Inhibition of female mating by male accessory gland substances in the ground beetle Leptocarabus procerulus

The ground beetle Leptocarabus procerulus (Chaudoir) possesses seminal substances that have a physical function to form mating plugs and a physiological function to induce female refractory behaviour, which act together to hinder female remating. Little is known about the physiological properties of the substances inducing female refractory behaviour, especially with respect to their secretory organ, dose‐dependency, molecular characteristics and the effect of female maturity. By injecting male‐derived substances into females, substances that induce female refractory behaviour are shown to be produced in the male accessory gland but not in the testis. Injection of extracts from the accessory gland increases the female refractory period at moderate doses but not at lower or higher doses. By contrast, injection of extracts from the testis reduces the female refractory period at high doses. The lack of an effect of accessory gland substances at higher doses could be the result of an anomalous effect of unnaturally large doses of seminal products by direct injection, the toxicity of seminal substances that deter female responses, or counteraction by injected substances that promote female receptivity. The accessory gland substances lose their activity when heated, although the testis substances do not. Females without mature eggs tend to reject mating entirely, although variation in the number of mature eggs (one or more) is not associated with the female refractory period, indicating the limited effect of female reproductive maturity. These findings may help to clarify the physiological basis of the evolution of the elaborated male mating behaviour in L. procerulus.     

Hemolymph loss during nuptial feeding constrains male mating success in sagebrush crickets

Although costs of mating have been widely documented in females,intrinsic costs of copulation have been poorly documented inmales, and there is little evidence that such costs constrainmale mating success under natural conditions. Male sagebrushcrickets, Cyphoderris strepitans, offer females an unusual somaticfood gift at copulation that may constitute a significant costof copulation: females chew on the ends of the males' fleshyhind wings and ingest hemolymph seeping from the wounds theyinflict. Previous studies have shown that once a male has mated,his probability of obtaining an additional copulation is reducedrelative to that of a virgin male seeking to secure his firstmating. If the future mating prospects of nonvirgin males arediminished because of the costs of copulation, this could stemeither from the resources required to manufacture a new spermatophoreor through the energy needed to replenish hemolymph lost throughfemale wing-feeding. To distinguish between these two alternatives,we experimentally depleted virgin males of varying amounts hemolymphin a way that mimicked hemolymph loss of nonvirgin males, withoutthe attendant costs of spermatophore production. After theyhad been treated, males were released in the field and recapturedover the course of the breeding season to monitor their matingsuccess. Control males mated significantly sooner than did malesdepleted of hemolymph. We conclude, therefore, that the depletionof hemolymph that occurs through female wing feeding is sufficientby itself to diminish a nonvirgin male's ability to secure anothermating.     

The effects of male body size on territorial and mating success in the landmark-defending fly Hermetia comstocki (Stratiomyidae)

Abstract.

• 1 Males of Hermetia comstocki Williston compete for territorial control of certain agaves and yuccas. Winners copulate with females that visit these plants solely to acquire a mate.
• 2 Males vary in body weight by more than an order of magnitude and larger flies almost always defeat smaller ones in aerial contests for control of landmark territories.
• 3 The mean body size (as measured by wing-length) was significantly greater for males retaining residency at a site for at least one hour compared to males unable to do so. Likewise, males able to return to a perch site in the study area on more than one day were larger on average than males unable to do so.
• 4 Male preferences for landmark territories remained similar across years. Large males dominated the perch landmarks most likely to be occupied by males and most likely to be visited by females.
• 5 Despite the fighting and territorial advantages enjoyed by large males, the mean size of males found mating with females was not significantly larger than that of the general population.
• 6 The apparent failure of large males to secure a statistically significant mating advantage may be a statistical consequence of the small sample size of males observed mating. On the other hand, any mating advantage of large males may be reduced because (a) receptive females visit many different landmarks, (b) females mate with the first male they encounter at a landmark, regardless of his size, (c) there are usually many vacant landmarks available for smaller males, and (d) even popular territories are often open to small males, thanks to the low site-tenacity of territory owners.

