Mate guarding and sperm displacement in the water strider Gerris lateralis Schumm. (Heteroptera: Gerridae)

SUMMARY. 1. Field and laboratory observations on the mating behaviour of Gerris lateralis Schumm. allowed three distinct phases to be distinguished: (i) a precopulatory phase (1.5min, SD=1.3), (ii) copulation (16.2min, SD=12.9), and (iii) a postcopulatory phase. The duration of the postcopulatory phase, during which the male rode passively on the back of the female without genital contact, varied considerably (11 min to > 48h). Females appeared reluctant in all matings, and matings were forced by males.
2. Laboratory experiments showed that the females were able to store sperm for more than 30 days without decrease in fertilization rate. In double mating experiments, where partially sterilized males were used, it was demonstrated that sperm displacement was extensive. The last male to mate fertilized approximately 80% of the eggs.
3. It is concluded that the postcopulatory behaviour is beneficial to males in terms of paternity assurance, and it is interpreted as a mate guarding behaviour.     

The Effects of Perceived Mating Opportunities on Patterns of Reproductive Investment by Male Guppies

Males pay considerable reproductive costs in acquiring mates (precopulatory sexual selection) and in producing ejaculates that are effective at fertilising eggs in the presence of competing ejaculates (postcopulatory sexual selection). Given these costs, males must balance their reproductive investment in a given mating to optimise their future reproductive potential. Males are therefore expected to invest in reproduction prudently according to the likelihood of obtaining future matings. In this study we tested this prediction by determining whether male reproductive investment varies with expected future mating opportunities, which were experimentally manipulated by visually exposing male guppies (Poecilia reticulata) to high or low numbers of females in the absence of competing males. Our experiment did not reveal consistent effects of perceived future mating opportunity on either precopulatory (male mate choice and mating behaviour) or postcopulatory (sperm quality and quantity) investment. However, we did find that male size and female availability interacted to influence mating behaviour; large males visually deprived of females during the treatment phase became more choosy and showed greater interest in their preferred female than those given continuous visual access to females. Overall, our results suggest males tailor pre- rather than postcopulatory traits according to local female availability, but critically, these effects depend on male size.     

Field Observations on the Mating Behavior of Aclees sp. cf. foveatus Voss (Coleoptera: Curculionidae), an Exotic Pest Noxious to Fig Orchards

Aclees sp. cf. foveatus Voss is a new and exotic pest recently reported as responsible for severe damages to Italian fig orchards and nurseries. Investigating its mating behavioral sequence could help to unravel mate assessment and choice dynamics of this pest, adding useful information to build-up behavior-based control strategies. In this study, we observed A. sp. cf. foveatus mating behavior under field conditions. The mating behavior is divided into precopulatory, copulatory and postcopulatory phases. Simultaneous antennal tapping and rostral rubbing acts performed by the male on female’s body raises male’s chances to copulate, while males that performed only antennal tapping on the partner’s body did not achieved mating success. Copulation attempt phase lasted 37.80?±?7.65 s. Copulation lasted 1116.00?±?229.73 s and was followed by a motionless postcopulatory phase (8.40?±?1.21 s). Same-sex sexual interactions were observed among A. sp. cf. foveatus males. Male-male sexual interactions lasted about 140.17?±?19.45 s and were composed of antennal tapping and rostral rubbing followed by one or more mounting attempts. Further research is ongoing to investigate the exact nature of male- and female-borne olfactory and tactile cues routing mate recognition in A. sp. cf. foveatus.     

Mating Behavior of the Coffee Berry Borer, Hypothenemus hampei (Ferrari) (Coleoptera: Curculionidae: Scolytinae)

The mating behavior of the coffee berry borer, Hypothenemus hampei (Ferrari), was observed under laboratory conditions. Pairs of adult virgin male and female beetles were placed in the wells of a polystyrene microtiter plate, one pair per well. The mating activity of each pair was recorded for 24?h. The mating behavior of the coffee berry borer was similar to that of other Scolytinae and was clearly divided into precopulatory, copulatory and postcopulatory phases. The beetles started to mate within a few hours of emergence. Repeated mating occurred during the 24-hour period and increased in frequency with age. However, we cannot address multiple matings in H. hampei, since we did not simulate the female-biased sex ratio of this species and the experimental design did not allow females to avoid additional mating attempts by males. In addition, further studies are necessary that focus on the effectiveness of sperm transmission and direct and indirect effects of multiple matings on the H. hampei females and their offspring.     

