Distastefulness as a defense mechanism in Aplysia brasiliana (Mollusca: Gastropoda)

An unusual courtship pattern for fiddler crabs is described from field observations in Panama. This behavior pattern, referred to here as “directing,” differs considerably from the more frequently observed communal courtship system found in close relatives of Uca deichmanni. A male involved in “directing” approaches a female and attempts to carry or maneuver her into his burrow for mating. The female usually struggles to escape from the male. This activity often attracts other males which attempt to “direct” the female if she escapes from the first male. A male is most successful in “directing” a female into his burrow if a) he is larger than the female, b) the female is wandering (a sign of physiological receptivity) prior to the “directing” attempt, and c) several males attempt to “direct” the female at once. The results suggest that females are choosing mates by inciting several males to compete for them. The males which successfully “direct” the struggling females are probably the most fit males.     

Male‐mimicking females increase male‐male interactions,and decrease male survival and condition in a female‐polymorphic damselfly

Biologists are still discovering diverse and powerful ways sexual conflicts shape biodiversity. The present study examines how the proportion of females in a population that exhibit male mimicry, a mating resistance trait, influences conspecific males’ behavior, condition, and survival. Like most female‐polymorphic damselflies, Ischnura ramburii harbors both “andromorph” females, which closely resemble males, and sexually dimorphic “gynomorph” counterparts. There is evidence that male mimicry helps andromorphs evade detection and harassment, but males can also learn to target locally prevalent morph(s) via prior mate encounters. I hypothesized that the presence of male mimics could therefore predispose males to mate recognition errors, and thereby increase rates of costly male‐male interactions. Consistent with this hypothesis, male‐male interaction rates were highest in mesocosms containing more andromorph (vs. gynomorph) females. Males in andromorph‐biased mesocosms also had lower final body mass and higher mortality than males assigned to gynomorph‐majority treatments. Male survival and body mass were each negatively affected by mesocosm density, and mortality data revealed a marginally significant interaction between andromorph frequency and population density. These findings suggest that, under sufficiently crowded conditions, female mating resistance traits such as male mimicry could have pronounced indirect effects on male behavior, condition, and survival.     

Sexual dimorphism and courtship behavior in Drosophila prolongata

Sexual dimorphism is often derived from sexual selection. In sexually dimorphic Drosophila species, exaggerated male structures are used for specific behaviors in male-to-male competition or courtship toward females. In Drosophila prolongata, a member of the melanogaster species group, males have enlarged forelegs whereas females do not. However, the adaptive role of the enlarged forelegs is unclear because little is known about the behavior of D. prolongata. In this study, the courtship behavior of D. prolongata was investigated in comparison with closely related species. Males of D. prolongata use their forelegs in a specific behavior, “leg vibration”, in which the male vigorously vibrates the female’s abdomen by extending his forelegs from in front of her. Leg vibration was observed immediately before “attempting copulation”, indicating that it has an adaptive role in the mating process. In contrast, leg vibration was not observed in closely related species. Because the large forelegs are necessary to accomplish leg vibration, it was suggested that the sexual dimorphism of D. prolongata forelegs is currently under the influence of sexual selection in courtship behavior.     

SPECIES ISOLATION,GENITAL MECHANICS,AND THE EVOLUTION OF SPECIES-SPECIFIC GENITALIA IN THREE SPECIES OF MACRODACTYLUS BEETLES (COLEOPTERA,SCARABEIDAE, MELOLONTHINAE)

