Chapter 24. The Origin of Species “Both in space and time, we seem to be brought somewhat near to that great fact—that mystery of mysteries—the first appearance of new beings on this Earth.” — Darwin 4/21/2017

What is a species? Biological species concept defined by Ernst Mayr population whose members can interbreed & produce viable, fertile offspring reproductively compatible 4/21/2017

Biological species concept Eastern Meadowlark Western Meadowlark Similar body & colorations, but are distinct biological species because their songs & other behaviors are different enough to prevent interbreeding 4/21/2017

Diversity & Taxonomy The Tree of Life species are the smallest unit at the ends of branches basic unit for organizing & categorizing living things smallest unit by which we measure diversity 4/21/2017

How and why do new species originate? Reproductive isolation biological barriers that impede members from producing viable offspring before vs. after fertilization pre-zygotic barriers before the zygote post-zygotic barriers after the zygote 4/21/2017

displaying to attract females Pre-zygotic barriers Impede mating or hinder fertilization if mating occurs habitat isolation temporal isolation behavioral isolation mechanical isolation gametic isolation male Frigate bird displaying to attract females 4/21/2017

Ecological isolation Two species may occupy different habitats within same area so may encounter each other rarely 2 species of garter snake, Thamnophis, occur in same area, but one lives in water & other is terrestrial lions & tigers could hybridize, but they live in different habitats: lions in grasslands tigers in forest 4/21/2017

Temporal isolation Species that breed during different times of day, different seasons, or different years cannot mix gametes Eastern spotted skunk (L) & western spotted skunk (R) overlap in range but eastern mates in late winter & western mates in late summer 4/21/2017

Behavioral isolation Courtship rituals that attract mates & other unique behaviors to a species are effective reproductive barriers The most comedic species of the Galapagos Islands is the Blue Footed Booby, what a ridiculous outfit and expression! Their name is in fact taken from the Spanish 'bobo' which means clown. The Blue Footed Boobies above display part of their humorous courtship ritual whereby they raise their feet one at a time and then swivel their heads away from the prospective mate looking to the sky. Other interesting Booby features are the highly evolved airbag systems in their skulls which allow them to dive bomb into the sea for fish from great height, and the egg and hatchling nesting boundaries they make which are rings of Boobie poop. They aren't the only Booby on the island — there are also Masked and Red Footed Boobies about. Blue footed boobies mate only after a courtship display unique to their species 4/21/2017

Gray-Crowned Cranes engaged in courtship display, Kenya What can you say? 4/21/2017

Mechanical isolation Morphological differences can prevent successful mating Even in closely related species of plants, the flowers often have distinct appearances that attract different pollinators. These 2 species of monkey flower differ greatly in shape & color, therefore cross-pollination does not happen. The most comedic species of the Galapagos Islands is the Blue Footed Booby, what a ridiculous outfit and expression! Their name is in fact taken from the Spanish 'bobo' which means clown. The Blue Footed Boobies above display part of their humorous courtship ritual whereby they raise their feet one at a time and then swivel their heads away from the prospective mate looking to the sky. Other interesting Booby features are the highly evolved airbag systems in their skulls which allow them to dive bomb into the sea for fish from great height, and the egg and hatchling nesting boundaries they make which are rings of Boobie poop. They aren't the only Booby on the island — there are also Masked and Red Footed Boobies about. 4/21/2017

Mechanical isolation For many insects, male & female sex organs of closely related species do not fit together, preventing sperm transfer lack of “fit” between sexual organs: hard to imagine for us, but a big issue for insects with different shaped genitals! The selection is intense because it directly affects offspring production -- it is affecting sex itself Damsel fly penises 4/21/2017

Gametic isolation Sperm of 1 species may not be able to fertilize eggs of another species variety of mechanisms chemical incompatibility sperm cannot survive in female reproductive tract biochemical barrier so sperm cannot penetrate egg receptor recognition: lock & key between egg & sperm Sea urchins release sperm & eggs into surrounding waters where they fuse & form zygotes. Gametes of different species—red & purple —are unable to fuse. 4/21/2017

Postzygotic barriers prevent hybrid zygote from developing into a viable, fertile adult reduced hybrid viability reduced hybrid fertility hybrid breakdown 4/21/2017 zebroid

Reduced hybrid viability Genes of different parent species may interact & impair the hybrid’s development Species of salamander genus, Ensatina, may interbreed, but most hybrids do not complete development & those that do are frail. 4/21/2017

Reduced hybrid fertility Even if hybrids are vigorous they may be sterile chromosomes of parents may differ in number or structure & meiosis in hybrids may fail to produce normal gametes Mule are vigorous, but sterile What’s wrong with having 63 chromosomes? Odd number! Cannot pair up in meiosis. Horses have 64 chromosomes (32 pairs) Donkeys have 62 chromosomes (31 pairs) 4/21/2017 Mules have 63 chromosomes!

