Sexual strategies Flashcards
Give two examples for sex determination systems in fish
- Single genetic locus (e.g. linked to a single chromosome)
XX XY = homogametic female
ZZ ZW = homogametic male sex determination
XX XO = males have one less chromosome
- Polygenic loci (Multiple sex determining genes that may contribute varying amounts to determining the sex of an individual)
What determines the sex of most fish species?
genetic and environmental factors
What role does the sex ratio in rearing sea brass and eels play for the economy of these aquacultures?
European seabass typical sex ratio = 69%
male at 21 C
Rearing at 15 degrees for up to 3 months
doubles number of females to approx 60%
Decreases precocious males from 29% to
10 - 20% (males mature earlier than females investing energy into sexual reproduction rather than growth -> economic loss)
A. anguilla (Roncarati et al., 1997)
European eel elvers held at different densities (g/m3) - Higher density favours male - 800 (69%), 1600 (78%), 3200 (96%)
Reduced biomass
What controls reproductive function in fish?
In all vertebrates, reproductive function is controlled by the combined action of the
hypothalamus, the pituitary, and the gonads
What is gonochorism?
fixed sex either male or female
sex change: protogyny?
Female to male (spotty)
sex change: protandrous?
male to female (clown fish)
sex change: bidirectional?
male to female and female to male (green coral goby)
Hermaphrodites
either partner can act as male or female
explain the differentiation patterns in sex change among fishes
What is a protogynous hermaphrodite?
what is the evolutionary advantage for it with bluehead wrasses as an example?
What would be the implication for aquaculture for this species?
Protandrous hermaphrodites refer to organisms that are born male and at some point in their lifespan change sex to female.
Protogynous hermaphrodites; IP males exist.
IP males have large testes try to position themselves near females during egg
release this incurs aggression of TP males.
Sometimes form large aggregations of IP males waiting for females to join.
Sex change occurs if male bluehead wrasse are removed,
behavioural sex change precedes gonadal sex change
• Process is independent of gonadal signalling – gonadectomy
• Estrogen produced in brain seems to inhibit behavioural sex change
What is group synchronous ovarian development and in what species does it occur?
two or more clutches of oocytes in different stages of development that are successively ovulated
e.g. European seabass (as many as four clutches)
yellowtail
What is asynchronous ovarian development and in what species does it occur?
Daily relative fecundity and fertilization in Pagrus pagrus
