Locomotion, the movement of organisms through their environment, is not only a defining characteristic of life but also a crucial component for the survival and propagation of species. This section elaborates on the reasons organisms have developed the need for movement and sheds light on the awe-inspiring adaptations marine mammals have embraced to conquer aquatic realms.
Reasons for Locomotion
While movement might seem like a basic function, the reasons for such motion are vast and often complex. Here, we’ll delve deeper into why various species find it necessary to move.
Foraging for Food
- Herbivores: Creatures like the African elephant trek large distances in search of foliage, moving to new areas when resources become scarce. Elephants may even remember and revisit locations where they previously found ample food.
- Carnivores: Predatory animals such as the Arctic polar bear cover expansive areas hunting for seals. Their keen sense of smell and sight drive their movements as they seek out prey.
- Omnivores: Species like raccoons change locations based on the availability of both plant and animal food sources.
Image courtesy of Rod Waddington
Escaping from Danger
- Speed: Gazelles utilise their rapid speed to escape cheetahs, one of the fastest predators. Their agility and acceleration are crucial to evading capture.
- Camouflage and Hide: Creatures like the chameleon adapt their colours to blend into their environment, reducing the need for rapid movement but employing short bursts when necessary.
- Group Movement: Schools of fish move synchronously, creating an illusion of a larger organism, deterring potential predators.
Image courtesy of Chiswick Chap
Searching for a Mate
- Territorial Movements: Male lions patrol their territories, ensuring no rivals are attempting to woo their pride’s females.
- Mating Calls and Displays: Birds like the peacock use elaborate tail displays, coupled with specific movements, to attract potential mates.
- Migration for Mating: Certain species, like the Atlantic salmon, migrate hundreds of miles to return to their birthplace for spawning.
Image courtesy of Jebulon
Migration
- Seasonal Changes: Birds such as the Arctic tern migrate from the Arctic to the Antarctic, chasing endless summer and ensuring ample food supply.
- Breeding Grounds: Sea turtles return to the very beaches where they hatched, covering vast oceanic distances, to lay their eggs.
- Avoiding Predation: Planktonic migrations occur daily in oceans, where tiny organisms move vertically in the water column to evade predators.
Image courtesy of Rasmussen29892
Adaptations for Swimming in Marine Mammals
The world beneath our oceans’ surfaces is vast and challenging. For marine mammals to thrive, specific evolutionary changes have proven necessary.
Streamlining
- Body Shape: Creatures like the orca, or killer whale, showcase a torpedo-like shape, reducing resistance as they move through water, conserving energy.
- Smooth Skin: Most marine mammals have smooth skin, often with a covering of tiny, streamlined hair, further reducing drag.
Limb Adaptations for Flippers
- Forelimbs Morphology: The bones in the flippers of marine mammals like the humpback whale show homology with terrestrial mammals, but they are flattened and elongated for effective swimming.
- Hindlimb Evolution: Over time, the hindlimbs of many marine mammals have regressed or disappeared, as seen in whales. In seals, they've evolved into rudders for steering.
Tail Adaptations for Flukes
- Enhanced Musculature: The tail region of dolphins contains a powerhouse of muscles, allowing them to achieve impressive speeds and make sharp turns.
- Fluke Efficiency: The flukes, being flat and horizontal, enable up-and-down motion, which is more energy-efficient than the side-to-side movement observed in fish.
Changes to Airways for Periodic Breathing
- Breath Holding: Marine mammals like the sperm whale can hold their breath for over an hour, diving deep to hunt squid.
- Efficient Oxygen Use: A higher concentration of haemoglobin and myoglobin in their muscles allows marine mammals to utilise oxygen more effectively.
- Exhalation and Inhalation: The forceful exhalation, visible as a spout in whales, quickly expels carbon dioxide and facilitates rapid inhalation of fresh air.
FAQ
The difference in tail orientation between fish and marine mammals is a result of their evolutionary lineage and locomotive needs. Fish, having evolved in water, have vertically oriented tails (caudal fins) that move from side to side during swimming. This movement is efficient for rapid acceleration and quick turns, essential for both predator and prey fish species. Marine mammals, however, evolved from terrestrial ancestors. When they transitioned back to aquatic habitats, their spine's movement adapted to an up-and-down motion, resulting in horizontally oriented tails or flukes. This movement is more energy-efficient for long-distance swimming and sustained speeds, aligning with the needs of marine mammals.
While speed is a significant advantage, gazelles employ other strategies to increase their evasion success. One such tactic is 'stotting' or 'pronking', where the gazelle leaps high into the air with stiff legs. This behaviour serves multiple purposes: it can signal to predators that the gazelle is fit and would be a challenging chase, potentially deterring the pursuit. It also provides the gazelle with a broader view of its surroundings, helping it identify escape routes. Additionally, zig-zag running or sudden change in direction during a chase can throw off predators, making capture more difficult. These combined strategies, coupled with speed, enhance the gazelle's chances of evading threats.
Counter-shading is a type of camouflage seen in many marine animals, including some marine mammals like sharks and dolphins. The animal's dorsal (top) side is darker than the ventral (bottom) side. This gradient in colouration offers a dual camouflage mechanism. When viewed from above, the darker dorsal side blends with the deep ocean waters. Conversely, when viewed from below, the lighter ventral side matches the brighter surface water, illuminated by sunlight. This adaptation aids marine mammals in evading predators and, for predatory species, in approaching prey without being easily detected.
Marine mammals often need to dive deep and stay submerged for extended periods, necessitating adaptations for efficient oxygen storage. A higher concentration of haemoglobin in their blood and myoglobin in their muscles facilitates this. Haemoglobin binds to oxygen in the lungs and transports it to tissues, while myoglobin stores oxygen within muscle cells. With elevated concentrations of these proteins, marine mammals can store more oxygen, supporting their bodily functions during long dives. This adaptation is particularly beneficial for deep-diving species, like sperm whales, enabling them to remain submerged and hunt for prolonged durations without frequent trips to the surface to breathe.
Marine mammals have developed specialised adaptations to combat the cold temperatures of aquatic habitats. One primary adaptation is the presence of blubber, a thick layer of fat situated beneath the skin. This blubber not only serves as an energy reserve but also acts as a critical insulator, preventing heat loss and ensuring the core body temperature remains stable. Furthermore, many marine mammals exhibit counter-current heat exchange in their flippers and fins. This system ensures that cold blood returning from the extremities gets warmed by the outgoing warm blood, thereby minimising heat loss. These adaptations are essential for marine mammals, such as seals and whales, allowing them to thrive in chilly aquatic environments.
Practice Questions
Animals exhibit locomotion primarily for foraging for food and escaping from danger. Foraging is the act of searching for and obtaining food, a crucial behaviour for survival. For instance, the African elephant, a herbivore, often travels vast distances in search of foliage, moving to regions with abundant resources when food becomes scarce in one location. On the other hand, escaping from danger is vital for organisms to evade predators. The gazelle exemplifies this, using its remarkable speed and agility to escape predators such as cheetahs. Their rapid acceleration and swift movements are essential in avoiding capture and ensuring survival.
One significant adaptation marine mammals have developed for swimming is the evolution of streamlined body shapes. The streamlined, torpedo-like shape of organisms like the orca, or killer whale, reduces resistance as they move through water. This reduction in drag conserves energy, allowing the orca to swim efficiently at high speeds and travel long distances in search of food or during migrations. Additionally, a streamlined body also aids in stealth, enabling predators like the orca to approach prey without creating much disturbance in the water. This evolutionary feature is crucial for the orca's hunting success and overall survival in marine ecosystems.
