Number Of Matings Research Articles

Revisiting the variance-based selection model of diploid drone production for multiple mating in honey bees

The high number of mates of honeybee queens has lead to the proposal of several adaptive explanations. The competing hypotheses to explain multiple mating in honeybees and some other social insects have been mostly evaluated empirically with comprehensive theoretical analysis lacking behind. We report on the mathematical analysis of the diploid drone hypothesis for multiple mating, which suggests that multiple mating evolved as a safeguard against the production of infertile male offspring. In accordance with earlier models, our analysis shows that multiple mating does not reduce the average value of diploid drone production but reduces its variance. We combine this observation with a colony growth model to assess the impact of this reduction in variance to the colony fitness. Considering a plausible parameter space for the honeybee, we conclude that the reduction in variance of diploid drone production can be a significant selective force for multiple mating. We have also described rules of a game for which a problem of finding the best strategy is equivalent to the above biological problem of bee mating. We made a significant progress in the general solution of this game and conjectured that the best strategy is strongly related to the geometry of rational numbers.

The sex lives of parasites: Investigating the mating system and mechanisms of sexual selection of the human pathogen Schistosoma mansoni

The mating systems of internal parasites are inherently difficult to investigate although they have important implications for the evolutionary biology of the species, disease epidemiology, and are important considerations for control measures. Using parentage analyses, three topics concerning the mating biology of Schistosoma mansoni were investigated: the number of mates per adult male and female, variance in reproductive success among individuals, and the potential role for sexual selection on male body size and also mate choice for genetically dissimilar individuals. Results indicated that schistosomes were mostly monogamous, and evidence of only one mate change occurred over a period of 5–6weeks. One male was polygynous and contained two females in its gynecophoral canal although offspring were only detected for one of the females. Even though they were primarily monogamous and the sex ratio near even, reproductive success was highly variable, indicating a potential role for sexual selection. Male body size was positively related to reproductive success, consistent with sexual selection via male–male competition and female choice for large males. However, relatedness of pairs was not associated with their reproductive success. Finally, genetically identical individuals differed significantly in their reproductive output and identical males in their body size, indicating important partner and environmental effects on these traits.

THE EVOLUTION OF DOMINANCE IN SPOROPHYTIC SELF-INCOMPATIBILITY SYSTEMS. II. MATE AVAILABILITY AND RECOMBINATION

Sporophytic self-incompatibility (SSI) is a self-pollen recognition system that enforces outcrossing in plants. Recognition in SSI systems is typically controlled by a complex locus (S-locus) with separate genes that determine pollen and stigma specificity. Experimental studies show that S-alleles can be dominant, recessive, or codominant, and that the dominance level of a given S-allele can depend upon whether pollen or stigma specificity is examined. Here and in the companion paper by Llaurens and colleagues, the evolution of dominance in single-locus SSI is explored using numerical models and simulation. Particular attention is directed at factors that can cause S-allele dominance to differ in pollen versus stigma. The effect of recombination between the S-locus and modifier locus is also examined. The models predict that limitation in the number of compatible mates is required for the evolution of S-allele dominance in the stigma but not in the pollen. Tight linkage between the S-locus and modifier promotes the evolution of S-allele dominance hierarchies. Model results are interpreted with respect to published information on the molecular basis of dominance in SSI systems, and reported S-allele dominance relationships in a variety of species. These studies show that dominant S-alleles are more common in the pollen than in the stigma, a pattern that when interpreted in light of model predictions, suggests that mate limitation may be relatively infrequent in natural populations with SSI.

Female mate choice across spatial scales: influence of lek and male attributes on mating success of blue-crowned manakins.

