Domestication reduces the capacity to escape from predators

www.elsevier.com/locate/jembe

Journal of Experimental Marine Biolo

Domestication reduces the capacity to escape from predators

Katherina B. Brokordt a,*, Miriam Fernandez b, Carlos F. Gaymer a

a Center for Advanced Studies in Arid Zones (CEAZA), Departamento de Biologıa Marina, Universidad Catolica del Norte, Larrondo 1281,

Coquimbo, Chileb Center for Advanced Studies in Ecology and Biodiversity (CASEB), Estacion Costera de Investigaciones Marinas, Departamento de Ecologıa,

Pontificia Universidad Catolica de Chile, Chile

Received 2 May 2005; received in revised form 23 May 2005; accepted 8 August 2005

Abstract

Phenotypic plasticity in response to variations in predatory pressure frequently occurs in wild populations, but it may be more

evident and critical in species subjected to high exploitation rates and aquaculture. The Chilean scallop Argopecten purpuratus is

becoming a domesticated species and the production of hatchery-reared scallops (closed environment), has implied the develop-

ment of successive generations of individuals deprived of several stimuli normally present in their natural habitats (e.g. predators).

We compared the escape capacities between wild and cultured A. purpuratus and also evaluated the effect of reproductive

investment on the escape response capacities. Wild and cultured scallops, at different reproductive stages (maturing, mature and

spawned), were stimulated to escape with the predatory sea star Meyenaster gelatinosus. We recorded: (1) the time to reaction, (2)

the total number of claps, the duration of the clapping response and the clapping rate until exhaustion, (3) the time they spent closed

after exhaustion, and (4) the proportion of claps recovered, the duration of the clapping response and the clapping rate after 20 min

of recuperation. We found that wild A. purpuratus (1) reacted earlier when contacted by their natural predator, (2) escaped faster

(greater clapping rates), (3) spent less time with their valves closed when exhausted, and (4) most of their escape capacities (i.e.

claps number; clapping time; capacity of recuperation) were less affected by the energetic requirements imposed by gonad

maturation and/or spawning than in cultured scallops. We considered that all these aspects of the escape response would make wild

scallops less vulnerable to predation than cultured scallops, thus decreasing predation risk. Given the reduction of escape

performance in cultured scallops, we suggest that this aspect should be considered for the success of culture-based restocking

programs.

D 2005 Elsevier B.V. All rights reserved.

Keywords: Argopecten purpuratus; Cultured scallops; Escape response; Reproductive cost; Restocking; Wild scallops

1. Introduction

Predation is a major factor causing mortality in wild

populations, and consequently species have evolved a

varied set of response mechanisms to avoid or decrease

predation pressure (Sih, 1987). Passive defensive

mechanisms (e.g. morphological traits) as well as active

0022-0981/$ - see front matter D 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.jembe.2005.08.007

* Corresponding author. Tel.: +56 51 209929; fax: +56 51 209812.

E-mail address: [email protected] (K.B. Brokordt).

responses (e.g. escape behaviours) often have direct

energetic costs (Sih, 1987; Kleinman et al., 1996) and

consequently, many animals have evolved flexible

mechanisms that may be developed or lost over short

periods, depending on the predation risk (Havel, 1987;

Legault and Himmelman, 1993; Reimer et al., 1995;

Reimer and Tedengren, 1996; Rochette et al., 1998).

Morphological, physiological and behavioural respon-

ses to predation seem to be attenuated in culture-reared

fishes in comparison to wild populations (Huntingford,

gy and Ecology 329 (2006) 11–19

K.B. Brokordt et al. / J. Exp. Mar. Biol. Ecol. 329 (2006) 11–1912

2004). This suggests the important selective pressure

of predation, but also suggests that changes in the

genetic structure, and in the phenotypic response of

individuals to predation, may occur in species subjected

to high exploitation rate and aquaculture (Huntingford,

2004).

