Macroevolution How do species arise How do we

Macroevolution : How do species arise? How do we go from species A to Species B? Mom, Dad… There’s something you need to know… I’m a MAMMAL!

Tip! Use a simple flow chart to organize your information…. Speciation Barriers! Geographic Allopatric Sympatric Pre-zygotic Types A -F Post-zygotic Ex. Hybrids

What IS a Species? “Biological species concept” u u population whose members can interbreed & produce viable, fertile offspring reproductively compatible Distinct species: songs & behaviors are different enough to prevent interbreeding Eastern Meadowlark

What is the first step to speciation? § END Gene flow § between groups! (reproductive isolation )

Once gene flow ends. . Populations can: 1. Diverge genetically via mutation 2. Be subject to natural selection pressures 3. Experience genetic drift

1. Obviously…different types of geographic isolation can occur… § 2 different types of isolation can be… u allopatric § geographic separation between groups u sympatric § Group still live in same area

There are many other ways to keep groups apart including Reproductive isolating mechanisms Such mechanisms § Arise as populations move apart (diverge) § They are Heritable aspects of body form § They can be functions of body parts Or Behaviors (that prevent interbreeding among species)

There are two types of reproductive isoolating mechanisms § Pre-zygotic isolating mechanisms (prevents successful mating/pollination) § Post-zygotic isolating mechanisms (inability of new individuals to mate successfully)

2. PRE- zygotic (reproduction) § Obstacles to mating or to fertilization if mating occurs geographic isolation behavioral isolation ecological isolation temporal isolation mechanical isolation gametic isolation

A. Geographic isolation Ammospermophilus spp Most common mode of speciation physical barrier arises and ends gene flow u We call this: allopatric speciation u (“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

B. Ecological isolation § Species occur in same region, but occupy different habitats (microenvironments) so rarely encounter each other They are…reproductively isolated 2 species of garter snake, Thamnophis, occur in same area, but one lives in water & other is terrestrial

Ex. lions & tigers could hybridize, but they live in different habitats: lions in grasslands tigers in rainforest

C. Temporal isolation: timing of reproduction differs § Species that breed during different times of day, different seasons, or different years cannot mix gametes u u Another form of reproductive isolation WE call this: sympatric speciation : new species form within home range of an existing species and in the absence of a physical barrier! § Means: “same country” Eastern spotted skunk (L) & western spotted skunk (R) overlap in range but eastern mates in late winter & western mates in late summer

D. Behavioral isolation Unique behavioral patterns & rituals isolate species 1. 2. identifies members of species attract mates of same species (females of different species are not impressed!) § courtship rituals, mating calls § reproductive isolation Blue footed boobies mate only after a courtship display unique to their species

Recognizing your own species courtship songs of sympatric species of lacewings courtship display of Gray-Crowned Cranes, Kenya firefly courtship displays

E. Mechanical isolation sympatric speciation Morphological differences can prevent successful mating Even in closely related species of plants, the flowers often have distinct appearances that attract different pollinators. (You have to have the RIGHT pollinator!) Plants

For example: Black sage (left) v White Sage (right) Only smaller bees (honeybees) can pollinate Black Sage; larger bees cannot be supported by smaller flowers Filaments stick out above petals making it impossible for little honeybees to access anthers: larger bumble bees OK!

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

3. POST-zygotic barriers (ex. Hybrids) These will prevent hybrid offspring from developing into a viable, fertile adult (3 ways) 1. 2. 3. reduced hybrid viability reduced hybrid fertility hybrid breakdown zebroid

A. Reduced hybrid viability sympatric speciation § Genes of different parent species may interact & impair the hybrid’s development § Or recent divergence of genes cause some missing or some extra genes; incompatible! Species of salamander genus, Ensatina, may interbreed, but most hybrids do not completely develop; those that do are frail.

B. Reduced hybrid fertility § Even if hybrids are vigorous they may be sterile u chromosomes of parents may differ in number or structure & meiosis in hybrids may fail to produce normal gametes Mules are vigorous, but sterile Horses have 64 chromosomes (32 pairs) Donkeys have 62 chromosomes Mules have 63 chromosomes! (31 pairs)

C. Hybrid breakdown sympatric speciation § 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.

How Fast can we go from Species A to Species B?

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

Stephen Jay Gould (1941 -2002) § Harvard paleontologist & evolutionary biologist punctuated equilibrium u prolific author u § popularized evolutionary thought

Phyletic Gradualism – Darwin and Lyelle § Gradual divergence over long spans of time Species stay stable for long periods of time u assume that big changes occur as the accumulation of many small ones u

Punctuated Equilibrium – Gould/Eldridge § Rate of speciation is not constant rapid bursts of change u long periods of little or no change between u Occurs with drastic change in environments u Time

Is Evolution goal-oriented? No! 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.

View Mr. Anderson’s “Speciation and Extinction”

Any Questions? ? 2007 -2008