Download Host selection by the cleaner shrimp Ancylomenes pedersoni: Do

Journal of Experimental Marine Biology and Ecology 413 (2012) 87–93
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Journal of Experimental Marine Biology and Ecology
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Host selection by the cleaner shrimp Ancylomenes pedersoni: Do anemone host
species, prior experience or the presence of conspecific shrimp matter?
Maite Mascaró a,⁎, Lizbeth Rodríguez-Pestaña b, Xavier Chiappa-Carrara a, Nuno Simões a
a
b
Unidad Multidisciplinaria de Docencia e Investigación, Facultad de Ciencias, Universidad Nacional Autónoma de México, Sisal, Yucatán, México
Posgrado en Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, México D.F. México
a r t i c l e
i n f o
Article history:
Received 13 February 2011
Received in revised form 23 November 2011
Accepted 25 November 2011
Available online xxxx
Keywords:
Ancylomenes (=Periclimenes) pedersoni
Bartholomea annulata
Cleaner shrimp
Condylactis gigantea
Preference
Sea anemones
a b s t r a c t
In the symbiotic association that exists between cleaner shrimp Ancylomenes pedersoni (=Periclimenes pedersoni) and host sea anemones, specificity varies among populations, and shrimp are believed to search among
different individual hosts for favourable positions from which to attract client fish. Four laboratory-based experiments were conducted to test host selection of A. pedersoni between the following: i) Bartholomea annulata
(corkscrew anemone) and Condylactis gigantea (condy anemone), ii) B. annulata, with or without a conspecific
resident, iii) a previously known or unknown B. annulata, and iv) a previously known or unknown C. gigantea.
Preference (active selection) was distinguished from mere passive association by comparing shrimp acclimation
to anemones offered in choice and no-choice (control) situations. The results were analysed using asymmetrical
χ2 contingency tables (in each experiment, n = 60) where expected frequencies were obtained with maximum
likelihood estimators. Shrimp acclimated more frequently to B. annulata than to C. gigantea, but they acclimated
similarly to anemones with or without another resident and to those B. annulata and C. gigantea anemones that
were familiar rather than unfamiliar. However, none of the χ2 values were statistically significant
(χ2df = 1 = 0.48, 0.19, 0.42, 0.42; overall p > 0.45), suggesting that preference may not be responsible for the association between adult A. pedersoni and its host anemones observed in the field. Differences in the frequency of
association may be due to factors other than the active decisions made by shrimp when presented with more
than one alternative host.
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
Several species of the shrimp genus Periclimenes establish symbiotic
relationships with sea anemones, but the costs and benefits of such
associations are still uncertain (Bauer, 2004; Fautin et al., 1995).
While some studies suggest commensalism where only shrimp obtain
protection from predators (Bruce, 1976), other studies consider mutualism as the basis for the interaction in which anemones obtain either
protection from shrimp (McCammon, 2010) or an additional source of
nitrogen from shrimp faeces (Spotte, 1996).
Differences in the degree of host specialisation can be mediated by
habitat use because some of these species are considered to be cleaner
shrimp that remove parasites and decayed tissue off of client fish
(Kotter, 1997; Limbaugh et al., 1961; Mahnken, 1972; Zhang et al.,
1998). In general, Periclimenes (sensu lato) that do not clean fish are
considered to be host-specific, whereas cleaner shrimp search among
different anemone species for favourable positions from which to
attract fish (e.g., Feder, 1966; Guo et al., 1996; Limbaugh et al., 1961;
Nizinski, 1989; Williams, 1984). Moreover, as in other associations,
⁎ Corresponding author. Tel./fax: +52 988 9120147.
E-mail address: [email protected] (M. Mascaró).
0022-0981/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jembe.2011.11.026
the degree to which resident shrimp are host-specific varies with both
the shrimp and host species and can differ from one population to another within the distribution range (Silbiger and Childress, 2008 and
examples therein).
Ancylomenes pedersoni (Chace, 1958) (reported as Periclimenes pedersoni until recently; Okuno and Bruce, 2010) is distributed from Cape
Lookout, North Carolina, down the east coast of the United States and
around the west coast of Florida, to the Bahamas, West Indies, Bonaire,
Netherland Antilles and Belize (Chace, 1958, 1972; Williams, 1984).
