Study Systems

• Microbial evolution is quite distinct from other research topics in the CRE. Nonetheless, microbes (and microbial evolution) are important drivers of evolutionary change across all systems, including those relating to reproduction. The Escherichia coli genome was first sequenced in 1997 and there are now over 60,000 prokaryotic genome entries in NCBI. Prokaryotic genomicists are awash in data and studies of genome evolution can now be designed to address a multitude of question surrounding the natural history (including ecological and host interactions) and functional capacities of microbes. CRE members have contributed to a number of studies relating to the evolutionary genomics of virulence in eubacteria and metabolic pathway profiling to establish environmental interactions in archaeal species from extreme habitats that are recalcitrant to laboratory study.

• Mimulus guttatus – The yellow monkey flowers are a great system to investigate transitions in reproductive strategies. This western North American wildflower species is highly variable with geographically widespread and interfertile annual and perennial populations inhabiting different soil environments. The annual populations thrive in a Mediterranean climate, characterized by a wet autumn, winter and spring, followed by intense summer drought. The perennial populations are protected from the summer drought by growing in soils that remain wet year round due to their proximity to springs or rivers. Differences in life history strategies, including the timing of flowering and allocation to vegetative structures, reflect strong local adaptation to these different habitats. We are examining the ecological conditions and evolutionary and genetic mechanisms underlying differences between the ecotypes. Research on M. guttatus is facilitated by a draft genome sequence several resequenced lines, seed stock from over 500 populations, and the availability of inbred lines and mapping populations.

• This genus is an excellent system in which to study the evolution of sexual selection in a comparative context. Most importantly, the genus combines diversity in pollination and sexual system, with multiple lineages that are either wind or animal pollinated, and dioecious and outcrossing or hermaphroditic and partially selfing. We are using this diversity to investigate female (ovule) interactions with the growing pollen tube. Wind pollinated plants that receive a diversity of pollen grains from unrelated donors are expected to experience stronger sexual selection than related animal pollinated congeners.

• Ambrosia artemisiifolia – This wind pollinated annual weed that is best known for its copious amounts of allergenic pollen. We are using this monoecious plant (separate female and male flowers on the same individual) to investigate variation in allocation to female and male flower production. Sex allocation in this species is variable, and determined by both genetic and environmental factors. We are using this variation to test sex allocation theory, including size-dependent sex allocation, adaptive plasticity, and male fitness gain curves.

• Although they do not possess characteristics commonly associated with most model organisms, non-human primate species have proven to be powerful models for the study of human disease and behavior. Notable amongst these is the macaque, Macaca mulatta, is an Old World Monkey that has been used widely as an experimental model and, more recently, for transgenic experiments. Macaques also serve as an important nonhuman primate model for the study of human infertility and our researchers played an integral role in the characterization of the rhesus macaque sperm proteome. In addition to being of great interest in relation to the evolution of humans and human-specific phenotypic traits, nonhuman primates exhibit remarkable diversity in their social systems and mating behavior. The rapidly increasing availability of sequenced genomes make this mammalian order an exciting target for genome-wide studies relating to reproductive genetics.

• Interest in mouse genetics began over a century ago with Haldane’s work on genetic linkage and the house mouse is now the well-established and most widely used model for the study of of mammalian biology, including a diverse repertoire of human diseases. Thousands of mutant strains are currently maintained and available to researchers. The house mouse has also been an invaluable model for the study of mammalian reproductive biology, and much of what we know about the molecular biology and genetics of reproduction stems from studies in the mouse or other members of the Rodent Order. Beyond its role as the best developed mammalian model organism, the house mouse and it’s close relatives in the genus Mus exhibit remarkable variation in their mating systems and associated traits relating to postcopulatory sexual selection. Recent genome sequencing efforts in this group have opened the door for comparative genomic studies relating to reproduction and sexual selection.

• This ecologically diverse taxon exhibits a wide range of mating systems, from monogamy to polygynandry. Consequently, they also exhibit extraordinary diversity in the size of their testes relative to all other mammals (0.12 to 8.4% of total male body mass). Because testes are metabolically expensive tissue (not to mention costly to fly around with) and because, as small flying mammals, bats live “economically” challenging lives, we examined the evolutionary relationship between investment in testes and in brains, the other most metabolically expensive tissue. Using comparative data on total brain and neocortex dimension, testis mass, and social and mating systems for 334 bat species, we showed that multiple mating by males, in the absence of multiple mating by females, has no evolutionary impact on relative brain dimension. In contrast, bat species with promiscuous females have relatively smaller brains than do species with females exhibiting mate fidelity. This pattern may be a consequence of the demonstrated negative evolutionary relationship between investment in testes and investment in brains.