Lekking males compete for females within and among leks, yet female choice is expected to work differently at each of these spatial scales. We used paternity analyses to examine how lek versus male attributes influence mate choice in the blue-crowned manakin Lepidothrix coronata. We tested the hypotheses that females prefer (i) to mate at larger leks where a larger number of potential mates can be assessed, (ii) to mate with unrelated or highly heterozygous males expected to produce high-quality offspring, (iii) to mate with males that display at higher rates, and that (iv) display honestly reflects male genetic quality. Our results show that (i) males at larger leks are not more likely to sire young, although females nesting close to small leks travel further to reach larger leks, (ii) siring males are not less related to females or more heterozygous than expected, (iii) within a lek, high-display males are more likely to sire young, and (iv) both male heterozygosity and display rate increased with lek size, and as a result display does not reliably reflect male genetic quality across leks. We suggest that female mate choice in this species is probably driven by a Fisherian process rather than adaptive genetic benefits.

TESTS OF SEX ALLOCATION THEORY IN SIMULTANEOUSLY HERMAPHRODITIC ANIMALS

Sex allocation is a crucial life-history parameter in all sexual organisms. Over the last decades a body of evolutionary theory, sex allocation theory, was developed, which has yielded capital insight into the evolution of optimal sex allocation patterns and adaptive evolution in general. Most empirical work, however, has focused on species with separate sexes. Here I review sex allocation theory for simultaneous hermaphrodites and summarize over 50 empirical studies, which have aimed at evaluating this theory in a diversity of simultaneous hermaphrodites spanning nine animal phyla. These studies have yielded considerable qualitative support for several predictions of sex allocation theory, such as a female-biased sex allocation when the number of mates is limited, and a shift toward a more male-biased sex allocation with increasing numbers of mates. In contrast, many fundamental assumptions, such as the trade-off between male and female allocation, and numerous predictions, such as brooding limiting the returns from female allocation, are still poorly supported. Measuring sex allocation in simultaneously hermaphroditic animals remains experimentally demanding, which renders evaluation of more quantitative predictions a challenging task. I identify the main questions that need to be addressed and point to promising avenues for future research.

ADAPTIVE PLASTICITY OF THE PENIS IN A SIMULTANEOUS HERMAPHRODITE

Acorn barnacles are important model organisms for the study of sex allocation. They are sessile, nonselfing hermaphrodites that copulate with penises that have been suggested to be phenotypically plastic. On wave-exposed shores, Semibalanus balanoides develop penises with relatively greater diameter whereas in wave-protected sites they are thinner. A reciprocal transplant experiment between wave-exposed and protected sites tested whether these exposure-specific morphologies have adaptive value. Mating success was compared over a range of distances to compare the ability of barnacles to reach mates. Barnacles that grew in the wave-protected site and mated in the wave-protected site fertilized more broods at increasing distances than those transplanted to the wave-exposed site. For barnacles that developed in the wave-exposed site, there was no difference in the ability to fertilize neighbors between sites of differing exposure. This study demonstrates the adaptive value of plasticity in penis morphology. The results suggest a trade-off between development of a penis adapted to wave exposure and the ability to fertilize distant mates. Barnacles in different physical environments are limited by different factors, which may limit numbers of potential mates, constrain optimal sex allocation strategies and alter reproductive behavior.

Seasonal changes in humidity level in the tropics impact body color polymorphism and desiccation resistance in Drosophila jambulina—Evidence for melanism-desiccation hypothesis

Drosophila jambulina exhibits color dimorphism controlled by a single locus but its ecological significance is not clear. Dark and light morphs differ significantly in body melanisation, desiccation resistance, rate of water loss, mating activity and fecundity. Interestingly, this species lacks clinal variation for body size, desiccation resistance and life history traits. For body melanisation, lack of geographical variation as well as plastic effects is not in agreement with a thermal melanism hypothesis. However, based on field data, there are seasonal changes in phenotypic frequencies of dark and light body color morphs which correlate significantly with variation in humidity levels. Under short-term (8 h) desiccation stress, we observed higher number of assortative matings, longer copulation period and increased fecundity for dark strains as compared with light strains. By contrast, both the morphs when exposed to high humid conditions exhibited higher assortative matings and fecundity for light strains as compared with dark strains. In tropical populations of D. jambulina, body color polymorphism seems to be maintained through humidity changes as opposed to thermal melanism. Thus, seasonal changes in the frequency of body color morphs in this tropical species supports melanism-desiccation hypothesis.

