Multiple mechanisms of phenotype development in the bluehead wrasse

Despite having detailed information on mechanisms mediating sex-typical behavior in many species, we have little understanding of whether the same mechanisms regulate these behaviors when they are performed in the same species under different social contexts. In the five field experiments of this study of bluehead wrasses (Thalassoma bifasciatum), a sex-changing fish, we examined the roles of arginine vasotocin (AVT) and the potent teleost androgen 11-ketotestosterone (11KT) in mediating sexual and aggressive behaviors typical of dominant males. We demonstrated that AVT appears necessary for the assumption of dominant territorial status in males and females, but is sufficient only in the socially dominant terminal phase (TP) male phenotype. Specifically, an AVP V(1) receptor antagonist prevented both TP males and females from gaining dominance over recently vacated territories. However, unlike TP males in a previous study, neither females nor initial phase males responded to AVT treatment with increases in display of TP male typical behaviors when under social conditions that inhibit sex change. Treating females with 11KT did not alter responsiveness to AVT, but did induce male coloration and courtship behavior that was not observed in oil-treated females. Combined with the results of a previous study, these results indicate that the ability of AVT to induce male-typical behavior differs among sexual phenotypes and that this differential responsiveness appears to be dependent on social context and not directly on exposure to 11KT. Furthermore, since 11KT can induce courtship behavior in females that is not affected by AVT, there may be different hormonal mechanisms mediating courtship behavior under different social contexts.     

Group spawning results from the streaking of small males into a sneaking pair: male alternative reproductive tactics in the threespot wrasse Halichoeres trimaculatus

In many protogynous wrasses, large males with bright coloration (terminal phase males, TP males) establish mating territories and pair-spawn with females. In contrast, small primary males with drab coloration (initial phase males, IP males) are non-territorial and adopt three alternative reproductive tactics—group spawning, streaking, and sneaking. We investigated how IP males of the threespot wrasse Halichoeres trimaculatus use these tactics in different situations. The mating frequency of the IP males was positively correlated with their courtship frequency, but not with their body size. Larger IP males tended to attack the smaller ones at the mating sites. This indicates that the larger IP males attempted to exclude the smaller ones from mating with the intention of minimizing the number of IP males involved in group spawning and ultimately leading to pair spawning (sneaking). However, the larger IP males were unable to completely exclude the smaller males because the intensity of the attack by the larger IP males was weak. Consequently, the smaller IP males could easily streak into the sneaking of larger IP males, thereby resulting in group spawning.     

Morphological ontogeny of the gonad of three plectropomid species through sex differentiation and transition

The gonadal ontogeny through sex differentiation and transition of three protogynous coral trout species, Plectropomus leopardus , P. maculatus and P. laevis was described, based on anatomical and germinal differences along the length of the reproductive tract. Gonads of immature and mature females, sex changing individuals (transitionals) and males were examined. Specific anatomical features that were compared between sexual phases included the presence and structure of sperm sinuses, gonadal musculature and germinal cell types. All three coral trout species first differentiated as an immature female. The sexual pattern of P. leopardus and P. maculatus was concluded to be diandric protogynous hermaphroditism (males were derived from the juvenile phase as well as through sex change of mature females). Plectropomus laevis was found to be monandric as males were only derived through sex change in mature females. Structural changes did not occur concomitantly with the germinal changes associated with sex change in these Plectropomus species, which is atypical for protogynous species described to date. Precursory sperm sinuses in the dorso-medial region of the gonad were present, although non-functional, in a proportion of immature and mature females of all three species. These proportions, however, varied between species depending on the sexual pattern. The structural and germinal changes observed were hypothesized as anatomical adaptations that aid in minimizing time spent in the (non-reproductive) sexual transition phase and maximizing flexibility in male development in the diandric species.     

Social factors of group spawning as an alternative mating tactic in the territorial males of the threespot wrasse <Emphasis Type="BoldItalic">Halichoeres trimaculatus</Emphasis>

In most labrid fishes, large males with bright terminal phase (TP) coloration normally defend mating territories and pair spawn after following (i.e., courting) solitary females. It has also been reported that the TP males may abandon their territories and participate in group spawning when mating groups of small non-territorial males with drab initial phase (IP) coloration frequently intrude into the territories of TP males. In the similar situation of the present study, however, the territorial TP males of the threespot wrasse, Halichoeres trimaculatus, did not always participate in group spawning but continued pair spawning. Only the TP males that had few opportunities to encounter solitary IP individuals participated in group spawning, frequently following the mating groups of IP individuals. It is therefore suggested that group spawning of the territorial TP males is regarded as a tactic of making the best of the bad situation by the TP males with few opportunities to pair spawn in an area where group spawning dominates.     

