Control of different mating systems in a coral reef fish by one environmental factor

The Red Sea coral-dwelling damselfish Dascyllus marginatus is organized in stable terri torial groups with males dominating all females. The fish live in pairs, harems or multi-male groups. Group size, and the number of sexually active males in a group, are correlated with coral size. Males monopolize and control the coral, attracting potential mates. The experimental alteration of coral sizes, using spherical Stylophora corals, resulted in an increase of male numbers, in artificially composed groups, with the increase of coral size. Thus pairs and harems were produced on small corals, multimale groups on big corals. Experiments with unisexual groups revealed a higher survival of females; males are more aggressive to each other, and cause a stronger emigration of subdominants. In D. marginatus, group size and the number of sexually active males are essentially restricted by one environmental factor: the number of available hiding places on a coral.     

Sexual dimorphism and food habits of the clingfish,Diademichthys lineatus,and its dependence on host sea urchin

Synopsis Stomach contents of the clingfish Diademichthys lineatus, 10–56 mm standard length, revealed changes in food habits with growth and sexual differences. Soon after settlement, D. lineatus obtained food from their host sea urchin (genus Diadema) and other associated symbionts. They became less dependent on the host with growth. The juveniles ate pedicellariae and sphaeridia of the host and commensal copepods, whereas the adult fish ate burrowing bivalves in corals as well as tube feet of their host and eggs of a commensal shrimp. The young fish were transitional in their food habits. The change in food habits of the fish coincided with behavioral changes; i.e. enlargement of home ranges and less dependency on the host. The adult females, having a longer snout, ate shrimp eggs and bivalves more frequently than the adult males, which ate tube feet of the host more often than the females did. Sexual difference in food habits was apparent after the sex of the fish became identifiable by comparing snout shapes. The polygynous mating system of this species suggests that conspicuous sexual dimorphism might have developed under sexual selection. However, niche partitioning of food is also likely to be related to this sexual dimorphism.     

Sexual selection versus alternative causes of sexual dimorphism in teiid lizards

Summary The presence and extent of sexual dimorphisms in body form (size and shape) of adult macroteiid lizards were investigated. Males were significantly larger than females in the temperate species, Cnemidophorus tigris, and in the tropical species, Ameiva ameiva and C. ocellifer. Young adult C. tigris males grew faster than young adult females within and between reproductive seasons. Adult males of all species had larger heads than adult females of the same body size; this difference increased with body size. Moreover, male C. tigris were heavier than females of the same snout-vent length. The causes and consequences of the sexual dimorphisms were also examined. The possible causes of body size are especially numerous, and distinguishing the relative influences of the various causal selection factors on body size is problematical. Nevertheless, observational field data were used to tentatively conclude that intrasexual selection was the cause of larger body size of C. tigris males relative to females because (1) larger males won in male aggressive interactions, (2) the winning males gained access to more females by repelling competitors and by female acceptance, (3) larger males consequently had higher reproductive success, and (4) other hypothetical causes of larger male size were unsupported.     

Both-ways sex change in monogamous coral gobies, Gobiodon spp.

Synopsis We confirmed both-ways sex change in the coral-dwelling gobies Gobiodon micropus, G. oculolineatus, G. quinquestrigatus and G. rivulatus rivulatus by mate-removal experiment in the field and by the aquarium experiment of keeping two consexual fish in a coral. Eight species of Gobiodon were found in Acropora corals on the reef flat of Sesoko Island, Okinawa, southern Japan. The 4 species mentioned above bred in monogamous pairs composed of a male and a female matched by size, and the male took care of eggs deposited on the coral branch. In G. quinquestrigatus and G. rivulatus rivulatus males were larger than females in newly formed pairs, and females grew faster than their mates until breeding. The growth-rate advantage in females seems to be the major factor in the evolution of female to male sex change. The gobies strongly depended on host corals, but they moved between the corals after mate loss or coral death to form new pairs. This provides opportunities for the evolution of male to female sex change; the ability to change sex in both directions reduces the frequency of risky movement between host corals to form new pairs. These conditions are very similar to those reported in the both-ways sex change of another coral-dwelling goby Paragobiodon echinocephalus.     