Comparisons of responses to predators between cul-

tured and wild animals show differences in both juve-

nile and adult stages in species of different taxa

(Haugum et al., 1999; Alvarez and Nicieza, 2003;

Lafrance et al., 2003). Hatchery reared juvenile brown

trout (Salmo trutta) approached dummy predators more

frequently than wild juveniles, and this bnaivenessQ wasdue to a decreased capacity to detect predation risk

(Ferno and Jarvi, 1998). Mussels exposed to predator

odours developed smaller and thicker shells, stronger

byssal attachment and a larger adductor muscle than

non-exposed mussels, which made them less vulnerable

to predation by sea stars and crabs (Hancock, 1965;

Reimer and Tedengren, 1996; Reimer and Harms-Ring-

dahl, 2001). In the scallops Pecten maximus and Pla-

copecten magellanicus, weaker shells (i.e. less resistant

to mechanical pressure) have been observed in cultured

stocks when compared to wild populations (Haugum et

al., 1999; Lafrance et al., 2003). Moreover, the intensity

of the escape response (i.e. swimming speed) was lower

in cultured than in wild juvenile P. magellanicus

(Lafrance et al., 2003) and mortality due to predation

was greater in cultured stocks of P. maximus (Haugum

et al., 1999).

Differences between cultured and wild populations

may also be affected by reproductive status, as invest-

ment in reproduction affects the energetic reserves

used for fleeing predators in several marine and ter-

restrial taxa (Koch and Wieser, 1983; Hughes and

Rayner, 1993; Brokordt et al., 2000a,b, 2003). Scal-

lops are exceptional among bivalve molluscs in having

an excellent swimming capacity, which is exhibited

upon detection of predators (Vogel, 1997). Investment

in reproduction (i.e. gonad maturation and spawning)

markedly reduced the capacity of sub-Arctic (Chlamys

islandica) and tropical (Euvola ziczac) scallops to

escape predators (Brokordt et al., 2000a,b). In both

species, investment in gonads led to an important

decrease in muscle glycogen content and in the

metabolic enzymes that support adductor muscle con-

traction and recuperation during and after the escape

response (Brokordt et al., 2000a,b; Brokordt and

Guderley, 2004). A similar trend was observed in

Argopecten purpuratus, which exhibits an important

decline of muscle carbohydrates and the enzyme octo-

pine dehydrogenase (implicated in muscle contraction

and recuperation), after gonad maturation (Martınez et

al., 2000).

Many marine and terrestrial wild populations have

declined over the past several decades, largely as a

result of fishing or hunting pressure (Brown and

Laland, 2001; Fuller, 2002; Letty et al., 2002; Friedman

and Finley, 2003). Most restocking programs of wild

populations rely on farm- or hatchery-reared stocks

(Brown and Laland, 2001; Friedman and Finley,

2003; Huntingford, 2004). However, the mortality

rates of hatchery reared individuals after release are

very high, mainly due to diseases and predation (Hatch-

er et al., 1996; Barbeau and McDowell, 1998; Brown

and Laland, 2001; Friedman and Finley, 2003). In Chile

the scallop A. purpuratus is becoming a fully domesti-

cated species, as ~90% of the individuals are kept in

suspended cultures along the Chilean coast (Stotz,

1999). Only two natural seabeds remain, and they

show low scallop densities and high predator (sea

stars and crabs) abundance (Ortiz et al., 2003; Stotz,

1999). Thus, the persistence of A. purpuratus popula-

tions in Chile will most probably rely on descendants of

bdomesticatedQ (cultured) scallops to restore natural

beds (Stotz, 1999). Moreover, the settlement of scallop

larvae on collectors, which in the past was exclusively

dependent on wild populations, is now strongly based

on larvae produced in hatcheries. Therefore, these ani-

mals are deprived of direct stimuli by natural predators

for several consecutive generations.

In the present study, we compared escape response

capacities between wild and hatchery cultured A. pur-

puratus, evaluating the effect of gonad maturation and

spawning. We discuss the implications of our results for

conservation and restoration of wild populations, given

the current increase of cultured stocks of several marine

species and the reliance of restocking on hatchery-

reared individuals.

