Factors affecting fecal glucocorticoid levels in semi-free-ranging female mandrills (Mandrillus sphinx)

Subordinate female cercopithecine primates often experience decreased reproductive success in comparison with high-ranking females, with a later age at sexual maturity and first reproduction and/or longer interbirth intervals. One explanation that has traditionally been advanced to explain this is high levels of chronic social stress in subordinates, resulting from agonistic and aggressive interactions and leading to higher basal levels of glucocorticoids. We assessed the relationships among fecal cortisol levels and reproductive condition, dominance rank, degree of social support, and fertility in female mandrills (Mandrillus sphinx) living in a semi-free-ranging colony in Franceville, Gabon. Lower-ranking females in this colony have a reproductive disadvantage relative to higher-ranking females, and we were interested in determining whether this relationship between dominance rank and reproductive success is mediated through stress hormones. We analyzed 340 fecal samples from 19 females, collected over a 14-month period. We found that pregnant females experienced higher fecal cortisol levels than cycling or lactating females. This is similar to results for other primate species and is likely owing to increased metabolic demands and interactions between the hypothalamus-pituitary-adrenal axis, estrogen, and placental production of corticotrophin releasing hormones during pregnancy. There was no influence of dominance rank on fecal cortisol levels, suggesting that subordinate females do not suffer chronic stress. This may be because female mandrills have a stable social hierarchy, with low levels of aggression and high social support. However, we found no relationship between matriline size, as a measure of social support, and fecal cortisol levels. Subordinates may be able to avoid aggression from dominants in the large enclosure or may react only transiently to specific aggressive events, rather than continuously expecting them. Finally, we found no relationship between fecal cortisol levels and fertility. There was no difference in fecal cortisol levels between conceptive and nonconceptive cycles, and no significant relationship between fecal cortisol level and either the length of postpartum amenorrhea or the number of cycles before conception. This suggests that the influence of dominance rank on female reproductive success in this population is not mediated through chronic stress in subordinate females, and that alternative explanations of the relationship between social rank and reproduction should be sought.     

Sexual swelling in mandrills (Mandrillus sphinx): a test of the reliable indicator hypothesis

Various hypotheses have been proposed to account for the functionof sexual swellings in female primates, but few empirical dataexist to test predictions arising from these hypotheses. Controversyhas recently arisen over a field study that appeared to supportthe predictions of the reliable indicator hypothesis. This hypothesisproposes that females compete for males or matings, that differencesin swelling size between females reliably advertise female quality,and that males use swelling characteristics to differentiallyallocate mating effort to females with certain swelling characteristics,hence to females of higher quality. To provide an independenttest of this hypothesis, we collected data concerning the sizeand coloration of 40 sexual swellings for 29 semi-free-rangingfemale mandrills, varying in age and parity, along with dataconcerning the behavior of males toward the females, and comparedthese with the long-term reproductive history of the females.We examined the following predictions: (1) swelling characteristicsare consistent across subsequent cycles for individual females,(2) swelling characteristics indicate aspects of female reproductivequality, and (3) males prefer to mate with females that showparticular swelling characteristics. Our results support prediction1; we found little change in swelling characteristics acrossswellings for individual females. However, we found no significantrelationships between female reproductive history and swellingcharacteristics and, thus, no support for prediction 2. Finally,we found only limited support for prediction 3; females withlarger (wider) sexual swellings were more likely to have a spermplug when maximally swollen. However, male mate-guarding wasnot significantly related to female swelling characteristics.Furthermore, in situations in which more than one female wasmaximally swollen, the alpha male (who has "free" choice) didnot show the most interest in the female with the largest swelling.We conclude that the reliable indicator hypothesis does notexplain variation in sexual swellings in female mandrills.     

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.     

Do Female Mandrills Prefer Brightly Colored Males?