Determinants of mating and sperm‐transfer success in a simultaneous hermaphrodite

The number of mating partners an individual has within a population is a crucial parameter in sex allocation theory for simultaneous hermaphrodites because it is predicted to be one of the main parameters influencing sex allocation. However, little is known about the factors that determine the number of mates in simultaneous hermaphrodites. Furthermore, in order to understand the benefits obtained by resource allocation into the male function it is important to identify the factors that predict sperm-transfer success, i.e. the number of sperm a donor manages to store in a mate. In this study we experimentally tested how social group size (i.e. the number of all potential mates within a population) and density affect the number of mates and sperm-transfer success in the outcrossing hermaphroditic flatworm Macrostomum lignano. In addition, we assessed whether these parameters covary with morphological traits, such as body size, testis size and genital morphology. For this we used a method, which allows tracking sperm of a labelled donor in an unlabelled mate. We found considerable variation in the number of mates and sperm-transfer success between individuals. The number of mates increased with social group size, and was higher in worms with larger testes, but there was no effect of density. Similarly, sperm-transfer success was affected by social group size and testis size, but in addition this parameter was influenced by genital morphology. Our study demonstrates for the first time that the social context and the morphology of sperm donors are important predictors of the number of mates and sperm-transfer success in a simultaneous hermaphrodite. Based on these findings, we hypothesize that sex allocation influences the mating behaviour and outcome of sperm competition.

Social Dominance and Courtship and Mating Behaviour in Rams in Non‐Competitive and Competitive Pen Tests

A group of 19 Merino rams was used to determine: (i) if body weight, age and testis characteristics are different between high (HR) and low-ranked (LR) rams, and (ii) how the competition between HR and LR rams for oestrous ewes affect their courtship and mating behaviour. Hierarchy was determined using the food competition test. The five first and five last ranked rams were individually exposed to oestrous ewes in pen tests, and the frequency of different courtship behavioural units, mounts and mates, and the time from test onset to each mate was recorded. The sexual behaviour of the five first ranked and the five last ranked rams was also tested in competition, pairing a HR and a LR ram. Age, body weight, body condition score, scrotal circumference, and testis firmness and resilience from HR and LR were not different. The display of courtship behavioural units was lower when rams were tested in competition but was not affected by the rank of the rams. The number of mates per test from HR rams was lower than that observed in LR rams when tested alone. While the number of mates decreased in LR rams in competition tests, it was not affected in HR rams. In summary, there was no relation between social rank and body weight, age or testis characteristics. LR rams were more effective than HR rams when mating oestrous ewes without competition. However, in competitive tests, although all rams modified their courtship strategies, LR rams were more affected by the presence of dominant rams than HR rams were by the presence of LR rams.

Hybridization behaviour between two common European cyprinid fish species – silver bream, Blicca bjoerkna and common bream, Abramis brama – in a controlled environment

Abstract The egg release–mating comparison, heterospecific matings and mating success under two hybridization conditions – (i) mixing one sex per species and (ii) mixing both sexes from each species – were investigated to determine whether silver bream Blicca bjoerkna and common bream Abramis brama can hybridize in nature.The results revealed that non-matings in hybridization experiments of silver bream females × common bream males can be explained by territorial and aggressiveness activities observed in common bream. In common bream females × silver bream males, heterospecific matings were observed but their numbers were significantly lower than the spawning numbers, and in this experiment, a female mated with one to four heterospecific males. In mixing both sexes from both species, similar spawning – mating numbers were observed but heterospecific matings accounted for only 27% of the total matings, with 24% accounting for heterospecific matings between common bream females and silver bream males, directly or by opportunism. Mating success was characterized by the occurrence of fertilized eggs after matings.Natural hybridization occurred preferentially between common bream females and silver bream males.

