Current Projects
Our lab explores fish-focused questions in the marine and freshwater realm. 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 our lab is working on that I would be happy to discuss more.
Stress Physiology
Previous research has shown that Heterandria formosa, a small, placental livebearing fish (pictured above), adjusts offspring size and number when living in high vs. low social densities (Leatherbury and Travis 2019), and that these characteristics are heritable (Levell and Travis 2023). However, it is unknown whether these treatments are physiologically stressful for them. Our lab is expanding on these experiments to investigate environmental effects of crowding and food restriction in Heterandria formosa.
Sperm Characters
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
Life History
The Eastern Mosquitofish, Gambusia holbrooki, belongs to the same genus as the Western mosquitofish Gambusia affinis, a highly invasive species around the world. Pior work shows that G. affinis is capable of invading marine environments involving changes in life history characters (Alcaraz and Garcia-Berthou 2007; Peterson and Peterson 1990), physiology (Tsai et al. 2017; Uliano et al. 2010), but little work has been done on G. holbrooki.
Photos via EmeraldKing-Aquatics
Gambusia affinis vs. holbrooki (Page and Burr 1991)
Gambusia affinis: six dorsal fin rays, male lacks teeth on the third ray of the gonopodium
Gambusia holbrooki: 7-8 rays, males have a toothed gonopodium
These two species also have different sex chromosomes (Black and Howell 1979)
Sexual Selection & Sexual Conflict in Syngnathids
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).
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.
We are currently investigating questions related to sexual selection in syngnathids in terms of potential hybridization among Syngnathus species.