in many formally monogamous species. Male pursuit of extrapair fertilizations is explained by the advantages of having offspring that receive essential paternal care from other males. Since females are capable of exercising a degree of control over the post-copulatory sperm competition, extrapair paternity cannot persist unless it confers fitness benefits on cuckolding females. Thus, extrapair paternity involves cooperation between mated females and extrapair males. On the other hand, paired males frequently exhibit strategies that minimize their loss of paternity and/or conserve paternal investment if paternity is lost. Hence, extrapair attributes of diverse species and populations reported in the literature are particular solutions of evolutionary games involving gender-specific cuckolding/anti-cuckolding strategies. Here we use methods of evolutionary game theory to study the role of male paternity guarding strategies in situations where females seek extrapair fertilizations for reasons of genetic compatibility and/or in pursuit of genetic diversity for their offspring. Our results indicate that in these circumstances pursuit of extrapair fertilizations is the only evolutionary stable female strategy. Males, on the other hand, have two, mutually exclusive, evolutionary stable strategies: full time pursuit of extrapair fertilizations and a compromise strategy wherein they protect in-pair paternity during their mate's fertile periods and pursue extrapair paternity the rest of the time. The relative merits of these two strategies are determined by the efficiency of male in-pair paternity defense, breeding synchrony, fitness advantages of extrapair over in-pair offspring, and the intensity of competition for extrapair fertilizations from floater males.     

Correlated evolution in parental care in females but not males in response to selection on paternity assurance behaviour

According to classical parental care theory males are expected to provide less parental care when offspring in a brood are less likely to be their own, but empirical evidence in support of this relationship is equivocal. Recent work predicts that social interactions between the sexes can modify co‐evolution between traits involved in mating and parental care as a result of costs associated with these social interactions (i.e. sexual conflict). In burying beetles (Nicrophorus vespilloides), we use artificial selection on a paternity assurance trait, and crosses within and between selection lines, to show that selection acting on females, not males, can drive the co‐evolution of paternity assurance traits and parental care. Males do not care more in response to selection on mating rate. Instead, patterns of parental care change as an indirect response to costs of mating for females.     

Extra-pair paternity in relation to male age in Bullock's orioles

Single-locus minisatellite DNA profiling was used to assign paternity in a population of Bullock's orioles, Icterus galbula bullockii, and to determine the contribution of age to a male's success in obtaining extra-pair paternity. There was a very low rate of intraspecific brood parasitism (2/202 = 1.0% of chicks). Older adult males lost less within-pair paternity and gained more extra-pair fertilizations than did yearling subadult males. This resulted in adult males benefiting from an annual reproductive success more than double that of subadult males. Behavioural observations, used to determine the role of female choice in extra-pair copulations (EPCs), indicated that females actively participate in EPCs and that they prefer to obtain them from older males. While it was possible that females obtained EPCs as an insurance against the possible infertility of their social mate, the results of this study fit best with the hypothesis that females were attempting to obtain better-quality genes for their offspring by obtaining EPCs with older, better-quality males.     

繁殖保障和延迟自交的研究进展

尽管植物在进化过程中面临不利自花授粉的选择,但许多植物仍维持混合的授粉机制。繁殖保障假说是解释自交进化的最重要因子之一,一直是植物生殖生态学和进化生物学关注的焦点之一。概述了近年来的主要研究热点及其进展,包括自交进化的遗传和生态机制及理论模型探讨、繁殖保障假说的提出、验证自交能否提供繁殖保障的例证、延迟自交的类型及延迟自交能否提供繁殖保障的例证等方面。介绍了我国在繁殖保障和延迟自交方面研究的现状和不足之处,结合国际上研究繁殖保障假说的发展趋势已由单季节、单种群、单因子的研究阶段过渡到多季节、多种群、多因子（自交方式及其所占比例、花粉折损、种子折损、自交率和近交衰退）的综合研究阶段,及由传统的、经典的研究方法过渡到应用现代实验手段（如SSR、SNP等分子标记）和先进仪器设备的研究阶段,提出今后研究中应注意的问题。有必要借用多学科（植物学、生态学和分子生物学）的方法及手段进行不同物种的对比和综合细致的研究。     

Male extraterritorial forays, age and paternity in the socially monogamous reed bunting (Emberiza schoeniclus)

Genetic studies have shown that extra-pair paternity is widespread among socially monogamous bird species. Yet, the role of males and females and their behavior leading to this mixed reproductive strategy is poorly understood. Here, we analyze paternity in relation to male age and mating behavior in the socially monogamous reed bunting (Emberiza schoeniclus). We report a positive relation between male extraterritorial forays and success in obtaining extra-pair fertilizations. Extraterritorial forays tended to increase in frequency with male age and older males sired a larger number of extra-pair offspring than young males. Identified extra-pair sires were old in nine out of ten cases. The likelihood of being cuckolded was not affected by male age. Although based on correlative data, our results highlight age-dependent explorative male behavior as a key determinant for the understanding of extra-pair mating in the reed bunting. We do, however, emphasize the need for further studies to reveal the role of females in extra-pair copulations and fertilizations.     

