There’s something you need to know… The Origin of Species Mom, Dad… There’s something you need to know… I’m a MAMMAL! 2007-2008

“That mystery of mysteries…” Darwin never actually tackled how new species arose… 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.

So…what is a species? Biological species concept defined by Ernst Mayr population whose members can interbreed & produce viable, fertile offspring reproductively compatible Distinct species: songs & behaviors are different enough to prevent interbreeding Humans re so diverse but considered one species, whereas these Meadowlarks look so similar but are considered different species. Meadowlarks Similar body & colorations, but are distinct biological species because their songs & other behaviors are different enough to prevent interbreeding Eastern Meadowlark Western Meadowlark

How and why do new species originate? Species are created by a series of evolutionary processes populations become isolated geographically isolated reproductively isolated isolated populations evolve independently Isolation allopatric geographic separation sympatric still live in same area

PRE-reproduction barriers Obstacle to mating or to fertilization if mating occurs geographic isolation ecological isolation temporal isolation behavioral isolation mechanical isolation gametic isolation

Geographic isolation Species occur in different areas physical barrier Ammospermophilus spp Geographic isolation Species occur in different areas physical barrier allopatric speciation “other country” 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

Ecological/Habitat isolation Species occur in same region, but occupy different habitats so rarely encounter each other reproductively isolated 2 species of garter snake, Thamnophis, occur in same area, but one lives in water & other is terrestrial Another example: lions & tigers - could hybridize, but they live in different habitats: lions in grasslands tigers in rainforest

Temporal isolation Species that breed during different times of day, different seasons, or different years cannot mix gametes reproductive isolation sympatric speciation “same country” Eastern spotted skunk (L) & western spotted skunk (R) overlap in range but eastern mates in late winter & western mates in late summer

sympatric speciation? Behavioral isolation Unique behavioral patterns & rituals isolate species identifies members of species attract mates of same species  courtship rituals, mating calls reproductive isolation 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

Recognizing your own species What can you say? courtship songs of sympatric species of lacewings courtship display of Gray-Crowned Cranes, Kenya firefly courtship displays

Mechanical isolation Plants sympatric speciation? Mechanical isolation Morphological differences can prevent successful mating reproductive isolation Plants 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.

Mechanical isolation Animals 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 I can’t even imagine! Damsel fly penises

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

POST-reproduction(postzygotic) barriers Prevent hybrid offspring from developing into a viable, fertile adult reduced hybrid viability reduced hybrid fertility hybrid breakdown zebroid

Reduced hybrid viability sympatric speciation? 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.

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 Mules 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) Mules have 63 chromosomes!

sympatric speciation? 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.

Rate of Speciation Current debate: Does speciation happen gradually or rapidly Gradualism Charles Darwin Charles Lyell Punctuated equilibrium Stephen Jay Gould Niles Eldredge Niles Eldredge Curator American Museum of Natural History

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

Punctuated Equilibrium Rate of speciation is not constant rapid bursts of change long periods of little or no change species undergo rapid change when they 1st bud from parent population Time

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.

Evolution is not goal-oriented An evolutionary trend does not mean that evolution is goal-oriented. Surviving species do not represent the peak of perfection. There is compromise & random chance involved as well Remember that for humans as well! Evolution is not the survival of the fittest. Rather it is the survival of the just good enough.

Any Questions?? 2007-2008