Current Projects
New College Students (or students from the Sarasota area in general) are welcome to contact me about project ideas you may have. This page has information about some of the projects I am working on that I would be happy to discuss.
Sexual Selection & Sexual Conflict in Syngnathids
Seahorses and pipefish in the family Syngnathidae have incredibly diversity and varying complexity of pouch morphology and thus paternal allocation potential. Syngnathids have historically been regarded as lecithotrophic, meaning offspring receive all nutrients from the egg’s yolk. Two pipefish species that are found in Florida, Syngnathus fuscus and S. floridae have been found to transport labelled amino acids to developing embryos (Kvarnemo et al. 2011; Ripley and Foran 2009). Transporting amino acids from the parent to offspring are considered to be an incipient pathway to direct provisioning of resources from parent to offspring (Morrison et al. 2017). A 2020 paper by Skalkos et al. found that the seahorse Hippocampus abdominalis is apparently patrotrophic, meaning the father provides the developing embryos with nutrients that go beyond what is contained in the original egg yolk, resulting in an offspring whose mass is larger than the initial egg. In the fish family I studied for my dissertation, Poeciliidae, matrotrophy has evolved at least nine times (Pollux et al. 2009), but most species in the family are lecithotrophic. Lecithotrophy is often associated with courtship behavior, pre-copulation sexual selection, and male secondary sexual characters.
Syngnathids are "ideal for studies of the evolution of reproductive complexity, because they exhibit multiple parallel origins of complex reproductive phenotypes" (Whittington and Friesen 2020).
Sperm Characters in Livebearing Fishes
Males of the Eastern Mosquitofish, Gambusia holbrooki, have two color morphs, silver and melanic; melanic scales containing patches of black pigmentation. Melanic males are relatively rare in nature, comprising 1-7% of males in most populations (Regan 1961). Melanic males experience less predation than silver males (Horth 2004), but females tend to avoid them, as they are more aggressive (Horth 2003). Melanic males are typically larger than silver males and have relatively large gonopodia, which is a modified anal fin to deliver sperm to females (Horth et al., 2010). It is not yet known whether sperm traits differ between silver and melanic males, though sperm number is positively correlated with male size (Locatello et al. 2008; O'Dea et al. 2014).
This figure from Lisa Horth shows the coloration of melanic vs. silver Gambusia holbrooki
Parent-Offspring Conflict in Livebearing fishes
During my dissertation, I studied livebearing fish in the family Poeciliidae to investigate questions surrounding the evolutionary consequences of placentation. In Poeciliidae, placentation has evolved independently at least eight times. Additionally, there is (in most cases) a sister species lacking a placenta for each species with a placenta.
A corollary of the shift towards internal, post-zygotic maternal provisioning is that there is a shift away from pre-copulatory sexual selection, and towards post-copulatory sexual selection. I am interested in investigating the potential for sperm competition and cryptic female choice (post-copulation) and examining how these factors influence paternity and subsequent maternal allocation based on paternal genotype.
​
I used the Florida-native Least Killifish, Heterandria formosa, to ask whether females might be capable of recognizing male genotypes and allocating resources accordingly. Amazingly, females do partition resources differently depending on the type of males they are mated to.