Lab members' research projects

Don't forget males or Limia!... also, hybrids are cool, but why are don't we find them in the wild?

Luis Arriaga (MS student)

Female mate choice has been studied a great deal, but male mate choice has been historically neglected. My first project focused on the evolution of male mate preference as it relates to female fecundity. Theory predicts that the strength of male mate choice should be correlated to female quality. In other words, males should prefer females based on how big a bang for their buck they get. In poeciliids, female quality in terms of fecundity is highly correlated with female size. What's interesting is that this correlation is different depending on the habitat from which the population originates. For example, females from toxic environments have evolved to have fewer and larger offspring than females from nontoxic environments. That means that the difference between the fecundity of small vs. large females in the cave is smaller than that of fish from the nontoxic environments. Males from nontoxic environments therefore have a comparatively bigger incentive to choose larger females, and they should therefore have a stronger preference for larger females than cave males. Whether this is true or not is the question that this project addressed.

Cuban Limia
Female Limia vittata

My second project focused on Limia. Limia is a very cool genus of poeciliids from the greater Antilles, but it has been severely neglected in terms of research. I wanted to begin to rectify this situation, so I looked at the behavior of three species (L. sulphurophila, L. perugiae, and L. vittata) in three different scenarios- male/male, male/male/female, and male/female.

My third project involved Poecilia mexicana. This species has a number of populations living in all combinations of cave/surface and toxic/nontoxic environments. These populations have evolved a number of different adaptations to deal with their respective environments, and as such they are undergoing the process of speciation. Interestingly, there is practically no gene flow between the toxic cave/nontoxic surface populations, even though there are no significant barriers to it. I therefore created hybrids between a population of toxic cave fish and another population of nontoxic surface fish, and I tested their fitness under food and light conditions meant to simulate cave and surface environments. Some of the variables measured were: survival, maturation rates, growth rates, fat content, number of babies, interbrood interval, fat content of the embryos and babies, among others.

I also worked on the website, including taking the photos in the "pictures" page. This is what the website used to look like.

I got my Master's in the spring of 2013.

Audience effects in the Amazon molly

Brandon S. Brown

My project uses the Amazon molly, Poecilia formosa, to analyze the effects of an audience on sexual behavior. The question I am trying to answer is do males and females adjust their sexual behavior due to the presence of other individuals? I will use different combinations of Poecilia latipinna males and females along with the P. formosa to documents the interactions among them. The results of my experience will help us to understand factors that allow the stable co-existence between a sexual species and an asexual, sperm-dependant associate.

Biotic and abiotic parameters affecting the coexistence of asexual P. formosa and their host P. latipinna: populations, community, predators, extreme temperature and land use

Claus Fischer

One of the more puzzling questions in ecology is the existence of species or lineages through time. Especially, how sexual species can coexist with asexual species, although the latter should have a clear advantage in reproductive output?

My diploma thesis focused on P. formosa, a clonal but sperm-dependent gynogenetic vertebrate species, which coexists with closely related sexual species like P. latipinna. Ecological differences could reduce competition between both species directly or indirectly through different mortality rates.

I studied both species in the field and tested experimentally for differences in thermal tolerance, differences in the susceptibility to predators and differences in food preferences as well as food consumption.

Mechanism of conditional signaling in the green swordtail

Elizabeth Hardy

I am studying the behavioral and hormonal mechanisms behind a conditional signal in male green swordtails, X. hellerii. The lateral stripe on adult green swordtails is important for social interactions, and has been considered a static, unchanging trait. However, males from a single observed population in Veracruz, Mexico can reversibly change the color of their stripe, and within a matter of minutes. I am investigating the modality with which males perceive each other and that triggers color change, as well as female preference for stripe color. Additionally, I am comparing color shifting in the presence of males from the same population and with two, non-shifting populations. Finally, I will be isolating hormones that may explain the physiological changes that occur in shifting males, specifically examining chromatophore expression.

Sexual-asexual coexistence in the species complex of the Amazon molly Poecilia formosa: the role of frequency dependent population dynamics

Katja U. Heubel

Stable coexistence of gynogenetic Amazons and its sexual host species may occur under weak male mate discrimination, density dependent mating, or ecological niche partitioning. In the current project, we study frequency dependent mechanisms that may regulate long-term coexistence of sexual and asexual females. Simulating the colonization of new habitats in a patchy environment, we are testing population regulation and coexistence of sperm-dependent asexual females and sexually reproducing females in a mesocosm experiment.
The evolution of sex, its origin and maintenance are part of the major puzzle of modern evolutionary biology. Compared to asexual reproduction, sex is a costly and at first sight ineffective mechanism, since it involves disadvantages like the production of males, leading to a reduced overall number of offspring. This leads to the question why the majority of species reproduces sexually.
The coexistence of the gynogenetic Amazon Molly (Poecilia formosa) and its sexual host species (P. latipinna and P. mexicana) represents a suitable model to explain how sexuality can persist despite its costs. For my diploma project I investigated which factors, especially on the behavioral level, might regulate the stability of the mating system by addressing the following main questions:

•    Do males from populations dominated by Poecilia formosa differ in mate choice decisions from males from populations in which P. formosa is rare?
•    Does the social environment influence conspecific and heterospecific sperm transfer in Poecilia latipinna males and what are the consequences for the fertilization success in Poecilia formosa?
•    Which association preferences do males show when confronted with shoals of different compositions?

