Male pipefish who get pregnant reduce investment in their offspring if they see a sexy female

This new paper in the Proceedings of the Royal Society B caught my eye because of its title (abstract here but paper behind a paywall; judicious inquiry might yield you a pdf).  Check out the title and the abstract, and I’ll explain a bit of the results below (I read the paper quickly):

First, a bit of biology. Many species of pipefish and seahorses have a reproductive system in which males become pregnant. What happens is that females produce their eggs and stick them into the brood pouches of males, who fertilize them and then protect them, control the salinity, and even nourish the eggs using materials from the male’s body.  Since there is a shortage of available male brood pouches compared to the number of females who want their eggs fertilized, there’s competition between females for male pouches—the reverse of the usual competition by males for access to female eggs when females get pregnant or lay eggs. (Don’t believe Richard Prum’s new book about this, in which he implies that there really isn’t male competition by males for females, even in humans where the data on male profligacy vs. female choosiness are clear.)

Since sexual selection is reversed in these species, you find reverse ornamentation as well: it is the females who are ornate compared to the drabber males. And males in tests prefer both larger and more ornate females above smaller or less showy females. Here is the difference in seahorse anatomy and a male giving birth:

Look at all those babies!

In the new paper, authors M. Cunha et al did three sets of studies:

  1. They gave pregnant males of black-striped pipefish the sight (in a divided aquarium) of new females, some larger, some smaller, and some about the same size as females who had already “impregnanted” the males. In the first study, those males who got to see larger females produced smaller offspring. This may be because they’re reducing their investment in past pregnancies in hopes of remating to a “fitter” or more attractive female and producing more and better offspring.
  2. The authors measured the incidence of aborted embryos in pregnant male pipefish, and showed that the presence of very large females on the other side of the divider increased the percentage of aborted embryos in the male (they didn’t test females of different size, but used large females vs no females). This suggests that males can somehow reduce their investment when seeing another attractive female, though they didn’t use females of different size (attractiveness), which would have been a marked improvement of the design.
  3. They looked at wild pipefish males whose embryos were at different stages of development, and found that the heterogeneity of embryo size within a male decreased as pregnancy proceeded, and this was correlated with marked reduction in brood size. This was not due to random culling of embryos, but to culling of either the smallest or largest embryos (they couldn’t determine which were culled), which the authors see as a a form of selective abortion.

Overall, although the data aren’t terribly strong, this suggests a form of post-fertilization sexual selection, in which males decide to abort or reduce investment in embryos if they see a better mating opportunity. To quote from the paper:

Male pipefish, triggered to invest less in ongoing pregnancies by the sight of a very large, sexy female, hence produced smaller and more heterogeneous offspring, while also reducing brood size. As in pipefish resources derived from aborted embryos are captured by the father, instead of being directly distributed among developing embryos [14], males stricken by a sexier female not only save energy reserves for a presumably more auspicious future reproductive event, but they also potentially seize resources from a less rewarding brood.

As I lacked the time to read this paper as closely as usual, readers may find problems with the paper or errors in my summary.


Cunha, M., A. Berglund, S. Mendes, and N. Monteiro. 2018. The ‘Woman in Red’ effect: pipefish males curb pregnancies at the sight of an attractive female. Proc. Roy. Soc. B. 285:20181335. Published online.


  1. ThyroidPlanet
    Posted August 22, 2018 at 11:49 am | Permalink

    BANNED in Pakistan

  2. Ken Kukec
    Posted August 22, 2018 at 11:56 am | Permalink

    I nominate for Jerry’s weirdest headline.

    • mikeyc
      Posted August 22, 2018 at 12:26 pm | Permalink

      Ook. I read that as “weirdest hairline”.

      In my mind was Jon Stewart going; “whhhhaaaaaaaa?”

      • Ken Kukec
        Posted August 22, 2018 at 12:59 pm | Permalink

        Nah, for weirdest hairline, I nominate Trump white power ranger Stephen Miller.

        • Claudia Baker
          Posted August 22, 2018 at 3:06 pm | Permalink

          “white power ranger” – lol

          • mikeyc
            Posted August 22, 2018 at 3:30 pm | Permalink

            I giggled at that too.

  3. Joe Dickinson
    Posted August 22, 2018 at 12:11 pm | Permalink

    Interesting work.

  4. mikeyc
    Posted August 22, 2018 at 12:33 pm | Permalink

    From where I sit, the paper is behind a pay wall.

    • Michael Fisher
      Posted August 22, 2018 at 1:26 pm | Permalink


      “(abstract here but paper behind a paywall; judicious inquiry might yield you a pdf)”

      = ask for a pdf

      • mikeyc
        Posted August 22, 2018 at 1:42 pm | Permalink

        Oops. Missed that. derp

  5. Torbjörn Larsson
    Posted August 22, 2018 at 3:22 pm | Permalink

    Going with the biology topic, here is a potentially clarifying result on one of the site Honorary Cat Species&trade (I believe it is):

    “A newly-discovered fossil turtle that lived 228 million years ago is shedding light on how modern turtles developed these traits. It had a beak, but while its body was Frisbee-shaped, its wide ribs hadn’t grown to form a shell like we see in turtles today.”