High opportunity for postcopulatory sexual selection under field conditions

In polygamous systems, male fitness is determined not only by mating success but also by fertilization success. Despite the growing interest over the past several decades in postcopulatory sexual selection, its relative importance compared to precopulatory sexual selection remains a subject of debate. Here, we use extensive behavioral observations of a seminatural population of Hawaiian swordtail crickets, Laupala cerasina, and molecular paternity assignment to measure the opportunities for pre‐ and postcopulatory selection. Because postcopulatory selection has the potential to operate at multiple stages, we also separately attribute its effects to factors specific to mating events versus factors specific to males. We find that variance in postcopulatory success is over four times as great as variance in precopulatory success, with most of it unexplained by male mating order or the number of nuptial gifts given. Surprisingly, we also find that male singing effort is under postcopulatory selection, suggesting that males who sing more frequently also have more competitive ejaculates. Our results are consistent with the hypothesis that high polyandry levels promote greater relative postcopulatory selection. They also highlight the need for detailed behavioral observations under conditions as natural as possible when measuring mating and reproductive success.     

DISENTANGLING PRECOPULATORY AND POSTCOPULATORY SEXUAL SELECTION IN POLYANDROUS SPECIES

Sexual selection operates on a sequence of events, from mating to offspring production. Which stages in this sequence undergo stronger selection, especially the relative importance of pre‐ versus postcopulatory processes, are intensely debated issues. Unequal siring success among mates of polyandrous females is classically taken as evidence for a large contribution of postcopulatory processes to the variance in male reproductive success (var(RS_m)). However, paternity skews also depend on the timing and number of copulations, a source of variation that should be considered precopulatory rather than postcopulatory. We develop a method for decomposing var(RS_m) accounting for copulatory activity and apply it to experimental mating groups of the snail Physa acuta. In our experiment, 40% of var(RS_m) emerges at the precopulatory stage, only half of which depends on variation in mating success (number of partners). Ignoring copulation characteristics can therefore lead to severe underestimation of precopulatory sexual selection. Moreover, although only 36% of var(RS_m) arises at the postcopulatory stage, this is when sexual selection on body weight mostly occurs. Finally, trade‐offs were detected between different components of precopulatory success, whereas pre‐ and postcopulatory success appear independent. Our study opens the way to a detailed quantitative understanding of sexual selection in polyandrous species.     

Wing pigmentation in territorial male damselflies, Calopteryx haemorrhoidalis: a possible relation to sexual selection

One striking characteristic in adult males of some odonate species is the presence of wing pigmentation. In Calopteryx species, males show a series of pre- and postcopulatory behavioural displays during which they face females while showing their pigmented wings. One hypothesis to explain the precopulatory flying displays and the associated wing pigmentation is that they may serve a sexual selection function. I investigated this in the territorial damselfly Calopteryx haemorrhoidalis. Males of this species defend aquatic substrates that females use for oviposition. Observational evidence indicated that males with a higher proportion of wing pigmentation were more likely to defend a territory, obtained more matings, had fewer gut parasites, survived in the study site and stayed in territories for longer. Experimental evidence suggested that the relationship mating success and wing pigmentation still held when controlling for the size of the substrate defended by territorial males. Similar to other studies in the Calopterygidae, these results suggest that wing pigmentation may be favoured by sexual selection. I discuss, however, whether an alternative function for male copulatory courtship displays and wing pigmentation, as sexual and/or species recognition, may also explain the evolution of these traits. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

A mixed model of the evolution of polygyny and sexual size dimorphism in mammals

The theory of sexual selection is the most widely accepted theory explaining the evolution of mating systems and secondary sexual characters. Polygyny is the most common mating system in mammals, and there is a strong correlation between the degree of polygyny and the degree of sexual size dimorphism skewed towards males. Sexual selection theory posits that polygyny in mammals has evolved through direct, precopulatory, intrasexual selection in males, and that sexual size dimorphism is a result of male competition for mates. New results that are being obtained with the use of molecular techniques and with comparative phylogenetic methods do not appear to support predictions from this classical model in full. In this article, an expansion of the classical model is presented that combines the effects of at least four forms of selection: natural, precopulatory intrasexual, postcopulatory intrasexual, and intersexual selection. This mixed model consists of an initial phase in which natural selection operates on body size, followed by a second phase dominated by sexual selection and involving increases in sexual dimorphism and coercive behaviour of males towards females. Sexual harassment induces female aggregation, thus creating social potential for polygyny. Males compete for access to the groups of females, following two possible evolutionary scenarios, directional or equilibrium sexual selection, both producing similar behavioural polygyny, but with differences in the intensity of intra-male precopulatory sexual selection. Predictions of the mixed model are as follows: 1) polygyny can exist without high variance in male reproductive success (a fundamental requirement in the classical model); 2) extra-group fertilisation can be common; 3) sexual size dimorphism evolved prior to polygyny; 4) sexual coercion is widespread; and 5) females reduce levels of sexual coercion by joining groups.     

