Female Fertile Period Research Articles

Male aggressiveness during the female fertile phase in relation to extra-pair paternity, plumage ornaments and female traits

In many bird species, physical aggression between males become more frequent during the female’s fertile period, as female encounters with extra-pair males are more frequent and can entail paternity losses. Male aggressiveness during this stage has been proposed as crucial for ensuring male reproductive success. Thus, plumage ornaments could represent honest signals of individual quality that could reflect the aggressiveness of paired territorial males. Furthermore, male aggressiveness could be related to mate quality or defensive capacity. We quantified extra-pair paternity in the broods and investigated the association of male and female traits with the aggressive behaviour of territorial paired males in a Spanish population of Pied Flycatchers (Ficedula hypoleuca), where territorial intrusions were simulated during the female fertile period by placing a taxidermic male mount close to the nest. We predicted that (1) more aggressive males should better protect their mates from intruding males and thereby reduce their paternity losses, (2) males with larger white patches and higher UV reflectance of wing patches should respond more strongly to intrusions, and (3) that males should be more aggressive when mated with higher quality females. We found evidence that males that responded less intensely to a territorial intrusion suffered a higher paternity loss, which offers strong support to the basic tenet of the theory of territoriality as paternity defence. Moreover, both the level of male aggressiveness and control of the territory increased with male UV reflectance of wing patches. Finally, we found, contrary to our prediction, that males were less aggressive when mated with more ornamented females.

Olfactory signals and fertility in olive baboons

Female primates signal impending ovulation with a suite of sexual signals. Studies of these signals have focussed on visual, and to a lesser extent, acoustic signals, neglecting olfactory signals. We aimed to investigate the information content of female olfactory signals in captive olive baboons (Papio anubis) and relate these to the female fertile period. We studied eight adult females living in four groups at the CNRS Station de Primatologie, Rousset-sur-Arc, France. We used vaginal cytology to detect ovulation. We investigated the volatile component of odour signals using solid-phase microextraction and gas chromatography-mass spectrometry. We found a total of 74 volatile compounds, of which we tentatively identified 25, including several ketones, alcohols, aldehydes, terpenes, volatile fatty acids and hydrocarbons that have been identified in odour profiles of other primates. Our results show that vaginal odour intensity differs with sexual cycle stage suggesting that odour might play a role in signalling female baboon fertility. We found differences in vaginal odour between females living in all-female and in mixed sex groups but we could not distinguish the effects of group composition, female age and identity. This study of olfactory signalling improves our understanding of how female primates advertise their sexual receptivity.

Female fertile phase synchrony, and male mating and reproductive skew, in the crested macaque

High social status is the primary determinant of reproductive success among group-living male mammals. Primates living in multimale–multifemale groups show the greatest variation in the strength of this link, with marked variation in reproductive skew by male dominance among species, dependent on the degree of female fertile phase synchrony, and the number of competing males. Here, we present data on two groups of wild crested macaques (Macaca nigra), living in the Tangkoko Reserve, Sulawesi, Indonesia. We investigated male monopolization of fertile females in 31 cycles of 19 females, and genetic paternity of 14 offspring conceived during the study period. We show that female fertile phase synchrony was low, that females had few mating partners in their fertile phase, and that dominant males monopolized a high proportion of consortships and matings, resulting in marked and steep mating and reproductive skew. We conclude that female cycle asynchrony provides the opportunity for strong direct male–male competition in crested macaques, resulting in monopolization of females by dominant males, consistent with their marked sexual dimorphism. Our study provides a test of the underlying factors that determine the relative occurrence and strength of different mechanisms of sexual selection, and the phenotypes that evolve as a result.

