Relative Mating Success Research Articles

Mating Competitiveness of Bactrocera dorsalis (Diptera: Tephritidae) Males From a Genetic Sexing Strain: Effects of Overflooding Ratio and Released Females.

The oriental fruit fly, Bactrocera dorsalis (Hendel), is a global pest that infests a range of fruit and vegetables. Males are attracted to methyl eugenol, and control is often achieved by the Male Annihilation Technique, where methyl eugenol + insecticide dispensers are deployed to eliminate males, preclude matings, and reduce population growth. The Sterile Insect Technique (SIT) has also been used to control B. dorsalis. The SIT involves the release of mass-reared, sterilized males to achieve matings with wild females, who then produce inviable eggs. Two key elements of SIT include the overflooding ratio achieved (sterile: wild males) and the strain type utilized, namely bisexual or genetically sexed (allowing male-only releases). Here, we describe the effects of these two factors on the mating competitiveness of a males from a genetic sexing strain of B. dorsalis, termed DTWP. Mating success was scored for DTWP versus wild males in field cages at ratios of 1:2, 1:1, 2:1, and 10:1 both when DTWP females were or were not concurrently released with DTWP males. Close correspondence was found between observed numbers of matings of particular male-female combinations and expected numbers based on the numbers of flies released of each sex and each strain. As a result, the proportion of total matings achieved by the DTWP across the eight treatments showed a corresponding increase with overflooding ratio. At a given ratio, DTWP males had a higher relative mating success when DTWP females were absent rather than present, although the reason for this was unclear.

The impact of competition on elephant musth strategies: A game–theoretic model

Mature male African Savannah elephants are known to periodically enter a temporary state of heightened aggression called “musth”, often linked with increased androgens, particularly testosterone. Sexually mature males are capable of entering musth at any time of year, and will often travel long distances to find estrous females. When two musth bulls or two non-musth bulls encounter one another, the agonistic interaction is usually won by the larger male. However, when a smaller musth bull encounters a larger non-musth bull, the smaller musth male can win. The relative mating success of musth males is due partly to this fighting advantage, and partly to estrous females' general preference for musth males.Though musth behavior has long been observed and documented, the evolutionary advantages of musth remain poorly understood. Here we develop a game–theoretic model of male musth behavior which assumes musth duration as a parameter, and distributions of small, medium and large musth males are predicted in both time and space. The predicted results are similar to the musth timing behavior observed in the Amboseli National Park elephant population, and further results are generated with relevance to Samburu National Park. We discuss small male musth behavior, the effects of estrous female spatial heterogeneity on musth timing, conservation applications, and the assumptions underpinning the model.

Characteristics of the Signals of Male Anoeconeossa bundoorensis Taylor and Burckhardt (Hemiptera: Aphalaridae) Associated with Female Responsiveness

Sexual selection requires intra-specific variation in the characteristics mediating mate choice. In species reliant on substrate-borne vibrational signalling (SBVS), differences in the attractiveness of individual signallers’ calls can influence relative mating success since they can indicate the quality of the sender. We used laser vibrometry and playback experiments to study duet signalling in a psyllid (Anoeconeossa bundoorensis Taylor and Burckhardt), in particular to identify characteristics linked to female responsiveness. Signals were sex-specific with the syllables (or calls) of the smaller males attaining higher frequencies than the syllables of the larger females. Male syllables build over time with more energy in the second half of the call while those of females have a more uniform energy distribution. Male syllables vary in the timing of the halfway point of energy production. We used playback to examine species recognition and female responsiveness to the first and second halves of male calls. We demonstrated that females responded only to calls of male A. bundoorensis and that they were more likely to respond to the first half of male calls. Based on the results of our second playback experiment, we found that a gradation in energy production is more important for eliciting a female reply than a uniform distribution of energy. Our findings show that the rate of energy production facilitates differentiation between syllables which could be used to indicate the quality of individual males as mates.

Colour polymorphism torn apart by opposing positive frequency-dependent selection, yet maintained in space.

