No reversion to single mating in a socially parasitic ant

Social Hymenoptera are ideal biological models for the study of the selective forces affecting the evolution of multiple mating (polyandry), because sister species can evolve different lifestyles and mating strategies. Single mating is predicted in workerless social parasites, because the key benefit of multiple mating in social insects, that is, the increase in genetic diversity among worker offspring, does not hold for workerless species. We compared the queen mating frequency between the ant Plagiolepis pygmaea and its derived social parasite P. xene. Previous studies showed that queens of the host P. pygmaea are obligately polyandrous. Here, pedigree analyses of mother–offspring combinations indicate that queens of the parasite P. xene did not revert to single mating; more than 50% of queens mated multiply, with 2–4 males. This result shows that reversal from multiple to single mating may be not selected in polyandrous social insect workerless parasites. We propose that such reversion does not occur when multiple mating is virtually cost free.     

INEXPLICABLY FEMALE‐BIASED SEX RATIOS IN MELITTOBIA WASPS

The sex ratio behavior of parasitoid wasps in the genus Melittobia is scandalous. In contrast to the prediction of Hamilton's local mate competition theory, and the behavior of numerous other species, their extremely female‐biased sex ratios (1–5% males) change little in response to the number of females that lay eggs on a patch. We examined the mating structure and fitness consequences of adjusting the sex ratio in M. australica and found that (1) the rate of inbreeding did not differ from that expected with random mating within each patch; (2) the fitness of females that produced less female‐biased sex ratios (10 or 20% males) was greater than that of females who produced the sex ratio normally observed in M. australica. These results suggest that neither assortative mating nor asymmetrical competition between males can explain the extreme sex ratios. More generally, the finding that the sex ratios produced by females led to a decrease in their fitness suggests that the existing theory fails to capture a key aspect of the natural history of Melittobia, and emphasizes the importance of examining the fitness consequences of different sex ratio strategies, not only whether observed sex ratios correlate with theoretical predictions.     

Little effect of delayed mating on fecundity or fertility of female fungus gnats Lycoriella ingenua

The effect of delayed female mating for the mushroom fungus gnat Lycoriella ingenua is investigated. We examine the effect of delaying female mating on the fertility and egg viability of female flies that have a mating delay of 0–5 days after emergence. Male fly age is held constant. Female age does not impact male acceptance and most flies copulate within seconds of pairing. We find that female flies experiencing mating delays of 0–4 days after emergence lay a similar number of eggs onto artificial substrates. Females that experience a mating delay of 5 days lay 54% fewer eggs than those that mate on day 0 (day of emergence). There is no effect of mating delay on the percentage of larvae that emerge. The results of the present study indicate that mating delays have little effect on the fertility or fecundity of the mushroom fungus pest L. ingenua.     

Population density and group size effects on reproductive behavior in a simultaneous hermaphrodite

Background  

Despite growing evidence that population dynamic processes can have substantial effects on mating system evolution, little is known about their effect on mating rates in simultaneous hermaphrodites. According to theory, mating rate is expected to increase with mate availability because mating activity is primarily controlled by the male sexual function. A different scenario appears plausible in the hermaphroditic opisthobranch Chelidonura sandrana. Here, field mating rates are close to the female fitness optimum, suggesting that mating activity remains unresponsive to variation in mate availability.     

Genetic evidence for the mating system and reproductive success of black sea bream (Acanthopagrus schlegelii)