    “”With Eorhynchochelys’s diapsid skull, we know that turtles are not related to the early anapsid reptiles, but are instead related to evolutionarily more advanced diapsid reptiles. This is cemented, the debate is over,” says Rieppel.”

    • Torbjörn Larsson
      Posted August 22, 2018 at 3:23 pm | Permalink

      Honorary Cat Species™

    • Christopher
      Posted August 22, 2018 at 6:52 pm | Permalink

      An excellent article, thank you so much for sharing! Turtle evolution is Fascinating, and they have been my favorite animal since I first picked one up (and was promptly bit on the thumb by it) and the pipefish are pretty cool as well.
      Two cool science stories for the price of one. Sweet deal.

  6. urthmothr
    Posted August 22, 2018 at 4:54 pm | Permalink

    Having some experience in animal behavior research, I’m curious about what hormones are triggered by the “more desirable” female so the male “chooses” to withhold resources from his current brood. I guess that’s the next step in the research.

  7. mikeyc
    Posted August 22, 2018 at 6:35 pm | Permalink

    Thank you Dr. PCC(e) for the PDF. I have read through it once now but will need further reading to assess their methods (will have to go over the data more before that). The paper is very well written; I mean the authors are skilled at writing in a way that non-experts can follow. It’s engaging and informative. It’s refreshing to see scientific papers written this way.

    Anyway, their lab experiments are more convincing than the field observations but I think they make the case that “syngnathid male pregnancy continues to show striking similarities with that of mammals as the brood pouch emerges as a privileged arena for selection and conflict.”

    They make some good points – the smallish effect they see on brood size undergoing this “Bruce effect*” can be understood in that unlike in mammalian examples of this “Bruce” effect, in syngnathids the female (who plays the role of the mammaliam male here) does not kill the offspring of her rivals, so it is not so surprising that the males would not institute a complete pregnancy block – there is advantage to having some of the “lesser” brood hatch. This is especially true since as syngnathid parents do nothing to raise their offspring, the male therefore doesn’t need to invest in anything post-partum. These features of syngnathian reproduction allow the males the opportunity to invest more of their brooding energy and resources to the broods with “better” potential while still allowing some of the “lesser” brood to survive. This is contrast to some mammalian examples.

    *I’m sorry but I can’t get out of my head the Python’s introductory line to the Australian wine skit; “Bruce, Bruce, Bruce and meself here are from Australia, land of sunshine and shaaaaaks”.

    • Christopher
      Posted August 23, 2018 at 9:12 am | Permalink

      Thanks for explaining the Bruce effect (disappointing that it had nothing to do with Springsteen), I’d never heard of it before this post. I’d also never heard of syngnathian either. An excellent addition to the post.

  8. Mark Sturtevant
    Posted August 22, 2018 at 9:42 pm | Permalink

    Perhaps it is limiting to do tests with pregnant male pipefish, so they could not do a range of tests. But I would have liked to see a broader range of tests rather than just better female / no female. Why not present the male with the [i]same[/i] female? That would assuredly be a female of equal quality & presumably the male would not know it was the same female. Do they then not reduce their current investment, or do they reduce their current investment? If the former, then that would be especially supportive of the Woman in Red hypothesis. If they reduce their investment, then male pipefish are mainly out there to spread their genes around.

  9. Posted August 23, 2018 at 8:34 am | Permalink

    Somewhere, somehow, someway, Todd Akin is feeling vindicated. He’s the Representative from Missouri who said victims of “legitimate rape” rarely get pregnant. (Akin later retracted his apology, and “defended his original comments.”)

  10. Posted August 23, 2018 at 11:40 am | Permalink

    I remember when an uncle of mine rented (early in the days of our social circle’s use of VCRs) _Lady in Red_ and was insisting that everyone see it, as the greatest thing ever.

    I cannot even remember a single thing from the movie!

  11. barn owl
    Posted August 23, 2018 at 1:42 pm | Permalink

    The neuroscientist in me is likely over-analyzing this study, but I’m trying to think of how the male pipefish can compare the size/attractiveness of the mother of his brood, with that of the new females. Does he have a visuospatial memory of the size or patterning of his prior mate (stored, natch, in his hippocampus) to which he can compare the appearances of the new females? Or is there some sort of visuospatial trigger point (if new female is longer than this line, dump your current babies)?

    Also, how could the wild pipefish cull embryos of a particular size? Dump them all out of the pouch and then sort the ones to put back in?

    • Posted August 24, 2018 at 11:51 am | Permalink

      Could they have a orifice of some kind that could be used as a filter?

      • barn owl
        Posted August 24, 2018 at 6:52 pm | Permalink

        I wonder if the male pipefish might sort the embryos with his mouth – certainly there would be enough sensory endings and a capability for oral stereognosis. I think pipefish, like seahorses, eat small crustaceans, fish, and other zooplankton, so there would already be neural mechanisms in place to accept/reject things by size and/or shape.

        • ThyroidPlanet
          Posted August 25, 2018 at 5:52 am | Permalink

          TIL the word “stereognosis”

  12. Posted October 12, 2018 at 4:23 pm | Permalink

    Poor embryos!

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