Dear All,
Thanks to all who responded to my questions on eggs resorbtion
(oosorbtion) and oversized polychaets. I'm very gratefull to Dr. E.
Bonsdorff, Dr. Daniel Martin, Dr. Kevin J. Eckelbarger, Dr. V.
Khaitov, Dr. Alastair Grant; and especially Dr. P. Olive for very
usefull personal introduction and comments.
I enclose the brief summary of received ideas and recomendations on
possible new investigations. I have wrote (Wed, 25 Sep 1996 12:47:05):
I'm an M.Sc student of the Ecology Department at Klaipeda University
(Lithuania) and now perform diploma work on the reproductional
strategies of brackish water polychaetes in Curonian lagoon (Baltic
Sea). In comparison to other Baltic Sea regions my polychaetes seem to
be of larger size (width, length and individual weight). Also, I have
some evidences on absence of normal reproductional development.
I think that worms are unable to develop gametes to mature stage or
spawn in oligohaline conditions (salinity below <1 PSU) and resorb
their inmature eggs before more saline water came.
Could anyone answer me:
1. Does any evidences exist on resorbtion of eggs among polychaetes or
macroinvertebrates in general ? 2. If so, then what are the most
characteristic features of this phenomena I can look at ? 3. What
kind of responses at individual level could be expected in conditions
of: a) organic enrichment and pollution, b) non-periodic changes of
salinity from nearly 0 up to 6 PSU ?
answer 1:
Eggs resorbtion is known phenomenon in eg. Nereis (Hediste) diversicolor
under certain circumstances (stress, low salinity, over-age etc); animals
who have not spawned often live an extra season, and get to be over-sized
for their species. However, they die off without spawning, and do not
contribute to population development.
answer 2:
It seems that your questions may be associated with problem of
poecyllogony in Polychaeta. Several species of worms may show different
modes of larval development: they may have planctotrophic larvae in one
place, but in other places this species may have lecitotrofic mode of
development. In the last situation there is so-called NURSE EGS, those do
not develop (and may be destroyed ?) and they are used as food for larvae.
answer 3:
It is essential to realise the different implications of oosorption for
iteroparous and semelparous worms. In an interoparous form such as the
Nephtyid species oosorption can occur and the energy saved can be used for
reproduction in a later year. Thus we have observed that oosorption occurs
quite frequently in Nephtys hombergi in the R Tyne. Some years the animals
become gravid with many eggs then fail to spawn and the unpsent eggs are
resorbed gradually over the sommer months. Presumable the energy can be
re-deployed as eggs in the next year. Sometimes the spawning failure is
partial in which case a few eggs may be released (1981 - Mar Biol. 63;
189-196 and in 1985 Mar Biol 88:235-246).
In Nereis the situation would be different because Nereis normally is
semelparous and so only breeeds once per lifetime. If oosorption set in
late the animal would presumably die and have zero fitness not having
produced gametes But, if the process of gamete resorption set in early and
the animal in effect delayed breeding for one more year this could
presumably be adaptive. It is interesting to note that this type of
oosorption can be induced in Nereid diversicolor by endocrinological
operations (see Golding and Juwono, 1994) so that is a distinct
possibility. You would have to show evidence of the survival of the
largest size class in the population from one year to the next without the
mortality that is normally associated with breeding.
In many animals oosorption can be stimulated by decerebration. The signs
would be vauolation of the eggs and indeed a disintigration of the
maturing eggs to produce a sort of soup in the body cavity.
_____________________________
Also I received some references, which can be useful:
Eckelbarger & Grassle. 1984. Role of ovarian follicle cells in
vitellogenesis and oocyte resorption in Capitella sp. I. Marine
Biology 79: 133-144.
Bogucki, M. 1962. Rearing Nereis diversicolor in laboratory
conditions. Przeglad Zool. VI: 232-234
Gentil, F., Dauvin, J.C. & Menard, F. (1990) Reproductive biology of
the Polychaete Owenia fusiformis Delle Chiaje in the Bay of Seine
(eastern English Channel). J. of Exp. Mar. Biol. Ecol. 142, 13-23
Blake J.A. Reproduction and larvae development of Polydora
from Northern New England (Polychaeta: Spionidae)//
Ophelia.-1969.-N7.-p.1-63.
Levin L.A., Creed E.L. Effect of temperature and food
availability on reproductive responses of Streblospio benedicti
with planctotrophic or lecithotrophic development // Mar.
Biol.-1986.-92,N1.-p.103-113.
Willson W.H. Sexual reproductive modes in polychaetes:
classification and diversity // Bull. of Mar.
Sci.-1991.-48,N2.-p.500-516.
Olive, P.J.W., Garwood, P.R. & Bentley, M.G. (1981) Oosorption and
reproductive failure in Polychaeta in relation to their reproductive
strategy. Bulletin de la Societe Zoologique de France 106, 263-268
Martin, D., Cha, J.-H. & Bhaud, M. (1996).- Consequences of oocyte
form modification in Eupolymnia nebulosa (Annelida, Polychaeta).
Invert. Reprod .
Many thanks and good luck to all listers
Darius
<darius at hgf.ku.lt>