2. Materials and methods

2.1. Sampling and reproductive conditioning of

scallops

Wild Argopecten purpuratus were sampled by

SCUBA diving from Puerto Aldea, one of the few

natural beds that remain in the Chilean coast, located

in Tongoy Bay, northern Chile (308 18V S, 718 33V W)

(Fig. 1). Hatchery reared scallops were obtained from a

scallop farm (Cultivos San Jose), also located in Tongoy

Bay (308 16V S; 718 35V W). Adult scallops (75–85 mm

in shell height) from both populations were transported

to the Central Culture Laboratory at the Universidad

CHILE

Coquimbo

Tongoy Bay

Puerto Aldea

0 1 2

TONGOY BAY

Km

25˚S

45˚S

90˚ 53˚

30˚S

71˚S 20’W

Tongoy

Wild scallops bed

Scallop culture

Pacific Ocean

•

•

Fig. 1. Location (!) of the wild and hatchery cultured Argopecten purpuratus scallop populations in Tongoy Bay, Coquimbo.

K.B. Brokordt et al. / J. Exp. Mar. Biol. Ecol. 329 (2006) 11–19 13

Catolica del Norte, Coquimbo. From each stock, 180

individuals were maintained and conditioned in twelve

200-l tanks (30 scallops per tank) with filtered sea water,

constant aeration and at 16 8C (suggested conditioning

temperature for A. purpuratus; sensu Martınez et al.,

2000). To standardize initial reproductive conditions,

scallops were induced to spawn by increasing the tem-

perature and adding excess microalgae. After spawning,

scallops from both stocks were then conditioned during

~80 days to reach complete gonad maturation (Martınez

et al., 2000). This period permitted standardization of

the nutritional status of both the wild and cultured

stocks. During the conditioning period, scallops were

fed with a mixture of microalgae (50% Isochrysis gal-

bana, 50% Chaetoceros calcitrans) at a daily food

ration of 5% the animals’ dry mass. The food ration of

microalgae was supplied by a continuous dropping sys-

tem. Reproductive stages were determined using quali-

tative and quantitative criteria. As qualitative criteria

and before the behavioural trials, we evaluated the

shape and colour of the gonad and the degree of vascu-

larization by secondary genital ducts which were ob-

servable through the gonad epithelium (Mason, 1958).

As quantitative criteria, we determined gonad stage

using the gonad index corrected by the size of the

scallop [(gonad mass� total soft tissues mass�1)� shell

shell height�1], as described by Bonardelli and Him-

melman (1995). Based on these assessments, three re-

productive stages were determined: maturing, mature

and spawned.

2.2. Evaluation of escape responses

We evaluated the escape capacities in laboratory

conditioned wild and cultured scallops, at three differ-

ent reproductive stages: maturing, mature and spawned

(24 h after induced spawning). The day after the beha-

vioural trials were conducted, scallops were dissected

for quantitative assessments of reproductive stage. Es-

cape responses were quantified at least in 54 scallops

for each reproductive stage, for each population.

Each experimental animal was individually placed in

25-l containers with filtered running sea water at

16 8C. Preliminary observations showed that when

A. purpuratus was stimulated by its natural predator,

the sea star Meyenaster gelatinosus (Ortiz et al., 2003),

they showed a strong escape response that is highly

stereotyped and consistent. The escape response started

with a series of valve claps (alternate adduction and

abduction of the valves). If the stimulus was maintained

Table 1

Two-way ANOVA used to compare gonad indices between wild and

cultured populations (P) of the scallop Argopecten purpuratus at three

different reproductive stages (RS)

Source df F P

Population 1 0.02 0.884

Reproductive stage 2 117.57 b0.001

P*RS 1 31.78 b0.001

Error 344

a

b

c

d d d

Maturing Mature Spawned0

0.05

0.1

0.15

Wild scallops

Cultured scallops

GI (

shel

l hei

ght)