Male mating success,sexual size dimorphism,and site fidelity in two species of Malacoctenus (Labrisomidae)

Synopsis In both Malacoctenus hubbsi and Malacoctenus macropus, males defended preferred oviposition sites from both other males and potential egg predators. In M. hubbsi, adult females were larger than adult males. Larger M. hubbsi males were not associated with territory parameters that were correlated with higher mating success, and male size was not correlated with mating success. Male size did affect mating success when territory parameters were statistically controlled for, but the failure of large males to associate with better territories eliminated any mating advantage for larger males. In M. macropus, males are larger than females. Larger males defended preferred oviposition sites, and had higher mating success than did smaller males. Male M. macropus also had much higher site fidelity than male M. hubbsi. These results suggest that the evolution of the differences in site fidelity and sexual size dimorphism between these two species may be due to sexual selection acting differentially in these two species.     

Gonad Morphology, Colony Demography and Evidence for Hermaphroditism in Gobiodon Okinawae (Teleostei, Gobiidae)

Gobiodon okinawae is a small-sized, obligate coral-dwelling goby. The majority of species in this Indo-Pacific genus exhibit an obligatory association with branching live corals and a number have been shown to be bi-directional hermaphrodites in which adults have the capacity to shift between male and female function. Gonadal histology in G. okinawae demonstrated that all individuals had either an ovotestis or an ovary. Some females had an ovary with vitellogenic oocytes, indicating adult female function. Hermaphrodites having an ovotestis were either functionally male, as evidenced by the presence of spermatozoa or, in one instance, functionally female so judged by the presence of vitellogenic oocytes. No individuals were found to have mature gametes of both sexes, although a number of hermaphrodites had an inactive ovotestis with no mature gametes of either sex. Based on size ranges for fish having different gonad morphologies, individuals in this species appear to develop first as a female. They then either mature and function solely as a female, or become hermaphroditic. Findings based on experimentally maintained individuals suggests that adult hermaphrodites can shift sexual function in either direction. Accessory gonadal structures (AGS) were found in both sexes. These consisted of two fully differentiated pairs of lobes, each compartmentalized internally by lumina and containing PAS+secretions. The secretions of the dorsally located AGS were colloidal while those of the ventrally located AGS were fibrillar and granular in nature. The presence of two sets of AGS among males appears to be characteristic of both Gobiodon and its putative sister genus, Paragobiodon. However, the occurrence of fully developed AGS in both females and males has not previously been reported and may be unique to G. okinawae.     

Female sexual swellings in the Asian colobine Simias concolor

During a preliminary study of pig-tailed langurs (Simias concolor) in the Pagai Islands, Indonesia, it was discovered that females exhibited conspicuous swelling of the urogenital triangle. The pig-tailed langur is the first Asiatic colobine found to have prominent sexual swellings and the only colobine with sexual swellings that lives in one-male groups. Because all anthropoids with conspicuous sex skin typically live in groups having female-biased adult sex ratios, it is possible that females might compete amongst themselves for the male in one-male groups, or the best males in multimale groups. Sexual swellings may therefore have resulted from sexual selection for signals attractive to males in female-female competition, as suggested earlier by Bercovitch (California Anthropologist 8:9–12, 1978). Prolonged observation of recognizable individuals will be required to test this hypothesis in the pig-tailed langur and other species.     

Growth and age of staghorn sculpins of the genus <Emphasis Type="Italic">Gymnocanthus</Emphasis> (Cottidae) in Peter the Great Bay and adjacent waters of Primorye (Sea of Japan)

Age and growth have been studied in four species of staghorn sculpins of the genus Gymnocanthus inhabiting Primorye (the Russian sector of the Sea of Japan). Large black edged and purplegray sculpins, G. herzensteini and G. detrisus, inhabited deeper waters compared with threaded sculpin G. pistilliger and (especially) whip sculpin G. intermedius. The size differences between different sculpin species could already be revealed in the diameter of mature oocytes and the length of hatching larvae and fries passing to the benthic phase of development. The maximum size in these species correlated with their maximum age. G. herzensteini, G. detrisus, G. pistilliger, and G. intermedius could attain the age of no less than 16+, 15+, 9+, and 7+, respectively. The gains in fish of the same age were also greater in species attaining greater size values. In all the species, females lived longer than males and were larger than males of the same age. Throughout the life cycle, the growth rate gradually came down; the decrease was especially pronounced during the period of sexual maturation. In the southern part of the geographic range, the specimens of purplegray sculpin attained smaller size and showed lower growth rate compared with the fish from the northern part of the range. The threaded sculpin demonstrated the inverse relationships. In general, females were dominating in samples of staghorn sculpins; however in small and medium size groups, the proportion of males was greater, which was due to their smaller, compared with females, absolute gains. In elder groups, the proportion of males gradually went down, as they were dying earlier than females.     

