Genitalia are often the battleground of warfare between the sexes
Genitalia are some of the most diverse structures in nature, and this diversity goes beyond what is needed for simple transfer of male gametes into the female. Because genitalia are structures that interact directly during copulation, coevolution between males and females is likely. Male genitalia can evolve through selection for males to either seduce females, outcompete rival males who also copulate with the female, or to directly counteract female interests bypassing her choice or directly harming her to increase male success. Females of course evolve genital features that allow them to prevent such male imposed costs. I have discovered that ducks are a great example of this arms race, and this discovery has had an important effect on understanding the role of sexual conflict in evolution. Males have evolved explosive penis eversion that allows them to inseminate females quickly despite their resistance, females have evolved convoluted genitalia that prevent males from everting their whole penis in the female oviduct, and species with different levels of male coercion have different genital morphology: from simple genitalia when no coercion takes place, to very convoluted when coercion is common. In other groups, females can evolve to detect subtle differences between males, and to manage sperm from preferred males. In my lab we study vertebrates: Ducks, Snakes and more recently Bats (in collaboration with Dr. Teri Orr, a postdoctoral fellow in my lab).
Tinamou mating system and egg color
Tinamous are poorly studied neotropical birds with exclusive male parental care. They are close relative to ostriches and other flightless birds. They lay incredibly colorful eggs that are somewhat paradoxical given that they are laid directly on the ground. I found that despite the presence of exclusive male care and very high incubation constancy, great tinamou males take care of up to 30% of chicks that they did not sire. This is likely the result of high predation pressure that increases the demand for eggs. Females are always moving between males and they can easily carry sperm from previous matings. Rather than waiting for sperm from previous matings to become unviable, a process that could take many days, male tinamous simply mate with the females and take her eggs quickly to complete a clutch. The female then moves on and lays eggs. We also recently discovered that the visual system of tinamous allows them to see ultraviolet spectrum.
Early last year my research was attacked by extreme right wing media after a story was published about how I got federal funding to study duck penises. I have since started a campaign to support scientists who are similarly attacked, and to educate other scientists about how we can act to prevent these unfounded political attacks from being a viable strategy in the first place.