The question asked was why male genitalic structures have diverged in three syntopic species of Macrodactylus beetles. Four hypotheses were evaluated: 1. The ways in which male genitalia mesh with internal female structures indicate that selection for species isolation via mechanical exclusion (“lock and key”) is unlikely to explain the genitalic differences. 2. The specific mate recognition hypothesis also clearly fails to explain genitalic differences due to the implausibility of postulated environmental effects on genitalia, and lack of postulated coevolution of male and female morphologies. 3. Selection for species isolation via differences in genitalic stimulation (sensory lock and key) is unlikely due to relatively infrequent cross-specific pair formation and intromission in the field, and “excessive” numbers of species-specific genitalic structures and male courtship behavior patterns which nevertheless occasionally fail. It also fails to explain the frequent failure of intraspecific copulations to result in sperm transfer. This hypothesis cannot, however, be rejected as confidently as the previous hypotheses. 4. Conditions under which sexual selection by cryptic female choice could take place are common. Females frequently exercise their ability to prevent sperm transfer by conspecific males even after intromission has occurred, and females generally mate repeatedly, probably with different males. Males behave as if cryptic female choice is occurring, courting assiduously while their genitalia are within the female. Sexual selection by female choice could thus contribute to the divergence in genitalic structures.     

Between fighting and tolerance: reproductive biology of wingless males in the ant Cardiocondyla venustula

Male reproductive tactics vary widely across the species of the ant genus Cardiocondyla, from obligatory lethal combat among co‐occurring males to complete mutual tolerance. The African species C. venustula Wheeler, 1908 has an intermediate phylogenetic position between taxa with fighting males and taxa with tolerant males and also shows an intermediate male behavior. Males from 2 native populations in South Africa and a population introduced to Puerto Rico attacked and killed freshly eclosing rivals but rarely engaged in deadly fights with adult competitors. Instead, several males per colony established small “territories” in their natal nests and defended them against other males. Males with a stable territory had more contact with female sexuals than nonterritorial males and more frequently engaged in mating attempts. In controlled choice experiments, female sexuals did not show any preference for particular males. We suggest that male territoriality in C. venustula is an adaptation to the seasonal production of large numbers of female sexuals by multiple mothers.     

Genetic-gonadal-genitals sex (3G-sex) and the misconception of brain and gender,or, why 3G-males and 3G-females have intersex brain and intersex gender

The categorization of individuals as “male” or “female” is based on chromosome complement and gonadal and genital phenotype. This combined genetic-gonadal-genitals sex, here referred to as 3G-sex, is internally consistent in ~99% of humans (i.e., one has either the “female” form at all levels, or the “male” form at all levels). About 1% of the human population is identified as “intersex” because of either having an intermediate form at one or more levels, or having the “male” form at some levels and the “female” form at other levels. These two types of “intersex” reflect the facts, respectively, that the different levels of 3G-sex are not completely dimorphic nor perfectly consistent. Using 3G-sex as a model to understand sex differences in other domains (e.g., brain, behavior) leads to the erroneous assumption that sex differences in these other domains are also highly dimorphic and highly consistent. But parallel lines of research have led to the conclusion that sex differences in the brain and in behavior, cognition, personality, and other gender characteristics are for the most part not dimorphic and not internally consistent (i.e., having one brain/gender characteristic with the “male” form is not a reliable predictor for the form of other brain/gender characteristics). Therefore although only ~1% percent of humans are 3G-“intersex”, when it comes to brain and gender, we all have an intersex gender (i.e., an array of masculine and feminine traits) and an intersex brain (a mosaic of “male” and “female” brain characteristics).     

Behavior of males in a reproductive aggregation of the banded demoiselle Calopteryx splendens (Insecta, Odonata)

The view according to which damselfly males practice two alternative reproductive tactics of access to females is critically discussed. It is widely accepted that some males (“territorial” ones) have priority as potential female partners, while others (“sneakers” or “wanderers”) are incapable of retaining an individual territory. They have a chance of mating only by intruding briefly into the area defended by a “territorial” male when a female is present there. Thus, the tactics of a “territorial” male consists in waiting for a female in its territory and copulating with it “by agreement,” whereas non-territorial males resort to forced copulations. By observation of individually marked males (48 out of 118) it was shown that every male could be regarded as “territorial” during a certain period and as a “wanderer” before and after it. Thus, no correlation between the modes of space use by a male (residence/mobility) and the characters of its external morphology and/or signal behavior appears to be possible in principle. According to the data obtained, a more plausible explanation is that the female chooses not the male but the best area for oviposition. In addition, it was ascertained that adherence to forced copulations cannot constitute successful “tactics” since they rarely result in insemination, neither by “territorial” nor “non-territorial” males. In other words, we are dealing not with certain alternative tactics (i.e., specialized adaptive mechanisms that have evolved in the species) but simply with the results of different sets of circumstances at a given moment.     

