Tutorials
,Study questions day 1: The concept of adaptations
Study instructions:
Read: Animal Physiology pages 9-11 From “Natural selection is a key process of evolutionary
origin” until “This Book’s Approach (...)”, 26-32 From “Evolutionary processes” until the end of
the Chapter
Watch: https://youtu.be/ei0FAt8k44Q
Read the information below
Book Page 9-11 Summary:
- “Natural selection is the increase in frequency of genes that produce phenotypes that raise the
likelihood that animals will survive and reproduce.”
- “And adaptation is a physiological mechanism or other trait that is a product of evolution by natural
selection.”
- Why the trail is beneficial/ an asset: adaptive significance
o Example: Fireflies. The mechanisms that is able to produce light is an adaptation, however,
the mate attraction is the adaptive significance. The firefly light-producing mechanism
evolved by natural selection
Book Page 26-32 Summary:
- “Evolution is a change of gene frequencies over time in a population of organisms.”
- “Natural selection creates a better match between animals and their environments.”
- “A trait is an adaptation if it has come to be present at high frequency in a population because it
confers a greater probability of survival and successful reproduction in the prevailing environment
than available alternative traits. Thus, adaptations are products of the process of natural selection.”
- Nonadaptive evolution: “Because of a chance, an allele that provides a lower probability of survival
and reproduction than an available alternative comes to be the predominant allele in the
population.”
- “Processes in which chance assumes a preeminent role in altering gene frequencies are termed
genetic drift.” There is always a chance. In what genes go on, which genes split up, mass deaths...
- Founder effect: “the founding individuals (of an island) may by chance be genetically
nonrepresentative of the population from which they came.”
- “The control by an allele of a single gene of two or more distinct and seemingly unrelated traits is
called pleiotropy.”
o Example Mosquitos: “The allele of an enzyme-coding gene has two effects on
mosquitos that simultaneously has two effects. The allele both (1) increase the
resistance of the mosquitoes to organophosphate insecticides and (2) decrease the
physiological tolerance of the mosquitoes to the cold of winter. Selection will favor the
allele discussed because it confers insecticide resistance, but the allele will also diminish
the odds of winter survival.”
- “A trait may have evolved as an adaptation to an ancient environment yet persist even though the
environment has changed. In the new environment, the trait may no longer be beneficial and thus
may not be an adaptation.”
- Techniques to study the question of adaption when nature fails to provide an ideal natural
experiment:
o “The comparative method: seeks to identify adaptive traits by comparing how a
particular function is carried out by related and unrelated species in similar and
dissimilar environments. This method is based on the premise that although we cannot
see evolution occurring in the past, the many kinds of animals alive today provide us
with many examples of outcomes of evolution, and patterns we identify in these
outcomes may provide insights into processes that occurred long ago.”
o “Studies of laboratory populations over many generations: changes in gene
frequencies can be observed over multiple generations in laboratory populations of
fast-breeding animals such as fruit flies. By exposing such populations to specific,
controlled conditions (e.g., high or low desiccation stress), physiologists may observe
, which alleles are favored by selection when a particular condition prevails. [...] The
selection that occurs in cases like this is usually considered to be laboratory selection or
artificial selection because humans are manipulating the circumstances.”
o “Single-generation studies of individual variation: Individuals in a natural population of
a single species typically vary in their physiological properties. [...] Such natural
variation among individuals can be exploited to carry out single-generation experiments
to determine which traits are most advantageous.”
o “Creation of variation for study: Biologists may be able to create variation in a trait that
shows little or no natural variation among individuals of a species (e.g., morphological
manipulations). [...] One newer approach is to employ genetic manipulations. [...],
knockout animals that lack the functional copies of a gene of interest can be produced,
or RNA interference (RNAi) can be employed to block transcription of a gene.”
o “Studies of the genetic structures of natural populations: Natural populations are
sometimes genetically structured in revealing ways. Genetic clines provide excellent
examples. A genetic cline is a progressive change in allele frequencies or gene-
controlled phenotype frequencies along a environmental gradient. Genetic patterns [...]
often point to ways in which natural selection differs in its effect from place to place.”
o “Phylogenetic reconstruction: the goal is to determine the structure of the family tree
(the ancestry) of groups of related species, often using molecular genetic data. Useful:
(1) when in evolutionary history each trait evolved and (2) whether a trait evolved
independently more than once; several independent origins in one environment
suggest that a trait is adaptive to the environment.
