Social Behavior of Males and Simultaneous Hermaphrodites in the Lantern Bass

Serranus baldwini (Serranidae), the lantern bass, is a small, gleaning carnivore found in turtle grass and rubble substrates in the Caribbean. Small S. baldwini are simultaneous hermaphrodites, but large members of this species are males. The males patrol territories in which several hermaphrodites reside. Hermaphrodites spawn as females with the resident males and rarely spawn as males themselves. Unlike the pattern in reciprocating hermaphrodites, courtship is largely a male function in S. baldwini. Males are much more active and aggressive than are hermaphrodites. In reciprocally spawning species, interactions among mates are more symmetrical. The behavior patterns found in the serranines reflect the differences in mating systems in a manner similar to that found in other organisms and is consistent with current mating system theory.     

Protandric simultaneous hermaphroditism in the shrimps Lysmata bahia and Lysmata intermedia

Abstract. The sexual system of two peppermint shrimps, Lysmata bahia and Lysmata intermedia, inhabiting intertidal fossil coral terraces at Bocas del Toro, on the Caribbean coast of Panama, was examined. Dissections suggested that the population of each species consisted of functional males and functional simultaneous hermaphrodites. Males have cincinulli and appendices masculinae on the first and second pair of pleopods, respectively, gonopores located at the coxae of the third pair of walking legs, and ovotestes with a well‐developed male portion full of sperm, but an undeveloped female portion. Hermaphrodites lacked appendices masculinae and cincinulli. However, they have male gonopores and ovotestes with well‐developed ovaries full of mature oocytes and testes with sperm. When hermaphrodites were maintained in pairs, both molted and spawned eggs (to beneath abdomen) that continued developing after 3 d, demonstrating that hermaphrodites can reproduce as males and inseminate other hermaphrodites acting as females. The possibility of self‐fertilization or parthenogenetic reproduction was tested and disregarded, because hermaphrodites reared in isolation spawned oocytes that failed to develop, disappearing from the abdomen after 2 d. Males reared in pairs mature as hermaphrodites in <50 d, showing the ability of males to mature as hermaphrodites. These results demonstrate that L. bahia and L. intermedia are protandric simultaneous hermaphrodites, as reported for all species of this genus whose sexual system has been examined. However, the studied species featured a lifestyle, termed “tropical‐low abundance,” here not recognized previously for the genus; they occur in low abundances in tropical environments, they do not develop symbiotic associations with sessile invertebrates, and they are not conspicuously colored. Information on the sexual systems and lifestyles of more species needs to be examined before these observations can be placed into a comparative context within the genus.     

Variation in reproductive success and gonadal allocation in the simultaneous hermaphrodite,Serranus fasciatus

Summary This paper examines the correlates of individual size, reproductive success, gonadal allocation, and growth in a hermaphroditic reef fish. Individuals in S. fasciatus mature as simultaneous hermaphrodites; large individuals subsequently lose female function and become functional males. Daily female reproductive success was highly correlated with both hermaphrodite size and amount of female gonadal tissue. Three separate comparisons gave a positive correlation between male reproductive success and male gonadal allocation: (1) Males had higher levels of male gonadal allocation and male reproductive success than hermaphrodites. (2) The percent of gonad allocated to male tissue in hermaphrodites was higher in the year they had higher male mating success. (3) Male gonadal tissue of hermaphrodites was positively correlated with male reproductive success in the year that male reproductive success by hermaphrodites was higher and more variable. There was no evidence for a trade-off between male function, female function, and growth among hermaphrodites. Many of these patterns have also been observed in plants, but the selective pressures leading to these patterns in S. fasciatus and plants are probably quite different.     

Implications for the Maintenance of Androdioecy in the Freshwater Shrimp, Eulimnadia texana Packard: Encounters between Males and Hermaphrodites are not Random

Androdioecy is a mixed‐mating system in which there are males and hermaphrodites but no pure females. Few species exhibit such a mating system. Eulimnadia texana is a branchiopod crustacean that has recently been identified as an androdioecious species. This system is ideal for testing questions related to the evolution of sexual reproduction. We are testing a model that predicts androdioecy to be a stable mixed‐mating system under certain conditions. Specifically, we investigated whether encounters between males and hermaphrodites are random or if either sex seeks out the other for mating. Focal male or hermaphrodite clam shrimp were presented with stimulus shrimp of the other sex or kept alone. Swimming speed and time spent within different areas of a test chamber were recorded. Males did not alter mean swimming speed or spend more time than expected by chance near partitioned hermaphrodites. Hermaphrodites, however, decreased mean swimming speed in the presence of males and also spent more time than expected by chance near partitioned males, suggesting that hermaphrodites respond to male chemical and/or visual stimuli. Modified swimming behaviour probably facilitates inter‐sexual contact, thereby increasing opportunities for out‐crossing above that expected by random encounters.     

