Unit 2 - Chapter 4 - Sex & Societies Flashcards
Sexual reproduction in organisms:
Benefits?
Limitations?
Sexual reproduction = Fusion of gametes (sperm + egg) from two different individuals, typically of opposite sex.
Ex: plants, animals, fungi (dogs, cats, birds, insects, flowering plants, etc)
Limitations: needs a mate, fewer offspring made, energy expenditure (finding a mate, courtship, the act of procreation)
Benefits :
1. genetic variation, recombination & adaptation
2. elimination of harmful mutations (can purge mutations through natural selection b/c inferior individuas have reduced probability of reproducing and actually passing on their genes)
Asexual reproduction = no fusion of gametes. single individual produces offspring that are genetically identical or very similar to itself (binary fission, budding, fragmentation, parthenogenesis)
Ex: bacteria, dandelions, starfish, lizards, some fungi like yeast.
Contrast Isogamy & anisogamy?
These are 2 forms of sexual reproduction that differ in the size and motility of the gametes involved:
KEY DISTINCTIONS ARE SIZE, MOTILITY, QUANTITY, FERTILIZATION.
- ISOGAMY : fertilization of gametes from 2 individuals are similar in size and motility. Quantity of gametes from each is the same. No distinction between male and female gametes. Organisms often have two morphologically identical gametes or gametangia.
- ANISOGAMY : fertilization of gametes from 2 individuals differ in sizes or and/or motility. Distinction between male and female. Male gamete smaller, more motile, more numerous (quantity is more from males). Females, the opposite.
What are 3 patterns of genetic sex determination?
What are examples of environmental sex determination?
Three patterns of genetic sex determination are:
- XX/XY system: In this system, individuals with two X chromosomes (XX) develop as females, while individuals with one X and one Y chromosome (XY) develop as males. Ex: mammals, including humans.
- ZZ/ZW system: In this system, individuals with two Z chromosomes (ZZ) develop as males, while individuals with one Z and one W chromosome (ZW) develop as females. Ex: birds, some reptiles, and certain fish species.
- X0 system: In this system, individuals with one X chromosome (X0) develop as males, while individuals with two X chromosomes (XX) develop as females. Ex : insects, such as grasshoppers.
Examples of organism that undergo environmental sex determination :
- Turtles : where the incubation temperature of the eggs determines the sex of the offspring (warmer temp = females, cooler temp = males)
- Crocodiles : same
- Fish : water temp or social cues can influence sex development.
CAN IT BE ADAPTIVE?
YES, It allows organisms to adjust their sex ratios based on environmental conditions, which can be beneficial for population dynamics and species survival. By producing males or females in response to environmental cues, organisms can optimize reproduction and adapt to changing conditions.
Dioecious plants?
Monoecious plants?
Hermaphrodite plants?
- DIOECIOUS : male & female reproductive structures on separate plants. Requires cross pollination b/w male and female plants to produce seeds. Why? Increases genetic diversity & reduces risk of self-fertilization. Ex: kiwi, asparagus, holly shrub
- MONOECIOUS : aka. polygamous plants, separate male and female flowers or cones on the same plant, meaning there are male flowers/cones and then separately, female flowers and cones, but on the same plant. Cross pollination is required for fertilization to occur.
- HERMAPHRODITE : aka. monoecious, both reproductive structures on same flower, meaning each flower has both male and female reproductive organs, but still on the same plant. . capable of self-fertilization, but can also cross-pollinate with others allowing for increased genetic variation within populations. Ex: maize, sunflowers, apple tree, peach tree, earthworms, some snails.
Furthermore:
Simultaneous hermaphrodites: Simultaneous hermaphrodites possess both male and female reproductive organs at the same time. They can self-fertilize, meaning they can reproduce with themselves, or they can mate with other individuals of the same species. Earthworms and some snails are examples of simultaneous hermaphrodites.
Sequential hermaphrodites: Sequential hermaphrodites are individuals that possess either male or female reproductive organs but have the ability to change their sex during their lifetime. There are two types of sequential hermaphroditism:
a. Protandrous hermaphrodites: These organisms start their life as one sex, usually male, and later change to the opposite sex (female). Examples include clownfish and wrasses.
b. Protogynous hermaphrodites: These organisms start their life as one sex, usually female, and later change to the opposite sex (male). Some species of fish, such as groupers and parrotfish, exhibit protogynous hermaphroditism.