     

Body size,male aggression,and male mating success in the cottonwood borer,Plectrodera scalator (Coleoptera: Cerambycidae)

The natural history and mating system ofPlectrodera scalator exhibit several unusual characteristics. Larvae and adults feed on the wood and foliage, respectively, of the same plant,Populus deltoides. The population sex ratio, based on censuses of oviposition areas, is female-biased. Females are significantly larger than males, yet males are intensely aggressive. Larger males tend to win escalated battles, which involve grasping of antennae with mandibles, but smaller males can defeat larger males if they grasp their opponent's antenna first. Most escalated fights involve possession of a female, but prior possession does not play a role in determining the outcome of these fights. The size-dependent fighting advantage does not translate into a mating advantage for larger males. There is no significant difference in elytron length or body mass between mating and single males. Larger females are not preferred as mates. The mating system appears to be a mixture of female-defense and scramble-competition tactics. One advantage to males of aggression may be in its effect on sperm precedence. Males appear to be able to remove previously deposited sperm from a female's reproductive tract.     

Correlates of male mating success in two natural populations of the damselfly lschnura graellsii (Odonata: Coenagrionidae)

Abstract.

• 1 Two natural populations of Ischnura graellsii were studied in north-west Spain by means of mark-release-recapture techniques. Recaptured males were a random sample of the original marked population with regard to date of marking. At O Rosal a greater proportion of young males than old males disappeared after marking; at Lourizán recaptured males were larger than unrecaptured ones.
• 2 The number of matings observed in both populations showed great daily variation. Most of the variation is accounted for by climatic variables. Most males (56–65%) and many females (41–45%) were never observed to mate.
• 3 Male LMS was highly correlated with lifespan in both populations. At O Rosal, male LMS was also positively correlated with body length, and mated males were larger than unmated males. This surprising result for a non-territorial species was due to the positive correlation between date of marking and size. There was a positive correlation between body size and mobility for males at O Rosal, but mobility was not correlated with male LMS.
• 4 As predicted by sexual selection theory, the standardized variance in male LMS was greater than in female LMS. Variation in mature lifespan explained 16% of variance in male LMS at Lourizán and 28% at O Rosal.

     

Size and mating success in males of the western harvester ant,Pogonomyrmex occidentalis (Hymenoptera: Formicidae)

Mating success in males of the lek mating ant species,Pogonomyrmex occidentalis, increases with increased body size. We estimated the magnitude of the selection coefficients on components of size by collecting males in copula and comparing their morphology to that of males that were collected at the lek but that were not mating. Four characters, body mass, head width, wing length, and leg length, were measured for a sample of 225 mating and 324 nonmating males and 225 females. Significant direct selection favors increased wing length and leg length. Multiple regression of transformed variables (principal components) indicated that the increased mating success of larger males is a function of all four characters. We found no evidence of positive assortative mating on the basis of any individual character or on the multivariate general size variable (the first principal component).     

Sexual conflict and ecology: Species composition and male density interact to reduce male mating harassment and increase female survival

Sexual conflict is a pervasive evolutionary force that can reduce female fitness. Experimental evolution studies in the laboratory might overestimate the importance of sexual conflict because the ecological conditions in such settings typically include only a single species. Here, we experimentally manipulated conspecific male density (high or low) and species composition (sympatric or allopatric) to investigate how ecological conditions affect female survival in a sexually dimorphic insect, the banded demoiselle (Calopteryx splendens). Female survival was strongly influenced by an interaction between male density and species composition. Specifically, at low conspecific male density, female survival increased in the presence of heterospecific males (C. virgo). Behavioral mating experiments showed that interspecific interference competition reduced conspecific male mating success with large females. These findings suggest that reproductive interference competition between con‐ and heterospecific males might indirectly facilitate female survival by reducing mating harassment from conspecific males. Hence, interspecific competitors can show contrasting effects on the two sexes thereby influencing sexual conflict dynamics. Our results call for incorporation of more ecological realism in sexual conflict research, particularly how local community context and reproductive interference competition between heterospecific males can affect female fitness.     