Field studies report A. pedersoni to be a symbiotic cleaner shrimp
frequently associated with Bartholomea annulata, to a lesser extent
with Condylactis gigantea, and occasionally with other anemones
(Chace, 1972; Mahnken, 1972; Silbiger and Childress, 2008; Williams
and Bunkley-Williams, 2000). However, in Quintana Roo, Mexico,
A. pedersoni has never been observed to be associated with C. gigantea
(Campos-Salgado, 2009), although several authors have reported this
specific association at other locations in the Great Caribbean (Criales
and Corredor, 1977; Mihalik, 1989; Spotte et al., 1991; Wicksten,
1995) and the Gulf of México (Sisal Banks and Alacranes Reef; Simoes,
N., pers. obs.).
There is also considerable variation in the grouping pattern exhibited by cleaner shrimp of the genus Periclimenes. Several authors
mention that A. pedersoni are often found alone, in pairs, or in groups
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M. Mascaró et al. / Journal of Experimental Marine Biology and Ecology 413 (2012) 87–93
of 5–6 individuals (Mahnken, 1972; Stanton, 1977). In the Mexican
Caribbean (Campos-Salgado, 2009; unpublished data), 63% of the
B. annulata recorded had no A. pedersoni, 21% had 1 individual, 9% had
2 individuals, and 7% had groups of 3–5 shrimp. Groups of more than
10 shrimp of different sizes that are associated with only one host
have occasionally been observed (Campos-Salgado, 2009; Wicksten,
1995). There have been reports of considerable aggression between
individuals competing for favourable positions within a host to obtain
food, both under laboratory conditions and in the wild (Mahnken,
1972). While these observations suggest that shrimp that are already
present in an anemone may constitute an adverse stimulus for other
A. pedersoni to acclimate to that particular host, previous residents
could act as positive stimuli and attract more individuals. Huebner
(2010) reported that the number of fish being cleaned at any particular
station increased significantly with the number of A. pedersoni associated to the host. This suggests an advantage for client fish to stop at anemones that host several shrimp. However, for such gregarious behaviour
to constitute an advantage for A. pedersoni, individual shrimp would
need to benefit from the aggregation (e.g., if the mean rate of food intake
per individual shrimp increased in stations with several A. pedersoni
compared with those with only one or two shrimp).
Symbiotic decapods associated with sessile marine macroinvertebrates live in well-established microhabitats (i.e., sessile hosts; Baeza
and Stotz, 2003), and the shrimp-anemone relationship constitutes an
ideal model to study host preference. However, the associations that
are often observed in natural conditions do not necessarily reflect
preference for a particular host species or individual because their distribution may be the result of ecological factors, such as host abundance,
or inter- and intra-specific competition and predation (Gwaltney and
Brooks, 1994; Khan et al., 2003; Silbiger and Childress, 2008) that forces
residents to associate with less-preferred hosts. Some authors have
established that preference is the outcome of a behavioural choice
that is displayed by an organism (Singer, 2000) and that its adequate
identification and understanding can only be achieved with appropriate
experimental controls in which the subjects under study are presented
with no-choice situations (Underwood and Clarke, 2005; Underwood
et al., 2004). These authors argue that in testing hypotheses about
selective behaviour, it is necessary to distinguish active selection or
preference for a particular resource from passive or mechanical selection that is the result of physical properties, such as prey or habitat
availability (Barbeau and Scheibling, 1994; Jackson and Underwood,
2006; Underwood et al., 2004). Based on these definitions and this
methodological approach, a series of four experiments on the selective
behaviour of A. pedersoni were conducted to determine whether the
observed patterns of association with its host anemones B. annulata
and C. gigantea in the field are the result of a behavioural and active
choice.
2. Materials and methods
A. pedersoni (105), B. annulata (76) and C. gigantea (54) were
captured during several SCUBA expeditions from Puerto Morelos to
Majahual, Quintana Roo from August 2007 to March 2008. Based on
the patterns of distribution and the abundance of shrimp and anemones
of different sizes and reproductive conditions described for the Mexican
Caribbean (Campos-Salgado, 2009), only A. pedersoni (1.5-2.5 cm
length), B. annulata and C. gigantea (5–10 cm diameter of the oral disc
of completely distended anemones) were used in the experiments.
