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BACKGROUND: The widespread occurrence of feminized male fish downstream of some wastewater treatment works has led to substantial interest from ecologists and public health professionals. This concern stems from the [...]

A comparative analysis of sperm competition and sex change across fish species was carried out. The results confirm the hypothesis that female-biased sex ratios and risk of sperm competition are evolutionary correlates of female-first sex-change.

A bidirectional pattern of male trait evolution and sensory trade-off signal divergence in surfperch are investigated. It is shown that sensory systems with trade-offs in detection abilities produce bidirectional biases and that signal design properties match these biases.

Abstract: This paper deals with the analysis of images of biological tissue that involves ring structures, such as tree trunks, bivalve seashells, or fish otoliths, with a view to automating [...]

The idea that morphological traits can evolve in response to mating preference and/or competition for mates is further studied. A molecular insight into the development of the swordtail and its history is put forth.

Research into genetic mating and biological parentage has revealed that some 70-95% of offspring is parented by nest-guarding fish, while around 33% of nests are cuckolded.

Research is presented concerning the preferences which were expressed by female sand gobies under conditions which varied the male-male interactions during mating. The impeding of female choice by male-male interactions is discussed.

A new study of the social behaviour and mating pattern of the pipefish Corythoichthys haematopterus shows the first instance of sex role reversal in syngathids.

An understanding of the evolution of the reproductive behaviour of fish must take into account sexual conflict. A new study investigates the sexual strategies of male and female cardinalfish, which breed in sandy areas around coral colonies. Results show females move between coral colonies to find mates more often than males and frequently change their mates to shorten interspawning periods. Mate searching appears to increase mortality, possibly reducing competition between females for males. Filial cannibalism by males may be avoided if there is low mating availability. Further details of the study are presented.

The metabolic rates associated with specific social and territory maintenance behaviors of the cooperatively breeding cichlid Neolamprologus pulcher were measured using a respirometer to examine the energy expenditures resulting from the helping behavior of the specie. Pair males were found to invest almost exclusively in intrafamily agonistic behavior, while pair females and helpers shared investment in brood care and territory maintenance. The behavioral energy expenditure of helpers was found to be strongly influenced by their submissive behavior.

The relationship between spawning success and courtship was examined in bower-building cichlid fish from Lake Malawi, Africa. The results showed that the structure of a phenotypic character was inversely proportional to the male parasitic load, with spawning males having substantially fewer dilepipid cestodes in their livers compared to non-spawning males. Moreover, spawning males have substantially heavier gonads compared to unsuccessful males. Results also revealed a correlation between reproductive success and relative liver weight.

Convict cichlids, Cichlasoma nigrofasciatum, were used in the investigation of the influence of mate size on mate switching. Size-mismatched and size-matched pairs were reared in a partitioned aquarium. When the partition was removed, the mismatched pairs re-sorted 46% of the time while size-matched pairs remained intact most of the time. Size determines the dominance relationship between two competing pairs of Cichlasoma nigrofasciatum. When there is a size disparity between the male and the female partner, the pair with the larger male dominates.

Large size provides an advantage in mating success among male Japanese medakas, Oryzias latipes, because females of this species consistently prefer larger males over smaller ones to mate with. This may be because smaller males become sperm-depleted sooner than larger males in repeated matings. O. latipes males and females have similar body sizes because of the reproductive advantages size confers, higher fecundity among females and mating success among males.

The hypothesis that the swordtail fish, Xiphophorus cortezi, females prefer symmetrical sexual signals was tested by determining whether females switched their preference between two males with or without a symmetrical number of bars. The bars were manipulated in such a way that other male traits were controlled. Observations revealed that females switched their preference between a pair of males when switching which male was symmetrical for bar number. This result suggests that females prefer a symmetrical bar number.

Studies show that mate choice by females is influenced by asymmetry in male ornaments and is sensitive to degrees of fluctuating asymmetry. A new study investigates the effect of spot asymmetry on female choice in the Trinidadian guppy. Results show that female guppies, given the choice between pairs of males with differing spot symmetry, strongly prefer symmetry in spot patterns.

Female swordtail Xiphophorus cortezi seem to gain information about species identity from the olfactory stimulus provided by conspecific and closely related heterospecific males. This information is useful in the early stages of mate recognition. However, it appears that the olfactory stimulus is not involved in mate preference. It is clear that both the chemical cue and the ability of the female to detect and preferentially respond to it are developing extremely quickly in northern swordtails.