The evolution from females to hermaphrodites results in a sexual conflict over mating in androdioecious nematode worms and clam shrimp

The nematode worm Caenorhabditis elegans and the clam shrimp Eulimnadia texana are two well‐studied androdioecious species consisting mostly of self‐fertilizing hermaphrodites and few males. To understand how androdioecy can evolve, a simple two‐step mathematical model of the evolutionary pathway from a male–female species to a selfing‐hermaphrodite species is constructed. First, the frequency of mutant females capable of facultative self‐fertilization increases if the benefits of reproductive assurance exceed the cost. Second, hermaphrodites become obligate self‐fertilizers if the fitness of selfed offspring exceeds one‐half the fitness of outcrossed offspring. Genetic considerations specific to C. elegans and E. texana show that males may endure as descendants of the ancestral male–female species. These models combined with an extensive literature review suggest a sexual conflict over mating in these androdioecious species: selection favours hermaphrodites that self and males that outcross. The strength of selection on hermaphrodites and males differs, however. Males that fail to outcross suffer a genetic death. Hermaphrodites may never encounter a rare male, and those that do and outcross only bear less fecund offspring. This asymmetric sexual conflict results in an evolutionary stand‐off: rare, but persistent males occasionally fertilize common, but reluctant hermaphrodites. A consequence of this stand‐off may be an increase in the longevity of the androdioecious mating system.     

ECOLOGICAL ASPECTS OF SEX EXPRESSION IN SUBDIOECIOUS SCHIEDEA GLOBOSA (CARYOPHYLLACEAE)

The importance of ecological factors such as sex lability, spatial segregation, and resource allocation in the evolution of dioecy were examined in Schiedea globosa. S. globosa is a subdioecious species with equal numbers of plants possessing strictly male or female function and a small proportion of hermaphrodites. The propensity for labile sex expression was under both environmental and genetic control; some plants with male function became hermaphroditic (by producing female flowers) under better growing conditions in the field and in the greenhouse. There was some spatial segregation of the sexes. Because of sex lability, more hermaphrodites than males occurred on moister slopes. Although there were not measurable sex-related differences in mortality within or between two flowering seasons, more females than males and hermaphrodites occurred at the bottom of slopes. Males and females produced the same number of ramets and inflorescences, but females had a greater number of flowers per inflorescence. Males and females had the same number of ovules (vestigial in males), but females had larger ovules and longer stigmas. Hermaphrodites and males had the same amount of pollen per flower despite the production of fruit by the hermaphrodites. In hermaphrodites, there was no apparent tradeoff within flowers between pollen production and ovule production. These results indicate that spatial segregation, sex lability, and environmental conditions influence allocation patterns of S. globosa, and in combination with high inbreeding depression and selling rates, may promote the further evolution of dioecy in S. globosa.     

Is sexual selection operating in the androdioecious clam shrimp,Eulimnadia texana (Crustacea: Conchostraca)?

Experiments were performed to document the existence of intersexual or intrasexual selection in the clam shrimp,Eulimnadia texana. Individuals within this species are either males or hermaphrodites. Hermaphrodites can self their own eggs or outcross with a male, but they cannot outcross with other hermaphrodites. Theoretical considerations suggest that both intrasexual and intersexual selection could be occurring on the part of the hermaphrodites and the males. When males were given a choice between two non-gravid hermaphrodites of different sizes, they did not exhibit a mating preference based upon size. When two males of different sizes were isolated with a single nongravid receptive hermaphrodite, the hermaphrodite showed no preference between the two males. There was evidence, however, of male-male competition for receptive hermaphrodites and of mate guarding on the part of the males. During aggressive encounters between twp males, the larger of the two had a significant advantage over the smaller, and larger males were always the victors hermaphrodite takeovers occurred as a result of male-male conflict. Hermaphrodites appear to control the mating process both by struglling with males when they are not receptive to them and by selfing in the presence of males. This suggests that hermaphrodites withhold receptivity cues from males, or produce non-receptivity cues, when they are going to self. Though hermaphrodites do not appear to select males based upon size, they make a selection between selfing and outcrossing by controlling the use of receptivity signals.     