Although secondary sexual adornments are widespread in male primates, few studies have examined female choice for these characters. Mandrills (Mandrillus sphinx) present an extreme example of sexual dimorphism, with males exhibiting an array of striking adornments. The most dominant adult male in a group exhibits the brightest and most extensive red coloration, while the other males are less brightly colored. I examined whether female mandrills prefer brightly colored males using data on periovulatory sexual behavior during the 1996 mating season for all males 8 years old (n = 5) and all parous females (n = 9) in a semifree-ranging colony at CIRMF, Gabon. Brightness of male coloration is significantly positively correlated with time spent within 2 m of females, female responsibility for proximity, number of sexual presentations received, % approaches accepted by females, and % inspections with which females cooperated. Females also groomed only the brightest male. Behaviors indicating female preference are not correlated significantly with male dominance rank, and partial correlations confirm that the influence of male color on female behavior is stronger than that of male rank. With the influence of male dominance rank controlled, correlation coefficients between female behaviors and male mating success are high and positive. In further support of the hypothesis that females show mate choice for brightly colored males, independent of dominance rank, I report an unusual case wherein the alpha male fell in rank without loss of coloration. He experienced no significant change in female responsibility for proximity, sexual presentations received, or female reaction to approaches or inspections, though he was no longer observed to mate. Accordingly, female mandrills attend to differences in male secondary sexual characters and favor brightly colored males. As brightly colored males are also dominant this reinforces the influence of male-male competition on male reproductive success and may explain the very high reproductive skew in mandrill males and their extraordinary appearance.     

Ontogenetic colour change signals sexual maturity in a non-territorial damselfly

Conspicuous colouration increases male reproductive success through female preferences and/or male–male competition. Despite the advantages of conspicuous colouration, inconspicuous male morphs can exist simultaneously in a population due to genetic diversity, condition dependence or developmental constraints. We are interested in explaining the male dichromatism in Xanthagrion erythroneurum damselflies. We reared these damselflies in outdoor insectaries under natural conditions and showed that this species undergoes ontogenetic colour changes. The younger males are yellow and change colour to red 6–7 days after their emergence. We took red and yellow male reflectance spectra and found that red males are brighter than yellow males. Next, we aimed to determine whether ontogenetic colour change signals sexual maturity with field observations and laboratory experiments. Our field observational data showed that red males are in higher abundance in the breeding territory, and they have a higher mating frequency than yellow males. We confirmed these field observations by enclosing a red and a yellow male with two females and found that yellow males do not mate in presence of red males. To determine whether colour change signals sexual maturity, we measured mating success of males before and after colour changes by enclosing a single male at different age (day 3-day 7) and colour (yellow, intermediate and red) with a single female in a mating cage. Males did not mate when yellow but the same male mated after it changed colour to red, suggesting the ontogenetic colour change signals sexual maturity in this species. Our study shows that male dichromatism can be age-dependent and ontogenetic colour change can signal age and sexual readiness in non-territorial insects.     

Effects of Sexual Selection Upon Sperm Morphology and Sexual Skin Morphology in Primates

We review possible effects of sexual selection upon sperm morphology, and sexual skin morphology, in primates. Comparative morphometric studies, involving 31 species representing 21 primate genera, revealed a positive relationship between volume of the sperm midpiece, occurrences of multiple partner matings by females, and large relative testes sizes, which indicate sperm competition. The midpiece houses the mitochondria required to power sperm motility. Hence, sperm competition may have influenced the evolution of increased mitochondrial loading in species where females mate with multiple partners during the fertile period. Females of some Old World monkey species and female chimpanzees exhibit large estrogen-dependent sexual skin swellings during the follicular phase of the menstrual cycle. Studies of mandrills support the conclusion that swellings act primarily as sexually attractive, graded signals and that swelling size may indicate current reproductive quality. Measurements of the genitalia in chimpanzees indicate a secondary function for female swellings. The swelling increases the operating depth of the female's vagina by 50% during the fertile phase of her cycle. Males have evolved long, filiform penes capable of placing sperm close to the os cervix during competitive multipartner matings. This may exemplify how morphologic specializations in females can influence the coevolution of advantageous genitalic specializations in males: the phenomenon that Eberhard (1985) dubbed cryptic female choice.     