- “Traditionally, biologists have emphasized averages. When measurements have been made on
large numbers of individuals in a population, the measurement have been averaged, and only the
averages have been used for further analysis. By contrast, the biologists who focus on
“personalities” are hypothesizing that when the individuals in a population exhibit consistent
individual differences, this individual variation may be important in its own.”
o For example, some humans have a relatively high rate of O 2 consumption and excel at
long-distance races, whereas other have a medium to low O 2 consumption and might
excel better at sports such as weightlifting.
YouTube Video: “1.4 – Evolutionary Thinking: Why it is Problematic and How to Recognize it” [13:12]
- Adaptation can be problematic: It is the central character in “just-so” stories, often coupled to an
imaginary environment in the evolutionary past that has just the characteristics needed to make a
favorite hypothesis plausible.
- Claims of adaptation should not be accepted unexamined. Any hypothesis of adaptation needs to
be tested against alternatives.
- Evolutionary biologists have developed several criteria for recognizing adaptations, such as:
o Natural Selection (“The best”)
Natural selection on a trait exists given a correlation between variation in the
trait and variation in reproductive biomass.
A response to natural selection occurs when some variation in the trait is
heritable.
You document heritable changes in the trait that result from a demonstrated
correlation of trait state with reproductive success.
Example: The many cases of experimental evolution. The adaptations is the
amount of change that has occurred due to natural selection.
o The perturbation criterion (“Convincing”)
This criterion requires both a predictive model and an experiment.
An adaptation is that state of a trait predicted by a model that is tested (and
confirmed) by using some method to perturb the phenotype from the optimal
state and to demonstrate that the fitness of the perturbed phenotypes is lower
that the fitness of the predicted one.
Example: Clutch size experiments on kestrels.
o The functional criterion (“Induced responses convincing”)
, Defines adaptation as an appropriate plastic response.
An adaptation is a change in a phenotype that occurs in response to a specific
environmental signal and has a clear functional relationship to that signal and
improvement in growth, survival, or reproduction.
Otherwise, it does not appear.
Example: Spines and helmets in Daphnia are induced by dissolved molecules
associated with predators whose efficacy is reduced by spines and helmets.
They have a reproductive cost and are not produced in the absence of the
predators.
Example: Bent shells in barnacles make them resistant to snail predators but
reduce their fecundity (Fruchtbarkeit).
Example: Snails parasitized by castrating digenetic trematodes reproduce
earlier.
o The design criterion (“Plausible if Lauder’s questions answered)
Adaptation can be recognized by its complexity and conformity to a priori
design specification – by its resemblance to something that an engineer might
design.
Any complex organ that performs a difficult function efficiently, e.g., the dark-
adapted human eye, which can detect arrival of photons produced by a single
match at a distance of 10km.
o The Evolutionary Stable Strategy (ESS) or invasion-resistance criterion (Only as good
as mutant’s trait – rather difficult to arrange experimentally)
Think of a population with a trait that is a candidate for adaptation.
To test the adaptation claim, allow the population to be systematically and
repeatedly invaded by all possible alternative states of the trait in all orders and
combinations.
If the candidate adaptation can resist invasion by alternative states, then we
can say that it is an adaptation in the sense of an evolutionary strategy that
resists invasion by competitors.
Cases not covered by the ESS criterion
A beats B beats C beats A eternal cycles, e.g., rock-paper-scissors
game.
The state that resists all invaders is not attainable in phenotype space.
(There might be a constraint in the system.)
Negative frequency-dependence yielding an adapted set of
phenotypes, not a single best-adapted phenotype. (The stable state of
a population is a mixture of things, rather than a single thing.)
Cases where the invasion challenge is hard to arrange and the ability to
resist invasion has not been convincingly tested.
Lauder’s 5 Questions about Claims of Adaptation:
1. Have experiments been done to support the claimed function?
2. Has the performance of the trait in the fulfillment of that function been compared with
alternative states of the trait?
3. Do phylogenetic analyses suggest that the state claimed to be an adaptation is repeatedly
associated with the kind of natural selection needed to produce that adaptation?
4. Could the trait have been selected to this state as a byproduct of selection on other traits?
5. Is it a spandrel? Might the claim of adaptation be confounded by an inappropriate abstraction
of a piece of the organism from the larger whole in which it is naturally embedded?
Bottom Line: Adaptation is only problematic if not tested or testable. Beware untestable claims of
adaptation.
