Rates and trends of evolution

Rates and trends of evolution
evolution msc

1. University of education lower mall
campus Lahore









Topic:
Rates and Trends of evolution

2. Subject: Evolution and principle of
systematics

3. Contents
Introduction
Nannoplanton tree and diversity history
Evolutionary trends
Types of evolution
 Divergent
i. Allopatric
ii. Parapetric
iii. Peripatric
iv. Sympatric
 Convergent
 Parallel evolution
 Coevolution
Dollo’s law of irreversibility
Copes law
Exclusion law
Rate of evolutionary change
Hypothesis to explain the rate of evolution
References

4. Rate of Evolutionary Change:
Rate of evolution is a measurement of the rate of genotype change of
species and organisms over a period.
Evolutionary change can be estimated by examining fossils and
species that are related to each other
To provide robust information about evolution we need to study
biological groups that fossilize readily and provide abundant specimens
from widespread localities. Calcareous nannofossils are present in
almost all marine sediments stretching back over 200 million years, and
billions of specimens are present in very small samples of sediment
(<1cm
3
) by only one of these, or by both.

5. Nannoplankton family tree and diversity history:
This allows us to reconstruct their evolutionary history, e.g. first
appearance, times of high diversity or extinction, etc., and to investigate
the relationship between evolutionary trends and possible
 Controlling factors:
 Climate
 Ocean chemistry
 Tectonics.

6. Nannofossils have been particularly useful in understanding rapid and
catastrophic events, such as the large meteorite impact event that
occurred at the end of the Cretaceous (65.5 million years ago).
It was event that ended the reign of dinosaurs on land, and ammonites
and large reptiles in the sea, but it also almost obliterated several
plankton groups in the oceans, including nannoplankton and planktic
foraminifera.
Nannoplankton studies provide detailed records of the precise timing
and recovery associated with this mass extinction event and show that
the extinction was geological instantaneous and global, eradicating the
oceanic species but with survivorship limited to the hardier,
opportunistic forms that lived in shelf-sea environments.
Recolonizations of the oceans was rapidly achieved through the
descendants of these survivor specie

Evolutionary trends

Which may be defined broadly as identifiable patterns in which the
overall evolution of a trait
McKinney (1990) suggested, “The concept of ‘trend’ is arguably the
single most important in the study of evolution,”

7. Alroy (2000) described their study as “one of the oldest and more
intriguing topics in evolutionary biology,”
Gould (2002) noted, “Trends occurs in a given direction within a group
for a prolonged period represent the primary phenomenon of evolution
at higher levels and longer time scales.” It is therefore critical that the
nature, generality, underlying causes, and significance of trends neither
overlooked nor overstated.

8. Fig shows the evolutionary trends
Evolutionary trends represent directional changes in the average value of
a given characteristic, such as body size (e.g., Alroy 1998) or some
measure of complexity (e.g., number of cell types or differentiation of
serially repeated limbs; Valentine et al. 1994; Adamowicz et al. 2008),
among species and their descendants over prolonged periods of time.
The values of an undefined physical trait (“morphology”) of older
species are given in gray, and those of newer species are shown in white.
In a, new species that differ from their ancestors in this morphological
trait have appeared, but this has included both increases and decreases in
the parameter in question in roughly equal measure, which means there
has been no net change in the average and thus no trend with regard to
this feature.
In b, increases have occurred but decreases have not been possible,
perhaps because of a physical limitation. In this case, there is an increase
in the average of the trait in younger versus older species, but this is

9. because of the fact that diversification was free to happen in only one
direction.
In c, there is a clear increase in the value of the trait in the whole
distribution; in fact, nearly the entire initial distribution with lower
values has been replaced over time. Figure from Wagner (1996),
reproduced by permission of Blackwell
Types of Evolution
Summary Types of Evolution
Evolution over time can follow several different patterns. Factors such
as environment and predation pressures can have different effects on the
ways in which species exposed to them evolve.
Three main pattern of evolution:
 Divergent
 Convergent
 Parallel evolution.
 Coevolution

10. Divergent Evolution:
When people hear the word "evolution," they most commonly think of
divergent evolution, the evolutionary pattern in which two species
gradually become increasingly different. This type of evolution often
occurs when closely related species diversify to new habitats. On a large
scale, divergent evolution is responsible for the creation of the current
diversity of life on earth from the first living cells. On a smaller scale, it
is responsible for the evolution of humans and apes from a common
primate ancestor.

