Nuptial Coloration Research Articles

Year-to-year differences in plasma levels of steroid hormones in pre-spawning chum salmon

Changes in plasma levels of steroid hormones in pre-spawning chum salmon ( Oncorhynchus keta) were examined for 6 years in association with sexual maturation. Fish were sampled along their homing pathway from the coastal sea to the spawning ground from 1995 to 2000. Plasma levels of testosterone (T), 11-ketotestosterone (11KT), estradiol-17β (E 2), 17α,20β-dihydroxy-4-pregnen-3-one (DHP), and cortisol were determined by enzyme immunoassays. Sexual maturity was comprehensively estimated by gonadosomatic indices, histology of gonads, nuptial color, spermiation or ovulation ratio. Since the plasma levels of steroid hormones and sexual maturation differed from year to year, they were compared with year-to-year variation of sea surface temperature (SST) of coastal sea to study influence of oceanographic environment on these physiological data. The SST of the migratory route varied among the years, so that we classified the 6 years into cool, intermediate, and warm years. Concerning maturity, the males that returned to the natal hatchery in the warm years were sexually more advanced than those in the cool years. Furthermore, histological data suggested that final oocyte maturation occurred before arrival at the hatchery in one of the warm years, i.e., 1999, while it occurred at the hatchery in one of the intermediate years, i.e., 2000. In the males, T and 11KT levels increased significantly on midway of the homing route in the warm years, whereas they did not show any noticeable changes in the cool years. Furthermore, the levels of T and 11KT on midway of the homing route in the warm years, i.e., 1998 and 1999, were significantly higher than those in one of the cool years, i.e., 1995, in both sexes. In the females, the levels of E 2 decreased during upstream migration. Conversely, those of DHP considerably elevated at spawning ground in all years examined. The levels of cortisol were different from year to year regardless of the SST. The present results showed that there were year-to-year differences in plasma levels of steroid hormones and maturity, and some of them may be influenced by the year-to-year variation of SST.

The effect of arginine vasotocin on courtship behaviour in a blenniid fish with alternative reproductive tactics

In a sex−role reversed population of the peacock blenny, Salaria pavo, two alternative male types are present: (a) older and larger nest−holder males that defend nests in which females come to spawn, and (b) younger and smaller sneaker males that mimic female−courtship behaviour and nuptial colouration in order to try to sneak fertilizations during spawning episodes. In this study the effects of exogenous administration of arginine vasotocin (AVT, 3 μg/g body weight) on the behaviour of nest-holder males, sneakers and females was tested. AVT induced the expression of female courtship behaviour in sneakers and female nuptial colouration in sneakers and in females, but failed to promote the expression of male courtship behaviour in both male types.

Mate Choice and Mating Pattern in a Stream Goby of the Genus Rhinogobius

The mate choice and mating pattern of a benthic goby Rhinogobius sp. CB (cross band type) were investigated in the Kamo River, Shikoku, Japan. During the breeding season, gravid females assumed a nuptial color and either males or females initiated a courtship display. Males preferentially courted a female of similar size to lead her to his nest, whereas females courted more frequently when they encountered a large male. Eggs in any one nest were always at the same developmental stage. Sampling data of nesting males and females indicated that, in more than half the nests, males gathered more than one female before spawning. In some nests with eggs, two or three females had spent ovaries, indicating that the eggs were laid by multiple females within a short span of time. However, a comparison between the total number of eggs which females would spawn in one nest and the number of eggs actually deposited suggested that eggs were contributed by one female in most nests. This low level of polygyny in spite of multiple female availability is attributed to a limited available spawning area of the nest.

Male traits associated with alternative reproductive tactics in Gobius niger

Male black goby Gobius niger, adopting parental or sneaking tactics, differed in secondary sex traits (elongation of the 4th ray of the first dorsal fin and black nuptial colouration) thus allowing the classification of wild-caught males. Parental males were larger and older than sneaker males, suggesting that the mating tactic is an expression of an ontogenetic gradient. Males adopting alternative tactics differed also in primary sex traits, including their testes and their two pairs of accessory structures: the seminal vesicles and mesorchial glands. Sneaker males had a higher investment in testes, while parental males showed larger seminal vesicles and more developed mesorchial glands. Histological analyses also showed that seminal vesicles from parental males presented some functional differences from those of sneakers. In the former these organs were devoted solely to mucin secretion, while in the latter they stored sperm and had a lower activity of secretion. Seminal vesicle features influenced ejaculate (sperm trail) characteristics and performance. Parental male trails were richer in mucins, but poorer in sperm than trails deposited by sneakers. As a consequence, while sneakers produced trails that released a large amount of immediately active sperm, trails laid by parental males released less sperm more constantly over a long time.