Mating success of male bushy-tailed woodrats: when bigger is not always better

To determine the factors that regulate mating opportunitiesof male bushy-tailed woodrats (Neotoma cinerea), we used stepwisemultiple regression on measurable morphological and behavioraltraits. DNA fingerprinting was used to determine the paternityof juveniles, allowing mating success (the number of femalesmated with), and reproductive success (the number of offspringfathered) to be quantified. Both measures of male success weresignificantly related to the growth rate of males while reproductivelyactive. The most successful males were those that had higher growthrates, indicating that there is relatively little cost (weightloss) associated with successful mating in male woodrats. Ourfindings demonstrate that although this species is highly sexuallydimorphic, large body size does not influence mating success.In addition, it appears that male mating success cannot be predictedfrom morphological measures and may instead be determined bybehavioral or olfactory cues.     

Adaptive speciation when assortative mating is based on female preference for male marker traits

Adaptive speciation occurs when frequency-dependent ecological interactions generate conditions of disruptive selection to which lineage splitting is an adaptive response. Under such selective conditions, evolution of assortative mating mechanisms enables the break-up of the ancestral lineage into diverging and reproductively isolated descendent species. Extending previous studies, I investigate models of adaptive speciation due to the evolution of indirect assortative mating that is based on three different mating traits: the degree of assortativity, a female preference trait and a male marker trait. For speciation to occur, linkage disequilibria between different mating traits, e.g. between female preference and male marker traits, as well as between mating traits and the ecological trait, must evolve. This can lead to novel speciation scenarios, e.g. when reproductive isolation is generated by a splitting in the degree of assortativeness, with one of the emerging lineages mating assortatively, and the other one disassortatively. I investigate the effects of variation in various model parameters on the likelihood of speciation, as well as robustness of speciation to introducing costs of assortative mating. Even though in the models presented speciation requires the genetic potential for strong assortment as well as rather restrictive ecological conditions, the results show that adaptive speciation due to the evolution of assortative mating when mate choice is based on separate female preference and male marker traits is a theoretically plausible evolutionary scenario.     

Genetic architecture of sensory exploitation: QTL mapping of female and male receiver traits in an acoustic moth

The evolution of extravagant sexual traits by sensory exploitation occurs if males incidentally evolve features that stimulate females owing to a pre‐existing environmental response that arose in the context of natural selection. The sensory exploitation process is thus expected to leave a specific genetic imprint, a pleiotropic control of the original environmental response and the novel sexual response in females. However, females may be subsequently selected to improve their discrimination of environmental and sexual stimuli. Accordingly, responses may have diverged and the original genetic architecture may have been modified. These possibilities may be considered by studying the genetic architecture of responses to male signals and to the environmental stimuli that were purportedly ‘exploited’ by those signals. However, no previous study has addressed the genetic control of sensory exploitation. We investigated this question in an acoustic pyralid moth, Achroia grisella, in which a male ultrasonic song attracts females and perception of ultrasound likely arose in the context of detecting predatory bats. We examined the genetic architecture of female response to bat echolocation signals and to male song via a cartographic study of quantitative trait loci (QTL) influencing these receiver traits. We found several QTL for both traits, but none of them were colocalized on the same chromosomes. These results indicate that – to the extent to which male A. grisella song originated by the process of sensory exploitation – some modification of the female responses occurred since the origin of the male signal.     

Intentional multiple mating by females in a species where sneak fertilization circumvents female choice for parental males

This paper describes how individual female ocellated wrasse Symphodus ocellatus distribute their spawning among males and nests in space and time. It is based on previously collected genetic data of larvae from ten different nests (used to reconstruct half and full‐sibling groupings both within and among nests on multiple days) and behavioural data of marked females across the reproductive season. Both the genetic analyses and behavioural observations confirm that female S. ocellatus intentionally engage in multiple mating, by repeatedly spawning at the same nest on different days and at several different nests (up to 12 spawning events over 3 weeks), leading to mixed paternity among her young. The main benefit of such high and intentional multiple mating is probably insurance against brood failure due to nest predation, desertion or poor paternal care by the male. These findings reveal that even in systems where females attempt to avoid male‐controlled mixed paternity, they may still engage in intentional multiple mating due to these potential benefits.     