Female mate choice and species recognition between two closely related cichlid fish of Lake Malawi,Metriaclima estherae and M. callainos

Cichlids are one of the most diverse and colourful groups of freshwater fishes in the world. Despite much investigation, the factors that promote speciation in these fishes are still uncertain. However, previous studies suggest that sexual selection on male colour is one of the main drivers of speciation among these fishes. Metriaclima estherae is a polymorphic cichlid species from Lake Malawi, and thus provides an ideal model for the investigation of the importance of colour as a species recognition cue. M. callainos is a closely related and morphologically similar species, with male colour pattern very similar to that of M. estherae. We tested female choice by giving females of the two species a choice between conspecific and heterospecific males in the presence and absence of visual (colour) and chemical cues. The results show that females of M. callainos were able to reliably recognize conspecific males, even when colour was eliminated as a cue. However, females of M. estherae did not prefer conspecific males, although they were able to discriminate between red and blue conspecific colour morphs by using chemical cues. These results suggest that species recognition cues may differ even among closely related species of cichlid fish, and that female preferences for male coloration may be weak in certain species.     

Social organization of white‐headed langurs (Trachypithecus leucocephalus) in the Nongguan Karst Hills,Guangxi, China

The number of males per group is the most variable aspect of primate social organization and is often related to the monopolizability of females, which is mainly determined by the number of females per group and their reproductive synchrony. Colobines show both inter‐specific and intra‐specific variations in the number of males per group. Compared with other colobine species, little is known about the social organization of white‐headed langur (Trachypithecus leucocephalus), despite its endangered status and unusual limestone habitat. As a part of a long‐term study of the white‐headed langurs in the Nongguan Karst Hills, Guangxi, China, we quantitatively investigated their social organization by analyzing census data from 1998 to 2003. The population censuses revealed that the predominant social organization of bisexual groups was the one‐male group, similar to a previous report on this species and many other Asian colobines. In such groups, one adult male associated with 5.1 adult females, 0.1 sub‐adult males, 2.6 juveniles and 2.9 infants on average, with a mean group size of 11.7 individuals. In addition, three multi‐male groups were recorded, consisting of 2–3 adult males, 1–5 adult females, 0–2 sub‐adult males, 0–7 juveniles and 0–2 infants. They did not contain more adult females than the one‐male groups and were unstable in group membership. The langurs outside bisexual groups were organized into small nonreproductive groups or lived as solitaries. The nonreproductive groups averaged 1.3 adult males, 1.3 sub‐adult males and 2.6 juveniles. Juvenile females were present in such groups on 52.4% of all occasions. As predicted by the monopolization model, the prevalence of the one‐male pattern in this species may mainly be attributed to the small number of females in the group. The possible reasons for the occurrence of multi‐male groups and the presence of juvenile females in nonreproductive groups are also discussed. Am. J. Primatol. 71:206–213, 2009. © 2008 Wiley‐Liss, Inc.     

Males,but not females,contribute to sexual isolation between two sympatric species of <Emphasis Type="Italic">Gambusia</Emphasis>

Reproductive isolation restricts genetic exchange between species. Various pre- and post-mating barriers, such as behavior, physiology and gametic incompatibility, have been shown to evolve in sympatry. In certain scenarios, isolation can be asymmetrical, where species differentially prefer conspecifics. We examined sexual isolation via conspecific mate preference between Gambusia affinis and G. geiseri in both sexes. To investigate male contribution to sexual isolation, we compared the number of mating attempts (gonopodial thrusts) directed at either a conspecific or a heterospecific female, in both species. We also examined sperm priming and expenditure in males in the presence of conspecific or heterospecific females. We then measured female preference for either a conspecific or heterospecific male, in both species. We found that males of both species preferred to mate with conspecific females, but showed no difference in sperm production or expenditure between conspecific and heterospecific females. Females of both species did not prefer conspecific over heterospecific males. Our results suggest that sexual isolation might be mediated by male mate choice in this system and not female choice, suggesting that there is asymmetrical reproductive isolation between the sexes in G. affinis and G. geiseri, but symmetrical species isolation.     