Male traits associated with alternative reproductive tactics in Gobius niger

Male black goby Gobius niger, adopting parental or sneaking tactics, differed in secondary sex traits (elongation of the 4th ray of the first dorsal fin and black nuptial colouration) thus allowing the classification of wild‐caught males. Parental males were larger and older than sneaker males, suggesting that the mating tactic is an expression of an ontogenetic gradient. Males adopting alternative tactics differed also in primary sex traits, including their testes and their two pairs of accessory structures: the seminal vesicles and mesorchial glands. Sneaker males had a higher investment in testes, while parental males showed larger seminal vesicles and more developed mesorchial glands. Histological analyses also showed that seminal vesicles from parental males presented some functional differences from those of sneakers. In the former these organs were devoted solely to mucin secretion, while in the latter they stored sperm and had a lower activity of secretion. Seminal vesicle features influenced ejaculate (sperm trail) characteristics and performance. Parental male trails were richer in mucins, but poorer in sperm than trails deposited by sneakers. As a consequence, while sneakers produced trails that released a large amount of immediately active sperm, trails laid by parental males released less sperm more constantly over a long time.

The role of male visual and chemical cues on the activation of female courtship behaviour in the sex‐role reversed peacock blenny

Chemical cues during courtship in peacock blenny Salaria pavo did not add significantly to the response of visual stimuli and females did not court when a male was not visible. The results showed that female S. pavo courtship behaviour was elicited exclusively by male visual features and not by a multicomponent signal in different sensory modalities. The time spent by females courting the male and exhibiting the nuptial colouration during visual trials correlated with the size of the male's crest, suggesting a signalling function for this trait. Alternative hypothesis for the function of the putative pheromones released by the male's anal gland are discussed. Evidence that female sexual motivation decreases towards the end of the breeding season is also provided, which should be considered in future mate choice experiments.

Are there two subspecies of Red-billed Quelea, Quelea quelea, in southern Africa?

Two subspecies of the Red-billed Quelea, Quelea quelea lathamii and Q. q. spoliator, have been described from southern Africa on the basis of differences in dorsal colouration in non-breeding plumage, but the validity of spoliator has often been challenged. We examined museum specimens of both subspecies, including paratypes of spoliator, and recorded plumage characters of breeding and non-breeding queleas in the wild. These data suggest that 'typical' lathamii and spoliator merely represent two extremes of a continuous variation in colour, with the majority being intermediate. Significantly, breeding males whose plumage types span the range between spoliator and lathamii occur together in the same colonies. Furthermore, variation in male nuptial colouration, which has provided the basis for distinguishing the subspecies of Red-billed Queleas elsewhere in Africa, shows no association with differences in dorsal plumage colour. We also present data on the timing of breeding of the two taxa which suggest that reproductive isolation sufficient to maintain two separate subspecies within southern Africa is unlikely to occur. We conclude, therefore, that because spoliator individuals cannot be reliably separated from lathamii on morphological criteria and, because both forms are likely to breed in the some places at the some times, the subspecies spoliator does not reflect any meaningful phylogenetic division. The Red-billed Quelea is therefore represented by Q. q. lathamii alone in southern Africa.

Forebrain AVT and courtship in a fish with male alternative reproductive tactics

In this paper, we present the results of cellular and molecular studies on the neuroendocrine correlates of male sexual polymorphism in a population of the blenniid fish Salaria pavo (Risso). Bigger and older males defend nests, whereas smaller and younger males mimic female nuptial coloration and behavior to gain access to nests and sneak fertilizations. In this population, sex-role reversal in courtship also occurs (i.e., females are the courting sex). Immunocytochemistry and in situ hybridization were used to examine the production of arginine vasotocin (AVT) peptide and messenger RNA, respectively. The expression of AVT mRNA on a per-cell basis was correlated with mating behavior, rather than with sex morphotype, which suggests that the greater level of AVT mRNA expression in females and sneakers is correlated with the production of courtship behavior. On the other hand, the number and size of AVT peptide-producing cells in both male types is higher or larger, respectively, than in females, which suggests that it is correlated with sex morphotype, rather than with mating behavior.

The Role of Nuptial Coloration in Female Holbrookia maculata: Evidence for a Dual Signaling System

The Role of Nuptial Coloration in Female Holbrookia maculata: Evidence for a Dual Signaling System

Sensory drive and nuptial colour loss in the three‐spined stickleback

Three‐spined sticklebacks Gasterosteus aculeatus, from the Chehalis River drainage. Washington, U.S.A., that have lost the mosaic nuptial signal were more likely to be found in tannin stained sub‐drainages whereas those expressing the mosaic nuptial signal were more likely to be found in sub‐drainages that were not tannin stained. This result is consistent with the sensory drive model.