The lek mating system of Hetaerina damselflies (Insecta: Calopterygidae)

Summary We investigated whether territorial males of Hetaerina damselflies show lekking behaviour using experimental techniques and observations: (i) we altered potential vegetation substrates to determine whether this affected the number of female visitations and matings; (ii) by removing territorial males and allowing other males to occupy the territory, we determined whether females changed their visitation and mating number; (iii) we observed whether vegetation substrates were present and used, and whether lighting conditions affected male territorial behaviour; (iv) we documented female pre- and post-copulatory behaviour to examine whether female choice occurred; and (v) we investigated whether male traits were linked to mating success. Our results revealed that (1) vegetation substrates were rarely found in territories and even when vegetation was present, it did not affect female visitation and mating number; (2) males constantly moved to more illuminated places and females had little opportunity to exert choice due to harassment from males; (3) females oviposited outside territories; and (4) males with larger wing pigmentation and body size obtained a larger mating number because they were more likely to acquire a territory and/or displace other males while in tandem. This is the first documented evidence that odonate males display a lek mating system.

Can protected mountain areas serve as refuges for declining amphibians? Potential threats of climate change and amphibian chytridiomycosis in an alpine amphibian population

In June 2004 and June 2005, we checked 40 and 134 ponds respectively for alive and dead alpine newts, common toads, common frogs, and their clutches on the “Kirchfeld” plateau in the Northern Limestone Alps of Austria. We found several hundred dead common frogs and alpine newts in the two consecutive years and also observed an unusually high number of heterospecific matings between common toads and common frogs in 2004. In order to test whether the observed mortalities were caused by disease, we screened 98 individuals of the three species for chytridiomycosis, a highly infective fungal disease, in 2008. All samples proved to be negative. We therefore assume that the high losses for the common frog population (26 % in 2004 and 9 % in 2005) during the spring migration, as well as the breakdown of the temporal premating isolation between the common frog and common toad, were caused by temperature anomalies alone, i.e. sudden low temperatures after a warm spring period. The high number of dead alpine newts found in 2005 was negatively correlated to the oxygen saturation of the ponds, frequently covered by ice during the early breeding season. We discuss the possible effects of climate change on phenological timing, breeding isolation and chytridiomycosis in alpine amphibian populations. 19

Double and Triple Matings Associated with Reproductive Performance in First-Serviced and Reserviced Female Pigs in Commercial Herds

The objective of this study was to investigate associations of the number of matings and services with reproductive performance in high-performing and ordinary herds. The data included 113,265 service and 92,248 farrowing records in 117 herds. A service included single or more matings of a female pig (female) during a 10-day estrus period. Two herd groups were built on the basis of the upper 25th percentile of pigs weaned per mated female per year: high-performing (> or = 22.8 pigs) and ordinary herds. Mixed-effects models were used to analyze reproductive performance. Relative frequencies (%) of single, double and triple or more matings were 3.4, 27.4, and 69.2% in high-performing herds, respectively, and were 4.6, 59.3 and 36.1% in ordinary herds, respectively. Percentages of reserviced females in high-performing and ordinary herds were 7.3 and 13.0%, respectively. Triple or more-mated (TM) gilts had 3.5% higher farrowing rates than double-mated (DM) gilts (P<0.01), but similar pigs born alive (PBA) to DM gilts in the first service group in both the herd groups. In the first service group, TM sows had 0.8% higher farrowing rates and 0.2 more PBA than DM sows in high-performing herds (P<0.01). In the reservice group, TM gilts and TM sows had farrowing rate similar to DM gilts and DM sows in high-performing herds. In conclusion, performing triple matings was a better practice for first-serviced females than performing double matings. Double matings may be sufficient for reserviced females.

