Convergent Evolution -What Is It?

Convergent evolution – an introduction

Snowy owls (Bubo scandiacus)

Bubo scandiacus male snowy owl sitting on a branch

…and Polar bears (Ursus maritimus) inhabit Arctic and sub-Arctic regions.

Polar bear (Ursus maritimus) jumping on Spitsbergen Island, Svalbard, Norway

Both species are predators…

snowy owl (bubo scandiacus) attacks lemming

Attacking a lemming

…that rely on surprise to catch their prey.

polar bear (Ursus maritimus) catching a seal

Both species have white coats which make them effective hunters able to stalk their prey unnoticed…

snowy-owl-on-the-fields© christophermartinphotography.com

…by blending into the harsh environments in which they live.

polar bear on ice flows seen from a distance is an example of convergent evolution because it has a white coat like owls©lifeonthinice.org

The ancestral color of Snowy owls and Polar bears was brown; their white coloration is an adaption that both species have evolved.

Snowy owls are descended from brown coated ancestors that lived in North Africa four million years ago. Snowy owls are the only owls of the Bubo genus to have evolved white coats.

Owls from the Bubo genus

Owls from the Bubo genus

When their brown coated ancestors started hunting in Arctic habitats 3.5 million years ago, it was the light coated individuals that were the more successful hunters.

The evolutionary pressure was to evolve lighter and lighter colored coats until a new species with a white coat appeared -the Snowy owl.

Similar selection pressures drove the evolution of the Polar bear. It is believed that the Polar bear split from a brown bear ancestor during the Paleolithic era between 479,000 and 343,000 years ago.

It was at that time that the Polar bear’s ancestral species, the brown bear (Ursus arctos)

Alaska Brown Bear Hallo Bay, Katmai National Park, Alaskaflickr.com/photos/tmarschner/2728816091/in/photostream/

…. started hunting in Arctic environments. Those brown bears with the lighter colored coats were the more successful hunters better placed to breed and pass on their lighter coated genes to subsequent generations.

blonde grizzly and normal grizzly fighting

Two brown bears fighting

Eventually a new species of bear, the Polar bear, evolved.

polar bear and grizzly bear compared

The white coloration of Snowy owls and Polar bears is one example of convergent evolution.

Convergent evolution defined

Convergent evolution occurs where two or more completely unrelated species evolve similar traits or adaptions. The ancestors of neither species possessed the trait or adaption.

Species acquire identical traits or adaptions when living in similar habitats or facing similar environmental conditions. The trait or adaption they evolve makes them better placed to hunt, survive and breed.

fusiform shape which narrows at both ends

Fusiform shape

There are many, many examples of convergent evolution in existence. Some other noteworthy examples are discussed below:

Convergent evolution- similar body forms

The Ichthyosaur, a marine reptile, became extinct 95 million years ago. It had a streamlined fusiform shaped body…

ichthyosaurs swimming in a Triassic sea

… very similar to the fusiform shaped body of a shark…

Caribbean reef sharkAlbert Kok creativecommons.org/licenses/by-sa/3.0/

…and that of the dolphin.

Atlantic Spotted Dolphin - Stenella Plagiodonsheilapic76 flickr.com/photos/53344659@N05/4978423771

In addition to their fusiform shapes, all three organisms evolved similar dorsal, pectoral and tail fins. They used these fins to maintain balance and help them maneuver quickly through the water

shark ichthyosaur and dolphin pectoral and dorsal fins

The ichthyosaur, shark and dolphin all evolved their body forms independently of each other. The ichthyosaur evolved from a land reptile, the shark from a fish, and the dolphin from a land mammal.

ichthyosaur dolphin and shark are examples of convergent evolution

Convergent evolution – spines on backs

Marsupial echindas (Tachyglossus aculeatus) from Australia…

Wild shortbeak echidnaflagstaffotos.com.au

… and mammalian hedgehogs from Europe (Erinaceus europaeus) are not related.

hedgehogcommons.wikimedia.org/wiki/File:Igel.JPG#/media/File:Igel.JPG

Both have independently evolved ‘spines’ on their backs. Spines are tough, modified, hollow hairs…

spines and fur of an echidna

Spines of an echidna

…stiffened with keratin- the same substance that fingernails are made of.