Mating behavior of Aegla platensis (Crustacea, Anomura, Aeglidae) under laboratory conditions

The mating behavior of several decapod crustaceans has been extensively studied; however, this aspect of anomuran biology is still poorly known in some groups. Aeglids are the only anomurans inhabiting freshwaters, and the mating behavior of the species in this family is unknown. We provide the first account of the mating behavior of an aeglid, Aegla platensis, under laboratory conditions. The precopulatory phase was characterized by male agonistic display, male approach, and courtship. Males exhibited the agonistic display toward immature and mature females, but only physiologically mature females allowed males to approach. Male approach led to display of courtship behaviors (body vibration, thrust, body lifting, and abdomen flapping). During the copulatory phase, males and females touched each other with the antennae (antennae touch), and males positioned themselves beneath the females (supine position). Although sperm transfer was not directly observed, a “white mass” was detected among oocytes in the female abdominal chamber shortly after some copulations. Finally, in the postcopulatory phase, males guard females during the process of egg attachment. Despite their morphological similarities with other anomurans, the mating behavior of aeglids seems to be unique, and the freshwater environment appears to have an important role in driving these differences.     

Correlated evolution between targets of pre‐ and postcopulatory sexual selection across squamate reptiles

Sexual selection reflects the joint contributions of precopulatory selection, which arises from variance in mating success, and postcopulatory selection, which arises from variance in fertilization success. The relative importance of each episode of selection is variable among species, and comparative evidence suggests that traits targeted by precopulatory selection often covary in expression with those targeted by postcopulatory selection when assessed across species, although the strength and direction of this association varies considerably among taxa. We tested for correlated evolution between targets of pre‐ and postcopulatory selection using data on sexual size dimorphism (SSD) and testis size from 151 species of squamate reptiles (120 lizards, 31 snakes). In squamates, male–male competition for mating opportunities often favors large body size, such that the degree of male‐biased SSD is associated with the intensity of precopulatory selection. Likewise, competition for fertilization often favors increased sperm production, such that testis size (relative to body size) is associated with the intensity of postcopulatory selection. Using both conventional and phylogenetically based analyses, we show that testis size consistently decreases as the degree of male‐biased SSD increases across lizards and snakes. This evolutionary pattern suggests that strong precopulatory selection may often constrain the opportunity for postcopulatory selection and that the relative importance of each selective episode may determine the optimal resolution of energy allocation trade‐offs between traits subject to each form of sexual selection.     

Beobachtungen zum Paarungs- und Aufzuchtverhalten der Wasserspitzmaus Neomys fodiens (Soricidae)

Five European Water Shrews (Neomys fodiens) were kept in an indoor enclosure of 2.7 m² where one couple mated regularly. Multiple copulations appeared over a period of about 12 hours. Ten litters with 56 offspring were born and 33 survived. The female gave birth to her latest litter at an age of about 20 month, 2 month later as the end of the reported lifespan in nature. The period of fertility lasted 336 days and is comparable to those of Crocidura. At the end of this period three times signs of pseudopregnancy were detected: After copulating the female started building her nest and intensified this behaviour after about three weeks, at the end of the expected “gestation” swollen nipples could also be noticed, but no offspring inside the nest. The female died at an age of about 38 month.After successful copulations a copulatory lock was achieved and the female could track her mate. The mating behaviour can be classified as follows: a) male entering female's territory, b) precopulatory chasing, c) approaching of the mates, d) mounting and repeated copulations attempts, e) successful copulation, male slipping down from female's back, f) copulatory lock and resting, g) cleaning sexual organs, h) continuing chasing and further copulations or i) displacing the male and finishing sexual behaviour. Driving off the male from female's territory could last some time. No special calls were uttered in the close context of copulatory behaviour, only the known ones while chasing, some low contact calls inside the nest and aggressive calls while driving off the male.     