Decision-making in group departures of female domestic geese

AbstractGroup-living animals have to make trade-offs to reach consensus and travel together. We investigated the recruitment processes underpinning decision-making at departure in a group of 20 female domestic geese (Anser domesticus) kept in semi-free-range conditions. Two observers continuously videotaped the behaviours of the birds. Data were analyzed using multiple regression analyses. We found that decision-making was a continuous and distributed process. Departure was preceded by an increase in the arousal state of group members and their initial orientation influenced recruitment. Patterns of group movement could be predicted from the behaviours of individuals before departure. Individuals' locations, moves and signals could act as passive or communicative cues. A higher number of vocalisations and arousal behaviours led to a larger number of individuals recruited. Some individuals were more efficient than others in recruiting followers but any geese could initiate a movement. First movers recruited a higher number of mates when they had a greater number of neighbours. Not only the first mover but also the behaviours of the second and third movers prompted further individuals to follow. There was no evidence that geese were able to intentionally recruit others, rather they synchronized and adjusted each other's motives until reaching a consensus.

Another genetically promiscuous ‘polygynous’ mammal: mating system variation in Neotoma fuscipes

Polygyny is widely thought to be the dominant mating system in mammals. However, more recent genetic work casts doubt on this view. Variation in mating systems has been found in both males and females within and across mammalian species. The causes and consequences of mating system variation have important implications for understanding the population and evolutionary dynamics of species. To better understand mating system variation, both in mammals and more generally, this study analyses genetic mating system variation in dusky-footed woodrats, Neotoma fuscipes. Contrary to expectation, there was little support for polygyny at the genetic level. Instead, the study populations were characterized by promiscuity and monogamy, in both males and females. At higher densities, variance in the numbers of mates and offspring were higher in breeding males than in females, as is often observed. However, this trend was reversed in low-density, coniferous forest habitat. Model selection revealed that the best model of successfully mated pairs includes population density, operational sex ratio and individual pairwise distances as predictors. Higher densities coupled with male-biased sex ratios appear to decrease the probability of mating and decrease opportunities for polygamy, particularly in females. Although woodrats display sexual size dimorphism, male body size had no detectable effect on mating success. This study questions the prevalence of polygyny in mammals and demonstrates the need for more detailed, genetic investigations of mating systems. Future studies are needed to explore the complex interactions among mating system determinants and test hypotheses of sex-specific mating system variation.

Analysis of body size and fecundity in a grasshopper

We used linear regression, nonlinear regression and principal component analysis to examine the relationships among morphology, fecundity, and mating variables for lab-reared adult female Romalea microptera (Beauvois) (fam. Romaleidae) grasshoppers. Morphological variables included head width, pronotum length, femur length, adult eclosion mass, maximum mass reached before the 1st oviposition, and maximum mass reached before the 2nd oviposition. Fecundity (= reproductive) variables included clutch size Pod 1, clutch size Pod 2, total eggs Pods 1 2, mass Pod 1, mass Pod 2, time between adult eclosion and Pod 1, time between Pod 1 and Pod 2, and time between eclosion and Pod 2. Mating variables included number of matings and age of 1st mating. Most morphological variables were strongly positively correlated, and morphological variables (especially femur length, eclosion mass, and maximum body mass reached prior to oviposition) predicted many fecundity variables. Maximum body mass reached prior to laying Pod 1 was highly correlated with maximum body mass reached prior to laying Pod 2 (r =0 .93), and clutch size Pod 1 predicted clutch size Pod 2 (r = 0.72). However, time to oviposit (= interval between adult eclosion and oviposition) was generally unrelated to body size, body mass, or clutch size or mass. Hence, clutch size and pod mass are strongly determined by body size and mass at adult eclosion, but timing of oviposition is independent of body size and mass at eclosion. The results also suggest that early mating speeds oviposition, but that excessive mating reduces female fecundity, as measured by clutch size.

