Inferences on mating and sexual systems of two Pacific Cinetorhynchus shrimps (Decapoda,Rhynchocinetidae) based on sexual dimorphism in body size and cheliped weaponry

Sexual dimorphism in body size and weaponry was examined in two Cinetorhynchus shrimp species in order to formulate hypotheses on their sexual and mating systems. Collections of Cinetorhynchus sp. A and Cinetorhynchus sp. B were made in March, 2011 on Coconut Island, Hawaii, by hand dipnetting and minnow traps in coral rubble bottom in shallow water. Although there is overlap in male and female size, some males are much larger than females. The major (pereopod 1) chelipeds of males are significantly larger and longer than those of females. In these two Cinetorhynchus species, males and females have third maxillipeds of similar relative size, i.e., those of males are not hypertrophied and probably not used as spear-like weapons as in some other rhynchocinetid (Rhynchocinetes) species. Major chelae of males vary with size, changing from typical female-like chelae tipped with black corneous stout setae to subchelate or prehensile appendages in larger males. Puncture wounds or regenerating major chelipeds were observed in 26.1 % of males examined (N = 38 including both species). We interpret this evidence on sexual dimorphism as an indication of a temporary male mate guarding or “neighborhoods of dominance” mating system, in which larger dominant robustus males defend females and have greater mating success than smaller males. Fecundity of females increased with female size, as in most caridean species (500–800 in Cinetorhynchus sp. A; 300–3800 in Cinetorhynchus sp. B). Based on the sample examined, we conclude that these two species have a gonochoric sexual system (separate sexes) like most but not all other rhynchocinetid species in which the sexual system has been investigated.     

A novel sexual pattern in serranid fishes: simultaneous hermaphrodites and secondary males in Serranus fasciatus

Synopsis Gulf of California populations of Serranus fasciatus are composed of functional simultaneous hermaphrodites and males. This is the first serranid known to have this sexual pattern which is functionally intermediate between the typical serranid patterns of simultaneous and protogynous hermaphroditism. Males of S. fasciatus are derived from hermaphrodites by resorption of ovarian tissue and proliferation of the extant testicular band. Distinct sexual roles are evident in spawning events. Hermaphrodites gain female function by pair spawning with males (124 and 125 observed spawns) and rarely with other hermaphrodites (1 of 125). Hermaphrodites gain male function by sneak spawning (9 of 125) and rarely by pair spawning with other hermaphrodites. Males exclusively pair spawned with hermaphrodites. Despite its unusual sexual pattern, S. fasciatus appears allied with other Serranus species based on similarities in gonad morphology.     

The sexual arms race and phenotypic correlates of mating success in the waterstrider,Aquarius remigis (Hemiptera: Gerridae)

Intersexual conflicts over mating decisions may have an important impact on the evolution of mating behaviours and strategies and may develop into an arms race between the sexes. In waterstrider species, where intersexual conflict is known to occur, the evolution of male traits that allow them to overcome female reluctance to mate is expected. Reproductively active waterstriders,Aquarius remigis, were videotaped in the laboratory to examine the influence of total body length and front femoral width of males, male: female body size ratio, and female reproductive condition (number of mature eggs) on three variables associated with mating success: duration of the premating struggle, duration of mating, and number of successful matings. None of these behaviors was significantly correlated with the size ratio of the mating pair. However, total body length was negatively correlated with premating struggle duration, male front femoral width was positively correlated with number of successful matings, and number of mature eggs in females was positively correlated with duration of both the premating struggle and the mating itself. The relative influence of male sexual armaments and female choice on the outcome of mating interactions is discussed.     

