Lecture 3 - Revision Flashcards
What is male courtship behaviour
Sexually dimorphic behaviour only males perform in Drosophila
What are the measurable parameters of courtship
- Total time courting during observation period.
- Latency to initiate courtship
- Latency to copulation
- Courtship steps performed (order, latency, and total duration)
Courtship initiation behaviours
Orientation whilst following the female - sees and smells female
Tapping - male tastes pheromones from female
Wing extension (1 or two) - vibrates wings to sing a courtship song - females hears and smells this
Licking - male hears and tastes
Copulation - female has to correctly position herself for copulation
In D. melanogaster, copulate for 20 minutes when they pass sperm and protein (sex peptide) to female reproductive system which has an impact on female nervous systems
How are courtship signals visualised
Visual - Red light to remove visual stimuli - males don’t court as well if lacking vision
Olfactory - Measure using mutant flies lacking olfaction - Or83b knocked out leads to no olfaction - don’t court as well
Auditory - Measure using mutant flies lacking audition - has more of an effect on females and females need to hear courtship song
Gustatory - Measures using mutant flies lacking gustation - start courting but don’t progress very well onto attempting copulation
What two senses are the most umportant in courtship initiation
Visual and olfaction
What pheromones do female fruit flies secrete?
7, 11-heptacosadiene and 7, 11-nonacosadeine on surface of their cuticle
Attractive to males and allow males to identify females of same species
What pheromones do male fruit flies secrete?
11-cis vaccenyl acetate, 7-tricosene and 7-pentacosene
Attractive to females (and young males)
Inhibit or elicit aggression in other males
Visual signals in courtship
Specific class of courtship visual projection neurons
LC10 visual projection neurons required tracking fly-sized object
LC10 neurons sense moving visual objects
Activation of LC10 neurons elicits courtship
Object motion -> Unilateral LC10 activation -> Ipsilateral turn and wing extension
Auditory signals - male love song
- Females recognise males via species-specific love song (pulse sine song), hears via arista on antennae
The song of a male of the appropriate species stimulates the female to become receptive to copulation.
Genetic specifications of fly courtship
- Courtship is governed by a genetic hierarchy that directs aspects of sexual differentiation
- Fruitless is first regulatory gene, essential for male sexual behaviour
- Female behaviour governed by both doublesex and fruitless
Sex determination pathway
Females have two X chromosomes, males have one
From pre-mRNAs:
sxl (sexlethal) produces RNA binding SXL protein in females via regulated splicing, whilst no SXL protein is produced in males via default splicing
tra (transformer) produces RNA binding TRA protein by SXL protein in females via regulated splicing, whilst no TRA protein is produced in males via default splicing as extra stop codon present.
Default splicing produces male and regulated splicing produces female doublesex and fruitless, where TRA2 and TRA are required in production of these in females
Mutant phenotypes of genes
dsx null mutants can carry out most courtship except one part of courtship song
Expression of male dsx in females resulted into transformation into males but don’t perform male courtship
fru null mutant males are phenotypically male but don’t show courtship behaviour.
Less severe fru mutations and allelic combinations produces males that display defects in different courtship stages.
Transcription and patterns of fru gene
Transcribed from 4 promoters
Transcripts from P1 promoter are the sexually dimorphic ones
Transcripts from P2-4 are lethal if knocked out and are from males and females
Where is FRU in the nervous system?
Suboesophageal ganglia
Around antennal lobes
Lateral regions of brain
Expressed in sensory neurons, in both olfactory and gustatory receptors
Neuroanatomical dissection of courtship behaviour
- Genetically modify a brain area
- Measure effect on behaviour e.g. if behaviour seen, conclude region is involved
If nor change in behaviour, then not involved in controlling behaviour - Visualise/identify modified cells/neurons
- Repeat with multiple discrete and/or overlapping patterns of brain modification to identify brain regions/cells involved in or required for behaviour.
Experiments conducted in neuroanatomical dissection of courtship behaviour
First experiments used male/female genetic mosaics - gynandromorphs - to identify sexually dimorphic regions of the CNS in male courtship.
GAL4/UAS refined locations of sexually dimorphic brain circuitry using UAS-traF driven by GAL4 - distinct patterns of expression in CNS.
UAS transgenes were used to alter neuron activity in identifying non-sexually dimorphic circuitry e.g. UAS-shi(ts), UAS-Ttx
Olfactory processing
OR67d (cis-vaccenyl acetate) binds neurons on DA1 glomeruli
Or47b (male and female fly odors) binds neurons on VA1lm glomeruli
Ir84a (phenylacetic acid and phenylaldehude) binds neurons on VA2 glomeruli
Neurons send signals to pheromone processing center, where courtship behaviour is initiated, and some decending neurons send signals
Gustatory processing
Pheromones detected using receptors located on Foreleg tarsi and mouthparts e.g. Gr32a, Gr39a etc send signals to subesophageal ganglion where fru is expressed, before neurons send these signals to gustatory processing centres
Courtship initiation song
