Biology Reference
In-Depth Information
Figure 46 shows the chronological sequence of changes in
FSHR
and
LHR
levels in the ovary and testis, when sex is rapidly changed from female
to male and then to female each within a short span of four days. These
fi ndings suggest the important role played by the hypothalamic-pitutary-
gonadotropic axis in realizing rapid sex change.
3.7 Gonadal differentiation
The occurrence of hermaphroditism in fi shes is well documented (e.g.,
Pandian, 2010) and are common among, for example, Sparidae, Scaridae
and Serranidae, in which hermaphroditism is the rule rather than exception
(Buxton, 1989). The hermaphrodites may have arisen independently in more
than 10 lineages (Warner, 1978). In accordance with different patterns of
hermaphroditism, a brief account on gonadal differentiation is provided.
Self fertilizing hermaphrodite:
Genetically different groups
(Turner et
al., 1992) of
homozygous isogenic clones
of
Kryptolebias marmoratus
naturally
reproduce
uniparentally
in waters from southern Florida through much
of the West Indies to Venezuela (see Pandian, 2010). These attributes are
shared by no other vertebrates known so far. Following self fertilization
(Fig. 47), the eggs are incubated intraparentally for 2-3 days and then
extraparentally for 14 days (Harrington, 1967). On incubation at 26ºC,
hermaphrodites are produced but primary male, when incubated at < 19ºC.
Exposure of hatchlings to 28ºC generate secondary males. In its natural
habitats, secondary males may fertilize 2-3% hermaphrodites (Tatarenkov
et al., 2009).
The estimates of Germ Cells (GCs) in rivulus is perhaps the only
contribution to date reporting on dimorphic trends of the mitotic
proliferation of GCs as a function of early embryonic and post-embryonic
stages in hermaphrodites and males. Harrington (1975) considered body
length as more appropriate than time scale, as the latter is subjected to
wider changes, especially due to differences in incubation temperature.
Figure 48, reconstructed and redrawn using Harrington's data, clearly
shows the sexually dimorphic trends for the mitotic proliferation of GCs
(approximately the PGCs) in hermaphrodites and male rivulus. Though
accelerated from 30-31 stages, the proliferation of GCs rapidly increases to
about 680 in hermaphrodites but to about 340 only in males. These trends
unequivocally resemble those of PGCs in
O. latipes
and
O. niloticus
(see Fig.
13). Hence it is likely that sex in the selfi ng
K. marmoratus
is also determined
by
Dmrt.
A publication confi rming this suggestion would make a milestone
in this area of research.
Indeed Rhee et al. (2008) have reported the presence
of
Dmrt1
in the rivulus.
