Biology Reference
In-Depth Information
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Male ratio
Fig. 42.
Relationships between male ratio and transitional load (□) carried during the life spawn
(●) of some protogynous hermaphrodites. (data are drawn from Table 20 of Pandian, 2010).
In formalizing the 'size advantage model', Warner (1975) has shown
that if age-specifi c reproductive output increases more rapidly with body
weight for one sex than the other and if the curves relating to fecundity
with body size/age cross each other, then in principle an age or body size,
at which an individual may reproductively profi t by switching gender.
Many scientists (e.g., Avise and Mank, 2009) have not recognized that
body size-fecundity relation can differ from that of age-fecundity, and
fi shes may also experience menopause stage. Whereas fecundity increases
with body size of fi sh, it does not during the period of terminal age (see
Pandian, 2010, Fig. 43). When a fi sh has attained > 70% of its maximum age,
it is approaching reproductively more or less inactive menopause stage at
its terminal life span . In different populations of the guppy
P. reticulata,
this period of terminal life span has been estimated to range between 12
and 15% of total life span (Reznick et al., 2006). The empirical estimation
predicts that sequential hermaphrodites change sex, when they reach 80%
of their body size (Allsop and West, 2003). When all the recent information
is taken together, it seems that the sequentials reach a body weight of 80%
of their maximum, corresponding to the completion of 80-85% of their life
span, when they produce negligible number of eggs (in relation to body
weight and time, Fig. 27, 31) or cease to produce eggs, the protogynous
hermaphrodites switch to males.