PHYSIOTHERAPEUTIC ACTIVITY IN THE TREATMENT OF PENETRAL GENE PAIN / PENETRATION WITH A FOCUS ON THE MANUAL THERAPY APPROACH IN WOMEN AT MENACME

Genital-pelvic pain / penetration disorder (DGPP) includes vaginismus, dyspareunia and vulvodynia, where the following symptoms are present: Presence of fear or anxiety related to vulvovaginal or pelvic pain in anticipation, during or as a result of vaginal penetration, in addition to the presence of tension or hardening of the pelvic floor muscles during the attempt of vaginal penetration. Adequate sexual function is considered an important factor for quality of life, being recognized by WHO (World Health Organization) regarding the presence of sexual dysfunction as a public health problem, recommending its investigation for causing important changes in quality of life and in the relationship with your partner. It is identified that the role of the physiotherapist becomes relevant in the process of identification and rehabilitation of genito-pelvic pain, justifying the importance of studies on this topic. In order to analyze the role of the physiotherapist in the treatment of pelvic genital pain / penetration with a focus on the approach of manual therapy in women at menacme, a narrative review of the literature was carried out, where 17 articles were used as a basis for research and data collection. During the analysis of the articles, it was defined that DSFs tend to appear in the female fertile phase, causing pain and discomfort. In the reviews covered in this study, it was analyzed that DGPP is a complex syndrome in which the sensation and intensity of pain are felt in different places. With this the diagnosis becomes difficult taking into account the shame and / or blocking of the woman in reporting a sexual complaint. Through a physical therapy assessment, in order to check the tone and function of the pelvic floor muscles, the existence and location of tender points, as well as the understanding of voluntary contractions and rests of these muscles, a therapeutic planning with the use of interventions is outlined. specific measures in self-relaxation and anxiety control techniques, improving body awareness. It is concluded that there is effectiveness in exploring self-knowledge to improve the quality of life of women who suffer from this problem, providing positive results in a short period, thus contributing to the improvement of the sexual function of women with DSFs (Female Sexual Dysfunctions).

The crust of a male: does size matter when females are fertile?

Mammalian odors are frequently sexually dimorphic, with males often exhibiting a stronger, or otherwise distinct, odor relative to females, which can be especially useful for nocturnal species with reduced use of vision. Some male bats exhibit intense odors to attract females and reproduce, presumably as a consequence of a high concentration of testosterone. This usually coincides with the fertile period of females, which can be difficult to recognize visually because female mammals rarely advertise their precise reproductive condition. Recently, a novel odorous crust was discovered on the forearms of adult male fringe-lipped bats, Trachops cirrhosus. To understand its reproductive significance, we explored potential relationships between the size of the crust and testosterone concentration, testes size, female reproductive state, ectoparasite load, and body condition. We sampled bats during the mating season and determined crust size, testosterone concentration (plasma), testes volume, precise reproductive status of females (vaginal smears), body condition (ratio of body mass and forearm length), and ectoparasite load. Crust size (0–38 mm2) was positively correlated both to testosterone concentration (0.7–36.4 ng mL−1) and to relative testes volume (6.3–349.1 mm3). During the sampling period, vaginal smears confirmed that all females were in estrus. Ectoparasite load in males was significantly lower than in females, although both sexes were in similar body condition. Our results suggest that testosterone concentration is a key factor in the exhibition of a larger crust and presumably a stronger odorous signal to estrus females during the reproductive season. Male secondary sexual characteristics are critical for attracting females for mating. Male odor, in particular, can be indispensable in nocturnal species, as visual signals may lose their effectiveness under dark conditions. The most important male hormone, testosterone, increases the development of male exclusive traits, including odors. In the Neotropics, reproductive male fringe-lipped bats exhibit large odorous crusts on their forearms. The largest male crusts correspond with the highest concentration of testosterone, a relationship we find in the mating season, when vaginal smears confirm females are fertile. We also show that males with crusts have low ectoparasite loads. Our results suggest that the male crust could potentially reveal critical information. Our research highlights the significance of testosterone in the expression of male exclusive traits.

