//
you're reading...

Biology

How the anglerfish gets its light

Paper:   Baker, L. J., Freed, L. L., Easson, C. G., Lopez, J. V, Sutton, T. T., Nyholm, S. V, & Hendry, T. A. (2019). Diverse deep-sea anglerfishes share a genetically reduced luminous symbiont that is acquired from the environment. Elife, 8:e47606, 1–21. 

 

Just a few of the many examples of bioluminescent organisms including a) bacterial colonies (image from wikimedia) b) fungi (image from wikipedia) c) a firefly (image from wikimedia) and d) a pyrosome (image from wikipedia

Organisms living in the inky black waters of the deep-ocean see no sunlight – they live at depths far greater than warm, life-breeding sunlight can penetrate. Yet, these animals are not condemned to a life devoid of light. Many animals make their own light in a process known as bioluminescence.

In fact, bioluminescence is common in our world and found even in shallow waters and on land. A wide variety of organisms have evolved the capacity to create light: bacteria, insects, fungi, and fish are just some of the individuals that use bioluminescence. These organisms can either produce their own light (as is the case for lanternfishes and dragonfishes) or they rely on help from other organisms, called symbionts. Oftentimes, symbionts are bacteria capable of producing their own bioluminescence. An animal that cannot inherently produce its own bioluminescence may instead develop a symbiotic relationship with bacteria – the animal provides a safe home for the glowing bacteria somewhere in its body and, in exchange, the bacteria provides the animal with  the bioluminescent glow it could not otherwise produce.

 

The wonders of the weird and wacky anglerfish

Of course, one of the most notorious bioluminescent critters is the anglerfish, named for the glowing lure which protrudes from its head. There are over 160 species of deep-sea anglerfishes living in the deep, bathypelagic waters of our ocean (between 1000-4000 m below the surface). While their striking (and, admittedly, slightly spooky) appearance has garnered the fish widespread attention, we still do not know a whole lot about anglerfish biology because they live in waters that are often too deep for scientists to reach. Only a few anglerfish have been caught on video in their natural habitat and most of our knowledge of these fish comes from specimens that are caught in nets and preserved for later examination.

– Just a few examples of the many different species of bioluminescent anglerfishes (image from wikimedia commons)

The little that we do know about these fish is pretty dang cool, though. Anglerfish live in the deep-ocean where there is no sunlight, extremely high pressures, and extremely low temperatures. Only female anglerfish are bioluminescent and rely on bacterial symbionts to produce their light. Anglerfish appear to live mostly solitary lives; except, of course, once they have found a mate. It can be hard to find a suitable mate in a vast, dark ocean (especially without the help of an anglerfish tinder) so when a male anglerfish finds his preferred female companion, he grabs on and doesn’t let go. Literally. Male anglerfish, which are much smaller than their female counterparts, will bite onto the female’s body, attaching itself for the rest of its life. In some species, the attachment is so complete that the male’s body fuses to the female and he becomes a parasitic mate. When the female is ready to breed, the male is conveniently already there to fertilize her eggs, which she lays in an egg raft that will float up into the sunlit waters of the upper ocean. The baby anglerfish will hatch and grow, eventually making their way back into the deeper ocean waters and females will develop their prominent lure.

How do you turn this thing on?

While scientists have long-known that female anglerfish are bioluminescent and rely on bioluminescent bacterial symbionts to, they still do not know exactly why anglerfish produce light – whether to attract prey and mates or to avoid and confuse predators – and how the anglerfish acquire the help of their glowing bacterial symbionts in the first place.

Organisms (the host) can obtain bacterial symbionts either by 1) coming in contact with bacteria in the environment and then assimilating these bacteria into their own body or 2) through direct transmission from other individuals – usually when a parent directly passes the bacteria on to its offspring (called “vertical transmission”). Because some bacteria are directly passed down from parent to offspring through the generations they can co-evolve with their host species. The bacteria may become specifically adapted to living within a host and might lose the ability to function independently in the environment (termed obligate symbionts). For instance, they might lose genes that allow them to grow cell walls or structures that can help them move around.  On the contrary, bacterial symbionts that are typically acquired through environmental contact are usually perfectly capable of living on their own, but are also able to live symbiotically within a host (termed facultative symbionts).

Scientists do not know how anglerfish obtain their symbionts or if the bacteria are obligate or facultative symbionts. There are two species of bacteria which form symbiotic relationships with anglerfishes – both within the genus Enterovibrio (side note: while the bioluminescent symbionts are beneficial, other species of bacteria in this order cause human illnesses, including cholera). Interestingly, both of these bacterial species have small genomes (50% smaller than their relatives) and lack some common genes found in species that live independently in the environment (like those used for motility). This small genome size suggests these bacteria would be obligate symbionts that are handed down vertically from parent to offspring, but what we know about anglerfish life-history seems to preclude this possibility. Larval and juvenile anglerfish have little to no contact with adults and do not even have a lure to house these bioluminescent bacteria until later in life. So how and when do anglerfish acquire their bacterial symbionts and achieve the ability to glow?

Illustration of a female humpback anglerfish (image from wikipedia)

 

Have bioluminescent bacteria evolved within their anglerfish hosts?

A team of scientists headed by researchers at Cornell and Nova Southeastern Universities had to take a novel approach to answer this question. Given the serious challenges of studying anglerfish and their bacterial symbionts in the field or lab, the team turned to genetic tools to investigate how different anglerfish species and their symbionts were related to one another.

The team examined 6 different groups of anglerfishes and the bioluminescent bacteria living within their lures. The researchers expected that if bacteria were handed down from parent to offspring (acquired through vertical transmission), the bacteria would have evolved within their specific host species. Therefore, different lineages of the bacterial symbiont would be different from one another but their evolution would mirror the evolutionary lineages of the anglerfish species. On the other hand, if the bacterial symbionts were acquired through the environment, these bacteria would not have evolved within a specific host species and the bacterial lineages would be more similar to one another, regardless of the anglerfish host they had colonized.

After analyzing the genetic sequences of the anglerfish and their symbionts, the scientists were able to see how they were all related to one another. They found that the bacteria did not drastically differ from each other, despite the evolutionary differences of their anglerfish hosts. This finding suggests that the bacterial symbionts do not evolve within their hosts and are not vertically transmitted from parent to offspring, but rather that anglerfish must be acquiring their symbionts directly from the environment. To verify this possibility, the scientists took water samples at locations where anglerfish were found. They discovered the species of symbiotic bacterial present in the water, further supporting the hypothesis that anglerfish obtain their symbionts from the environment

While this discovery helps to answer some questions about anglerfish biology, it uncovers just as many about their symbiotic bacteria. It is astonishing that these symbiotic bacteria, which appear to lack some of the critical machinery to live independently in the ocean, are able to persist in the environment for long enough and over a wide enough range to be picked up by anglerfish hosts. Scientists must conduct more research to illuminate the complicated relationship between anglerfish and their glowing bacterial symbionts.

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 9 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 12 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