A role for sperm in regulation of egg-laying in the Nematode <Emphasis Type="Italic">C. elegans</Emphasis>

Background  

In insects and in mammals, male sperm and seminal fluid provide signaling factors that influence various aspects of female physiology and behavior to promote reproductive success and to compete with other males. It is less apparent how important such signaling is in the context of a self-fertile hermaphrodite species. We have addressed this question in the nematode Caenorhabditis elegans, which can reproduce either by hermaphrodite self-fertilization or by male-hermaphrodite mating.     

Male sexual ornament size is positively associated with reproductive morphology and enhanced fertility in the stalk-eyed fly <Emphasis Type="Italic">Teleopsis dalmanni</Emphasis>

Background  

Exaggerated male ornaments and displays often evolve in species where males only provide females with ejaculates during reproduction. Although "good genes" arguments are typically invoked to explain this phenomenon, a simpler alternative is possible if variation in male reproductive quality (e.g. sperm number, ejaculate content, mating rate) is an important determinant of female reproductive success. The "phenotype-linked fertility hypothesis" states that female preference for male ornaments or displays has been selected to ensure higher levels of fertility and has driven the evolution of exaggerated male traits. Females of the stalk-eyed fly Teleopsis dalmanni must mate frequently to maintain high levels of fertility and prefer to mate with males exhibiting large eyespan, a condition-dependent sexual ornament. If eyespan indicates male reproductive quality, females could directly increase their reproductive success by mating with males with large eyespan. Here we investigate whether male eyespan indicates accessory gland and testis length, and then ask whether mating with large eyespan males affects female fertility.     

Differential costs of reproduction in females and hermaphrodites in a gynodioecious plant

Background and Aims

Plants exhibit a variety of reproductive systems where unisexual (females or males) morphs coexist with hermaphrodites. The maintenance of dimorphic and polymorphic reproductive systems may be problematic. For example, to coexist with hermaphrodites the females of gynodioecious species have to compensate for the lack of male function. In our study species, Geranium sylvaticum, a perennial gynodioecious herb, the relative seed fitness advantage of females varies significantly between years within populations as well as among populations. Differences in reproductive investment between females and hermaphrodites may lead to differences in future survival, growth and reproductive success, i.e. to differential costs of reproduction. Since females of this species produce more seeds, higher costs of reproduction in females than in hermaphrodites were expected. Due to the higher costs of reproduction, the yearly variation in reproductive output of females might be more pronounced than that of hermaphrodites.

Methods

Using supplemental hand-pollination of females and hermaphrodites of G. sylvaticum we examined if increased reproductive output leads to differential costs of reproduction in terms of survival, probability of flowering, and seed production in the following year.

Key Results

Experimentally increased reproductive output had differential effects on the reproduction of females and hermaphrodites. In hermaphrodites, the probability of flowering decreased significantly in the following year, whereas in females the costs were expressed in terms of decreased future seed production.

Conclusions

When combining the probability of flowering and seed production per plant to estimate the multiplicative change in fitness, female plants showed a 56 % and hermaphrodites showed a 39 % decrease in fitness due to experimentally increased reproduction. Therefore, in total, female plants seem to be more sensitive to the cost of reproduction in terms of seed fitness than hermaphrodites.     

Costs of receipt and donation of ejaculates in a simultaneous hermaphrodite

Background  

Sexual conflicts between mating partners can strongly impact the evolutionary trajectories of species. This impact is determined by the balance between the costs and benefits of mating. However, due to sex-specific costs it is unclear how costs compare between males and females. Simultaneous hermaphrodites offer a unique opportunity to determine such costs, since both genders are expressed concurrently. By limiting copulation of focal individuals in pairs of pond snails (Lymnaea stagnalis) to either the male role or the female role, we were able to compare the fecundity of single sex individuals with paired hermaphrodites and non-copulants. Additionally, we examined the investment in sperm and seminal fluid of donors towards feminized snails and hermaphrodites.     