Do males bond? A study of male-male relationships in Nicobar long-tailed macaques Macaca fascicularis umbrosus

In primates, males compete for a mate, which is a non-sharable resource. This makes the conditions less conducive for males to have stable relationships. One such special kind of relationship is a bond where the interactions are reciprocated, equitable and differentiated. Bonds in macaque societies are based on the degree of within-group contest competition for mates which is dependent on the synchronization of female fertile phase and reliability of fertility signals. Species of the Fascicularis group, including Nicobar subspecies, show intermediate reliability in the signals with mild peaks, and studies have shown reciprocity but no differentiation. We conducted a study on a group of wild Nicobar long-tailed macaques Macaca fascicularis umbrosus to understand the existing patterns of male-male relationships. We examined whether there is reciprocity in affiliation among the individuals and whether the rate of affiliation is balanced. We also measured the dominance linearity and steepness in the group to understand the monopolizability of females. We used social network analysis to understand whether the relations are differentiated based on hierarchical position and whether the high-ranking individuals are the most central individuals in the distribution of grooming in the group. We found that there is reciprocity among the males although that is not equitable. There was no rankrelated differentiation of affiliation among the males of the group. Instead, the identities of individuals influenced affiliation patterns. Our results correspond to the existent strong relationships but lack of social bond otherwise found in the Fascicularis group of macaques.

Genetic monogamy despite frequent extrapair copulations in "strictly monogamous" wild jackdaws.

“Monogamy” refers to different components of pair exclusiveness: the social pair, sexual partners, and the genetic outcome of sexual encounters. Avian monogamy is usually defined socially or genetically, whereas quantifications of sexual behavior remain scarce. Jackdaws (Corvus monedula) are considered a rare example of strict monogamy in songbirds, with lifelong pair bonds and little genetic evidence for extrapair (EP) offspring. Yet jackdaw copulations, although accompanied by loud copulation calls, are rarely observed because they occur visually concealed inside nest cavities. Using full-day nest-box video surveillance and on-bird acoustic bio-logging, we directly observed jackdaw sexual behavior and compared it to the corresponding genetic outcome obtained via molecular parentage analysis. In the video-observed nests, we found genetic monogamy but frequently detected forced EP sexual behavior, accompanied by characteristic male copulation calls. We, thus, challenge the long-held notion of strict jackdaw monogamy at the sexual level. Our data suggest that male mate guarding and frequent intrapair copulations during the female fertile phase, as well as the forced nature of the copulations, could explain the absence of EP offspring. Because EP copulation behavior appeared to be costly for both sexes, we suggest that immediate fitness benefits are an unlikely explanation for its prevalence. Instead, sexual conflict and dominance effects could interact to shape the spatiotemporal pattern of EP sexual behavior in this species. Our results call for larger-scale investigations of jackdaw sexual behavior and parentage and highlight the importance of combining social, sexual, and genetic data sets for a more complete understanding of mating systems.

Copulatory behaviour in the Bonelli´s Eagle: Assessing the paternity assurance hypothesis.

We examined copulatory behaviour in the Bonelli´s Eagle (Aquila fasciata) at nesting sites in the eastern zone of the Baetic Cordillera, southern Spain, between 2010 and 2012. We observed the copulatory behaviour of 15 pairs during the pre-laying period. Bonelli´s Eagles commenced sexual activity ca. 69 days before egg-laying. Ninety-six percent of mounting attempts were successful. Bonelli´s Eagle pairs averaged 99.8 copulation attempts per clutch, with an average copulation frequency of 0.86 copulation attempts per day. Pairs displayed a daily bimodal pattern of copulation activity, with copulations occurring most frequently in the evening. We used our data to test three predictions with regard to the paternity assurance hypothesis. Prediction 1, that within-pair copulations increase with local breeding density, was rejected because our models showed no evidence for it. Prediction 2, that within-pair copulations increase during the female fertile period, was marginally supported. Finally, Prediction 3, that mate attendance increases during the female fertile period, was also rejected because mate-guarding did not increase as the fertile period approached. However, mate-guarding was positively correlated with within-pair copulation frequency. Moderate copulation rates compared to other raptors and the absence of mate-guarding suggest that, in the study area, Bonelli´s Eagles exhibit only partially adaptive behaviour to assure their paternity. A possible explanation could be related to the low number of extra-pair encounters observed (opportunities for which appear to be rare), although the gradual increase in within-pair copulations during the female fertile period is consistent with the sperm competition hypothesis. The results are discussed based on the signalling hypothesis, which proposes that raptors signal territory ownership to conspecifics, and possibly to other raptor species, by copulating frequently and conspicuously in the defended nesting area.