Sexual size dimorphism and selection in the wild in the waterstrider Aquarius remigis: Body size,components of body size and male mating success

Sexual size dimorphism is assumed to be adaptive and is expected to evolve in response to a difference in the net selection pressures on the sexes. Although a demonstration of sexual selection is neither necessary nor sufficient to explain the evolution of sexual size dimorphism, sexual selection is generally assumed to be a major evolutionary force. If contemporary sexual selection is important in the evolution and maintenance of sexual size dimorphism then we expect to see concordance between patterns of sexual selection and patterns of sexual dimorphism. We examined sexual selection in the wild, acting on male body size, and components of body size, in the waterstrider Aquarius remigis, as part of a long term study examining net selection pressures on the two sexes in this species. Selection was estimated on both a daily and annual basis. Since our measure of fitness (mating success) was behavioral, we estimated reliabilities to determine if males perform consistently. Reliabilities were measured as ? statistics and range from fair to perfect agreement with substantial agreement overall. We found significant univariate sexual selection favoring larger total length in the first year of our study but not in the second. Multivariate analysis of components of body size revealed that sexual selection for larger males was not acting directly on total length but on genital length. Sexual selection for larger male body size was opposed by direct selection favoring smaller midfemoral lengths. While males of this species are smaller than females, they have longer genital segments and wider forefemora. Patterns of contemporary sexual selection and sexual size dimorphism agree only for genital length. For total length, and all other components of body size examined, contemporary sexual selection was either nonsignificant or opposed the pattern of size dimporhism. Thus, while the net pressures of contemporary selection for the species may still act to maintain sexual size dimorphism, sexual selection alone does not.     

Sexual selection in a moth: effect of symmetry on male mating success in the wild

Sexual selection is generally caused by female choice and male–malecompetition. In female choice process, female preference isfavored indirectly and/or directly by sexual selection. In indirectselection, females expressing the preference might gain indirectgenetic benefits. In direct selection, females expressing thepreference might gain direct benefits or avoid male-imposedcosts. The white-tailed zygaenid moth Elcysma westwoodii ismonandrous, and males often gather around a female to mate withher, suggesting a high opportunity for sexual selection on maletraits. We quantified phenotypic selection on male morphologyin this species in the field. The morphological characters analyzedincluded body weight, antenna length, forewing length, hindwing length, hind wing tail length, genital clasper length,and the fluctuating asymmetry (FA) of these bilateral traits.In E. westwoodii, selection favored males with more symmetricgenital claspers, as well as longer and more symmetrical hindwings and antennae. Negative correlations between FA and sizewere also detected in the clasper and the antenna. Our resultssuggest that FAs of male traits, in particular the genital clasper,may have indirect and direct influences on mating success. Duringa copulatory attempt, an E. westwoodii male will try to graspthe female's abdominal tip with his claspers but often failto do so because of the female's reluctance to mate. The femaleabdominal tips are smooth and strongly sclerotized and couldthus be difficult for males to grasp. We hypothesize that moresymmetrical male claspers are more efficient in overcoming femalereluctance.     

Male "macho" mammals exploiting females versus male "Don Juan" birds exploited by females: the opposite-sex exploitation (OSEX) theory

We hypothesize that the general differences in breeding systems between birds and mammals results from a different outcome of the between-sex arms race. The arms race has been won by male mammals that can impose their mating decision over females, but has been lost by male birds because of the extreme specialization of forearms that do not allow males to trap and hold females during copulation. Male birds compensate for their inability to force copulation by developing "Don Juan" behaviour to persuade females to accept copulation.     

Multiple mating increases cocoon hatching success in the earthworm Eisenia andrei (Oligochaeta: Lumbricidae)

In simultaneous hermaphrodites with reciprocal mating, multiple mating may be a male strategy that conflicts with female interests, and therefore an intra‐individual sexual conflict regarding the number of matings may be expected. The evolutionary outcome of this sexual conflict will depend on the costs and benefits that extra mating entails for each sexual function. In the present study, we investigated the costs and benefits of multiple mating on cocoon number, cocoon mass, and cocoon hatching success in the redworm Eisenia andrei, a simultaneous hermaphrodite with reciprocal insemination, by manipulating the number of matings with different partners. We did not detect any reduction in the female reproductive output (number and mass of cocoons) with increasing number of mating partners. However, we found that multiple mating showed benefits for female reproduction that increased the hatching success of the cocoons. This effect may be a result of increased quantity and/or diversity of sperm in the spermathecae of multiple mated earthworms. Further studies are required to clarify the mechanism underlying the increased cocoon hatching success when redworms engage in multiple matings. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.