Amazon Molly Poecilia Formosa Research Articles

Dietary niche overlap in sympatric asexual and sexual livebearing fishes Poecilia spp.

The present study investigated the spatiotemporal patterns in trophic resource use in a system of a gynogenetic poeciliid fish, the Amazon molly Poecilia formosa, and its sexual congeners the sailfin molly Poecilia latipinna and the Atlantic molly Poecilia mexicana using gut contents analysis. No statistically significant differences in trophic resource use were found between sexual and gynogenetic species, but gut contents varied significantly across sites and over time. In addition, variation in trophic morphology (i.e. gut length) was significant across sites but not species, and laboratory experiments indicated that gut length is phenotypically plastic. Overall, trophic differentiation between coexisting asexual and sexual Poecilia appears to be minimal, and it is unlikely that niche differentiation contributes to a stable coexistence of the two reproductive forms.

The impact of social context on male mate preference in a unisexual-bisexual mating complex

Male sailfin mollies Poecilia latipinna were tested in five different treatments that varied in the relative frequency of heterospecific gynogens (Amazon molly Poecilia formosa) to conspecific females to determine whether social interactions among males within a population causes some males to mate with heterospecific females. Male P. latipinna inseminated a significantly higher proportion of conspecific females and fertilized a significantly higher number of conspecific eggs regardless of the treatment. Nonetheless, preference for conspecific females was not exclusive as a range of 20 to 50% of heterospecific females were fertilized. Social interactions among males may best explain the results and may therefore play an important role in the maintenance of unisexual--bisexual mating complexes.

Prudent males, group adaptation, and the tragedy of the commons

For almost five decades three threads have coexisted in the evolutionary and ecological literature, with their links only recently becoming visible and some of them still not properly addressed. These are the levels of selection debate, the metaphor of the tragedy of the commons, and the evolutionary study of sexual conflict. We analyze the eco-evolutionary dynamics of a curious system where an asexual all-female fish species (the Amazon molly Poecilia formosa) requires sperm from other species as a developmental trigger, without utilizing the genes from sperm. The dynamics of such a system bear strong resemblance to host–parasite dynamics, and populations of the sexual ‘host’ species persist much better if males avoid mating with Amazons. However, such avoidance may compromise their current mating success, and if this is the case, prudent mating becomes an altruistic trait that helps to keep an accumulating problem of a competing species at bay, and Amazon-free space can be seen to form a common good that a population should maintain for future generations. A model shows that the evolution of altruistic mating restraint is possible but selection for short-term gains means that it will remain less than perfect. This helps to explain why the anomalous gynogenetic system can persist, but it also raises questions about what kinds of traits can be classified as adaptations when optimization is not perfect and traits evolve to achieve short-term goals better than long-term performance. Contributing to the levels of selection debate, we encourage researchers to study the implications of the different timescales involved in the eco-evolutionary process.

Morphology, testes development and behaviour of unusual triploid males in microchromosome‐carrying clones of Poecilia formosa

In a microchromosome-carrying laboratory stock of the normally all-female Amazon molly Poecilia formosa triploid individuals were obtained, all of which spontaneously developed into males. A comparison of morphology of the external and internal insemination apparatus and the gonads, sperm ploidy and behaviour, to laboratory-bred F(1) hybrids revealed that the triploid P. formosa males, though producing mostly aneuploid sperm, are partly functional males that differ mainly in sperm maturation and sexual motivation from gonochoristic P. formosa males.

Feeding rates in the sailfin molly Poecilia latipinna and its coexisting sexual parasite, the gynogenetic Amazon molly Poecilia formosa

Feeding rates of the gynogenetic Amazon molly Poecilia formosa and one of its sexual hosts, the sailfin molly Poecilia latipinna, were measured under winter and summer temperature conditions. Food consumption of the unisexual P. formosa in winter conditions was significantly higher than that of P. latipinna, and it is hypothesized that the resulting food stress might have an important influence on the population composition of these closely related fishes via higher winter mortality in P. formosa.

Differences in thermal tolerance in coexisting sexual and asexual mollies (Poecilia, Poeciliidae, Teleostei)

This study reports significant differences between the gynogenetic Amazon molly Poecilia formosa and one of its sperm hosts, and the sexual sailfin molly Poecilia latipinna in the critical temperatures at which individual fishes lost motion control. Based on these measurements, it is suggested that cold snaps occurring in winter, but not summer temperatures, can significantly change population composition of these closely related fishes by inflicting higher mortality on P. formosa.

How to go extinct by mating too much: population consequences of male mate choice and efficiency in a sexual–asexual species complex

