The evolution of an annual life cycle in killifish: adaptation to seasonally ephemeral aquatic environments through embryonic diapause
An annual life cycle is characterized by growth, maturity, reproduction, and death condensed into a short season, with the production of embryos (seeds, cysts, or eggs) capable of surviving harsh conditions. More typically associated with desert annual plants, the evolution of an annual life cycle in vertebrates is extremely rare. Killifish have adapted to life in seasonally ephemeral water bodies across much of Africa and South America through the evolution of an annual life cycle. These 'annual killifish' produce hardy desiccation resistant eggs that undergo multiple stages of diapause (developmental arrest with a slowing of metabolic rate) and remain buried in the soil for long periods after the fish have perished due to the drying of their habitat. My PhD research examined the evolution of this life cycle and how the adaptations of annual killifish allow for survival in extreme environments.
The evolution of placentas in Poeciliid fishes: testing adaptive and conflict hypotheses
One of the grand challenges in the field of evolutionary biology is to explain the evolution of complex traits. The placenta, an intimate fusion of maternal and fetal tissues for sustenance and physiological exchange, is a complex organ found in many animal groups (e.g. mammals, some sharks and rays, bony fishes, and lizards), and its origin requires explanation. Species in the live-bearing fish family Poeciliidae have independently evolved placentas numerous times from non-placental ancestors. This unique biological situation provides the raw material to test alternative hypotheses that make contrasting predictions regarding the selective factors favoring its evolution. As part of my NSF postdoc, I utilized the biological collections of numerous museums to assemble a species-level data set on reproductive mode, life-histories, and habitat for the family Poeciliidae. I then used phylogenetic comparative methods to test the predictions of adaptive and conflict hypotheses for the evolution of the placenta , and demonstrate a causal interaction between the evolution of the placenta, male sexual selection, and rate of speciation.
The evolution of parental care diversity in Amphibians
Not only does parental care affect the fitness of offspring and parents, but it also has profound consequences for social evolution - it leads to both cooperation and conflict within families, is associated with changes in species’ life history strategies, is related to mating system and sexual selection, and is one of the main drivers for the evolution of sociality. Thus, unravelling how parental care evolves and is evolutionarily maintained has important implications for our understanding of many aspects of animal life. Using phylogenetic comparative methods and data for over 1300 amphibian species, my postdoc advisor, Isabella Capellini, and I are addressing questions such as whether some care forms are more common because they are easier to evolve; whether short term care is a first necessary step for the evolution of prolonged care; whether the sexes differ in care form and duration, and how this in turn determines the evolutionary origin and persistence of biparental care. Our results indicate that egg attendance, one of the simplest care behaviours, is gained and lost more frequently than any other care form, while complex adaptations, like brooding and viviparity, are gained at low rate and infrequently if ever lost. Prolonged care from the egg to later developmental stages evolves from temporally limited care, but, unexpectedly, it is as easily lost as it is gained. Finally, biparental care is evolutionarily unstable regardless of whether the parents perform complementary or similar care duties. By considering the full spectrum of parental care adaptations, we reveal a more complex and nuanced picture of how care evolves, is maintained, or is lost.