Download Sex: Origin and Evolutionary Relevance

Sex: Origin and
Evolutionary
Relevance
RONALDO FERNANDES
Universidade Federal do Rio de Janeiro
Museu Nacional
[email protected]
Biologist take on
Astrobiology
Life shapes planets
Life shapes planets
 Human
impact is extensive
Life shapes planets
 Human
impact is extensive
Shaped
the terrain
Human
influence
Life shapes planets
 Human
impact is extensive
Shaped
the terrain
Changed
the composition of the
atmosphere
Human
influence
Life shapes planets
 Human
impact is extensive
Shaped
the terrain
Changed
the composition of the
atmosphere
Increased
the acidification of the oceans
Human
influence
Life shapes planets
 Human
impact is extensive
Shaped
the terrain
Changed
the composition of the
atmosphere
Increased
Added
the acidification of the oceans
new materials to the surface
Human
influence
Life shapes planets
 Human
though
interference is not necessary,
Life shapes planets
 Human
interference is not necessary,
though
 Vegetation
shaped the land
Biotic
influence
Life shapes planets
 Human
interference is not necessary,
though
 Vegetation
shaped the land
 Photosynthesis
changed the atmosphere
fixing CO2 and freeing O2
Biotic
influence
Life shapes planets
 Human
interference is not necessary,
though
 Vegetation
shaped the land
 Photosynthesis
changed the atmosphere
fixing CO2 and freeing O2
 Oxigen
changed the minerals
Biotic
influence
Life shapes planets
 Holmes
(2003) explored a scenario
where life come to be extinct on Earth
Life shapes planets
 Without
photosynthesis, CO2 will quickly
accumulate in the atmosphere,
depleting the oxygen
Life shapes planets
 Without
photosynthesis, CO2 will quickly
accumulate in the atmosphere,
depleting the oxygen
 The
greenhouse effect will rise
temperatures and sea level
Life shapes planets
 Without
photosynthesis, CO2 will quickly
accumulate in the atmosphere,
depleting the oxygen
 The
greenhouse effect will rise
temperatures and sea level
 Without
vegetation soil will wash off into
the seas leaving a bare rock and sand
surface
Life
shapes
planets
Life shapes planets
 In
the long run, the greenhouse effect,
through positive feedback, can increase
to levels similar to Venus, leaving Earth
uninhabitable
Life shapes
planets
Evolution: Basic
concepts
Evolution
 Evolution
is the change in the heritable
characteristics of biological populations
over successive generations
Evolution
 Evolution
is the change in the heritable
characteristics of biological populations
over successive generations
 As
such, there are evolutionary
mechanisms that increase or decrease
variation in populations over successive
generations
Mechanisms
 Natural
Selection
 Mutation
 Genetic
Drift
 Genetic
Hitchhiking
 Genetic
Flow
Mechanisms
 Natural
Selection
Natural Selection
 Originally
introduced in 1859 by a joint
presentation of Alfred Wallace and
Charles Darwin
Natural Selection
 Originally
introduced in 1858 by a joint
presentation of Alfred Wallace and
Charles Darwin
 Further
elaborated in 1859 by Darwin’s
book, On the Origin of the Species
On the
origin of
species
(1859)
Natural Selection
1.
Phenotypic Variation
2.
Differential Fitness
3.
Heritability of Fitness
The
descent of
man
(1871)
Sexual Selection
Sex
 Why
Sex?
Ameivul
a nativa
Ameivula nativa
 Parthenogenic
species
Ameivula nativa
 Parthenogenic
•
species
All individuals are female
Ameivula nativa
 Parthenogenic
 Compared
species
to other similar species, a
female of Ameivula nativa produces
about twice the number of females of a
sexual species
Ameivula nativa
 Parthenogenic
species
 Compared
to other similar species, a
female of Ameivula nativa produces
about twice the number of females of a
sexual species
 If
sex is so costly, why even bother?
Cost of sex
 Near
all Eukaryotes are sexual species
Cost of sex
 Near
•
all Eukaryotes are sexual species
Sort of. Fungi and protozoans don’t have
males and females but, still, produce a
number of mating types
Cost of sex
 Near
 Also,
all Eukaryotes are sexual species
it is possible that most if not all
asexual Eukaryotes are descendants of
sexual species
Cost of sex
 Near
all Eukaryotes are sexual species
 Also,
it is possible that most if not all
asexual Eukaryotes are descendants of
sexual species
•
Considering that sex needs a lot of
energy, it is likely to be related to the
origin of the Eukaryotes, about the time
O2 would become easily available
Trichoma
s giemsa
Cost of sex
 Near
all Eukaryotes are sexual species
 Also,
it is possible that most if not all
asexual Eukaryotes are descendants of
sexual species
 Being
such a widespread feature suggest
it might be an adaptive advantage
Sex amplifies variation
 August
Weismann (1889)
Sexual reproduction can also increases the differences
between individuals… Such differences afford the
material by means which natural selection is able to
increase or weaken each character according to the
needs of the species.
Sex amplifies variation
 It
is possible that sex evolve to generate variation.
Sex amplifies variation
 It
is possible that sex evolve to generate variation.
 However…
Sex amplifies variation
 It
is possible that sex evolve to generate variation.
 However…
1.
Sex not necessarily increase variation
Variability
decrease
caused by
sex
Sex amplifies variation
 It
is possible that sex evolve to generate variation.
 However…
1.
Sex not necessarily increase variation
2.
