you're reading...

Sharkbites Saturday

A Species Hiding in Plain Sight

Quattro, Joseph M., et al. “Sphyrna Gilberti Sp. Nov., a New Hammerhead Shark (Carcharhiniformes, Sphyrnidae) from the Western Atlantic Ocean.” Zootaxa, vol. 3702, no. 2, 2013, p. 159. doi:10.11646/zootaxa.3702.2.5.


Portnoy, David., et al. “Hybridization between a cryptic species pair, Sphyrna lewini and Sphyrna gilberti, in the western North Atlantic.” Sharks International Conference, João Pessoa, 3-8 June, 2018.


A Blast from the Past

Picture this, you are out collecting samples of sharks when you stumble across some individuals with some quirks; you were pretty sure what species they are, but now you’re not so sure. This is exactly what happened to fish biologist Dr. Carter R. Gilbert in 1967. Gilbert had caught several scalloped hammerheads (Sphyrna lewini), but when he started dissecting them, there were several individuals among them with noticeably less vertebrae in their backbone. Although this difference was noted, the scientific community attributed the difference to individual variation. Scientist would soon learn, however, that Dr. Gilbert was on to something.

Taking a Second Look

Scalloped Hammerheads off coast of Costa Rica Author: Barry Peters (Wikipedia)

Fast forward almost 40 years, scientists have new technology available to them, and the power to sequence and analyze DNA is now at their disposal. Dr. Joseph Quattro and colleagues captured 80 sharks along the coast of South Carolina from 2001 to 2003 that were identified as Scalloped Hammerheads. They sequenced the sharks’ DNA and took body measurements. In line with Dr. Gilbert’s findings, the team noted variation between the sharks’ physical characteristics. However, there was not enough evidence to indicate that these differences were more than variation between individuals. Once again, the only notable difference was in the number of vertebrae. However, the DNA told a completely different story.


DNA: The Key to Unlocking the Mystery

Model of a DNA double helix; Source: Public Domain

In this study, small pieces from the fins called fin clips were taken from the sharks. DNA was extracted from these pieces of tissue much like DNA can be extracted from a cheek swab in a kit to determine ancestry. When Quattro and his team analyzed the DNA, they found that the sharks were part of two genetically distinct groups, and that these were not just two distinct populations, but completely different species. So, in 2013 the team named the new species, Sphyrna gilberti, after the biologist who first noted these differences, Dr. Gilbert. As the new species was found off the coast of South Carolina, it has fittingly been called the Carolina Hammerhead. The Carolina Hammerhead is what biologists call a cryptic species, which is a species that looks almost identical to another species but is a genetically distinct species. Identifying whether a specimen is a Scalloped Hammerhead, or a Carolina Hammerhead requires genetic testing or lethal sampling, which makes estimating population sizes and distributions difficult.

An Answer that Unleashes More Questions

Diagram of a hybridization event; Created by: Jasmin Graham

Now that scientists know this hidden species exists, it has raised even more questions. Dr. David Portnoy recently gave a presentation at Sharks International, a conference of shark scientists, advocates and policy makers, in which he addressed some of these questions. Dr. Portnoy hopes to determine if these species mate, and if their offspring are capable of reproducing. Mating across two different species is called hybridization. There are several known species that hybridize. A hybrid that many are familiar with is a mule, which is the product of a male donkey and a female horse. Mules are hybrids that are sterile, or incapable of reproducing, but not all hybrids are sterile. Some hybrids can and do reproduce in the wild. If these two species are capable of mating and are doing so regularly, this has some serious conservation implications. Dr. Portnoy shared some preliminary data at the Sharks International conference, but we will all have to keep an eye out for his publication to see if he can provide some answers to these new questions.

Why Do We Care?

IUCN Risk Categories with abbreviations expanded by Peter Halasz (Wikipedia)

You may be asking yourself, why any of this matters. Who cares how many species of hammerheads there are out there? Who cares if there are two species that look identical? Who cares if they mate with each other? Aside from it being a window into an interesting phenomenon in the formation of species, it also has serious conservation implications.

The Scalloped Hammerhead, along with several other members of the hammerhead family, is an endangered species according to the International Union for Conservation of Nature (IUCN). To be listed as an endangered species, a species must have an extremely low population size and be at risk of extinction. There aren’t many Scalloped Hammerheads left, which we already knew, but there could be even lower numbers than previously estimated. Who knows how many Carolina Hammerheads were inadvertently counted towards the Scalloped Hammerhead population? There is not currently enough data on the Carolina Hammerhead population, but population sizes for this species are likely low as well. This means that policy makers may in fact be dealing with two endangered species instead of just one. In addition, if they mate, this raises even more questions: do hybrids have a similar, better or worse survival rate than each individual species? If they are mating, the number of hybrids could increase as the populations of both species continue to decline. There is much scientists don’t know about how these two species interact with each other or how they will interact in the future. Scientists also don’t yet understand what these interactions could mean in terms of their survival. There is much to be learned, but one thing is for sure: conservation of these hammerhead species just got a lot more complicated.


No comments yet.

Post a Comment


  • 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