Audience effects in mollies

Amber Makowicz

I am studying audience effects in sailfin mollies, P. latipinna, and amazon mollies, P. formosa.  Audience effects is essentially two individuals interacting with an audience present and how the interacting pair changes their behavior according to the type of audience.  I am focusing on sexual harassment and whether or not harassment is influenced with the presence of a male audience or the size of these males.  The audiences that I use are movies that are play back on a computer screen to the interacting pair.

Mate choice in mollies

Jennifer Place

I am doing honors research with Amazon and Sailfin Mollies. I am interested in male mate choice in the Sailfin Mollies. Many studies have shown that male Sailfins prefer conspecific Sailfin female over the asexual, heterospecific Amazon Molly. Other studies have shown no preference. However, the Amazon Molly mating system is dependent upon male choice. I am interested in how male preference changes when a cost is involved. I would predict that when males have to spend more energy to get to the female, they will show a greater preference for conspecific females over heterospecifics. In my experiment, males will be made to swim against a current to get to the female. I expect that the energy the male spends will alter with the female's value. To this end, I will vary the female species, size, and quality in my experiment. I may also show videos of different audiences to see how they affect male choice. Such audiences would be other males, predators, Amazon females or Sailfin females.

Behavioral ecology of the Cave molly

Martin Plath

Cave mollies
Cave mollies
In this project I study adaptations of fishes to life in lightless subterranean habitats. In a comparative approach I examine the ecology, behavior, parasitology and reproductive life history traits in the cave molly (Poecilia mexicana) and in surface-dwelling mollies.

The habitat of the cave molly, the south Mexican “Cueva del Azufre” is unique in its combination of darkness and toxic H2S. My major interests are the evolution of male mating tactics and male and female (non-visual) mating preferences in relation to extreme environmental conditions and lightlessness.

Life history of mollies

Rüdiger Riesch

Mainly I am interested in two aspects of Poecilia-life history evolution:

(A) What life history traits contribute to the stability in a sexual/asexual mating complex of fishes (Amazon mollies, Poecilia formosa & Sailfin mollies, Poecilia latipinna). To understand how stable coexistence in the P. latipinna/ P. formosa–mating complex can be maintained, it is important to obtain thorough information concerning life-history traits of both species. For my dissertation project, I address the following questions: (1) Are there differences in the life histories of P. formosa and P. latipinna? (2) How do life history traits relate to the maintenance of the stable coexistence in the P. latipinna/ P. formosa–mating complex?

(B) What life history adaptations allow for colonization of extreme habitats? In Tabasco, southern Mexico, two populations of the Atlantic molly (Poecilia mexicana) have invaded a toxic (H2S-rich) and a non-toxic cave. In this system I am studying toxic (H2S) and non-toxic surface- and cave-habitats to investigate how extreme environments (darkness and toxicity) have selected for different life history traits.

Influence of male size and competition on male mating preference in the Sailfin molly

Felicia Schwake

Amazon mollies are gynogens and reproduce asexually but require sperm, commonly from male Sailfins, to trigger embryogenesis. Sailfin mollies are a sexual species that commonly live in the same habitat as Amazon mollies. Theoretically, Amazon mollies should cause Sailfin mollies to go extinct because of their ability to increase in numbers more quickly. In turn, Amazon mollies would go extinct because of their need for a sperm donor. I’m interested in how these two species are able to live in stable coexistence. One possible mechanism is male choice. In theory, males should not mate with Amazon mollies because they gain no fitness-relevant offspring. Also, Amazon mollies must compete with female Sailfin mollies. Currently, my project is trying to determine if larger male Sailfin mollies force smaller male Sailfin mollies into proximity and mating situations with Amazon mollies.

Taking a close look at sex: Amazon mollies and their parasites

Michael Tobler (Ph. D. student)

amazon molly
Amazon molly

The evolution and maintenance of sex and recombination is still a major and unresolved paradox in evolutionary biology. Currently, one of the most widely accepted hypotheses, the Red Queen hypothesis, states that recombination provides an immediate advantage in biotic interactions. More specifically, the Red Queen hypothesis argues that recombination results in genetically diverse offspring that, contrary to the uniform offspring of asexuals, are difficult targets for parasites and diseases.

The Amazon molly, Poecilia formosa, is one of the few clonal vertebrates, reproduces gynogenetically and thus always has to coexist with a closely related sexual species. The mating system of P. formosa and its sexual relatives is an ideal model system to investigate advantages of sexual reproduction and testing the predictions of the Red Queen.


Current projects focus on:

  • spatial and temporal patterns of parasitisation in natural populations of sexual and asexual mollies
  • population genetics of sexual and asexual mollies including genes at MHC-loci, especially the temporal variation in clonal diversity of P. formosa
  • the immunocompetence of sexual and asexual mollies under controlled experimental conditions
  • the effects of Blackspot disease on the life history and the behavior of mollies

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