The sex of captured shrimp was not recorded, but all individuals were
non-ovigerous. Shrimp were captured using fine nets, and anemones
were carefully removed from the substratum to minimize damage to
animals and reefs. Taxonomic descriptions by Chace (1972) and
Gonzalez-Muñoz (2008) were used to correctly identify shrimp and
anemone species, respectively. Captured organisms were individually
placed in small plastic containers, previously perforated to allow
water exchange. The containers were kept in a large plastic holder
with abundant seawater and constant aeration to ensure survival during transportation to the Unidad Multidisciplinaria de Docencia e Investigación, Facultad de Ciencias, Universidad Nacional Autónoma de
México, at Sisal, Yucatán, México where experiments were conducted
from September 2007 to March 2008. An identification code was
assigned to each individual to make it possible to retrieve detailed information about its capture. Hosts and anemones captured at the same
location were never used in the same trial to prevent previous contact
between the host and the shrimp from potentially affecting selective
behaviour. To comply with statistical independence, individual shrimp
were used only once in the same experiment. Anemones were used
several times in the same experiment, but were isolated for 15 days between subsequent trials. A. pedersoni that were separated from both
B. annulata and C. gigantea for 15 days have been shown to lose protection from the nematocysts of these anemones, but re-acclimate if
allowed contact with hosts (Rodriguez-Pestaña, 2007).
Shrimp and anemones were isolated and maintained in fibre-glass
aquaria connected to two separate closed-water recirculation systems
for a period of 15–45 days prior to the trials. This was performed to
prevent any chemical contact between the hosts and the anemones
during maintenance and to ensure that selection was based on anemone characteristics alone. Seawater in both recirculation systems was
kept at 35 ± 1‰ salinity and 25± 1 °C using automatic chillers and
occasional partial water exchanges. In addition, seawater in the anemone recirculation system was kept at approximately constant concentrations of ammonia (NH4+/NH3+: 0 mg L -1), nitrates (NO3-: 5 mg L -1),
nitrites (NO2-: 0 mg L -1), phosphates (PO4=: 0.1 mg L -1) and pH (8.2),
which were measured every fifth day using colorimetric methods. Photoperiod was kept constant at 12 h:12 h, and commercially available,
high-intensity lamps for seawater aquaria (10,000 K, DYMAX OB Lighting with two T5 light tubes, white and blue) were used to maintain light
conditions adequate for endosymbiotic microalgae in anemones. Anemones were left to attach to small rocks or gastropod shells to facilitate
relocation and quick full expansion of their tentacles. Shrimp were fed
frozen Artemia spp., polychaetes, penaeid larvae (mysis) and diced
mussels ad libitum 3 times a day. Anemones were fed a similar diet
every 3 days.
We conducted four anemone host choice experiments with A. pedersoni (Table 1). The first experiment was intended to test if patterns of
host specificity can be explained by active selection or preference of
the shrimp for B. annulata. The second experiment was designed to
test if the presence of another shrimp of the same species, approximate
Table 1
Choice (CH) and no-choice (NCH1 and NCH2) anemone treatments presented to A. pedersoni during experiments on host-species selection (Experiment 1); selection of B. annulata with vs.
without a previous conspecific resident (Experiment 2); selection of previously known vs. unknown B. annulata (Experiment 3); and selection of previously known vs. unknown C. gigantea
(Experiment 4). Ba = B. annulata; Cg = C. gigantea.
No choice treatments
Experiment 1
Experiment 2
Experiment 3
Experiment 4
Choice treatment
NCH1
NCH2
CH
2 Ba
2 Ba with resident
2 known Ba
2 known Cg
2 Cg
2 Ba without resident
2 unknown Ba
2 unknown Cg
1 Ba + 1 Cg
1 Ba with resident + 1 Ba without resident
1 known Ba + 1 unknown Ba
1 known Cg + 1 unknown Cg
M. Mascaró et al. / Journal of Experimental Marine Biology and Ecology 413 (2012) 87–93
size and reproductive condition (nonovigerous, conspecific shrimp) incited active selection for that individual anemone. The conspecific
shrimp were acclimated to anemones prior to selection trials and
were presented simultaneously with the hosts to the focal shrimp.
The third and fourth experiments with B. annulata and C. gigantea,
respectively, were designed to test whether previous acclimation to a
particular individual anemone (known anemone) motivated subsequent active selection for that same individual. The shrimp were acclimated to each anemone one at a time and allowed to interact for at
least 24 h, after which the shrimp were separated from each host for
at least 15 days prior to selection trials.
