http://aerg.canberra.edu.au/library/sex_general/2002_Devlin_Nagahama_sex_determination_in_fish_review.pdf

Sex determination and sex differentiation in fish: an overview of genetic, physiological, and environmental influences

PRONOUNCED sex differences in mating competition are a prominent feature of many animal breeding systems. These differences are widely attributed to sex differences in parental investment1,2which bias the ratio of sexually receptive females to males3 (the operational sex ratio), generating more intense competition between members of one sex, usually males3–5. Unfortunately, relative parental investment1 is usually impossible to measure in species where both sexes invest in their offspring6,7 and there is currently no empirical basis for predicting the pattern of mating competition in these species. In contrast, the potential rate of reproduction by males and females (measured as the maximum number of independent offspring that parents can produce per unit time) is both more directly related to the operational sex ratio and more easily estimated in natural populations7. Here we show that among species where males care for the young, the sex with the higher potential reproductive rate competes more intensely for mates than the sex with the lower potential rate of reproduction.

Sexual selection and the potential reproductive rates of males and females

Organisms compete for various resources in the course of sexual reproduction. First, there is intrasexual competition for obtaining mates. Then, there is the need to exclude reproductive competitors who might displace or affect the individual's own gametes (e.g., sperm competition, egg dumping). There is competition for sites that are used to raise progeny andtor that will optimally support them, and it may be highly advantageous to monopolize the resources that are essential for offspring survival and development. In this chapter I review our current knowledge of the ways in which fish compete at these different levels. I further describe how competition for resources may lead to cooperative behavior, even between the competitors themselves. Finally, I draw attention to the model character of fish social systems and suggest crucial directions for future research.

Sneakers, Satellites, and Helpers: Parasitic and Cooperative Behavior in Fish Reproduction

Global climate change is having devastating effects on habitat structure in coral-reef ecosystems owing to extreme environmental sensitivities and consequent bleaching of reef-building scleractinian corals. Coral bleaching frequently causes immediate loss of live coral and may lead to longer-term declines in topographic complexity. This review identifies coral cover and topographic complexity as critical and distinct components of coral-reef habitats that shape communities of coral-reef fishes. Coral loss has the greatest and most immediate effect on fishes that depend on live corals for food or shelter, and many such fishes may face considerable risk of extinction with increasing frequency and severity of bleaching. Coral loss may also have longer-term consequences for fishes that require live corals at settlement, which are compounded by devastating effects of declining topographic complexity. Topographic complexity moderates major biotic factors, such as predation and competition, contributing to the high diversity of fishes on coral reefs. Many coral-reef fishes that do not depend on live coral are nonetheless dependent on the topographic complexity provided by healthy coral growth. Ecological and economic consequences of declining topographic complexity are likely to be substantial compared with selective effects of coral loss but both coral cover and topographic complexity must be recognised as a critical component of habitat structure and managed accordingly. Urgent action on the fundamental causes of climate change and appropriate management of critical elements of habitat structure (coral cover and topographic complexity) are key to ensuring long-term persistence of coral-reef fishes.

Effects of climate -induced coral bleaching on coral -reef fishes — ecological and economic consequences

Climate change will impact coral-reef fishes through effects on individual performance, trophic linkages, recruitment dynamics, population connectivity and other ecosystem processes. The most immediate impacts will be a loss of diversity and changes to fish community composition as a result of coral bleaching. Coral-dependent fishes suffer the most rapid population declines as coral is lost; however, many other species will exhibit long-term declines due to loss of settlement habitat and erosion of habitat structural complexity. Increased ocean temperature will affect the physiological performance and behaviour of coral reef fishes, especially during their early life history. Small temperature increases might favour larval development, but this could be counteracted by negative effects on adult reproduction. Already variable recruitment will become even more unpredictable. This will make optimal harvest strategies for coral reef fisheries more difficult to determine and populations more susceptible to overfishing. A substantial number of species could exhibit range shifts, with implications for extinction risk of small-range species near the margins of reef development. There are critical gaps in our knowledge of how climate change will affect tropical marine fishes. Predictions are often based on temperate examples, which may be inappropriate for tropical species. Improved projections of how ocean currents and primary productivity will change are needed to better predict how reef fish population dynamics and connectivity patterns will change. Finally, the potential for adaptation to climate change needs more attention. Many coral reef fishes have geographical ranges spanning a wide temperature gradient and some have short generation times. These characteristics are conducive to acclimation or local adaptation to climate change and provide hope that the more resilient species will persist if immediate action is taken to stabilize Earth’s climate.