In summary, dioecious plants have separate male and female plants, hermaphrodite plants possess both male and female reproductive structures on the same individual, and monoecious plants have separate male and female flowers or cones on the same individual plant. Simultaneous hermaphrodites possess both male and female reproductive organs at the same time, while sequential
Inbreeding:
Why do organisms avoid it?
Strategies by separate sex organisms and hermaphroditic organisms?
AVOIDANCE: because inbreeding has detrimental effects on genetic health and long-term survival of the population
* increased likelihood of expressing harmful recessive traits & accumulating genetic disorders. Why important? leads to reduced fitness, decreased reproductive success, lower population viability, decreased genetic diversity (crucial to adaptation to changing environments and ability to cope with diseases or other challenges)
STRATEGIES:
Same-Sex:
* Dispersal : find mates in other populations or areas
* Have developed visual cues, pheromones or other signals to assess genetic compatibility of potential partner
* Developed social structures: primates have complex social structures that have multi-female-male societies that allow mating with other populations
Hermaphroditic :
* Sequential: some can change their sex during their lifetime and this can avoid outcrossing with unrelated organisms
* Self-incompatibility : some have mechanisms such as alleles or molecular mechanisms that inhibit self-fertilization, and this encourages cross-fertilization with others
* Spatial & Temporal Separation : may have the flowers maturing at different times on the same plant, reducing the chance of self-fertilization.
SEX RATIOS:
50:50 ratio?
Frequency-Dependent Selection?
When would this be beneficial?
Operational Sex Ratio (OSR)?
- 50:50 ratio is a common pattern observed in many species (but not all!). Ecological factors (resource availability, social dynamics, environmental conditions) can cause deviations from the 50:50
- Frequency Dependent Selection : occurs in species with genetic sex determination. Fitness of particular phenotype (in this example, being male or female) depends on its relative frequency in the population. Leads to an equilibrium where neither sex has a selective advantage over the other.
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frequency-dependent selection can act as a stabilizing force maintaining a 50:50 sex ratio: When one sex becomes more abundant in a population, it can lead to increased competition for mates among individuals of that sex. This can create selective pressures favouring the rarer sex, as individuals of that sex have increased access to mates. The resulting decrease in the abundance of the rarer sex helps to restore the balance in the sex ratio
OSR : - # of available males/# of available females (in a population at a certain time)
- Birth sex ratio only reflects the males and females at birth. The OSR reflects age, behaviour, and reproductive status that affects males and females during reproduction
- Several conditions can cause the OSR to deviate from the birth ratio:
1. Sexual behaviour and activity: if one sex is a lot more active in the mating rituals or displays or competitions, this leads to a higher proportion of sexually active males compared to females ( skewed OSR, as a consequence)
2. Age Structure : The age distribution within a population can influence the operational sex ratio. If there is a higher proportion of sexually mature males or females in a particular age group, it can affect the overall balance of available mates.
3. Mortality or Emigration : if there’s death or moving of either species, then there will be a skewed OSR (Ex: males could experience a higher mortality rates)
CONSEQUENCE:
A consequence of a skewed operational sex ratio is the potential for increased competition for mates among individuals of the rarer sex. When one sex becomes relatively more abundant, individuals of the opposite sex may have more options and may be able to be more selective in choosing their mates. This can result in intense competition among individuals of the rarer sex, potentially leading to behaviors such as mate guarding, aggressive competition, or increased investment in reproductive displays to enhance mating opportunities.
Moreover, a skewed operational sex ratio can have implications for population dynamics and evolutionary processes. It can affect reproductive success, mating patterns, and the potential for sexual selection. A significant imbalance in the operational sex ratio can impact population growth rates, genetic diversity, and the overall fitness of individuals in a population.
MATING SYSTEMS:
What is anisogamy?
4 types of mating systems?
ANISOGAMY: form of sexual reproduction that produces 2 distinct types of gametes (sperm & eggs). Sperm (small, highly motile, produced in numerous quantities, energetically inexpensive to make, low probability of fertilizing an egg due to size) & eggs (larger, non-motile, energetically costly to produce, has higher probability of successful fertilization due to size and more resources) – these are the constraints on their reproductive success including males having to compete with other males and even having access to mates and females being more selective in choosing a mate and investment in parental care.