Reproductive life history variation among colour morphs of the pygmy grasshopper Tetrix subulata

Individuals of pygmy grasshoppers ( Tetrix subulata [L.] Orthoptera: Tetrigidae) exhibit genetically coded discontinuous variation in colour pattern. To determine whether reproductive performance is likely to be affected by colour pattern, this study investigated variation in body size and reproductive life-history characteristics among individuals belonging to five different colour morphs. The proportion of reproductive females (i.e. females with eggs) declined significantly as the season progressed (from 100% in mid-May to 40% in mid-June), but no such seasonal trend was apparent for body size, clutch size or egg size. Colour morphs differed significantly in body size, and these size differences accounted for most of the variation in clutch size and egg size. Colour morphs also differed in the regression of egg size on clutch size, suggesting that trade-offs between number and size of offspring might vary among morphs. Finally, I found a negative relationship across colour morphs between the proportion of females with eggs and average clutch size. This suggests that individuals belonging to certain colour morphs produce a relatively large number of clutches per unit time, at the expense of fewer offspring in each clutch, compared to other morphs. Collectively, my results indicate that different colour morphs of T. subulata may have different reproductive strategies. These differences may reflect variation in thermoregulatory capacity or differences in probability of survival induced by visual predators.     

Parasite Prevalence, Abundance, and Diversity in a Semi-free-ranging Colony of Mandrillus sphinx

We examined parasite prevalence, abundance of protozoan cysts and helminth eggs in the feces, and number of parasitic taxa in a population of mandrills (Mandrillus sphinx) in semi-free-ranging conditions in their habitat range, with respect to the annual cycle, sex, age, dominance rank, and female reproductive status. We identified 3 taxa of amebic protozoa (Entamoeba coli, E. histolytica/dispar complex, and Endolimax nana), 1 ciliate protozoa (Balantidium coli), and various nematodes. Prevalence ranged from 1 observation in 874 samples for Trichuris and Mammomonogamus (nematodes) to 100% for Entamoeba coli and Endolimax nana. Daily observation, consistency of fecal samples, and periodic veterinary examination indicated that the mandrills were all healthy, suggesting that the presence of intestinal parasites in the provisioned population is well tolerated. Parasite prevalence, abundance in the feces, and number of taxa varied significantly across the annual cycle. Nematode egg prevalence and abundance were lowest during the dry season. We found no sexual difference and no influence of female dominance rank on parasitic infections. Nematode prevalence increased significantly with age in females, but not in males. There was no influence of age on prevalence of other taxa, abundance in the feces, or number of taxa. Abundance of nematode eggs in the feces was higher in pregnant than in lactating or cycling females. However, births are seasonal in the mandrill colony, and pregnant females were present during the months when nematode egg abundance was also higher in males, suggesting that this may be an influence of climatic seasonality in addition to, or instead of, female status.     

Sex steroid correlates of female-specific colouration,behaviour and reproductive state in Lake Eyre dragon lizards, <Emphasis Type="Italic">Ctenophorus maculosus</Emphasis>

In some species, females develop bright colouration to signal reproductive status and exhibit behavioural repertoires to incite male courtship and/or reduce male harassment and forced copulation. Sex steroids, including progesterone and testosterone, potentially mediate female reproductive colouration and reproductive behaviour. We measured associations among plasma profiles of testosterone and progesterone with variation in colour expression and reproductive behaviour, including unique courtship rejection behaviours, in female Lake Eyre dragon lizards, (Ctenophorus maculosus). At onset of breeding, progesterone and testosterone increased with vitellogenesis, coincident with colour intensification and sexual receptivity, indicated by acceptance of copulations. As steroid levels peaked around the inferred ovulation time, maximal colour development occurred and sexual receptivity declined. When females were gravid and exhibited maximal mate rejection behaviours, progesterone levels remained consistently high, while testosterone exhibited a discrete second peak. At oviposition, significant declines in plasma steroid levels, fading of colouration and a dramatic decrease in male rejection behaviours co-occurred. Our results indicate a generally concordant association among steroid levels, colouration, behaviour and reproductive events. However, the prolonged elevation in progesterone and a second peak of testosterone was unrelated to reproductive state or further colour change, possibly suggesting selection on females to retain high steroid levels for inducing rejection behaviours.     