Behavioral assay and chemical characters of female sex pheromones in the hermit crab <Emphasis Type="Italic">Pagurus filholi</Emphasis>

Males of the hermit crab Pagurus filholi perform assessment behavior toward females, as a preliminary step of precopulatory guarding, during the reproductive season. It is known that such behavior is elicited by female sex pheromones, but the compounds involved have never been characterized in this species. Several experiments were conducted to develop a reliable bioassay along with purification procedures to identify potential compounds with pheromonal activity in Pagurus filholi. We developed a bioassay protocol to assess pheromonal activity by using an empty shell with cotton containing either artificial seawater (control) or test water. We measured and compared the time duration of male assessment behavior toward each shell if the test water contained female sex pheromones. Ultra-filtering of seawater samples potentially containing pheromones showed that the compound was <1 kDa in molecular weight. Males showed precopulatory assessment behavior toward “female conditioned” water samples treated with open column purification and eluted with MeOH, suggesting that compounds triggering male behavior were low polar molecules. Molecules with pheromonal activity were not volatile after freeze drying, effective even after heating to 90 °C, and remained active in seawater at 12 °C even after 6 days from sample collection, which suggests a rather stable characteristic of the female sex pheromones of this species.     

Male Competition in a Wandering Spider (Cupiennius getazi,Ctenidae)

We describe male-male competition in a wandering spider living on plants (Cupiennius getazi, Ctenidae) and discuss it within the general context of the mating system. 1. Males produce vibratory courtship signals (duration about 20 s) and competition signals (2 s). Upon exposure to female silk, males produce almost exclusively courtship signals (98%) if alone or in the presence of a female. In the presence of a rival alone, an average of 25% of a male's vibratory signals are courtship signals and 75% competition signals. In the presence of both a rival and a female, an average of 50% are courtship and 50% competition signals. Females respond to both male courtship and/or competition signals with vibratory courtship whereas males react by vibratory competition. The intensity of the reaction of both males and females is independent of the signal type. 2. Males displaying vibratory signals move slowly over the plant and repel attacks from rivals and females with extended front legs. Pairs of males interact in three ways. (i) Both males produce vibratory signals; one of them leaves the plant (53% of 90 trials). (ii) Both males vibrate, approach and touch (20%) or pounce on each other (20%). (iii) A male approaches the signalling opponent without producing vibrations and attacks him (7%). This is a conditional vibrocryptic tactic. The presence of a female incites male competition. Males do not interact with the female but approach each other (in 24% of the 26 trials “vibrocryptically”) and escalate more often (88%) and more quickly to overt fight than in the absence of a female. The male remaining on the plant approaches the female. 3. Male-male fights are ritualized. During 64 bodily contacts no male was injured. Males exposed to female silk and males using the vibrocryptic tactic were more often the winners of an interaction than males not exposed to female silk and than males vibrating while approaching their rival. The outcome of fights is not correlated with age, leg length, body weight and rate of signalling when no female is present. In contrast, body weight and leg length determine the outcome when a responding female is present, the larger male being the winner. 4. Intrasexual and intersexual interactions suggest that both male competition and female choice mechanisms may regulate sexual selection in this species.     