Selection acting on individuals is not predicted to maximize population persistence, yet examples that explicitly quantify conflicts between individual and population level benefits are scarce. One such conflict occurs over sexual reproduction because of the cost of sex: sexual populations that suffer the cost of producing males have only half the growth rate compared to asexuals. Male behaviour can additionally impact population dynamics in a variety of ways, and here we study an example where the impact is unusually clear: the riddle of persistence of sperm‐dependent sexual–asexual species complexes. Here, a sexually reproducing host species coexists with an ameiotically reproducing all‐female sperm parasite. Sexual–asexual coexistence should not be stable because the proportion of asexually reproducing females will rapidly increase and the relative abundance of the sexually reproducing host species will decline. A severe shortage of males will lead to sperm limitation for sexual and asexual females and the system collapses. Male mate choice could reduce the reproductive potential of the asexual species and thus potentially prevent the collapse. In the gynogenetic (sperm‐dependent parthenogenetic) Amazon molly Poecilia formosa and its host (P. latipinna or P. mexicana), males discriminate against asexual females to some extent. Using a population‐dynamical model, we examine the population dynamics of this species complex with varying strengths of male discrimination ability and efficiency with which they locate females and produce sperm. The sexual species would benefit from stronger discrimination, thus preventing being displaced by the asexual females. However, males would be required to evolve preferences that are probably too strong to be purely based upon selection acting on individuals. We conclude that male behaviour does not fully prevent but delays extinction, yet this is highly relevant because low local extinction rates strongly promote coexistence as a metapopulation.

Microsatellites for the gynogenetic Amazon molly,Poecilia formosa: useful tools for detection of mutation rate, ploidy determination and overall genetic diversity

The Amazon molly Poecilia formosa is a model system forstudying the evolution of sex (Turner 1980; Schartl 1995)and skin cancer development (Schartl et al. 1997). Only veryfew variable microsatellites are known for this species. Mi-crosatellites, however, have already proven to be very usefultools for diverse genetic analyses (Lampert et al. 2005). Herewe report the results of cross-amplification of 63 microsatel-lite loci, originally developed for Xiphophorus, tested in theAmazon molly and its two parental species P. mexicana andP. latipinna. Eight microsatellite loci were found to be poly-morphic. Sixteen primers allowed species identification an deight primers allowed diagnosis of different ploidy levels inP. formosa. These microsatellites will be useful to gain newinsights into the population structures, clonal variability andreproductive biology of a mixed species reproductive com-plex, and also into the genetic mechanism underlying cancerformation.P. formosa, the Amazon molly, is a small freshwa-ter fish species that occurs in the northeastern part ofMexico and extends into the USA (Texas). It is an all-female species and was the first vertebrate discovered toreproduce clonally (Hubbs and Hubbs 1932). Its repro-ductive mode is gynogenesis:females produce unreducedeggs, but need sperm from a closely related sexual speciesto trigger the onset of oocyte development. The male’s

Limia vittata as host species for the Amazon molly: no evidence for sexual reproduction

DNA fingerprinting demonstrated no sexual reproduction of the gynogenetic Amazon molly Poecilia formosa with Limia vittata as host species, in contrast with a single report that claims to have found sexual reproduction with such matings.

EVOLUTIONARY ORIGIN OF A PARTHENOFORM, THE AMAZON MOLLY POECILIA FORMOSA, ON THE BASIS OF A MOLECULAR GENEALOGY.

The appearance of vertebrate species that reproduce without genetic recombination has been explained by their origin from a rare hybridization event between members of two distantly related species. For the first recognized vertebrate unisexual, the Amazon molly Poecilia formosa, mostly morphological and biochemical genetic information has been available so far with respect to its evolutionary origin. DNA sequence analyses of transcribed portions of the genome (tyrosine kinase proto-oncogenes) demonstrated its hybrid state unequivocally. Both alleles can be traced in a DNA sequence-based phylogenetic tree to extant species that represent the parental species or that are closely related to the corresponding extinct forms, namely P. mexicana limantouri and a so far taxonomically ill-defined north Mexican subspecies of the P. latipinna/P. velifera complex. A rough estimate from the mutation rates dates the hybridization event further back than would have been predicted on the basis of "Muller's ratchet" for an ecologically successful species.

The effects of chronic exposure to asbestos fibers in the Amazon molly Poecilia formosa

Abstract Amazon mollies were exposed for 6 months to several concentrations of coarse and fine asbestos particles suspended in their aquarium water. At the end of this period, the fish were serially sectioned and the tissues examined for lesions. Pathological changes were found in the kidneys, the major site of accumulation of the mineral fibers after their entry into the body through the intestinal mucosa. There was no evidence of entry of particles through the gill epithelium. Epithelial hypertrophy and secondary lamellar telangiectasia of the gills appeared to be the result of physical abrasion by the asbestos particles. There was no cellular injury in the liver or the muscles.

Aging changes in the kidneys of two poeciliid fishes, the guppy Poecilia reticulatus and the Amazon molly P. formosa

Histological surveys of the kidneys of two poeciliid fishes, the Amazon molly Poecilia formosa and the guppy P. reticulatus, throughout their lifespans showed no regular aging trends. Few kidney lesions were found in the Amazon molly until very late in life, 60 months or more, when obsolescent glomeruli and dilated renal tubules occurred. Guppies showed involutional changes of the renal system earlier, and the lesions became more severe with age, particularly in male fish. Hemopoietic tissue was reduced in amount in older fish of both species. Guppies of a year and older had marked accumulation of melanin in the melanomacrophage centers of the kidney, and the amount present increased with age. By contrast, there was little melanin deposition in mollies until almost the end of the lifespan. Hyaline droplets were consistently seen in the renal tubules of the mollies, but were rare in guppies. The degenerative changes in the kidneys of these two teleosts are similar to those seen in the kidneys of aging mammals. Despite the loss of normal structure in older fish, it seemed unlikely that degeneration of the kidney was directly involved in aging and death.