Effects of body size and shape on mating frequency in the brachypterous grasshopper Podisma sapporensis

In many insect species, males with larger body sizes are more successful at securing mates. Previous studies on the brachypterous grasshopper Podisma sapporensis have shown that male mating frequency varies greatly among populations. Here we test the hypothesis that differences in male mating success among populations are linked to differences in body size and shape. To do so, we collected males and females from three localities and conducted cross-breeding experiments. Overall, we found no link between mean male body size and mean number of matings across populations. However, stepwise regression indicates that within the populations, males with longer thoraxes and shorter hind femurs, mated more frequently, whereas females with longer thoraxes mated more frequently. These results suggest that in males, having short hind femurs, relative to body size, rather than body size itself, contributes positively to mating success — perhaps because of an advantage in holding onto females while avoiding females' resistance.

Female preference for male phenotypic traits in a fiddler crab: do females use absolute or comparative evaluation?

While mate choice is often assumed to be based on an absolute value that may reflect underlying male quality, many mating systems facilitate the comparative evaluation of males. Females can encounter a number of potential mates, either sequentially or simultaneously, before making a mate choice decision. Consequently, the attractiveness of one male may depend on the attractiveness of other males a female has previously encountered. To examine whether female choice in the fiddler crab Uca mjoebergi is based on the comparative evaluation of males, I altered the social context in which a set of males were encountered. Using a robotic crab system to manipulate claw size and wave rate directly, I determined female preference for two male options in the absence and presence of an asymmetrically dominating decoy option. The decoy male option was designed to change the relative attractiveness of the initial two male options. The presence of the decoy significantly altered the absolute preference, but not the relative preference, for the two male options. While this study clearly demonstrates that female U. mjoebergi are not using strict absolute preferences when ranking each male's attractiveness, it does not conclusively support comparative evaluation mechanisms. One possibility is that sexually selected traits in a complex signalling system often vary in how reliably they reflect male quality, and females may use a combination of absolute and comparative measures when assessing male quality.

The relationship between number of potential mates and mating skew in humans

In nonhuman animal mate choice, a small number of (usually male) options typically leads to an unequal distribution of selections (usually by females) across the options, indicating adaptive choice; conversely, an increasing number of mate options typically yields less inequality of choices across the options. We examined mating skew, a measure of this inequality in mating choices, among humans by considering the offers made by participants in 118 speed-dating sessions of various sizes. Overall, the relationship between a number of indices of mating skew and option set size (the number of opposite-sex participants in the speed-dating session) was positive, with larger sessions producing more mate choice inequality. This result contrasts with the negative relationship between skew and option set size found in nonhuman animals. We interpret these results as the outcome of similar choice mechanisms but different cues used by humans versus other species when making a choice from an abundance of mates.

Sexual selection and senescence: do seed beetle males (Acanthoscelides obtectus, Bruchidae, Coleoptera) shape the longevity of their mates?

Although the reasons why organisms age and die are generally well understood, it has recently been suggested that an optimal life span has evolved not only as the result of trade-offs between reproductive performances early and late in life, but also that a balance between the costs and benefits of the number of mating has also played an important role in the evolution of ageing in both sexes. By using four seed beetle (Acanthoscelides obtectus) lines selected for different life history traits, but which have also inadvertently created monoandrous and polyandrous conditions, we showed that males evolved to affect the mortality patterns of females in a way consistent to the postmating sexual selection generated by sexually antagonistic co-evolution theory. Monoandrous males, irrespectively of body weight and other life history traits specific to their lines, evolved to increase the longevity of control females kept under starvation and suppressed fecundity, compared with males that originated in the lines with effectively polyandrous conditions. When females were allowed to lay eggs, the effects of males from different lines and mating type history on the senescence of females were substantially weaker. We found that males in the line that was evolved to decelerate senescence and polyandrous conditions stimulate the earlier onset of females’ oviposition, relative to males stemmed from the line with accelerated senescence and monoandrous conditions. This fact may explain the absence of difference in the mean longevities between the control females mated to these males and highlight the importance of sexual selection in the evolution of ageing.