Patterns of Evolution Ever wondered why birds and

Patterns of Evolution

Ever wondered why birds and mosquitoes both have wings, even if they aren’t related? The answer lies in today’s lesson. Today we’re going to learn about convergent and divergent evolution.

Convergent evolution occurs when two or more unrelated species evolve to develop similar adaptations as a result of being subject to similar selection pressures (factors which may reduce reproductive success).

Selection pressures are environmental factors which may reduce reproductive success in a population. Examples of selection pressures include: Disease Parasitism Pollutants Competition predation

Convergent evolution results in analogous structures with different origins but have evolved to appear similar or have similar functions.

Examples of convergent evolution are the wings of birds, dolphins and sharks, and many species of alpine plants.

Divergent evolution, however, occurs when two or more species arises from a common ancestor due to different ecological niches, usually by allopatric speciation. RECAP: Allopatric speciation is the process where new species are formed from one common ancestor while in different geographical areas.

Different selection pressures in the different environments results in the two populations diverging. Different phenotypes get selected for to meet the demands of the different environments, resulting in the production of two new species. RECAP: Phenotype is an organism’s observable traits.

Divergent evolution Take notes

Divergent evolution produces homologous structure. These are anatomical structures that have the same origins but have evolved different functions. For example, the forelimb bones of crocodiles, birds, humans, whales, bats and all other vertebrates are the same and are arranged in a similar pattern, but the limbs perform different functions in each animal.

Homologous structures show us that evolution works primarily by modifying pre-existing structures.

Adaptive radiation is a type of divergent evolution. It is a process in which organisms change rapidly from an ancestral species into an abundance of new forms.

Summary notes of Convergent/Divergent Evolution Practice question Work through the ‘Land lobsters and Metrosideros trees – patterns of evolution’ question.

Parallel evolution and Co-Evolution There are two more patterns of evolution that you need to know about. Along with divergent and convergent evolution, you need to know about parallel evolution and co-evolution.

Coevolution is used to describe cases where two (or more) species reciprocally affect each other's evolution. Each party in a co-evolutionary relationship exerts selective pressures on the other and, over time, the species become mutually dependent on each other. Bees are excellent pollinators and collect nectar from many flower types. Coevolution is a likely consequence when different species have close ecological interactions with one another. These relationships include: Predator-prey relationships Parasite-host relationships Mutualistic relationships such as those that have arisen between plants and their pollinators (photos, right). Beetles are an ancient group with many modern species. Their high diversity has been attributed to coevolution with flowering plants.

Acacia-Ant Coevolution Flower structure has evolved in many different ways in response to the many types of animal pollinators. Ant This makes it relatively easy to deduce pollinator type from the appearance of flowers (and vice versa). Plants and animals involved in such pollination associations often become highly specialized in ways that improve pollination efficiency: innovation by one party leads to some response from the other. Thorn Swelling The long, hollow thorns of the swollenthorn Acacia provide living space for the aggressive stinging Pseudomyrmex ants which patrol the plant and protect it from herbivores. The Acacia provides the ants with protein-rich food. Photo courtesy of Alex Wild Flowers and their pollinators have coordinated traits known as pollination syndromes.

Flowers and their Pollinators Flower structure has evolved in many different ways in response to the many types of animal pollinators. Flowers and their pollinators have coordinated traits known as pollination syndromes. This makes it relatively easy to deduce pollinator type from the appearance of flowers (and vice versa). Plants and animals involved in such pollination associations often become highly specialized in ways that improve pollination efficiency: innovation by one party leads to some response from the other. The sweet fragrance of many flowers is attracts their nectar seeking pollinators, but flowers pollinated by many flies can give off dung or rotten meat smells.

When organisms that are ecologically intimate, they influence each other’s evolution. We say that coevolution is occurring. Predators and prey, hosts and parasites are examples of ecologically intimate organisms.

So for example, an evolutionary change in the biology of a plant, might affect the biology of a herbivore that eats the plant, which in turn might affect the evolution of the plant, which might affect the evolution of the herbivore…and so on.

Us humans are an excellent example of co-evolution. We often selfishly benefit ourselves, while changing other species. For example, the giant panda bears found in Asia, are becoming more and more endangered. This is largely due to the immense population China has. Losing that species then affects many other species.

Predators and Coevolution Predators have evolved to exploit prey; hunting ability is paramount so they have adaptations to improve hunting efficiency, including: Speed, strength, and stamina Good vision and hearing Offensive weapons (teeth, claws) Hunting strategies such as group cooperative behavior Prey have evolved numerous strategies to protect themselves from predators, including: Large size and strength Protective coverings Defensive weapons (e. g. horns) Toxicity Lions may hunt cooperatively to increase their chances of securing a kill from swift, herding species such as zebra.

In situations such as predator/prey, host/parasite, the fitness of one organism directly impacts the fitness of the other. For example, the increase in the speed of the gazelle will make it more difficult for the lion to feed itself (a decrease in fitness), while the same increase in speed provides an obvious increase in fitness for the prey.

The organisms are therefore exerting a selection pressure on one another: faster gazelles create a selection pressure for a faster or smarter lion, which in turn selects for even greater prey speed.

Coevolution and Mimicry Palatable insect species may evolve to resemble toxic or unpalatable species. This is called Batesian mimicry. Plants may evolve mimicry to protect themselves from herbivores: The dangerous common wasp …and its harmless Batesian mimic, the wasp beetle Photo courtesy of Missouri Botanical Gardens Female Helicornius butterflies will not lay their eggs on plants already occupied by eggs, because their larvae are cannibalistic. Passionfruit plants have exploited this by creating fake yellow eggs on leaves and buds. Passionfruit plant (Passiflora) with egg mimics

Parasites and Coevolution Trypanosomes provide an example of host-parasite coevolution. They must evade their host defenses, but… Virulence is constrained because they must keep their host alive. Photo courtesy of CDC Molecular studies show that Trypanosoma brucei coevolved in Africa with the first hominids around 5 mya. However, T. cruzi contact with human hosts occurred in South America only after settlements were made by nomadic cultures. Trypanosome parasites in human blood

Watch Coevolution Take notes

Parallel evolution occurs when species share a common ancestor (but not related) and evolve in similar ways independent of other species. Parallel evolution

Parallel evolution happens because the two different species, though they don’t necessarily share a common ancestor, experience similar kinds of environmental pressures and survive only by undergoing similar adaptations.

There is no clear-cut distinction between parallel and convergent evolution, since the degree of relatedness between evolutionary starting points may vary from very close, to very distant. The closer the evolutionary starting points, the more convergent evolution merges with parallel evolution.

A good example of parallel evolution is elephants and extinct mammoths. Both animals are closely related but their similarities evolved independently.

Tasks Draw a table comparing the different types of evolution. Explain the difference between parallel evolution and convergent evolution.