The evolution of sex roles in mate searching

Searching for mates is a critical stage in the life cycle of most internally, and many externally, fertilizing species. Males usually invest more in this costly activity than females, but the reasons for this are poorly understood. Previous models have shown that female‐biased parental investment, including anisogamy, does not by itself select for male‐biased mate searching, so it requires additional explanations. Here, we correct and expand upon earlier models, and present two novel hypotheses that might explain the evolution of male‐biased mate searching. The “carry‐over hypothesis” states that females benefit less from searching if the associated costs affect other stages of the life cycle, rather than arising only while searching. It is relevant to the evolution of morphological traits that improve searching efficiency but are also expressed in other contexts. The “mating window hypothesis” states that females benefit less from searching if their life cycle includes intervals during which the exact timing of mating does not matter for the appropriate timing of reproduction (e.g., due to sperm storage or delayed embryo implantation). Such intervals are more likely to exist for females given the general pattern of greater female parental investment. Our models shed new light on classic arguments about sex role evolution.     

The complexity of mating decisions in stalk‐eyed flies

All too often, studies of sexual selection focus exclusively on the responses in one sex, on single traits, typically those that are exaggerated and strongly sexually dimorphic. They ignore a range of less obvious traits and behavior, in both sexes, involved in the interactions leading to mate choice. To remedy this imbalance, we analyze a textbook example of sexual selection in the stalk‐eyed fly (Diasemopsis meigenii). We studied several traits in a novel, insightful, and efficient experimental design, examining 2,400 male–female pairs in a “round‐robin” array, where each female was tested against multiple males and vice versa. In D. meigenii, females exhibit strong mate preference for males with highly exaggerated eyespan, and so we deliberately constrained variation in male eyespan to reveal the importance of other traits. Males performing more precopulatory behavior were more likely to attempt to mate with females and be accepted by them. However, behavior was not a necessary part of courtship, as it was absent from over almost half the interactions. Males with larger reproductive organs (testes and accessory glands) did not make more mating attempts, but there was a strong tendency for females to accept mating attempts from such males. How females detect differences in male reproductive organ size remains unclear. In addition, females with larger eyespan, an indicator of size and fecundity, attracted more mating attempts from males, but this trait did not alter female acceptance. Genetic variation among males had a strong influence on male mating attempts and female acceptance, both via the traits we studied and other unmeasured attributes. These findings demonstrate the importance of assaying multiple traits in males and females, rather than focusing solely on prominent and exaggerated sexually dimorphic traits. The approach allows a more complete understanding of the complex mating decisions made by both males and females.     

Behaviors associated with tube-sharing in Microdeutopus gryllotalpa (Costa) (Crustacea:Amphipoda)

An earlier study showed that the onset of precopulatory behavior, or tube-sharing, in the amphipod crustacean Microdeutopus gryllotalpa (Costa) generally occurred toward the end of the females' intermolt period. Tube-sharing ended when the female molted and copulation occurred. It was hypothesized that after copulation the male would leave the female's tube, travel to another receptive female's tube, and begin tube-sharing with the new female (the “cruising male hypothesis”).The present study confirms this hypothesis for laboratory cultures. In addition, the study describes a female-typical and male-specific behavior (“blocking” and “intermittent pleopod beats”). These behaviors are only expressed during interactions between one individual who is entering, and another individual who is residing in the tube.     

Sneaky Monkeys: An Audience Effect of Male Rhesus Macaques (Macaca mulatta) on Sexual Behavior

Males and females have different sexual interests and subsequently may show conflicting sexual strategies. While dominant males try to monopolize females, promiscuity benefits females and subordinate males. One way to escape monopolization by dominant males is to copulate in their absence. We tested this inhibitory effect of males on the sexual behavior of their group members in captive group‐living Rhesus macaques. Copulations between females and nonalpha males almost exclusively took place when the alpha male was out of sight. Furthermore, the inhibiting effect was not unique for the alpha male. An upcoming nonalpha male also inhibited copulations of its group members, and three other nonalpha males inhibited female copulation solicitations. Females adjusted their behavior to the presence of bystander males, as they initiated and accepted initiations more often in absence than in presence of bystander males. Although not significant, in males, a similar pattern was found. The observed reduction in mating behavior in presence of bystander males is in accordance with an “audience effect,” in which the behavior is modulated in relation to the presence or absence of third parties. This audience effect may serve as an important mechanism to reduce (aggressive) interruptions of subordinate male copulations.     