All four experiments were carried out by presenting each A. pedersoni with the following: i) two similar anemones of a first type (nochoice treatment 1; NCH1), ii) two similar anemones of a second type
(no-choice treatment 2; NCH2), and iii) two different anemones of
types 1 and 2 (choice treatment; CH; Table 1). Care was taken so that
individual anemones in each pair were similar in the diameter of the
oral disc, but expansion state of the anemone was not taken into
account. Sixty independent and randomly selected shrimp were used
in each experiment (20 replicatesx 3 treatments per experiment).
Prior to each trial, the corresponding anemones were introduced
into the two furthest ends of a 50 × 20× 20 cm (L × W × D) glass aquarium filled with seawater (~20 L). Both seawater and room conditions
were similar to those used during the maintenance of experimental animals. After 30 min, aeration was removed, and an individual A. pedersoni was introduced into the centre of the aquarium. Aeration was
removed to reduce the influence of the direction of water flow and
water-borne chemical cues that could affect host selection. The shrimp
were video recorded and allowed to acclimate to any of the alternative
hosts. A shrimp was considered to be acclimated to an anemone when it
remained on top of, among or under (oral Ddisk) the anemone's tentacles or at a distance b3 cm from the most distal portion of the tentacles
for at least 1 h. Shrimp that had not acclimated within 7 h to any of the
anemones offered were recorded as such and included in the statistical
analysis. The criteria to define these terms were taken from Stanton
(1977), Mahnken (1972) and acclimation experiments previously
conducted in our laboratory with these species (Rodriguez-Pestaña,
2007). A total of 5 experimental aquaria were used, which were fully
cleansed with running seawater between trials to prevent any previous
treatment from affecting the outcome of the next trial.
To test the hypothesis that A. pedersoni actively selected one of the
two alternatives offered in each experiment, the difference in the
frequency of shrimp acclimated to the two options in the CH treatment
should be greater than that in NCH treatments. If frequencies in the CH
and NCH treatments were similar, then shrimp would acclimate to
hosts in a similar fashion regardless of whether different alternatives
were available. If alternatives were not available, the observed patterns
of association to hosts could not be attributed to the exercise of an active
choice. This can also be expressed as:
Hexp :
q1 q2
> ;
p1 p2
where the null hypothesis is:
Hnull :
q1 q2
¼ ;
p1 p2
where q1 and q2 are the proportion of shrimp acclimated to options 1
and 2 in the CH treatment, and p1 and p2 are the proportion of shrimp
acclimated to options 1 and 2 in NCH treatments, respectively. Because
the options in the NCH treatments were similar, p1 and p2 were
obtained by adding shrimp that were acclimated to both of the hosts
offered in NCH1 and NCH2, respectively. Data from each experiment
were analysed by means of χ2 in asymmetrical contingency tables
where the observed proportions were used to derive maximum likelihood estimators for the expected proportions under the null hypothesis
89
(Underwood and Clarke, 2005). With this procedure, better estimates of
frequencies under the null hypothesis were obtained and the effect of a
small sample size was reduced (Underwood and Clarke, 2005). In addition, the sample size of n = 60 adequately complied with the Roscoe
and Byars rule (Zar, 1999), thus ensuring that bias in the contingency
tables and the χ2 used was negligible.
3. Results
Mean duration of selection trials was 4 h ± 50 min, with 1 h 30 min
and 6 h 15 min as the minimum and maximum duration, respectively.
No shrimp acclimated to both hosts in any of the experimental trials.
Experiment 1. The results of the experiment on host species selection
showed that 39 (65%) A. pedersoni acclimated to one of the anemones
present in the aquaria (Fig. 1A), and, overall, more shrimp acclimated
to B. annulata (29) than to C. gigantea (10). However, statistical analysis
revealed no significant differences between acclimation frequencies to
B. annulata and C. gigantea between choice and no-choice situations
(χ2df = 1 = 0.48; p = 0.49; Table 2). This indicated that the difference in
acclimation of A. pedersoni to the two species of anemones was not
the result of an active selection. The number of shrimp that did not acclimate to any of the anemones that were presented within a 7 h period
varied between treatments. A relatively high percentage of shrimp
(65%) did not acclimate to C. gigantea even when this species was the
only alternative in the aquaria (Fig. 1A).
