Re: Breeding

So are you saying the sperm/ovum interaction in fowls is different from
mammals? Specifically, the enzymatic reaction which occurs when a sperm
contacts the ovum layer or zona pellucida, , if I understand correctly,
creates an enzyme which rejects competeing sperm from reacting with the ovum
thus allowing it to make exclusive contact with the nucleolus. Does this
happen different in chickens?

---Mike




" Jill" <news@xxxxxxxxxxxxxxxxxxxxx> wrote in message
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"krys" <krys.brennand@xxxxxxxxx> wrote in message
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Thought that you might find this interesting:
In 1978 Compton et al. found that sperm is stratified by genotype
within the hen's sperm host glands & remains stratified over time
witthin a gland. The glndd empties by sustained superficial leakage
over time.
The significance being that they demostrated that the sperm from the
last insemination or mating were the first sperm cells to be released
for the purposes of fertilization.

best wishes
Krys


Interesting
It fits with the mating behaviour [each cockerel trying to be "the last"]
and I have read that in other avian species
But its been observed by the results of hatching that the "contamination"
remains viable ?

Sperm competition in birds
TR Birkhead


Sperm competition in birds occurs when a female is inseminated by more
than one male during a single breeding cycle. Despite most birds being
socially monogamous, sperm competition is widespread and results in
frequent extra-pair paternity. Sperm competition is a fundamental part of
sexual selection since it results in differential reproductive success
among males. Male adaptations to sperm competition include relatively
large testes, large sperm stores and long spermatozoa, mate guarding and
frequent pair copulations. Females show no obvious morphological
adaptations to sperm competition but, by controlling whether copulations
are successful, they probably determine its frequency and extent. Despite
this, the evolutionary benefits females acquire from extra-pair
fertilizations are poorly understood. Experiments in which females are
inseminated with equal numbers of spermatozoa from two males usually show
last male sperm precedence. Understanding the mechanism of sperm
competition requires understanding of why the last male to inseminate a
female fertilizes a disproportionate number of eggs. The data from sperm
competition studies on the domestic fowl, turkeys and zebra finches are
consistent only with a passive sperm loss model of sperm competition. The
mechanism is as follows: after insemination, spermatozoa enter the sperm
storage tubules located in the oviduct, from which they are lost at a
constant rate over days or weeks. All else being equal, the interval
between two inseminations determines the probability of fertilization: the
second of two inseminations fertilizes most eggs simply because, by the
time fertilization occurs, fewer of these spermatozoa have been lost.
Other factors also affect the outcome of sperm competition: the timing of
insemination relative to oviposition, the differential fertilizing
capacity of males and differences in the numbers of spermatozoa
inseminated; as a consequence, last male sperm precedence is not
automatic. On the basis of the mechanism of sperm competition, the optimal
strategy for both males and females to maximize their likelihood of
extra-pair fertilization is to copulate with an extra-pair partner as
close as possible to the onset of oviposition.








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