Characterization of a spawning pheromone of Pacific herring
Date
2017-06-01
Authors
Schnorr von Carolsfeld, Joachim
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Abstract
Pacific herring, Clupea harengus pallasi, possesses a pheromone in
the milt and testes that triggers spawning behaviour in reproductively
mature individuals of both sexes, and plays a role in synchronizing the
school spawning that is distinctive of this species. The pheromone was
found to be effective as a transient olfactory stimulus in eliciting a
behavioural response that varied in the degree of expression and time
course. Stimulus strength was found to influence the time course of the
response, whereas differences in maturity, evident through examination of
plasma levels of steroids, were correlated with a propensity to respond to
the pheromone. Input from factors other than the spawning pheromone
appear to be needed to elicit prolonged spawning; some of these factors
also act through olfaction. Immediate effects of stress were not found to
influence the response to the spawning pheromone.
Plasma levels of reproductive steroids of herring during the
spawning season were measured with radioimmunoassays. Peak levels of 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) were found to coincide with final maturation in females and the initiation of milt production in
males, suggesting that this steroid is the maturation-inducing steroid of
this species. Other features found to be distinctive of the reproductive
physiology of the herring included low plasma levels of the unconjugated
maturation-inducing steroid, high levels of 17α-progesterone (17-P) and
3α,17α-dihydroxy-5β-pregnan-20-one (3α,17-P-5β), and high levels of
glucuronated steroids. Structural investigation of the pheromone with
liquid chromatography/ mass spectrometry showed that it consists of at
least two components which do not elicit a behavioural response
individually. One of these compounds is sulphated 17,20β-P.
The structure of proteinaceous hormones involved in controlling
reproduction of the herring was also investigated. It was shown that this
species possesses three forms of gonadotropin-releasing hormone (GnRH) in
the brain, one with a structure that has not been reported before. These results
indicate that the presence of three GnRH forms is a primitive, rather than
derived, condition in the teleosts. The structure of the (β-subunit of
gonadotropin II (GtH ll-β) of herring was also deduced by isolation of a cDNA
for this molecule. The structure of the herring GtH ll-β was found to be quite
different from other teleost molecules of this kind, and a phylogenetic analysis
of known GtH ll-β structures suggests that the β-subunit of both mammalian
gonadotropins may be most closely related to the β-subunit of teleost GtH-l.
Description
Keywords
Pacific herring, Fishes, Pheromones