Sexually dichromatic protogynous angelfish Centropyge ferrugata (Pomacanthidae) males can change back to females

Protogynous hermaphroditism, female-to-male sex change, is well known among reef fishes where large males monopolize harems of females. When the dominant male disappears from a harem, the largest female may change sex within a few weeks. Recently, from experiments with some protogynous haremic fishes in which two males' cohabitated, it was confirmed that sexual behavior and gonads were completely reversible according to individual social status. However, the ability to reverse secondary-developed sexual body coloration has never been examined in any protogynous fish. We conducted two male cohabitation experiments with the protogynous haremic angelfish, Centropyge ferrugata, which has conspicuous sexual dichromatism on the dorsal fin. Smaller males of C. ferrugata soon performed female-specific mating behaviors when they became subordinated after losing a contest. They then completed gonadal sex change to females 47 or 89 d (n=2) after beginning cohabitation. In the course of the reversed gonadal sex change, male-specific coloration on the dorsal fin changed to that of a female. Thus, the sex of C. ferrugata, including secondary developed sexually dichromatic characteristics, can be completely reversible in accord with their social status.     

Gonadal steroids affect LHRH preoptic cell number in a sex/role changing fish

In diandric sex-reversing fishes, sexually active males and females (primary phase) regularly transform into an alternative reproductive morph, terminal-phase males, that are morphologically and behaviorally distinct. The transformation from primary to terminal phase is associated with a twofold increase in the number of luteinizing hormone-releasing hormone (LHRH) immunopositive cells in the forebrain preoptic area, a region involved in both the initial development and daily control of reproductive physiology and behavior. We now show that implants of 11-ketotestosterone induce increases in LHRH cell number in both primary phase sexes to the level observed in field-collected terminal phase males. Conversely, gonadal steroids had no effect on the number of LHRH preoptic cells in terminal phase males, suggesting that this is indeed a terminal stage in the development of this species. These results demonstrate that transition to the terminal phase by both sexes involves a parallel and convergent change in LHRH cell number, which utilizes an evolutionarily conserved mechanism of sexual differentiation: the inductive effects of gonadal steroid hormones.     

Dynamic phenotypic correlates of social status and mating effort in male and female red junglefowl,Gallus gallus

Despite widespread evidence that mating and intrasexual competition are costly, relatively little is known about how these costs dynamically change male and female phenotypes. Here, we test multiple hypotheses addressing this question in replicate flocks of red junglefowl (Gallus gallus). First, we test the interrelationships between social status, comb size (a fleshy ornament) and body mass at the onset of a mating trial. While comb size covaried positively with body mass across individuals of both sexes, comb size was positively related to social status in females but not in males. Second, we test for changes within individuals in body mass and comb size throughout the mating trial. Both body mass and comb size declined at the end of a trial in both sexes, suggesting that mating effort and exposure to the opposite sex are generally costly. Males lost more body mass if they (a) were socially subordinate, (b) were chased by other males or (c) mated frequently, indicating that subordinate status and mating are independently costly. Conversely, females lost more body mass if they were exposed to a higher frequency of coerced matings, suggesting costs associated with male sexual harassment and female resistance, although costs of mating per se could not be completely ruled out. Neither competitive nor mating interactions predicted comb size change in either sex. Collectively, these results support the notion that sex‐specific costs associated with social status and mating effort result in differential, sex‐specific dynamics of phenotypic change.     