Social and seasonal influences on the reproductive cycle in female mandrills (Mandrillus sphinx)

We present 12 years of perineal swelling data for a semifree-ranging colony of mandrills (Mandrillus sphinx), and evaluate the influence of rank, parity, and seasonality on reproductive parameters. Female sexual swellings showed a seasonal pattern, with August the median month of ovulation. Overlapping periovulatory periods did not decrease the likelihood of conception. Females showed their first genital swelling at age 3.6 years (n = 28; range, 3.2-4.6 years), and higher-ranking females experienced their first swelling earlier than low-ranking females. Median postpartum amenorrhea (PPA) duration was 208 days (n = 92; range, 74-538 days). PPA was longer in primiparous females than in multiparous females, but PPA duration was unrelated to female rank. Median follicular phase duration was 24 days for the first cycle after parturition (n = 84; range, 12-40 days), shortening to 17 days in subsequent cycles (n = 55; range, 6-39 days). The follicular phase was longer in nulliparous females than in parous females, but was unrelated to female rank. Median cycle length (from one sexual swelling breakdown to the next) was 38 days (n = 57; range, 18-108 days). Eighty-seven percent of conceptions occurred within two cycles, and half of the nulliparous females conceived during their first swelling cycle. Lower-ranking females were more likely to require more cycles to conceive than higher-ranking females. The cycling phase was significantly longer in nulliparous females than in parous females, and was also significantly longer in lower-ranking females than in higher-ranking females. We discuss the influence of provisioning on female reproductive parameters, the influence of parity and rank on the different phases of the interbirth interval, and the evolution of long and variable follicular phases in mandrills.     

Pterin-based ornamental coloration predicts yolk antioxidant levels in female striped plateau lizards (Sceloporus virgatus)

1. Maternal investment in egg quality can have important consequences for offspring fitness. For example, yolk antioxidants can affect embryonic development as well as juvenile and adult phenotype. Thus, females may be selected to advertise their yolk antioxidant deposition to discriminatory males via ornamental signals, perhaps depending on the reproductive costs associated with signal production. 2. Female striped plateau lizards (Sceloporus virgatus) develop pterin-based orange colour patches during the reproductive season that influence male behaviour and that are positively associated with the phenotypic quality of the female and her offspring. Here, we assessed one potential developmental mechanism underlying the relationship between offspring quality and female ornamentation in S. virgatus, by examining the relationship between ornament expression and yolk antioxidant levels. 3. As expected, concentrations of the yolk antioxidants vitamin A, vitamin E and carotenoids (lutein and zeaxanthin) were strongly positively intercorrelated. Eggs from larger clutches had fewer antioxidants than eggs from smaller clutches, suggesting that females may be limited in antioxidant availability or use. Fertilized and unfertilized eggs did not differ in yolk antioxidant levels. 4. The size of a female's ornament was positively related to both the concentration and total amount of yolk antioxidants, and ornament colour was positively related to yolk antioxidant concentration. Thus, in S. virgatus, female ornaments may advertise egg quality. In addition, these data suggest that more ornamented females may produce higher-quality offspring, in part because their eggs contain more antioxidants. As the colour ornament of interest is derived from pterins, not carotenoids, direct resource trade-offs between ornaments and eggs may be eliminated, reducing reproductive costs associated with signalling. 5. This is the first example of a positive relationship between female ornamentation and yolk antioxidants in reptiles and may indicate the general importance of these patterns in oviparous vertebrates.     

