STUDYING ADAPTATION: EVOLUTIONARY ANALYSIS

Chapter 10 in the 4th edition, Chapter 9 in the 3rd.

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review questions

Introduction

1. Adaptation
2. Adaptationist 

9.1 -- ALL HYPOTHESES MUST BE TESTED: 
         The GIRAFFE'S NECK RECONSIDERED

1. Hypothesis: Giraffes have long necks for feeding high in trees. 
   1. Lamarckian evolution
      1. Lamarck's Vitalism from the emuseum
   2. Darwinian natural selection 
   3. Flaws in "obvious" hypothesis 
      1. Giraffes prefer to feed at shoulder height. [Fig. 8.2] 
      2. Male giraffes use their heads and necks as clubs for combat during mating [Fig. 8.3]
      3. Neck size and social interaction in giraffes [table 8.1] 
         1. Neck size and male social interactions. 
         2. Neck size and female choice 
   4. All Hypotheses must be tested. 
   5. Alternative explanations must also be considered. 
      1. Differences among populations or species not necessarily adaptive.
      2. Not every use of a trait is why it evolved. 
      3. Not every adaptation is perfect. 
      4. Vestigial traits (no longer functional) 
   6. How do we recognize adaptations? 
      1. Experimental manipulations 
      2. Observations 
      3. The comparative method 

9.2 -- EXPERIMENTAL APPROACHES 

What is the function of wing markings and wing waving displays of the Tephritid fly Zonosemata?

1. Is the tephritid fly Zonosemata vittigera a "sheep in wolf's clothing"? [Fig. 8.4]. 
   1. "Do the wing markings and the wing waving of Z. vittigera mimic the threat displays that jumping spiders use on each other, and thereby allow the flies to escape predation?" 
2. Create a set of hypotheses to be tested 
   1. H1: The flies do not mimic jumping spiders. Perhaps the wing flicking displays are used in courtship. (Null Hypothesis). 
   2. H2: The flies mimic jumping spiders but use the markings to deter non-jumping spider predators. 
   3. H3: The flies mimic jumping spiders and this mimicry functions to deter predation by the jumping spiders themselves. 
3. Devise a way to manipulate the system [Figure 8.5]
   1. Five experimental groups 
      1. A: untreated control 
      2. B: control for effects of operation 
      3. C: wing waving without markings
      4. D: wing markings without waving 
      5.  E. no markings or waving 
4. Specify a matrix of tests and how they would support or reject each hypothesis [Fig. 8.5 bottom] 
5. Do the experiment 
   1. A, C, and E were captured and eaten by non-jumping spider predators. 
   2. A and B avoided predation by jumping spiders [Fig. 8.6]. 
6. Conclusions 
7. Bias (accuracy) and precision [Fig. 8.7] 

9.3 -- OBSERVATIONAL STUDIES Behavioral Thermoregulation 

1. Physiological abilities of desert iguana (an ectotherm) as a function of body temperature (thermal performance curves [Fig. 8.8 plotted lines]) 
   1.  Prediction: ectotherms will use behavioral thermoregulation to maximize physiological efficiency.
   2. Results: histogram of actual distribution of body temperatures of active iguanas [Fig. 8.8]
   3. Are iguanas choosing particular temperatures or do they just happen to live in favorable environments?
   4. Is the choice of temperature adaptive? 
2. Do Garter Snakes Make Adaptive Choices When Looking for a Nighttime Retreat?
   1.  Body temperature of garter snakes in nature [Fig. 8.9] is relatively constant.
   2. Prediction: the best place for a snake to spend the night is under a rock of medium thickness [Fig. 8.10]. 
      1. WHY? 
   3. C. Adaptive choice by snakes for medium thickness rocks at night [table 8.2] 

9.4 -- THE COMPARATIVE METHOD

• tests patterns across species such as correlations among traits, or correlations between traits and features of the environment 

Why Do Some Bats Have Bigger Testes Than Others? 

1. Social group size versus testes mass in Old World fruit bats [Fig. 8.11]. 
2. Hypothesis: large testes are an adaptation for winning sperm competition. 
   1. sperm competition. 
      1. mating systems 
      2. predictions 
3. Observation: significant positive correlation between relative testes size and group size
4. Problem with analysis: Is breeding system independent of phylogeny? 
   1. The actual Hypothesis: "every time a species has evolved larger group size, it has evolved larger relative testis size" 
   2. Is each species independent of the others? 
   3. Does the sample include clusters of closely related species? 
   4. Each cluster, not each species, may be the independent sample or "event" (Fig. 8.12)
   5. Controlling for the effects of phylogeny: phylogenetically independent contrasts
      1.  Develop a cladistic phylogeny (fig 8.13a) 
      2. Identify pairs of species that have diverged from common ancestor: (fig. 8.13b)
      3. Determine the amount of change in each character = contrast (fig. 8.13c)
      4. If contrasts are correlated, each time a species evolved a larger group size than its sister species, it also evolved larger relative testis size (fig. 8.13d) 
   6. Correlated evolution of group size and testis size in 17 species of fruit bats has 12 data points (Fig. 8.14). 
   7. Conclusions. 

