Comes from ad (to or toward) and aptus (a fit) • Evolutionary context – • genetically-based change in response to a problem • achieved through the process of natural selection. • A period of time passes before adjustment occurs Adaptation
We identify traits as adaptationsonly when they are evolved for the solution of a specific problem (selectedfunction or purpose). • Adaptation - a working definition: a genetically based trait or integrated suite of traits that has evolved in response to selection for the function that it currently performs and that increases the fitness of its possessor • Just because a trait has a specific effect does not mean that the trait is adaptive for that purpose. Adaptation is both a process and a state of being (a phenotypic trait or character)
Selection acts only on what is before it and not with an end goal in mind. • Selection may lead to adaptations that … are either a further modification of traits already present (by changing their use) or… • selection may act to eliminate traits • All of the trends in selection that cause traits to change over time are adaptive but the changes are not done with some pre-determined end goal in mind Evolution is blind!
Many traits evolved under one selective regime but are now being used under a very different selective regime. • The current function may not reflect the context in which the trait was originally evolved • Need to distinguish current utility from historical origin Identifying adaptations can be difficult and care must be taken
What kind of story do the slides tell us • What was the original explanation for the adaptive value of the Giraffe neck? • What other possibilities have now been investigated? • Does the giraffe neck give any feeding advantage to those who possess it? Giraffes
the neck is now cooptedfor use in feeding higher in the trees than other organisms can. • Sometimes the term pre-adaptation is used for such co-opted traits But pre-adaptation is a bad label to use here. • The term exaptation has been suggested by Stephen Gould • refer to situations in which traits perform a certain function now but either arose originally for some other function or had no function at all originally If the giraffe neck was actually selected for as a means of defeating other males in a battle over females, then
In male giraffes if long necks were originally adapted for fighting then their current advantage for feeding would be an exaptation (originally arose for a different adaptive reason) • but in females long necks would be a spandrel since they originally arose with no adaptive value for females but now may impart a feeding advantage. • Examples of exaptations: bone tissue skull sutures Gould has also proposed the use of the term spandrel for an adaptation that originally arose with no adaptive purpose at all but now has adaptive value
Seeks to find adaptive explanation for every trait in organisms • Much difference of opinion on this approach • Everything is not adaptive. Some things are actually maladaptive or non-adaptive. Some traits or variations in traits are actually selectively neutral • Adaptations are not always perfect • Need to keep in mind that Adaptation is also constrained by compromises, trade-offs and correlations with other traits • We will discuss each of these ideas later Adaptationist program
To determine that a trait is actually an adaptation we need to…. • determine what the trait is for and then …. • show that individuals that have that trait actually contribute more genes to the next generation than the individuals that don’t have the trait • The obvious answer is not always the right one Various types of studies are involved in the attempt to explain what is happening in an evolutionary context
Giraffe story in the text • What are the two current hypotheses? • The case of the giraffe demonstrates the importance of being able to look at things with fresh eyes and come up with alternative hypotheses. • Examine the picture to the left does it suggest a third possible hypothesis for long necks?
Experiments • Observational studies • Comparative studies Three major approaches to determining adaptive significance of traits
What is being investigated? Experimental exampleZonosemata (snowberry) flies and jumping spiders
Zebra Jumping spiders stalk their prey. Warn others of their species off with leg waving behavior A prey of the jumping spider, the snowberry fly, exhibits a curious behavior that resembles the leg-waving of the jumping spider. QUESTION: Why do the flies wave their striped wings?
What are 3 hypotheses that might explain this behavior? Experimental exampleZonosemataflies
What were some of the controls used in the experiment and why was each important? • What was the experimental set-up Experimental exampleZonosemataflies
What predictions were made? Experimental exampleZonosemataflies
What were the experimental results? Experimental exampleZonosemataflies
RESULTS Retreat Stalk and attack Kill
What important points of experimental design are demonstrated in the Snowberry Fly example?
What were the control groups in this experiment? • Why were they important? • Allow us to work towards eliminating competing hyotheses. Effective Controls
What were some of the things considered here? • Same arena • Method of presentation of flies • Timing of presentation • Others? Handling all treatments exactly alike
What needed to be randomized and why? • Order the flies were presented in • Others? Radomization
Sample size needs to be large enough for statistical analyses. • Replicated experiments reduce the amount of distortion because sample size is larger which lowers the amount of bias. • Allow the measurement of variation in data points. Repetition
Observational Studies With Garter Snakes
When are these type of studies done? • In this method we need to show two things: 1. Occurrence of trait is non random in the population 2. The observed trait is adaptive Example – Garter Snake study How did this study show that snake movements is an adaptation to control body temperature? Observational Studies
Watched snakes, where they spent their time and what their body temps were • Found that they maintain their body temperatures between 28 and 32 degrees Celsius. • Discovered options for thermoregulation sun/shade, under rocks (thin, medium, thick), or moving up or down in burrows. Show they are choosing a particular temperature more often than would happen by random movements
Studied thin, medium and thick rocks. • Predicted only medium rocks work for the right temps both night and day. • Most snakes found under rocks. Found that of the 3, all could be used to effectively maintain desired daytime temps but only rocks could provide enough warmth at night
Compared availability of thin, medium and thick rocks in the habitat to the frequency that each was used by garter snakes • All rocks are equally represented in the habitat so if random events, the snakes should be found equally under each type of rock. • Results …. Now have to show that being under medium rocks is not random behavior
Tests for patterns across species • Proper application of comparative methods requires knowledge of the evolutionary relationships among the species under study. • Example bat studies Comparative Studies
Bats: Is the larger size of testes in some bats adaptive due to sperm competition? • Do bats from larger social groups have larger testes because there is more competition for passing on their genes? Example of comparative study
The testes size could still be related to who evolved from whom. • Perhaps the larger testes groups are simply from one common ancestor and the smaller from another. • Need to do a correction for this If we replace the individual points for A, B and C and for D,E and F with a single point representing their most recent common ancestor we get…. But the data could be skewed by evolutionary relationships.
Plot sister species independently When species diverge from a common ancestor does the species that evolves larger group sizes also evolve larger testes? Erase lines Drag point closest to the vertical axis to the origin
Bat results: show that when a bat species evolved larger group sizes than its sister species, it also tended to evolve larger testes for its body size.
De Meester’s second experiment No stocking Heavy Stocking Reduced stocking
In order to show that one thing has evolved from similar structures in ancestors must be able to … 1. Establish the ancestral condition 2. Understand the transformational sequence, how and why the characters changed through time Every Adaptive Trait Evolves from something else
Video demonstrating transitional adaptations Whale evolution You may review this video at http://www.pbs.org/wgbh/evolution/library/03/4/quicktime/l_034_05.html
Adaptations work with what is available Many structures are far from optimally designed