Genetic evidence for the mating system and reproductive success of black sea bream (Acanthopagrus schlegelii)

Understanding the mating system and reproductive success of a species provides evidence for sexual selection. We examined the mating system and the reproductive success of captive adult black sea bream (Acanthopagrus schlegelii), using parentage assignment based on two microsatellites multiplex PCR systems, with 91.5% accuracy in a mixed family (29 sires, 25 dams, and 200 offspring). Based on the parentage result, we found that 93.1% of males and 100% of females participated in reproduction. A total of 79% of males and 92% of females mated with multiple partners (only 1 sire and 1 dam were monogamous), indicating that polygynandry best described the genetic mating system of black sea bream. For males, maximizing the reproductive success by multiple mating was accorded with the sexual selection theory while the material benefits hypothesis may contribute to explain the multiple mating for females. For both sexes, there was a significant correlation between mating success and reproductive success and the variance in reproductive success of males was higher than females. Variation in mating success is the greatest determinant to variation in reproductive success when the relationship is strongly positive. The opportunity for sexual selection of males was twice that of females, as well as the higher slope of the Bateman curve in males suggested that the intensity of intrasexual selection of males was higher than females. Thus, male–male competition would lead to the greater variation of mating success for males, which caused greater variation in reproductive success in males. The effective population number of breeders (N_b) was 33, and the N_b/N ratio was 0.61, slightly higher than the general ratio in polygynandrous fish populations which possibly because most individuals mated and had offspring with a low variance. The relatively high N_b contributes to the maintenance of genetic diversity in farmed black sea bream populations.     

Pectoral fin size in a fish species with paternal care: a condition-dependent sexual trait revealing infection status

1. The three-spined stickleback, Gasterosteus aculeatus L., is a territorial fish with exclusive male parental care. Males oxygenate the eggs with fanning movements of their pectoral fins. The present authors investigated whether the apparent sexual differences in the functional demands of the pectoral fins have resulted in sexual differences in fin size. If males have relatively larger pectoral fins, females may use this as a signal to aid their mate choice for good fathers. Therefore, further objectives were to study the condition-dependency of relative pectoral fin size in males and the relationship with male parasite load. 2. Reproductively active males possessed relatively larger pectoral fins than females in both wild-caught and laboratory-bred fish. 3. In the field, caring males with relatively large pectoral fins were in better physical condition and had more food in their stomachs. 4. Relatively small pectoral fins and poor body condition were associated with infection by the intestinal parasite Pomphorhynchus laevis (Acanthocephala), the prevalent parasite species in the study population.     

Environmental determinants of butterflyfish social systems

Synopsis Butterflyfishes (Chaetodontidae) display a variety of social systems, including monogamous pair-bonds, harems, and schooling with group spawning. The range of reproductive options available to butterflyfishes is shaped by their general life history characteristics, such as broadcast spawning with widely dispersed pelagic larvae, large body size and low adult mortality. The distribution and quality of food resources are major determinants of group size and mobility, thereby influencing the relative costs and benefits of available options, and determining specific social systems. Planktivorous and corallivorous butterflyfishes exemplify the relationship between food resources and social systems. Pelagic plankton is a patchy, but temporally and spatially unpredictable food resource which is efficiently exploited by fish in mobile schools. Neither sex is able to monopolize food resources necessary for the other sex, and plantivorous butterflyfishes appear constrained to spawn in groups. In contrast, corals are stable and predictable in space and time, favoring residence in one area and territorial defense of that space by coral-feeding butterflyfishes. Females defend food resources from other females, and males defend territories containing a female from other males. Males attempt to defend areas containing more than one female, but are unsuccessful. A monogamous social system results. This system favors the evolution of cooperative behavior between mates to increase female fecundity, as long as the male has an opportunity of sharing in that reproduction. Mate removal experiments conducted on two monogamous coral-feeding species,Chaetodon multicinctus andChaetodon quadrimaculatus reveal a division of labor between male and female pair-mates. Paired males assume most of the territorial defense activities, allowing their mates to feed more.     

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.     

Testosterone Control of Male-Type Sexual Behavior in the Tammar Wallaby (Macropus eugenii)

In the tammar wallaby,Macropus eugenii,the expression of male-type sexual behavior is apparently determined by the activating effects of testicular hormones in adulthood. The incidence of male-type copulatory behavior and sexual checking behavior was compared in intact (control) males, control females, testosterone-treated females, and three groups of males castrated either postnatally (24–26 days of age), prepubertally (14.5 months of age), or in adulthood. All three groups of castrated male wallabies showed a very low incidence of male sexual behavior in adult life, comparable to that shown by the untreated females. Adult female wallabies with 100-mg testosterone implants showed a high incidence of male sexual behavior which was indistinguishable from that shown by intact males. The results suggest that sex differences in male-type behavior in the tammar wallaby are due to short-term inductive effects of testosterone acting on a sexually indifferent brain. There is no evidence of any long-term organizational effects of testosterone acting in fetal or neonatal life on the neural pathways controlling male-type sex behavior in this marsupial mammal.     