Understanding the mating system and reproductive success of a species provides evidence for sexual selection. We examined the mating system and the reproductive success of captive adult black sea bream (Acanthopagrus schlegelii), using parentage assignment based on two microsatellites multiplex PCR systems, with 91.5% accuracy in a mixed family (29 sires, 25 dams, and 200 offspring). Based on the parentage result, we found that 93.1% of males and 100% of females participated in reproduction. A total of 79% of males and 92% of females mated with multiple partners (only 1 sire and 1 dam were monogamous), indicating that polygynandry best described the genetic mating system of black sea bream. For males, maximizing the reproductive success by multiple mating was accorded with the sexual selection theory while the material benefits hypothesis may contribute to explain the multiple mating for females. For both sexes, there was a significant correlation between mating success and reproductive success and the variance in reproductive success of males was higher than females. Variation in mating success is the greatest determinant to variation in reproductive success when the relationship is strongly positive. The opportunity for sexual selection of males was twice that of females, as well as the higher slope of the Bateman curve in males suggested that the intensity of intrasexual selection of males was higher than females. Thus, male–male competition would lead to the greater variation of mating success for males, which caused greater variation in reproductive success in males. The effective population number of breeders (N_b) was 33, and the N_b/N ratio was 0.61, slightly higher than the general ratio in polygynandrous fish populations which possibly because most individuals mated and had offspring with a low variance. The relatively high N_b contributes to the maintenance of genetic diversity in farmed black sea bream populations.     

CORRELATED INBREEDING AMONG RELATIVES: OCCURRENCE,MAGNITUDE, AND IMPLICATIONS

Understanding the magnitude and causes of genetic and phenotypic resemblance among relatives is key to understanding evolutionary processes. Contrary to basic expectation, individual coefficients of inbreeding ( f) were recently hypothesized to be intrinsically correlated across parents and offspring in structured populations, potentially creating an additional source of phenotypic resemblance in traits that show inbreeding depression. To test this hypothesis, we used individual‐based simulations to quantify the parent–offspring correlations in f arising under random mating in populations of different size, immigration rate, and mating system. Parent–offspring correlations in f were typically positive (median r≈ 0.2–0.4) in relatively small and isolated populations. Relatively inbred parents therefore produced relatively inbred offspring on average, although the magnitude of this effect varied considerably among replicate populations. Correlations were higher given more generations of random mating, greater variance in reproductive success, polygynous rather than monogamous mating, and for midparent–offspring rather than parent–offspring relationships. Furthermore, f was also positively correlated across half‐siblings, and closer relatives had more similar inbreeding coefficients across entire generations. Such intrinsic resemblance in f among relatives could provide an additional genetic benefit of mate choice and bias quantitative genetic analyses that do not account for correlated inbreeding depression.     

The importance of pre-mating barriers and the local demographic context for contemporary mating patterns in hybrid zones of Eucalyptus aggregata and Eucalyptus rubida

The frequency of hybridization in plants is context dependent and can be influenced by the local mating environment. We used progeny arrays and admixture and pollen dispersal analyses to assess the relative importance of pre‐mating reproductive barriers and the local demographic environment as explanations of variation in hybrid frequency in three mapped hybrid zones of Eucalyptus aggregata and E. rubida. A total of 731 open‐pollinated progeny from 36 E. aggregata maternal parents were genotyped using six microsatellite markers. Admixture analysis identified substantial variation in hybrid frequency among progeny arrays (0–76.9%). In one hybrid zone, hybrid frequency was related to pre‐mating barriers (degree of flowering synchrony) and demographic components of the local mating environment (decreasing population size, closer proximity to E. rubida and hybrid trees). At this site, average pollen dispersal distance was less and almost half (46%) of the hybrid progeny were sired by local E. rubida and hybrid trees. In contrast, at the other two sites, pre‐mating and demographic factors were not related to hybrid frequency. Compared to the first hybrid zone where most of the E. rubida (76%) and all hybrids flowered, in the remaining sites fewer E. rubida (22–41%) and hybrid trees (0–50%) flowered and their reproductive success was lower (sired 0–23% of hybrids). As a result, most hybrids were sired by external E. rubida/hybrids located at least 2–3 km away. These results indicate that although pre‐mating barriers and local demography can influence patterns of hybridization, their importance can depend upon the scale of pollen dispersal.     