FOUR TYPES OF MATING SYSTEMS:
- MONOGAMY: long-term pair bonds w/ single partner. Both parents contribute to parental care and the ‘extra’ parent gains more through parental care then from seeking more breeding opportunities. Ex: Grey wolves (Canis lupus), Swans (Cygnus spp).
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- POLYGYNY (#1 type of polygamy) : male with multiple females. Males compete for females, who are very selective in choosing mates and results in a few dominant males mating with multiple females (Ex : lions & elephant seals)
- POLYANDRY (#2 type of polygamy) : females with multiple males. Rare, but occurs when males provide significant parental care or where there is a high degree of sperm competition. Reproductive success can be limited by availability of high-quality males. (spotted sandpipers & Jacanas)
- PROMISCUITY: (aka polygynandry) no long-term pair bonds, and multiple mating partners for both males/females. Generally limited parental care and competition for either mate is intense. Also, limited social bonds (or none at all), ( ex : Bonobos & Dunnocks)
SEXUAL SELECTION :
A) Fundamental Asymmetry of Sex –
What are the 2 major types of sexual selection? with examples.
The fundamental asymmetry of sex results from the fact that, in most species, females invest more in their offspring than do males.
Why is this pattern important? 2 reasons:
1. Female fitness is limited by the ability to gain resources needed to produce more eggs and healthier offspring, so females produce relatively few offspring during lifetime.
2. Male fitness is limited by the # of females he can mate with, and he can mate frequently because sperm are so energetically inexpensive.
Sexual selection: natural selection for sex-specific traits that increase REPRODUCTIVE SUCCESS.
Con’t: SEXUAL SELECTION
B) What are 2 major types of Sexual Selection?
Overall, sexual selection is needed b/c it contributes to the evolution of traits & behaviours that increase reproductive success. The traits may NOT enhance survival or fitness, BUT it does make them more attractive to mates:
TWO MAJOR TYPES:
1. INTRASEXUAL SELECTION : competition between individuals of the same sex (generally males) for access to mates. Often leads to evolution of traits and behaviours that enhance competitive abilities (larger body size, weaponry (antlers/horns), aggressive behaviours). Traits help to outcompete rivals and gain mating opportunities. Leads to increased reproductive success.
2. INTERSEXUAL SELECTION : when individuals of one sex (generally females) choose mates based on specific traits or behaviours. Often driven by preference of one sex for certain attractive or advantageous traits displayed by the opposite sex. Traits are known as ‘ornaments’ or ‘courtship displays’ (plumage, bright colours, complex songs, etc). Leads to increased reproductive success b/c the birds with these traits get favoured as mates.
Con’t: SEXUAL SELECTION:
Define sexual dimorphism
Pic below: there is strong selective pressure for sexual dimorphism in elephant seals due to their mating system & reproductive strategy. (Polygyny) – dominant male, called a ‘beachmaster’ mates with multiple females and this results in intense male-male competition for females. Larger size plays a significant role:
1. Male-Male competition (larger size & dominance)
2. Female preference (they want a dominant male who is the largest and most physically imposing - perceived genetic quality and fitness translates to higher offspring survival)
3. Resource defence (larger size secures an area with resources)
4. Sperm Competition (larger seals produce larger # of high-quality sperm, increasing chances of fertilizing eggs and higher reproductive success)
- where males & females of a species differ in their physical or behavioural traits (phenotypic differences)
- Ex: size, colouration, ornamentation, behaviour, reproductive structures.
- Examples : with size dimorphism, male lions are larger and heavier than females. Male birds may have more elaborate colours on their plumage. With behaviours, male birds may display intricate courtship dances or songs to woo females.
- these traits differ from primary sexual characteristics!
- Advantage of larger males: enhanced competitive ability so male will be better in physical combat, win aggressive encounters, secure more mating opportunities, better defend territories; females may prefer larger males due to perceived genetic fitness, be better providers, higher survival rates.
- Advantage of larger females: enhanced fecundity; better resources for offspring such as larger nests, more food, better protection; enhanced competive ability so female can compete over limited resources or limited mates or even high-quality mates.