The hypothesis that intra-specific mate-choice copying is adaptive under certain conditions is tested using guppies, Poecilia reticulata. A study replicating the influential work of Dugatkin is presented. The study shows no tendency towards female mate-choice copying in guppies and it is concluded that further research needs to be undertaken before the existence of such behaviour can be confirmed.

A study was conducted on the mating preferences of the female gynogenetic Amazon molly. Species of molly used in the experiment included the Poecilia formosa, Xiphophorus multilineatus and Poecilia latipinna. Results showed that experience can influence a female's mating preference, whereby sexually mature females may switch their preferences due to individual interactions with males. Moreover, the change in preferences may be due to the degree of male sexual behavior.

Males of Poecilia latipinna and Poecilia mexicana species prefer conspecific females to female Amazon mollies for copulation. However, this preference is lower in Poecilia mexicana than in Peocilia latipinna. Both species of males can distinguish between conspecific females and Amazon mollies. Male Poecilia latipinna are reluctant to mate with females of heterospecific species, male Peocilia mexicana favor Poecilia formosa over female Poecilia latipinna. Male Poecilia mexicana's attraction to Peocilia formosa may, therefore, be related to maternally derived genetic component.

Direct selection or drift plays the major role in the evolution of female mating preferences among different populations of Xiphophorus pygmaeus. A series of three studies spanning over five years indicate that female preference for large male body size vary between populations. The analysis of the distribution and subsequent spread of large X. pygmaeus shows that female preference for large male body size is negatively correlated with male traits of large size.

The response to a male signal in the northern swordtail fish, Xiphophorus, depends on the sex of the receiver. The signal, a pattern of vertical bars helps in attracting females and discouraging rival males. The male response and male signal coevolve more closely when compared to the response of the female to the same male signal. Congruency between the male response and signal occurs in X. multilineatus and X. nigrensis whereas the female response and the same signal are congruent in X. multilineatus.

The filial cannibalism in mouthbrooding males of the cardinal fish, Apogon doederleini, in southern Japan is related to the mating techniques of females that reduce inter-spawning intervals by changing mates. This cannibalism occurs within a day of spawning. Males prefer to eat broods produced by smaller and non-resident females. They change mates after cannibalism, and re-mate faster than males whose broods are removed. Cannibalistic males are able to indulge in multiple mating by eating their first brood and rearing the next one.

The influence of sex ratio on the reproductive behavior and mating success of Pomatoschistus minutus was investigated. The results showed that sex ratio rather than density caused differences in the intra-sexual behavior of both males and females. It was also shown that changes in the sex ratio caused changes in the competition for mates and that individuals adjusted their mating behavior according to the sex ratio.

The effect of the parasitic trematode, Crypotocotyle sp. on male mate choice of pipe fish, Syngnathus typhle is observed. The pipefish develop black spots in the skin from the parasite. The parasite was not transmitted from one to the other pipefish. The males distinguish among the females by the usage of visual cues such as the black spots. The males contacting with the unparasitized females are benefitted by fertilizing more eggs.

A study was conducted to determine the relationship between competition and sexual behaviour in the male and female Japanese medaka. The aggressive behavior of males and monopolization behaviour of females were analyzed by placing new females inside the tank synchronously and asynchronously. The results showed that mating success was higher in the asynchronous and that the success of males was determined by their persistence and ability to pursue the females. There were no evidences to support the positive relationship between mating success and aggression.

Analysis of the endocrine and behavioral features of male and female anemonefish, Amphiprion melanopus, during their protandrous sex change indicates that sex change induces aggressive behavior after female removal, with its frequency gradually declining in the 5, 10 and 20-day female-removed samples. However, the reduction in aggression is higher than the baseline male levels. Introduction of an intruding component into sex-changing individuals results in alterations in the territorial defence activity of females, suggesting the non-involvement of plasma steroids in the changes.

Individual differences in attractiveness were incorporated into the theory of condition-dependent sexual selection in a study of courtship behavior of guppies. Large attractive males reduced their courtship under high light levels, supporting the differential cost hypothesis rather than the differential-benefit hypothesis for correlations between sexually selected traits. Bright lights might have exposed large males to predator risk. The discovery that changing environmental conditions can alter the distribution of individual male mating success in guppies has implications for the co-evolution of female choice and sexually selected traits.