Reflectance spectra and mating patterns support intraspecific mimicry in the colour polymorphic damselfly <Emphasis Type="Italic">Ischnura elegans</Emphasis>

Coexistence of female colour morphs in animal populations is often considered the result of sexual conflict, where polymorphic females benefit from reduced male sexual harassment. Mate-searching males easily detect suitable partners when only one type of female is present, but become challenged when multiple female morphs coexist, which may result in frequency-dependent mate preferences. Intriguingly, in damselflies, one female morph often closely resembles the conspecific male in body coloration, which has lead to hypotheses regarding intra-specific male-mimicry. However, few studies have quantitatively evaluated the correspondence between colour reflectance spectra from males and male-like females, relying instead on qualitative visual assessments of coloration. Using colour analyses of reflectance spectra, we compared characteristics of the body coloration of ontogenetic male and female colour morphs of the damselfly Ischnura elegans. In addition, we evaluated whether males appear to (1) discriminate between immature and mature female colour morphs, and (2) whether male-like females experience reduced male mating attention and low mating frequencies as predicted from male-mimicry. Spectral reflectance data show that immature female morphs differ substantially in coloration from mature individuals. Mating frequencies were much lower for immature than mature female morphs. For the male-like female morph, measures of colour were statistically indistinguishable from that of both immature and mature conspecific males. Mating frequencies of male-like females were lower than those of other mature female morphs under field and experimental conditions. Together, our results indicate that males may use the observed spectral differences in mate choice decisions. Furthermore, male-like females may be regarded as functional mimics that have reduced attractiveness and lowered rates of sexual harassment by mate-searching males.     

Aggressive Behavior and Courtship Rejection in Brightly and Plainly Colored Female Keeled Earless Lizards (Holbrookia propinqua)

Relationships between bright secondary sexual coloration and behavior were studied in female Holbrookia propinqua, which develop striking orange and yellow colors during the breeding season. In tethered introduction studies, brightly colored females performed aggressive courtship rejection behaviors toward conspecific males; plainly colored females were not aggressive toward males, but attempted to avoid them. Responses of females of the two color patterns toward conspecific females of both color phases were not detectably different. Experimental introductions of lizards with coloration modified by paint showed that females of both color patterns recognize any other lizard bearing the bright female colors as female, regardless of actual sex. Both the orange and yellow components were shown to contribute to sex recognition. The yellow component alone allowed accurate sex identification, but only half the females responded to males painted with only the orange female component as if they were females. Because females did not behave differently toward other females on the basis of coloration, the hypothesis that bright coloration evolved as an adaptive signal between females is rejected. The dark ventrolateral stripes of male and plainly colored females did not appear to affect intraspecific social responses by females.     

Behavioral Components of Sex Role Reversal in the Tettigoniid Bushcricket Ephippiger ephippiger

Facultative sex role reversal is found in species of tettigoniid bushcrickets in which males invest heavily in matings or offspring by producing large, nutritious spermatophores. On high-quality diets such species show conventional sex roles, but under low-quality diets males become the choosier sex. Comparative work suggests that Ephippiger ephippiger (Tettigoniidae, Ephippigerinae) has one of the largest described spermatophores (up to 40% of the male body weight). Here we examine the behavior of this species under variable diet conditions in the laboratory and find evidence of sex role reversal under poor-quality diet conditions. We also examine the behavioral components of sex role reversal. In the reversed condition, rejections of mating attempts are almost solely by the male and contests are almost solely between females. Role-reversed males sing less frequently and at a much reduced intensity. We use geographic variation in the calling song of this species to assess the strength of female phonotactic discrimination between races. This is not significantly reduced despite sex role reversal. We therefore suggest that the male and female aspects of the acoustic sexual communication system differ in that male components change most during facultative sex role reversal.     

Early gonadal development and primary males in the protogynous epinepheline, Cephalopholis boenak

Early gonadal development of the protogynous epinepheline, Cephalopholis boenak, was examined histologically in 289 specimens with standard length (L_S) of 42–130 mm, collected from May 2000 to April 2002 in Hong Kong waters, to determine male developmental pathways and establish its sexual pattern. All juvenile gonads developed an ovarian lumen with primary‐growth stage oocytes and scattered spermatogenic tissue prior to sexual differentiation and first sexual maturation. From this bisexual phase containing both female and male tissues, some gonads differentiated as ovaries with further oocyte growth to cortical‐alveolus and vitellogenic stages, the rest differentiated as testes with the proliferation of spermatogenic tissue and the formation of a sperm sinus. All testes retained the lumen and primary‐growth stage oocytes, and sperm sinuses ran within the gonad wall. Unlike most protogynous species, among functional males it was impossible to distinguish those resulting from juveniles through sexual differentiation (i.e. primary male) from those resulting from functional females through sex change (i.e. secondary male) based solely on testicular morphology. A proportion‐spermatogenic‐tissue index (I_ST) was, therefore, developed and determined to be a reliable quantitative indicator for distinguishing differentiating, primary males before a sperm sinus was evident, from differentiating females during sexual differentiation. Since sexually transitional specimens with the concominant appearance of degenerating vitellogenic, or later, stage oocytes and spermatogenic tissue in the gonads were previously noted from Hong Kong, diandric, protogynous hermaphroditism is confirmed in C. boenak. For species, such as this and other epinephelines, in which all males have the same testicular morphology, a complete analysis of a wide range of body sizes from juveniles to adults is necessary for understanding male developmental pathways, and determining sexual pattern.     