Precopulatory mating behavior and sexual dimorphism in the amphipod Crustacea

Accounts in the literature of precopulatory mate-guarding in gammaridean amphipods are that males use one of two strategies for mating: either they mate-guard by carrying or attending their mates until they are ready to molt and be fertilized, or they do not guard, instead searching benthically or swarming pelagically at the time that females are ready to molt. Mate-guarding by carrying has been documented for species of the superfamilies Gammaroidea, Talitroidea, and Hadzioidea. Mate-guarding by attending has been found in the more sedentary Corophioidea and Caprellidea. Non-mate-guarders that search pelagically are species of Ampeliscoidea, Lysianassoidea, Phoxocephaloidea, Oedicerotoidea, and Pontoporeioidea. Non-mate-guarders that mate-search benthically are species of Eusiroidea, Crangonyctoidea, and Haustorioidea. Mate-guarding and non-mate-guarding males develop different secondary sex characters at maturity. Mate-guarding males have enhancements for fighting and signalling. These alterations are more elaborate in males that attend their mates than in males that carry their mates. Non-mate-guarders that search pelagically develop enhancements for swimming and sensing. Non-mate-guarders that remain benthic exhibit little change at maturity. Most mate-guarding males develop their secondary sexual characters over several molts and mate over more than one instar. Pelagic mate-searchers develop their secondary sexual characters at the last molt and mating is confined to the last instar. Females of most mate-guarding species are iteroparous, while fewer than half of non-mate-guarding species are so. It is hypothesized that mate-guarding arose more than once in the evolutionary history of amphipod Crustacea.     

Differential mating success of virgin female katydidsRequena verticalis (Orthoptera: Tettigoniidae)

Male katydids (Orthoptera: Tettigoniidae) invest in offspring through nutrients provided in a large spermatophore. Previous research with Requena verticalishad shown that almost all of the investment of males mating with recently mated (4 days previously) females is in eggs fertilized by the female's previous mate. Thus males are predicted to discriminate against such females as mates. In experiments placing males with both a virgin and a female mated 4–5 days previously, virgin females obtained almost all matings. Although male discrimination of mates was noted in the experiments, there was no evidence that such discrimination was against nonvirgins in both this experiment and one in which a single virgin or mated female was placed with a male. Instead, the results suggest that the differential mating was a result of interfemale competition. The mating advantage held by virgin females over nonvirgins appeared to be lost once the latter had oviposited. Finally, there was no evidence from both single- and paired-female experiments that males preferred larger females as mates.     

Context-dependent effects of tail-ornament damage on mating success in black grouse

Male black grouse (Tetrao tetrix) may receive damage to theirtail ornaments, the lyre, during goshawk predation attemptsand during fights with other males. In this study we confirma previous observation that black grouse males with damagedtail ornaments suffer reduced mating success. In males thatheld territories on the edge of the leks, tail damage was unrelatedto mating success, whereas in central males damage was negativelycorrelated with mating success. We tested experimentally whetherabsence of damage is used by females in mate choice. In maleswith edge territories, intact, control males had higher matingsuccess than males with cut tails, but in males with centralterritories, lyre cutting had no effect on mating success. Theseresults suggest two interpretations. First, female choice alsodepends on factors other than tail damage such as position onthe lek and dominance. Second, the effect of tail damage iscontext dependent; in males that otherwise meet females standards(e.g., dominant males), the effect of tail damage is negligible,but in less dominant males, tail damage could be used by femalesin mate selection. The second interpretation provides an explanationfor why the data on unmanipulated and manipulated birds differ.In experimental central birds, factors other than tail damageprobably determine male mating success, whereas in experimentaledge birds such factors are probably absent and therefore taildamage is relatively more important. In central unmanipulatedbirds, however, males with natural damage are probably not chosenbecause tail damage and absence of other attractive traits arecorrelated. The absence of an effect on peripheral unmanipulatedbirds may be explained by their overall low mating success     

Male parental care, female reproductive success, and extrapair paternity

Birds differ considerably in the degree of male parental care,and it has been suggested that interspecific variation in extrapairpaternity is determined by the relative importance of benefitsto females from male parental care and good genes from extrapairsires. I estimated the relationship between extrapair paternityand the importance of male parental care for female reproductivesuccess mainly based on male removal studies, using a comparativeapproach. The reduction in female reproductive success causedby the absence of a male mate was positively correlated withthe male contribution to feeding offspring. The frequency ofextrapair paternity was negatively related to the reductionin female reproductive success caused by the absence of a mate.This was also the case when potentially confounding variablessuch as developmental mode of offspring and sexual dichromatismwere considered. A high frequency of extrapair paternity occursparticularly in bird species in which males play a minor rolein offspring provisioning and in which attractive males providerelatively little parental care. Bird species with frequentextrapair paternity thus appear to be those in which directfitness benefits from male care are small, females can readilycompensate for the absence of male care, and indirect fitnessbenefits from extrapair sires are important.     