Lonely hearts advertisements reflect sexually dimorphic mating strategies

Lonely hearts personal advertisements (LHPA) became popular during the 1980s and now appear in nearly every major newspaper. They appear to reflect common male and female reproductive themes. Our analyses of 49 advertisements written by males and 49 advertisements written by females indicate that males offer resources to females and ask for youth and attractiveness, and that females offer youth and attractiveness and ask for resources. When subjects judge these advertisements on a 5-point scale, advertisements are easily grouped into three levels of attractiveness. The attributes of preferred advertisements are defined by those things offered not those things sought. Words or phrases extracted from these advertisements are readily categorized by subjects along a 5-point dimension of desirability. Males and females generally agree on the degree of preference for these 105 words or phrases (r = 0.94), yet differ in degree of preference on 39. Words or phrases preferred by females focus on commitment (e.g., “loving,” “monogamous,” “unattached”). Those preferred by males focus on sexual qualities (e.g., “good figure,” “sexy,” “young”). Individuals of both sexes who indicate a high level of self-confidence prefer words or phrases indicating adventuresome and outgoing qualities. Lack of self-confidence is related to preference for inward-directed qualities. When advertisements are artificially constructed from these words or short phrases, the rating of the advertisements corresponds to the desirability of the individual words. A factor analysis of the words reveals three major factors: (1) words that males prefer; (2) words that females prefer; (3) words that neither males nor females prefer. More highly rated words appear in Factors 1 and 2 than in Factor 3. A survey of 91 lonely hearts advertisement writers demonstrate the same sex differences in what individuals seek and what they offer. Males seek attractivity and offer resources; females seek resources and offer attractivity. After the numerous responses are categorized, only about eight categories for solicitations and eight categories of offers are evident. Interests in resources and attractivity prevail and show sexual dimorphism. Interests in the six remaining categories are nearly identical for the two sexes. Males receive fewer responses to their advertisements than do females. Lengthy advertisements do better for males and shorter ones do better for females. LHPA appear to reflect sexual differences in reproductive concerns. They offer an obvious entry into the motivational systems underlying sexual interactions.     

Sexual behavior in a one-male unit of Rhinopithecus bieti in captivity

Data regarding the sexual behavior of black-and-white snub-nosed monkeys (Rhinopithecus bieti) were collected in 1998 in a one-male unit in captivity by all-occurrences sampling during the mating season. Before the present study, little was known about the sexual behavior of this species. This study showed that female solicitation is mainly expressed as “prostration plus glancing laterally” (PG) or “sitting plus head moving up and down” (HM), and male solicitation is exhibited by the “grunt bared-teeth display.” The mount-to-ejaculation ratio was 5.2 on average, and single-mount ejaculations (SMEs) were observed in only 4.4% of mounts on days with at least one ejaculation. Therefore, the main copulatory pattern of this species is multiple-mount ejaculation (MME). Females initiated 72% of 18 ejaculatory mounts. Females initiated more ejaculatory mounts than non-ejaculatory ones. In general, the patterns of sexual behavior in this species are similar to those reported for other Colobines. Zoo Biol 23:545–550, 2004. © 2004 Wiley-Liss, Inc.     

Recognition of social relationships in bridging behavior among Tibetan macaques (Macaca thibetana)

Bridging behavior among male Tibetan macaques (Macaca thibetana) was studied in a free-ranging group at Mt. Huangshan, China. This behavior was defined as a type of affiliative behavior in which two individuals simultaneously lifted up one infant. Bridging behavior occurred after an adult male carried an infant to another male or approached another male who was holding an infant. Each male frequently held and groomed a particular infant in the group, which was named an “affiliated” infant of the male. Males were more frequently provided with their affiliated infant by other males than with other non-affiliated infants. This finding suggests that male Tibetan macaques recognized the affiliative relationship between a male and his affiliated infant, and chose that infant for bridging behavior on the basis of this knowledge. Such choice might be important for effective bridging behavior or other affiliative interactions between males. © 1995 Wiley-Liss, Inc.     