Close-up-of-hedgehog-spines

 Spines of a hedgehog

Both animals range far and wide searching for small invertebrates to eat. They are vulnerable to attack from larger predators as they hunt for food. Their spines are an effective defense against being attacked.

Convergent evolution- ‘echolocation’

Bats hunt at night and often live in dark caves.

bat approaching a cactus flower

© Merlin D Tuttle Bat Conservation International batcon.org

Dolphins sometimes hunt in murky waters where it is difficult to see.

Bottlenose-dolphin-female-and-calf

Both animals have independently evolved an incredibly sophisticated way of ‘seeing’ in conditions where there is little light.

They emit high-pitched sounds….

bats echolocation

 ….that reflect off objects before returning to the animals’ auditory systems for the information to be processed.

ecolocation diagram of dolphinseportfolios.upou.edu.ph

Using ‘ecolocation’ these animals are able to build up a ‘sonic map’ of their surroundings.

radar screen pixabay.com/en/proximity-radar-enemy-green-150698

Bats’ echolocation sytem not only allows them to successfully hunt prey; it allows them to communicate with each other and ‘see’ where they are flying in the dark.

bat catching insect in darkness© Michael Durham at Durmphoto.com

Likewise the echolocation system of dolphins allows them to ‘see’ in murky water, navigate their surroundings, communicate and hunt.

River Dolphin

 Amazon river dolphin (Inia geoffrensis)  flickr.com/photos/joachim_s_mueller/4052401470

Convergent evolution- awake and asleep at the same time!

Chickens have an amazing ability to sleep and stay awake at the same time. This chicken shows how it is done! It has one eye open and one eye shut.

Unishemispheric slow wave sleep in chicken with one eye shut and one eye open  Photos courtesy Your Chickens magazine

The left side (or hemisphere) of the chicken’s brain is asleep while the right hemisphere is fully awake and alert to danger. Chickens have evolved the ability to watch out for predators even when sleeping!

But when they trust someone they shut both eyes- indicating that both brain hemispheres are capable of sleeping at the same time!

two eyes of chicken fully shut showing that both brain hemispheres are asleepPhotos courtesy Your Chickens magazine

Other species that have developed this extraordinary ability to shut down one half of their brains at a time (called ‘unihemispheric slow-wave sleep’ or ‘USWS’) include dolphins….

dolphins sleeping inwater © joanocean.com

…..and manatees.

manatee sleeping© David R Schrichte savethemanatee.org

Unihemispheric slow-wave sleep is especially useful to aquatic mammals; it gives them the ability to sleep while at the same time knowing when they have to rise to the surface to breathe.

Convergent evolution- tongues of amphibians

Plethodontid salamanders from forest habitats of north-west America….

Plethodontid salamander catches prey with long sticky tongue

…… and Parson’s chameleons (Calumma parsonii) from the rainforests of Madagascar have independently evolved the ability to catch prey with their l-o–n–g sticky tongues!

Parsons-chameleon -Calumma parsonii-catching-insect-prey-on-tongue

The tongue of a Plethodontid salamander can accelerate at a speed of 1,740 meters per second squared! Protraction and retraction of the tongue can occur within 20 milliseconds! (twenty thousandths of a second). The tongue of the Parson’s chameleon is equally fast!

Convergent evolution- similar eyes

Believe it or not human beings…

black-man-eyes-close-up-16x9ohe.gov.pg

and octopuses…

Common octopus close up of eyes

have independently evolved advanced camera eyes that are remarkably similar.

human eye and octopus eye are examples of convergent evolution genome.cshlp.org/content/14/8/1555.full.pdf

The whole evolutionary process started when the remote ancestors of humans and octopuses developed simple camera eyes…

Nilsson and Pelger stage 8 fish eye formed

…while swimming in Cambrian seas 544 million years ago.

Cambrian explosion showing diversity of marine lifensf.gov/news/mmg/mmg_disp.jsp?med_id=59611&from=mmg

The octopus can trace the evolution of its advanced camera eyes back to the two tentacled Nectocaris pteryx that lived 505 million years ago.