Dominance,Coloration, and Social and Sexual Behavior in Male Drills <Emphasis Type="Italic">Mandrillus leucophaeus</Emphasis>

Sexual selection has driven the evolution and elaboration of a wide variety of displays and ornaments in male nonhuman primates, including capes, cheek flanges, and sexual coloration. Among the most sexually dimorphic of all primates is the drill (Mandrillus leucophaeus), the males of which can be 3 times the mass of females, possess large canines, and exhibit extremely bright sexual skin coloration. However, the function of male coloration in this species has never been examined. Here, we present data on male color (measured objectively using digital photography), dominance rank, measures of male-female association, and key sexual behaviors, of adult male drills (n = 17) living in four semi free-ranging enclosures at the Drill Rehabilitation and Breeding Center in Nigeria. We test the hypothesis that male coloration is a badge of status, indicating dominance rank, and the hypothesis that male coloration attracts females. We found that male coloration did indicate rank, and that high ranking, strongly colored males were more likely to associate with adult females, and more specifically with fully tumescent females. These males also engaged in more sexual activity. However, measures of male-female association and sexual behaviors were not related to male color once rank had been taken into consideration; i.e., for males of a given rank, females did not prefer those that were more colorful. We discuss the results in light of what is known about the wild drill social system, in which unfamiliar individuals may come together in “supergroups,” and in which quality indicators of competitive ability may be particularly important.     

Bi-directional sex change and gonad structure in the gobiid fish <Emphasis Type="Italic">Trimma yanagitai</Emphasis>

Bi-directional sex change in the deep-water gobiid fish Trimma yanagitai was examined. The gonads of all individuals consisted of ovarian and testicular elements, and an accessory gonadal structure. In no gonads were both testicular and ovarian parts simultaneously active. Bi-directional sex changes occurred during the rearing experiments in aquaria under conditions of which there was co-existence of two males or plural females. The sex of individuals could be determined by their relative body size or social dominance: the largest individuals acting as male and the remainder as female.     

Gonadal steroids affect LHRH preoptic cell number in a sex/role changing fish.

In diandric sex-reversing fishes, sexually active males and females (primary phase) regularly transform into an alternative reproductive morph, terminal-phase males, that are morphologically and behaviorally distinct. The transformation from primary to terminal phase is associated with a twofold increase in the number of luteinizing hormone-releasing hormone (LHRH) immunopositive cells in the forebrain preoptic area, a region involved in both the initial development and daily control of reproductive physiology and behavior. We now show that implants of 11-ketotestosterone induce increases in LHRH cell number in both primary phase sexes to the level observed in field-collected terminal phase males. Conversely, gonadal steroids had no effect on the number of LHRH preoptic cells in terminal phase males, suggesting that this is indeed a terminal stage in the development of this species. These results demonstrate that transition to the terminal phase by both sexes involves a parallel and convergent change in LHRH cell number, which utilizes an evolutionarily conserved mechanism of sexual differentiation: the inductive effects of gonadal steroid hormones.     

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.     

Male red coloration,female mate preference,and sperm longevity in the cyprinid fish Puntius titteya

In recent decades, the link between the exaggeration of male sexual ornaments and ejaculate quality has received much attention. When males with conspicuous sexual ornaments have high-quality ejaculate, females are believed to obtain benefits, such as high fertilization success and offspring with good genes, by choosing mates on the basis of male ornamentation. In this study, we examined the relationships among male body coloration, female mate preference, and sperm longevity in the sexually dichromatic fish Puntius titteya. Males of this species assume a bright red coloration over the entire body, and neither sex invests in the parental care of eggs. In the female preference test, females preferred males with redder body coloration over their counterpart males with duller coloration. In addition, the sperm longevity test indicated that redder males had sperm with greater longevity. These results suggest that the red coloration of males in this species may signal sperm longevity and that females can mate with males with higher quality sperm by choosing redder males.     