Con’t: SEXUAL SELECTION :
C) What is meant by the ‘Good Genes Hypothesis’
How was it tested in Zebra Finches?
- concept in evolutionary biology that proposes that certain traits/behaviours displayed by individuals serve as indicators of their genetic quality (these genes enhance survival, reproductive success, resistance to disease)
- Related to ‘Intersexual Selection’, colourful markings and other types of courtship displays signal that males have good genes.
- Zebra Finches : Researchers manipulated the carotenoid intake of finches (obtained through det and can act as an indicator or overall health and immune function). Females preferred darker orange beaks, indicating higher carotenoid intake, leading females to percieve the males as healthier and having better genetic quality. Offspring with darker orange fathers do have higher immune responses and can effectively fight off infections. This study showed how females appeared to select mates based on the expression of a trait that reflected genetic quality.
SOCIALITY:
A) 3 types of Social Systems?
Benefits ?
Limitations?
- refers to the organization & interactions of individuals within a group – and how they form social bonds and engage in cooperative behaviours.
3 TYPES OF SOCIAL SYSTEM:
- SOLITARY: live and forage alone, no lasting social bonds, no cooperative behaviours, except for mating (ex: tigers)
- GROUP-LIVING : live together in cohesive groups, often stable social hierarchies and division of labour, cooperative social behaviours (ex: chimpanzees, wolves, ants/bees)
- EUSOCIAL : most advanced form of sociality. Large, cooperative groups with reproductive division of labour and overlapping generations. (ex: honey bees & naked mole rats)
BENEFITS: enhanced defense, improved foraging efficiency, increased reproductive success (shared parental care, protection of offspring, cooperation in raising young)
LIMITATIONS : increased competition with available resources, Disease transmission (close proximity), social conflicts(can lead to excluding members, aggression, competitions for resources), for something to be beneficial for the fitness of the group – the entire group, all organisms, need to do the same behaviour. No ‘cheaters’ in the system.
SOCIALITY:
B) COMPETITION
C) COOPERATION
A) COMPETITION :
* more individuals = more mouths to feed
* There is an optimal group size
* As group size increases, competition increases
* Reproductive skew : more males in a group, less offspring.
B) COOPERATION :
* Why is it done? Increased foraging efficiency, as opposed to doing it alone; enhanced defense against predators; reproductive benefits due to individuals helping raise others’ offspring, shared parental care which increases survival of offspring; resource sharing such as food, nesting sites, which leads to group fitness
What is Group Selection? “a theoretical framework that suggests natural selection can act at the level of the group or population rather than solely at the individual level. It proposes that traits or behaviors that benefit the group as a whole can be favored, even if they may be detrimental to individual fitness. The idea behind group selection is that groups with individuals who cooperate or exhibit behaviors that benefit the group will outcompete other groups and, therefore, the traits promoting group success will persist over time”
Major flaw of this theory? Individual selection. In order to shape the evolution of traits, all members must participate, even if it’s detrimental to their individual fitness. Individual selection is a stronger force and can override group selection.
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BENEFITS :
1. Group Augmentation Hypothesis : refers to the process by which the size or composition of a group affects the fitness of its members (meaning if a larger size benefits the group, any behaviour from an individual will ultimately benefit the group), providing:
a) increased group survival – cooperative behaviours and traits that benefit the group can enhance group survival against predation, resource scarcity, environmental challenges (enhancing fitness AND reproductive success of group)
b) division of labour – favours development of specialised roles within a group, leading to more efficient group functioning (enhancing fitness AND reproductive success of group)
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Reciprocal Altruism Hypothesis (and the conditions needed): Where an individual helps another at a cost to itself.
Also, refers to the form of cooperation where individuals perform altruistic acts toward others, with the expectation of receiving a benefit in return at a later time (basically, mutually beneficial)
* Conditions: sociality between members of group, ability to recognize and remember others, ability to punish or exclude non-cooperators.