Mating behavior and time budget of an androdioecious crustacean,Eulimnadia texana (Crustacea: Conchostraca)

The clam shrimp,Eulimnadia texana (Crustacea, Conchostraca), is found in freshwater ephemeral environments throughtout the United States. Individual clam shrimp of this species are either hermaphroditic or male, a relatively rare mating system for animals known as androdioecy. Comparison of sex ratios between four neighboring populations ofE. texana in Southern New Mexico showed wide variation in the ratio of males to hermaphrodites with males making up as much as 42% of some populations and not occurring at all within others. Since little is known about the behavior of this species, an ethogram and time budget were prepared based on observations of laboratory populations. Males attempt to clasp hermaphrodites prior to mating. Precopulatory mate guarding occurs in this species. Outcrossing generally occurs during mate guarding and after the hermaphrodite molts. Hermaphrodites, however, seem to control the mating process. Successful mating by males never occured if the hermaphrodite struggled with him; hermaphrodite will self in the presence of males.     

Biology of the harlequin fish Othos dentex (Serranidae), with particular emphasis on sexual pattern and other reproductive characteristics

Key biological characteristics of the harlequin fish Othos dentex, a representative of a monospecific genus of the Anthiinae (Serranidae), were determined from samples collected around reefs on the south coast of Western Australia. The females of this relatively long‐lived species (maximum recorded age in this study = 37 years) attained only a slightly greater maximum total length and age than males and neither the length nor the age‐frequency distributions showed a conspicuous sex‐based bimodality. Furthermore, gonads from a wide size and age range of O. dentex were shown by histology, at several locations along their length, to always comprise exclusively either ovarian or testicular tissues. Thus, O. dentex is a gonochorist, a sexual pattern only previously recorded definitively for one other anthiine serranid, i.e. Epinephelides armatus, which also occurs in south‐western Australia. Similar to E. armatus, O. dentex possesses ‘solid’ testes with a central sperm duct, thereby differing in structure from those typically found in serranids, in which there is a central membrane‐bound ‘ovarian’ lumen and peripherally located sperm sinuses. The gonadal characteristics and sexual pattern of these two gonochoristic anthiines are not consistent with a recent proposal for the trends exhibited by the evolution of gonochorism and protogyny within the Serranidae. Othos dentex has indeterminate fecundity and a protracted spawning period (7 months) and, on the basis of underwater observations and a low gonado‐somatic index (I_G) for males, is a pair spawner, which is unusual for a gonochorist of a serranid or member of a related family. While the large spots on the lower half of the body of O. dentex are shown quantitatively to be similarly yellow in juveniles and adult females, they then become blue in males at maturity and this intensifies during the spawning period, when they presumably play an important role in agonistic interactions among males and courtship with females. The attainment of maturity and rapid growth by O. dentex early in life may reflect selection pressures to reduce predation mortality during that period. Total mortality in the population is moderately low during later life, implying that the current fishing pressure on O. dentex is relatively light.     

Simultaneous spawning by female stream goby Rhinogobius sp. and the association with brood cannibalism by nesting males

A laboratory experiment was conducted by varying the undersurface area of nesting substratum and the number of females in an experimental tank to elucidate the determinants of the mating pattern in the stream goby, Rhinogobius sp. cross‐band type. Males with larger nests tended to attract two or more females to their nest in a tank. Moreover, males spawned simultaneously with multiple females and entire brood cannibalism by males was rarely observed under a female‐biased sex ratio. When males spawned with a single female with low fecundity, however, entire brood cannibalism occurred at a high frequency, suggesting that a male guarding a nest with fewer eggs consumes the brood. Therefore, spawning behaviour of females that leads to a large egg mass would decrease the risk of entire brood cannibalism. In this species, simultaneous spawning by multiple females in a nest serves as a female counter‐measure against entire brood cannibalism. These results suggest that a conflict of interest between the sexes through brood cannibalism is a major determinant of simultaneous spawning.     