Pre‐ and postcopulatory sexual selection favor aggressive,young males in polyandrous groups of red junglefowl

A challenge in evolutionary biology is to understand the operation of sexual selection on males in polyandrous groups, where sexual selection occurs before and after mating. Here, we combine fine‐grained behavioral information (>41,000 interactions) with molecular parentage data to study sexual selection in replicated, age‐structured groups of polyandrous red junglefowl, Gallus gallus. Male reproductive success was determined by the number of females mated (precopulatory sexual selection) and his paternity share, which was driven by the polyandry of his female partners (postcopulatory sexual selection). Pre‐ and postcopulatory components of male reproductive success covaried positively; males with high mating success also had high paternity share. Two male phenotypes affected male pre‐ and postcopulatory performance: average aggressiveness toward rival males and age. Aggressive males mated with more females and more often with individual females, resulting in higher sexual exclusivity. Similarly, younger males mated with more females and more often with individual females, suffering less intense sperm competition than older males. Older males had a lower paternity share even allowing for their limited sexual exclusivity, indicating they may produce less competitive ejaculates. These results show that—in these populations—postcopulatory sexual selection reinforces precopulatory sexual selection, consistently promoting younger and more aggressive males.     

A new role for antennation in paper wasps (Hymenoptera,Vespidae): antennal courtship and sex dimorphic glands in antennomeres

Summary. Males of Polistes dominulus perform antennal vibrations and grasping of female antennae during pre-copulatory and copulatory phases. Male antennation plays a relevant role in mating success. In several antennomeres of males of P. dominulus and Vespa crabro, a further species in which we observed male antennation, we found secretory cells of class 1 and 3 associated to the same release site. In P. dominulus, class 3 cells with ampulla-like reservoirs and class 1 cells release their secretion through hairless multiporous areas. In V. crabro, tyloid-like structures are associated with large apodemes. The as yet unidentified secretion of these glands may act as a contact or low-volatile sex pheromone during courtship behaviour.Received 4 December 2003; revised 16 August 2004; accepted 7 September 2004.     

A quantitative description of copulatory and associated behaviors of captive marmosets (Callithrix jacchus)

Measurements of male and female copulatory behavior in pairs of common marmosets were made during 30-min mating tests (n = 170). For the male,both frequencies and latencies of mounting, pelvic thrusting, and ejaculatory behaviors were analyzed. For the female, frequencies of proceptive displays (tongue-flicking) and of sexual receptivity were measured. The sexual and associated behavior of the marmoset is compared to that of other primates and the suitability of this species for laboratory studies of neurohumoral mechanisms and sexual behavior is assessed.     

Precopulatory behaviour of male rats: developmental aspects and dependence on female's solicitation

Sexual communication between sex partners can involve just one sensory modality or a combination, depending upon such factors as species, habitat, and context. Ethological aspects of sexual communication has been widely documented in rodents. In rats, sexual communication between male and female varies according to the production of signals by a female that signal receptivity, proceptivity, and attractivity. However, in the laboratory experiment, such approach is often neglected. In the present study, two types of stimulus female--Lordotic and Darting--were used with the aim to examine developmental changes in precopulatory behaviour of males. Besides the dependence of the male's precopulatory repertoire on the strength of proceptive stimuli emitted by the female was studied. Male rats ranging from 30 to 175 days of age were observed under the dyadic interaction. It was found: (a) Precopulatory behaviour of the 30-day-old males was not clear-cut, the males devoted more time to social investigation of adult (Darting) female. (b) All the 40-day-old males exhibited precopulatory behaviour in the range of the repertoire displayed by adult animals. (c) Precopulatory activity of juvenile (45-day-old) as well as of adult (90-day-old) males exposed to Lordotic female was significantly lower as compared with that exhibited by males toward Darting female. (d) Copulatory readiness of males increased with the age, in fact, all animals aged from 75-135 day were able to pass from the precopulatory into the copulatory phase of sexual interaction. (e) Although the 175-day-old males exhibited pronounced precopulatory activity, they did not initiate copulations. The implications of each of these findings are discussed from the point of view of both the developmental aspects and the stimulus-response relationships. To sum up, the development of normal flow of sexual behaviour of male rats proceeds simultaneously with the development of physiological and morphological parameters. The appearance of precopulatory behaviour is less dependent on the internal (hormonal) readiness than copulatory behaviour. The connection of both phases, i.e. precopulatory and copulatory, is terminated at about Day 75, and is the key moment of sexual interaction from the point of view of reproductive success. In fact, a successful course of sexual interaction is codetermined by the intensity of behavioural stimuli and/or by the completeness of proceptive patterns provided by the female partner. It is clear that the reproductive process cannot be completed without some degree of communication. The deterioration of sexual interaction found in males aged 175 day seems to be the consequence of their absolute heterosexual abstinence.(ABSTRACT TRUNCATED AT 400 WORDS)     