Paternal investment in relation to size in the deathwatch beetle,Xestobium rufovillosum (Coleoptera: Anobiidae), and evidence for female selection for large mates

Male X. rufovillosumdonate on average 13.5% of their body weight to the female during copulation. The weight transferred is significantly greater in heavier males and declines in subsequent matings. When virgin females are offered a choice of several mates, they tend to mate with a heavy male. Females appear to be selective during courtship, refusing to mate with light males. Artificial weights attached to males increase the frequency of acceptance as mates by females, but not significantly. The evolutionary origins and significance of a large paternal investment and apparent female selection for heavy mates are discussed.     

Nest-site size as a short-term constraint on the reproductive success of paternal fishes

Synopsis Because female signal blennies, Emblemaria hypacanthus (Pisces: Chaenopsidae), exhibited a preference for the larger of two males in laboratory mate-choice experiments, male reproductive success was predicted to be positively correlated with male size in field populations. This prediction was met at one field site, but not a second where shelter size, rather than male size, was the primary correlate of male reproductive success. This finding appeared to be the consequence of the relatively small size of shelters (vacant gastropod shells) at the second site. At this site, significantly more males had their shelters filled with eggs and variance in male reproductive success was lower than at the first site. Limited area for deposition of eggs is potentially an important constraint on the short-term reproductive success of paternal males of shelter- or crevice-spawning fishes.     

Female mate choice in a mating system dominated by male sexual coercion

In poeciliid fishes, males can gain copulation either by courtingfemales or through sexual coercion. In some species these twotactics coexist. However, in about half of the poeciliids,males do not display, females never cooperate during copulationand all matings are achieved by thrusting the intromittentorgan toward the genital pore of apparently unaware females.In one of these species, the eastern mosquitofish (Gambusiaholbrooki), the probability of insemination is influenced bythe time females are previously deprived of males, suggestingthat females exert some control over the occurrence of matingeven in a system apparently dominated by sexual coercion. Inthe present study we investigated the tendency of female mosquitofishto approach males in relation to their reproductive status and the time they were previously deprived of males. The tendencyto approach males increased in females that were previouslydeprived of males and in females that had recently given birth.When allowed to choose between males, male-deprived femalespreferred larger males and normally pigmented over melanisticmales. Females preferred groups of three males over a singlemale, whereas the preference for three males over a group ofone male and two females was only marginally significant. Collectively,these results suggest that, even when coercive mating is theonly tactic adopted by males, females may be able to influencethe outcome of these attempts, and thus exert some controlover the paternity of their offspring.     

Sexual selection, sexual size dimorphism and Rensch's rule in Odonata

Odonata (dragonflies and damselflies) exhibit a range of sexual size dimorphism (SSD) that includes species with male-biased (males > females) or female-biased SSD (males < females) and species exhibiting nonterritorial or territorial mating strategies. Here, we use phylogenetic comparative analyses to investigate the influence of sexual selection on SSD in both suborders: dragonflies (Anisoptera) and damselflies (Zygoptera). First, we show that damselflies have male-biased SSD, and exhibit an allometric relationship between body size and SSD, that is consistent with Rensch's rule. Second, SSD of dragonflies is not different from unit, and this suborder does not exhibit Rensch's rule. Third, we test the influence of sexual selection on SSD using proxy variables of territorial mating strategy and male agility. Using generalized least squares to account for phylogenetic relationships between species, we show that male-biased SSD increases with territoriality in damselflies, but not in dragonflies. Finally, we show that nonagile territorial odonates exhibit male-biased SSD, whereas male agility is not related to SSD in nonterritorial odonates. These results suggest that sexual selection acting on male sizes influences SSD in Odonata. Taken together, our results, along with avian studies (bustards and shorebirds), suggest that male agility influences SSD, although this influence is modulated by territorial mating strategy and thus the likely advantage of being large. Other evolutionary processes, such as fecundity selection and viability selection, however, need further investigation.     

Male competition and female choice interact to determine mating success in the bluefin killifish

Whether male competition and female choice act in concert, independently,or in opposition is a critical issue for understanding sexualselection. In complex social systems, the outcomes of pairwiseinteractions may not be accurate indicators of how sexual selectionemerges. We investigated how female choice and male competitioninteract in the bluefin killifish, Lucania goodei, in a 3-stagedexperiment where 1) females could choose between 2 males, 2)those males could interact in the presence of that female, and3) females and males could freely interact and spawn. In thepairwise stages (1 and 2), females displayed pronounced preferencesbetween males and male competition produced a distinctly dominantindividual. None of the morphological traits, including color,measured in males were associated with either female preferenceor male dominance. When all 3 fish interacted (stage 3), maleactivity level was the sole predictor of spawning success. Maleswith elevated activity levels were more aggressive toward malesand females, exhibited intensified courtship, and obtained morespawns. Female preference did not predict the number of spawnswith a male, but it did predict her latency to spawn; femalesspawned more quickly with preferred males. Thus, male competitionand female choice interact to determine reproductive success,but there is evidence for conflict and a cost to females ofassociating with dominant males. Reproductive success in thisspecies is not easily predicted from simple measures of morphologyor female preference and is influenced by complex social interactions,both between males, and between males and females.     

