Copulatory plug displacement and prolonged copulation in the Iberian rock lizard (Lacerta monticola)

Male Iberian rock lizards (Lacerta monticola) produce copulatory plugs that adhere firmly inside the female cloaca and occlude both oviducts. These plugs do not prevent rival male insemination, as they neither reduce female attractiveness or receptivity to rival males nor do they function as chastity belts. Prior to copulation, males bite various regions of the female body, including the cloacal region. A previous plug in the female cloaca is expelled only after rival male intromission. We hypothesized that: (1) such male pre-copulatory behaviours function to loosen plug adherence to the female cloaca, thereby facilitating intromission, and that (2) the hemipenis plays a role in displacing a previous plug prior to the delivery of a new plug. Neither of these hypotheses was supported. Instead, our results indicate that rival males can intromit the hemipenis past a previous plug in the female cloaca and deliver their own plug underneath it. Consequently, previous plugs are pushed away from the oviductal openings and even dislodged from the female cloaca. Copulation duration was determined both by the time used by males to deliver a plug and by the fact that males prolonged copulation beyond plug delivery. There seemed to be sexual conflict over prolonged copulation, which was resolved by the male/female head-length ratio. The adaptive value of Iberian rock lizard copulatory plugs and prolonged copulation in Iberian rock lizards is discussed in the context of sperm competition.Communicated by S. Downes     

Effects of testosterone supplementation on chemical signals of male Iberian wall lizards: consequences for female mate choice

In some lizards, female mate choice is influenced by chemicals secreted by males, e.g., via the femoral glands. Secretions of the femoral glands are under direct androgenic control and vary seasonally with androgen production. However, whether increased testosterone (T) levels affect the concentration and chemical composition of secretions or their attractiveness to females is unknown. We manipulated T levels of male Iberian wall lizards, Podarcis hispanica, with silastic implants. Differential tongue-flick rates indicated that females detected and discriminated between femoral secretions of control and T-implanted males based on chemical cues alone. Females showed greater responses to secretions of T-males, which might suggest that T increased the concentration of chemical signals. Further analyses by gas chromatography–mass spectrometry indicated that T supplementation induced qualitative changes in lipid composition of femoral secretions. T-males had decreased relative proportions of cholesta-5,7-dien-3-ol in secretions, which might be related to the negative effects of T on the immune system and on lipid metabolism. However, experiments of choice of males’ scent showed that females neither preferred nor avoided the scent marks of T-males but preferred males that maintained higher proportions of cholesta-5,7-dien-3-ol in secretions, independently of the experimental manipulation. Thus, because this steroid is negatively affected by T, there might be trade-offs among increasing T levels to increase the production of chemical secretions, maintain metabolism, and attract females.     

Chemosensory discrimination of familiar and unfamiliar conspecifics by lizards: implications of field spatial relationships between males

The ability of territorial lizards to discriminate between scents of neighbors and non-neighbors might contribute to decreasing the costs of aggressive interactions. To test this hypothesis, we conducted a field study to analyze the spatial relationships between male Iberian rock-lizards, Lacerta monticola. We then used the same individuals in a laboratory experiment to test whether male lizards can use chemical cues to discriminate between familiar conspecific males (those whose home ranges overlapped) and unfamiliar conspecific males (those whose home ranges did not overlap, and whose home range centers were at least 50 m apart). Differences in tongue-flick rates in the presence of chemical cues suggested that male L. monticola discriminated between odors of familiar and unfamiliar males. The behavioral responses were also dependent on relative differences in body size between the responding male and the unfamiliar male that donated the scent: There was a significant negative correlation between tongue-flick rates emitted in cages of unfamiliar males and the body size differences between males. In contrast, when the donor of the scent was a familiar male, the tongue-flick rate was not dependent on body size differences. These results are compatible with individual discrimination through chemical cues in male L. monticola.     

