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|Title: ||Chemical cues and energy cost associated with the induction of anti-predatory responses in the green-lipped mussel perna viridis|
|Other Titles: ||Yu you dao fei cui yi bei zuo chu fan bu shi xing wei xiang guan de hua xue xin xi he neng liang xiao hao|
|Authors: ||Yang, Fung Yin (楊鳳燕)|
|Department: ||Department of Biology and Chemistry|
|Degree: ||Master of Philosophy|
|Issue Date: ||2008|
|Publisher: ||City University of Hong Kong|
|Notes: ||CityU Call Number: QL430.7.M95 Y36 2008|
xviii, 194 leaves : ill. (some col.) 30 cm.
Thesis (M.Phil.)--City University of Hong Kong, 2008.
Includes bibliographical references (leaves 164-194)
|Abstract: ||Aquatic animals are known to perceive and assess the risk of predation by means
of chemical cues which are either released from predators, or from prey that have
either been captured or injured. The ability to develop adaptive responses to increase
resistance against predators is crucial; failure to avoid a predator can be lethal. The
green-lipped mussel Perna viridis is a tropical and subtropical species distributed
widely in Asia and plays a crucial role in structuring intertidal communities. It is
susceptible to predators such as crabs and muricid gastropods. The present study
investigated the inducible anti-predator responses of P. viridis, upon exposure to
different types of chemical cues and the energy cost associated with these responses.
Byssal threads are strong proteinaceous fibres which are secreted by the byssal gland of the mussel. They are essential to a mussel’s defence against predation; an
increase in the attachment strength can effectively reduce dislodgement by predators.
A laboratory experiment was conducted to investigate the byssal thread production
by juvenile P. viridis in response to waterborne cues from damaged conspecifics or
damaged heterospecifics from the black mussel Brachidontes variabilis. The byssal
thread production and the mobility of the mussels were studied for 96 hours. P.
viridis which was exposed to damaged conspecifics produced the thickest (27.3%
thicker than control) and longest (21.7% longer than control) byssal threads and were
followed by those exposed to damaged heterospecifics with values being 23.1% and
15.5% higher, as compared to the control. The byssus volume increased by 133.6%
and 60.0% in the damaged conspecific and damaged heterospecific treatments,
respectively. P. viridis exposed to the damaged conspecifc cues also had higher
mobility. Results showed that P. viridis is able to differentiate different
damage-released chemical cues and respond according to its associated risk level.
The finding that damaged heterospecific cues can trigger anti-predator response in
mussels by adjusting its byssus production is novel.
Most of the studies on anti-predator responses in mussels and other aquatic
animals were laboratory experiments; rarely have such experiments been performed in the field, despite the fact that the results achieved there would be more
ecologically relevant. P. viridis was exposed to the predatory crab Thalamita sima, in
the field for 48 hours and byssal thread production was examined and compared with
those exposed to either deposit-feeding gastropods or the control, without any cues.
It was the first time a field study on this topic was undertaken in subtropical waters.
Although considerably lower magnitude of responses was found in the field, this
study has verified that P. viridis, in both laboratory and field conditions, produced
longer and thicker byssal threads when they were exposed to predators as compared
with other treatment groups. Caution should be exercised when making predictions
based on laboratory experiments. More ecologically relevant, field-manipulated
experiments are recommended for the future.
Forming clumps is one of the behavioural features of mussels. Early studies have
shown that mussels at the centre of a clump suffer lower predation than those at the
edge. However, their growth and reproduction are also reduced when compared with
mussels either located at the edge of a clump or that are solitary. The location of the
mussels may determine the extent of the anti-predator responses, which is induced
upon exposure to predation-related chemical cues. The hypothesis was tested in a
laboratory experiment with clumping behaviour and byssal thread production of juvenile P. viridis being investigated in response to waterborne cues from damaged
conspecifics or damaged heterospecifics, B. variabilis. The formation of clumps was
monitored for 48 hours, and the byssal thread production of mussels located at
various positions on and in the clumps was determined at the end of the experiment.
The results did not reveal any evidence of the induction of clumping behaviour by
damaged alarm signals. Instead, solitary mussels and those found at the edges of the
clumps in the damaged conspecific treatment produced significantly more byssal
threads, which were twice and 39.8%, respectively more than those located within
the clumps. A similar trend was observed in the length of byssal threads in which
solitary mussels and edge mussels produced 22.7% and 16.0% longer, respectively,
threads than the mussels located within the clumps. In addition, the results showed
that mussels exposed to broken green mussels produced the greatest volume, the
highest number and longest byssal threads, over mussels in other treatments,
irrespective of their spatial positions. The results coincided with the hypothesis that
the level of anti-predator response elicited by mussels is determined by the spatial
position of the mussels in the clump.
Scope for growth (SFG), which represents the energy available for growth and
reproduction after maintenance requirements are met, was employed to determine
and quantify the cost of anti-predator responses to P. viridis. Physiological responses, including absorption efficiency, clearance rate, excretion rate and respiration rate
were measured for mussels exposed to chemical cues from damaged conspecifics or
predators feeding on different prey over a two-week period. Lower clearance rate and
absorption efficiency were observed in P. viridis exposed to unfed crabs or crabs
feeding on conspecific mussels. A decrease in the clearance rate and an increase in
the respiration rate were also observed for P. viridis exposed to damaged
conspecifics. Subsequently, a 62.8% and 58.6% reduction in the SFG was found for
treatments with unfed crabs or crabs feeding on conspecific mussels, respectively, as
compared to the control. The results suggest that there is an apparent fitnesss cost
involved in the induction of anti-predator responses. Growth potential of P. viridis
may be severly reduced under predation risk in view of the trade-offs between
investments in inducible defences and energy acquisition. This sub-lethal effect not
only affects the growth rate and population dynamics of P. viridis but may cascade
through the phytoplankton abundance, altering the food web structure.|
|Online Catalog Link: ||http://lib.cityu.edu.hk/record=b2340605|
|Appears in Collections:||BCH - Master of Philosophy |
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