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be seen whether the self-fertilizing hermaphrodite
Kryptolebias marmoratus
and gamete exchanging hermaphrodites
Serranus baldwini
and
S. fasciatus
are also somatic XX females and whether the loss of an X chromosome due
to non-disjunction produces XO males, induced by exposure to different
temperatures in
Kryptolebias
and reproductive senescence in S
erranus.
Like the secondary gonochores, all sex changing hermaphrodites
commence with gonads that are already differentiated into ovary/ovotestis
(see Figs. 3 and 4). Hence hermaphroditism has been derived from secondary
gonochores possessing non-functional bisexual gonad. Most monandric sex
changers pass through a common pathway (Table 4). Typically, the labrids,
gobiids and parapercids, possessing undelimited type of gonad commence
with bisexual gonads; on differentiation into ovaries, functional females
are developed. Concomitant with sex change, the ovaries degenerate and
functional testes are derived from the former ovarian wall (see Fig. 53) and
the secondary males are produced (Fig. 4). However, the sparids possess
delimited type of gonad and commence with ovaries, which subsequently
differentiate into the bisexual gonad. In the serranid
Cromileptes altivelis
alone, the gonadal primordium, following the formation of ovarian cavity,
directly differentiates into ovary and testis. The situation is similar to that
of somatic hermaphroditism, in which the appearance of ovarian lumen is
formed prior to the differentiation of the ovary and testis.
There is a uniform and common ontogenetic sex differentiation pathway
for the diandric protogynic sex changers. In all of them, undifferentiated
gonad and gonad with ovarian lumen (e.g.,
Pagrus pagrus
) or ovarian
gonad is formed the fi rst (Table 5). However, they all differentiate into
bisexual gonads. On further differentiation, ovaries and testis of primary
males are formed. With the onset of sex change, the ovaries in female are
degenerated and the testes of secondary male are derived from the ovarian
wall of the female. There is paucity of information on sex differentiation
of protandric sex changers. They seem to be derived from a special type of
juvenile hermaphrodites (Fig. 4).
1.4 Impact of new techniques
This topic is a continuum of the earlier topics in this series. The fi rst one
Sexuality in Fishes is based on 460 or so publications from 175 literature
sources that describe mostly observations supported by histological studies
with occasional fi eld or laboratory experimental observations on the
succession of harem master by an α-female or harem mistress by an α-male.
Cytogenetic contributions from over 600 publications that are scattered in
175 and odd literature sources formed the backbone of the second topic
'Sex Determination in Fish'. In this topic, relevant information from 620
publications that are very widely scattered in more than 210 literature
