The effects of sexual experience and female receptivity on courtship-rape decisions in male guppies, Poecilia reticulata (Pisces: Poeciliidae)

This paper examines the effects of prior sexual experience and of female receptivity on the probability that male guppies will court females with high or low intensity displays or attempt rape. There were no differences in behaviour between males with a history of high copulation success and those with low copulation success. Males with receptive females exhibited higher levels of high intensity displays and fewer rape attempts than males with unreceptive females, regardless of prior experience. The results are discussed in terms of sexual selection and the selective advantage of behavioural plasticity in which different sexual behaviour patterns are chosen with respect to the probability of a successful mating at a given time.     

Secondary reduction of preference for the sword ornament in the pygmy swordtail Xiphophorus nigrensis (Pisces: Poeciliidae)

Female mating preferences can be secondarily lost for a number of reasons. We examined the preference of female pygmy swordtails, Xiphophorus nigrensis, for the sword, a conspicuous extension of the caudal fin in some males. Females failed to show a preference for conspecific males with swords when presented with live males naturally varying in sword length, with live males of manipulated sword length, and with synthetic animations of males expressing natural variation in sword length. Females showed a significant bias against swords when presented with synthetic animations bearing supernormal sword characteristics. The reduced preference for swords, relative to closely related fish, may result from an increase in the cost of choice due to predation risk, selection against mating with heterospecifics, or changes in the spatial and contrast properties of the conspecific signal.     

Polymorphism and pair formation in the mosquitofish Gambusia holbrooki (Pisces: Poeciliidae)

Synopsis Pair formation was studied in a polymorphic population of Gambusia holbrooki in a brackish drainage canal in Southern Florida. All females and the majority of males were gray colored and only 5% of the males were black spotted. A small fraction of the population formed pairs, composed of a female and a male that swam synchronously and close together for several minutes. During pairing the male often achieved gonopodial contact with the female. Black spotted males occurred in pairs ten fold more frequently than expected under random pairing. The major behavioral mechanism accounting for the disproportionate occurrence of spotted males in pairs is, probably, the preference of females for these males.     

Changes in electrolytes,urea and free amino acids of Poecilia reticulata embryos following high salinity adaptation of the viviparous female

Vitellogenic or pregnant females of the viviparous Teleost Poecilia reticulata were gradually adapted to hypertonic saline with an ionic concentration approximating that of sea water. After 2 or 7 days adaptation, the total content in electrolytes, urea and free amino acids was determined in the bodies of the females and in their oocytes and intrafollicular embryos. Significant changes in electrolytes levels were only detected in females as a noticeable drop (30–40%) in Na⁺ concentration and a sharp rise in K⁺ level. Slower Cl⁻ increase was evidenced. The urea concentration appeared rather high in mature oocytes (30 mM/kg) and in young embryos. Electrolytes but also urea and amino acid pool level changes were displayed in oocytes and embryos after adaptation of the females to concentrated saline. A sharp but transitory increase in K+ content (40–120%) was noticed in embryos. The urea concentration rose up to 50 mM/kg (i.e. +85%) in young embryos and amino acid pool concentration reached 75 mM/kg (i.e. +140%) in embryos at more advanced stages. The significance of urea synthesis and accumulation in mature oocytes and embryos is discussed together with the mechanisms of response to osmotic changes of electrolytes, urea and amino acid pool level control systems through the maternal orgnism.     

