Predators & defenses
 
photograph of several plumose anemones, one of which is extruding its acontia

The main defense of anemones is nematocysts, especially those on the tentacles and on interior mesenterial filaments (acontia), if these can be protruded through the body wall or extended from the mouth.  Some species swim or crawl away from danger, and an alarm pheromone has been identified. 

NOTE  lit. “javelin” or “dart” G.  Many species of sea anemones have acontia, but only a few utilise them in defense.  Mostly, the acontia are used within the gastrovascular cavity to tangle and sting to death recently ingested prey


Several Metridium senile individuals, one of which (upper Right)
is partially extruding its acontia from the mouth

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  Defenses
  Defenses are considered in this section, and PREDATORS in another.
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Acontia/nematocysts

  Defenses such as acontia/nematocysts, crawling/release of attachment, swimming, and alarm pheromone are considered in this subsection.
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photographs comparing nematocysts in acontial and tentacles in the anemones Metridium senile and M. farcimen

Studies in Anacortes, Washington show that lengths of both acontial threads and acontial nematocysts in the anemones Metridium farcimen and M. senile scale significantly with increasing body size, indicating a selection for more damaging acontial defenses in larger-sized anemones. graph comparing acontial lengths in two anemones Metridium senile and Metridium farcimenThe magnitude of size increase is not large, only about 27% over a 750-fold increase in body mass for M. farcimen, and 18% over a 70-fold increase for M. senile.  The authors additionally note that scaling exponents are significantly smaller for nematocysts in the capture tentacles than for ones in the acontia.  They explain this by the fact that food size of Metridium does not increase substantially with body size, and so a comparable scaling in nematocyst size would not be expected in the capture tentacles. Note also the considerably larger size of acontial nematocysts as compared with tentacle nematocysts (photographs on Left, 1000X). When the authors compare same-sized individuals of M. farcimen (a subtidal species) and M. senile (an intertidal/shallow subtidal species), they find significantly larger acontial nematocysts in the former photograph of plumose anemone showing acontial threads protruding from holes in the body columnspecies (seegraph). They explain this on the basis of greater predation pressure on M. farcimen in its subtidal habitat, although the justification for this argument is not strong.  However, as noted by the authors, more acontial threads, longer acontia, more nematocysts, and larger acontial nematocysts in larger individuals should improve deterrence potential against predators.  Kramer & Francis 2004 Biol Bull 207: 130; see also Hand 1954 The Wasmann J Biol 12: 345 for detailed information on types of cnidae found in west-coast sea anemones.

Metridium senile extruding acontia
from pores in the body wall 0.8X



NOTE apparently, holding the anemone upside-down out of water causes it to extrude its acontia, which then hang down by gravity and can be measured



NOTE the scaling exponents for acontia length in the 2 species range from 0.45-0.60, which is significantly greater than the value of 0.33 expected for isometric scaling of length against body size, and thus is positively allometric.  In comparison, the scaling exponents for nematocyst length against body size in the acontia range from 0.04-0.05, which is far below an expectation based on isometric scaling.  Selection for allometric scaling in biology usually means that something significant is going on, although what this is, may not always be obvious

 

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Research study 2
 

A study with possible relevance to defenses of sea anemones notes that aqueous dialysed extracts of several west-coast species when tested by intraperitoneal injection into laboratory mice have the following levels of toxicity:

Higer toxicity: Anthopleura elegantissima and A. xanthogrammica.  A dose of 2ml extract per 100g of mouse kills the mouse in10-20min. 
Lower toxidity: Metridium senile, Corynactis californica, Urticina crassicornis, U. lofotensis, and U. coriacea.  The same dose of the first species listed (M. senile), in comparison with the “higher toxicity” data above, kills the mouse in about 170min.  Other than demonstrating that different sea anemones have different toxicities to mice, the functional significance of the study is not explained.  Martin 1963 Pac Sci 17: 302.

NOTE  this removes larger molecules such as proteins, as found in nematocyst toxins, and amines

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Crawling/release of attachment

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The leather star Dermasterias imbricata is a predator of sea anemones. Studies at the Bamfield Marine Science Centre, British Columbia show that series of photographs showing release of attachment by a sea anemone being attacked by a leather star Dermasterias imbricata courtesy Don Ross, U Albertaan anemone polyp (not identified by the authors) will, on contact with the asteroids Dermasterias imbricata and Patiria miniata, expand their oral discs, constrict their columns, and detach their pedal discs (this takes 33sec, on average).  Other asteroid species do not elicit this response.  Of 5 species of Urticina tested by the authors, only U. piscivora shows similar behaviour, and only to Dermasterias.  Re-attachment occurs within minutes when the pedal disc contacts a surface to which it can adhere.  In that the pedal-disc release is mediated by a train of electrical pulses in the slow conduction system, the behaviour appears to be similar to release of attachment and swimming in Stomphia spp. Lawn & Ross 1982 Biol Bull 163: 188; photos courtesy Don Ross, U Alberta.

NOTE a non-nervous conducting system mediated by cells in the outer epithelial layer of the body.  Anemone species commensal with hermit crabs are induced to detach by the potential host by a gentle stroking of the column with the chelae.  An identical response can be induced in some west-coast anemones, such as Anthopleura elegantissima, by gentle stroking with glass rod or chopsticks - a behaviour in this non-commensal species that appears not to have been studied

NOTE for a description of swimming in Stomphia, see the following section

 

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Research study 2

 

Later studies on Urticina piscivora at the Bamfield Marine Sciences Centre, British Columbia show that small individuals when attacked by a leather star Dermasterias imbricata will release their attachment to the substratum and float away. Large anemones show no response, while intermediate-sized individuals sometimes respond slowly.  If they survive and re-attach, the down-shore tumble may place them in spatial refuge, out of contact with shallow-water leather stars.  Tests with 19 other seastar species yield negative results, as do tests with 4 other Urticina species.  Elliott et al. 1985 Can J Zool 63: 1921.

