Jamieson, B.G.M. 1995e. Evolution of
tetrapod
spermatozoa with particular reference to amniotes. In Advances in
Spermatozoal Phylogeny and Taxonomy. Jamieson, B.G.M., Ausio, J.
and Justine, J.-L. eds. pp. 343-358. Mémoires du Muséum
national d'Histoire Naturelle, vol. 166, Paris.
Synapomorphies of tetrapod sperm appear to
be: nuclear 'shoulders'; elongation, relative to dipnoans, of two
longitudinal
elements (dense fibres) peripheral to the axoneme adjacent to doublets
3 and 8;
and, questionably, development of an annulus. A lissamphibian
synapomorphy
relative to Neoceratodus may
have been loss of one undulating membrane,
leaving
a single undulating membrane adjacent to the fibre of doublet 3.
Amniote
synapomorphies (retained in Chelonia and Sphenodontida) include:
elongation of
the distal centriole through the entire length of the moderately
elongate
midpiece; subspheroidal mitochondria, with concentric cristae; a
fibrous
sheath; nine peripheral axonemal fibres; inward projections
(longitudinal
columns) of the fibrous sheath aligned with fibres 3 and 8; loss or
transformation of the retronuclear body, present in dipnoans and (as
the neck
structure) urodeles. A possible crocodilian synapomorphy is a thick
dense sheath
around the singlets of the axoneme or the distal centriole.
Synapomorphies of
birds are loss of the subacrosomal cone and, less certainly derived,
adhesion
of all nine dense fibres to their axonemal doublets (also in
monotremes). The
conical acrosome, fibrous sheath, and elongate centriole of ratites are
symplesiomorphies not proving monophyly. Restriction of the endonuclear
canal
to the anterior region of the nucleus in other non-passerines and
passerines
may be a synapomorphy of these, homoplasic with crocodiles and derived
ratites
(emu). Squamate synapomorphies are: loss of endonuclear canals with
restriction
of the perforatorial rod to a prenuclear location; intermitochondrial
bodies;
forward extension of the fibrous sheath into the midpiece; a
paracrystalline
subacrosomal cone; and, homoplasically, shortening of the centriole.
Mammal
sperm are distinguished by loss of the perforatorium (and canal),
homoplasic
with some non-ratite birds, great reduction of the centrioles, and, in
therians, (apomorphic?) detachment of peripheral fibres, except
sometimes 3 and
8, from the doublets.