Characterization of age and cuticular hydrocarbon variation in mating pairs of house fly,Musca domestica,collected in the field

House flies, Musca domestica L., were collected in copula over two summers from six dairies located in three climatically distinct regions in the U.S.A. southern California, Minnesota and Georgia. Ages of males and females from a total of 511 mating pairs were estimated using pterin analysis. Cuticular hydrocarbon profiles and gonotrophic ages of females also were evaluated. Mean age of mating males ranged from 54 to 102 degree‐days (DD) (4–10 days based on field air temperatures), depending on the farm. Very young males (< 10–20 DD) and old males (> 200 DD) were rare in mating pairs. Mean female age at mating ranged from 20 to 46 DD (2.5–4 days). All mating females had eggs in the early stages of vitellogenesis and 99.2% were nulliparous. However, some older and parous females were collected, demonstrating that re‐mating can occur in the field. Head width measurements of mating pairs suggested that assortative mating by size did not occur. The cuticular hydrocarbon profiles of females were determined, with emphasis on (Z)‐9‐tricosene (muscalure). Overall, only 55% of mating females had detectable amounts (> 4 ηg per fly) of (Z)‐9‐tricosene. Of the females that had detectable (Z)‐9‐tricosene, variation in amount per female was high in all fly populations, and thus was not statistically related to the size or age of the mating female. The proportion of mating females with detectable levels of (Z)‐9‐tricosene varied by geographic region. Seventy‐one, 63, and 27% of females from southern California, Minnesota and Georgia had detectable amounts of (Z)‐9‐tricosene. Principal components analysis of the eight most abundant hydrocarbons from mating females, by state, revealed state‐level distinctiveness of hydrocarbons in house fly populations, which may reflect genetic variation associated with environmental stresses in those geographical zones.     

Delayed mating and reproduction in the autumn gum moth Mnesampela privata

• 1 The success of mating disruption using synthetic sex pheromones depends not only on preventing mating, but also on delaying mating in the target insect. Using the geometrid pest of Eucalyptus plantations, Mnesampela privata (Guenée), we determined the effect of delaying mating when imposed on males only, females only or on both sexes simultaneously, for 1, 3, 5 and 7 days.
• 2 Delayed mating had a significant negative impact on reproduction, with a 0.89‐fold decrease in the likelihood of mating and a 0.67‐fold decrease in the likelihood of that mating resulting in fertile eggs for every day that mating is delayed. A mating delay of 7 days reduced the mean number of viable eggs laid to 4–13% of that laid by moths paired immediately after emergence.
• 3 Male only imposed mating delays had a significantly lower effect on reducing the likelihood of pairs mating than when both sexes were delayed. A delay imposed on one sex only or on both sexes simultaneously, however, had a similar negative impact on the proportion of fertile matings as well as on the total number of fertile eggs laid.
• 4 Longevity of mated female and male M. privata was significantly different between mating delay treatments, with a significant decline in female longevity when they mated with older males.
• 5 The underlying mechanisms causing a decline in female reproductive output when a mating delay was imposed on males versus females are discussed in relation to the reproductive biology of M. privata and the potential of using mating disruption strategies to control populations in Eucalyptus plantations.

     

Female‐borne cues affecting Psyttalia concolor (Hymenoptera: Braconidae) male behavior during courtship and mating

Knowledge of the mechanisms that regulate courtship and mating behavior in Psyttalia concolor (Szépligeti)–a koinobiont endophagous solitary parasitoid of the olive fruit fly, Bactrocera oleae (Rossi), and of other fruit flies–is essential to its mass rearing and management. Augmentative releases of P. concolor for olive fruit fly control started in the Mediterranean areas in the 1950s and still continue with limited success. We determined the influence of visual and chemical cues on courtship and mating behavior of this braconid and the possible effect of the mating status of males and females in the perception of these cues. Our results suggest that integration of visual and chemical stimuli are fundamental for mate location and courtship. Indeed, the optimal response of the male was achieved when physical and chemical cues were simultaneously presented and vision and olfaction worked synergistically.     

CHLOROPLAST INHERITANCE IN COSMARIUM TURPINII BRÉB.