RESEARCH PAPER: Multiple Sexual Ornamentation Signals Male Quality and Predicts Female Preference in Minnows

Sexual ornamentation often consists of multiple components. Different sexual signals may indicate different aspects of mate quality or reflect quality in different time scales. On the other hand, same signals can have a dual function and are used both in male–male competition and courtship. Many fish species are capable of rapidly altering their colouration (ephemeral colour changes), but this capability is usually ignored in sexual selection studies. Here, we used experimentally manipulated social environments to study the ephemeral colour changes in multicomponent sexual signals of male minnows (Phoxinus phoxinus) during male–male competition and female choice. We found that the dominant males courted the females more actively and had redder and/or darker skin colouration than the subordinate males. Furthermore, darkness difference between subordinate and dominant males increased in the presence of female, which suggests that the male–male competition may increase the honesty of signalling and thus facilitate female choice. In support of this hypothesis, females had a strong behavioural preference towards the more colourful males, which may indicate female choice. As colourful males often had a higher social status than paler individuals, it is possible that females base their preference on male status, not only the colouration per se. In any case, our results suggest that sexual ornamentation of male minnows may signal status, courting activity and superior quality of the males and that these signals may have a dual function in both male–male competition and female choice. Females preferred different ornamental traits (dark and red colour patterns) relatively equally, indicating that mate choice is based on multiple cues.     

Does Estradiol Modulate Sexual Solicitations in Female Rhinopithecus roxellana?

Studies of the relationship between sexual behavior and reproductive endocrinology in females offer critical insight into sexual selection, mate choice, and female reproductive strategies in primates. We examine the relationship between sexual solicitations and urinary estradiol in female Sichuan golden monkeys (Rhinopithecus roxellana) living under semiwild conditions at the Shanghai Wild Animal Park, China. We collected data on the frequency of sexual solicitations and urinary samples on 4 adult females during 2 mating seasons. We determined urinary estradiol levels via radioimmunoassay. Our results indicate that during the ovarian cycle, solicitation focused on the periovulatory period around the estradiol peak. The frequency of female solicitations rose to a peak after the peak of estradiol level, suggesting that ovarian steroids modulate sexual behavior during the fertile phase of the ovarian cycle. We also found that females frequently solicited matings during pregnancy, most of which the α male accepted and that resulted in copulations. During pregnancy, however, there was no obvious relationship between sexual solicitation and urinary estradiol. We conclude that in Rhinopithecus roxallana, sexual behavior and estradiol production do not strictly correlate during different parts of the reproductive cycle. We discuss additional relationships between social interactions, dominance, sexual behavior, and endocrine function.     

Condition and brightness of structural blue‐green: motmot tail‐racket brightness is related to speed of feather growth in males,but not in females

Coloration plays an important role in sexual and social communication, and in many avian species both males and females maintain elaborate colours. Recent research has provided strong support for the hypothesis that elaborate female traits can be maintained by sexual or social selection; however, most research on female ornamentation has focused on pigment‐based colours, and less is known about how structural colours are maintained. Both sexes of the turquoise‐browed motmot (Eumomota superciliosa) have a blue‐green racket‐tipped tail, and it remains unknown if tail coloration serves as a sexual or social signal in one or both sexes. Here, we describe sexual dichromatism in the blue‐green portion of the tail racket, and we test for a relationship between coloration and condition, as indicated by growth bars. Tail colour of both sexes has a similar spectral shape, and there is significant, although moderate, sexual dichromatism: males are brighter than females, and males have marginally greater blue‐green saturation than females. The length of feather grown per day is positively related to overall feather brightness, but this relationship is only present in males. The relationship between male coloration and condition suggests that tail colour has the potential to convey information about individual quality during mate choice or contest competition. The lack of a similar relationship in females suggests that female tail colour does not convey the same condition‐dependent information that we suggest may be reflected by male colour. Female tail colour may therefore reflect other aspects of condition, be involved in other (non‐condition‐dependent) forms of communication, or be expressed as a non‐functional byproduct of genetic correlation between the sexes. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 673–681.     