Chemical ornaments of male lizards <Emphasis Type="Italic">Psammodromus algirus</Emphasis> may reveal their parasite load and health state to females

Evidence for parasite-mediated sexual selection has been found in many species that use visual ornaments to attract females. However, in many animals, variation in female responses to scents of parasitized males suggests that parasitic infections might also affect information conveyed by pheromones (i.e., chemical ornaments). Thus, pheromones might also function in parasite-mediated sexual selection. We show here that female lizards Psammodromus algirus responded differently to femoral gland secretions of males according to the parasite load and health of these males. Scents of healthier males elicited more tongue flicks (a chemosensory behavior) by females, suggesting that these scents were more attractive. Chemical analyses showed that parasite load and the T-cell-mediated immune response were related to the variability in the proportions of some lipids in secretions of males. Further trials testing the chemosensory responses of females to chemical standards indicated that females actually discriminated the chemicals related to males’ health from other chemicals found in secretions. We suggest that these chemical ornaments may provide reliable information on the health and degree of parasitic infection of a male.     

Effectiveness of the mating plug in Atrophaneura alcinous (Lepidoptera : Papilionidae)

Summary At mating, males of Atrophaneura alcinous plug the female copulatory duct with a secretory material, but some females copulate several times and can receive spermatophores from different males up to three times. Remating by plugged females mostly takes place shortly after the first mating, when the freshly formed first plug has not completely hardened. A freshly formed plug can be pressed aside or tunneled by the male aedeagus, and thus intromission and subsequent spermatophore transfer are sometimes possible. This is not always the case, however, and larger plugs are more likely to prevent aedeagus intrusion even if they are not completely hardened. Also, a few females remated a day after the first mating or later, when the first plug is already very hard. Completely hardened plugs are more effective than freshly formed ones; later mating males can thrust the aedeagus into the ductus bursae only when the plug is less than ca 1.2 mg (dry weight). The occurrence of female re-mating in plug-forming species thus does not necessarily mean that the plug is ineffective. Offprint requests to: K. Matsumoto     

Symmetry, male dominance and female mate preferences in the Iberian rock lizard, Lacerta monticola

Female preference for dominant males is widespread and it is generally assumed that success in male-male competition reflects high quality. However, male dominance is not always attractive to females. Alternatively, relatively symmetric individuals may experience fitness advantages, but it remains to be determined whether males with more symmetrical secondary sexual traits experience advantages in both intra- and intersexual selection. We analysed the factors that determine dominance status in males of the lizard Lacerta monticola, and their relationship to female mate preference, estimated by the attractiveness of males' scents to females. Sexually dimorphic traits of this lizard (head size and femoral pores) appear to be advanced by different selection pressures. Males with relatively higher heads, which give them advantage in intrasexual contests, were more dominant. However, head size was unimportant to females, which preferred to be in areas marked by relatively heavier males, but also by males more symmetric in their counts of left and right femoral pores. Chemicals arising from the femoral pores and other glands might honestly indicate quality (i.e. related to the symmetry levels) of a male to females and may result from intersexual selection. Females may use this information because the only benefit of mate choice to female lizards may be genetic quality. Chemical signals may be more reliable and have a greater importance in sexual selection processes of lizards than has previously been considered.     

Multiple color signals may reveal multiple messages in male Schreiber’s green lizards, <Emphasis Type="Italic">Lacerta schreiberi</Emphasis>

Multiple traits may either signal different characteristics of a male or be redundant. These multiple signals may convey different messages if they are intended for different receivers (e.g., male or females) that have different interests. We examined the functions of multiple colorful visual traits of male Schreiber’s green lizard (Lacerta schreiberi). Results showed that interindividual variation in the characteristics of coloration of males can be related to variation in morphology, health state, dominance status, and pairing status, but that different relationships were found for each color signal. For example, dominant males had brighter “blue” throat and with higher values of ultraviolet (UV) and bluish coloration and darker and greenish dorsal coloration than subordinate males. Health state was also reflected in coloration; males with a higher immune response had “blue” throats with lower amounts of UV coloration, but had “yellow” chests with higher amounts of UV coloration. Males found guarding females also differed in coloration from males found alone. These data suggest that characteristics of coloration of the different multiple signals may reveal different messages for different receivers, either male or female conspecifics. The development of the different signals, based on different morphological and physiological mechanisms and trade-offs, may allow signal reliability of multiple colorful traits in different social contexts.     

