Nile Crocodiles May Look Tough, But They Can Be Sensitive Too
July 2, 2013

Nile Crocodiles May Look Tough, But They Can Be Sensitive Too

Brett Smith for - Your Universe Online

Crocodiles may look tough, but they can also be very sensitive -- particularly when it comes to detecting touch, temperature, or chemicals in their watery environment.

Previous research has shown that crocodilians, which includes alligators, gharials and caimans, detect a multitude of information through integumentary sensory organs (ISO) found in their skin and a new study recently published in the journal EvoDevo has revealed how these organs work in greater detail.

According to study authors from the University of Geneva in Switzerland, ISO capabilities of crocodilians are unparalleled in any other vertebrate.

"ISO sensors are remarkable because not only are they able to detect many different types of physical and chemical stimuli, but because there is no equivalent in any other vertebrates," said co-author Michel Milinkovitch, a professor of genetics and evolution at the university. "It is this transformation of a diffuse sensory system, such as we have in our own skin, into ISO which has allowed crocodilians to evolve a highly armored yet very sensitive skin."

Crocodilians have evolved tough epidermal scales and bony plates to defend against rivals and would-be predators. The protective scales are the result of cracked, hardened skin -- their shape being determined more by chance than genetics. The scales do have genetically expressed and highly sensitive dome pressure receptors (DPR) or ISOs.

The study researchers examined the formation and function of ISOs in Nile crocodiles (Crocodylus niloticus) and the spectacled caiman (Caiman crocodilus). The team found ISOs appear on the head of both embryonic caimans and crocodiles before their skin begins to crack and develop into scales. Nile crocodiles go on to develop ISOs all over their body.

Using molecular techniques, the Swiss team was able to locate the neurons which interact with the ISOs. They noted markers usually found in many different kinds of neurons were present in the tiny organs.

The researchers also used electrophysiology to better understand the nature of ISOs. The technique involves recording nerve impulses while applying a variety of stimuli. These results confirmed the molecular findings, the researchers said.

In both animals the ISOs are capable of detecting mechanical, thermal and chemical information, giving them the combined ability to detect a wide range of information, except for salinity. Nile crocodiles are able to detect salinity using salt glands on their tongues. This information helps them to adjust osmolarity in their hyper-saline environments.

Mechanical information from the ISOs allows the animals to sense surface waves and find prey, even at night. The thermal information tells the reptiles when to maintain body temperature by either basking in the sun or cooling in the water. The chemical sensors may help them to sense the most habitable environments, the researchers said.

Nile Crocodiles live throughout Sub-Saharan Africa and are considered to be the second largest reptile in the world. Although it can live in salt water environments, the croc prefers freshwater deltas and brackish water. Nile crocodiles are aggressive predators, but also highly social within their own species, often sharing basking areas and even large prey.