It takes two: Seasonal variation in sexually dimorphic weaponry results from divergent changes in males and females

Sexually dimorphic weaponry often results from intrasexual selection, and weapon size can vary seasonally when costs of bearing the weapon exceed the benefits outside of the reproductive season. Weapons can also be favored in competition over nonreproductive resources such as food or shelter, and if such nonreproductive competition occurs year‐round, weapons may be less likely to vary seasonally. In snapping shrimp (Alpheus angulosus), both sexes have an enlarged snapping claw (a potentially deadly weapon), and males of many species have larger claws than females, although females are more aggressive. This contrasting sexual dimorphism (larger weaponry in males, higher aggression in females) raises the question of whether weaponry and aggression are favored by the same mechanisms in males and females. We used field data to determine whether either sex shows seasonal variation in claw size such as described above. We found sexual dimorphism increased during the reproductive season due to opposing changes in both male and female claw size. Males had larger claws during the reproductive season than during the nonreproductive season, a pattern consistent with sexual selection. Females, however, had larger claws during the nonreproductive season than during the reproductive season—a previously unknown pattern of variation in weapon size. The observed changes in female weapon size suggest a trade‐off between claw growth and reproduction in the reproductive season, with investment in claw growth primarily in the nonreproductive season. Sexually dimorphic weaponry in snapping shrimp, then, varies seasonally due to sex differences in seasonal patterns of investment in claw growth, suggesting claws may be advantageous for both sexes but in different contexts. Thus, understanding sexual dimorphisms through the lens of one sex yields an incomplete understanding of the factors favoring their evolution.     

Female signals enhance the efficiency of mate assessment in satin bowerbirds (Ptilonorhynchus violaceus)

Recent evidence suggests that males adjust their sexually selecteddisplay traits in response to female behaviors during courtships.Little is known, however, about whether females signal to influencemale displays and whether females benefit from this interaction.Male courtship displays in the satin bowerbird (Ptilonorhynchusviolaceus) are highly intense and aggressive. Females may usethese displays as indicators of mating benefits, but these displaysoften startle females and disrupt courtship. Previous studieshave shown that successful males decrease female startling byadjusting their display intensity according to female crouchingbehaviors, suggesting that crouching behaviors function as signals.Here we address whether female crouching is a signal by usingobservations of natural courtship behaviors. In addition, weexamine why females differ in signaling and whether femalesbenefit from signaling. First, we find that female crouchingis related to the likelihood that females will be startled bymale displays, suggesting that crouching signals the degreeof display intensity that females will tolerate from a malewithout being startled. Second, we find that female tolerancefor intense display increases during successive courtships asfemales assess potential mates, and that female tolerance mayalso be affected by age and condition. Third, we find evidencethat females that reduce startling by signaling their intensitytolerance are more efficient in mate searching. These resultssuggest that females signal to influence how males display theirsexually selected traits, and by doing so, females may increasetheir benefits in mate choice.     

Pigment-based skin colour in the blue-footed booby: an honest signal of current condition used by females to adjust reproductive investment

In monogamous species, the value of present reproduction is affected by the current condition of the mate, and females may use male ornaments to evaluate his condition and adjust their level of investment according. Many animals display colour in fleshy structures which may be accurate indicators of quality due to their potentially rapid response to changes in condition. Here we show that in the blue-footed booby, Sula nebouxii, male foot colour is structurally (collagen arrays) and pigment based. In 48 h foot colour became duller when males were food deprived and brighter when they were re-fed with fresh fish. Variation of dietary carotenoids induced comparable changes in cell-mediated immune function and foot colour, suggesting that carotenoid-pigmentation reveals the immunological state of individuals. These results suggest that pigment-based foot colour is a rapid honest signal of current condition. In a second experiment, we found that rapid variation in male foot colour caused parallel variation in female reproductive investment. One day after the first egg was laid we captured the males and modified the foot colour of experimental males with a non-toxic and water resistant duller blue intensive make-up, mimicking males in low condition. Females decreased the size of their second eggs, relative to the second egg of control females, when the feet of their mates were experimentally duller. Since brood reduction in this species is related to size differences between brood mates at hatching, by laying lighter second eggs females are facilitating brood reduction. Our data indicate that blue-footed booby females are continuously evaluating their mates and can perform rapid adjustments of reproductive investment by using dynamic sexual traits. We suggest that this fine-tuned adjustment may be widespread in socially monogamous animals.     