Male achromatic wing colouration is related to body condition and female reproductive investment in a dichromatic species,the upland goose

In many bird species, achromatic plumage patch size can serve as a male status signal, but the use of variations in the achromatic colours themselves as a quality signal has only recently come into focus. In our study, we sought to determine whether achromatic plumage reflects individual quality in the upland goose (Chloephaga picta leucoptera). We examined the relationship between male head and wing reflectance, male condition and female reproductive investment. We found that males with darker specula and greater contrast between the white wing coverts and the speculum were in a better body condition. Variations in the brightness of the white plumage were not a quality signal in the upland goose. The information gleaned from the wing colouration of male upland geese could be used during mate selection, when females choose their mate on the basis of the outcomes of aggressive encounters. During these fights, the males expose their white coverts and their specula, which are normally tucked beneath body feathers.     

The response of tsetse flies to artificial baits in relation to age, nutritional and reproductive state

In various vegetation types in Zimbabwe, the catches of Glossina pallidipes Austen and G. morsitans morsitans Westw. (Diptera: Glossinidae) at a target baited with odour (acetone, 1-octen-3-ol and two phenols) were positively correlated with catches of the same species at an unbaited net. No correlation existed between target catches and hand net catches of tsetse flies sitting on the vegetation. G. pallidipes females caught at a target and at an unbaited net were older than those caught from vegetation. Of the female G. pallidipes caught at the target, 46% were in the first 3 days of pregnancy. Of those caught at the unbaited net, significantly fewer, 21%, were in this stage. G. pallidipes males caught from vegetation contained more fat (3.07±0.333 mg) than those caught at the unbaited net (2.06±0.339 mg) or at the target (2.19±0.218 mg). It is inferred that target catches consisted predominantly of tsetse which were already in flight when they sensed the stimuli from the target, and that target catches were biased towards female G. pallidipes in the first 3 days of pregnancy.     

Male courtship attractiveness and paternity success in Photinus greeni fireflies

Although female mate choice and male sperm competition have separately attracted much attention, few studies have addressed how precopulatory and postcopulatory episodes of sexual selection might interact to drive the evolution of male traits. In Photinus fireflies, females preferentially respond to males based on their bioluminescent courtship signals, and females gain direct benefits through male nuptial gifts acquired during multiple matings over several nights. We experimentally manipulated matings of P. greeni fireflies to test the hypothesis that postcopulatory paternity success might be biased toward males that are more attractive during courtship interactions. We first measured male courtship attractiveness to individual females using field behavioral assays. Females were then assigned to two double-mating treatments: (1) least attractive second male-females were first mated with their most attractive male, followed by their least attractive male, or (2) most attractive second male-females mated with males in reverse order. Larval offspring produced by each female following these double matings were genotyped using random amplified polymorphic DNA (RAPD) markers, and male paternity was determined. Contrary to prediction, firefly males that were more attractive to females based on their bioluminescent courtship displays subsequently showed significantly lower paternity, reflecting possible male trade-offs or sexual conflict. Differences in male paternity were not related to male body condition, testes or accessory gland mass, or to variation in female spermathecal size. Additionally, this study suggests that changes in phenotypic selection gradients may occur during different reproductive stages. These results indicate that it is crucial for future studies on sexual selection in polyandrous species to integrate both precopulatory and postcopulatory episodes to fully understand the evolution of male traits.     

Male mating success, reproductive success and multiple paternity in a natural population of sand lizards: behavioural and molecular genetics data

Sand lizard Lacerta agilis females characteristically mate with several males which, in staged mating experiments, results in multiple paternity of the offspring. In order to investigate multiple paternity in a natural population and interpret male reproductive behaviours in terms of sired young, we sampled the blood of females, potential fathers and hatchlings, and determined paternity using multilocus DNA fingerprinting as well as the variation at a single locus detected by the probe (TC) _n . The paternity analyses were preceded by a laboratory experiment in which we established that the parental alleles identified by the single locus probe were inherited in a Mendelian way. Our molecular data demonstrated that 12 out of 13 males (92%) that sired offspring were correctly identified from the 56 sexually mature males in the population. Also smaller males were accepted as sexual partners by the females, but sired fewer young in competition with larger males and were less able to maintain prolonged post-copulatory mate guarding. This may result in that some sexually successful males are only observed inside a female's home range, but never in pair-association with the female.     

Male reed buntings do not adjust parental effort in relation to extrapair paternity

Parental effort is considered to be costly; therefore, malesare expected to provide less care to unrelated offspring. Theoreticalmodels suggest that males should either reduce their care tothe entire brood or alternatively distinguish between relatedand unrelated nestlings and direct provisioning to kin whenpaternity is in doubt. Reed buntings (Emberiza schoeniclus)have been found to have high levels of extrapair paternity (EPP,i.e., offspring of a male other than the male attending thenest; 55% of offspring), and males are therefore under strongselection pressure to adjust their parental effort accordingto the proportion of EPP in their brood. In this study, we investigatedwhether male reed buntings exhibit a reduction in paternal care(incubation and provisioning nestlings) in relation to decreasedpaternity. We also assess whether males bias their provisioningtoward kin. We measured incubation time, provisioning rates,and food allocation to individual nestlings using video recordingsat the nests. Microsatellite DNA analysis was used to analyzethe paternity of offspring. In direct contrast to a previousstudy on the same species, our results provided no indicationthat males lowered their effort with decreased paternity. Furthermore,in nests of mixed paternity, males did not bias their provisioningbehavior to kin. It remains to be investigated whether the absenceof a relationship between paternity and paternal care can beascribed to absence of reliable paternity cues or whether thebenefits of reducing paternal care did not outweigh the costsin our study population. We found no evidence that the levelof paternal care affected male survival or offspring mass, suggestingthat both the benefits and costs of any reduction in paternalcare would have been low.