Fertility, fecundity and gonadosomatic index of Poecilia reticulata (Pisces: Poeciliidae) in Heredia, Costa Rica

Between September and November of 1998, 1 432 females of Poecilia reticulata were collected in a pond in Santo Domingo, Heredia, Costa Rica. The average total length of females was 34.43 +/- 7.26 mm (range 17.80 and 51.50 mm) and the average total weight of 0.69 +/- 0.48 g (range 0.06 and 2.32 g). This species is a viviparous matrotrofic and the specimens were sexually mature. The total length-fertility relationship was F = 0.527e 0.1171Lt (r2 = 0.9404). The average fertility was 56.1 +/- 43.6 (eggs + embryos) (range 8.0 and 197.6). The total length-fecundity relationship was Fo = 0.695e(0.1076Lt (r2 = 0.9376). The average fecundity was of 49.0 +/- 36.0 (oocytes + ova) (range 7.0 and 179.0). The total length-gonadosomatic index relationship was IGS = 0.0014 e0.134 Lt (r2 = 0.8581). The average gonadosomatic index was 0.25 +/- 0.27% (range 0.02 and 1.31%).     

Trade-off between growth rate and aggression in juvenile coho salmon, Oncorhynchus kisutch

In juvenile salmon and trout, there seems to be a positive phenotypic correlation between individual aggression level and growth rate. Aggressive fish are dominant, and they obtain and defend territories, giving them access to good feeding sites. Being aggressive may increase predation risk, and may also carry costs such as increased metabolic demand, with effects on growth. To test the hypothesis that there is a trade-off between individual growth rate and aggression, we mated 12 female coho salmon with two unique males each, creating 24 full-sibling families. Growth of individually marked fish from each family was estimated in a situation where food could not be monopolized. Thereafter, individual fish were tested for mirror-elicited agonistic behaviour. We found significant variation between families in early growth rate, with a high heritability (1.04). There was also significant between-family variation in agonistic behaviour, but activity was generally low and heritability was low (0.25) and not significant. Growth rate and agonistic behaviour were negatively correlated. These results imply that aggressive behaviour has an energetic cost. Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.      

Life history of Gambusia holbrooki (Pisces, Poeciliidae) in the Ebro delta (NE Iberian peninsula)

We studied age, growth and reproduction of an introduced poeciliid, Gambusia holbrooki (Agassiz, 1859), in the Ebro delta marshes. Maximum ages observed were 2⁺ in females and 0⁺ in males. Growth commenced in March and continued until September. Females reached greater sizes, had a higher rate of growth and lived longer than males. The largest sizes found were 63 mm versus 32 mm . Multiple spawning occurred throughout the reproductive cycle (from May to September). The average brood size per female reached its maximum in July in the parental cohort (86 embryos/) and in August in the offspring cohort (29 embryos/). After reproduction the parental cohort decreased drastically. The relationship between fecundity (F) and total length (mm) was calculated for each month of the reproductive period. Sex-ratio deviated significantly from unity.Viviparity, several broods and large larvae provide G. holbrooki with several advantages over oviparous species. The capacity to adjust its life history to a particular environment could explain the life history differences between those in the Ebro delta and other populations.     

Zur Genetik und biologischen Bedeutung des Aggressionsverhaltens von Poecilia sphenops (Pisces,Poeciliidae)

The aggressive behaviour of hybrids between an epigeous and a cave-dwelling form of the toothcarp Poecilia sphenops was investigated in order to test whether a genetically determined reduction of aggressive behaviour exists in the cave population. The scores for five different elements of this behaviour as well as for the duration of fights support this hypothesis and suggest that aggressive behaviour in Poecilia spbenops is controlled by a closely linked polygenic system. On the basis of laboratory and field investigations, to aggressive behaviour is attributed the function of giving large ♂♂ a reproductive advantage within the framework of a body-size dependent rank order. Small ♀♀ appear to counteract this onesided selective advantage through a special strategy of sexual behaviour.     