Correlates of copulatory success in a fallow deer lek

Summary We studied the behavior and copulatory success of fallow deer (Cervus dama) males at a lek. We recorded 471 copulations in 3 years. Most males did not copulate. The top three males accounted for between 60 and 90% of copulations each year. Lek attendance time was the major determinant of male copulatory success, but territory location also affected the number of copulations achieved. Copulatory success was correlated with the number of females in a male's territory and possibly with dominance status, but not with fighting success or fighting rate. All males that defended lek territories were 5 years of age or older. Copulatory success may improve with age. Body condition appears to be an important determinant of male copulatory success, because only males in superior condition could defend a lek territory for up to 2 weeks. Males do not feed while defending lek territories. Foraging ability during the year probably determines condition at the onset of the rut. Females appear to choose mates at least partially on the basis of location, preferring males located near traditional routes. Females may ultimately select mates in the best body condition.     

Interpopulational differences in chemical composition and chemosensory recognition of femoral gland secretions of male lizards Podarcis hispanica: implications for sexual isolation in a species complex

Summary. Molecular studies suggest that the Iberian wall lizard, Podarcis hispanica, forms a species complex with several monophyletic types. In Central Spain two of these types are spatially not isolated and may interact. Sex pheromones are important for species recognition and, thus, differences between lizards’ types in chemicals used in intraspecific communication could lead to reproductive isolation. Analyses by GC-MS showed that the femoral gland secretions of adult males of different types were different. Males of one type had twelve exclusive compounds, and proportions of some shared compounds differed. This presumably would reflect selection for the persistency and efficiency of chemical signals in different environments; less volatile compounds and with a higher chemical stability being favoured in the type of lizards inhabiting more humid climatic conditions. Differential tongue-flick rates to scents from femoral secretions indicated that males were able to detect and discriminate between males of different types based on chemical cues alone. In contrast, females detected but did not seem able to discriminate between scents of the two types of males. Thus, multiple factors might be simultaneously acting either against or in favor of speciation, leading, on the one hand, to genetic differences between types, but, on the other hand, probably precluding an effective reproductive isolation in areas where both types of lizards may interact.     

Scent marking pheromones in lizards: cholesterol and long chain alcohols elicit avoidance and aggression in male Acanthodactylus boskianus (Squamata: Lacertidae)

Femoral gland secretions are believed to play an important role in chemical communication and social organization of lizards. In spite of this, few studies have investigated the chemical composition and the behavioural roles of these secretions. The lacertid lizard Acanthodactylus boskianus is a good example, having these well-developed glands in both sexes. We used GC–MS chemical analysis of gland secretions and y-maze choice test bioassays to investigate the ability of the lizards to detect and respond to different synthetic blends made from compounds identified in the gland secretions. Based upon the GC–MS quantification data, we selected representatives of the main chemical groups (steroids, alcohols, acids, alkanes) detected in the lizard secretions and used these in a behavioural bioassay against controls. Males showed significant avoidance behaviour for cholesterol and alcohol blends, combined with agonistic behaviour towards these stimuli. Females did not show any significant selection to particular odour combinations. The data support the hypotheses that lizards can potentially use femoral gland secretions in chemical odour trails and utilize scent to mark territories and potentially also to establish dominance hierarchies. Cholesterol and long chain alcohols are suggested as potential candidates functioning as scent marking pheromones in A. boskianus.     

Interpopulational variation in chemosensory responses to selected steroids from femoral secretions of male lizards, Podarcis hispanica, mirrors population differences in chemical signals

Chemical signals are important for mate and species recognition. If variation in chemical signals occurs between populations of the same species, these differences could later preclude mating between populations and lead to speciation. In the Iberian wall lizard, Podarcis hispanica, the lipophilic fraction of femoral secretions of males is mainly a mix of steroids and fatty acids. Among steroids, the most abundant compounds are cholesterol and cholesta-5,7-dien-3-ol, which are implicated in intraspecific communication and sexual selection. Interpopulational differences in chemical signals of males, and in response to these chemicals, could contribute to reproductive isolation between populations, which would explain the known genetic differences between these populations. Chemical analyses indicated that five distinct populations of this lizard from Madrid (Central Spain) differed in the proportions of two steroids (cholesterol and cholesta-5,7-dien-3-ol) in femoral secretions. Moreover, lizards discriminated and had high chemosensory responses (i.e., high tongue-flick rates) to these steroids, but showed interpopulational differences. Lizards from populations with cold temperatures and high relative humidity (i.e., northern Madrid) elicited higher responses to these steroids, whereas the converse occurred for lizards from populations occupying dry and hot habitats (i.e., southern Madrid). Interestingly, the magnitude of the chemosensory responses to cholesta-5,7-dien-3-ol in each population mirrored the abundance of this compound in secretions of males of that population. These results suggest that the importance of cholesta-5,7-dien-3-ol in males’ secretions might be lower for lizards from the southern populations. These differences in the relative importance of chemical signals could explain reproductive isolation and cryptic speciation between populations of this lizard.     

