Biology Reference
In-Depth Information
of physical presence and interactions of a territorial male. Interestingly,
Lorenzi et al. (2006) exposed a harem of females of goby
Lythryprus dalli
to the (i) physical absence of the male, (ii) presence of the male behind
a barrier that allowed visual and olfactory interactions but prevented
physical interactions and (iii) presence of the male behind a porous screen
that allowed olfactory interactions but prevented physical and visual
interactions. The α-female changed sex only in the physical absence of the
male. However, the effects of sex change alone are unlikely to explain the
rarity of sex changers (Kazancioglu and Alonzo, 2009). Many theoretical
considerations have regarded sex change as adaptive in the context of size-
advantage hyphothesis.
Sex changers maintain sex ratios ranging from one male for every two
or three females and thereby increase reproductive output. Analyzing male
sex ratio among the different patterns of protogynous hermaphrodites,
Pandian (2010) found reductions in male ratios to 0.31, 0.30, 0.23 and
0.22 in monoandric monochromatic, monoandric dichromatic, diandric
dichromatic and haremic protogynous hermaphrodites, respectively. Quite
independently, Molloy et al. (2007) too estimated the male ratio as 0.29 for
14 protogynous hermaphrodites. They have also estimated that the sex
changing males invested just 20% of that of gonochores, while the females
about 50% of that of the gonochores. Thus the protogynous sex changers
seem to invest less on gonads, perhaps to neutralize the cost involved in sex
change. The facts that theoretical considerations have not taken into account
are (i) the sexually non-performing
transitional load
on the sexually active
population and (ii) the fraction of life span, during which the transitionals
persist in the population of protogynous hermaphrodites. Considering 16
protogynous species belonging to seven families, Pandian (2010) estimated
the mean
transitional load
as 10.4% of the population and
transitional life span
as 31.6% at the mean male ratio of 0.33 (Fig. 42). In fact the male ratio seems
to regulate the
transitional load
and percentage of
transitional life span.
Various models have attempted to explain the curious but unique
patterns of hermaphroditism in fi sh. The “low density model” explains
simultaneous hermaphrodism as advantageous, despite the fact that they
have to meet the high fi xed costs for each sexual function and inherent
antagonisms between male and female hormonal or other physiological
system. The 'risk of movement model' has attempted to explain the existence
of serial hermaphroditism; “intense predation pressure on patch-structured
reefs make mate search movements very risky for small and sparsely
distributed fi sh like gobies, thus giving a selective advantage to any stay-
at home individual, who facultatively switch gender as the need arises”
(Avise and Mank, 2009).