Female sand goby fish display significantly lower levels of mate-choosing behavior in the presence of predation threats by codfish. Observations show that searching for a mate increases predation risk and is therefore reduced by the female sand goby who otherwise indulges in extensive mate searching behavior. This observation can be generalized to other species as well. Various explanations can be offered for the restriction of searching behavior such as increased exposure, stress and suppression of spawning instincts during predation threat.

The relationship between female spawning patterns and male mating success and the potential constraints on sexual selection due to nest space limitations in the sand goby (Pomatoschistus minutus) were investigated. The results showed that male mating success depended on both nest size and male size. Females preferred to mate with bigger males because their bigger nests can accommodate more eggs, thus increasing mating success.

Brains and types of behavior among sexuall mature vertebrates are portrayed as having two phenotypic states: male and female. However, mating systems and the behavioral tactics employed by the two sexes are far more diverse than conveyed by this simple intersexual dichotomy. For example, in many species, sexually mature may practice one of two alternative mating tactics. Recent studies of a sound-producing teleost fish now show that intrasexual dimorphism of vocal motor phenotypes among males accompanies the intrasexual divergence of types of reproductive behavior. Thus, one group of males, like females and juveniles, lacks the behavioral, neurophysiological and morphological traits typical of the sexually differentiated vocal motor pathway of the second group. The results are an explicit demonstration that for any one species: (1) alternative mating tactics can be paralleled by alternative phenotypes for the neurons that determine tactic-specific types of behavior, and (2) reproductive maturation is not obligatorily linked to the expression of neuronal secondary sex characteristics.

A commentary is presented concerning the studies which have been undertaken on fluctuating asymmetries to determine the level of importance they have in the sexual preferences of female swordtail fish.

The ecological modulation affects sex roles in a natural population of the blenniid fish, Salaria pavo. The female initiation of mating predominates over male intra-sexual competition, active courtship and developed epigamic characters in males. More than one female of S. pavo comes to the nest and each female mates with different males during the breeding season. The males are selective in admitting the females to the nest. The ability of females to spawn determines the male courtship behavior for the nest sites.

A study conducted to analyze the factors associated with the sexual preferences of female fishes while selecting a male partner is discussed.

A study investigating the use of chemoreceptors by female swordtail fish (Xiphophorus birchmanni) to assess the nutritional status of males for mating is presented.

A study conducted to examine the impact of heat treatment, on resistance to forced copulation by mosquitofish (Gambusia holbrookieastern), is presented.

The sexual differences in body size preferences are investigated in the poeciliid fish, Brachyrhaphis rhabdophora. The results indicate that the comparison of the mating preference of the sexes reveals both intersexual and intrasexual differences.

Sexual harassment is expected to conflict with other activities such as foraging because female mosquitofish invest considerable time and energy in avoiding unwanted copulations. However, sexual conflict is expected to be important in shaping association patterns of female mosquitofish with conspecifics of both sexes as male sexual activity has a large impact on a female's feeding efficiency and possibly on her survival and reproduction.

An investigation was undertaken to find whether sailfin molly females copy the choice of other females when they are prevented from copying immediately after observing a model female next to a previously nonpreferred male. The conclusion states that females remember individual males with whom a model female had interacted, even after one day.

Vertebrate species, including humans, display a wide range of sexual behaviors. The great sexual diversity exhibited by fishes, and the neurobiological correlates of vertebrate sexual strategies are discussed.

Alternative mating strategies are common in nature and are generally thought to increase the intensity of sexual selection. However, cuckoldry can theoretically decrease the opportunity for sexual selection, particularly in highly polygamous species. We address here the influence of sneaking (fertilization thievery) on the opportunity for sexual selection in the sand goby Pomatoschistus minutus, a marine fish species in which males build and defend nests. Our microsatellite-based analysis of the mating system in a natural sand goby population shows high rates of sneaking and multiple mating by males. Sneaker males had fertilized eggs in [approximately equals] 50% of the assayed nests, and multiple sneakers sometimes fertilized eggs from a single female. Successful males had received eggs from 2 to 6 females per nest (mean = 3.4). We developed a simple mathematical model showing that sneaking in this polygynous sand goby population almost certainly decreases the opportunity for sexual selection, an outcome that contrasts with the usual effects of cuckoldry in socially monogamous animals. These results highlight a more complex and interesting relationship between cuckoldry rates and the intensity of sexual selection than previously assumed in much of the literature on animal mating systems. microsatellites | mating systems | paternity | polygyny