9.5 PHENOTYPIC PLASTICITY

1.  Same genotype produces different phenotypes in different environments. 
2. May or may not be adaptive. 
3. Phenotypic Plasticity in Behavior: Water Fleas and Fish 
   1. Variation in phototactic behavior in the asexual Daphnia [Fig. 9.16] 
      1. Three lakes [Fig 8.17], with populations showing considerable variation in phototactic behavior. Similar variability in all 3. 
      2. Fish select for Daphnia that avoid well-lit areas when fish are present 
   2. B. Phenotypic plasticity can evolve. 

EVERY ADAPTIVE TRAIT EVOLVES FROM SOMETHING ELSE 

1. Evolution uses structures that are already present
   1. Preadaptation
   2. Exaption: taking on a new function 
2. Reconstructing History 
   1. Establish homology.
   2. Determine the ancestral condition 
   3. Understand the transformational sequence. 
3. How did the Mammalian Ear Evolve? [Figs. 8.18-8.21]
   1.  The mammalian middle ear [Fig. 8.18] 
   2. An early tetrapod, Acanthostega, has a stapes [fig. 8.19]
   3. Location of the hyomandibula in fish and the stapes in tetrapods [Fig. 8.20]
   4. Evolution of the mammalian middle ear [Fig. 8.21]

9.6 -- TRADE-OFFS AND CONSTRAINTS 

• Organisms cannot simultaneously optimize all aspects of phenotype (or all aspects of fitness). 
• Organisms are not perfect.
• Factors limit adaptive evolution

Female Flower Size in Begonia: A Tradeoff 

1. Begonia is monoecious
2. Only the male flowers produce nectar. 
3. Advantageous for bees to only visit male flowers. 
4. Advantageous to female flowers to attract bees. 
5. Female flowers are virtually identical to male flowers [Fig. 8.22a]. Why? 
   1. Hypothesis 1.: The more closely the female flower resembles the male, the more likely it is to be visited. [Fig 8.23a left] 
   2. Hypothesis 2.: The more closely the female flower resembles the larger, more nectar rich male, the more likely it is to be visited. [Fig 8.23a right]. 
   3. Hypothesis 2 is supported by tests with artificial flowers [Fig 8.23b and c] 
6. Why aren't female flowers larger to induce bees to visit them with pollen?
   1. Is it maladaptive? 
   2. Does Begonia lack the genetic variation needed to produce larger female flowers? 
   3. Is there a constraint because flowers occur in inflorescences [Fig. 8.22b]? 
   4. The trade off between large flowers and numerous flowers [Fig. 8.23d]. 

Flower Color Change in Fuchsia: A Physiological Constraint 

1. Fuschia changes flower color from green to red after about 5.5 days [Fig 8.24]
2. By this time, nearly all of the pollen been exported and the stigmas are no longer receptive to pollen. 
3. It would be adaptive to get rid of flowers at this time, in order to conserve plant resources. 
4. Why are the red flowers are retained for another 5 or 6 days? 
   1. Hypothesis 1: red flowers attract pollinators to tree, where they then visit and pollinate green flowers 
      1. Prediction. 
      2. Experiments. 
   2. Hypothesis 2: Physiological constraint prevents sepals from dropping until after egg is fertilized. 
      1. Pollen tube formation and growth of abscission layer. 
      2. Flowers drop 5 days after time of fertilization. 
      3. Change in color (green to red) signals to pollinators (birds) not to waste resources on already pollinated flowers.  Why is this advantageous?

Hosts Shifts in an Herbivorous Beetle: Constrained by a lack of genetic Variation? 

1. Shifts between beetle species and host plant(s) [Fig 8.25] 
   1. Shifts illustrates that adaptive evolution can be constrained by a lack of genetic variation 
   2. Beetles can for the most part only feed on plants that are closely related or fed on by beetles that are close relatives [Table 8.4]. 

9.7--Selection acts on different levels

9.8 -- STRATEGIES FOR ASKING INTERESTING QUESTIONS 

1. Question conventional wisdom.
2. Define and directly test the predictions made by hypotheses.
3. Question and test assumptions underlying the hypotheses.
4. Study natural history.

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