Polymorphic warning signals in aposematic species are enigmatic because predator learning and discrimination should select for the most common coloration, resulting in positive frequency-dependent survival selection. Here, we investigated whether differential mating success could create sufficiently strong negative frequency-dependent selection for rare morphs to explain polymorphic (white and yellow) warning coloration in male wood tiger moths (Parasemia plantaginis). We conducted an experiment in semi-natural conditions where we estimated mating success for both white and yellow male moths under three different morph frequencies. Contrary to expectations, mating success was positively frequency-dependent: white morph males had high relative fitness when common, likewise yellow morph males had high relative fitness when instead they were common. We hence built a model parameterized with our data to examine whether polymorphism can be maintained despite two sources of positive frequency dependence. The model includes known spatial variation in the survival advantage enjoyed by the yellow morph and assumes that relative mating success follows our experimentally derived values. It predicts that polymorphism is possible under migration for up to approximately 20% exchange of individuals between subpopulations in each generation. Our results suggest that differential mating success combined with spatial variation in predator communities may operate as a selection mosaic that prevents complete fixation of either morph.

BATEMANATER: a computer program to estimate and bootstrap mating system variables based on Bateman's principles.

Bateman's principles continue to play a major role in the characterization of genetic mating systems in natural populations. The modern manifestations of Bateman's ideas include the opportunity for sexual selection (i.e. I(s) - the variance in relative mating success), the opportunity for selection (i.e. I - the variance in relative reproductive success) and the Bateman gradient (i.e. β(ss) - the slope of the least-squares regression of reproductive success on mating success). These variables serve as the foundation for one convenient approach for the quantification of mating systems. However, their estimation presents at least two challenges, which I address here with a new Windows-based computer software package called BATEMANATER. The first challenge is that confidence intervals for these variables are not easy to calculate. BATEMANATER solves this problem using a bootstrapping approach. The second, more serious, problem is that direct estimates of mating system variables from open populations will typically be biased if some potential progeny or adults are missing from the analysed sample. BATEMANATER addresses this problem using a maximum-likelihood approach to estimate mating system variables from incompletely sampled breeding populations. The current version of BATEMANATER addresses the problem for systems in which progeny can be collected in groups of half- or full-siblings, as would occur when eggs are laid in discrete masses or offspring occur in pregnant females. BATEMANATER has a user-friendly graphical interface and thus represents a new, convenient tool for the characterization and comparison of genetic mating systems.

Colony size, but not density, affects survival and mating success of alternative male reproductive tactics in a polyphenic mite, Rhizoglyphus echinopus.

Among acarid mites, a number of species are characterised by the presence of discontinuous morphologies (armed heteromorphs vs. unarmed homeomorphs) associated with alternative mating tactics (fighting vs. scramble competition). In Rhizoglyphus echinopus, expression of the fighter morph is suppressed, via pheromones, in large, dense colonies. If this mechanism is adaptive, fighters should have relatively lower fitness in large and/or dense colonies, due to costs incurred from fighting, which is often fatal. In order to test these predictions, we quantified the survival and mating success of fighters and scramblers in colonies of equal sex and morph ratios; these colonies either differed in size (4, 8, or 32 individuals) but not density or differed in density but not size (all consisted of 8 individuals). We found that the relative survival and mating success of fighters was inversely related to colony size, but we did not find a significant effect of colony density. The higher mating success of fighters in small colonies was due to the fact that, after killing rival males, these fighters were able to monopolise females. This situation was not found in larger colonies, in which there was a larger number of competitors and fighters suffered relatively higher mortality. These results indicate that morph determination, guided by social cues, allows for the adaptive adjustment of mating tactics to existing demographic conditions.Electronic supplementary materialThe online version of this article (doi:10.1007/s00265-014-1787-7) contains supplementary material, which is available to authorized users.

Competitor size, male mating success and mate choice in eastern mosquitofish, Gambusia holbrooki

Males usually compete for mates but, by choosing a favourable social environment (e.g. avoiding stronger competitors), males might increase their reproductive success. We first tested whether the mate choice of male eastern mosquitofish depended on the size of potential competitors. In two-choice trials, focal males preferred to associate with a group of large males over a group of small males. However, when both stimulus groups also contained females, focal males associated equally often with the group with large males and the group with small males. We then quantified the effect of competitor size on the relative mating success (proportion of all mating attempts) of males competing for access to a female. In mating trials, the relative mating success of focal males increased with focal male size. In addition, focal males had higher mating success when competing in a group of small males than a group of large males. We suggest that the benefits of associating with small male competitors in a mating context (greater mating success) are balanced by other benefits that have led to a general preference for associating with larger males.