Sexually dimorphic muscles in the forelimb of the Japanese toad,Bufo japonicus

During the breeding season, male anurans display clasping behavior by holding females with their forelimbs. This behavior is peculiar to males, and may require specializations in forelimb musculature. The present study revealed that five kinds of forelimb muscles were heavier in the male Japanese toad than in the female: the flexor carpi radialis (FCR), the flexor antibrachii medialis caput superius (FAMsup), the abductor indicis longus (AIL), the extensor carpi radialis caput superius (ECRsup), and the flexor antibrachii lateralis superficialis caput superius (FALSsup). In addition, one breast muscle, the coracoradialis (CR), was also heavier in males than in females. A quantitative analysis of muscle fibers processed for myosin ATPase activity showed that, in such “sexually dimorphic muscles” of the female, both fast (twitch) and slow (tonic) muscle fibers were of smaller diameter than in other forelimb muscles of both sexes (all male muscles plus “nondimorphic muscles” of the female). Moreover, both types of fibers were less numerous than in the corresponding muscles of the male. These results suggest that the “sexually dimorphic muscles” are used especially for clasping by the male and are degenerative or subnormal in the female. Slow muscle fibers were neither peculiar to, nor abundant in, these clasping muscles, although they may well be necessary for tonic and prolonged contractions of the forelimb muscles during clasping. The mechanism of sexual dimorphism may be a direct action of androgens on clasping muscles or an indirect action on clasping muscles via the innervating motoneurons.     

Male Siamese Fighting Fish, Betta splendens, Increase Rather than Conceal Courtship Behavior when a Rival is Present

The impact of social environment on mating success is especially pronounced in species where both intraspecific and interspecific selection influence reproduction, such as the Siamese fighting fish. Males alter male–male interactions when either a male or female audience is present, but how males change their behavior toward a female when a rival male is present is unknown. This study addresses whether males alter their behavior toward a female in a way that would prevent a rival male from interrupting courtship. The behavior of male Siamese fighting fish toward a dummy female was examined under various degrees of visual cover, both in the presence and absence of a rival male, to investigate whether males use concealment provided by the structural environment to their advantage. While males did not use barriers to conceal courtship as hypothesized, males altered their behavior by increasing courtship and monitoring their nest when a rival was visible. This increase in courtship is in contrast to most studies on courtship in the presence of a rival that find a reduction in courtship behavior. Males spent more time opercular gill flaring when no barriers were present, suggesting that males may be trying to court the female and communicate to the rival simultaneously. There was also a trend for aggression toward the female and the rival to decrease as screen length increased. Thus, males compensate for the presence of a rival by adjusting their courtship and aggressive behaviors, which could have important implications for courtship success.     

Indirect female choice mediated by sex pheromones in the hermit crab Pagurus filholi

Males of the hermit crab Pagurus filholi perform precopulatory guarding behavior, and solitary males often show aggressive behavior to take away guarded females. Males behave coercively while guarding females, so direct mate choice by females seems difficult in such a situation. By performing several experiments we examined possible indirect female choice of hermit crab. Males were attached to a shell by their left cheliped to look like guarding pairs (fake guarding pairs). The shells were filled with cotton containing either seawater or pheromone water. The fake guarding pair with only seawater caused male–male combat in 60% of trials whereas with pheromone water combats occurred in 88% of trials. Mean duration of male–male combat was significantly longer in trials with drops of seawater containing pheromones than in those without pheromones. These results suggest guarding pairs themselves cause male–male combat by visual stimulation, that female sex pheromones have further significant function in the recognition of guarding pairs and intensification of male–male combat, and that females release sex pheromones while they are guarded. As a result of the combat, the larger male ended up guarding a female. This strongly suggests that females choose males indirectly by exploiting male–male competition induced by sex pheromones under male coercive behavior.