INDIRECT BENEFITS:
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Kin Selection Hypothesis : a concept that explains altruistic behavior based on the idea that individuals can enhance their own inclusive fitness by helping close relatives – helping to increase reproductive success b/c you are closely related to this relative and both of you have relatively the same genes…so essentially, these related genes will all get passed on, even if it’s not from you directly. Therefore, ‘indirect’ benefits
* helping to raise others’ offspring
* protecting relatives
* can be favoured by natural selection due to indirect benefits it provides to the individual’s genetic lineage
* Costs and benefits? LOOK AT HAMILTON’S RULE below
QUESTION IN-CLASS:
Why does it seem ALTRUISM is paradoxical?
a) all altruistic behavaviour is actually selfish
b) alleles that cause animals to behave altruistically should be selected against these alleles
c) altruism does not actually help others
d) animals behave altruistically to save their species but sometimes it their behaviour harms their species
e) none of the above
B) alleles that cause animal to behave altruistically should be selected against
Hypothesis : ‘Group Selection’ doing it for the good of the group. Improves fitness of group.
GENETICS OF SOCIAL BEHAVIOUR:
- Hamilton’s Rule?
- How to genetically contribute to the next generation?
At least 2 ways to contribute GENETICALLY to the next generation:
1. individual produces it’s own offspring
2. individual produces no offspring and helps relatives reproduce
Helping to raise 2 siblings is equivalent to raising how many of your own offspring? 1
HAMILTON’S RULE: a trait favoured by natural selection, if the benefit to others (B) multiplied by the relatedness (R) is GREATER than the cost to the individual (C)
r = 0.42 (relatedness – proportion of shared genes)
B = 6.1 (Benefit to the recipient - # of offspring being produced)
C = 0.5 (Cost to the altruistic individual - what they’d be able to produce if they were by themselves)
(0.42)(6.1) > 0.5
2.562 > 0.5
Is it a successful strategy? YES (left side GREATER than right side). So dominant turkey with bigger bands will have better reproductive success. Females will prefer the group of turkeys that band together: Related to the ‘Good Genes Theory’ AND ‘Intersexual Selection’ AND ‘Kin Selection’ – and better genes and bigger size is perceived as contributing to the survival of their offspring.
So, why would other males (or siblings) band together with this dominant male? Because it must be good genes because parents had 3-4 males in the same litter. As opposed to 1 lone male in a litter.
Define Eusociality.
What is unique about the mode of sex determination in eusocial insects?
How did this mode of sex determination contribute to the eusocial colonies in these insects?
Pic below:
siblings share 75% of genes because males are only haploid. (bees, molerats, ants, wasps)
EUSOCIALITY : refers to an advanced form of social organization found in some animal species, particularly among certain insects. Eusocial species live in highly cooperative groups or colonies where there is reproductive division of labor and overlapping generations. Eusocial colonies typically consist of one or a few reproductive individuals (known as queens or kings) and non-reproductive individuals (known as workers) that assist in colony maintenance, foraging, and caring for the brood. Typically occurs in groups where there is a high degree of relatedness (ants, bees, molerats)
- UNIQUENESS: haplodiploidy. Haplodiploidy is a form of sex determination where females develop from fertilized eggs and are diploid, meaning they have two sets of chromosomes. On the other hand, males develop from unfertilized eggs and are haploid, having only one set of chromosomes.
- CONTRIBUTION : The key contributions of this mode of sex determination to eusocial colonies are as follows:
- Relatedness asymmetry: Haplodiploidy leads to higher relatedness among sisters than between parents and offspring. As males develop from unfertilized eggs, they have no fathers and share half their genetic material with their sisters. This results in a higher degree of relatedness among sisters in the colony compared to the offspring and their parents.
- Kin selection and inclusive fitness: The high relatedness among sisters enhances the benefits of cooperation and altruistic behavior. Since workers are more closely related to their sisters (who are potential future offspring) than they would be to their own offspring, they can increase their inclusive fitness by helping in the rearing of their sisters’ offspring.
- Evolution of reproductive altruism: The haplodiploid system creates a reproductive imbalance where queens are the primary reproductive individuals, while workers are largely sterile and do not reproduce. This division of labor promotes the evolution of reproductive altruism, where workers forgo their own reproduction to assist the reproductive individuals (queens) and enhance the colony’s overall fitness.
Therefore, the unique mode of sex determination in eusocial insects, with haplodiploidy resulting in high relatedness among sisters, has played a pivotal role in the evolution of eusocial colonies. It has facilitated the evolution of cooperative behaviors, reproductive division of labor, and the emergence of highly organized societies with specialized castes, where workers selflessly support the reproductive success of the colony.
