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2 Midshipman Life History
The plainfi n midshipman fi sh is an excellent model to investigate the neural and
endocrine mechanisms underlying vocal-acoustic communication across vertebrates because much of the animal’s life history and social behavior is dependent on
the production and detection of social acoustic signals (Bass and McKibben 2003 ;
Forlano et al. 2015b ). In the summer reproductive season, type I or “singing” males
excavate and defend nests in the rocky intertidal zone of northern California and the
Pacifi c Northwest, USA and court females at night by producing a long duration (>1
min) advertisement call, the “hum,” generated by simultaneous contraction of vocal
musculature along the sides of the swim bladder (Bass and McKibben 2003 ; Cohen
and Winn 1967 ). The type I male’s advertisement call is a multiharmonic signal
with a fundamental frequency that ranges from 90 to 100 Hz at temperatures of
15–16 °C (Bass et al. 1999 ; Ibara et al. 1983 ) and the call’s harmonics can extend
up to 700 Hz (Brantley and Bass 1994 ; McIver et al. 2014 ). There also exists a second male morph known as a type II male that employs an alternative reproductive
tactic that consists of satellite and/or “sneak” spawning to steal fertilizations from
type I males spawning with females. Type II males do not produce advertisement
calls or build nest sites but instead invest more energy in testes size to compete with
type I males for spawning (Bass 1996 ). The testes of type II males can be as large
as 15–20 % of their body weight and presumably have more sperm than that of type
I males (Bass 1996 ; Brantley and Bass 1994 ). Reproductive females are attracted to
the advertisement call of males and localize potential mates by pinpointing the
source of the humming male in his nest, spawn once by depositing eggs on the roof
of the male’s nest where fertilization occurs, and then return off shore after spawning is completed, while nesting type I males continue to court and spawn with other
females and care for the young alone (Bass 1996 ; Bass and McKibben 2003 ; Forlano
and Bass 2011 ).
Nesting type I males provide all the parental care of the developing offspring and
will vigorously guard and defend their nest from egg predators. The developing nest
larvae take approximately 50–60 days at a temperature of 15 °C to absorb their yolk
(Alderks and Sisneros 2013 ) before they detach from the nest, become free swimming, and then move into the shallow sea grass beds for food and safety.
2.1 Seasonal Plasticity of the Midshipman Auditory Sense
Behavioral studies of female midshipman to simulated advertisement calls show
that gravid females (full of eggs) exhibit robust phonotaxis to natural and synthetic
advertisement calls. This unconditioned phonotaxic response of gravid females is
clearly unambiguous and results in the localization of the sound source, whereas
recently spawned females (void of eggs) do not exhibit phonotaxis or sound source
localization, nor show any interest in the advertisement call (McKibben and Bass
P.M. Forlano and J.A. Sisneros
2 Midshipman Life History
The plainfi n midshipman fi sh is an excellent model to investigate the neural and
endocrine mechanisms underlying vocal-acoustic communication across vertebrates because much of the animal’s life history and social behavior is dependent on
the production and detection of social acoustic signals (Bass and McKibben 2003 ;
Forlano et al. 2015b ). In the summer reproductive season, type I or “singing” males
excavate and defend nests in the rocky intertidal zone of northern California and the
Pacifi c Northwest, USA and court females at night by producing a long duration (>1
min) advertisement call, the “hum,” generated by simultaneous contraction of vocal
musculature along the sides of the swim bladder (Bass and McKibben 2003 ; Cohen
and Winn 1967 ). The type I male’s advertisement call is a multiharmonic signal
with a fundamental frequency that ranges from 90 to 100 Hz at temperatures of
15–16 °C (Bass et al. 1999 ; Ibara et al. 1983 ) and the call’s harmonics can extend
up to 700 Hz (Brantley and Bass 1994 ; McIver et al. 2014 ). There also exists a second male morph known as a type II male that employs an alternative reproductive
tactic that consists of satellite and/or “sneak” spawning to steal fertilizations from
type I males spawning with females. Type II males do not produce advertisement
calls or build nest sites but instead invest more energy in testes size to compete with
type I males for spawning (Bass 1996 ). The testes of type II males can be as large
as 15–20 % of their body weight and presumably have more sperm than that of type
I males (Bass 1996 ; Brantley and Bass 1994 ). Reproductive females are attracted to
the advertisement call of males and localize potential mates by pinpointing the
source of the humming male in his nest, spawn once by depositing eggs on the roof
of the male’s nest where fertilization occurs, and then return off shore after spawning is completed, while nesting type I males continue to court and spawn with other
females and care for the young alone (Bass 1996 ; Bass and McKibben 2003 ; Forlano
and Bass 2011 ).
Nesting type I males provide all the parental care of the developing offspring and
will vigorously guard and defend their nest from egg predators. The developing nest
larvae take approximately 50–60 days at a temperature of 15 °C to absorb their yolk
(Alderks and Sisneros 2013 ) before they detach from the nest, become free swimming, and then move into the shallow sea grass beds for food and safety.
2.1 Seasonal Plasticity of the Midshipman Auditory Sense
Behavioral studies of female midshipman to simulated advertisement calls show
that gravid females (full of eggs) exhibit robust phonotaxis to natural and synthetic
advertisement calls. This unconditioned phonotaxic response of gravid females is
clearly unambiguous and results in the localization of the sound source, whereas
recently spawned females (void of eggs) do not exhibit phonotaxis or sound source
localization, nor show any interest in the advertisement call (McKibben and Bass
P.M. Forlano and J.A. Sisneros