ON THE OPPORTUNITY FOR SEXUAL SELECTION, THE BATEMAN GRADIENT AND THE MAXIMUM INTENSITY OF SEXUAL SELECTION

Bateman's classic paper on fly mating systems inspired quantitative study of sexual selection but also resulted in much debate and confusion. Here, I consider the meaning of Bateman's principles in the context of selection theory. Success in precopulatory sexual selection can be quantified as a "mating differential," which is the covariance between trait values and relative mating success. The mating differential is converted into a selection differential by the Bateman gradient, which is the least squares regression of relative reproductive success on relative mating success. Hence, a complete understanding of precopulatory sexual selection requires knowledge of two equally important aspects of mating patterns: the mating differential, which requires a focus on mechanisms generating covariance between trait values and mating success, and the Bateman gradient, which requires knowledge of the genetic mating system. An upper limit on the magnitude of the selection differential on any sexually selected trait is given by the product of the standard deviation in relative mating success and the Bateman gradient. This latter view of the maximum selection differential provides a clearer focus on the important aspects of precopulatory sexual selection than other methods and therefore should be an important part of future studies of sexual selection.

INTERACTIONS BETWEEN ENVIRONMENTAL STRESS AND MALE MATING SUCCESS MAY ENHANCE EVOLUTIONARY DIVERGENCE OF STRESS-RESISTANTDROSOPHILAPOPULATIONS

Adaptation of natural and laboratory-selected populations of Drosophila to desiccation stress results in enhanced water conservation abilities, and thus increased stress resistance. In this study, we tested whether laboratory selection for desiccation resistance is also reflected in increased mating success of adapted D. melanogaster males under desiccating conditions. Adapted flies perform better under stressful conditions, and as expected males from desiccation-selected populations exhibited significantly higher relative mating success in comparison with controls after 5-6 h of desiccation. However, we show evidence for a trade-off between survival under stressful conditions and mating success in nonstressful and even mildly stressful environments (2.5-3 h of desiccation), where males from selected populations were involved in only approximately 40% of observed copulations. This suggests that mutations favored by natural selection, associated with survival when resources are limited, may only be favored by sexual selection above a minimal "threshold" stress level. At milder stress levels increased resistance comes at a cost of lower relative mating success, and thus reduced fitness. This interaction between stress and relative male mating success of adapted and nonadapted males could interrupt gene flow, thus facilitating divergence of resistant populations from the ancestral population.

Indirect mate choice, direct mate choice and species recognition in a bower‐building cichlid fish lek

Sexual selection arising through female mate choice typically favours males with larger, brighter and louder signals. A critical challenge in sexual selection research is to determine the degree to which this pattern results from direct mate choice, where females select individual males based on variation in signalling traits, or indirect mate choice, where male competition governs access to reproductively active females. We investigated female mate choice in a lekking Lake Malawi cichlid fish, Hemitilapia oxyrhynchus, in which males build and aggressively defend sand 'bowers'. Similar to previous studies, we found that male reproductive success was positively associated with bower height and centrality on the lek. However, this pattern resulted from males holding these territories encountering more females, and thus their greater success was due to indirect mate choice. Following initial male courtship, an increase in the relative mating success of some males was observed, but this relative increase was unrelated to bower size or position. Crucially, experimentally manipulating bowers to resemble those of a co-occurring species had no appreciable effect on direct choice by females or male spawning success. Together, these results suggest indirect mate choice is the dominant force determining male-mating success in this species, and that bowers are not signals used in direct mate choice by females. We propose that, in this species, bowers have a primary function in intraspecific male competition, with the most competitive males maintaining larger and more central bowers that are favoured by sexual selection due to higher female encounter rates.

Exposing Entire Adult Holding Rooms Containing Sterile Male Mediterranean Fruit Flies to OrangE Oil Increases the Mating Success of Those Males in Field-cage Trials

A previous study demonstrated that exposing entire rooms holding mass-reared males of the Mediterranean fruit fly, Ceratitis capitata (Wied.), to the aroma of ginger root oil increased mating success relative to that observed for non-exposed males. Here, we followed the same experimental protocol to test whether the aroma of orange oil similarly enhanced male mating performance. Working at an eclosion facility in California, we exposed trailers (132 m3) containing ≈ 14 million C. capitata males from a genetic sexing (tsl, temperature sensitive lethal) strain to orange oil aroma for 24 h and compared mating success of non-exposed or ginger root oil-exposed tsl males in field-cage trials (in which tsl males competed against males from a standard, bisexual strain for females from this same standard strain). Both orange oil- and ginger root oil-exposed tsl males achieved a significantly greater proportion of the total matings than non-exposed (to any aroma) tsl males. No difference in relative mating success was observed between orange oil- and ginger root oil-exposed tsl males. As orange oil is considerably less expensive than ginger root oil, its use could reduce costs substantially.