Volatile compounds monitoring as indicative of female cattle fertile period using electronic nose

Fertility in dairy cows has declined over the last 50 years, due to changes in endocrinal parameters. The accurate estrus determination would increase artificial insemination (AI) efficiency in cattle, offering great financial return, providing genetic improvement and genetic or acquired diseases control. Thus, an efficient electronic nose system developed with polyaniline based sensors doped with different acids for estrus determination in female cattle has been reported. In the proposed olfactory technology, disposable swabs for material collected from the perigenital area and vagina of the animals were used avoiding rectal manipulation, as well as disposable sensors, conferring ease handling and health safety for estrus determination process. The results showed the olfactory system accurately determined the estrus, best AI moment (12 h after estrus detection), and diestrus (corpus luteum phase) in cows, could be efficiently used to indicate the best AI time in cattle.

Factors affecting the egg-laying pattern of Forficula auricularia (Dermaptera: Forficulidae) in three climatologically different zones of North America

AbstractEgg-laying patterns of the European earwig, Forficula auricularia Linnaeus (Dermaptera: Forficulidae), from three climatologically different areas; Montréal, Québec, Canada, Vancouver, British Columbia, Canada, and San Francisco, California, United States of America; were compared in laboratory. Three different egg-laying patterns were observed. Among the biotic parameters studied; previtellogenic follicular atresia, number of oocytes per ovariole at imaginal moult, female life expectancy, and ovarian activity explained female successful responses to local weather conditions. Follicular atresia, combined with a low number of oocytes, impeded oviposition in a low percentage of females from Montréal. It also impedes the production of a third brood in the Vancouver population, and of a fourth brood in the San Francisco population. Both female life expectancy and length of ovarian activity also had a significant impact on the oviposition pattern in the three climatic regions. Under the cold temperate climate of the Montréal area, only one brood was produced due to the short period of female fertility. Longer period of fertility and life expectancy enabled females to produce two broods in the milder temperate climate of Vancouver, and three broods in the San Francisco climate. Our results strongly suggest an exaptation enabling the native European populations of F. auricularia to adapt successfully in North America.

Testosterone, territorial response, and song in seasonally breeding tropical and temperate stonechats

BackgroundTestosterone facilitates physiological, morphological, and behavioral changes required for breeding in male vertebrates. However, testosterone concentrations and the link between its seasonal changes and those in reproductive behaviors vary greatly among species. To better understand the impact of tropical and temperate environments and life history factors on this variation, we have compared testosterone, territorial behavior and song performance across sequential stages of the breeding season in males of 16 closely related taxa of East African tropical and West European temperate stonechats (Saxicola spp), which all breed during a short breeding season, but differ in migratory behavior, seasonal territory-acquisition and pace of life.ResultsWe found that generally, the profiles of testosterone and territorial behavior were similar across latitudes. African stonechats with a slow pace of life had equally high peak testosterone concentrations and responded as aggressively to an intruder as European stonechats with a fast pace of life. However, song performance at the beginning of the breeding season was lower in African than in European stonechats. The differences in song performance were not associated with variation in testosterone levels between tropical and temperate stonechats.ConclusionsThe results suggest a very similar role for testosterone as a mediator of high intensity territorial aggression during the fertile period of females in tropical and temperate stonechats, which all are highly seasonal, locally synchronous breeders. A potential explanation may be high risk of extra-pair copulations which has been associated with synchronous breeding. Interestingly, an association was not consistent for song performance. Our data suggest that song performance can be disassociated from peak testosterone levels depending on its role in breeding behavior. Despite similar testosterone levels, European males, which early in the breeding season acquire territories and mates, showed greater song performance than African stonechats, which maintain year-round territories and pair-bonds. Taken together, our study comparing related taxa of old world songbirds suggests that short breeding seasons may be a major selective force for high peak testosterone levels during breeding regardless of latitude and pace of life, but that particular behaviors, in our case song, can be uncoupled from peak testosterone levels.

