Sexual reproduction is an evolutionary puzzle.

 

By all accounts, uniparental reproduction (only one adult needed to reproduce) is the most efficient solution to producing offspring. However, biparental reproduction (offspring produced via two parents reproducing with one another) is far more common in our natural world. This is quite perplexing, particularly because males do not directly contribute offspring, thus reducing the number of potential offspring by half as opposed to uniparental reproduction. We may see biparental reproduction so often because while it has its drawbacks, it allows for something that is incredibly important for evolution to occur: recombination. When populations need to keep pace with their changing environment, novel gene combinations can allow a population to co-evolve. Parasites could be one of these environmental factors driving the need for co-evolution due to their negative costs on individuals (from taking an organism's nutrients to sometimes even castrating or killing them).

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Even further down the rabbit hole, you can encounter something known as "sex-biased parasitism," where the sexes in the species are differentially impacted by parasites. There is fascinating web of mechanisms that can drive this bias, but this interaction is often overlooked, and we know little about it outside of male-female systems. 

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Furthermore, if organisms do reproduce with one another rather than through uniparental means, how do they select a partner? With potentially heavy consequences for their offspring if they make a poor choice, what can organisms use to gain information about another individual's quality? What are they paying attention to?

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I am exploring these areas through a particularly unique fish species: the mangrove rivulus (Kryptolebias marmoratus). Native to the mangrove forests of Florida, the Caribbean, and Belize, the seemingly unassuming rivulus has a fascinating life history and suite of adaptations. Capable of surviving for two months out of water and tolerating various ranges of salinities, the rivulus is equipped for surviving the fluctuations that come with living in the mangrove forests. They have an androdiecious reproductive system, and typically the males only account for up to 2% of the population. So, why do these males persist? How do they convince hermaphrodites to mate with them? Why do some locations have few males while others have more? Is this associated with the parasite community?

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My PhD research will use several approaches to investigate proximate and ultimate mechanisms of outcrossing in this unique system. We traveled to Belize and the Florida Keys during the summer of 2024 to sample different populations for parasites, and we also traveled to the Tampa, Florida area in 2023 and 2024 to sample. I have also done a large laboratory study exploring what traits individuals pay attention to, and how their response to these traits is affected by the other individual's sex.

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Want to see what we saw in Belize and the Florida Keys? Check out my short film below.

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