Female Defensibility in a Small Troops of Japanese Macaques vis-à-vis Nontroop Males and Copulation on the Periphery of the Troop

I provide data compiled over 4 yr on the mating behavior in small troops of wild Japanese macaques on Yakushima Island. The key parameters are the number of sexually receptive females, the number of nontroop males (NTMs), and copulation on the periphery of the troop. I analyzed the following aspects: 1) changes in the proportion of copulation with high-ranking males (HRMs) and NTMs, 2) variations in factors such as fluctuation in the number of sexually receptive females and troop males and their effects on the number of visiting NTMs, 3) the effect of attempted interruption of mounting series by other males, and 4) some aspects of copulation on the periphery of the troop. Throughout the study, 56% of the total number of females mated most frequently with the α-male in a single mating season. However, the relative mating success of HRMs varied over the years and between individuals. The number of visiting NTMs varied depending on the number of receptive females and troop males. Females tended to mate with the NTMs when they appeared around their troops. The direct effect of interruption of the mounting series by other males is equivocal. The females mated with the low-ranking males (LRMs) and NTMs on the periphery of the troop, which increased the possibility of mounting series ending with ejaculation. Females actively sought opportunities for copulation on the periphery of the troop by moving there or initiating close proximity with LRMs and NTMs there. On Yakushima Island, the mating success of HRMs was not always as high as that predicted by the priority of access model. The injury status of the HRM, the number of visiting NTMs, and female choice are all considered to influence a male’s mating success.

Variation in Male Calling Behaviour and Relation to Male Mating Success in the Strawberry Poison Frog (Dendrobates pumilio)

AbstractCalling behaviour and the characteristics of the males’ call are important for mate attraction, female mate choice and male mating success in anurans. In this study I investigated the variation in calling activity and the variation in one spectral (dominant frequency) and four temporal properties (call rate, call duration, duty cycle and pulse rate) of the advertisement call of strawberry poison frogs, Dendrobates pumilio, in two Costa Rican populations during two study periods. Regarding all call properties, no differences were found between populations or years, but between‐male variation was significantly higher than within‐recording and within‐male variation. Dominant frequency was less variable within and among males than temporal call properties and I classified the former as static and the latter as intermediate properties of the call. No call property seemed to be strongly affected by body length or weight. Moreover, I used behavioural observations to relate male calling behaviour to mating success. Calling activity was more variable between males and accounted for more variability in mating success in multiple regression models than any call property. Some call properties (call rate, dominant frequency and pulse rate) were also related to male mating success in one or two study periods. These call properties are probably important for females during courtship to assess their prospective mate and/or for competitive male–male interactions. Furthermore, I compared call properties and mating success of some males for which data were available for both study periods. Pulse rate was lower in the second than in the first year, suggesting age‐related changes in this call property. Moreover, male D. pumilio increased their relative mating success from the first to the second study year. Together with other studies, the data of this study suggest that, in anurans, endurance rivalry contributes more to variation in male mating success than does female choice based on male characteristics.

Body size and mating success in Pyrrhocoris apterus (Heteroptera)

The effects of body size on mating success and duration of copulation were investigated in Pyrrhocoris apterus. Under laboratory conditions relative mating success of small and large males was investigated in groups of 2 males (majority sex) : 1 female (minority sex). Large males were recorded significantly more often in copulation than small males when the female was large but not when the female was small. This was also the case when the group size was 24 males : 12 females or population density decreased by increasing the area of the experimental arena. In groups of 2females : 1 male, large females were recorded in copulation significantly more often than small females when the male was large but not when the male was small. Proportion of individuals of the minority sex that copulated was similar for males and females, regardless of body size. The average duration of copulation was similar for small and large males, but shorter for small than large females. The difference in the duration of copulation of small and large females was greater when it was with small rather than large males. The prolonged guarding of large females by small males may be explained by a trade-off between increasing the probability of inseminating an uneasily accessible high quality partner and copulating with more females.

Male variation in mating success after female numbers are reduced

A significant decline was found in the quantity of eggs that polygynous male beaugregory damselfish Stegastes leucosticus received after reducing the number of available females, which indicated that a significant number of females was removed from the experimental community. The operational sex ratio (OSR) hypothesis, which presumes that a sex becomes increasingly more selective as the number of alternative mates increases, was not supported as the variance in male mating success was unchanged after the females were removed. The relative mating success among males was also unchanged. That is, male ranks remained relatively the same (pre‐test and post‐test) after the removal of females. The large variance in male mating success within this species may be a function of polymorphic mate preferences exhibited by females that may be based on male location.