Experiment 2. The results of the experiment on selection of B. annulata
with or without a previous symbiotic conspecific showed that 42 (70%)
of the A. pedersoni acclimated to one of the B. annulata present in the
aquaria (Fig. 1B). Overall, 24 A. pedersoni acclimated to B. annulata
that were already hosting a symbiotic shrimp, and 18 A. pedersoni acclimated to B. annulata with no shrimp already present. Statistical analysis
revealed no significant differences between acclimation frequencies to
B. annulata with or without a shrimp already present between choice
and no-choice situations (χ 2df = 1 = 0.19; p = 0.66; Table 2). This thereby demonstrates that A. pedersoni did not exhibit any preference for B.
annulata with or without an earlier conspecific resident. The number
of shrimp that did not acclimate to any anemone within a 7 h period
in this experiment was similar between treatments, with 35%, 20%
and 35% in NCH1, NCH2 and CH treatments, respectively (Fig. 1B).
Experiment 3. The results of the experiment on fidelity to an individual B. annulata showed that 40 (66.7%) A. pedersoni acclimated to one of
the anemones present in the aquaria (Fig. 1C). Of these, 18 shrimp acclimated to previously known individuals, and 22 shrimp acclimated to
unknown individuals. Statistical analysis of the data revealed no significant differences in acclimation frequencies to either alternative under
choice and no-choice situations (χ 2df = 1 = 0.42; p = 0.52; Table 2).
These results showed that A. pedersoni did not exhibit any preference
for previously known or unknown individual B. annulata. The number
of shrimp that did not acclimate to any anemone within a 7 h period
was similar between treatments (35%, 30%, and 35%, for NCH1, NCH2,
and CH treatments, respectively; Fig. 1C).
Experiment 4. The results of the experiment on fidelity to an individual C. gigantea showed that 43 (71.7%) of the shrimp acclimated to one
of the anemones present in the aquaria (Fig. 1D). Overall, more A. pedersoni acclimated to individual C. gigantea that had previously hosted
that shrimp (26), than to anemones with which the shrimp had no
previous experience (17). However, differences in acclimation frequency with both alternatives were similar in choice and no-choice situations (χ2df = 1 = 0.42; p = 0.52) thereby demonstrating that
A. pedersoni did not acclimate more frequently to known individuals
as a result of active selection. The number of shrimp that did not acclimate to any of the anemones that were presented within a 7 h period
varied between treatments. A relatively high percentage of shrimp
90
M. Mascaró et al. / Journal of Experimental Marine Biology and Ecology 413 (2012) 87–93
Fig. 1. Percentage of the shrimp A. pedersoni that acclimated to (A) B. annulata and C. gigantea (Experiment 1), (B) B. annulata with and without a previous resident conspecific
shrimp (Experiment 2), (C) previously known and unknown B. annulata (Experiment 3), and (D) previously known and unknown C. gigantea (Experiment 4). No-choice treatments
(NCH1, NCH2) and choice treatments (CH) are as described in Table 1. Values are calculated considering the total number of shrimp in each treatment (n = 20).
(55%) did not acclimate to unknown C. gigantea, even when these individuals were the only alternative in the aquaria (Fig. 1D).
4. Discussion
Results of selection trials showed that A. pedersoni acclimated to
certain anemones more frequently than to others (Fig. 1), but no statistical evidence could be found to support that this behaviour was a
consequence of active choice. Such findings are relevant in that they
suggest that local ecological factors, rather than behavioural preference,
are responsible for the observed patterns of distribution in these hostshrimp associations.
When offered both anemone species simultaneously (Experiment 1;
CH treatment), more shrimp selected B. annulata than C. gigantea
(Fig. 1A). This difference, however, was statistically similar both when
shrimp were (CH treatments) and were not presented with a choice
of alternative host species (NCH1 and NCH2 treatments) (Table 2).
Thus, there is not enough evidence to confirm that active choice or preference caused the differences in association that were observed in
Experiment 1.
It is often assumed that animals are associated with a particular habitat because they prefer it and have rejected others available (Crowe
and Underwood, 1998). However, previous studies on the selective
behaviour of a variety of marine invertebrates have stressed the difficulty in distinguishing experimental evidence of preference (also called
active selection) from simple, or even complex patterns of association
(also called passive selection) (Chapman, 2000; Underwood et al.,
2004). Some authors maintain that only by comparing the frequency
Table 2
Number of A. pedersoni that acclimated to anemones B. annulata and C. gigantea under different conditions and those that did not acclimate to any of the anemones present in the
aquaria during experiments on host-species selection (Experiment 1); selection of B. annulata with vs. without a previous conspecific resident (Experiment 2); selection of previously known vs. unknown B. annulata (Experiment 3); and selection of previously known vs. unknown C. gigantea (Experiment 4). The estimated number of shrimp (maximum
likelihood) in each case is shown in parentheses. Choice (CH) and no-choice (NCH1 and NCH2) anemone treatments for all experiments are defined as in Table 1; n = 60 replicates
(20 individuals per treatment) were used in each experiment.