-1

Fig. 2. Gonad index (GI) corrected by the size of the scallop [(gonad

mass� total soft tissues mass�1)� shell height�1], for wild and cul-

tured Argopecten purpuratus conditioned and sampled at three dif-

ferent reproductive stages. Values represent meansFS.E. (n =58 per

reproductive stage, per population). Means sharing the same letter are

not significantly different ( Pz0.05) as indicated by LS means a

posteriori multiple comparisons.


until exhaustion (i.e. scallops did not respond during 2

min), most scallops closed their valves firmly and

remained closed for a certain period, after which the

valves slowly reopened. Based on these behaviours, we

ran the following experiment. Scallops were left undis-

turbed during 5 min before stimulation, in order to

reduce handling stress (Ordzie and Garofalo, 1980).

Then, we stimulated escape responses by touching the

scallops’ mantle edge with an arm of M. gelatinosus,

recording several indicators of scallops’ escape re-

sponse: (1) btime to reactionQ, which is the time elapsed

between the first contact between the sea star arm and

the mantle edge of the scallops and the first clap; this

initial reaction was an indicator of the reactiveness of

scallops to the contact with their predator; (2) the total

number of claps, (3) the duration of the clapping re-

sponse (clapping time) and (4) the clapping rate until

exhaustion. After exhaustion, the experimental animals

were allowed to recuperate for 20 min, which was

sufficient for recovering ~80% of the initial escape

response capacity as indicated by preliminary trials.

We recorded the time that the animals remained with

the valves closed after exhaustion and we then started a

new predator stimulation period, recording the follow-

ing behaviours: (1) the total number of claps, (2) clap-

ping time after recuperation and (3) clapping rate after

recuperation. All the behaviours recorded before and

after the recuperation period were indicators of the

scallops’ escape capacities. We report the results of

the initial stimulation as follows: time to reaction,

number of initial claps, initial clapping time, initial

clapping rate, and the behaviours after recuperation:

proportion of claps recovered, clapping time after recu-

peration and clapping rate after recuperation.

2.3. Statistical analyses

Two-way ANOVAs were used to test the null hypoth-

esis of no differences between scallop populations (wild

and cultured), and reproductive status on gonad index

for each escape response variable (Sokal and Rohlf,

1981). When the assumptions of normality and homo-

scedasticity were not met, the data were ln-transformed.

Normality was tested using a Shapiro–Wilk’s test (SAS,

1999) and homogeneity of variances using a Levene test

(Snedecor and Cochran, 1989). In cases where assump-

tions were not met, ANOVAs were applied to both the

raw and to rank-transformed data and we presented the

results of the former when they were the same for the

two analyses (Conover, 1980). Multiple pairwise com-

parisons tests (LS means) were used to test a posteriori

for specific differences (PV0.05) (SAS, 1999).

3. Results

3.1. Reproductive stages

In both wild and cultured Argopecten purpuratus,

gonad index changed significantly between reproduc-

tive stages, increasing after gonad maturation and de-

creasing after spawning (Table 1, Fig. 2). A significant

interaction between the population and the reproductive

stage indicated that the reproductive status had a dif-

ferent impact according to the population (Table 1).

Maturing animals from wild populations showed sig-

nificantly lower gonad indices than maturing indivi-

duals from cultured populations, but mature animals

from wild populations showed a greater gonad index

than cultured ones (P b0.05; Fig. 2). Maturing animals

from wild populations did not differ from spawned

individuals from both populations (P N0.05). After

spawning both wild and cultured scallops presented

similar gonad masses (P N0.05; Fig. 2).