Short‐Term Nutritional Limitation Affects Mating Behaviour and Reproductive Output in Dwarf Spiders

Mating decisions can vary considerably depending on individual experience, mate availability and nutritional status. Here, we applied short‐term dietary restrictions to adult female spiders that were well fed during the juvenile stage in an effort to understand whether and how brief periods of food shortage can influence male and female mating decisions and mating behaviour. To assess whether responses vary between closely related species, we conducted the same experiment on the dwarf spiders Oedothorax retusus and O. apicatus. During courtship and mating, males of both species offer secretion to females from glandular tissue in their prosoma. Females were subject to food shortage over a period of 3 wks (‘low‐diet’ treatment, LD) or fed regularly (‘high‐diet’ treatment, HD). We compared courtship probability, mating probability/behaviour, and reproductive output between dietary groups and species. In both Oedothorax species, females in the LD treatment were less likely to mate and more aggressive towards males. Furthermore, LD females produced egg sacs that were significantly lighter than were those of the HD females. Effects of food deprivation on copulation duration, gustatory behaviour and oviposition latency differed between species. Our study shows that short periods of dietary restriction during the adult stage can strongly affect mating behaviour and reproductive output with differences between closely related species.     

Maintenance of adaptive differentiation by Wolbachia induced bidirectional cytoplasmic incompatibility: the importance of sib-mating and genetic systems

Background  

Bacteria of the genus Wolbachia are reproductive parasites widespread among arthropods. The most common effect arising from the presence of Wolbachia in a population is Cytoplasmic Incompatibility (CI), whereby postmating reproductive isolation occurs in crosses between an infected male and an uninfected female, or when a male is infected with a different strain of Wolbachia to that of the female (bidirectional CI). Previous theoretical models have demonstrated that bidirectional CI can contribute to the genetic divergence of populations in haploid and diploid organisms. However, haplodiploid organisms were not considered in these models even though they include Nasonia parasitoid wasps – the best example of the implication of Wolbachia in ongoing speciation. Moreover, previous work did not investigate inbreeding mating systems, which are frequently observed in arthropod species.     

Optimization of age difference between mates maximizes reproductive output

The influence of the age difference between mates on the reproductive output of an aphidophagous ladybird, Propylea dissecta (Mulsant) (Coleoptera: Coccinellidae) was studied. This was done by varying the ages of either the males or females and keeping that of the other sex constant. The optimum age difference for maximum reproductive output was also identified. This study is the first attempt in insects. Pairs in which the female was five days older than the male resulted in the highest number of progeny. The number of progeny produced in this pair was however not statistically different from pairs in which females were 0 and 10 days older than the males. Synchronization between age-specific daily oviposition and viability trends was observed in groups with high reproductive output. Asynchronization amongst male and female ageing trajectories was found responsible for the reduced reproductive output. This study reveals that if the female is 5–10 days older than the male at a young age, then there is increased likelihood of production of maximum number of progeny.     

Reproductive hacking: A male seminal protein acts through intact reproductive pathways in female Drosophila

Seminal proteins are critical for reproductive success in all animals that have been studied. Although seminal proteins have been identified in many taxa, and female reproductive responses to receipt of these proteins have been documented in several, little is understood about the mechanisms by which seminal proteins affect female reproductive physiology. To explore this topic, we investigated how a Drosophila seminal protein, ovulin, increases ovulation rate in mated females. Ovulation is a relatively simple physiological process, with known female regulators: previous studies have shown that ovulation rate is promoted by the neuromodulator octopamine (OA) in D. melanogaster and other insects. We found that ovulin stimulates ovulation by increasing OA signaling in the female. This finding supports a model in which a male seminal protein acts through “hacking” a well-conserved, regulatory system females use to adjust reproductive output, rather than acting downstream of female mechanisms of control or in parallel pathways altogether. We also discuss similarities between 2 forms of intersexual control of behavior through chemical communication: seminal proteins and pheromones.     

How to be an attractive male: floral dimorphism and attractiveness to pollinators in a dioecious plant

Background  

Sexual selection theory predicts that males are limited in their reproductive success by access to mates, whereas females are more limited by resources. In animal-pollinated plants, attraction of pollinators and successful pollination is crucial for reproductive success. In dioecious plant species, males should thus be selected to increase their attractiveness to pollinators by investing more than females in floral traits that enhance pollinator visitation. We tested the prediction of higher attractiveness of male flowers in the dioecious, moth-pollinated herb Silene latifolia, by investigating floral signals (floral display and fragrance) and conducting behavioral experiments with the pollinator-moth, Hadena bicruris.     

