Sexual dimorphism Flashcards
what is the main determinant of sexual determination/dimorphism in Drosophilia
the X autosome ratio - triggers alternative gender dependent slicing cascades of both dosage compensation and somatic and neural sex determination
describe the gender-dependent splicing cascade that leads to male CNS dependent gender dimorphism in drosophila
The SEX LETHAL (SXL) protein is not expressed during early male development (due to the 1X:2A ratio).
As a result, it does not initiate sustained functional Sxl or transformer (tra) mRNA and protein expression.
In the absence of functional TRA protein, TRANSFORMER 2 (TRA2) regulates male-specific splicing of the fruitless (fru) gene in a subset of CNS neurons, which leads to the production of BTB-zinc finger FRUM protein isoforms.
FRU^M initiates a transcriptional programme responsible for almost all CNS-dependent gender dimorphism including courtship behaviour.
what are the crucial sexual dimorphisms in the Manduca sexta (tobacco hawk moth)
the macula cellular cortex is only in the male (senses female pheromones with its antennae)
males have thicker antennae and larger olfactory glomeruli in the brains antennal lobe (specialised for odorant mediated sex specific behaviours)
female invest a lot of energy in their gametes and only let the most evolutionary impressive males to fertilise them
what is (sex chromosome) dosage compensation
the process by which organisms equalize the expression of genes between members of different biological sexes.
eg In fruit flies the males boost the expression from the single x chromosome
in fruit flies what contributes to male soma and behaviour and female soma
Double sex DSX and fruitless FRU contribute to males soma an behaviour
only double sex contributes to female soma
what sexually dimorphic courtship behaviours are shown by male Drosophila melanogaster (the innate mating behaviour)
a | The male fruit fly orientates towards the female, then follows her,
b | taps her,
c | sings a species-specific courtship song by vibrating one wing.
d | Finally, he licks the genitalia of the female,
e | curls his abdomen in an attempt to copulate with her.
what is the purpose of male Drosophila tapping/licking in the innate mating behaviour
detecting taste smell and somatosensory cues (whether it is a female, whether they recently mated)
what do fru3 mutant phenotypes affect?
courtship song, transfer of sperm and seminal fluid
optogenetic stimulation of neurons expressing the fruitless FRU gene produces what (in male drosophila)
causes fly to produce male specific behaviour in a random pattern
fruitless free genotypes of drosophila exhibit what behaviour
the flies will court each other – forming conga lines of courting males (fruitless behaviour)
what is the binary Gal4-UAS system
a biochemical method to study gene expression to get transgene expression in a pattern of your choice
targetted reporter gene expression is created by two transgenes:
P-Gal4, expressing the foreign transcription factor GAL4 in the pattern of promotor P
UAS-Transgene, which uses GAL4 binding sites (UAS) to produce transgene expression
where are Fru M neurons found
in the brain projecting through the ventral nerve cord, the muscle required for copulation, some for external genitalia (penis and clasper), sensory neurons that are specific in the leg antenna, proposis.
what structures in drosophila brain is larger in males than in females
da1 glomerulus bigger in male (receiving input from olfactory sensory neurons in antennae) + VAlv, VL2a
the antenna lobe senses phenylacetic acid and other food odours that act as aphrodisiac.
upon detection of males pheromones what happens in the male drosophila brain
suppression of coutship behaviours by pathway from olfactory sensers -> DA1 ORN -> DA1 PN -> DCI -> DNI -> VNC
how can drosophila differentiate between males and females
Two fru sensory neurons in front leg, one sense female hydrocarbons the other male by tapping off the
how to allow females to express fru gene (drosophila melongaster)
Create female fluy that expressed male fruitless protein – via correcting female specifics splicing by removing the exon that adds a stop codon.
why dont female drosophila express the Fru protein
the female-specific splicing caused by binding of Tra/Tra2 yields a transcript that includes a second exon, which has a stop codon and does not produce a functional protein
what are P1 cells (drosophila)
the group of Fru cells responsible for most of mating behaviours in males
how do we know the female fruit fly brain is equipped with latent circuitry underlying male like behaviour
Temperature-induced stimulation of pC1 cells in ♀triggers ♂-like courtship of both ♀ & ♂ - this function maps to dsx-pC1 neurons (equivalent to fru P1 neurons)
what does the P1 cluster of neurons do (in male fruit fly)
central control of ♂ courtship
Integrates sensory and dopaminergic (motivational) input)
Controls output via Descending Neurons > Ventral Nerve Cord
Courtship song
Copulation
how do Fru^M neurons participate in different aspects of courtship
Sensory Input
Auditory (courtship song)
Olfactory (pheromones, food-associated aphrodisiacs)
Gustatory (pheromones)
Visual
P1 cluster: central control of ♂ courtship
Is the male brain dispensable for male copulation?
yes
Fruit flies - decapitation of male during copulation leads to successful copulation. The brain is not required the ventral nerve cord is.
There was an increased duration for matings in which wild-type Drosophila melanogaster males were decapitated shortly after copulation initiation
what directs the musculature of male copulation in fruit flies
Circuit of doublesex-expressing neurons in the equivalent of the spinal cord controls copulation itself:
Glutamatergic motor neurons that coordinate the joining of genitals
GABA-ergic inhibitory interneurons that promote release of genitals by opposing the motor neurons
mechanosensory neurons that connect to brain and abdominal ganglion
what control female mating receptivity in fruit flies
In virgin females, pC1 neurons integrate auditory, olfactory, and somatosensory inputs and in turn activate vpoDNs (vaginal plate opening descending neurons, which also receive auditory input more directly).
vpoDNs project axons to the ventral nerve cord to promote vaginal plate opening, which is essential for copulation.
pC1 neurons receive tonic excitation from SAG neurons of the ventral nerve cord, which are activated by sex peptide sensory neurons (SPSNs)
what happens in the chemistry of virgin female fruit flies after they mate
They receive sperm and seminal fluid - fluid has signalling molecule sex peptide sensed by sensory neurons in female reproductive tract inhibits female receptivity for a period of time including vaginal plate opening.
- After mating, the sex peptide inhibits SPSNs, thereby reducing the excitatory drive onto SAG neurons and pC1 neurons
what structure has the sex-specific memories of being rejected in male drosophila
FruM mushroom body g neurons
what does the male birdsong signal
Signal to females: Species Individual identity Location Readiness to mate Compete with rivals Territory Neighbour vs stranger
what happens in the stages after hatching in the learning process of birdsong (in zebra finches)
in days after hatching. During the sensory stage, a young bird listens to and memorizes a tutor song. During the sensorimotor stage (25-90 days), he sings an immature song and compares it to the tutor song he memorizes. The song takes its mature form at the crystallized stage (90 days)
what do the song pathways consist of in zebra finches
consisting of HVC, RA, and the brainstem motor nuclei that regulate muscle contraction in the vocal and respiratory systems, is responsible for song production. The anterior forebrain pathway, consisting of LMAN, area X, and DLM, is essential for song learning. Dopamine neurons project to and modulate neurons in area X.
what animal experiences seasonal neurogenesis
songbirds – adult neurogenesis does occur in seasonal patterns, (possibilities for neurodegenerative diseases)
what sexual dimorphism is shown in the bird brain
Volumes of nuclei making up the song circuits (area X, HVC, and RA) are larger in males than in females in both canaries and zebra finches (bottom). Area X is unrecognizable in zebra finch females.
what is unique about the sexual characteristics of the Aspidoscelis uniparens (whiptail lizard)
they are all female and the sexually dimorphic behaviour is related to the hormone cycle