Did not acclimate
Experiment 1
NCH1
NCH2
CH
B. annulata
17 (17.2)
–
12 (10.9)
C. gigantea
–
7 (6.3)
3 (4.0)
Experiment 2 (B. annulata)
NCH1
NCH2
CH
With resident
16 (16.1)
–
8 (7.3)
Without resident
–
13 (12.7)
5 (5.7)
4 (3.9)
7 (7.3)
7 (7)
Experiment 3 (B. annulata)
NCH1
NCH2
CH
Known
13 (12.6)
–
5 (6.1)
Unknown
–
14 (14.3)
8 (6.9)
7 (7.4)
6 (5.7)
7 (7)
Experiment 4 (C. gigantea)
NCH1
NCH2
CH
Known
16 (15.7)
–
10 (11.2)
Unknown
–
9 (9.6)
8 (6.8)
4 (4.3)
11 (10.4)
2 (2)
3 (2.9)
13 (13.7)
5 (5)
M. Mascaró et al. / Journal of Experimental Marine Biology and Ecology 413 (2012) 87–93
distribution of events (e.g., prey consumed, shells taken, hosts chosen,
etc.) under choice and no-choice conditions can passive selection be
discarded and active selection be experimentally confirmed as the
behavioural cause of the association (Jackson and Underwood, 2006;
Liszka and Underwood, 1990; Olabarria et al., 2002). This is because
preference can only be displayed by an individual when it is presented
with more than one option (Barbeau and Scheibling, 1994). For example, a symbiotic shrimp that always chooses a live host over an inert
rock does not necessarily indicate preference for the live host if the extent to which the rock constitutes an alternative is not taken into account. The fact that preference is not corroborated does not imply that
there are artificial differences in the frequency of associations that is observed in the field, and other mechanisms should be put forward to explain such differences. By contrast, if preference is mistakenly
confirmed, then explanations other than those based on behaviour
may be overlooked.
Previous studies on Periclimenes shrimp have shown that under
laboratory conditions individuals selected those species of host anemones with which they were frequently found associated in the field
(Guo et al., 1996; Gwaltney and Brooks, 1994; Khan et al., 2003;
Silbiger and Childress, 2008). It is possible that those laboratory results
merely confirmed differences in the frequency of association that
depend strongly on local ecological factors and to a lesser extent on
behavioural traits involving preference because both the relative
frequencies of association and host species may vary throughout the
distribution range of symbiotic shrimp (Criales, 1984; Guo et al., 1996;
Levine and Blanchard, 1980; Wicksten, 1995). In a field study from
Isla Contoy to Xcalak on the Caribbean coast of Mexico, CamposSalgado (2009) found that 698 of the 704 A. pedersoni recorded were
associated with B. annulata, and none were found associated with C.
gigantea. However, A. pedersoni has been reported to associate with C.
gigantea in part of its distribution range (Criales, 1984; Silbiger and
Childress, 2008; Williams and Bunkley-Williams, 2000). These contrasting field results and the lack of an active choice shown in this study
(Table 2; Fig. 1A) indicate that ecological features operating at a local
scale must be involved in determining the observed patterns of association in these species.
While both anemone species simultaneously occur at most sites
along the Caribbean coast of Mexico, their abundance and occurrence
vary with depth, substrate depressions, crevices or holes at different
sections of the reef (i.e., reef lagoon, edge or front) (Campos-Salgado,
2009). Moreover, A. pedersoni is mostly found on top or among B. annulata tentacles (Mahnken, 1972) and moves from between hosts
(Huebner, 2010; Limbaugh et al., 1961). Such behaviour is explained
by the way in which A. pedersoni search for favourable positions to
clean fish, both within an individual anemone and among anemones
within the same patch (Nizinski, 1989; Williams, 1984). In his study
on cleaner shrimp in the Virgin Islands, Mahnken (1972) frequently
found associations of many A. pedersoni per individual B. annulata in
sandy areas of the reef where there was increased traffic of large fish
that were ready to be cleaned. It is possible that on the coast of Quintana
Roo, B. annulata is more frequent than C. gigantea in reef areas that are
easily accessed by large fish, hence explaining the pattern of the distribution of association of A. pedersoni with its hosts in the region.