Directional changes in sexual size dimorphism in shorebirds, gulls and alcids

The Charadrii (shorebirds, gulls and alcids) are one of the most diverse avian groups from the point of view of sexual size dimorphism, exhibiting extremes in both male-biased and female-biased dimorphism, as well as monomorphism. In this study we use phylogenetic comparative analyses to investigate how size dimorphism has changed over evolutionary time, distinguishing between changes that have occurred in females and in males. Independent contrasts analyses show that both body mass and wing length have been more variable in males than in females. Directional analyses show that male-biased dimorphism has increased after inferred transitions towards more polygynous mating systems. There have been analogous increases in female-biased dimorphism after transitions towards more socially polyandrous mating systems. Changes in dimorphism in both directions are attributable to male body size changing more than female body size. We suggest that this might be because females are under stronger natural selection constraints related to fecundity. Taken together, our results suggest that the observed variation in dimorphism of Charadrii can be best explained by male body size responding more sensitively to variable sexual selection than female body size.     

Mating preferences in a species flock of Mexican pupfishes (Cyprinodon, Teleostei)

Female mating preferences were examined in three members of an evolutionarily young Cyprinodon lineage from Laguna Chichancanab, Yucatan, Mexico. In separate experiments, females of C. beltrani and C. labiosus , and C. beltrani and C. maya were simultaneously presented with conspecific and heterospecific males and given the opportunity to spawn with either or both. These three species showed different degrees of conspecific mate recognition: complete for C. maya , intermediate for C. labiosus , and indiscriminate for C. beltrani. We conclude that only C. maya is reproductively isolated and that C. beltrani and C. labiosus still hybridize in nature. Whereas between C. beltrani and C. maya mate choice is symmetric, it is asymmetric between C. beltrani and C labiosus. The results of the mating trials are consistent with mitochondrial DNA data which indicate that C. maya is genetically the most distinct species in the flock. They are also supported by experiments on visually and chemically mediated mate preferences.     

Correlates of male mating success in the lekking great snipe (Gallinago media): results from a four-year study

To investigate behavioral or morphological traits importantas mate choice cues, we measured selection differentials (s)as the covariances between each trait and male mating success,and directional selection gradients (J3) from multiple linearregression of the standardized traits on male mating success.Data from two leks in four consecutive years were included,and the annual data were analyzed separately. The main findingsare: (1) the distribution of male mating success proved to beless skewed than those found in many other lekking species,(2) only a few traits yielded significant selection gradients,(3) the importance of age on male mating success changed acrossyears, (4) females may use traits with a high variance as matechoice cues, and (5) individual males achieved similar matingsuccesses between years. Attendance and age were the traitsmost consistently correlated with male mating success, but notraits showed significant selection gradients in all years.Our results indicate that variable sexual selection pressuresexisted between years, but the high correlation found betweenthe mating success of individual males in successive seasonsalso indicates that permanent differences in male traits areimportant. Key words: lek, mate choice, sexual selection.     

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

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

Male mating success and survival in the field with respect to size and courtship song characters inDrosophila littoralis andD. montana (Diptera: Drosophilidae)

We investigated the importance of male song and morphological characters to the male mating success in a two-year field study in natural populations ofD. littoralis andD. montana. We compared the properties of mating flies with those of a random male sample taken at the same time and place. InD. littoralis the male's size had no effect on his mating success, while inD. montana small males had a mating advantage in the field during the first study year. Females preferred males with short sound pulses in both species. We also examined the relationship between male morphological and song characters and viability by collecting male flies in late summer and comparing the means of male characters to those of overwintered flies the next spring. InD. littoralis male size had no effect on overwinter survival. InD. montana large flies survived better than small flies. In both species the shifts in song characters during the winter dormancy were opposite to those caused by sexual selection. Our results, accordingly, imply a possible balance between the forces of sexual and natural selection, which act in opposing directions on attractive male traits.