A time-sequence functional analysis of mating behaviour and genital coupling in Drosophila: role of cryptic female choice and male sex-drive in the evolution of male genitalia

Male genitalia in Drosophila exemplify strikingly rapid and divergent evolution, whereas female genitalia are relatively invariable. Whereas precopulatory and post-copulatory sexual selection has been invoked to explain this trend, the functional significance of genital structures during copulation remains obscure. We used time-sequence analysis to study the functional significance of external genitalic structures during the course of copulation, between D. melanogaster and D. simulans. This functional analysis has provided new information that reveals the importance of male-driven copulatory mechanics and strategies in the rapid diversification of genitalia. The posterior process, which is a recently evolved sexual character and present only in males of the melanogaster clade, plays a crucial role in mounting as well as in genital coupling. Whereas there is ample evidence for precopulatory and/or post-copulatory female choice, we show here that during copulation there is little or no physical female choice, consequently, males determine copulation duration. We also found subtle differences in copulatory mechanics between very closely related species. We propose that variation in male usage of novel genitalic structures and shifts in copulatory behaviour have played an important role in the diversification of genitalia in species of the Drosophila subgroup.     

Sperm competition and the evolution of precopulatory weapons: Increasing male density promotes sperm competition and reduces selection on arm strength in a chorusing frog

Sperm competition theory assumes a trade‐off between precopulatory traits that increase mating success and postcopulatory traits that increase fertilization success. Predictions for how sperm competition might affect male expenditure on these traits depend on the number of competing males, the advantage gained from expenditure on weapons, and the level of sperm competition. However, empirical tests of sperm competition theory rarely examine precopulatory male expenditure. We investigated how variation in male density affects precopulatory sexual selection on male weaponry and the level of sperm competition in the chorusing frog Crinia georgiana, where males use their arms as weapons in male–male combat. We measured body size and arm girth of 439 males, and recorded their mating success in the field. We found density‐dependent selection acting on arm girth. Arm girth was positively associated with mating success, but only at low population densities. Increased male density was associated with higher risk and intensity of sperm competition arising from multimale amplexus, and a reversal in the direction of selection on arm girth. Opposing patterns of pre‐ and postcopulatory selection may account for the negative covariation between arm girth and testes across populations of this species.     

Experimental evolution exposes female and male responses to sexual selection and conflict in Tribolium castaneum

Between-individual variance in potential reproductive rate theoretically creates a load in reproducing populations by driving sexual selection of male traits for winning competitions, and female traits for resisting the costs of multiple mating. Here, using replicated experimental evolution under divergent operational sex ratios (OSR, 9:1 or 1:6 ♀:♂) we empirically identified the parallel reproductive fitness consequences for females and males in the promiscuous flour beetle Tribolium castaneum. Our results revealed clear evidence that sexual conflict resides within the T. castaneum mating system. After 20 generations of selection, females from female-biased OSRs became vulnerable to multiple mating, and showed a steep decrease in reproductive fitness with an increasing number of control males. In contrast, females from male-biased OSRs showed no change in reproductive fitness, irrespective of male numbers. The divergence in reproductive output was not explained by variation in female mortality. Parallel assays revealed that males also responded to experimental evolution: individuals from male-biased OSRs obtained 27% greater reproductive success across 7-day competition for females with a control male rival, compared to males from the female-biased lines. Subsequent assays suggest that these differences were not due to postcopulatory sperm competitiveness, but to precopulatory/copulatory competitive male mating behavior.     

The importance of pre-and postcopulatory sexual selection promoting adaptation to increasing temperatures

Global temperatures are increasing rapidly affecting species globally. Understanding if and how different species can adapt fast enough to keep up with increasing temperatures is of vital importance. One mechanism that can accelerate adaptation and promote evolutionary rescue is sexual selection. Two different mechanisms by which sexual selection can facilitate adaptation are pre- and postcopulatory sexual selection. However, the relative effects of these different forms of sexual selection in promoting adaptation are unknown. Here, we present the results from an experimental study in which we exposed fruit flies Drosophila melanogaster to either no mate choice or 1 of 2 different sexual selection regimes (pre- and postcopulatory sexual selection) for 6 generations, under different thermal regimes. Populations showed evidence of thermal adaptation under precopulatory sexual selection, but this effect was not detected in the postcopulatory sexual selection and the no choice mating regime. We further demonstrate that sexual dimorphism decreased when flies evolved under increasing temperatures, consistent with recent theory predicting more sexually concordant selection under environmental stress. Our results suggest an important role for precopulatory sexual selection in promoting thermal adaptation and evolutionary rescue.