WHY DO MALES EXIST?
Sexual females produce both sons and daughters, while asexual females make only daughters. Since only females produce offspring, this "cost of males" predicts that sex should be rare because asexual females will leave many more descendants than will sexual females. In reality, however, sex predominates. Despite years of study, why sex is so common despite the cost of males remains unclear, and is considered one of the most important unanswered questions in evolutionary biology. A clear understanding of the advantages of sex, which is distinguished from asexuality by the production of genetically variable offspring, is also of direct relevance to understanding the value of preserving genetic diversity within and among populations, species, and ecological communities.

HOW ARE SEXUALS AND ASEXUALS DIFFERENT?
The expectation that sex should be rare is based on the assumption that sexuals and asexuals are similar. In other words, the two-fold cost of sex will be diminished or even negated if asexual females experience disadvantages that negatively affect their ability to produce daughters. Accordingly, our research is focused on the many ways in which asexuals and sexuals might differ.

RESEARCH PROJECTS
Many research projects in our lab use Potamopyrgus antipodarum, a freshwater snail native to New Zealand. Natural lake populations of this snail vary in the frequency of obligately sexual and obligately asexual individuals, which sets the stage for investigation of why sex persists in some populations but not others. This species has been the focus of research into the maintenance of sex for nearly 20 years, and is now the best-characterized natural system available for studying why sexual reproduction is so common. While our research is based in evolution, we bring together ideas and tools from ecology, behavior, and molecular/cell biology to study sex in P. antipodarum. Several of the main research themes in our lab are outlined below.

Mutation accumulation. One set of projects revolves around testing the hypothesis that asexuality is rare because sex is required to prevent the accumulation of harmful mutations. We are using DNA sequence data to address these questions in P. antipodarum. Related projects assess whether mutation accumulation in asexual P. antipodarum lineages has detectable negative effects.

Disadvantages of polyploidy. Another major research focus in our lab is centered on the consequences of the higher ploidy of asexual vs. sexual snails. Like most sexual organisms, sexual P. antipodarum have two chromosome sets, while asexual P. antipodarum (like most asexuals) have at least three. Changes in ploidy level can dramatically affect key organismal traits such as cell size, body composition, and growth rate. We are using a variety of approaches to determine whether these possible consequences of polyploidy affect asexual P. antipodarum in a manner that could help compensate for the costs of sex.

Population dynamics of asexuals. We have also used laboratory experiments to demonstrate that asexual females have a negative impact on one another's reproduction. We are conducting research into snail behavior and population ecology to better understand why and how this happens, especially in light of the fact that P. antipodarum is invading freshwaters in Europe, Australia, and North America. Since the invasive populations are nearly all asexual, our research can provide new understanding of invasion dynamics as well as sex, and perhaps inspire ideas about how better to control the invading populations.

Graduate Students
I will consider taking new graduate students for the fall of 2010:

Prospective graduate students with interests in evolutionary biology and especially the evolution and ecology of mating systems and sex who would like to consider joining my lab should email me (maurine-neiman@uiowa.edu) to discuss the possibility of applying to the graduate program.

Press release: http://blogs.nature.com/news/blog/2008/08/making_sense_of_sex_1.html