Sex allocation in a simultaneous hermaphrodite, the zebra goby Lythrypnus zebra: insights gained through a comparison with its sympatric congener, Lythrypnus dalli

Synopsis The sexual pattern of the zebra goby Lythrypnus zebra, is an apparent exception to sex allocation theory. Most L. zebra are simultaneous hermaphrodites (i.e., have active female and male gonadal tissue), yet it appears they do not reproduce as males and females simultaneously. Understanding the maintenance of simultaneous hermaphroditism in L. zebra could expand sex allocation theory. In this study, I used a comparison with the blue-banded goby, Lythrypnus dalli, a sympatric congener with a qualitatively similar sexual pattern, to investigate the role of male spawning rate, body size and sexual flexibility in determining the sexual pattern of L. zebra and to isolate differences between the species that might explain their differing sexual patterns. Using field measurements of male nesting success, I found no differences between the species in the body size of nesting males suggesting that large size is associated with successful male reproduction in both species. In addition, nesting males spawned at approximately three times the rate of females in both species; thus, reproduction via male function can be equally advantageous relative to adopting the female role. However, the nest longevity of L. zebra males was shorter than that of L. dalli males, suggesting reproduction via male function may be less reliable in L. zebra. Finally, under laboratory conditions, L. zebra females tended to prefer large mates, and L. zebra were able to re-allocate in both directions, exhibiting a greater capacity to switch than L. dalli. Given these results, I suggest that switching between the sexes plays a greater role in maintaining simultaneous hermaphroditism in L. zebra than L. dalli, perhaps because male reproduction is not as consistent in L. zebra. Sexual flexibility may be an important factor affecting patterns of sex allocation, generally.     

Seasonal changes in reproductive and physical condition, sexual dimorphism, and male mating tactics in the jewelled blenny Salarias fasciatus

To investigate seasonal changes in reproductive and physical condition, sexual dimorphism, and mating tactics in the jewelled blenny Salarias fasciatus, monthly collections were conducted on the fringing reef in northern Okinawa, Japan. Monthly variation in the female gonadosomatic index suggested that the breeding season of this species is from April to June. The physical condition and hepatosomatic index of both sexes considerably deteriorated during the course of the breeding season. Such declines may be primarily due to egg production in females and brood care in males. Males’ elongated anal spines were longer than females’, but no other apparent sexual dimorphisms were detected, indicating that S. fasciatus exhibits a low degree of sexual dimorphism. Examinations of testes size and the testicular gland area during the estimated breeding season revealed that the gonadosomatic index values of smaller males did not differ from those of larger males. This result may differ from other blenny species that exhibit alternative male reproductive tactics. However, patterns of male testicular glands of S. fasciatus were similar to those of other blennies with alternative tactics, i.e., smaller males had poorly developed testicular glands compared with larger males.     

Population distribution,host-switching,and chemical sensing in the symbiotic shrimp <Emphasis Type="Italic">Lysmata pederseni</Emphasis>: implications for its mating system in a changing reef seascape

Lysmata pederseni, a protandric simultaneously hermaphroditic shrimp that inhabits the tube sponge Callyspongia vaginalis, is monogamous in the central and southeastern Caribbean Sea. We tested the null hypothesis of monogamy in a northern Caribbean population. In the Florida Keys, shrimps did not inhabit host individuals in pairs with a frequency greater than expected by chance alone. Hermaphrodites inhabited sponges solitarily and often brooded embryos. Hermaphrodites do not store sperm and need to be inseminated shortly after molting to fertilize a new batch of eggs. Thus, males and/or other hermaphrodites are likely switching among host individuals in search of sexual partners. Field experiments demonstrated low shrimp host fidelity. Host residence time was ~2 times shorter for males than for hermaphrodites. We inferred a polygynandrous mating system in L. pederseni from the Florida Keys, with male-role and young hermaphrodites often moving among sponges in search of older, more sedentary, female-role hermaphrodites. We expected shrimps to use water-borne chemical cues originating from conspecifics or sponges to locate sexual partners. Experiments demonstrated that shrimps were attracted to water-borne cues originating from sponges but not conspecifics. We have described the mating system of a reef-associated shrimp in a fast-pace shifting seascape increasingly dominated by sponges and vanishing stony corals. In the central and southeastern Caribbean Sea, with greater coral cover and lower sponge abundance than in the Florida Keys, the same species is monogamous. Whether or not similar shifts in the social organization of other coral reef-dwelling marine organisms are occurring due to contemporary changes in seascapes is a relevant topic that deserves further attention.     

