you're reading...

Developmental Biology

Sex Change 101: it Starts in the Brain

Dodd, L.D., Nowak, E., Lange, D., Parker, C.G., DeAngelis, R., Gonzalez, J.A. and Rhodes, J.S., 2019. Active feminization of the preoptic area occurs independently of the gonads in Amphiprion ocellaris. Hormones and behavior, 112, pp.65-76.

Carpet Anemone with True Percula Clownfish and Blue Hepatus Tang by Brian Daniel Eisenberg. Licensed under CC BY-NC 2.0

The preoptic area (POA) is the portion of the hypothalamus responsible for regulating reproductive physiology and behaviour. During sexual development, the POA is completely restructured. Mammalian gonads are also completely restructured during development including maturation of eggs and sperm, and release of sexual hormones. Rat masculinization occurs following spikes in male sex hormones (known as androgens). Because estrogens, female reproductive hormones, are not secreted during development in the same way, mammalian feminization was long believed to be a passive process. This idea is now being challenged, but the signal to begin development is yet unknown. The concept of mammalian feminization is a typical chicken-or-the-egg type problem. Does the brain tell the gonad to begin sexual development? Or does the gonad tell the brain? Here, Dodd et al., use sequential hermaphrodite Amphiprion ocellaris, the common clownfish (a.k.a Nemo) to explore this concept.


Sequential hermaphroditism?

Clownfish form mating pairs with the female being the largest and most dominant in the group. When a new group is formed, dominance is established amongst the mature males. The dominant male will then undergo feminization, transforming into a female. If an existing group loses its female, then the mature male will transform into the dominant female, and one of the undifferentiated (immature) fish will mature into a male. Because clownfish development is easily manipulated (remove the female), they make excellent models for developmental biology.

Conceptual diagram of clownfish sequential hermaphroditism created by B. Biggar from images by Unknown Author, licensed under CC BY-NC-ND.


The Study

In a laboratory, thirty-four mature males were removed from their female partners and randomly paired up. Pairs were observed for the first hour after pairing, where individuals approached each other and began the battle for dominance. They were then observed every day until dominance had been established (within a few days). Once there was a clear hierarchical structure, pairs were sampled at 3 weeks, 6 months, 1 year, and 3 years for hormones in the blood; brain and gonad histology  were also examined at these times.


The Sex Change

Over the three years, the dominant fish grew, while the subordinate one did not, leading to a visible differentiation in morphology. The brain of the dominant fish began feminizing with an increase in the number of POA cells. Gonadal tissue degenerated in both members of the pair, possibly to divert energetic costs while reproduction was not necessary. In clownfish, mature males have the reproductive organs of both sexes (ambisexual). Testicular tissue makes up ~70% of the gonad, while non-vitellogenic (non-viable) eggs are ~30%. Throughout feminization, testicular tissue continues to degenerate until none is left. The final step to a successful sex change is fill the gonad with 100% vitellogenic-oocytes (viable eggs).  Despite plenty of evidence of sex change occurring, only three of the seventeen pairs completed gonadal sex change within the time frame of this study.

A, B. Length and weight of studied fish. Bars go between each pair. Symbols show the time since start of study. C, D. Length and weight vs sampling time. Horizontal bars represent the mean, vertical bars the confidence interval.


So… Which Comes First?

In this study, feminization of the POA occurred first. Male gonad tissue began degenerating early on but did not appear to be directly related to the sex change. Female gonad tissue did not differentiate until much later, and sexual hormones did not change until even after this! In other words, clownfish brains undergo sex change before the gonad; sometimes even years before!

It appears that sex change begins in the brain, and sex organs can remain ambisexual until some yet-unknown signal conveys the message to complete the process.


Back to the mammals

If these results hold true for mammals, we might expect female development to begin in the brain, possibly years before changes in sex organs. These results may not directly apply to mammals, but they give the first evidence of active feminization, an interesting story, and a good place to start with future work.


One Response to “Sex Change 101: it Starts in the Brain”

  1. Interesting study!

    Posted by Jacquie Biggar | August 22, 2019, 1:51 pm

Post a Comment


  • by oceanbites 2 months ago
    Happy Earth Day! Take some time today to do something for the planet and appreciate the ocean, which covers 71% of the Earth’s surface.  #EarthDay   #OceanAppreciation   #Oceanbites   #CoastalVibes   #CoastalRI 
  • by oceanbites 3 months ago
    Not all outdoor science is fieldwork. Some of the best days in the lab can be setting up experiments, especially when you get to do it outdoors. It’s an exciting mix of problem solving, precision, preparation, and teamwork. Here is
  • by oceanbites 3 months ago
    Being on a research cruise is a unique experience with the open water, 12-hour working shifts, and close quarters, but there are some familiar practices too. Here Diana is filtering seawater to gather chlorophyll for analysis, the same process on
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  on  #oceanbites  we are featuring Hannah Collins  @hannahh_irene  Hannah works with marine suspension feeding bivalves and microplastics, investigating whether ingesting microplastics causes changes to the gut microbial community or gut tissues. She hopes to keep working
  • by oceanbites 5 months ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 7 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 8 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 8 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 9 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 9 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 10 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 11 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 11 months ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
WP2Social Auto Publish Powered By : XYZScripts.com