Can a man be infidel and still have it all? Read on to find out one way in which cryptic mate choice and offspring provisioning works in animals
Conceived, written and presented by Claire Haynes, Olivia James and Caroline Shevlin
for course BIOL 4585-001 Evolution of mating systems (J-term, 2021)
Class of 2021, University of Virginia
Dear Dr. Tatiana,
I am a S. abaster male living off the coast of Western France. Up until yesterday, I was happily pregnant with my first brood, but now I’ve run into trouble. I was swimming along when another female caught my eye. She’s much more attractive than my girlfriend, she’s large and has the prettiest stripes. Now I wish I weren’t pregnant so I could court this new girl. What should I do?
Sincerely,
The Playa of Sur Mer
Dear Playa,
Lucky for you, since pipefish males are the ones who carry the offspring, you have the unique ability to modulate your energy expenditure through your brood pouch! Your brood pouch, Syngnathus abaster, is a well-defined sack on your tail with two pouch folds that partially or fully enclose the eggs. Due to the progressive role-reversal in your species, males have the power to exercise cryptic choice. Good for you for normalizing stay-at-home dads! This means that you have the ability to be choosy about your mate both before and after mating by re-allocating the resources you give to the offspring. Your brood pouch has a vein that carries nutrients both ways. Upon seeing this more attractive female, you can suck nutrients from your young in order to save more resources to mate with her at a later time. This is similar to a phenomenon that we see in many species of female mammals, called a pregnancy block. A pregnancy block is when pregnant females terminate their pregnancy by literally blocking the nutrients going to the embryo, freeing up their resources for another potential offspring.
Your situation reminds me of a movie from the 1980s starring Gene Wilder, titled Woman in Red. In the film, a married man meets a sultry and captivating woman and attempts to leave his marriage for her. Similarly, your attention has been caught by this attractive female, and you're tempted to follow in Wilder’s footsteps. Here’s my advice to you: if you see another female that you are interested in, but you are already pregnant, don’t have a complete pregnancy block. Studies in the lab of your fellow black-striped pipefish males have indicated that when shown a more attractive female, males tend to have less, smaller offspring. What does this mean? As I mentioned earlier, you, my friend, have the ability to remove nutrients from your brood pouch and save them for yourself. This means you can have the best of both worlds – offspring now and resources to make better offspring with this new female. Like the males in the lab, you should not block your entire pregnancy. Though smaller and less in number, your offspring are not at risk of being killed by the new female, so it is beneficial for you to have some offspring now and some offspring through a new pregnancy with her. Don’t worry though, even though you should continue with your current pregnancy, you can re-capture enough resources to become successfully pregnant again.
It also may be reassuring to know that you are not alone in this predicament. Female mice also have the choice to terminate their pregnancy in the presence of other males. In fact, in mammals, this occurrence is relatively common and called the Bruce effect. Female mice who have been pregnant for 24 hours or less will lose their pregnancy in the presence of a new male. Recently, the Bruce effect was observed in nature in wild geladas, where females would choose to terminate their pregnancies upon the rise of a new alpha male. The Bruce effect in female mammals such as these likely has a different reasoning behind it than you in your situation. Rather than freeing up resources for a new male in order to have more fit offspring, females terminate their pregnancies in order to avoid infanticide by the foreign male. It would not make sense to use up valuable resources and energy in completing a pregnancy if your offspring won’t survive for long in the presence of this new male. Therefore, pregnancy blocks are beneficial to both the females and the new male, who can now mate with her.
However, there are many other examples of male fish that share your incentives. The Egyptian mouthbrooder will ingest his own offspring in order to redistribute the energy he put into producing the offspring so he can save energy for a more valuable succeeding brood. It can be a method of controlling brood size. This behavior is seen when there is a high availability of mates, so that fathers are ensured that the consuming of their offspring is not for naught. Additionally, there are two forms of filial cannibalism, total and partial, where total refers to consuming all of one’s offspring where partial refers to eating only a portion of the offspring. When in doubt, make sure you have enough potential mates to replace your offspring, and don’t consume them all when you could benefit from having some offspring survive!
If absorbing and/or eating your offspring makes you feel like a horrible parent, allow me to ease your discomfort with another example. Penduline tits (yes, a rather odd name) have an even odder behavior that involves eccentric nests. Made of spiderwebs, animal hair, and hidden entrances, nests are interesting pear-shaped caves that one would assume would result in A+ parental care. However, parents abandon their offspring at a rate of 40%, meaning that 2 out of 5 penduline tit broods perish due to abandonment. Why does this happen? The same reasoning that you want to lower your brood in favor of another female. This conflict between choosing which offspring to invest in drives all of these unique behaviors, from pregnancy blocks to filial cannibalism, to plain abandonment.
As you can see your situation is, while difficult, not an uncommon one. Many species have evolved specific mechanisms to alleviate the conflict between offspring care and energy investment, just like you have evolved your brood pouch. As seen in the Egyptian mouthbrooders when there is a high number of potential mates, ensure that you have a chance of siring a more valuable brood in the future before depleting your current brood’s resources. Parenting comes with many difficult decisions, especially in the wild. Whatever you decide to do, be reassured that it is natural and that your body is providing you with a choice.
All the best,
Dr. Tatiana
REFERENCES
Cunha, M., Berglund, A., Mendes, S., & Monteiro, N. (2018). The ‘Woman in Red’ effect: pipefish males curb pregnancies at the sight of an attractive female. Proceedings of the Royal Society B: Biological Sciences, 285(1885). https://doi.org/10.1098/rspb.2018.1335
Deal, N. D. S., & Wong, B. B. M. (2016). How Mate Availability Influences Filial Cannibalism. The Quarterly Review of Biology, 91(1). https://doi.org/10.1086/685303
FitzGerald, G. J. (1992). Filial cannibalism in fishes: Why do parents eat their offspring? Trends in Ecology & Evolution, 7(1). https://doi.org/10.1016/0169-5347(92)90190-M
Klug, H., & Bonsall, M. B. (2007). When to Care for, Abandon, or Eat Your Offspring: The Evolution of Parental Care and Filial Cannibalism. The American Naturalist, 170(6). https://doi.org/10.1086/522936
Kvarnemo, C., Mobley, K. B., Partridge, C., Jones, A. G., & Ahnesjö, I. (2011). Evidence of paternal nutrient provisioning to embryos in broad-nosed pipefish Syngnathus typhle. Journal of Fish Biology, 78(6). https://doi.org/10.1111/j.1095-8649.2011.02989.x
Paczolt, K. A., & Jones, A. G. (2010). Post-copulatory sexual selection and sexual conflict in the evolution of male pregnancy. Nature, 464(7287). https://doi.org/10.1038/nature08861
Pogány, Á., Szentirmai, I., Komdeur, J., & Székely, T. (2008). Sexual conflict and consistency of offspring desertion in Eurasian penduline tit Remiz pendulinus. BMC Evolutionary Biology, 8(1). https://doi.org/10.1186/1471-2148-8-242
Roberts, E. K., Lu, A., Bergman, T. J., & Beehner, J. C. (2012). A Bruce Effect in Wild Geladas. Science, 335(6073). https://doi.org/10.1126/science.1213600
This article was written by Claire, Olivia and Caroline as part of their capstone project for the course I taught on evolution of mating systems in J-term 2021 at University of Virginia. To know more check out rachanabhave.wixsite.com/teac#tatiana #rulesofengagement #teaching