11. Divergent evolution is the process in which a trait held by a common
ancestor evolves into different variations over time. A common example
of divergent evolution is the vertebrate limb. Whale flippers, frog
forelimbs, and your own arms most likely evolved from the front
flippers of an ancient jawless fish. Because they share a common
evolutionary origin, these are examples of homologous structures.
An important consequence of divergent evolution is speciation, the
divergence of one species into two or more descendant species.
Speciation can occur four major ways:
 Allopatric speciation occurs when a population becomes
separated into two entirely isolated subpopulations. Once the
separation occurs, natural selection and genetic drift operate on
each subpopulation independently, producing different
evolutionary outcomes.

12.  Peripatric speciation is somewhat similar to allopatric speciation,
but specifically occurs when a very small subpopulation becomes
isolated from a much larger majority. Because the isolated
subpopulation is so small, divergence can happen relatively rapidly
due to the founder effect, in which small populations are more
sensitive to genetic drift and natural selection acts on a small gene
pool.
 Parapatric speciation occurs when a small subpopulation remains
within the habitat of an original population but enters a different
niche. Effects other than physical separation prevent interbreeding
between the two separated populations.

13. Genetically isolated populations is so small, however, the founder
effect can still play a role in speciation.
 Sympatric speciation, the rarest and most controversial form of
speciation, occurs with no form of isolation (physical or otherwise)
between two populations.

14. Parallel evolution:
Parallel evolution is sometimes difficult to distinguish from convergent
evolution. Parallel evolution occurs when different species start with
similar ancestral origins, and then evolve similar traits over time. This
kind of thing happens because the two different species, though they do
not necessarily share a common ancestor, experience similar kinds of
environmental pressures and survive only by undergoing similar
adaptations.
A classic example of parallel evolution found among plants, in which
several similar but distinct forms of leaf evolved in parallel and are
evident today.

15. Coevolution:
Coevolution occurs when closely interacting species exert selective
pressures on each other, so that they evolve together in a kind of
conversation of adaptations. Examples of coevolution are common
among predator-prey and host-parasite pairs.
Examples of coevolution occur among
Hummingbirds and the flowers from which they seek nectar and
unwittingly pollinate.

Convergent Evolution:

Convergent evolution is the process in which species that are not closely
related to each other independently evolve similar kinds of traits.

16. For example
Dragonflies, hawks, and bats all have wings. None of these organisms
owes its wings to genes inherited from any of the others. Each kind of
wing evolved independently, suggesting that the trait of flight is a useful
one for the purpose of survival and reproduction. These independently
evolved wings are called analogous structures.
Convergent evolution causes difficulties in fields of study such as
comparative anatomy. Convergent evolution takes place when species of
different ancestry begin to share analogous traits because of a shared
environment or other selection pressure.
For example:
Whales and fish have some similar characteristics since both had to
evolve methods of moving through the same medium that is water.

17. Parallel Evolution:

Parallel evolution occurs when two species evolve independently of
each other, maintaining the same level of similarity. Parallel evolution
usually occurs between unrelated species that do not occupy the same
or similar niches in a given habitat

18. Dollo's law:
A law proposed by Louis Dollo, describing evolutionary irreversibility:
once regarded as inevitable, but now considered to apply mainly in
special cases.
The potential for further useful mutation may well be very limited in
highly specialized organisms, since only those mutations that will allow
the organism to continue in its narrow niche will normally be
functionally possible.

19. In such cases, there is therefore a self-perpetuating, almost
irreversible, evolutionary trend, so much so that it is regarded virtually
as a law, Dollo's law. The trend results from steady directional selective
pressure, or orthoselection reinforced by specialization.

Cope's rule:


Copes law:

Cope's rule, named after American paleontologist Edward Drinker
Cope,
Postulates that population lineages tend to increase in body size
over evolutionary time

20. It was never actually stated by Cope, although he favored the
occurrence of linear evolutionary trends.

It is sometimes also known
as the Cope–Depéret rule,


Cope's rule states that evolution tends to increase body size over
geological time in a lineage of populations.
Evolutionary trends towards an increase in body size are common in the
fossil record. For example, the Eocene ancestors of modern horses were
about the size of a dog. Since then, in the lineages showing the largest
increases, horses have evolved to become as much as 10 times heavier.
Cope's rule is named after the paleontologist Edward Drinker Cope.
Figure: over the last sixty million years, the average weight of horses has
increased ten times.
Exclusion principle:
The competitive exclusion principle, sometimes referred to as Gause's
Law of competitive exclusion or just Gause's Law, states that two
species that compete for the exact same resources cannot stably coexist.