3.2. Escape responses

We found strong differences in reactions to predator

stimulation between wild and cultured scallops (Table

2, Fig. 3). Significant interactions between the popula-

tion and the reproductive stage again indicated that the

Table 2

Two-way ANOVAs used to compare escape responses variables

between wild and cultured populations (P) of the scallop Argopecten

purpuratus at three different reproductive stages (RS)

Source df F P

Time to reaction

Population 1 90.38 b0.001


P*RS 2 4.91 0.008

Error 341

Number of initial claps



P*RS 2 6.23 0.002

Error 342

Initial clapping time



P*RS 2 10.96 b0.001

Error 340

Initial clapping rate


Reproductive stage 2 5.17 0.006

P*RS 2 8.51 b0.001

Error 340

Time spent closed



P*RS 2 1.44 0.239

Error 236

Proportion of claps recovered



P*RS 2 5.03 0.007

Error 331

Clapping time after recuperation



P*RS 2 14.46 b0.001

Error 315

Clapping rate after recuperation



P*RS 2 5.91 0.003

Error 316

reproductive status had a different impact according to

the population (Table 2). Wild animals showed a faster

reaction to predators, regardless of the reproductive

stage (Fig. 3A). Cultured scallops were particularly

slow to react in maturing and spawned stages (Fig.

3A). Maturing cultured scallops showed a significantly

higher number of initial claps (first stimulation) com-

pared to maturing wild ones (Fig. 3B). However, the

number of initial claps did not differ between wild and

cultured populations for mature and spawned indivi-

duals (Fig. 3B). Cultured scallops clapped for a longer

time than wild ones for maturing and spawned indivi-

duals, but not for mature ones (Fig. 3C). In contrast,

wild scallops clapped at higher rates (initial clapping

rate) than cultured ones for both maturing and spawned

individuals (Fig. 3D). Although the reproductive stage

did not affect the time that the valves remained closed

after exhaustion (time spent closed), differences between

wild and cultured populations were found (Table 2, Fig.

3E). Scallops from wild populations remained with the

valves closed for a shorter time after exhaustion than

cultured scallops, for both maturing and mature indivi-

duals (Fig. 3E). After 20 min of recuperation from

exhaustion, both wild and cultured maturing scallops

recovered ~75% of their initial number of claps (Fig.

3F). Gonad maturation and spawning decreased the

proportion of claps recovered in cultured scallops, but

not in wild ones (Fig. 3F). Both wild and cultured

scallops maintained their patterns of clapping time

and clapping rate (Fig. 3G, H). As shown for the initial

clapping time of cultured scallops, clapping time after

recuperation for these scallops decreased after gonad

maturation and spawning. However, in wild scallops

there was only a slight decrease in clapping time after

spawning (Fig. 3G). Clapping rate after recuperation of

cultured scallops increased after gonad maturation, but

in wild scallops clapping rate increased after spawning

(Fig. 3H).

4. Discussion

Our study shows that wild Argopecten purpuratus,

compared to cultured ones: (1) reacted earlier when

contacted by their natural predator, the sea star Meye-

naster gelatinosus, (2) exhibited higher clapping rates,

(3) spent less time with their valves closed when

exhausted, and (4) most of their escape capacities

were less affected by the energetic requirements im-

posed by gonad maturation and/or spawning. All the

differences mentioned above would make wild scallops

less vulnerable to predation than cultured scallops.

Thus, future restoration of natural beds based on seed-

min

0

10

20

30

40

B. Number of initial clapsa

b

cbc bc

num

ber

c

0

0.2

0.4

0.6

A. Time to reaction

a

b

dd

d

c

0

1

2

3

4

Wild scallops

Cultured scallops

C. Initial clapping time

bc bcc

c

b

a

min

0

5

10

15

20

25

D. Initial clapping rate

a a aa

bb

clap

s m

in-1

0

5

10

15

20

25

0

1

2

3

E. Time spent closed

bb

bb

a a

min

0

1

2

3

4

Maturing Mature Spawned

G. Clapping time after

recuperationa

b

d

bc

cdbcm

in

0

20

40

60

80

F. Proportion of claps

recovereda

ab ab

cd

bc

d

%

Maturing Mature Spawned Maturing Mature Spawned

H. Clapping rate after

recuperation

bbc

b

bcc

a

clap

s m

in-1

Maturing Mature Spawned

Fig. 3. Escape responses in wild and cultured Argopecten purpuratus after stimulation with their predator, the sea star Meyenaster gelatinosus, at

three reproductive stages (maturing, mature and spawned). Values represent meansFS.E. (n =40–58 per reproductive stage, per population). Means

sharing the same letter are not significantly different ( Pz0.05) as indicated by LS means a posteriori multiple comparisons.


ing cultured scallops would probably reduce the

chances of success of restocked populations. Although

no study has evaluated the relationship between escape

response capacities and predation rates for scallops in

the natural environment, a quicker response (rather than

the number of claps) to evade dredge capture has been

shown to increase survival of the scallop Aequipecten

opercularis in natural beds (Jenkins et al., 2003).