Indirect fitness benefits are not related to male dominance in a killifish

Recent theoretical and empirical studies have shown that male dominance is often at odds with female mate preference and that indirect (genetic) benefits of mate choice may not be related to male dominance. We tested whether female preference corresponded to male dominance and whether mating with dominant males conveyed benefits to offspring fitness in a small freshwater fish, the African annual killifish Nothobranchius korthausae (Cyprinodontiformes), a species without parental care. The experimental design used controlled for the effect of male age, possibility of sperm and egg depletion, and accounted for a potential that females express their preference through maternal effects by manipulation of egg mass during ovulation. By sequentially mating females with males of known dominance, we found that female N. korthausae showed no mate preference in terms of egg numbers deposited with respect to male dominance or body size and no congruent mate preference to specific males was detected. However, males sired offspring with consistently higher hatching success and the effect was repeatable across individual females. Thus, some males provided females with indirect benefits related to additive genetic quality (“good genes”) and expressed via increased hatching rate, but this benefit was not related to male dominance status or body size.     

Responses of female lizards,<Emphasis Type="Italic"> Lacerta monticola</Emphasis>, to males' chemical cues reflect their mating preference for older males

Female mate choice based on visual traits appears to be rare in lizards. Field observations suggest that females of the lizard Lacerta monticola preferred to mate with larger/older males. Although older males are usually green and larger, and younger males brown and smaller, there is some overlap in size and coloration between age classes. Thus, visual cues may not always be reliable indicators of a male's age. We hypothesized that female mate-choice preferences may be based on males' pheromones, which might transmit information about characteristics such as age. In a laboratory experiment, we analyzed the effect of age of males on attractiveness of their scents to females. When we offered scents of two males of different age, females associated preferentially with scents of older males. This suggested that females were able to assess the age of males by chemical signals alone, and that females preferred to be in areas scent-marked by older males. Thus, females may increase their opportunities to mate with males of high quality, or may avoid harassment by sneaking young males. This result agreed with field observations on females mating with old males, and rejection of advances by young males. Our results also suggested that female preference for older males may depend on their own body size. Large females showed a strong preference for older males, whereas smaller females were not so selective. This, together with males' preference for large females, might lead to size-assortative matings. We suggest that the quality and/or quantity of male pheromones could communicate to the female heritable male genetic quality (i.e. age) and thereby serve as the basis of adaptive female choice in lizards.Communicated by W.E. Cooper     

Copulatory plugs do not assure high first male fertilisation success: sperm displacement in a lizard

Sperm competition selects for opposing male defensive and offensive reproductive traits, and its outcome may be determined by the effectiveness to which one trait has evolved to out-compete the other. We tested the effectiveness of a first male plug physical interference with a second male insemination (defence) vs the effectiveness of plug and associated sperm displacement by a second male (offence) on the outcome of sperm competition in Iberian rock lizards. We conducted a double mating experiment where we compared the proportion of eggs per clutch fertilised by the same second males (against the same first males) when they copulated with females 30 min (first male plug adhered firmly inside the female cloaca) and 4 h (first male plug loosely adhered or shed from the female cloaca) after first males. We found that second males fertilised the majority of the eggs per clutch in the 30-min treatment, whereas fertilisations were equally shared between the two males in the 4-h treatment. These results show that plugs have little defensive effectiveness, and thus, do not assure high first male fertilisation success. Instead, sperm displacement appears to be associated with plug displacement. That is, because sperm embedded in first male plugs, and displaced from competition for fertilisations by second males, is expected to increase in number with decreasing time allowed for female sperm transport, second males thus enjoy higher fertilisation success. This study shows that offensive plug displacement out-competes plug defensive role in Iberian rock lizards. Moreover, it reveals sperm displacement as a novel sperm competition mechanism in reptiles.     

