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|Title: ||The physiological ecology and life history strategies of the nudibranch molluscs 'Adalaria proxima' (Alder & Hancock) and 'Onchidoris muricata' (Müller) (Gastropoda: Opisthobranchia)|
|Authors: ||Havenhand, Jonathan Neil|
|Supervisors: ||Todd, Christopher|
|Issue Date: ||1987|
study investigated the physiological ecology, larval biology
genetics of the nudibranch molluscs Adalaria proxima
(A & H)
and Onchidoris muricata
(Müller). These two species are annual, simultaneous hermaphrodites and are ecologically
very similar with the exception that A. proxima reproduces by
means of pelagic
lecithotrophic larvae whereas Omuricata has long-term planktotrophic larvae. The aim of
the study was therefore to determine the selective pressures which resulted in the evolution of
different larval types in these two species, and to ascertain the ecological and population
genetic consequences thereof.
energy budgets comprising the major components (consumption, growth,
respiration and reproduction) were constructed for laboratory populations of each species. In
both A. proxima and O. muricata,
feeding rate displayed an asymptotic increase with
Mean feeding rates of
A. proxima were greater than those of comparable O. muricata
and overall assimilation efficiency was higher in A. proxima than in O. muricata.
This difference was reflected in the somatic growth rates which were correspondingly greater
in A. proxima than in O. muricata.
growth efficiencies were broadly comparable between
the two species, however, growth of
A. proxima was approximately linear
over' time whilst
displayed a curvilinear, almost exponential, pattern.
This is interpreted as
demonstrating that some form
of constraint (possibly feeding rate) operated on the growth
not on those of
Respiration rates were found to be relatively constant within given animals, but
significant differences were found between individuals. The
allometry of respiration rate
was not constant; Omuricata demonstrated a more rapid
respiration rate with
size than did A. proxima.
respiration rate did
reflect variations in the energy partitioned to either growth or reproduction.
Reproductive patterns in the two species were dissimilar. A. proxima
spawn masses containing fewer, larger ova than those laid by O. muricata
addition, the spawning period of
A. proxima was shorter than that of
105 days respectively). Both
species exhibited a similar
(proportional) degree of somatic
catabolism over these periods. The
consequently more rapid
interpreted as the necessary utilization of an energy resource (i. e. the soma) caused by
inability to meet the energy demands of reproduction through feeding alone.
the case in Oanuricata individuals
which exhibited a much smaller maximum body size and
were able to feed at a sufficiently rapid rate to maintain reproduction.
In the latter case, the
longer reproductive period served to maximise the total reproductive output.
"Reproductive Effort" (RE)
generally indicated that the RE
was considerably greater than that of
such differences have been used in the literature to classify the
respective costs of
different larval types or
"reproductive strategies", the variability of the
RE's obtained from
measures used here has led to the suggestion that the
of association between RE
and reproductive strategy which
has been reported
(partially) be attributable to the different
Studies of the embryonic and larval
period showed that the egg-to-juvenile period of
O. muricata was approximately 50% longer than that of
This difference was
primarily attributable to the extended pelagic development of
of the degree of
dispersal, and hence gene-flow, between populations of these species were
tested by investigating the biochemical genetics of such populations. No data were available
for O. muricata,
but A. proxima populations proved to be more genetically heterogeneous
than had been expected. It is therefore concluded that actual pelagic dispersal may be
considerably abbreviated over that expected on the basis of
model is developed to explain the possible consequences of
egg-to-juvenile periods (which
accrue from different larval types) on
the ecology of the
benthic adult, and on overall energy partitioning to reproduction.
(probable) proximate causes and effects of the different reproductive traits exhibited by
A. proxima and Oanuricata
are shown, it has not
been possible to determine the exact
selective pressures which caused A. proxima to diverge from the ancestral "O. muricata"
stock through the evolution of a pelagic lecithotrophic larva.|
|Publisher: ||University of St Andrews|
|Appears in Collections:||Biology Theses|
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