Enemies are not always dear: male song sparrows adjust dear enemy effect expression in response to female fertility

The dear enemy effect arises when territorial animals respond more intensely to unfamiliar strangers than to familiar neighbours. This widespread behavioural phenomenon occurs because strangers represent a threat to both an animal's territory and parentage, whereas neighbours represent a threat only to parentage. Recent research in birds demonstrates some flexibility in the dear enemy effect across the breeding season. Given that neighbours often sire extrapair young, male animals may benefit by responding more aggressively to neighbours during periods of female fertility. Here we investigate the hypothesis that the dear enemy effect varies with female fertility by testing the prediction that male birds will respond more strongly to neighbours when their own mates are fertile than when they are not fertile. We conducted a playback experiment with wild song sparrows, Melospiza melodia, repeating playback sessions to paired territorial males over the course of a breeding season, including periods when females were fertile and periods when they were not. Male song sparrows displayed a dear enemy effect only when their social mate was not fertile. We conclude that male song sparrows adjust behaviour towards neighbours based on their own mate's fertility status, presumably because neighbours threaten a territorial male's parentage during his breeding partner's fertile period. When paternity is not at stake, reduced aggression towards neighbours may enhance fitness, but when paternity is at stake, normal levels of aggression towards neighbours may be favoured as a mate-guarding tactic.

Group display in the socially monogamous Northern Double-collared Sunbird (Cinnyris reichenowi)

Several sunbird species (Nectariniidae) exhibit group display, but the function of this behaviour still remains unclear. We test two hypotheses (reproductive tactic and joint territory defence) to explain the function of this behaviour using data gathered on Northern Double-collared Sunbirds (Cinnyris reichenowi) from the Cameroon Mountains. Sunbirds exhibited group display throughout the breeding cycle. Groups of birds were mainly comprised of neighbouring pairs aggregated at territory boundaries. The frequency of group displays varied significantly among individuals and over the breeding cycle, with the highest frequency during the pre-breeding period and the lowest during egg-laying (∼female's fertile period). Time spent on group display was significantly longer at the end of breeding. Off-territory forays were recorded for both males and females, males significantly increased the time spent on these forays during incubation. Extra-pair copulations were recorded only in five cases for females (4%) suggesting that most off-territory forays were motivated by feeding on nectar in neighbouring territories. Therefore, we suggest that the behaviour is used for joint territory defence rather than as an information centre for choosing mates for extra-pair copulations. Its function for choosing primary mates is also unlikely, because group displays were mainly observed in complete pairs.

Experimentally Simulating Paternity Uncertainty: Immediate and Long-Term Responses of Male and Female Reed Warblers Acrocephalus scirpaceus

In many socially monogamous species, both sexes seek copulation outside the pair bond in order to increase their reproductive success. In response, males adopt counter-strategies to combat the risk of losing paternity. However, no study so far has tried to experimentally prove the function of behaviour for paternity assurance. Introducing a potential extra-pair partner during the female fertile period provides a standardised method to examine how pair members respond immediately (e.g. increase mate guarding or copulation frequency) or long term (e.g. later parental investment and paternity uncertainty). In this study on a socially monogamous passerine species, we experimentally confronted pairs of reed warblers with a conspecific male (caged male simulating an intruder) during egg-laying. Our results revealed that occurrence of an intruder during that period triggered aggression against the intruder, depending on the presence of the female. The male territory owner also attacked the female partner to drive her away from the intruder. Thus territory defence in reed warblers also serves to protect paternity. The increase in paternity uncertainty did not affect later paternal investment. Paternal investment was also independent of the actual paternity losses. In females, the experiment elicited both, immediate and long-term responses. E.g. female copulation solicitations during the intruder experiment were only observed for females which later turned out to have extra-pair chicks in their nest. In relation to long term response females faced with an intruder invested later less in offspring feeding, and had less extra-pair chicks in their nests. Extra-pair paternity also seems to be affected by female quality (body size). In conclusion female reed warblers seem to seek extra-pair fertilizations but we could demonstrate that males adopt paternity assurance tactics which seems to efficiently help them to reduce paternity uncertainty.