Nectocaris pteryx© Marianne Collins

The evolution of advanced camera eyes in humans can be traced all the way back to the common ancestors of all mammals, fish, reptiles and amphibians that first crawled out of the sea some 375 million years ago.

tiktaalik roseae crawling out of the sea

Tiktaalik roseae bioweb.uwlax.edu/bio203/f2013/raabe_mic2/reproduction.htm

The need to evolve advanced camera eyes resulted from evolutionary pressures to improve vision in order to see both predators and prey in complex sea and land environments.

It just so happens that advanced camera eyes evolved in octopuses in the sea and in tetrapods (including us humans) on land!

Convergent evolution- long ‘noses’ edged with teeth

The green sawfish (Pristis zijsron)….

green sawfish resting on sea bed with long snout and teeth which is an example of convergent evolution

….is unrelated to the Bahamas sawshark (Pristiophorus schroederi)

bahamas-sawshark (Pristiophorus schroederi) has a rostrum which is an example of convergent evolution© sharksider.com/bahamas-sawshark

Both species of fish have evolved long noses (‘rostrums’) edged with teeth which they use to slash and disable their prey.

They also use their rostrums to dig for prey that may be hiding. Their rostrums are also useful tools which they use to defend themselves against predators.

Both species live in similar habitats -on or near the sea floor.

Convergent evolution -oversized fingers

The third fingers of aye-ayes (Daubentonia madagascariensis) from Madagascan rainforests…

aye aye showing elongated fingers polaris.psu.edu

… and the fourth fingers of striped possums (Dactylopsila trivirgata) from Australian rainforests are very long.

striped possum showing enlarged fourth finger is an example of convergent evolutionzoochat.com/1322/striped-possum-dactylopsila-trivirgata-30242/

Both animals use their elongated fingers in identical ways to hunt for prey.

They tap on the bark of trees and listen out for a returning echo which informs them about the presence of wood boring insect lavae under the bark.

aye-aye-using-thin-elongated-third-finger-to-fing-grubs-in-wood

Once they have located the lavae they use their sharp teeth to gnaw at the bark to create a small hole.

They then use those same long middle fingers to hook the lavae out of the hole…

aye aye pulling grubs out of a hole in the bark

…which they then eat.

striped possum eating grub Image credit: thefeaturedcreature.com

Convergent evolution -‘mimicry’ in snakes

The non venomous Scarlet King snake (Lampropeltis elapsoides) ….

Scarlet King snake (Lampropeltis elapsoides) of Florida © Alan Cressler at wildflorida.com

….has evolved to look very similar to the venomous Eastern Coral snake (Micrurus fulvius).

eastern coral snakewildlifetrappersandrescue.com

Both species live in the south-east of the United States.

By evolving to resemble Coral snakes, Scarlet King snakes are less likely to be eaten by predators!

Children living in areas of the United States where both snakes live are taught to identify the difference between the two species.

how to tell the difference between a coral snake and a scarlet king snake

In this example of convergent evolution, a harmless species ( the Scarlet King snake) has evolved to look like a harmful species (Eastern Coral snake). This phenomenon is called Müllerian mimicry.

Convergent evolution- ‘mimicry’ in insects

The Monarch butterfly (on the left) has evolved to closely resemble the Viceroy butterfly (on the right)

Monarch_Viceroy_Mimicry_Comparison

Predators try to avoid eating both species because they taste so disgusting!

  • So why have both species evolved to resemble each other so closely ?

Take this Blue jay bird; in this image it can be seen eating a Monarch butterfly and finds the taste so revolting that it is promptly sick.

Blue jay eats a Monarch butterfly and vomits

Supposing, the next time it goes out hunting,the Blue jay finds a Viceroy butterfly to eat instead of a Monarch. What will it do?

Ignore the Viceroy butterfly and eat peanuts instead!

Blue_Jay_with_PeanutSaforrest at wikpedia GFDL/CC-by-SA 3.0

The Blue jay would avoid eating the Viceroy butterfly because it so closely resembles a Monarch butterfly.

Two similar looking species of butterfly increase their chances of survival because predators learn to avoid eating both species.

Once a predator has had a bad experience eating one species, it is less likely to make the same ‘mistake’ again! This is an example of the phenomenon we call Batesian mimicry.