21. Evolutionary Change, Rate of evolution
Resources
Rates of evolution change vary widely, among characteristics, and
among species. Evolutionary rate of change can be estimated by
examining fossils and species that are related to each other.
The rate of change is governed partly by the life span of the species
under examination; species whose individuals have short life spans are
generally capable of changing more quickly than those that have a
longer life span and reproduce less often. Yet, even short-lived species
such as bacteria, which have generation times measured in minutes, may
not manifest noticeable evolutionary changes in a human’s lifetime.

22. One technique that has been used to examine the rate of evolutionary
change is DNA analysis. This technology involves identifying the
percentage of similarity between samples of DNA from two related
organisms under study.
The greater the similarity, the more recently the organisms are
considered to have diverged from a common ancestor. The information
that is obtained in this manner is compared to information obtained from
other sources such as the fossil records and studies in comparative
anatomy.
There are two competing hypotheses designed to describe the rate of
evolutionary change:
One is called the punctuated equilibrium hypothesis. This states that
there are periods of time in which evolutionary change is slow—periods
of stasis or equilibrium. These are interrupted or punctuated by periods
of rapid change. Rapid change may occur
For example
when a small population is isolated from a larger parent population.
Most small populations die out, but those that survive may be able to
evolve more quickly because new genes can spread more quickly in a
small population. If the species recolonizes a wider range, its rate of
evolutionary change will slows down and the species appears to make an

23. abrupt appearance in the fossil record, which is unlikely to preserve any
given individual and so is weighted toward common species.
The other primary hypothesis is that of gradual change:
This states that species evolve slowly over time. In this hypothesis, the
rate of change is slow, and species that do not change quickly enough to
develop traits enabling them to survive will die. On this view, the
sudden appearance of most species in the fossil record is due to the
extreme rarity of fossilization events. The fossil record is thus like a
movie film with 99% of the frames cut out and only a random selection
of moments retained.
Although some species such as the sequoia (redwoods) or crocodiles
have maintained distinct and similar characteristics over millions of
years, some species such as the cichlids in the African rift lakes have
rapidly change in appearance over mere thousands of years. Most
evolutionary biologists today acknowledge that there is evidence that
both gradual and sudden evolutionary change occur. The question is not
which occurs, but which occurs more often, and why either dominates in
any given case.
Several factors can influence evolutionary rate.:
The mutation rate

24. The rate at which random changes in appear in a species’ DNA. Higher
mutation rates enable faster evolutionary change, in principle. However,
in the field mutation rates do not seem to have major effects on limiting
evolution because diversity in morphological evolution (evolution of
physical characteristics) does not correlate well with DNA mutation
rates.
Yet in some special cases, especially in microorganisms, evolution rates
do depend on mutation rates. A good example is the rapid evolution of
resistance to antiviral drugs by the human immunodeficiency virus
(HIV), which causes acquired immunodeficiency syndrome (AIDS).
HIV has a very high mutation rate and allowing any virus to survive a
course of medications can allow survivors of them medication to evolve
resistance. This is why it is important for persons with AIDs to take their
medicine consistently.
Selective pressure can also influence evolutionary rate. Selective
pressure can be imagined as the importance of a given feature in a given
environment. If a certain species of bird is accustomed to using fine,
narrow beaks to extract seeds from a certain bush for food, but a drought
kills off many of those bushes while leaving another kind of bush with
large, heavy-shelled seeds relatively intact, then there would be selective
pressure for beaks to become heavier and shorter in this group. That is,
birds who randomly happened to have bills better suited to eating the

25. available food would have a better chance of eating well and
reproducing, so each new generation of birds would be descended from
these heavier-beaked individuals. This form of natural selective pressure
has been recorded on a painstaking, bird-by-bird basis over years among
Darwin’s finches in the Galápagos Islands.
Scientists have discovered that some species of bacteria and yeast,
including the primary bacterium of the human digestive
system, Escherichia coli, can change their mutation rate in response to
environmental stress. More stressful environments trigger mechanisms
allowing more mutations, which enables faster evolution and therefore
adaptation of the species to the changing environments. In effect, certain
species turn up the speed control on their own evolution in response to
environmental factors
References:
Dronamraju, Krishna R. and Bruce J. MacFadden. “Fossil Horses and
Rate of Evolution.” Science. 308 (2005): 1258.
Pagel, Mark, et al. “Large Punctuational Contribution of Speciation to
Evolutionary Divergence at the Molecular Level.” Science. 314 (2006):
119-121.

26. Pawar, Samraat S. “Geographical Variation in the Rate of Evolution:
Effect of Available Energy or Fluctuating Environment?” Evolution. 59
(2005): 234-237.
Rosenberg, Susan M. and P.J. Hastings. “Modulating Mutation Rates in
the Wild.” Science. 300 (2003) 1382-1383.