Das erste, mir bekannte deutschsprachige Guppybuch

Variegated patterns on the caudal fin are a common and popular trait in guppy strains commercially cultured in Singapore. Gene control of this highly variable mosaic pattern of black spots and patches of different shapes and sizes on a brightly colored tail fin was elucidated by reciprocal crosses between the Green Variegated (GV) strain and wild-type (WT) stock. F₁ progenies were produced by single-pair crossing between GV and WT, while the F₂ generation was obtained from full-sib mating between F₁ males and F₁ females. Data for the F₁ and F₂ generations were segregated according to phenotypes and sex, and tested by chi-square analyses. Inheritance of variegated tail patterns appears to be determined by a single locus on the X- and Y-chromosomes. Genotypes of males and females of the GV strain are proposed to be X_VarY_Var and X_VarX_Var, respectively. The allele for variegated tail patterning, Var, is dominant over that of the wild-type, Var+, which does not exhibit these patterns. Recombination frequency between the Var locus and sexdetermining region (SdR) in male guppies was estimated to be about 1.9% (map distance ≈1.9 map units). The segregation and mode of inheritance of the Var gene are illustrated by genetic models

The present letter is a response to the paper „Interallelic interaction between the autosomal Blond and the sex-linked Nigrocaudatus gene in the guppy (Poecilia reticulata)” (Petrescu-Mag et al 2007).
Key Words: Guppy, Poecilia reticulata, Gold, Blond, Nigrocaudatus

Poecilia obscura, new species, is described from the Oropuche system, Trinidad. A mitochondrial DNA-sequence based molecular phylogenetic analysis revealed the status of the new species as a separate taxon. It is most closely related to the Common guppy, P. reticulata and to the recently described species, P. wingei. It can also be distinguished by morphometrics and gonopodial characteristics from these two species, although the ranges for all values overlap. A definition of the new species on morphology criteria alone is thus impossible. Therefore, P. obscura forms a cryptic species complex with the two other species. P. winge i is now unequivocally defined by the molecular phylogeny as a valid species. The three guppy species are included in the subgenus Acanthophacelus Eigenmann (1907), which is considered as generically different from all other taxa of the Poeciliinae sensu Parenti (1981).
Key words: molecular phylogeny, sexual dimorphism, freshwater fish, artificial introduction, hybridization, cryptic species complex

Given multiple matings from females, sexual selection continues after insemination in the form of postcopulatory sexual selection. This process is formed by two main mechanisms: sperm competition (competition of sperm of two or more males for the fertilization of the eggs of the same female) and cryptic female choice. These act as powerful selective pressures for the evolution of reproductive biology of both males and females. The aim of this thesis is to analyze the relative importance of sperm competition and cryptic female choice in determining a male reproductive success. The study species is the guppy (Poecilia reticulata), a freshwater fish, ovoviviparous with internal fertilization. Using artificial insemination, I studied if females can obtain fecundity benefits from mating with colourful males (as predicted by Sheldon's Phenotype-linked fertility hypothesis), the role of sperm number and sperm quality for sperm competition success, repeatability of a male's fertilization success and the role of MHC genes in non directional cryptic female choice. This technique allows to control for many potential confounding variables, as order of mating, number of sperm inseminated and cryptic female choice. From the experiments, it emerges that directional processes in this species are more important for fertilization success rather than non directional processes, even if a part of variance in fertilization success is explained by a male's similarity for MHC genotype with the female.

Post-mating reproductive isolating mechanisms may be among the earliest reproductive barriers to emerge among incipient species. Trinidadian guppy, Poecilia reticulata, populations in the Caroni and Oropouche drainages in Northern Trinidad exhibit marked genetic divergence and provide an ideal system in which to search for these barriers. We inseminated virgin females with equal amounts of sperm from two males, a ‘native’ male from the female's own population and a ‘foreign’ male from the other drainage. Artificial insemination ensured that mating order and mate choice did not affect the outcome. Paternities were assigned to the resulting broods using microsatellite markers. As predicted, sperm from native males had precedence over foreign sperm. Moreover, this effect was symmetrical for both drainages. In contrast, we detected no native sperm precedence in controls, in which females received sperm from the same and another population within the same drainage. Our results show that gametic isolation can arise between geographically proximate, though genetically divergent, populations of a single species and highlight the potential role of this process in speciation.
Keywords: speciation, sperm competition, internal fertilization, genetic divergence, post-mating pre-zygotic isolation

Among different teleost fish species, diverse sex-determining mechanisms exist, including environmental and genetic sex determination, yet chromosomal sex determination with male heterogamety (XY) prevails. Different pairs of autosomes have evolved as sex chromosomes among species in the same genus without evidence for a master sex-determining locus being identical. Models for evolution of Y chromosomes predict that male-advantageous genes become linked to a sex-determining locus and suppressed recombination ensures their co-inheritance. In the guppy, Poecilia reticulata, a set of genes responsible for adult male ornaments are linked to the sex-determining locus on the incipient Y chromosome. We have identified >60 sex-linked molecular markers to generate a detailed map for the sex linkage group of the guppy and compared it with the syntenic autosome 12 of medaka. We mapped the sex-determining locus to the distal end of the sex chromosome. We report a sex-biased distribution of recombination events in female and male meiosis on sex chromosomes. In one mapping cross, we observed sex ratio and male phenotype deviations and propose an atypical mode of genetic sex inheritance as its basis.