Evolution of Multicellularity Basic properties of the living

Evolution of Multicellularity "Basic properties of the living world emerge out of this cycle of cooperation and conflict: ” Dr. Rick Michod Farr & Steeves, UA, EEB, Michod Lab Images courtesy of wikipedia. com and Michod lab

What is complexity? • What makes something complex? o Synonyms for complex: complicated, intricate, involved • Simple: easy to understand, not elaborate § Ex. Prokaryotic cell, bacteria • Complex: composed of many parts, a composite § Ex. Eukaryotic cell, animals Write 3 simple things, and 3 complex things that you own Farr & Steeves, UA, EEB, Michod Lab

Complexity in nature • There are myriad examples we can use to talk about complexity. • Specifically, the transition of unicellular organisms into multicellular organisms • To do this we can look at algae o Ex. Chlamydomonas to an intermediate organism, to Volvox ( a series of transitions becoming more complex) Farr & Steeves, UA, EEB, Michod Lab

Unicellular to Multicellular • How could organisms like Chlamy have evolved into an organism like Volvox? • Let’s look at some pictures and let you hypothesize. • Remember, when hypothesizing use if, then, and because. Farr & Steeves, UA, EEB, Michod Lab

Examples of volvocine species varying in cell number, colony volume, degree of specialization, and proportion of somatic cells Michod, R. E. (2007) Proc. Natl. Acad. Sci. USA 104, 8613 -8618 Farr & Steeves, UA, EEB, Michod Lab Copyright © 2007 by the National Academy of Sciences

Fig. 1. Volvocine green algae arranged according to typical colony radius R Short, M. B. et al. (2006) Proc. Natl. Acad. Sci. USA 103, 8315 -8319 Farr & Steeves, UA, EEB, Michod Lab Copyright © 2006 by the National Academy of Sciences

Michod, R. E. et al. Integr. Comp. Biol. 2003 43: 64 -73; doi: 10. 1093/icb/43. 1. 64 Farr & Steeves, UA, EEB, Michod Lab

Timeline of volvocine evolution Herron, M. D. Comm. Int. Biol. 2: 368 -370. Farr & Steeves, UA, EEB, Michod Lab

Scientists think the following steps describe the transition from unicellular to multicellular life. • Groups of cells form. • Groups increase in size. • Cells within the groups cooperate and specialize. • The group must mediate the conflict among cells so that cheating becomes less likely. • The group, by virtue of specialization, becomes indivisible and, hence, an individual. Farr & Steeves, UA, EEB, Michod Lab Michod, Sociality and Sex, 2008

Time to synthesize • Write down some examples used to discuss biological complexity. • Write down some evidence that suggest unicellular organisms like Chlamydomonas may have evolved into a more complex organism like Volvox. Farr & Steeves, UA, EEB, Michod Lab

Concepts • • • Prisoner’s dilemma Niche Altruism Eusociality Kinship Cooperation, conflict, resolution Farr & Steeves, UA, EEB, Michod Lab

What are some forms of cooperation? • The origin of helping someone else out is a mystery • It seems anti-Darwinian (every man for himself, need to pass on genes, keeping your genes alive) • However, some organisms seem to behave (consciously or unconsciously) for the benefit of others in a special form of cooperation o We call this Altruism or altruistic behavior Farr & Steeves, UA, EEB, Michod Lab

Altruism • When one gives up its selfishness to help out or benefit a larger group • This would be the opposite of what? Farr & Steeves, UA, EEB, Michod Lab

Altruism example Female worker bees o Stingers are barbed to pierce skin, but at what cost? o Stingers are attached directly to the bee’s abdomen and when removed gets ripped out leading to the bees death in minutes o So in the end, who benefits? § The rest of the hive! Farr & Steeves, UA, EEB, Michod Lab

Altruism cont. • Other examples: o Many small birds will give out a “warning call” when a hawk or other predator is around o How might giving this “warning call” hurt (or cost) the caller that makes it? Farr & Steeves, UA, EEB, Michod Lab

Eusocial behavior • Eusocial insects, such as ants, display interesting eusocial traits: o 1. The mother takes care of the young even if it isn’t her own o 2. Division of labor: some don’t reproduce but give protection to the group o 3. Overlapping of generations, grandparents help raise the young Farr & Steeves, UA, EEB, Michod Lab

Eusocial characteristics • Division of labor § There are workers, soldiers, and reproductive queens § How does this create a cooperative system? Farr & Steeves, UA, EEB, Michod Lab

No individuality for each ant • This means the entire colony can then be seen as a “superorganism” or a single larger organism Farr & Steeves, UA, EEB, Michod Lab

Individuality vs. Cooperation Farr & Steeves, UA, EEB, Michod Lab

Individuality vs. Cooperation Farr & Steeves, UA, EEB, Michod Lab

Kinship • Kin means relative, someone related • Would you give up your life for someone in your family? -If you answered “yes”, why? -This is called Kin Selection -You may do this because your kin (family member) shares some of your genes, so even if you die, some of your genes survive -The passing of your genes is known as Fitness Farr & Steeves, UA, EEB, Michod Lab

Time to synthesize! • What is cooperation? • Do your organs cooperate? Do your cells? Does your DNA? • List 3 positive aspects of being cooperative. • List any drawbacks you see with being cooperative. Farr & Steeves, UA, EEB, Michod Lab