Sexual cannibalism facilitates genital damage in <Emphasis Type="Italic">Argiope lobata</Emphasis> (Araneae: Araneidae)

Sperm competition is a potent driving force in evolution leading to a remarkable variety of male adaptations that prevent or reduce fertilization by rivals. An extraordinary defensive strategy against sperm competition has evolved in a number of web spiders where males break off parts of their paired genitalia in order to obstruct the copulatory openings of females (mating plug). A recent comparative analysis on the family level reports that genital damage is most frequent in species with sexual cannibalism although, as yet, a functional association between sexual cannibalism and genital damage has not been found. Using the moderately sexually cannibalistic orb-web spider Argiope lobata, we show for the first time that males cannibalized during their first copulation damaged their pedipalps with significantly higher probability (74%) than males that escaped (15%). Of all males that damaged their genitalia, 44% were able to place a genital fragment inside the copulatory opening of the female, resulting in a relatively low total plugging rate of 14%. Successful obstruction of the female copulatory opening reduced the share of paternity of subsequent males (P ₂ = 0.06%), thus, indicating that genital damage may have evolved as a response to sperm competition in this species as well. However, the low incidence of successful plugging and the strong relationship between sexual cannibalism and genital damage suggest that apart from paternity protection, the nature of genital damage in A. lobata is further shaped by sexual conflict or cryptic female choice.     

Role of sex and breeding status in grooming and total tick load of impala

The lesser mouse lemur (Microcebus murinus) is a prosimian primate which presents evidence of sex ratio bias of offspring that agrees with the direction of bias predicted by the local resource competition model for facultative sex ratio adjustment. That is, females overproduced sons when grouped prior to mating, whereas isolated females exhibited the opposite tendency. In this solitary species, social communication relies heavily on urinary chemical signals. To test the hypothesis that sex biases induced by social factors may be linked to urinary cues, isolated females were exposed (n = 76) or not (control group, n = 16) to urinary cues from other reproductively active females from the beginning of the breeding season (induced by long photoperiod) until oestrus. During that period, females were either continuously (n = 17) or partially (n = 59) exposed to chemosignal stimulation. Females in oestrus were placed in contact with a breeding male and subsequently isolated until they gave birth. All females entered oestrus but the timing of oestrus was significantly delayed by 1 week in urine-exposed females. A general depressive effect of long-term urine exposure on fecundity was demonstrated, involving fewer impregnations, higher abortion frequency and smaller litter sizes. Among females giving birth (n = 55) to a total of 129 young, a significant positive correlation was found between sex ratio bias towards males and the duration of urine exposure. However, the shift in sex ratio at birth depended on the duration of urine stimulation during a sensitive period extending from the beginning of the long photoperiod until the beginning of the follicular phase. In the absence of urinary cues during the sensitive period, females significantly overproduced daughters (32% males of 53 newborn). As urine exposure increased during the sensitive phase, the proportion of males in litters increased from 54% males (n = 50) in partially urine-exposed females to a significant bias towards males (69.2% of 26 newborn) in totally exposed females. The biased sex ratio in response to chemical cues did not show consistent relationships with maternal body weight, parity or litter size. Although the intrinsic mechanisms involved in sex-biased conceptions are not known, chemical cues could interact with the photoperiodic control of gonadotropin secretions. Received: 14 January 1995/Accepted after revision: 26 November 1995     

The scent of dominance: female field crickets use odour to predict the outcome of male competition

Pheromones may convey information about mate quality and social status. In the field cricket Gryllus integer, females mount the males for copulation, such that males cannot coerce females to mate. We examined whether virgin G. integer females preferred the scent of potentially dominant males to that of subordinate males. First, we collected pheromones by confining males on filter paper. Next, we offered filter paper from each of two size-matched males and control paper to females that had never been exposed to males, and measured the time spent by the female on each kind of paper. Finally, dominance status of the males in each size-matched pair was determined by pitting the two males against one another in agonistic contests. When offered filter paper from subsequently dominant versus subsequently subordinate males, females spent more time on the paper from the dominant male than the subordinate male, and much less time on control paper. Thus, pheromones may inform female G. integer about a male's potential to achieve dominant social status. Male pheromones were also associated with the female's tendency to mount a male. In contrast to cockroaches, where females prefer the scent of subordinate males (presumably to avoid risk of injury), female crickets prefer the scent of potentially dominant males and are more likely than males to wound their mating partners.     