Chloroplast inheritance was studied in Cosmarium turpinii Bréb. with respect to both vegetative and zygotic transmission. Analyses were carried out on (1) reciprocal haploid x diploid crosses with respect to the number and size of the zygotic chloroplasts, (2) differential survival of chloroplasts in hypnospores of different mating type strains, and (3) the position of the chloroplasts in diploid zygotes. Morphological evidence indicates that the chloroplasts in the mature zygote are derived from the (+) mating type gamete with an infrequent contribution from the (–) mating type gamete. Additional evidence suggests that the chloroplast material of each of 2 Bones arising from the zygote is derived from the plastid material of a semicell of a gamete. Differential survival of the chloroplasts is interpreted as a result of physiological differences between cells of complementary mating types.     

How many daddies: microsatellite genotyping reveals polyandry in a live‐bearing clinid fish Muraenoclinus dorsalis

Fishes belonging to the family Clinidae in South Africa display super‐embryonation, a rare reproductive mode were females gestate broods at different gestational stages, but little is known regarding the mating systems of this family. Here we tested the hypothesis that multiple males would contribute not only to the offspring of each female, but that several males would contribute to each brood, by sampling Muraenoclinus dorsalis from three sampling locations along the west and south‐west coast of South Africa. Larval (n = 97) and maternal (n = 14) genotpyes, generated with newly developed microsatellites, were used to estimate the number of potential mates per female. Our results show that up to 78% of females displayed multiple mating with an average of 2·1–2·2 males. In addition, 39–42% of females displayed polyandry with an average of 1·5–1·6 sires per brood. This study provides the evidence for multiple mating and polyandry within a clinid fish characterized by super‐embryonation that offers important baseline information regarding rare reproductive strategies, highlighting several gaps in our knowledge concerning clinid reproduction and mating systems.     

SEXUAL REPRODUCTION IN PANDORINA UNICOCCA1

The effects of nutrients and light on sexual reproduction were investigated in 2 mating pairs of Pandorina unicoca. Strains 101–104 required nitrogen deficiency for sexual differentiation. Sulfur deficiency also appeared to be effective in evoking sexual differentiation. The time required for sexual differentiation of strains 103–104 after removal of KNO₃ and MgSO from the medium was 24 hr. Addition of KNO₃ and MgSO₄ after 24hr did not reverse sexual differentiation. Light was required during the first 10–12 hr. Strains 105–106 did not require a period of sexual differentiation and, exhibited mating activity in the presence of nitrogen and sulfur in the medium. Both mating pairs required light for the mating response and calcium was necessary for zygote formation. The pH range for mating activity was determined.     

MATING PREFERENCE AND ITS RELEVANCE TO ADAPTATION IN DROSOPHILA MELANOGASTER: INVERSION POLYMORPHISM AND DDT RESISTANCE

The importance of adult mating success as a component of fitness influencing inversion polymorphism in two DDT-resistant populations of Drosophila melanogaster was investigated. The polymorphism involved In(3R)P and the Standard (St) gene arrangement. In population 731R the St/St females showed greater mating propensity than In/In females, while in population J2 the In/In females showed a significant positive association between mating propensity and the percentage of St/St males present. Mating preference data showed that St/St males were selectively favored over In/In males in both populations. No differences were observed between St/St and St/In karyotypes in either population. Frequency-dependent mating in the form of a rare male mating disadvantage for the In/In males tested against the St/St males in 731R was observed; the St/St males in this case showed a marginally significant rare male mating advantage. Thus, mating success as well as previously measured fecundity and fertility all indicate a selective advantage of the St chromosome over the In chromosome in both populations. This fitness relationship does not predict the equilibrium condition of 70–80% St/In, 20–30% In/In, and 0–10% St/St found in the DDT environment, whereas previously collected larval viability data and estimated adult survivorship do. In at least one population (731R), the adult mating success data do predict the dynamics of the polymorphism in the absence of DDT, whereas viability does not. These results, although limited to two populations under two environments (presence or absence of DDT), suggest that the relationship between adaptation to the environment under study and various components of fitness needs to be investigated fully before assessing which fitness components are most important in determining the effects of natural selection in specific populations.     