A high percentage of shrimp did not acclimate to C. gigantea even
when no other alternative was present in the aquaria (Table 2;
Fig. 1A). This could be explained if shrimp were insufficiently protected
against the neurotoxins in the nematocysts of C. gigantea, as has been
reported for A. pedersoni with Stichodactyla helianthus (Gwaltney and
Brooks, 1994). However, previous experiments that compared the acclimation of A. pedersoni to B. annulata and C. gigantea (Rodriguez-Pestaña,
2007) showed that shrimp acclimated to these anemones by displaying
similar exploratory and grooming behaviours, regardless of host
species. Rodriguez-Pestaña also showed that A. pedersoni that had not
acclimated within 7 h to an individual host of either B. annulata or
C. gigantea did not make physical contact with the anemone, display
91
any grooming behaviour or acclimate to that host within the following
24 h (Rodriguez-Pestaña, 2007). Despite these similarities, a greater
proportion of shrimp acclimated to B. annulata (80%) than to C. gigantea
(20%; Rodriguez-Pestaña, 2007). Both the acclimation experiments by
Rodriguez-Pestaña (2007) and those described in the present study
were conducted with shrimp and anemones collected from the Mexican
Caribbean. These were then kept in laboratory aquaria for periods
15–45 days prior to the experiments without the presence of client
fish. Consequently, the fact that the A. pedersoni in the present study
acclimated to most (but not all) of the B. annulata and some of the
C. gigantea that were offered implies that the experimental shrimp possessed the physiological (biochemical) and behavioural mechanisms
necessary to acquire protection from both anemone species. These
results strongly suggest that patterns of association observed at any
particular site are partly determined by local processes, and care must
be taken when extrapolations are made to other sites within the
geographic distribution of the species.
When given a choice, A. pedersoni associated in relatively similar
frequencies with individual B. annulata with or without an earlier
conspecific shrimp (Fig. 1B). Moreover, statistical analysis demonstrated that even small differences in these frequencies were not due to active choice (Table 2), suggesting that territoriality in A. pedersoni does
not influence host choice through behavioural preference. Even when
resources are plentiful, interference between individuals when searching and/or using a resource constitutes evidence of competition
(Sheridan et al., 1984) that often leads to the display of agonistic interactions or territorial behaviours.
Such behaviour among shrimp in natural conditions has been
described for A. pedersoni (Mahnken, 1972) and Ancylomenes anthophilus (Sargent and Wagenbach, 1975) and depends on the sex, reproductive condition and size of individuals occupying a single host
(Knowlton, 1980; Mahnken, 1972). A. pedersoni that were used both
as previous residents and focal individuals in the present study ranged
from 1.5 to 2.5 cm long and were never ovigerous. While uncontrolled
differences in shrimp sex could have affected host selection in
Experiment 2, the lack of significant differences cannot be related to
the rather small differences in size and reproductive condition of individual shrimp occurring randomly within the 60 replicate trials. However, it is possible that the influence of territorial behaviour was not
evident because the ultimate resource to be defended (client fish) was
absent from the aquaria, and the effect of a simultaneous resident in
the anemone lacked immediate consequences for the experimental individual. In addition, it is possible that the conditions of the trials did not
stimulate competition by interference between shrimp because shrimp
were fed before the trials and because the maximum number of shrimp
in any aquarium was limited to 3. Sargent and Wagenbach (1975)
found that A. anthophilus did not exhibit territorial behaviour unless
fish that were ready to be cleaned were introduced into the aquaria.
The absence of territorial behaviour can be expected in laboratory conditions where stimuli that induce territoriality have been removed.
Thus, in the future, both field and laboratory-based experiments of
host preference should consider aspects such as predation risk, limiting
resources and competition for food.
