Pregnancy is an important biological innovation that has evolved convergently hundreds of times in fish, mammals, reptiles, amphibians, and invertebrates. While many viviparous lineages nourish developing embryos from egg yolk alone, complex placentae that transport large quantities of organic nutrients to the have evolved independently at least sixteen times in vertebrates. The placenta has arisen via homologous associations of the same extraembryonic membranes and uterine tissues in mammals and reptiles. Analogous placentae have also evolved multiple times in sharks and teleost fish (anamniotes), but from different ancestral structures, because their embryos lack the amniote-specific extraembryonic membranes.
My team are currently combining morphological, transcriptomic and proteomic approaches to determine how placentae support embryonic development in lizards, seahorses, sharks, and mammals. This work is shedding light on the fundamental biology of the placenta in poorly studied species. For example, we are determining the mechanisms underpinning nutrient transport in a placental shark that enable an almost 3,000 % increase in embryonic mass over just 4.5 months of development, and identifying the functions of male (!) placentae in seahorses. Our research also contributes to new knowledge in evolutionary biology, by testing whether the same genes have been independently recruited to support placental function across diverse animals.