Differentiation in Hermaphrodites - Genetic Sex Differentiation in Fish - page 133

Fig. 55. Schematic illustration of gonadal development and differentiation in primary male
and female in a diandric protogynic hermaphrodites. The gonadal differentiation in diandrics
pass through an initial juvenile hermaphroditism. In others , primary males can change
to female and a female also can switch over to primary male. OL = Ovarian lumen, SC =
Spermatogonial cysts
females too re-differentiate into a 'secondary male'. Munday et al. (2006)
have shown that the juveniles of T. bifasciatum may choose to differentiate
into primary males or females, depending on the female population size in a
location. From their long time fi eld and aquarium observations, Kuwamura
et al. (2007) have shown that a primary male of H. trimaculatus changes
to female and an adult female, even after a few spawnings, changes into
primary male, i.e., H. trimaculatus is a bidirectional serial hermaphrodite.
Kojima et al. (2008) were the fi rst to sex reverse the primary IP male to female
of H. trimaculatus by E 2 -treatment. Following the treatment, spermatogenic
germ cells in the testis underwent rapid degeneration with concomitant
appearance of female germ cells. The E 2 -treatment suppresses the expression
of genes involved in steroidogenesis in the testis such as 11β hydroxylase
and Dmrt1, and reduces androgen receptor transcripts.
These observations have clearly revealed that (i) the morphotypes, such
as primary male (IP), functional female and TP male are only phenotypes
and are not genotypes, as has been considered for a long time and (ii) these
morphotypes have retained the bipotential gonadal germ cells and germ
cells supporting somatic cells, even after sexual maturation and miltings
or spawnings: Most remarkably, these phenotypic morphotypes among