Female dominance rank and behavior during artificial menstrual cycles in social groups of rhesus monkeys (Macaca mulatta)

We recently reported (Michael & Zumpe: American Journal of Primatology 15:157–170, 1988) evidence for the hypothesis that copulations by pairs of rhesus monkeys are linked more closely to the ovulatory phase of the female's menstrual cycle when a male has access to several females in different cycle phases rather than access to females in the same cycle phase. We have now used data from this earlier study to assess the role of female dominance. Artificial menstrual cycles were induced with hormone injections in two of four ovariectomized females in eight social groups (each consisting of one male and four females). The artificial cycles were either synchronized or offset by 7-day increments. There were differences in the behavioral interactions of the higher-ranking (dominant) and lower-ranking (subordinate) hormone-treated females in each group. The amount of male sexual activity received by dominant and subordinate females differed little, but dominant females initiated significantly more sexual activity (P<.0001) than did subordinate females. Dominant females were significantly more aggressive (P<.0001) toward other females and received more direct and redirected aggression from males. Males generally initiated and maintained more social contacts with dominant than with subordinate females, and dominant females were less active than subordinates in initiating and maintaining social interactions with males. The findings provide new evidence for both female mate competition and mate choice by males for higher-ranking females.     

The influence of social factors on juvenile sexual differentiation in a diandric,protogynous grouper <Emphasis Type="Italic">Epinephelus coioides</Emphasis>

The influence of social factors on juvenile sexual differentiation was explored in a diandric, protogynous grouper Epinephelus coioides. Experimental social units were established as singles, pairs and quartets using sexually undifferentiated juveniles at an age of 22 weeks post-hatching (WPH); all gonads were examined histologically at 130 WPH, the age of first sexual maturation. The percentage of primary males was about 39% at the end of the experiment, higher than the <5% obtained under mariculture conditions or from wild stocks for similar age or body size. This study demonstrated for the first time that social factors can significantly influence juvenile sexual differentiation in E. coioides.     

A social basis for the development of primary males in a sex-changing fish

An example of alternative male strategies is seen in diandric protogynous (female first) hermaphrodites, where individuals either mature directly as male (primary males) or first reproduce as female and then change sex to male (secondary males). In some sex-changing fishes, the testes of primary males appear anatomically similar to those of non-sex-changing species, whereas the testes of secondary males have anatomical evidence of their former ovarian function. Here, we provide evidence that in the bluehead wrasse, Thalassoma bifasciatum, these strikingly different male phenotypes arise from differences in the ontogenetic timing of environmental sex determination, timing that can be experimentally altered through changes in the social circumstances. Juveniles differentiated almost exclusively as females when reared in isolation, regardless of whether they were collected from a reef with a high proportion of primary males or from a reef with a low proportion of primary males. In contrast, one individual usually differentiated as a primary male when reared in groups of three. Our results indicate that primary males of the bluehead wrasse are an environmentally sensitive developmental strategy that has probably evolved in response to variation in the reproductive success of primary males in populations of different sizes.     

Social status determines sexual phenotype in the bi-directional sex changing bluebanded goby Lythrypnus dalli

The behavioural mechanisms and patterns of protandrous sex change in bluebanded gobies Lythrypnus dalli were investigated and compared to the well-described behaviour patterns of protogynous sex change. To do this, unisex groups of males and females were established; behavioural and anatomical changes were recorded over a 42 day period as social status and sexual phenotype were determined. In all cases, social status, rather than the expression of a particular behaviour, accurately predicted final sexual phenotype. Rates of submissive behaviour, but not aggressive behaviour, were predictive of each discrete status class. Multiple individuals changed sex simultaneously if their sexual phenotype and social status were discordant, a novel finding suggesting that once a social hierarchy is established, individuals determined their sexual phenotype, regardless of initial sex, based on a simple operational principle: if subordinate express female, if dominant or not subordinate express male. This work demonstrates that similar mechanisms underlie sex change in both directions in L. dalli and potentially other sex changing species.