Circannual changes in the secondary sexual adornments of semifree-ranging male and female mandrills (Mandrillus sphinx)

Male mandrills (Mandrillus sphinx) have spectacular secondary sexual adornments. These include red and blue sexual skin on the face, rump, and genitalia; a sternal scent-marking gland; and a "fatted" rump. Mandrills are seasonal breeders, and in other seasonally-breeding primate species members of both sexes may show increased expression of secondary sexual characteristics during the mating season. We examined changes in male secondary sexual adornments and testosterone levels, in relation to seasonal changes in the female reproductive cycle and sexual skin morphology, in two semifree-ranging mandrill groups. Females showed circannual changes in sexual skin tumescence, and periods of tumescence peaked from May-July in a long-established group. However, formation of a second, smaller group, two years previous to commencement of the study, disrupted the seasonal pattern of sexual skin tumescence and births. As the groups occupied adjacent enclosures, it appears that social factors, as well as physical environment, affected the seasonal patterning of reproduction in females. Male mandrills, by contrast, did not exhibit marked circannual changes in secondary sexual traits. Although adult male testicular volume and circulating testosterone levels increased significantly during the mating season, sexual skin coloration and rump "fattedness" showed no consistent changes with season. There was some evidence to suggest that maturing males (ages 5-8 yr) showed increased development of red sexual skin during mating periods, but once males had fully developed secondary sexual adornments, they remained stable throughout the year. The possible reasons for this are discussed in relation to intermale competition and social organization in mandrills.     

Social influences on reproductive development and fertility in female Djungarian hamsters (Phodopus campbelli).

Social influences on the sexual maturation of female Djungarian hamsters were investigated in two experiments. In the first experiment females were housed from weaning with an adult male, by themselves, or with a weanling sister. Maturation was accelerated in females housed with males as indicated by younger age at first ovulation, increased rates of ovarian and uterine growth, and lower LH levels at some ages. Maturation was delayed in females housed with sisters compared to those housed alone as measured by time of first ovulation and by lower estradiol levels at some ages. The most marked differences between groups occurred 8 to 12 days after weaning, suggesting that events during this period are particularly important in the social mediation of sexual maturation. In the second experiment the effects of reproductive suppression (caused by living with a sister) on the subsequent fertility of females housed with males were examined. If male-female pairs were housed in clean cages, no effects were observed; however, pairs housed in cages previously soiled by the female and her sister had fewer young surviving until 1 week of age despite no differences in the age of pregnancy onset or in the initial litter size. Thus, even cues present in unrenewed soiled bedding may have subtle but long lasting effects on reproductive function.     

Ultra-violet reflectance of male and female red grouse, Lagopus lagopus scoticus, sexual ornaments reflect nematode parasite intensity

In many birds, females prefer males with the biggest or brightest sexual ornaments, which might reflect a higher phenotypic quality, such as fewer parasites. Unlike humans, most birds detect near-ultraviolet (UV) light, and UV signals can play an important role in sexual signalling and mate choice. Using a spectrophotometer, we analysed the colour of red grouse Lagopus lagopus scoticus sexual ornaments (their combs). We first show that combs reflect both in the red (600–700 nm) and UV (300–400 nm) part of the spectrum. Second, we investigated whether comb size and colour, and UV reflectance in particular, reflected an aspect of individual quality: the intensity of infection by a main nematode parasite, the caecal threadworm Trichostrongylus tenuis . We first analysed comb size and colour variation, and parasite intensity variation, in relation to sex and age. Males had bigger and redder combs than females, but UV brightness was greater for female than for male combs. Comb colour also differed between age groups, with young birds of both sexes showing brighter UV than old birds. Young grouse also had fewer T. tenuis worms than old grouse. We further tested whether intensity of infection could be predicted from comb characteristics (size and colour) in male and female red grouse. We found that parasite intensity was not significantly related to comb size or red brightness, but fewer worms were predicted from brighter UV in combs, in both males and females. The results indicate that UV reflectance of combs have a quality revealing function and might play an important role in grouse mate choice: UV brightness of combs could enable both male and female red grouse to assess the parasite loads of a potential mate.