–SH and S–S involvement in Chlamydomonas mating

Reagents that block or cross-link sulfhydryl (–SH) groups and those that reduce disulfide (S–S) bonds have been tested for their effects on mating in Chlamydomonas reinhardii. Wild-type (wt) gametes of mating type + (mt⁺) and mt^?, and a fusion-defective mt^? mutant, gam-11, were studied. Differential sensitivities of mt⁺ vs mt^? and of wt mt^? vs gam-11 mt^? were analyzed. Concentrations of reagents that did not disrupt flagellar agglutination, the first stage of the mating reaction, were generally used. Pretreatment of mt⁺ gametes with the membrane permeable –SH reducing agent dithiothreitol (DTT) inhibits flagellar sexual signaling at concentrations that do not inhibit any part of the mating reaction of mt^? gametes. Wt mt^? is more sensitive than wt mt⁺ to inhibition by low concentrations of p-chloromercuribenzoate sulfonate (pCMBS), an organic mercurial. The membrane-impermeable reducing agent, reduced glutathione (GSH), also preferentially inhibits wt mt^?. Gam-11 mt^?, a fusion-defective mutant, which has been used to study the sensitivity of the adhesion of the plasma membrane-associated mating structures, is less sensitive to GSH and pCMBS inhibition that is wt mt^?. DDT and pCMBS cause an increase in mating structure adhesion in pretreated gam-11. The differential inhibition of pair and group formation during gam-11 × wt mt⁺ matings has suggested a possible mechanism for mating structure adhesion.     

Reproductive biology,multiple paternity and polyandry of the bull shark Carcharhinus leucas

To improve understanding of bull shark Carcharhinus leucas reproductive biology, we analysed reproductive traits from 118 bull sharks caught along Reunion Island coasts (Western Indian Ocean), including 16 gravid females. Specific microsatellite loci were used to investigate the frequency of multiple paternity. Males and females reached maturity at c. 234 cm and 257 cm total length (L_T), respectively, and litter sizes ranged from 5 to 14 embryos. Analysis of the 16 litters collected in various months of the year indicated that parturition occurs between October and December, with a size at birth c. 60–80 cm L_T and that the gestation period is probably c. 12 months. Assuming a 1 year resting period and a period of sperm storage (4–5 months) between mating (in June–September) and fertilisation, the reproductive cycle of bull sharks at Reunion Island would be biennial. At least 56.25% of the litters investigated were polyandrous, sired by 2–5 males. Several males that each sired several litters conceived during the same or distinct mating seasons were detected, suggesting both a seasonal aggregation of sharks to mate and some male fidelity to mating site. Altogether, these findings provide valuable information for both shark risk management and conservation of the species in the Western Indian Ocean.     

Mechanisms of reinforcement in natural and simulated polymorphic populations

Reinforcement speciation is the process whereby selection against hybrids drives the evolution of enhanced pre‐mating reproductive isolation. Work has focused on divergent mating preferences (assortative mating) but pre‐mating isolation can also arise via various migration modification behaviours, such as divergent habitat preferences. The relative importance of these two different mechanisms of reinforcement remains unclear. A recent theoretical model (Yukilevich–True model) found that relative fixation probabilities between these mechanisms can vary. Additionally, natural populations of Timema cristinae walking‐sticks exhibit variation (polymorphism) in both mechanisms, generating questions about the patterns expected for allele frequencies prior to fixation, during the early stages of the speciation process. In the present study, we report: (1) new analyses examining the correlation between fixation probabilities for assortative mating and migration modification in the Yukilevich–True model; (2) novel simulations examining allele frequencies in polymorphic populations; and (3) empirical patterns of reinforcement in T. cristinae in the context of theoretical predictions. Simulations of both types yielded congruent results, revealing that the outcome of reinforcement was dependent on the strength of selection. Under weak selection, reinforcement by either mechanism is unlikely. Under intermediate selection, the conditions favoring the rise and fixation of one mechanism favored the rise and fixation of the other. However, assortative mating evolved somewhat more readily than migration modification. Populations of T. cristinae, which experience such intermediate selection, supported these predictions. Under strong selection, the evolution of migration modification generally interfered with the evolution of assortative mating by decreasing migration between populations, thereby reducing selection for assortative mating. Congruence of the results for allele frequencies versus fixation probabilities suggests that similar patterns of reinforcement are expected during different stages of the speciation process. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 305–319.     