Climate change and the future for coral reef fishes

Reproductive ecology and ethology of 52 cichlid fishes were studied along the shore of Myako, east-middle coast of Lake Tanganyika. Seventeen species were substrate-brooders (guarders), 31 were mouthbrooders, and the remaining 4 were intermediate, performing prolonged biparental guarding of fry after mouthbrooding. Among the substrate-brooders maternal care (and polygyny) was seen about as frequently as biparental care. In most of the mouthbrooders only females took care of the brood, but in 3 species eggs and small larvae were mouthbrooded by females and larger fry by males. In most of the maternal mouthbrooders males defended mating territories which females visited to spawn. The mating system differed from lekking in that there was no concentration of territories and males fed within them. In the remaining maternal mouthbrooders males and overlapping home ranges and only temporarily defended courtship sites in each bout of spawning. Brood size, egg size, breeding site, and sexual differences in body size and color are described. The relationship between parentalcare patterns and mating systems within the family Cichlidae are discussed.

Parental care and mating systems of cichlid fishes in Lake Tanganyika: a preliminary field survey

Sex change in either direction by growth-rate advantage in the monogamous coral goby, Paragobiodon echinocephalus

New aspects of sex change in reef fishes are reviewed with special emphasis on recent studies in Japan. For protogyny, studies on both monandric and diandric species have been conducted, but the distinction of primary males from prematurational secondary males seems to need further examination. For protandry, detailed field studies on anemonefishes have revealed alternative life-history styles associated with movements between hosts before or after maturation. The most interesting new aspect has been the discovery of 2-way sex change within a species. Conditions for evolution of 2-way sex change are examined in relation to the size-advantage model and social control mechanisms. A fish may change sex when it becomes dominant in a mating group, but a dominant fish may also change sex in the reverse direction when its social status changes to subordinate through inter-group movement. Two-way sex change has hitherto been reported only from basically protogynous fishes (e.g., Gobiidae, Pomacanthidae, Cirrhitidae, Epinephelinae). Possibilities of the reverse sex change in the protandrous anemonefishes are discussed with data from some unpublished studies.

New aspects of sex change among reef fishes : recent studies in Japan

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.

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

Social relationships of the protogynous wrasse, Labroides dimidiatus, were investigated at the shallow rocky reefs of Shirahama, southern Japan, from 1972 to 1979. Individuals were tagged, and their behaviour and movements were recorded for at least one month. Home ranges of males hardly overlapped. Within a male's home range, 2 to 12 females resided and spawned with the male. Home ranges of females in a male's harem did not always overlap. Individuals whose home ranges largely overlapped (=members of a \"primary group\") had different social relationships, both in quantity and quality, from those between primary groups: e.g. within primary groups size-based dominance hierarchies were present, while between primary groups territoriality was found. Therefore, primary groups are regarded as the most basic social unit of the species. This unit was rather open for smaller individuals. Such social structure was primarily based on the \"size principle\": individuals of similar body size could not overlap their home ranges and had territorial relationships, while individuals of different body size could overlap their home ranges and when overlapped they had size-based dominance relationships. The size principle was also loosely applicable to smaller individuals. The process of protogynous sex-change is suggested to be controlled by the size principle, or the cooperating function of a dominance hierarchy within a primary group and territoriality between primary groups. In males, territoriality and dominance hierarchies seem to be directly related to the acquisition of mates. However, in females, they do not seem to be directly related to resources such as food: feeding territoriality, as has been suggested, does not seem to be the fact. The social structure of this species is compared with those of other labrids and haremic fishes, and the ecological requirements ofharems and the means of social control of sex-change are discussed.

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Tetsuo Kuwamura

Papers

Parental care and mating systems of cichlid fishes in Lake Tanganyika: a preliminary field survey

Sex change in either direction by growth-rate advantage in the monogamous coral goby, Paragobiodon echinocephalus

New aspects of sex change among reef fishes : recent studies in Japan

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

Social structure of the protogynous fish labroides dimidiatus