Evol Bio LT 3 : Sex and Sexual Selection

How does reproduction occur in Bacteria

1. Bacteria: No sex, but diverse as well 

   1. Thru conjugation, transduction, and transformation

What are the Possible drivers of Penile size and shape 

1. Locomotion : a fast moving animal cannot have a massive external genitalia 

2. Penile lock-and-key :  prevent cross species copulation 

3. Female Choice : the shape evolved to best stimulate female genitalia

4. Intra-sex competition :  scrape away another males semen  

What is sex

1. In essence involves the mixing and exchange of genetic material 

2. In the traditional meaning of the term (with meiosis), or without (parasex) like bacterial conjugation. 

What is anisogamy

1. Anisogamy- difference in gamete size (sperm vs egg) 

   1. Males- small, plenty and usually mobile gamete 

   2. Female-big, fewer, and well provisioned 

What is Hermaphrodism

1. Hermaphrodism: gives reproductive assurance at the expense of diversity 

   1. a species has both male and female gonads

What is Sexual Dimorphism

1. Sexual Dimorphism- may develop when a trait benefits one of the sexes, but not the other. 

   1. An organism has a trait that is different between male and females

What are Primary Sexual Traits

1. Traits which play a role in reproduction; genitalia 

What are Secondary Sexual Traits

1. Harder to explain by natural selection because it may not make sense in that light (and it’s a great clue about the truth in sexual selection) 

2. Selected for via sexual selection– used to attract mates (usually males have this) 

3. They may decrease survival, as long as it is compensated for by increased fitness

Why are male’s secondary sexual characteristics the one that is exaggerated? 

Due to the differences in the gametes of males and females

What is Bateman’s Principle

1. reproductive success is more varied in males than in females 

What is the Operational sex ratio

usually there are less females available for mating at any given time; males thus must compete 

Is there a possibility for role reversal? 

1. Yes

   1. When males take care of the young: 

Why might there be role reversals?

1. When males are assured that paternity is theirs, it is advantageous for them to guard the fertilized products 

2. Harsh environment necessitating male care: like penguins– females lose body weight after gestation necessitating immediate feeding. Males take over the care of the egg– or the egg dies 

Examples of Male vs Male Competition 

1. Fencing’ females or their resources 

2. Infanticide

What are Alternative Mating strategies and sperm competition 

1. Sperm scoop 

2. Size, mimicry, and sneak ‘attack’ 

3. See Paracerceis sculpta 

4. Alpha blocks 

5. Beta pretends to be female 

6. Gamma sneaks 

How is Sexual Selection done by Female Choice

1. Some traits provide no advantage in male-to-male combat 

2. Instead, the traits aim to convince females 

3. “Convince”- traits that the females are attracted to by virtue of their anatomy and physiology 

4. At the most basic: avoid mating with another species 

Why females choose: 

1. Direct Benefits : provide resources to increase survival of offspring (see image) 

2. Pleiotropic Effects : guppy and their love of orange ‘

3. Good genes mechanism : indicator traits they get the good genes

4. Fisher’s Runaway

What is Fisher’s Runaway

It explains how exaggerated physical traits in males (like a peacock's tail) evolved rapidly through female mate preference, triggering a genetic feedback loop that reinforces itself ove

How does Female Choice occur

1. Leks- males congregate and just ‘flex’ 

2. Females have sex with their choice, then leave 

3. Guppies attracted to orange because it is similar to their food= pleiotropy 

What are sex ratios

1. Evolution tends to favor equal sex ratios 

2. Hypothetical example where a mutation occurs and makes a female carry only sons 

What is Maynard Smith's cost

1. Parthenogenesis increases fitness; males decrease fitness by half 

   1. males cant produce offspring / hold a baby so females invest in it

How does Sex increase fitness in changing landscapes 

Appearance of combinations that will thrive, even if rare

Why does Selective interference favor sex and recombination 

1. Recombination allows for beneficial traits to come together 

2. Recombination can allow the liberation of a beneficial mutation from deleterious baggage 

3. Prevents the accumulation of bad genes in an individuals, as could happen in asexual reproduction 

What do hermaphrodites avoid doing

self-fertilization

Why do hermaphrodites avoid self-fertilization

Prevents inbreeding depression- loss of fitness due to the crossing of close relatives