Biology Reference
In-Depth Information
zebrafish undergo significant changes in body shape, losing larval fin folds,
developing or completing development of adult fins and fin rays (
Cubbage
& Mabee, 1996; Goldsmith et al., 2006; Patterson, Mook, & Devoto,
2008
), ossifying the axial skeleton (
Bird & Mabee, 2003; Elizondo
et al., 2005
), forming an adult pigment pattern (
Budi, Patterson, &
Parichy, 2008; Budi et al., 2011; Johnson, Africa, Walker, & Weston,
1995; Parichy & Turner, 2003b
), acquiring scales (
Sire & Akimenko,
2004
), and exhibiting maturation and remodeling of many organs,
including the lateral line (
Ledent, 2002; Nu˜ez et al., 2009; Webb &
Shirey, 2003
), central and peripheral nervous systems (
Larson, Gordon,
Lau, & Parichy, 2010
), gut, kidneys, and swimbladder (
Parichy et al., 2009;
Robertson, McGee, Dumbarton, Croll, & Smith, 2007
). Freshwater teleosts
tend to have less distinct periods of larval metamorphosis than marine or
diadromous species, but this postembryonic process still unequivocally occurs,
transforming the larval organism into a morphologically distinct juvenile form.
There are at least a few identified cases of paedomorphism in freshwater
species, with miniature
Paedocypris
and
Danionella
fish failing to undergo nor-
mal metamorphosis and becoming reproductively mature while maintaining a
larva-like overall morphology (
Britz, Conway, & R¨ber, 2009; Mayden &
Chen, 2010; R¨ber et al., 2007
). These paedomorphic genera illustrate ways
in which even relatively subtle metamorphic processes may be modified to
effect major morphological change.
3. ENDOCRINE CONTROLS OF TELEOST
METAMORPHOSIS
The coordinated occurrence of multiple disparate organ- and tissue-
specific events during teleost life-stage transitions suggests that “local” pro-
cesses are likely to be coordinated by “global” signals (and so are likely to
constitute bona fide metamorphoses, as defined above). Research into the
endocrine controls of postembryonic transitions in teleosts has focused
almost exclusively on spectacular examples of such metamorphoses; for
example, salmonid smoltification and flatfish metamorphosis. Yet, there is
evidence that more subtle transitional processes are controlled by conserved
endocrine mechanisms as well. Here, we outline what is known about
the hormonal contributions to teleost metamorphosis. TH appears to be a
key regulator of teleost metamorphosis, and most endocrine studies of meta-
morphosis have focused on this factor. Thus, we briefly review the