Cannibalize or care? The role of perceived paternity in the sand goby, <Emphasis Type="Italic">Pomatoschistus minutus</Emphasis>

Parental care is a costly part of reproduction. Hence, natural selection should favor males which avoid caring for unrelated young. However, the decision to abandon or reduce care requires cues which are evaluated to give information on potential reproductive value of the offspring. The prediction that male sand gobies, Pomatoschistus minutus, care for foreign eggs as long as they were spawned in their own nest and at least some of such cues are fulfilled was tested. Egg-guarding males that had recently taken part in a spawning event were given a clutch of eggs that was sired either by themselves or another male, in either their own or another male’s aquarium. Males that had not taken part in a spawning event were used as controls and were given eggs sired by another male. We measured the amount of filial cannibalism and nest building. Control group males did not care for eggs and ate them all before rebuilding the nest. In the other treatments, there were no significant effects of paternity, though males moved to another male’s aquarium increased their clutch area threshold and completely consumed larger clutches than males that were not moved. There was no intermediate response in any treatment in the form of increased partial filial cannibalism or less well-constructed nests. Our results suggest that egg-guarding males cannot distinguish between eggs sired by themselves and those sired by other males but are able to react to cues indicating paternity state. Males do not adopt eggs to attract females in P. minutus.     

Do female bank voles (Clethrionomys glareolus) mate multiply to improve on previous mates?

Contrary to classical sexual selection theories, females of many taxa mate with multiple males during one reproductive cycle. In this study, we conducted an experiment on the “trade-up hypothesis”, which proposes that females remate if a subsequently encountered male is potentially superior to previous mates to maximize the genetic quality of their offspring. We presented bank vole females (Clethrionomys glareolus) sequentially with two males of known dominance rank in different orders, i.e., either first subordinate and second dominant, first dominant and second subordinate, or two males that were equal in dominance (high ranking) and observed their mating behavior. We found that 92% of the females mated multiply and did not base their remating decision on male social status. Therefore, polyandry cannot be explained by the “trade-up hypothesis” based on dominance rank in this species. However, we found that dominant males sired significantly more offspring than subordinate males. This varied according to mating order: dominant males sired more offspring when they were second than when they were first. Moreover, litter sizes were significantly smaller when the dominant male was first (smallest relative success of dominant males) compared to litter sizes when mating order was reversed or both males equal in status. Our results suggest that even though multimale mating includes males that are of poorer quality and thus potentially decreases the fitness of offspring, most of a female’s offspring are sired by dominant males. Whether this is due to cryptic female choice, sperm competition, or a combination of both, remains to be tested.     

Do the size and age of mating plugs alter their efficacy in protecting paternity?

An obvious means to secure paternity is the production of a mating plug that blocks the female genital opening after mating. Although the mechanical efficacy and persistence of plugs on/in the female genital openings are key traits that determine the degree of paternity protection, these factors have hardly been explored. We therefore investigated the influence of the size of the amorphous plug material (experimentally terminated mating duration as a proxy) and age of the mating plug (time interval between copulations with two successive males) on the efficacy of the plug by analysing the mating success of subsequent males in the dwarf spider Oedothorax retusus (Linyphiidae: Erigoninae). Overall, subsequent males attempted to mate in 82 % of trials but only 32.5 % of these resulted in copulation, demonstrating that the plugs are effective safeguards against remating. Remating probability was significantly higher after previous short copulations (~small plug size) compared to long copulations (~large plug size). In the small plug group, fresh plugs (short remating intervals) were significantly less effective compared to older plugs. In the large plug group, remating probability was similarly low over all remating intervals. The observed copulations, however, do not necessarily result in sperm transfer, since sperm masses were found on the plugged female genital area. Our study on O. retusus shows that mating plugs are a powerful mechanical safeguard whose efficacy varies with plug size and age. We discuss these findings in the light of theoretical considerations on the evolution of effective mating plugs.