Sensory drive and nuptial colour loss in the three-spined stickleback

Sensory drive and nuptial colour loss in the three-spined stickleback

Sexual selection, reproductive isolation and the genic view of speciation

Sexual selection, reproductive isolation and the genic view of speciation

Rhodeus pseudosericeus sp. nov., a new bitterling from South Korea (Cyprinidae, Acheilognathinae)

A new bitterling, Rhodeus pseudosericeus sp. nov., is described on the basis of 31 specimens from five localities included in the Namhan River system, South Korea. The new species is distinguished from other Rhodeus species by the following combination of characters: branched dorsal fin rays 9–10 (mode 9); branched anal fin rays 9–11 (mode 10); longest simple ray of dorsal fin strong and stiff, distally segmented; pelvic fin rays i, 6–7; iris of males blackish; dorsal and anal fins of males grayish in breeding season; karyotype with 2n = 48 (8m + 20sm + 20st). Rhodeus pseudosericeus sp. nov. is similar to Rhodeus sericeus sericeus in the number of pelvic fin and branched dorsal fin rays and the melanophores present on the dorsal fin membrane, but differs from the latter in having a greater body depth, more branched anal fin rays, fewer vertebrae, a lower number of scales in the lateral series, and differing male nuptial coloration.

Divergent sexual selection enhances reproductive isolation in sticklebacks.

Sexual selection may facilitate speciation because it can cause rapid evolutionary diversification of male mating signals and female preferences. Divergence in these traits can then contribute to reproductive isolation. The sensory drive hypothesis predicts that three mechanisms underlie divergence in sexually selected traits: (1) habitat-specific transmission of male signals; (2) adaptation of female perceptual sensitivity to local ecological conditions; and (3) matching of male signals to female perceptual sensitivity. I test these mechanisms in threespine sticklebacks (Gasterosteus spp.) that live in different light environments. Here I show that female perceptual sensitivity to red light varies with the extent of redshift in the light environment, and contributes to divergent preferences. Male nuptial colour varies with environment and is tuned to female perceptual sensitivity. The extent of divergence among populations in both male signal colour and female preference for red is correlated with the extent of reproductive isolation in these recently diverged species. These results demonstrate that divergent sexual selection generated by sensory drive contributes to speciation.

Speciation in rapidly diverging systems: lessons from Lake Malawi.

Rapid evolutionary radiations provide insight into the fundamental processes involved in species formation. Here we examine the diversification of one such group, the cichlid fishes of Lake Malawi, which have radiated from a single ancestor into more than 400 species over the past 700 000 years. The phylogenetic history of this group suggests: (i) that their divergence has proceeded in three major bursts of cladogenesis; and (ii) that different selective forces have dominated each cladogenic event. The first episode resulted in the divergence of two major lineages, the sand- and rock-dwellers, each adapted to a major benthic macrohabitat. Among the rock-dwellers, competition for trophic resources then drove a second burst of cladogenesis, which resulted in the differentiation of trophic morphology. The third episode of cladogenesis is associated with differentiation of male nuptial colouration, most likely in response to divergent sexual selection. We discuss models of speciation in relation to this observed pattern. We advocate a model, divergence with gene flow, which reconciles the disparate selective forces responsible for the diversification of this group and suggest that the nonadaptive nature of the tertiary episode has significantly contributed to the extraordinary species richness of this group.

No effect of a parasite on reproduction in stickleback males: a laboratory artefact?

Experiments are often carried out in the laboratory under artificial conditions. Although this can control for confounding factors, it may eliminate important factors that under natural conditions mediate the interaction under investigation. Here, we show that different results can be gained in the field and in the laboratory regarding host-parasite interaction. In the field, courting three-spined stickleback males, Gasterosteus aculeatus, were less often infected with plerocercoids of a cestode tapeworm, Schistocephalus solidus, than shoaling males. However, when a random sample of males was allowed to nest and court females in individual aquaria in the laboratory, both uninfected and infected males built nests and courted females. Moreover, while the few infected males that courted females in the field expressed less red nuptial coloration than uninfected courting males, there was no difference in redness between infected and uninfected males in the laboratory. We argue that the different results gained in the field and in the laboratory are due to differences in the cost of reproduction, due to differences in the resource pool of the males. The favourable conditions in the laboratory exclude factors such as predation risk, social interactions, and fluctuating environmental conditions that may use up resources in the field and mediate the effect of the parasite.