Hybrid breakdown Hybrids may be fertile & viable in first generation, but when they mate offspring are feeble or sterile In strains of cultivated rice, hybrids are vigorous but plants in next generation are small & sterile. On path to separate species. 4/21/2017

Speciation Species are created by a series of evolutionary processes populations become isolated reproductively isolated geographically isolated isolated populations evolve independently Isolation allopatric physical separation sympatric still live in same area 4/21/2017

Allopatric speciation Allopatric = “other country” geographic separation migration physical barrier Harris’s antelope squirrel inhabits the canyon’s south rim (L). Just a few miles away on the north rim (R) lives the closely related white–tailed antelope squirrel 4/21/2017

Sympatric speciation Sympatric = “same country” some type of isolation even though populations live in same area what causes this isolation? behavioral differences non-random mating physiological differences chromosomal changes polyploidy mostly in plants: oats, cotton, potatoes, tobacco, wheat 4/21/2017

Adaptive radiation Evolution of many diversely adapted species when introduced to various new environmental challenges & opportunities Drosophila Geospiza 4/21/2017

Adaptive radiation in plants all descended from a common ancestor 5mya Silversword alliance 4/21/2017

Adaptive radiation Many ecological niches open Evolution of many diversely-adapted species from a common ancestor to fill niches Darwin’s finches mammals 4/21/2017

Review Speciation is a process populations become isolated geographic isolation different environmental conditions food, predators, disease, habitat different selection pressures genetic drift reproductive isolation sexual selection isolated populations evolve independently 4/21/2017

Current debate Does speciation happen gradually or rapidly perhaps in response to environmental change Gradualism Charles Darwin Charles Lyell Punctuated equilibrium Stephen Jay Gould Niles Eldredge Niles Eldredge Curator American Museum of Natural History 4/21/2017

Gradualism Gradual divergence over long spans of time assume that big changes occur as the accumulation of many small ones 4/21/2017

Punctuated Equilibrium Rate of speciation is not constant species undergo most change when they 1st bud from parent population as separate species, remain static for long periods of time Time 4/21/2017

Stephen Jay Gould (1941-2002) Harvard paleontologist & evolutionary biologist punctuated equilibrium prolific author popularized evolutionary thought Stephen Jay Gould (September 10, 1941 – May 20, 2002) was a New York-born American paleontologist, evolutionary biologist, and historian of science. He was the most influential and widely read writer of popular science of his generation. He served as a member of the faculty at Harvard University beginning in 1967. Toward the end of his life he served as the Alexander Agassiz Professor of Zoology at that university. He helped Niles Eldredge develop Eldredge's theory of punctuated equilibrium 1972, wherein evolutionary change occurs relatively rapidly in comparatively brief periods of environmental stress, separated by longer periods of evolutionary stability. According to Gould, this overthrew a key tenet of neo-Darwinism; according to most evolutionary biologists, the theory was an important insight but merely modified neo-Darwinism in a way fully compatible with what had been known before. Gould became widely known through his popular science essays in Natural History magazine, collections of essays like The Panda's Thumb and The Flamingo's Smile, and extended studies like Wonderful Life and others.Gould was an emphatic advocate of evolution and wrote prolifically on the subject, trying to communicate his understanding of contemporary evolutionary theory to a wide audience. A recurring theme in his writings is the history and development of evolutionary (and pre-evolutionary) thinking. His early research involved the study of the fossil record of snails (detailed in one of his essays). He was also an enthusiastic baseball fan and made frequent references to the sport (including an entire essay) and a very wide range of other topics. 4/21/2017

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Evolution is not goal-oriented An evolutionary trend does not mean that evolution is goal oriented. The modern horse is the only surviving twig of an evolutionary tree with many divergent trends. It does not represent the peak of perfection. There is compromise & random chance involved as well Remember that for humans as well! 4/21/2017

Some interesting evolutionary trends…. 4/21/2017

Convergent evolution Flight evolved 3 separate times evolving similar solutions to similar “problems” 4/21/2017

Australian Marsupials Parallel Evolution Fill similar niches; have similar adaptations, but are not closely related Niche Placental Mammals Australian Marsupials Burrower Mole Marsupial mole Anteater Numbat Anteater Nocturnal insectivore Marsupial mouse Mouse Climber Spotted cuscus Lemur Sugar glider Glider Flying squirrel Stalking predator Tasmanian cat Ocelot Chasing predator 4/21/2017 Wolf Tasmanian “wolf”

Mimicry convergent evolution based on similar (protective) appearance Monarch male poisonous Viceroy male edible 4/21/2017

Coevolution Predator-prey relationships Parasite-host relationships Flowers & pollinators 4/21/2017

Darwin Awards Named in honor of Charles Darwin, the father of evolution, the Darwin Awards commemorate those who improve our gene pool by removing themselves from it. The Darwin Awards salute the improvement of the human genome by honoring those who accidentally kill themselves in really stupid ways. Of necessity, this honor is bestowed posthumously. www.DarwinAwards.com 4/21/2017

Any Questions?? 4/21/2017