//
you're reading...

Biology

Can sperm cells make it in an acidified ocean?

Paper: Schlegel, P., Binet, M. T., Havenhand, J. N., Doyle, C. J., & Williamson, J. E. (2015). Ocean acidification impacts on sperm mitochondrial membrane potential bring sperm swimming behaviour near its tipping point. Journal of Experimental Biology, 218(7), 1084–1090. doi:10.1242/jeb.114900

Background

Organisms that can’t move or don’t move much, like corals or sea urchins, can’t “get a room” and mate like many of the animals we’re familiar with. Instead, they use a tactic called broadcast spawning, which is exactly what it sounds like – female animals release eggs into the water column, male animals release sperm, and they rely on water mixing to do the rest of the work for them. This strategy has been successful for marine animals because they all release such large quantities of gametes: some of them are bound to collide. What hasn’t been accounted for, though, is how the changing climate might lead to changes in this time-tested system of reproduction. To close that gap in our knowledge, this study looked at how sea urchin sperm swimming might be affected by future ocean acidification conditions.

Some work has already been done on sperm in broadcast spawners under acidified conditions, but the results so far have been inconclusive – some studies have reported slower swimming, other studies have reported no effect or even an enhanced effect on swimming. Scientists have hypothesized that the low pH of the surrounding water is slowing the sperm’s metabolism, and that stops it from swimming as fast or as long as it normally would. The energy that a sperm needs to swim around to find an egg comes from adenine triphosphate (ATP), which is made in a specific structure in the cell, the mitochondria. The mitochondria have to be at an optimal pH to make ATP, so if the pH is different than what it usually is, there won’t be as much energy being made for cell functions. Actively swimming sperm need a lot of energy, so the mitochondria need to be working at their optimal pH levels to make fertilization happen.

Methods

To investigate how effective sperm are under ocean acidification conditions, these researchers induced spawning events in Centrostephanus rodgersii, a sea urchin found in Australia that’s similar to the California sea urchin (Figure 1).

Figure 1: Centrostephanus rodgersii

Figure 1: Centrostephanus rodgersii

Those spawning events were done in three treatments – control pH (conditions now), medium pH (conditions by 2100), and low pH (conditions by 2300). pH was changed by bubbling the water with CO2 gas. Once the sea urchins spawned in those three conditions, the researchers took some of the sperm and stained it so that they could see how much ATP the sperm was making. The staining changes the color of the sperm to correspond to how much energy the sperm can make, measured as the mitochondrial membrane potential (MMP) – a highly mobile sperm will glow brightly in green, and a lethargic sperm will glow a faint orange color. The rest of the sperm was put under a microscope to see how well it swam around under those three different conditions. Under the microscope, they measured the fraction of sperm that were motile (able to move spontaneously and actively – a process that consumes energy) and swimming speed.

Results

Figure 2 – sperm responded negatively to lower-pH conditions. The in response ratio measures how much the perm in the pH treatment varied form the control treatment, and values that are negative mean that the sperm were negatively affected by the simulated ocean acidification treatment.

Figure 2 – sperm responded negatively to lower-pH conditions. The in response ratio measures how much the perm in the pH treatment varied form the control treatment, and values that are negative mean that the sperm were negatively affected by the simulated ocean acidification treatment.

In all lowered pH conditions, the sperm struggled – the percent of sperm that were active, average swimming speed, and energy all dropped in the lowest pH treatment. Interestingly, the percent motility and the average sperm swimming speed increased in the medium pH treatment (the two positive points in figure 2), which the researchers attribute to the sperm source – some males had sperm that were better in acidified conditions.

The researchers also found a positive correlation between sperm motility and swimming speed with MMP, shown in figure 3. This pair of graphs suggests strongly that the reason that less sperm swam at slower speeds because of the reduced MMP – when the sperm don’t produce enough ATP in the mitochondria, they’re unable to move as fast.

Figure 3 – relationship between sperm swimming speed (A), percent motility (B) and MMP. This graph shows that as the MMP of the sperm increases (represented by the FL2/FL1 ratio), so will the sperm’s swimming speed and the percent motility of all the sperm as a whole.

Figure 3 – relationship between sperm swimming speed (A), percent motility (B) and MMP. This graph shows that as the MMP of the sperm increases (represented by the FL2/FL1 ratio), so will the sperm’s swimming speed and the percent motility of all the sperm as a whole.

 

Discussion

Animals can usually tolerate a stressor like low pH up to a certain tipping point – at that point, whatever stressor it is will completely overwhelm the animal and it will be unable to perform it’s normal function. The researchers think that the pH levels expected by 2300 (the high treatment) is beyond the tipping point for these sea urchin sperm.

The reason the researchers saw the decrease in sperm swimming speed, motility, and MMP is because the delicate environmental balance inside the animal was disrupted. All animals, whether an amoeba or a sea urchin or a human, have to maintain an optimal cell environment for biochemical pathways such as ATP production to work. If something changes in the cell environment, such as a lower pH or a decreased temperature or increased salts, the cell machinery won’t function like it should – kind of like your phone not working when it gets too hot. Since these sea urchin sperm are exposed to an acidic environment, their cell machinery and pathways (the MMP) are not working the way they should and the sperm isn’t able to swim as well to find the egg it needs.

Interestingly, the researchers remind us that a decreased energy metabolism (represented by the MMP) means that the sperm can live longer. When the sperm isn’t using or producing as much energy, it saves its energy resources and can survive longer in the water column. That means that there could be an increase in sperm-egg fertilization – kind of like the tortoise and the hare, the slower swimmers might find an egg because they’ve got a longer time to do so. That could be good news for this species under ocean acidification, but there needs to be more work done with fertilization experiments to see if that really is the case.

What do you think? Will the slower, longer lived sperm help the species in the long run, or will the species suffer because their sperm aren’t fast swimmers?

Discussion

No comments yet.

Post a Comment

Instagram

  • by oceanbites 3 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 4 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 5 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 6 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 6 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 7 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 7 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 8 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 8 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 8 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 8 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 8 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 9 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 9 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 10 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 11 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 11 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 11 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 12 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 1 year 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