Field studies in the Virgin Islands report the most common associations of A. pedersoni to be in pairs or groups of 5–6 individuals
(Mahnken, 1972), whereas in the Mexican Caribbean cleaner shrimp
were often found alone or in pairs (30%), and less frequently in groups
of 3–6 individuals (7%; unpublished data). While the number and size of
symbiotic residents are limited by the number and size of anemone
hosts (Allen, 1972; Fautin, 1991), the presence of conspecifics on a
host anemone has also been considered to be an attractive incentive
for promoting further associations, both during larval settlement and
reproduction for different taxa (Jensen and Morse, 1984; Knowlton
and Keller, 1986; Sweatman, 1983). A grouping pattern such as this
could be explained if territorial and agonistic behaviours did not result
in the complete exclusion of subordinate shrimp from the host but in
92
M. Mascaró et al. / Journal of Experimental Marine Biology and Ecology 413 (2012) 87–93
a hierarchical arrangement in which dominant individuals obtain the
most favourable positions within the anemone. Mahnken (1972)
observed that the largest individuals were positioned on the tentacles
or near the oral disc of anemones (presumably the most favourable
position to attract client fish), while medium and small shrimp
occupied positions aligned around the anemone on the nearby sand.
Ongoing field experiments of the agonistic behaviour in A. pedersoni of
different sizes and reproductive conditions will help to understand
the distribution of shrimp on individual anemones.
When given a choice in Experiments 3 and 4, similar numbers of
cleaner shrimp acclimated to previously known and unknown B. annulata (Fig. 1C) and C. gigantea, (Fig. 1D; Table 2), indicating that A. pedersoni does not exhibit fidelity to individual hosts of these two anemone
species. Some symbiotic crustaceans show lifetime fidelity to only one
individual host (Hamel et al., 1999; Kropp, 1987), while others move
frequently between individuals of the same species (Correa and Thiel,
2003; Patton et al., 1985; Thiel et al., 2003). These results suggest that
A. pedersoni maintains a symbiotic association with more than one individual host, a behaviour which may enable it to increase its home range
and benefit from a diversity of positions within the reef in order to
access more client fish. A similar behaviour has been reported in the pistol shrimp, Alpheus armatus, that can mate with more than one female
that is associated with neighbouring B. annulata (Knowlton, 1980).
The absence of fidelity would be predicted if A. pedersoni were not
able to discriminate between two individual hosts of the same species.
This would result in similar frequencies of shrimp acclimating to either
alternative host, whether these were both known, both unknown or
one was known and one was unknown. In the experiment with B. annulata, A. pedersoni acclimated to hosts in similar frequencies, irrespective
of host treatment (Fig. 1C); however, this was not the case in
Experiment 4 with C. gigantea (Fig. 1D). Acclimation is probably related
to short-term memory because it is a physiological and behavioural
process mediated by visual and chemical stimuli. Magnussen et al.
(2003) related host fidelity to short-term memory and stated that
thresholds to discriminate individuals are determined by the host's
attributes that provide visual and chemical information that is retained
in the resident's memory. Anemones used as ‘known’ individual hosts in
the present experiments were separated from their corresponding
residents for 15 days prior to each trial. It is possible that a period of
15 days exceeds the short-term memory span of these shrimp, thus
precluding individual recognition. In addition, isolated, but otherwise
fed, shrimp could have learned that association with anemones was
no longer necessary to obtain food. The time needed for A. anthophilus
(Crawford, 1992) and A. pedersoni (Rodriguez-Pestaña, 2007) to lose
protection from the nematocysts of their respective hosts was well
within 15 days of isolation. However, under similar laboratory conditions, Rodriguez-Pestaña (2007) found that all A. pedersoni that were
separated from both B. annulata and C. gigantea for 15 days
re-acclimated when they were allowed contact with the hosts. Further
experiments using shorter separation times are needed to understand
the role of memory in individual recognition between hosts and
residents.
Results of all four selection experiments in the present study suggest
that preference is not responsible for the association between adult
A. pedersoni and its host anemones and that differences in the frequency
of association with B. annulata and C. gigantea are due to factors other
than active decisions made by shrimp when presented with more
than one alternative host. However, further investigations on the
three-way interaction between anemones (hosts), cleaner shrimp
(residents) and fish (clients) are needed to understand the frequency
and distribution of such complex assemblages in reef habitats.
Acknowledgments
This study was partially funded by grants PAPIITIN228107 and
PAPIIT-IN216506. LRP carried out MSc studies with the Postgraduate
Program of Marine Sciences and Limnology, National Autonomous
University of México. Substantial help on animal keeping and maintenance of aquarium systems was provided by the late Luis Enrique
Hidalgo Arcos. We are grateful to Dr Raymond Bauer and the anonymous referees who substantially improved the quality of this manuscript. [RH]
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