Morphologische und feinstrukturelle Untersuchungen an dem Gonopodium vonHeterandria formosa Agassiz, 1853 (Pisces,Poeciliidae)

Zusammenfassung Das Gonopodium vonHeterandria formosa wurde licht- und elektronenmikroskopisch (Raster- und Transmission) untersucht. Die Zahl der Afterflossenstrahlen schwankt zwischen 8 und 11. Die Analis vonHeterandria formosa ist in drei Abschnitte unterteilt: a) in einen vorderen, stark reduzierten Flossenteil (Strahlen I+II), b) in einen mittleren, begat-tungsfunktionellen Teil (= Gonopodium, Strahlen III–V), c) in einen hinteren, normalen Flossenteil (Strahlen VI–VIII/IX/X/XI). Strahl III ist das Haupt-stützelement des Gonopodium. Rasterelektronenmikroskopische Aufnahmen zeigen, daß der vordere Ast des Strahls IV eine proximale Zähnung aufweist und zu einem gattungscharakteristischen Haken ausgezogen ist. Das Suspensorium vonHeterandria formosa besteht aus vier Gonapophysen, neun Interhämalstacheln und einer Anzahl von Baseosten.Den äußeren Abschluß des Gonopodium bildet ein mehrschichtiges Epithel. Die Epithelzellen sind untereinander stark verzahnt bzw. durch Desmosomen miteinander verbunden. Auf der Oberfläche der Epithelzellen befinden sich mäandrisch verlaufende Mikroleisten. In den Epithelzellen werden vereinzelt freie Nervenendigungen gefunden. Den basalen Abschluß der Epithelzellen bildet eine Basalmembran wechselnder Stärke, an die sich stellenweise eine aus antagonistisch angeordneten Kollagenfibrillen bestehende Faserschicht anschließt. Die Basalmembran umschließt den zentralen Knochenteil. In diesem verlaufen verschiedene afferente und efferente Blutgefäße. Die Endothelzellen der afferenten Kapillarën bilden schmale Lamellen, die sich zum Teil überlappen und durch gap und/oder tight junctions miteinander verbunden sind.

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Morphological and ultrastructural studies on the gonopodium ofHeterandria formosa Agassiz, 1853 (Pisces, Poeciliidae)

Summary The structure of the gonopodium ofHeterandria formosa was studied by light- and electron microscopy (scanning and transmission EM). In adults the number of the analis fin rays varies between 8 and 11. The anterior part of the fin which is extremely reduced in size, contains rays I and II, the median part modified for use in copulation is stabilized by rays III to V, whereas the posterior part revealing ordinary size, contains rays VI to VIII/IX/X/XI. Ray III is the main supporting element of the gonopodium. The anterior ramus of ray IV bears proximal serrae and is elongated, thus forming a terminal hook of genus specifity. InHeterandria formosa the suspensorium consists of 4 gonapophyses, 9 interhemal spines and a number of baseosts.The peripheral part of the dermis of the gonopodium is made up by a multilayered epithelium. Most of the epithelial cells are extremely toothed with numerous desmosomes. Microridges of the outer cells form a meandrian surface pattern. There are few free nerve endings within the epithelium. A basement membrane of varying thickness separates the epithelium from an underlying thin layer of connective tissue which surrounds the central bone tissues of the gonopodium. Blood vessels and nerve fiber bundles are embedded in the bone tissue. The endothelial cells of the afferent capillaries form thin lamellae which are overlapped in part. The contacts of the endothelial cells are made up by gap or tight junctions. The functional morphology of the gonopodium is discussed corresponding to the anatomical and ultrastructural findings.

     

Multiple matings in the blue gourami, Trichogaster trichopterus (Pisces,Belontiidae)

The reproductive behaviour of the blue gourami, Trichogaster trichopterus, was examined in 15 bisexual pairs and 22 trios maintained in 75-litre aquaria for 23 days. During this time, 74 spawning episodes occurred among 26 different pairs and trios. Sixty-nine of these spawnings were directly observed. Both males and females were capable of mating repeatedly with the same or different partners with as little as 20 to 24 h separating successive spawnings. Females often mated with two males in the same afternoon, while only one male succeeded in mating with two females in one day. It is concluded that blue gouramis probably do not form pair bonds and that both sexes will mate with differet partners when the physical environment permits two or more males to maintain territories in the same aquarium.