• Birds are one of the most historically and widely studied taxonomical groups in relation to mating behavior, sexual selection and speciation. Despite extensive work on sexual selection – and an extraordinary body of work on postcopulatory sexual selection – far less is known about the molecular basis of gamete biology and postcopulatory processes in this group. This provides us with an exciting opportunity to apply transcriptomic and proteomic approaches using the recent wealth of genome sequences in both Galliformes and Passerines. Ongoing projects in the CRE include seminal fluid proteomics with several passerine speciation model systems.

• Gallus gallus – The polyandrous red jungle fowl, Gallus gallus, is the ancestor of domestic chickens. It has become a model system for the study of sexual selection and sexual conflict, including social dominance, the evolution of multimodal ornamentation, sperm competition and cryptic female choice. Recent studies have revealed very sophisticated adaptations to postcopulatory sexual selection in both sexes, including strategic sperm ejection by females and tailoring of sperm and seminal fluid by males. Working with Tom Pizzari (University of Oxford), we are conducting a proteomic examination of dynamic plasticity in G. gallus ejaculate composition.

• These charismatic beetles have undergone dramatic, multivariate diversification in the design of sperm and of the female reproductive tract. We’ve studied numerous species to explore how and why these interacting male and female traits co-diversify.

• Tribolium castaneum – As one of the most common pests of stored plant products worldwide, the red flour beetle has become a model system for studies of ethology and sexual selection in addition to food safety. This species has a mating system characterized by extreme promiscuity by both sexes. We have genetically engineered beetle lines with sperm heads that fluoresce red or green and are using these, for example, to track in vivo sperm performance and fate across numerous rematings by females in order to determine mechanisms of sperm precedence and to examine sex-specific costs and benefits of promiscuity.

• This taxon has been a model for the molecular study of ecological and behavioral adaptation. The availability of over 30 sequenced Lepidopteran genomes promises to revolutionize our understanding of this diverse taxonomic group (>180,000 species and ~10% of the total described species on earth), which includes important agricultural pests and plant pollinators. Of particular interest to reproductive biologists, sperm heteromorphism, the production of distinct sperm types during spermatogenesis, is nearly ubiquitous within this insect order. Surprisingly, the non-fertilization sperm morph (apyrene) is anucleate, contains no DNA and is often produced in quantities that far exceed that of the fertilizing (eupyrene) morph. The seemingly paradoxical maintenance of this heteromorphic sperm system is of great interest to us. To date, the sphinx moth Manduca sexta and the monarch butterfly Danaus plexippus have been the target of proteomic and transcriptomic studies by our group, but we are conducting similar analsyses, as well as functional and evolutionary studies with other Lepidoptera, obscura group Drosophila and hydradephagan beetles.

• The humble fruit fly hardly needs introduction. Knowledge of Drosophila melanogaster and its relatives’ genetics, proteomics and genomics, and it’s developmental, reproductive and behavioral biology make it an invaluable organism for studying natural selection, sexual selection and speciation. In addition, many of our evolutionary studies are comparative, taking advantage of the availability of hundreds of species, numerous sequenced genomes and well-resolved phylogenetic relationships to explore trait diversification, reproductive isolation and genotype-phenotype relationships. Yellow dung fly, Scathophaga stercoraria – Investigations by Geoff Parker of the yellow dung fly mating system revitalized interest in sexual selection theory and sparked the development of sperm competition and sexual conflict theory. Since the 1970s, S. stercoraria has remained one of the most studied model systems of sexual selection theory, with numerous investigations detailing the reproductive advantages of larger body size for males competing on cow dung. We are using this species to investigate the relationship between sex-specific reproductive tactics and resource distribution, as well the evolutionary maintenance of recently discovered, alternative male mating tactic.

• Scathophaga stercoraria – Investigations by Geoff Parker of the yellow dung fly mating system revitalized interest in sexual selection theory and sparked the development of sperm competition and sexual conflict theory. Since the 1970s, S. stercoraria has remained one of the most studied model systems of sexual selection theory, with numerous investigations detailing the reproductive advantages of larger body size for males competing on cow dung. We are using this species to investigate the relationship between sex-specific reproductive tactics and resource distribution, as well the evolutionary maintenance of recently discovered, alternative male mating tactic.

• These ant-like flies are emerging as model organisms in the study of behavioral ecology in general and sexual selection in particular.In fact, European and North American populations of S. punctum not only vary in male mating behavior but they also represent the only known documented example of a geographic reversal in sexual size dimorphism: males are larger than females in Europe and females are larger than males in N. America. This reversal is also accompanied by stark differences in female remating rates (polyandry), which is a critical determinant of the intensity of pre- and postcopulatory sexual selection acting on males. Using this unique system, we can study how variation in polyandry can lead to the diversification of critical biological traits on a wide geographic scale and the implications such diversification has for incipient speciation. We are also conducting evolutionary/phylogenetic studies of male-female reproductive trait diversification across numerous sepsid species.