Vertebrate Embryology
Updated 4 November 2004
Ontogeny – development of
the individual (gametogenesis to death). Cover quickly with much less detail than in
text (read accordingly!)
A.
Observation: vertebrates are structurally similar as adults
1.
Results from similar embryonic development (slide 1)
2.
To understand adult structure (especially comparative
structure), one must know how the general vertebrate
body plan is established in early embryonic development.
B.
Terms relative to where embryonic development occurs and how
the embryo is nourished
1.
Oviparous (outside maternal body, yolk - incubation);
primitive
2.
Viviparous (inside maternal body, maternal materials - gestation);
derived (>100 times independently; especially reptiles)
3.
Continuum between oviparity and viviparity
Stages of
embryonic development (apparent differences among vertebrates correlate with the
amount of yolk present in egg (e.g., mammal vs. ostrich); illustrate general
pattern with frog development
A.
Gametogenesis (2N®N; growth yolk)
B.
Fertilization (N+N®2N); zygote
C.
Cleavage and blastulation
(mitosis); morula; slide
2
D.
Gastrulation and neurulation; slide
2; slide 3
Critical stage,
highly active (movement), blastopore, formation of
gut, differentiation begins; highly variable in appearance (due to differences
in amount of yolk); 3 critically important reorganizations:
1.
Polarity established (body axis, R/L)
2.
Formation of 3 germ layers (ectoderm, mesoderm, endoderm)
3.
Strategic positioning of germ layers for mutual interaction
(induction); especially mesoderm
4.
Results in histogenesis (tissue
formation); 4 basic types:
a.
epithelium – cover surfaces; line body cavities, ducts,
vessels; glands
b.
connective – bone, cartilage, fibrous, adipose, blood
c.
muscle – muscle tissue
d.
nervous – nervous tissue (includes sensory organs, in part)
E.
Organogenesis
1.
slide 3;
gut, notochord, neural tube, somites, nephrotome, lateral plate, coelom,
pharyngeal arches, vertebrae, neural crest cells (unique to vertebrates)
2.
Fate of germ layers - general overview; slide 4
3.
Extraembryonic membranes and
placenta (respiration, nutrition; found in some fishes, amphibians, reptiles,
mammals – no birds)
1.
Metamorphosis
2.
Aging
3.
Reproductive senescence (not in some groups, e.g., turtles)
4.
Heterochrony (unequal rates
of somatic and sexual development; can have profound effects on the design of
an organism); types
a.
paedomorphosis (embryonic or
juvenile characteristics of ancestors appear in adult stages of descendents
(descendents resemble juveniles of their ancestors); two types:
1)
neoteny - somatic
development slows relative to normal sexual development; common in vertebrates
(e.g. many amphibians - mudpuppy)
2)
progenesis - sexual
maturity accelerated relative to normal somatic development; less common (e.g.,
Bolittoglossa)
b.
recapitulation (adult chacteristics
of ancestors appear in larval or juvenile stages of descendents)