Reduction in the attraction of males to females after mating in the rice leaf bug Trigonotylus caelestialium

The influence of mating on the extent to which males are attracted to females in Trigonotylus caelestialium (Heteroptera: Miridae) was examined. No differences in attraction of males to mated and virgin females were observed within 3–5 h of mating, but males became less attracted to females 1 to 2 days after the first mating. The difference in male attraction to mated vs virgin females disappeared at 4 days after mating. These results indicate that reduced attraction of males to mated females occurs after a certain time interval, and persists for a few days. Furthermore, males were less attracted to females that had mated with virgin vs recently mated males, i.e. males that had just mated with another female at 1 and 2 days after mating. The ejaculate expenditure of recently mated males was less than that of virgin males. Hence, the amount of male ejaculate transferred to females during mating, rather than the act of mating, might influence the attraction of males to females. The results demonstrate that mating reduces the attraction of males to females in T. caelestialium on the basis of direct observation of male behavior.     

Vibratory Communication in the Jumping Spider Phidippus clarus: Substrate‐borne Courtship Signals are Important for Male Mating Success

Recently, work has shown that multimodal communication is common throughout the animal kingdom but the function of multimodal signals is still poorly understood. Phidippus clarus are jumping spiders in which males produce multimodal (visual and vibrational) signals in both male–male (aggressive) and male–female (courtship) contexts. The P. clarus mating system is complex, with sex ratios and the level of male competition changing over the course of the breeding season. Vibrational signal components have been shown to function in male aggressive contests but their role in courtship has not been investigated. Here, we performed an experiment to test the role of vibrational signaling in courtship by observing mating success for males that were experimentally muted. We show that vibratory courtship signals, and in particular signaling rate, is an important component of mating success and potentially a target of female choice. While the ability to produce vibratory signals significantly increased mating success, some muted males were still able to successfully mate. In these trials, signaling rate also predicted mating success suggesting that redundant signal components may compensate for errors and perturbations in signal transmission or that vibratory signals function to enhance the efficacy of visual signals.     

REPRODUCTIVE ISOLATION BY SEX PHEROMONES IN THE CLOSTERIUM PERACEROSUM–STRIGOSUM–LITTORALE COMPLEX (ZYGNEMATALES,CHAROPHYCEAE)1

The Closterium peracerosum–strigosum–littorale (C. psl.) complex consists of unicellular algae and is known to be composed of several reproductively isolated mating groups of heterothallic strains. Group I‐E is completely isolated from mating groups II‐A and II‐B, groups II‐A and II‐B are partially isolated from each other, and only mating‐type plus (mt⁺) cells of group II‐A and mating‐type minus (mt^?) cells of group II‐B form zygotes. Based on the alignment of 1506 group I introns, significant phylogenetic relationships were observed among mating groups II‐A and II‐B, while mating group I‐E was distant from groups II‐A and II‐B. Sexual cell division in both mating‐type cells of group II‐A was stimulated in conditioned media in which cells of group II‐B had been cultured. When mt^? cells of group II‐B were stimulated in conditioned medium derived from group II‐A, mt⁺ cells of group II‐B did not respond to the conditioned medium. Conditioned media derived from group I‐E did not exhibit sexual cell division (SCD)–inducing activity against any strain except those within its own group. From the alignment of deduced amino acid sequences from orthologous protoplast‐release‐inducing protein (PR‐IP) Inducer genes, we detected a significant similarity among groups II‐A and II‐B, and mating group I‐E had low similarity to other mating groups. The existing degree of reproductive isolation can be partially explained by differences in molecular structures and physiological activities of sex pheromones of these heterothallic mating groups.