Viceroy and Monarch butterflies with meme don't eat us we both taste disgusting!

Viceroy butterfly (left) and monarch butterfly (right)

Convergent evolution- swim bladder

A swim bladder is a gas-filled organ that helps an organism control its buoyancy…

Swim bladder

Swim bladder of a rudd from ‘Scardinius’ group of fish 

…and stay at its chosen depth without wasting energy swimming.

swim bladder in fish © I.G. Jones at sharkyjones

Swim bladders have independently evolved in bony fish….

common rudd Scardinius erythropthalmus
Common rudd (Scardinius erythropthalmus) -Creative commons 3.0

...tuberculate pelagic octopuses…

tuberculate pelagic octopus has a swim bladder darksinistar.hubpages.com

…and Portuguese men ‘o war (Physalia physalis). The Portuguese man o’ war lives on the surface of the ocean. Its gas-filled bladder remains on the surface…

Portuguese-man-o-war-on-sea-surface showing gas filled bladder

while its venomous tenacles stay submerged.

portuguese man o war showing tentacles below the surface

Convergent evolution- in desert plants

Convergent evolution is also evident in plants. Take the cactuses (Cactaceae) of the Americas….

Cactaceae of the Americas exhibit convergent evolution lifeofplant.blogspot.co.uk

…and the euphorbs (Euphorbiaceae) of southern Africa.

Euphorbiaceae of Africa

Both species evolved in hot, waterless arid environments. Both have developed thick, fleshy stems in which they store water.

cactus-cross-section showing fleshy stem which stores waterImage credit: buzzle.com

Their true leaves have changed into spines that, among other things, reduce the amount of water the plant loses through evaporation.

Spines provide some protection against hungry herbivores -but not always!

land iguana eating prickly pear cactus in galapagos

Land iguana in Galapagos eating prickly pear cactus galapagosonline.wordpress.com

Convergent evolution -in carnivorous plants

Some plants are able to survive in nutrient deficient habitats such as wet, boggy, acidic soils. (see Spores, sphagnum moss and wetlands)

Plants living in nutrient deficient habitats have become carnivorous; this has given them the ability to acquire the vital nutrients they need.

Carnivorous plants trap insects in different ways.

Insects become trapped on the sticky tentacles of the Cape sundew (Drosera capensis)….

Drosera capensis Sundew carniverous plantCC BY-SA 3.0 Wikimedia Commons

drown in the water-filled cups of the Tropical pitcher (Nepenthes lowii)

Nepenthes lowii, a tropical pitcher carniverous plant“Murud N. lowii 20” by JeremiahsCPs CC BY-SA 3.0 Wikimedia Commons

or become emprisoned in the toothed, modified leaves of the Venus fly trap (Dionaea muscipula).

toothed modified leaves of venus fly trap Dionaea muscipula have snapped shut emprisoning a fly

Convergent evolution -in arthropods

Pillbugs and pill millipedes live in very similar habitats; they inhabit moist, humid forests and feed on dead plants on forest floors.

pill bugs and pill millipedesconvergent evolution Kazvorpal at English Wikipedia

When threatened by predators they curl up into defensive balls.

Pill-millipedes-curled-up-in-defensive-balls exhibit convergent evolution with pill bugs

Pill millipedes

Curling up into balls protects their soft undersides and presents predators with their more formidable exterior plated armor.

Convergent evolution -in extinct species

Of course, convergent evolution does not just occur in living species. There is much evidence for convergent evolution in species that are now extinct.

The herbivorous Doedicurus clavicaudatus was a heavily armored south american glyptodont that became extinct only 11,000 years ago 

Doedicurus clavicaudatusdinosaurusi.com

It had a tail club which was probably used in territorial and mating displays. It may have also been used for defense.

The Anklyosaurus magniventris became extinct 66 million years ago. Like the Doedicurus it was a herbivore; it had extensive body armor and a tail club which it used to defend itself.

Anklyosaurus magniventris with club tail

Science projects- convergent evolution

This Wikipedia article has many examples of convergent evolution you could research further.

Awesome Science Videos

Watch this Plethodontid salamander catch its prey with its amazing tongue!

Marvel at this aye-aye in action!

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