Gender plasticity and sexual system stability in Wurmbea

Background and aims

Sexually dimorphic populations are often located in drier habitats than cosexual populations. Gender plasticity (GP), whereby hermaphrodites alter female and male functions depending on resources, and sex-differential plasticity (SDP) between hermaphrodites and unisexuals are predicted to affect sexual system stability. Here, GP and SDP are evaluated in cosexual and gynodioecious Wurmbea biglandulosa and sub-dioecious and dioecious W. dioica.

Methods

GP was evaluated under two resource conditions, compared among sexual systems and assessed as to whether (1) males produced perfect flowers and (2) hermaphrodites altered investment in perfect (female function) and total (male function) flowers. SDP was assessed within sexual systems as differences between sex functions of hermaphrodites vs. unisexuals. Males and hermaphrodites were compared to assess whether size thresholds for female function differed among sexual systems. Plasticity costs were evaluated using correlations between female function and male traits in hermaphrodites, and in W. dioica by comparing hermaphrodite and male regressions between plant size and pollen production.

Key Results

In dioecious W. dioica no males exhibited GP, whereas 100 % did in gynodioecious and cosexual W. biglandulosa. In sub-dioecious W. dioica, resources affected GP (high, 66 %; low, 42 %). Hermaphrodites in all sexual systems reduced perfect but not total flowers under low resources. Unisexuals were unaffected, demonstrating SDP for female function only. Thresholds for female function were greater in sub-dioecious W. dioica than in W. biglandulosa. Plasticity costs were detected only in sub-dioecious W. dioica.

Conclusions

SDP for female function could assist female establishment in cosexual populations and maintain females in gynodioecious and sub-dioecious populations. Although the absence of male SDP should stabilize sub-dioecy, plasticity costs would render sub-dioecy unstable, favouring canalized males over hermaphrodites. This study highlights the importance of interactions between environmental conditions and hermaphrodite sex expression for the stability of dimorphic sexual systems.     

Sexual conflict in simultaneous hermaphrodites: evidence from serranid fishes

Synopsis Much of modern mating systems theory is founded on the assumption that a conflict of interests between males and females acts to shape reproductive strategies. If sexual conflict exists it should extend to simultaneous hermaphrodites. Here, the suggestion is made that hermaphrodite mating systems can be used to explore the assumptions associated with sexual conflict and (a) predictions about hermaphrodite mating systems, and (b) a comparative analysis of the mating systems described for a group of species of simultaneously hermaphroditic serranid fishes. Theories based on Bateman's principle predict that there should be a preferred role in hermaphrodites; i.e. the male role ought to offer potential fitness advantages to all serranids and serranid mating systems reflect this. The comparative analysis offers evidence that cheating in the male role is found in all of the species studied and explains the harem polygyny system of two species. This preference for the male role in this group offers the best evidence currently available for the existence of sexual conflict as a factor shaping mating systems.     

The role of dyadic interactions in the mixed-mating strategies of the mangrove rivulus Kryptolebias marmoratus

The mangrove rivulus Kryptolebias marmoratus a small cyprinodont fish native to tropical and subtropical waters from Florida to Brazil, is one of two known self-fertilizing, hermaphroditic vertebrates of which K. marmoratus displays androdioecy, a complex system of reproduction in which hermaphrodites and males are present. This study describes the behavioral repertoires observed during dyadic interactions in the laboratory. Kryptolebias marmoratus exhibited 23 distinctive acts or behaviors. Acts were divided into four categories: aggressive, submissive, neutral, and reproductive. Leading and following behaviors played important roles in the behavioral repertoires of these fish. In hermaphrodite-male dyads, males exclusively initiated the reproductive process and actively pursued hermaphrodites. When hermaphrodites were paired, there was no evidence that they behaved like other simultaneous hermaphrodites that alternate sexual roles (e.g. serranids). Hermaphrodites were extremely aggressive towards one another, and the aggressor established dominance rapidly. Male-male dyads were divided into two subdivisions based on the presence or absence of the caudal ocellus on one fish. A caudal ocellus on one male appeared to signal the possibility of a potential mating partner to males lacking it. Pairings of males without an ocellus were similar to hermaphrodite-hermaphrodite dyads in that both members of the pair were aggressive towards one another. These observations may be indicative of interactions taking place in natural communities or assemblages of fish in which both males and hermaphrodites occur and provide evidence on the role of dyadic interactions in the mixed-mating strategies [Current Zoology 56 (1): 6-17, 2010].     

