Evolution and adaptations of the Manta ray

The Manta ray is the largest of the ray species to inhabit earth’s ocean. These open ocean dwellers can grow to a record of 25ft in width, proving to be a huge spectacle when viewed in the wild. Mantas are know to be curious around humans and have even been viewed jumping out of the water. Although the reasons behind this is unknown. This huge wingspan allows to ray to glide effortlessly through the ocean, filtering water through is gills and feeding on plankton and fish larvae simultaneously and reaching speed of up to seven miles per hour. They also use their cephalic lobes when feeding to funnel water into their mouth, which is situated on the front of the rays disk shaped body. These feeding habits prove advantageous to the manta ray, as the oceans they inhabit, mainly warm tropical seas, are abundant in the microscopic animals the rays feed on.

But these characteristics haven’t always been present with the Manta ray, as it is believed that they have evolved from smaller, bottom dwelling rays. Such as the modern day stingray. Research has shown that due to competition or lack of food, the rays had to adapt their anatomy and change their feeding tactics in order to survive. This meant leaving the sea bed and reaching out to the open ocean.

One example of these adaptations is the Manta ray’s great size. Previous rays were much smaller than the modern day manta. The flattened shape of the ray however has been maintained. The flattened, disk shape body would have been advantages for previous rays when searching for food, such as mollusks and crustaceans (living on the sea bed), as they could swim flat against the bottom. It also allowed them to hide in sediment on the sea bed when hiding from predators. But as the ray evolved and moved to the open ocean they were able to grow too much greater widths, feeding on plankton and other small organisms.

Another difference between the modern day manta ray and its ancestor is the mouth was situated on the bottom of the ray’s body, instead of the front. This meant the ray could feed off the seabed whilst swimming, using it’s strong jaw and teeth to crush the shells of molluscs and crustaceans. As the rays moved to the open ocean, where food was free floating, this feature would be useless. This lead to the movement of the mouth, from the underside of the body, to the front. Allowing food to be filtered through the mouth, whilst the ray swam. Manta rays however have maintained their teeth, but they are used in courtship and mating and play no role in feeding. The shape of the ray’s mouth also changed, becoming much wider creating a large cavernous opening, to maximise the amount of food filtered through the gills when the manta is swimming. The cephalic lobes also developed. These are forward extensions of the cephalic fin and are used to funnel water into the mouth and can be seen in the image above.

Probably the most noticeable difference between the rays is the absence of a sting on the manta rays tail. A ray’s sting is used as a defense mechanism against predators, using a composition of enzymes, 5-nucleotidase and phosphodiesterase and the neurotransmitter serotonin. The enzymes cause tissue and cell death and serotonin causes severe muscle contraction. This would have been used when these rays were much smaller bottom dwellers, to defend from attack. Yet as rays moved to being larger pelagic mantas, they no longer required the sting to defend themselves and the sting was removed from the mantas tail, leaving a small indentation and a cartilage stump where the sting was situated. Yet Mantas do have predators, such as Orcas and large sharks.

References:

http://mcdougald.blogspot.com/2005/06/friday-manta-ray-blogging.html

http://www.elasmo-research.org/education/topics/lh_manta_faq.htm

http://underwaterhunters.blogspot.com/2009_05_01_archive.html

http://www.divetrip.com/manta_ray_bay.htm

8 years ago

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