Eat or Not to Eat: Reversed Sexual Cannibalism as a Male Foraging Strategy in the Spider Micaria sociabilis (Araneae: Gnaphosidae)

Reversed sexual cannibalism represents an unusual situation in which a male kills and consumes a female. We examined this rare phenomenon in the spider Micaria sociabilis, whose males were observed to regularly cannibalise old females. In this study, we investigated male motivation for such behaviour in the light of ecological conditions such as mate availability and prey availability. We found that male cannibalism is not affected by short‐term starvation but rather by male feeding history during the ontogenetic development in combination with prey availability during the adult stage. Males from the summer generation reached bigger sizes than males from the spring generation and females from both generations. They developed in the period with exceptionally high prey occurrence, but when they reached the adult stage, the prey availability decreased. In this period, we observed the highest frequency of cannibalism, however, only when the sex ratio was female biased. Reversed sexual cannibalism in M. sociabilis seems to represent an advantageous male foraging strategy, which is affected by prey availability and male feeding history, tuned by sex ratio and directed towards females of inferior quality.     

Male Mate Choice in Mixed Bisexual/Unisexual Breeding Complexes of Poecilia (Teleostei: Poeciliidae)

The livebearing all-female fish Poecilia formosa reproduces by gynogenesis, a modified form of parthenogenesis. P. formosa forms at least two breeding complexes: in its northern range it exists sympatrically with Poecilia latipinna and in its southern range with Poecilia mexicana. Differences between these complexes and their possible origin are discussed. Embryogenesis is triggered by sperm of males of these closely related sympatric species. Because inheritance is strictly maternal, from the male point of view energy and time invested are totally lost. In this study we wanted to elucidate whether males are able to distinguish between conspecific and parasitic females. It could be shown that males are able to distinguish females optically, but that this ability was obscured as soon as chemical and/or tactile contact was possible. Furthermore, we found that females in an attractive phase of their sexual cycle are always preferred, regardless of species. This is possibly the mechanism by which parasitic females obtain the matings they need to reproduce.     

Interspecific interactions and learning variability jointly drive geographic differences in mate preferences

Co‐occurrence of closely related species can cause behavioral interference in mating and increase hybridization risk. Theoretically, this could lead to the evolution of more species‐specific mate preferences and sexual signaling traits. Alternatively, females can learn to reject heterospecific males, to avoid male sexual interference from closely related species. Such learned mate discrimination could also affect conspecific mate preferences if females generalize from between species differences to prefer more species‐specific mating signals. Female damselflies of the banded demoiselle (Calopteryx splendens) learn to reject heterospecific males of the beautiful demoiselle (C. virgo) through direct premating interactions. These two species co‐occur in a geographic mosaic of sympatric and microallopatric populations. Whereas C. virgo males have fully melanized wings, male C. splendens wings are partly melanized. We show that C. splendens females in sympatry with C. virgo prefer smaller male wing patches in conspecific males after learning to reject heterospecific males. In contrast, allopatric C. splendens females with experimentally induced experience with C. virgo males did not discriminate against larger male wing patches. Wing patch size might indicate conspecific male quality in allopatry. Co‐occurrence with C. virgo therefore causes females to prefer conspecific male traits that are more species specific, contributing to population divergence and geographic variation in female mate preferences.     

Agonistic interactions with asymmetric body size in two adult-age groups of the annual killifish Millerichthys robustus (Miller & Hubbs, 1974)

In this study, the author evaluated two adult age groups of the Mexican rivulus Millerichthys robustus with body size asymmetries to determine the strategies used by an annual killifish during agonistic interactions of different ontogenetic stages. To achieve this goal, the author first characterized the ethogram of agonistic interactions of M. robustus composed of seven behavioural units in males and five behavioural units in females. The author then analysed agonistic interaction strategies used by males and females with body size asymmetries in two groups of different adult ages that represent different ontogenetic stages: (a) just after sexual maturity was reached, at 5 weeks of age, and (b) near natural death, at 24 weeks of age. The agonistic behaviour patterns of M. robustus were compatible with the logic of mutual assessment. Large males had an advantage during their interactions in both age groups, winning all of the encounters. Nonetheless, there was more aggression in 5-week-old fish encounters. In addition, small 24-week-old fish were more aggressive than small 5-week-old fish. These changing strategies may be because of the cost–benefits required during a fight at each ontogenetic stage. In the female encounters, size did not predict winners, as both small and large fish won a similar number of encounters, and some contests remained unresolved regardless of age group. There was a tendency for small females of any age to risk more than males in fights to maintain reproductive fitness.