Behavioural differences between wild and cultured

animals may be explained by: (1) different previous

experiences, (2) selection of some behavioural pheno-

types that increase rates of survival, and (3) the

inheritance of the selected behavioural characters

through several generations (Huntingford, 2004). The

production of several animal species in closed environ-

ments (e.g. farms, hatcheries) has led successive gen-

erations of individuals to lack exposure to stimuli

normally present in their natural habitat (e.g. predators).

Considering the plasticity of some phenotype traits (e.g.

behaviour, morphology) upon the presence–absence of

predators, we could predict that some responses of

individuals to natural stimuli could be attenuated or

even absent in reared organisms. Several studies have

demonstrated behavioural and morphological adjust-

ments to prevailing conditions of predation risk in

marine invertebrates (Cote, 1995; Reimer et al., 1995;

Reimer and Tedengren, 1996; Rochette et al., 1996;

Leonard et al., 1999). Whelks (Buccinum undatum)

from populations in the Bay of Fundy (western north

Atlantic, Canada), where their natural predator the sea

star Leptasterias polaris is absent, did not show the

characteristic escape response (Feder, 1967) observed

in populations from the Mingan Islands, where L. po-

laris is present (Rochette et al., 1996). However, escape

response learning has been observed in juvenile whelks

after short term exposure to predator odours (Rochette


et al., 1998). Social learning and training has also been

observed in hatchery-reared fishes (Brown and Laland,

2001).

Most behavioural comparisons between cultured and

wild aquatic species were accomplished on salmonid

fishes, given the great development of its aquaculture

and increasing reliance on cultured animals for restock-

ing programs (reviewed by Huntingford, 2004). Most

wild scallop beds in Iberoamerica have collapsed and,

as for salmonids, many restocking programs rely on

cultured stocks (Stotz and Mendo, 2001). Given the

high mortality rates of restocked scallops caused by

predation (Hatcher et al., 1996; Barbeau and McDo-

well, 1998), and the importance of the escape response

to avoid natural predators (Feder, 1972; Vogel, 1997;

Ordzie and Garofalo, 1980), it is surprising that few

studies provide evidence to compare the escape perfor-

mance between wild and cultured scallops and the

implications on mortality (Haugum et al., 1999;

Lafrance et al., 2003). Wild scallops Pecten maximus

exhibit harder shells than cultured scallops, which in-

creased their survival (~85%) compared to cultured

ones (~10%) when exposed to crab predation (Haugum

et al., 1999). As we found for wild maturing A.

purpuratus, wild juvenile Placopecten magellanicus

showed more intense escape responses (higher clapping

rates) than cultured juvenile scallops upon encounter

with the sea star Asterias vulgaris (Lafrance et al.,

2003). However, cultured juvenile P. magellanicus

responded with a greater number of claps, longer clap-

ping time and faster recuperation of clapping capacity.

Thus, in contrast to the better escape performance of

wild A. purpuratus, with the exception of the clapping

rate, wild P. magellanicus did not perform better than

cultured ones (Lafrance et al., 2003). Cultured A. pur-

puratus in the present study came from a stock reared

in hatchery for several generations. However, cultured

P. magellanicus juveniles were obtained from spat

collected from wild populations. Thus, the lower escape

behaviour performance observed in cultured A. purpur-

atus may be due, in addition to the lack of prior

experience with predators, to the absence of selection

of more performing escape traits which may have a

great importance in scallop beds (Huntingford, 2004).

