OVERVIEW
The Haag laboratory is based in the Department of Biology at the University of Maryland, College Park (UMD). We study the evolution of animal sexuality, focusing on cases where self-fertile hermaphroditism has evolved from male-female ancestors. These shifts to one-parent reproduction present fascinating developmental puzzles, but also have tremendous organismal significance. Using nematodes and mangrove killifish, we explore the developmental and genetic novelties required to allow a new strategy to emerge, and also the various consequences of adopting it.
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Haag, Fitch, & Delattre (2018)
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LAB NEWS
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New summer researchers
July, 2026 
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Thanks to NSF, we again welcomed new researchers this summer:
L-R: Lar, Andrew, Sammy |
Changing sex on their own terms
March, 2026
March, 2026
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Adult hermaphrodite (top) and secondary male (bottom) K. marmoratus. Photo by Eric
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Our latest paper on K. marmoratus is now out in Integrative Organismal Biology. In it, Jax Ficklin and co-authors report an interesting failure:
Because K. marmoratus hermaphrodites naturally change sex (sometimes), we imagined we could force them to do it on our timetable by adding exogenous androgens. Such hormone-driven sex change has been reported in many fish, both sequential hermaphrodites and non-sex-changing species. While this initially appeared to work, testis development never completed, and once removed from the hormones they snapped back to self-fertility. As K. marmoratus hermaphrodites naturally have testis tissue and male-like androgen titers, this may reflect an evolved capacity to prevent premature masculinization. |
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2025 summer researchers
July, 2025 |
Thanks to NSF, we again welcomed new researchers this summer:
L-R: Andrew, Ally, Ashley, and Lilly |
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Paper links sperm competition & speciation
January 29, 2025 
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Earlier work from the lab reported that sperm produced by males from outcrossing nematodes often go rogue when placed into a self-fertile hermaphrodite, sterilizing and killing her. More recently, we described MSS, a small sperm competition protein found in outcrossers, but lost in hermaphroditic species. This new study, led by Justin and Asan, connects the two phenomena: MSS enhances sperm function by conferring mild invasivity. |
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Eric's book released
November 20, 2024 
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After nearly a decade of effort, Eric is pleased to announce the publication of The Other Big Bang: The Story of Sex and Its Human Legacy, by Columbia University Press. If you are looking for an approachable overview of the evolution of sex and sexes, or are curious about how humans got to be the way we are, you may find it helpful. Learn more here. |
Congratulations to...
- Asan Turdiev, who in 2025 was awarded both an Ann G. Wylie Dissertation Fellowship and the Dr. M. Zain-Ul-Abedin Memorial Fellowship. Way to go, Asan!
- Asan Turdiev and Dr. Greg Reilly, who both gave posters at the 25th International Worm Meeting in Davis, CA
- Asan Turdiev and Dr. Justin Van Goor, who both gave talks at the EvoWorm 2024 conference in Vienna.
- Dr. Justin Van Goor, an NSF- and USDA-supported postdoctoral fellow in the lab from 2019 -2023, who begins his appointment as an Assistant Professor in the University of Missouri, Columbia's Department of Biological Sciences in Fall, 2024. He will focus his new lab on fig-associated nematodes. Go, Justin!
- Jax Ficklin, who successfully defended his doctoral dissertation, entitled "Sex and the Evolution of a Double Hermaphrodite", on July 13, 2023. Jax has been a student in the Biological Sciences Graduate Program's concentration area in Behavior, Evolution, Ecology, & Systematics.