Lecture 3 - Courtship and Mating

Question 1

Describe the steps of courtship in Drosophila: Orientation Tapping stage Wing vibration Licking Copulation

Answer 1

Orientation: Male and female come close to each other. Male recognises that female is there and orients to it. Tapping of female will cause recruit wing extension. Wing vibration is the ‘courtship song’ and he will circle female. - Female is always running away, after a while he stops her. - He licks her genitalia. He will keep repeating these behaviours and with each cycle he’ll add in tapping and licking and eventually he will copulate.

Question 2

What are the 4 courtship parameters?

Answer 2

1. *Total time* courting during observation period. 2. Latency to *initiate courtship*. 3. Latency to *copulation*. 4. *Courtship steps* performed

Question 3

Name courtship signals received at these steps: Orientation Tapping stage Wing vibration Licking

Answer 3

Orientation - visual and olfaction information. Tapping stage - taste information (drives wing extension). Wing vibration - olfactory information and vibration. Licking - positive taste information.

Question 4

LC10 visual projection neurons are necessary to perform directed courtship, because they’re required for tracking a fly-size object. What will happen when LC10 visual PNs are stimulated in Drosophila during courtship?

Answer 4

Object motion will cause unilateral LC10 activation, which will cause ipsilateral turn and wing extension. So, activation of LC10 neurons elicits courtship that is enhanced by courtship arousal.

Question 5

Female pheromones are … to males and are … specific. Females after they’ve mated induce … which will … courtship. Males also secrete … which are attractive to females, but those same … will … or … in other males.

Answer 5

Female pheromones are *attractive* to males and are *specie* specific. Females after they’ve mated induce *different pheromones* which will *inhibit* courtship. Males also secrete *pheromones* which are attractive to females, but those same *pheromones* will *inhibit* or *elicit aggression* in other males.

Question 6

Name an important pheromone that attracts females and surpasses courtship behaviour in males.

Answer 6

11-cis vaccenyl acetate or cVA.

Question 7

What are the neurons for cVA?

Answer 7

Or83b + subunit Or67d.

Question 8

How is cVA detected and processed? Think of: SNMP and lush.

Answer 8

Detection of cVA is facilitated by SNMP and lush (odour-binding protein). Lush undergoes a conformational change when it binds cVA, so that it can bind with sensory neuron. These are sexually dimorphic = they will go to different region in male than in female brain.

Question 9

Which glomeruli do Or67d-expressing neurons, which respond to male cVA, send their information to in the AL.

Answer 9

DA1 and VA1lm. (Or47b-neurons also send information).

Question 10

While Or67d ORNs express …, Or47b do not. Or67d/DA1 neurons target … second order neurons in a specific region of the … associated with pheromone processing. Ultimately these second order neurons form downstream … (via third and fourth order neurons) that terminate in the … ganglia. This causes stimulation of courtship.

Answer 10

While Or67d ORNs express *fru*, Or47b do not. Or67d/DA1 neurons target *fru-expressing* second order neurons in a specific region of the *lateral horn* associated with pheromone processing. Ultimately these second order neurons form downstream *fru-expressing connections* (via third and fourth order neurons) that terminate in the *abdominal* ganglia.

Question 11

From which neurons does VL2a glomerulus receive information from?

Answer 11

Ir84a-expressing neurons, which respond to odours derived from host food/ovipositional substrates.

Question 12

VL2a PNs are … from PNs responding to general food odour pathways, but they are … interconnected with the … pheromone pathways and target a specific area in the … involved in pheromone processing.

Answer 12

VL2a PNs are segregated from PNs responding to general food odour pathways, but they are anatomically interconnected with the VA1lm/DA1 pheromone pathways and target a specific area in the lateral horn involved in pheromone processing.

Question 13

Describe the pheromone pathway. Starting with Or67d + ORNs and ending with abdominal ganglion.

Answer 13

Or67d + ORNs –> DA1/VA1lm glomeruli in AL –> higher centres –> downstream fru-expressing connections.

Question 14

What does the courtship song do to females? And how does she detect this song? (Via which organ and how)

Answer 14

The song stimulates females to become receptive to copulation. The female ‘hears’ the song through her antennae. The feathery barista on her antennae vibrate –> the segments of the antennae move relative to each other and this movement is transducer to a neural input via Johnston’s organ. From Johnston’s organ it goes to a specific region in the brain.

Question 15

Where is Johnston’s organ located?

Answer 15

The organ is housed by the antennae segments joint, it’s a collection of 500 mechanosensory receptor neurons. Segments movement relative to each other is transducer to a neural input.

Question 16

Why are females unreceptive to mating after courtship?

Answer 16

Male sperm has the sex peptide (SP). In the female, SP activates a specific receptor SPR that activates a signalling pathway to modulate properties of fru-neurons.

Question 17

What happens to females lacking SPR?

Answer 17

They remain receptive to mating.

Question 18

Name the sex-specific genes in males and females.

Answer 18

Male: fruitless (fru-m). Female: fru-f and doubles (dsx).

Question 19

Describe the splicing process of the fruitless and doubles genes. Use: Sxl gene, Tra gene, etc.

Answer 19

The number of Xs determine whether the Sxl gene is turned on or not. In females Sxl gene is turned on –> SXL protein is produced –> directs splicing of Sxl pre-mRNA and Tra pre-mRNA in female specific pattern –> female specific TRA protein is produced –> regulates splicing of pre-mRNAs of Dsx and Fru-genes –> female specific DSX and FRU proteins. In males Sxl gene is turned off –> no TRA protein –> male specific patterns of splicing of Dsx and Fru-genes –> male specific DSX and FRU proteins.

Question 20

What are the consequences in these mutant phenotypes: ‘dsx’ null mutant males Expression of male dsx in females ‘fru’ null mutant male flies

Answer 20

‘dsx’ null mutant males - can carry out most aspects of courtship except one part of the courtship song. Expression of male dsx in females - resulted in transformation into males except they did not perform male courtship. ‘fru’ null mutant male flies - are phenotypically male but show no courtship behaviour.

Question 21

Name the GRNs of the foreleg tarsi in males that detect non-volatile pheromones.

Answer 21

Gr33a and Gr32a are thought to detect female specific pheromones (attractants). Gr39a is thought to detect male specific pheromones (aversive).

Question 22

How can males learn to predict mate succes? (how is courtship learned)

Answer 22

Obtaining a high rate of courtship succes requires male to discriminate sexually mature virgins from immature females, unreceptive females, and females of other species. Female pheromones can vary substantially. Courtship succes is learned through trial-and-error.

Question 23

How does a female decide to mate?

Answer 23

She decides based on her assessment of suitor’s quality and on her own readiness to mate (mature or immature virgin). Male quality: pheromones and courtship song.