Biol 4802 Evolution

Lecture 17, Chapter 11

Topics for today


Evolution can’t be totally random!


What about adaptations?

Adaptation of the growth and development process

Monstera tenuis

Fig. 11.11(new and old)

Adaptation that exploit other organisms

Some animals have features & behavior that only benefit the group

Not in new (Fig. 11.14 old)

Natural selection is the only evolutionary process that explains adaptation

How do we define adaptation?

·         Emphasis on today

“An adaptation is a phenotypic variant that results in the highest fitness among a specified set of variants in a given environment” Reeve and Sherman 1993

·         Emphasis on past

“For a character to be regarded as an adaptation, it must be a derived character that evolved in response to a specifc selective agent” Harvey and Pagel 1991

Cautionary notes

Fig. 11.18 (Fig. 11.17old)

Selection on some traits may be incidental

o   Hypothetical example

Fig. 11.5 (new and old)

Cooperative behavior may only appear to altruistic

Fig. 11.14(new and old)

Not all adaptations directly benefit the individual

How can we study natural selection and adaptation?

·         Experimental studies

o   Growth rate of short lived organisms

o   Experimental manipulation of adaptive trait

·         Comparative method

o   Trait convergence under similar selection

Examples of experimental approaches

Experimental study of growth rates

·         b-galactosidase breaks down lactase

·         Different mutant strains grown in competition with wild type

·         Lactose was sole energy source

·         Ratio of mutant vs. wildtype strains monitored over time

·         his+ codes for an enzyme that synthesizes histidine

·         his- defective

·         his+ and his- grown in competition with histidine

·         Surprising fluctuation in alleles

·         his alleles hitchhiking with advantageous mutations at other loci

Fig. 11.7(new and old)

Experimental manipulation

·         Do long tails enhance male reproductive success?

·         Conflicting selection pressures result in tradeoffs

Not in new (Fig. 11.9 old)

Comparative method

Observe unrelated organisms in similar environments

Develop hypotheses about traits that should repeatedly evolve if they are adaptive

Fig. 11.22 (Fig. 11.20 old)