What is Adaptation?

Definition of adaptation in biology

The definition of adaptation is:

Adaptation does not include an organism learning new behaviours unless these new behaviours are the result of a feature that is heritable (can be passed on to the next generation).

Depending on which exact aspect of adaptation is being considered, adaptation can be defined in three different ways in biology. Adaptation includes:

1. Evolution through Natural Selection that increases an organism's level of fitness.

2. The actual adapted state achieved through evolution.

3. The organism's observable (phenotypic) features or traits that have adapted.

Along with Speciation, adaptation allows for the massive diversity of species we have on Earth.

Features are adaptations

Phenotypic features, or traits, that are heritable are the adaptations we are concerned with in biology. Examples of phenotypic traits include everything from eye color and body size to the ability to thermoregulate and the development of certain structural traits, such as beak and snout morphology, as we describe in the next sections.

An organism’s traits or features are initially given by its genetic makeup or genotype. However, not all genes are expressed, and an organism’s phenotype depends on what genes are expressed, and how they are expressed. The phenotype depends on both the genotype and the environment.

Importance of adaptation in biology

Adaptation is vital for species' survival. Every living organism must adapt to its environment and find its Ecological Niche in order to survive. Adaptations allow organisms to survive in specific, sometimes even harsh, climates. They allow organisms to avoid predation through the development of camouflage or aposematism.

Adaptations can also give predators advantages, such as increased size, speed, and strength, as well as the development of specialized jaws or venom glands.

Another example would be the Indian gharial, which evolved a slender, sharp-toothed jaw in order to specialize in fish predation, rather than the more generalized diet of many other crocodilian species that have bulkier snouts.

Types of adaptations

Adaptive traits can involve an organism's behaviour, physiology, or structure, but they must be heritable. There can also be co-adaptations. We will discuss these in more detail below.

• Behavioural adaptations are actions that are hardwired into an organism from birth, such as hibernation and migration.
• Physiological adaptations are those that involve internal physiological processes, such as thermoregulation, venom production, saltwater tolerance and much more.
• Structural adaptations are usually the most visually apparent of adaptations and involve the evolution of structural modifications that change an organism's appearance in some way.
• Co-adaptation happens when a symbiotic evolutionary relationship for adaptation occurs between two or more species. For example, hummingbirds and many flower species have evolved adaptations that are mutually beneficial.

Examples of adaptations in biology

Let's see some examples for each type of adaptation we described above.

Behavioural adaptation: hibernation

Woodchucks (Marmota monax), also known as groundhogs, are a marmot species native to North America. While they are active during the summer months, they enter a prolonged period of hibernation from late fall to early spring. During this time, their internal temperature will decrease from around 37°C to 4°C!

Furthermore, their heartbeat will plummet to a mere four beats per minute! This is an example of a behavioural adaptation that allows woodchucks to survive harsh winters when little of the fruit and vegetation they consume is available.

Behavioural adaptation: migration

The blue wildebeest (Connochaetes taurinus) (Fig. 2) is a species of antelope native to Sub-Saharan Africa. Yes, despite their bovine-like appearance, wildebeest are actually antelopes.

Every year, blue wildebeest take part in the largest herd migration on Earth, when more than a million of them leave the Ngorongoro Conservation Area of Tanzania to travel across the Serengeti to the Masai Mara of Kenya, quite literally in search of greener pastures, due to seasonal rainfall patterns. The migration is so large that it can actually be seen from outer space!

Along the way, the wildebeest face predation from many large predators, particularly African lions (Panthera leo) and Nile crocodiles (C. niloticus).

Figure 2: Every year, over one million blue wildebeest take part in the largest herd migration on Earth. Source: Wiki Commons, Public Domain

Physiological adaptation: saltwater tolerance

The saltwater crocodile (C. porosus) is the world's largest reptile and, despite its common name, is a freshwater species (Fig. 3). True marine crocodiles went extinct millions of years ago.

It gets its common name from the fact that individuals from this species can spend extended periods at sea and commonly utilize it as a means of transport between river systems and islands. This sea-faring ability has allowed the species to colonize numerous islands in two continents, with a distribution ranging from eastern India through Southeast Asia and the Indo-Malay Archipelago to the easternmost Santa Cruz group of the Solomon Islands and Vanuatu!

In addition, individual crocodiles have been found well over 1000 miles from the nearest resident Populations on islands in the South Pacific, such as Pohnpei and Fiji.

Figure 3: A saltwater crocodile (right) and an Australian freshwater crocodile (C. johnstoni) (left) far upstream in the freshwater section of a river. Despite its common name, the saltwater crocodile is a freshwater species. Source: Brandon Sideleau, own work.

How is a freshwater species like the saltwater crocodile capable of surviving long periods at sea? By maintaining ionic Homeostasis through the use of specially adapted lingual salt excreting glands, which expel the unwanted chloride and sodium ions.

These salt-excreting glands are also present in some other crocodile species, most notably the American crocodile (C. acutus), which has a very similar Ecology to the saltwater crocodile, but is absent in alligators.

Structural adaptation: tusks

An interesting but less known example of an animal with a structural adaptation is the babirusa.

Babirusas (Fig. 4) are members of the Babyrousa genus in the Suidae family (which includes all pigs and other swine) and are native to the Indonesian island of Sulawesi, as well as some smaller neighbouring islands. Babirusas are visually striking due to the presence of large curved tusks on males. These tusks are large canines that grow upward from the top jaw and actually penetrate the skin of the upper snout and curve around toward the eyes!

Of all extant mammal species, only the babirusa has canines that grow vertically. Since the only natural predators that babirusas face are crocodiles (for which the tusks would provide no defence), it has been suggested that the tusks evolved not as a defence from predators but rather to protect the face and neck during competitive battles with other males.

Figure 4: An artist's rendering of a babirusa. Note the curved tusks penetrating the upper snout. Source: Wiki Commons, Public Domain

Co-adaptation: flower pollination by hummingbirds

The trumpet creeper (Campsis radicans) of North America is often referred to as the "hummingbird vine" due to how attractive it is to hummingbirds. These trumpet creepers have actually evolved traits, including red colouration, that attract hummingbirds, particularly the ruby-throated hummingbird (Archilochus colubris) (Fig. 5). Why? Because hummingbirds pollinate the flowers.

The hummingbirds also developed adaptations of their own to aid in the procuring of the flower's nectar in the form of changes to beak size and shape.

Figure 5: The ruby-throated hummingbird (left) and the trumpet creeper (right) have developed mutually beneficial adaptations. This is known as co-adaptation. Source: Wiki Commons, Public Domain

Now, I hope that you feel more confident in your understanding of adaptation!