Biology Reference
In-Depth Information
co-operative social organization of
Neolamprologus pulcher
shows reduced
levels of 11-KT and T, compared to a submissive helper male (Bender et al.,
2006). With excretion levels of high T and low 11-KT, the helpers pursue a
'stand-by strategy for breeding' to react quickly, if an occasion for breeding
arises (Bender et al., 2008). Hence hormones are mainly responsible for the
presence of these ontogenetic precocious/submissive male morphs.
Conversely, the other morphotypes such as parental and cuckolder,
hooknose and jack, haremic and pairing male morphotypes have a genetic
basis for differentiation. In the bluegill sunfi sh, parentals mature at the age
of 7+ and use a territorial strategy. Despite receiving and sharing equal
maternal genomes, the progenies sired by cuckolders precociously grow
fast, mature earlier and die before they ever reach the size of the mature
parental, i.e., there is no evidence that the cockolders ever become parentals
themselves (Gross, 1982, 1984). The nest-tending parentals provide less care
of their 'suspected' progenies; they may partially cannibalize or abandon
their 'suspected' brood (Neff, 2003a,b). These observations indicate that
there is a genetic basis for male differentiation into parentals and cuckolders
and apparently, cockolders sire cuckolders only. Contrastingly, there is
experimental evidence among salmonids that hooknoses do sire both
hooknoses and jacks bearing XY genotype. Heath et al. (2002) provided the
much desired fi rst evidence from the sires of the crosses: neofemale (XX)
x female (XX) and male (XY) x female (XX) of hooknoses of the chinook
salmon
O. tshawystscha.
They reported that the XY hooknose sired 31% jack
and 69% hooknose progenies, in comparision to 10% jack and 90% hooknose
progenies sired by XX neomale hooknose; they attributed the presence of
10% jack to autosomal effects. This is an important area, where experimental
evidences are urgently required to know (i) whether the salmonid jacks
also sire jacks and hooknoses or jacks only, and (ii) whether the parentals
of sunfi sh sire parentals alone or both parental and cuckolder progenies.
The fi ndings from these experiments shall pave the way to study and
understand the different elements, constituting the sex chromosome in these
salmonids and centrarchids, and the role of the elements in differentiation
of these male morphotypes.
The presence of two morphs namely territorial (type I) and sneaker
(type II) are described in
Porichthys notatus
(Bass, 1996)
.
The sneakers are
about 50% smaller but have nine-fold larger testes; they neither build nests
nor guard eggs, they do not produce the 'hum' calls like the territorials but
produce grunts like females. Development of their vocal motor circuitry as
function of age in these two morphs has shown that the sexual differentiation
in these morphs have a genetic base (Brantley and Bass, 1994). Similarly,
there are also larger and smaller morphs in
X. maculatus
(Schreibman and
Kallman, 1977) and
X. nigrensis
(Ryan and Causey, 1989). Sexual maturity