Do males time their mate-guarding effort with the fertile phase in order to secure fertilisation in Cayo Santiago rhesus macaques?

In contrast to most mammalian species, female sexual activity is not limited to the fertile phase of the ovarian cycle in anthropoid primates, which has long been proposed to conceal the timing of ovulation to males. It is now generally believed that females are still most attractive during the fertile phase, leading to high-ranking males successfully mate-guarding them specifically during this period. While studies conducted in species exhibiting exaggerated sexual swellings (probabilistic signal of the fertile phase) have generally supported this hypothesis, mixed support comes from others. Here, we investigated whether high-ranking males timed mate-guarding effort towards female fertile phases in rhesus macaques (Macaca mulatta). In this species, adult females do not exhibit sexual swellings, but undergo facial skin colour variation, an alternative oestrogen-dependent graded-signal of female reproductive status. We collected behavioural, hormonal and genetic paternity data during two mating seasons for one group of the free-ranging population of Cayo Santiago. Our results show that mate-guarding by top-ranking males did not completely cover the entire female fertile phase and that this tactic accounted for only 30–40% of all fertilisations observed. Males tended to prolong mate-guarding into the luteal phase (null probability of fertilisation), which mirrors the pattern of male attraction to female facial colour reported in an earlier study. These findings suggest that males may have limited knowledge regarding the exact timing of females' fertile phase in rhesus macaques, which presumably allows females to gain more control over reproduction relative to other anthropoid primate species.

Maintenance of Sperm Variation in a Highly Promiscuous Wild Bird

Postcopulatory sexual selection is an important force in the evolution of reproductive traits, including sperm morphology. In birds, sperm morphology is known to be highly heritable and largely condition-independent. Theory predicts, and recent comparative work corroborates, that strong selection in such traits reduces intraspecific phenotypic variation. Here we show that some variation can be maintained despite extreme promiscuity, as a result of opposing, copulation-role-specific selection forces. After controlling for known correlates of siring success in the superb fairy-wren (Malurus cyaneus), we found that (a) lifetime extra-pair paternity success was associated with sperm with a shorter flagellum and relatively large head, and (b) males whose sperm had a longer flagellum and a relatively smaller head achieved higher within-pair paternity. In this species extrapair copulations occur in the same morning, but preceding, pair copulations during a female's fertile period, suggesting that shorter and relatively larger-headed sperm are most successful in securing storage (defense), whereas the opposite phenotype might be better at outcompeting stored sperm (offense). Furthermore, since cuckolding ability is a major contributor to differential male reproductive output, stronger selection on defense sperm competition traits might explain the short sperm of malurids relative to other promiscuous passerines.

Testosterone, Plumage Colouration and Extra-Pair Paternity in Male North-American Barn Swallows

In most monogamous bird species, circulating testosterone concentration in males is elevated around the social female's fertile period. Variation in elevated testosterone concentrations among males may have a considerable impact on fitness. For example, testosterone implants enhance behaviours important for social and extra-pair mate choice. However, little is known about the relationship between natural male testosterone concentration and sexual selection. To investigate this relationship we measured testosterone concentration and sexual signals (ventral plumage colour and tail length), and determined within and extra-pair fertilization success in male North American barn swallows (Hirundo rustica erythrogaster). Dark rusty coloured males had higher testosterone concentrations than drab males. Extra-pair paternity was common (42% and 31% of young in 2009 and 2010, respectively), but neither within- nor extra-pair fertilization success was related to male testosterone concentration. Dark rusty males were less often cuckolded, but did not have higher extra-pair or total fertilization success than drab males. Tail length did not affect within- or extra-pair fertilization success. Our findings suggest that, in North American barn swallows, male testosterone concentration does not play a significant direct role in female mate choice and sexual selection. Possibly plumage colour co-varies with a male behavioural trait, such as aggressiveness, that reduces the chance of cuckoldry. This could also explain why dark males have higher testosterone concentrations than drab males.