Association behaviour of the self-fertilizing Kryptolebias marmoratus (Poey): the influence of microhabitat use on the potential for a complex mating system

Preliminary observations were conducted to identify conspicuous body postures and movements of males and hermaphrodites in the mangrove killifish Kryptolebias marmoratus . These behaviours were used quantitatively to examine the social interactions for experimental pairings of K. marmoratus of different sexual states ( i.e. simultaneous hermaphrodite and male) in an aquarium with an open-water area and simulated crab burrows. This allowed observation of behaviours that could not be observed in the field. Kryptolebias marmoratus , regardless of sexual state and experimental treatment, spent 40% of the time in the burrow. Hermaphrodites exhibited a preference for associating with males rather than other hermaphrodites. The observed complexity of displayed behaviours and interactions between paired conspecifics indicate that K. marmoratus has a rich repertoire of social behaviour not predicted for a strictly selfing species. Also, land crab burrows play an important role in their social interactions.     

A review of the potential of surface flow constructed wetlands to enhance macroinvertebrate diversity in agricultural landscapes with particular reference to Integrated Constructed Wetlands (ICWs)

Discriminating female mate preferences enhance the variance in reproductive success among males of a population and create a potential for sexual selection, which can account for trait evolution and diversification. Fish color patterns are among the prime targets of mate choice-driven sexual selection. Populations of the cichlid Tropheus from Lake Tanganyika display remarkable geographic color pattern variation, but the role of female choice in their rapid and rich phenotypic diversification is unclear. Males and females establish a pair bond prior to spawning monogamously, but as brood care is strictly maternal, female investment in reproduction is high and the operational sex ratio is male-biased. Therefore, variance in male reproductive success can accrue if individual males succeed repeatedly in securing a mate. To test this prediction in the red colored Tropheus moorii “Chimba”, four pairs of males were presented to a series of females and female mate preferences were inferred from pairwise interactions. There was a significant difference in mating success between the males of each pair (P < 0.001 over all trials), as—with one exception—females shared preferences for the same males. Male courtship activity was strongly correlated with female choice. Our experiment suggests that female choice contributes to the variance in male reproductive success in the tested population.     

The effects of sex ratio and density on the expression of gender in the polychaeteCapitella capitata

Summary Large natural populations of the marine polychaeteCapitella capitata (species type I) contain males, females, and occasionally, hermaphrodites. Environmental conditions control the occurrence of hermaphrodites. At low density or in groups with female-biased sex ratios, males develop into hermaphrodites, and hermaphrodites are common. Crosses suggest that females are heterogametic, and males and hermaphrodites are homogametic. Heterogametic females do not become hermaphrodites.This study shows that in homogametic individuals, environmental conditions determine not only the development of hermaphroditism but also the expression of initial gender. Homogametic individuals can express either male or female gender initially, and homogametic individuals of either gender can develop subsequently into simultaneous hermaphrodites. The choice of initial gender depends on isolation. Most homogametic juveniles become females if reared alone but males if reared with other conspecifics. Homogametic males readily develop into hermaphrodites if females are rare. In contrast, homogametic females rarely become hermaphrodites.     

Reproductive biology and relative male and female fitness in a trioecious cactus,Pachycereus pringlei (Cactaceae)

We describe the breeding system of an autotetraploid trioecious cactus, Pachycereus pringlei, provide estimates of the fitnesses of males and females relative to that of hermaphrodites, and discuss the role played by pollinators in the maintenance of three sexual morphs. Relatively high frequencies of females (45%) and males (26%) exist in coastal desert populations around Bahia Kino, Sonora, Mexico. They differ from hermaphrodites in flower size (females only), initiation of the flowering season, number of flowers produced per night and per season, sucrose content of nectar, and, in females, number of fruits produced per season under open pollination and in response to hand-pollination. Major similarities between the sex classes include overall plant size, nectar volume per flower, percent fruit set in open-pollinated flowers of females and hermaphrodites, seed mass and number of seeds per fruit, and pollen mass per flower in males and hermaphrodites. Hermaphrodites are self-compatible, and the selfing rate is high (65%). Levels of inbreeding depression in selfed fruits and seeds appear to be low. Fruit set is strongly pollinator-dependent in females but much less so in hermaphrodites. Relative fitness of males and females, as measured by annual production of pollen or seeds, is at least 1.5 times higher than that of the corresponding sex function in hermaphrodites. Given the high selfing rate and apparent lack of inbreeding depression, these fitness differences are insufficient to explain the occurrence of trioecy in this species.