American aquarium fishes

For many aquarists, information on their hobby is limited to goldfish and exotic tropical fishes commonly available in local pet stores. Existing guides ignore native species simply because few people have collected, kept, and successfully propagated them, and reliable information is difficult to find. In American Aquarium Fishes, Robert J. Goldstein and other serious aquarists, applying their specialized expertise on North fishes, have compiled a comprehensive guide to hundreds of native fishes suitable for the home aquarium. American Aquarium corrects misconceptions about minnows and suckers, pygmy sunfishes and dwarf catfishes, perches and their tiny relatives, the darters, and even the mysterious blind cave fishes. This first-of-its-kind guide provides step-by-step instructions on where to find, how to identify, how to catch, and how to keep and even breed myriad backyard fishes. Goldstein explains why fishes occur where they do and warns against putting fishes where they do not belong. He discusses protected species and offers guidance on the rules for collecting in each state. He also gives detailed instructions on how to transport and ship native fishes across the country and around the world.A chapter on aquarium plants by Richard Edwards, accompanied by 24 line drawings, provides details on collecting and propagating the most adaptable and beautiful aquatic plants likely to be encountered by fish collectors everywhere. The work is enhanced by over 350 spectacular photographs by Goldstein, William F. Roston, Richard Bryant, Fred C. Rohde, and Garold Sneegas, featuring vivid underwater images of spawners in full nuptial coloration. Goldstein has provided a unique tool for naturalists and a new dimension to the international hobby of breeding aquarium fishes. Destined to become the standard guide for housing and breeding fishes, Aquarium Fishes will be equally useful both to aquarists and biologists.

Comportement socio-sexuel et organisation spatiale chez l'Agame de Bibron, Agama impalearis

The social and sexual behaviour of a marked group of Agama impalearis was observed under natural conditions in an arid area of the central Jbilet mountains (Western Morocco) during spring 1995. Supplementary observations were made either in laboratory or in the field on unmarked individuals at different periods of the yearfrom 1993 to 1996. We examined the behavioural repertoire of adults. A quantitative analysis of field data allowed to assess relative time proportions and frequencies of the main behavioural categories. The diurnal emergence of animals from their refuges appears to be greatly influenced by temperature as agamas were observed to emerge in the field at different times of the day but at closely similar thermal conditions. The lizards are highly heliophilous and predominantly sit-and-wait foragers. Feeding behaviour, escape from ennemies, courtship, oviposition and other behaviours were described. Adult males are strongly territorial and have specific display action-patterns of aggressive behaviour. The displays involve postural change, pushups and head nodds. They were able to rapidly change their colours. The two sexes showed differences in nuptial colours and behavioural attitudes. Contrary to males, females exhibited neither pushup nor head nodds but a specific display with mouth-gaping when males are courting them. Monogamy is the predominant mating system and there is no real social hierarchy. Home ranges were larger in males and showed low overlaps. Basking and alert postures are predominant through activity time and pushups are the most frequent display.

Changes in expression and honesty of sexual signalling over the reproductive lifetime of sticklebacks.

Fitness costs of signalling are essential in order for reliable sexual signalling to prevail when the interests of the sexes conflict. This means that signalling can be subjected to a life history trade-off between present and future signalling effort. Here, I show that three-spined stickleback males (Gasterosteus aculeatus), who have a single breeding season during which they breed repeatedly, change their red nuptial coloration over the season depending on their body size at the start of breeding. Large males that completed several breeding cycles increased their red coloration over the season, whereas small males, who completed only a few cycles, did not. The increase in coloration was accompanied by an increase in parental success when males were energy constrained, but not when they had access to an unlimited food supply. Red coloration was thus an honest signal of male parental ability despite changes in signal expression when both signalling and parental care were costly and the investments in them changed simultaneously over the reproductive lifetime. However, the honesty of the signal varied over a lifetime. At the penultimate cycle, bright males cannibalized some of their eggs, probably to increase survival to the last cycle, whereas males cared for their offspring independent of coloration at the ultimate cycle.

Male-male competition ensures honest signaling of male parental ability in the three-spined stickleback ( Gasterosteus aculeatus )

The importance of socially imposed costs for the evolution and maintenance of honest sexual signals has received less attention than other costs. Here I show that male-male competition can increase the honesty of sexual signaling in relation to male parental ability in a species with flexible signaling. When four three-spined stickleback (Gasterosteus aculeatus) males were allowed to court a female first separately and then in competition, red nuptial coloration under competition reflected male parental ability more accurately than red coloration when separated. Parental ability was determined as the ability of the male to raise a clutch of eggs to the hatching stage under interaction with other breeding and non-breeding males. The increased honesty under competition was probably due to subordinate males of poor parental ability decreasing their color expression under interaction to reduce the risk of fights with superior males. However, socially imposed costs of signaling were probably not the main factors maintaining honest signaling, as red coloration reflected male parental ability also in the absence of competition, although less accurately. Nevertheless, the small-scale differences that male-male competition induced can significantly facilitate adaptive female choice and have large impacts on sexual selection.