California towhee vocal duets are multi-functional signals for multiple receivers

AbstractAvian vocal duets provide a model system for studying the evolution and production of complex signals which require input from multiple individuals. Duets serve a variety of communication functions in diverse species. To explore the function of duetting in California towhees (Pipilo crissalis) I collected behavioural data from a marked population, conducted sound playback experiments, and removed males from established pairs to observe the behaviour of new partners. Results indicate that California towhees use duets during extra-pair communication with conspecifics and during intra-pair communication between duetting partners. During the breeding season duetting frequency peaked during the chick-rearing period and was low during periods of high female fertility. Playbacks provoked similar levels of aggressive response from male and female territory holders. Mated pairs duetted in response to simulated intrusion by conspecific males, females and pairs. California towhee duets briefly increased in frequency after pairing, and showed no evidence of change due to learning. Duets facilitate spatial and behavioural coordination by mates, which should allow them to more effectively perform behaviours related to mutual reproductive success. No single existing hypothesis adequately explains vocal duetting among California towhees. Instead, duets function in multiple contexts and provide multiple potential benefits.

Color signal information content and the eye of the beholder: a case study in the rhesus macaque.

Animal coloration has provided many classical examples of both natural and sexual selection. Methods to study color signals range from human assessment to models of receiver vision, with objective measurements commonly involving spectrometry or digital photography. However, signal assessment by a receiver is not objective but linked to receiver perception. Here, we use standardized digital photographs of female rhesus macaque (Macaca mulatta) face and hindquarter regions, combined with estimates of the timing of the female fertile phase, to assess how color varies with respect to this timing. We compare objective color measures (camera sensor responses) with models of rhesus vision (retinal receptor stimulation and visual discriminability). Due to differences in spectral separation between camera sensors and rhesus receptors, camera measures overestimated color variation and underestimated luminance variation compared with rhesus macaques. Consequently, objective digital camera measurements can produce statistically significant relationships that are probably undetectable to rhesus macaques, and hence biologically irrelevant, while missing variation in the measure that may be relevant. Discrimination modeling provided results that were most meaningful (as they were directly related to receiver perception) and were easiest to relate to underlying physiology. Further, this gave new insight into the function of such signals, revealing perceptually salient signal luminance changes outside of the fertile phase that could potentially enhance paternity confusion. Our study demonstrates how, even for species with similar visual systems to humans, models of vision may provide more accurate and meaningful information on the form and function of visual signals than objective color measures do.

Extreme cost of male riding behaviour for juvenile females of the Zeus bug

Precopulatory male mate guarding is predicted to occur close to the female's fertile period. However, in many species mate guarding commences when females are juveniles and may be several moults from sexual maturity. Such behaviour is inconsistent with the above prediction. In the Zeus bug, Phoreticovelia disparata, sexual size dimorphism is very pronounced and adult males commence riding on the backs of juvenile fourth-instar females. Males derive direct benefits from this association but the fitness consequences of precopulatory male riding behaviour for females are unknown. We investigated the effect of male presence during juvenile development for female Zeus bugs. We found a dramatic cost of male riding for females allocated a mate from the fourth instar: they were less likely to survive to adulthood and had substantially reduced adult longevity. These costs were significantly reduced for females allocated a mate during their fifth instar or as adults. We found no evidence that male presence affected female development time, adult size, body shape or the number of melanized dorsal scars present on their abdomen. Our study indicates that adult females and older juvenile females (fifth instar) are adapted to bear the costs imposed by riding males but that sexual conflict is likely to be intense between males and fourth-instar females. We suggest that the Zeus bug mating system originates from both sexes striving to make the best of a bad job: males ride immature females in the absence of unguarded adult females and females permit riding males as a form of convenience polyandry.