Dynamic properties of the advertisement calls of gray tree frogs: patterns of variability and female choice

We assessed the potential for several acoustic properties of the advertisement calls of male gray tree frogs to affect relative mating success by relating patterns of variation in these properties to minimum differences required to elicit female choice. Dynamic properties (pulse number, PN; call rate, CR; and duty cycle, DC, the ratio of call duration to call period) varied much more within bouts of calling than a static property (dominant frequency, DF) but nevertheless exhibited significant between male variation in three of four breeding seasons. Many multiply recorded males consistently produced calls with values substantially above or below mean values of males recorded on the same nights. Nightly ranges of variation in PN and CR were often greater than the minimum differences required to elicit female preferences in the laboratory. In most experiments, females chose high-PN or fast-CR calls over low-PN or slow-CR alternatives, respectively, even if the preferred stimuli were farther away or 6-10 dB lower in sound pressure level (SPL), provided that differences in PN or CR were 100%. Consistent with these results, females did not always choose the closer of two calling males in the field. Nightly ranges of variation in DF rarely equaled the minimum difference required to elicit SPL independent preferences. Females preferred a stimulus of high-PN and slow-CR over an alternative of low-PN or fast-CR with the same acoustic on-time; in two experiments, females chose calls of high-PN over low-PN alternatives even though the playback of the high-PN call was interrupted and the low-PN call was broadcast continuously. Thus, female preferences were not merely based on the total time of acoustic stimulation. Responses of females tested twice in the same experiment suggest that phenotypic variation in preference was limited in our study populations.

Sexual isolation in Drosophila melanogaster: a possible case of incipient speciation.

It is generally believed that Drosophila melanogaster has no closely related species with which it can produce the viable and fertile hybrids that are essential for the genetic analysis of speciation. Following the recent report of molecular differentiation between a Zimbabwe, Africa, population and two United States populations, we provide evidence that strong sexual isolation exists between the D. melanogaster population in Zimbabwe and populations of other continents. In the presence of males of their own kind, females from most isofemale lines of Zimbabwe would not mate with males from elsewhere; the reciprocal mating is also significantly reduced, but to a lesser degree. The genes for sexual behaviors are apparently polymorphic in Zimbabwe and postmating reproductive isolation between this and other populations has not yet evolved. Whole chromosome substitutions indicate significant genetic contributions to male mating success by both major autosomes, whereas the X chromosome effect is too weak to measure. In addition, the relative mating success between hybrid and pure line males supports the interpretation of strong female choice. These observations suggest that we are seeing the early stages of speciation in this group and that it is driven by sexual selection. The genetic and molecular tractability of D. melanogaster offers great promise for the detailed analysis of this apparent case of incipient speciation.

Sex ratio and foundress number in the parasitoid wasp Bracon hebetor

Abstract. As predicted by the theory of local mate competition, the offspring sex ratios of many parasitoid wasps become increasingly male biased as the number of conspecific females ovipositing in a patch rises. The braconid wasp Bracon hebetor appears to be an exception. Recent experiments have suggested that wasps ovipositing in the presence of a conspecific female produce more daughters than solitary wasps. Larval competition is more intense when two females oviposit together and it has been suggested that females lay fewer sons in these circumstances because the resultant small males have poor mating success. Experiments are reported that (1) compare the sex ratio of solitary and paired B. hebetor; (2) investigate the importance of differential mortality and (3) explore the relative mating success of small and large wasps. Paired and solitary wasps produced the same sex ratio and there was no evidence of differential mortality. Small males were able to mate both large and small females and, at least in the laboratory, appeared to suffer no disadvantage in competition with larger males. There are statistical problems with some previous analyses of sex ratio and foundress number in B. hebetor, and there are also problems in making inference about adaptation from inbred strains of a naturally outbred species.

The effects of operational sex ratio on the relative mating success of extreme male phenotypes in the water strider Gerris odontogaster (Zett.) (Heteroptera; Gerridae)

The effects of operational sex ratio on the relative mating success of extreme male phenotypes in the water strider Gerris odontogaster (Zett.) (Heteroptera; Gerridae)

The effects of operational sex ratio on the relative mating success of extreme male phenotypes in the water strider (Zett.) (Heteroptera; Gerridae)

The effects of operational sex ratio on the relative mating success of extreme male phenotypes in the water strider (Zett.) (Heteroptera; Gerridae)