Impacts of male and food density on female performance in the brackish cladoceran Daphniopsis australis

The roles of male and food density in regulating female performance were investigated in the brackish cladoceran, Daphniopsis australis. Parthenogenetic females and ephippial females were tested using a 2 × 4 factorial experiment involving the presence and the absence of a male cross-classified with nil, low, medium and high food densities. For parthenogenetic females, the male presence and food density failed to trigger the switch from asexual to sexual reproduction, but the presence of male negatively affected parthenogenesis through egg abortion. Food density affected the animal longevity but depended on the male presence. The reproductive output was favoured by increasing food densities, but the male presence increased egg abortion, suggesting male being an added stress factor to parthenogenetic females. For ephippial females, food densities affected the frequency of switch from sexual to asexual modes in the absence and the presence of a male. However, the male enhanced switch frequency under low and high food densities. Longevity was increased with the male presence but was unaffected by food density. The ephippial females successfully produced diapausing eggs with the male presence. Although, ephippial females could switch to parthenogenesis but the reproductive output of switched ephippial females was inferior to that of parthenogenetic females since birth. The results reveal that the male presence and food density can impact the performance of female D. australis. Hence, this study provides an insight into the understanding of the reproductive biology of cladocerans and a possible alternative explanation for population dynamic of this species and other cladocerans in the field.     

Female mating receptivity inhibited by injection of male-derived extracts in Callosobruchus chinensis

The effects of male-derived extracts on female receptivity to remating were investigated in Callosobruchus chinensis (Coleoptera: Bruchidae). Injection of aqueous extracts of male reproductive tracts into the abdomen of females reduced receptivity. When aqueous extracts of male reproductive tracts were divided to three molecular weight (MW) fractions by ultrafiltration: <3, 3-14, and >14 kDa, the filtrate containing MW substances <3 kDa reduced female receptivity 3h and 1 day after injection, whereas the fraction containing MW substances >14 kDa inhibited receptivity 2 and 4 days after injection. Finally, male reproductive tract organs were divided into accessory gland, seminal vesicle, and testis. Aqueous extracts of testis reduced receptivity of females on the second day and at 3h, and aqueous extracts of accessory gland reduced receptivity of females on the second day after injection. On the other hand, aqueous extracts of seminal vesicle did not reduce female receptivity. The results indicate that more than one mechanism may be involved in producing the effects of male-derived substances on female receptivity; low MW male-derived substances, which possibly exist in testis, cause short-term inhibition, while high MW substances, which possibly exist in the accessory gland, inhibit female mating later than low MW substances in C. chinensis.     

Sexual dimorphism in a dioecious population of the wind-pollinated herb Mercurialis annua: the interactive effects of resource availability and competition

Background and Aims

Male-biased sex allocation commonly occurs in wind-pollinated hermaphroditic plants, and is often positively associated with size, notably in terms of height. Currently, it is not well established whether a corresponding pattern holds for dioecious plants: do males of wind-pollinated species exhibit greater reproductive allocation than females? Here, sexual dimorphism is investigated in terms of life history trade-offs in a dioecious population of the wind-pollinated ruderal herb Mercurialis annua.

Methods

The allocation strategies of males and females grown under different soil nutrient availability and competitive (i.e. no, male or female competitor) regimes were compared.

Key Results

Male reproductive allocation increased disproportionately with biomass, and was greater than that of females when grown in rich soils. Sexual morphs differentially adjusted their reproductive allocation in response to local environmental conditions. In particular, males reduced their reproductive allocation in poor soils, whereas females increased theirs, especially when competing with another female rather than growing alone. Finally, males displayed smaller above-ground vegetative sizes than females, but neither nutrient availability nor competition had a strong independent effect on relative size disparities between the sexes.

Conclusions

Selection appears to favour plasticity in reproductive allocation in dioecious M. annua, thereby maintaining a relatively constant size hierarchy between sexual morphs. In common with other dioecious species, there seems to be little divergence in the niches occupied by males and females of M. annua.     

No evidence for learned mating discrimination in male Drosophila pseudoobscura

Background  

Since females often pay a higher cost for heterospecific matings, mate discrimination and species recognition are driven primarily by female choice. In contrast, frequent indiscriminate matings are hypothesized to maximize male fitness. However, recent studies show that previously indiscriminate males (e.g., Drosophila melanogaster and Poecilia reticulata) can learn to avoid heterospecific courtship. This ability of males to discriminate against heterospecific courtship may be advantageous in populations where two species co-occur if courtship or mating is costly.     

Assortative mating in fallow deer reduces the strength of sexual selection

Background

Assortative mating can help explain how genetic variation for male quality is maintained even in highly polygynous species. Here, we present a longitudinal study examining how female and male ages, as well as male social dominance, affect assortative mating in fallow deer (Dama dama) over 10 years. Assortative mating could help explain the substantial proportion of females that do not mate with prime-aged, high ranking males, despite very high mating skew. We investigated the temporal pattern of female and male matings, and the relationship between female age and the age and dominance of their mates.