Variation through sex often reduces fitness
Fitness
reduction
caused by
sex
Modern models of sex evolution
 Selection
varies with time
Modern models of sex evolution
 Selection
•
varies with time
Sex can break genetic associations created by past
selection that are not favorable anymore
Modern models of sex evolution
 Selection
varies with time
•
Sex can break genetic associations created by past
selection that are not favorable anymore
•
The Red Queen hypothesis for evolution of sex
Red Queen
Modern models of sex evolution
 Selection
varies with time
•
Sex can break genetic associations created by past
selection that are not favorable anymore
•
The Red Queen hypothesis for evolution of sex
•
Sex can be an effective defense against parasites as it
allows hosts to shuffle their genes in combinations
harder to parasites to adapt to
Modern models of sex evolution
 Selection
varies with time
•
Sex can break genetic associations created by past
selection that are not favorable anymore
•
The Red Queen hypothesis for evolution of sex
•
Sex can be an effective defense against parasites as it
allows hosts to shuffle their genes in combinations
harder to parasites to adapt to
•
Studies with sexual and asexual snails seems to
conform to the Red Queen hypothesis
Modern models of sex evolution
 Selection
varies with time
 Selection
varies over space
•
If selection varies with space, migration can cause some
genetic associations to be locally detrimental
•
In such case, sexual species can quickly break
deleterious associations by crossing locals with
migrants
Modern models of sex evolution
 Selection
varies with time
 Selection
varies over space
 Rates
of sex vary among individuals
•
In many organisms, sex become more common if they
are in poor conditions
•
Under stress circumstances, an organism’ genotype may
not match the environment requirements
•
Sex would allow those organisms to quickly change
their genotype
Modern models of sex evolution
 Selection
varies with time
 Selection
varies over space
 Rates
of sex vary among individuals
 Populations
are finite
Modern models of sex evolution
 Selection
varies with time
 Selection
varies over space
 Rates
of sex vary among individuals
 Populations
are finite
•
In a finite population, it is conceivable that the best
genotypes could be lost in stochastic processes
•
Sexual organisms has a better chance to regain those
genotypes through recombination than asexual ones
through mutation
Sexual Selection
Sexual Selection
 Sexual
selection is a special case of
natural selection where mating success
is favored instead of fitness
Sexual Selection
 Sexual
selection is a special case of
natural selection where mating success
is favored instead of fitness
 There
are two kinds of sexual selection:
Sexual Selection
 Sexual
selection is a special case of
natural selection where mating success
is favored instead of fitness
 There
1.
are two kinds of sexual selection:
Members of one sex create a
reproductive differential by competing
among themselves for opportunities to
mate
Ritual
Male
Combat
Ritual
Male
Combat
Sperm
Competitio
n
Sexual Selection
 Sexual
selection is a special case of natural
selection where mating success is favored
instead of fitness
 There
are two kinds of sexual selection:
1.
Members of one sex create a reproductive
differential by competing among themselves
for opportunities to mate
2.
Members of one sex create a reproductive
differential in the other sex by selecting mates
Sexual
dimorphism in
Xiphophorus
Sexual Selection
 The
concept of sexual selection was
poorly received by the Victorian society
Sexual Selection
 The
concept of sexual selection was
poorly received by the Victorian society
 Wallace
was one of the main critics. He
accepted the competition among males
but reject the concept of female choice
Sexual Selection
 The
concept of sexual selection was poorly
received by the Victorian society
 Wallace
was one of the main critics. He
accepted the competition among males
but reject the concept of female choice
 Although
much of the reaction was
misogynist bias, Darwin also argued that
“man has ultimately become superior to
woman”
Sexual Selection
 Acceptance
started in 1930, when Fisher
further developed the theory and
introduced the Fisherian runaway, which
describes how sexual selection
accelerates the preference for a specific
ornament, causing both the trait and the
female preference for it to increase in a
positive feedback runaway cycle
Male
long-tailed
windowbird
Sexual Selection
 Recently,
there is a renewed interest in
sexual selection, with the proposal of
new theories:
Sexual Selection
 Recently,
there is a renewed interest in
sexual selection, with the proposal of
new theories:
•
The Handicap Principle suggests males
with a serious handicap that survive until
the age of reproduction may be regarded
as extremely fit by females, as they were
able to overcome their limitations
Sexual Selection
 Recently,
there is a renewed interest in
sexual selection, with the proposal of
new theories:
•
The Chase Away theory proposes the
evolution of exaggerated male display
characters is based on antagonistic
coevolution between sexes
Sexual Selection
 Recently,
there is a renewed interest in
sexual selection, with the proposal of
new theories:
•
The idea of sexual selection as protection
against extinction as it is efficient in
removing undesired traits from the
population
Sexual Selection
 Recently,
there is a renewed interest in
sexual selection, with the proposal of
new theories:
•
The Sensorial Exploitation, in which
exaggerated male traits may provide
sensory stimulation females find hard to
resist
Tungara
Frog
Tungara
Frog
Case study
 Frog
Physalaemus signifer, a common
species from Rio de Janeiro
Physalaemu
s signifer
Case study
 Frog
Physalaemus signifer, a common
species from Rio de Janeiro
 Ph.D.
thesis of Marcos Bilates
 Field
work was done mainly at Magé
between 2009 and 2011
 Experiments
Nacional
were done at the Museu
Case study
 Field
work revealed females did not have
a bias for heavier males
 Also,
coupling was independent from
overall size
 Finally,
no significant difference in size or
mass among singer and satellite males
Experiments
Case study
 Females
did not showed preference for:
•
Calls with an added chuck
•
Difference in the tone
•
Duration of the calls
Case study
 Females
did showed preference for:
•
Calls with more repetitions
•
Louder calls
Physalaemu
s signifer
Acknowledgments
 Marcos
Bilates
 Renato
Feio