Presence of primary and secondary males in a population of the protogynous Synbranchus marmoratus

Synbranchus marmoratus , the 'swamp eel', is a protogynous diandric fish. The primary and secondary males can be distinguished from each other easily by differences in gonadal morphology. Primary males have lobular, unrestricted testes with central efferent ducts. The secondary male has a 'lamellar' testis, efferent ducts are present in the ventral region (new formation), lateral supports and it is covered by the former ovarian capsule. The length of primary male varies from 13 to 88 cm while secondary males range from 56 to 91 cm. Transitional individuals vary between 45 and 60 cm in length. The swamp eel population studied is composed of 80% primary males and 20% secondary males. Although gonadosomatic indices are always higher in primary males, they increase in secondary ones as the newly acquired stage progresses. The lamellar organization of the gonad of secondary males, the absence of this kind of testis in individuals smaller than 56 cm, and the presence of hermaphroditic fish, is evidence for protogyny in this species.     

Sex Allocation in Lythrypnus (Gobiidae): Variations on a Hermaphroditic Theme

The gonadal sexual patterns of three Atlantic/Caribbean Lythrypnus (L. nesiotes, L. phorellus, L. spilus) are described, based on histological examination, and compared with previously described sexual patterns of L. dalli and L. zebra, from the eastern Pacific. Overall, there was striking similarity in the sexual patterns of all the species; each exhibited simultaneous hermaphroditism with a high degree of variability in allocation to male tissue among individuals. Among the five species whose sexual patterns are described, at least three distinct sexual patterns were identified. Lythrypnus dalli has an allocation pattern distinct from the other species, with populations consisting of primarily pure females, strongly female-biased hermaphrodites and pure males. Lythrypnus nesiotes was also found to be distinct from the other species, consisting primarily of pure females and strongly female-biased hermaphrodites and male-biased individuals (mean allocation to male tissue = 75%). In contrast to L. dalli, L. nesiotes had no pure males. Indeed, no other species examined included pure males. L. phorellus, L. spilus and L. zebra had much more intermediate allocation patterns than either L. dalli or L. nesiotes. Most individuals were female biased (<10% male tissue), and there were significant numbers of individuals with intermediate allocation (10–90% male). L. zebra differed somewhat from L. phorellus and L. spilus in that more strongly male-biased individuals were common in the sample (i.e., ranging in allocation from 90 to 98% male); this difference was not statistically compelling. This marked variation in allocation among closely related species suggests Lythrypnus is a useful model system to explore factors affecting allocation. For example, models developed for simultaneous hermaphrodites and appropriate for Lythrypnus predict that pure sexed individuals will be more common at higher density (e.g., because mating success is more certain). The observed interspecific variation supports this prediction – both L. dalli and L. nesiotes occur at high density and have the most extreme allocation patterns, whereas L. phorellus, L. spilus, and L. zebra occur at lower density and have more intermediate allocation patterns.     

Habitat Association and Social Structure of the Chocolate Hind, <Emphasis Type="BoldItalic">Cephalopholis boenak</Emphasis> (Pisces: Serranidae: Epinephelinae), at Ping Chau Island,Northeastern Hong Kong Waters

Synopsis The chocolate hind, Cephalopholis boenak, is the smallest and last remaining grouper of any abundance in Hong Kong waters. We investigated its habitat association and social structure to understand its sexual pattern and seek possible approaches to protect this species. Juveniles and adults are distributed in the same habitat and strongly associated with corals, in particular, Pavona decussata when available, for settlement and residence. Social groups of C. boenak are relatively small with a single male, one or two smaller females, and varying numbers of sexually inactive individuals (which are mature but sexually inactive, or juvenile). Males defend their boundaries by chasing neighbouring males and have significantly larger home ranges than females. Males visit females and sexually inactive individuals at one or more specific locations, consistently following similar paths. There was a positive linear correlation between body size and home range in individuals ≥90 mm TL. We observed male courtship in the reproductive season, within his home range during the late afternoon. Spawning behaviour is not associated with any particular moon phase and may occur more than once within the reproductive season. Although C. boenak is a diandric, protogynous hermaphrodite, primary and secondary males could not be distinguished by behavioural patterns in the field. Population management of this species should include habitat protection.     

Do the maximum sizes,ages and patterns of growth of three reef‐dwelling labrid species at two latitudes differ in a manner conforming to the metabolic theory of ecology?

The size and age data and patterns of growth of three abundant, reef‐dwelling and protogynous labrid species (Coris auricularis, Notolabrus parilus and Ophthalmolepis lineolata) in waters off Perth at c. 32° S and in the warmer waters of the Jurien Bay Marine Park (JBMP) at c. 30° S on the lower west coast of Australia are compared. Using data for the top 10% of values and a randomization procedure, the maximum total length (L_T) and mass of each species and the maximum age of the first two species were estimated to be significantly greater off Perth than in the JBMP (all P < 0·001) and the maximum ages of O. lineolata in the two localities did not differ significantly (P > 0·05). These latitudinal trends, thus, typically conform to those frequently exhibited by fish species and the predictions of the metabolic theory of ecology (MTE). While, in terms of mass, the instantaneous growth rates of each species were similar at both latitudes during early life, they were greater at the higher latitude throughout the remainder and thus much of life, which is broadly consistent with the MTE. When expressed in terms of L_T, however, instantaneous growth rates did not exhibit consistent latitudinal trends across all three species. The above trends with mass, together with those for reproductive variables, demonstrate that a greater amount of energy is directed into somatic growth and gonadal development by each of these species at the higher latitude. The consistency of the direction of the latitudinal trends for maximum body size and age and pattern of growth across all three species implies that each species is responding in a similar manner to differences between the environmental characteristics, such as temperature, at those two latitudes. The individual maximum L_T, mass and age and pattern of growth of O. lineolata at a higher and thus cooler latitude on the eastern Australian coast are consistent with the latitudinal trends exhibited by those characteristics for this species in the two western Australian localities. The implications of using mass rather than length as the indicator variable when comparing the maximum sizes of the three species and the trends exhibited by the instantaneous growth rates of those species at different latitudes are explored. Although growth curves fitted to both the L_T and masses at age for the males of each species lay above those for their females, this would not have influenced the conclusions drawn from common curves for both sexes.     

Density-dependent protogynous sex change in territorial-haremic fishes: models and evidence

Several hypotheses of the proximate control of protogynous (female-to-male)sex change propose that social group composition triggers sexchange, but they do not address how proximate cues are alteredby population density. I present three mutually exclusive encounter-ratethreshold hypotheses that assume that population density determinesrates of contact between social group members and that ratesof contact are cues for sex change. Different densities arepredicted to induce sex change, depending on the encountersassumed to be important in the sex change process (e.g., encounterswith smaller and larger individuals). Tests of the models usea pomacanthid angelfish(Centropyge potten) to show that continuedpresence of a smaller (female) conspecific is needed for sexchange, and that continued presence of a larger (male) conspecificcan either inhibit sex change or prevent its behavioral stimulation.Using constant social group composition, sex change is preventedat higher density but not at a lower density. The absolute encounter-ratethreshold hypothesis, which predicts sex change under intermediate-densityconditions, is the most probable model of the social controlof sex change in C.potteri     

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.