Results

The peak of yearling female matings was four days later than the peak for older females. Younger females, and especially yearlings, mated with younger and lower-ranking males than older females. Similarly, young males and lower-ranking males mated with younger females than older males and higher-ranking males. Furthermore, the timing of matings by young males coincided with the peak of yearling female matings, whereas the timing of older male matings (irrespective of rank) coincided with the peak of older female matings.

Conclusions

Assortative mating, through a combination of indirect and/or direct female mate choice, can help explain the persistence of genetic variation for male traits associated with reproductive success.     

Sexual conflict over the duration of copulation in Drosophila montana : why is longer better?

Background  

Conflicts of interest between the sexes are increasingly recognized as an engine driving the (co-)evolution of reproductive traits. The reproductive behaviour of Drosophila montana suggests the occurrence of sexual conflict over the duration of copulation. During the last stages of copulation, females vigorously attempt to dislodge the mounting male, while males struggle to maintain genital contact and often successfully extend copulations far beyond the females' preferred duration.     

Female mating receptivity after injection of male-derived extracts in Callosobruchus maculatus

The effects of male-derived extracts on female receptivity were investigated in Callosobruchus maculatus (Coleoptera: Bruchidae). Injection of aqueous extracts of the male reproductive tract into the abdomen of females reduced receptivity. Aqueous extracts of male reproductive tracts were divided to three molecular weight (MW) fractions by ultrafiltration: Fractions: (I) MW<3 kDa, (II) 3-14 kDa, and (III)>14 kDa. Fraction II reduced female receptivity from 3h after injection, and Fraction III reduced female receptivity from 2 days after injection. On the other hand, no effect on receptivity was found for Fraction I. Furthermore, male reproductive tract organs were divided into accessory gland, testis, and seminal vesicle including the ejaculatory duct. Aqueous extracts of the seminal vesicle reduced receptivity of females immediately following injection, while aqueous extracts of the accessory gland reduced receptivity at the second day. The results suggest that the components of Fraction II existed in the seminal vesicle, and those of Fraction III in the accessory gland. The results of the present and the previous studies in Callosobruchus chinensis, a species closely related to C. maculatus, were compared and are discussed from the viewpoint of the significance of ejaculation in the two species.     

Meiosis genes in Daphnia pulex and the role of parthenogenesis in genome evolution

Background  

Thousands of parthenogenetic animal species have been described and cytogenetic manifestations of this reproductive mode are well known. However, little is understood about the molecular determinants of parthenogenesis. The Daphnia pulex genome must contain the molecular machinery for different reproductive modes: sexual (both male and female meiosis) and parthenogenetic (which is either cyclical or obligate). This feature makes D. pulex an ideal model to investigate the genetic basis of parthenogenesis and its consequences for gene and genome evolution. Here we describe the inventory of meiotic genes and their expression patterns during meiotic and parthenogenetic reproduction to help address whether parthenogenesis uses existing meiotic and mitotic machinery, or whether novel processes may be involved.     

Masting uncoupling: mast seeding does not follow all mast flowering episodes in a dioecious juniper tree

Evolutionary selective forces, like predator satiation and pollination efficiency, are acknowledged to be major causes of masting (the variable, periodic and synchronic production of seeds in a population). However, a number of recent studies indicate that resources might also play an important role on shaping masting patterns. Dioecious masting species offer a privileged framework to study the role of resources on masting variation, since male and female plants often experience different reproductive costs and selective pressures. We followed masting and reproductive investment (RI) of the dioecious tree Juniperus thurifera in two populations along 10 years and studied the different response of males and females to experimentally increased water and nutrient availability in a third population. Juniperus thurifera females invested in reproduction three times more resources than males. Such disparity generated different resource‐use strategies in male and female trees. Tree‐ring growth and water use efficiency (WUE) confirmed that sexes differed in their resource investment temporal pattern, with males using current resources for reproduction and females using resources accumulated during longer periods. Watered and fertilized female trees presented significantly higher flowering reproductive investments than males and experienced an extraordinary mast‐flowering event. However, seeding RI and mast seeding were not affected by the treatment. This suggests that although resource availability affects the reproductive output of this species, there are other major forces regulating masting on J. thurifera. During 10 years, J. thurifera male and female trees presented high and low flowering years more or less synchronously. However, not all mast flowering episodes resulted in mast seeding, leading to masting uncoupling between flowering and seeding. Since flowering costs represent only 1% of females’ total reproductive investments, masting uncoupling could be a beneficial bet‐hedging strategy to maximize reproductive output in spite of unpredictable catastrophic events.