Recent studies in the scallops Chlamys islandica

and Euvola ziczac showed that reproductive invest-

ment decreased their capacity to recuperate from ex-

haustive escape response after stimulation with natural

predators (Brokordt et al., 2000a,b). The effect of

reproductive investment in cultured A. purpuratus

was stronger than in C. islandica and E. ziczac. Not

only the proportion of claps recovered after intense

escape decreased in cultured A. purpuratus, but also

the time to reaction (after spawning), the total number

of claps, the initial clapping time and the clapping

time after recuperation. In both C. islandica and E.

ziczac, the decrease observed in the capacity of recu-

peration was linked to an important decline in muscle

carbohydrates, as well as a decrease in muscle meta-

bolic capacity during gonad maturation and spawning

(Brokordt et al., 2000a,b). These muscle energetic and

metabolic reductions after gonad maturation, were also

observed in a previous study on A. purpuratus (de-

veloped under the same laboratory conditions as we

used) (Martınez et al., 2000), and this may explain the

decrease in the escape capacities of cultured A. pur-

puratus observed in the present study. Surprisingly,

our wild A. purpuratus were almost unaffected by

reproductive investment, and maintained most of

their escape capacities after gonad maturation and

spawning, even though during the period we condi-

tioned both cultured and wild scallops, the latter

invested more in reproduction as evidenced by a

greater gonad index. The lack of a negative effect of

reproductive investment on the escape capacities of

wild A. purpuratus is difficult to explain, given that

both wild and cultured scallops were conditioned until

gonad maturation and spawning under the same labo-

ratory conditions and during a period that may be

enough to standardize any original nutritional differ-

ence. We cannot eliminate the possibility of negative

effects of reproductive investment on energetic and

metabolic muscle status that we are evaluating in a

parallel study (Brokordt, unpublished data). On the

other hand, a positive association between genetic

variability and individual fitness has been demonstrat-

ed for a variety of plants and animals (Koehn and

Gaffney, 1984; Koehn and Hilbish, 1987; Zouros and

Pogson, 1994). Organisms with a high degree of

heterozygosity (genetically variable) have a surplus

of energy that may be used to increase fitness (e.g.

growth, reproductive output, escape and mobility ca-

pacities). Considering that hatchery-reared A. purpur-

atus are a product of a few numbers of progenitors

and are constantly under selective pressure for pro-

ductive traits, we might expect that wild scallops will

be more heterozygous and may use their surplus of

energy to reduce reproductive cost and its effect on

escape response performance. We are presently testing

this hypothesis.

In conclusion, wild and cultured A. purpuratus

showed strong escape responses upon contact with

the sea star M. gelatinosus, with wild scallops react-

ing earlier, clapping faster and spending less time


closed when exhausted. On the other hand, before

gonad maturation, cultured scallops clapped more and

longer than wild ones, but their escape capacities

were considerably affected by reproductive invest-

ment. The stronger escape responses and maintenance

of escape capacities during reproduction shown by

wild scallops, may favor their survival in the pres-

ence of predatory sea stars and crabs. Given the

reduction of escape performance in cultured scallops,

and as predation is known to be a major cause of

high mortalities in restocking programs (Barbeau et

al., 1996; Stotz and Mendo, 2001), we suggest that

this aspect should be considered in strategies of

restoration of natural scallop beds. Social learning

and training of hatchery-reared fishes prior to their

release into the wild has been applied successfully to

improve survival of individuals in restocking pro-

grams (Brown and Laland, 2001). Conditioning of

scallops with predator odours, as accomplished with

whelks (Rochette et al., 1998) could be a possibility to

increase responsiveness of scallops to predators before

restocking. We are presently evaluating this hypothesis.

Acknowledgements

We are grateful to R. Vera, G. Gonzalez, D. Jurado,

N. Leiva and G. Nunez, for their unconditional techni-

cal assistance. The paper was improved by comments

of M. Thiel. This research was supported by FONDE-

CYT #3020034 operating grant to K. B. Brokordt.

[SS]

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Domestication reduces the capacity to escape from predators