Because an anemone is virtually weightless in water it would
likely be carried away in even small current velocities

drawings of a sea anemone floating in the water after releasing its attachment
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Interestingly, the detachment response in sea anemones is not simply an “on or off” one, but is modulated by factors such as past feeding history.  The graph shows that better-fed anemones take longer to detach, but whether this owes to greater health and resilience of the fed ones, or to a sense by the starved ones that the spot they are in is a poor one anyway, is not known.  Anemones are known to crawl about less if dietary conditions are good.  Houtman et al. 1997 Mar Biol 128: 225. graph showing time for detachment in anemones in relation to how well fed they are
 

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Research study 4

 
On contact with Aeolidia papillosa, the green sea anemone Anthopleura xanthogrammica may sometimes inflate its column and detach itself from the substratum to escape being eaten. drawings of the great green anemone Anthopleura xanthogrammica releasing its attachment after contact by a predatory nudibranch Aeolidia
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Swimming

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Research study 1
 
photograph of a sea anemone Stomphia didemon

One of the more dramatic responses by a sea anemone to a predator is the quick and vigorous swimming induced in Stomphia spp. on contact with sea stars Dermasterias imbricata and Hippasteria spinosa. Studies using individuals collected in Puget Sound and San Juan Islands, Washington reveal the sequence of behaviours shown below.  Drawings modified from Sund 1958 Q J Microscop Sci 99: 401.

NOTE  there are at least two species of Stomphia in Puget Sound, S. coccinea and S. didemon, with a possibly third undescribed species being reported.  Ross 1979 Can J Zool 57: 943. The first description of Stomphia coccinea swimming is actually from lab observations done in the 1930s, but not in response to sea stars.  Stephenson 1935 The British Sea anemones Vol. 2  The Ray Soc., London.

Stomphia didemon 0.7X

 
first in a series of drawing showing detachment leading to swimming in an anemone such as Stomphia after being attacked by a predator body pulls down, tentacles and oral disc withdraw
second in a series of drawing showing detachment leading to swimming in an anemone such as Stomphia after being attacked by a predato body then expands slowly, elongates, and becomes turgid
third in a series of drawing showing detachment leading to swimming in an anemone such as Stomphia after being attacked by a predato body bends laterally and sometimes rotates
fourth in a series of drawing showing detachment leading to swimming in an anemone such as Stomphia after being attacked by a predato anemone detaches…this takes just a few seconds
fifth in a series of drawing showing detachment leading to swimming in an anemone such as Stomphia after being attacked by a predato thrashing-type swimming for several sec or min; distance traveled may be only a meter or less
sixth in a series of drawing showing detachment leading to swimming in an anemone such as Stomphia after being attacked by a predato comes to rest on its side; the anemone is flaccid and non-excitable at this stage
seventh in a series of drawing showing detachment leading to swimming in an anemone such as Stomphia after being attacked by a predato recovers in 1-2min and rights itself. Drawings modified from Sund 1958 Q J Microscop Sci 99: 401.
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Research study 2
 
A sure swimming response by Stomphia comes from contact with only 2 species of sea stars, Dermasterias imbricata and Hippasteria spinosa, and from contact with the nudibranch Aeolidia papillosa, where responses are 95-100% positive.  Sometimes, contact with rose stars Crossaster papposus (2%), blood stars Henricia leviuscula (3%), and sun stars Solaster dawsonii (5%) give positive responses.  Contact with 13 other sea-star species around Puget Sound, Washington elicits no responses.  Of the many sea stars tested, only Dermasterias and Hippasteria are known predators of StomphiaYentsch & Pierce 1955 Science 122: 1231; Robson 1961 J Exp Biol 38: 685; Ward 1965 J Exp Zool 158: 357. table showing sea stars causing the anemone Stomphis to swim
 
photograph of oral view of leather star Dermasterias imbricata
Oral view of Dermasterias imbricata 0.25X
photograph of sea star Hippasteria spinosa courtesy Randy Shuman, Seattle
Hippasteria spinosa 0.25X Photo courtesy Randy Shuman, Seattle
photograph of a blood star Henricia sp.
Blood star Henricia sp. 0.3X
photograph of a rose star Crossaster papposus
Rose star Crossaster papposus 0.4X
   
     
 
Research study 3
 

The swimming contractions in Stomphia are initiated and regulated by a pacemaker system of nerves that form a ring around the column.  Interestingly, excision experiments on the column of Stomphia coccinea show that while the same pacemaker system functions to control swimming after attack by Hippasteria and Aeolidia, different sensory pathways are involved – each specific to that particular predator. Robson 1961 J Exper Biol 38: 685.

NOTE  a European species Hippasteria phrygiana is used in this particular study, which is done on Stomphia specimens in Denmark

photograph of a sea anemone Stomphia coccinea
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Research study 4
 

Studies at Friday Harbor Laboratories, Washington show that if an object such as a pipe cleaner is rubbed on the aboral surface of the leather sea star Dermasterias imbricata and then touched to a single tentacle of Stomphia, it will cause the anemone to swim.  photograph of a leather star Dermasterias imbricataHowever, if Stomphia’s oral disc is flooded with food extract prior to the touch, the swimming response is inhibited.  Moreover, nematocyst discharge in Stomphia virtually ceases during swimming, from the moment the pedal disc is released to when it re-attaches.  Complete recovery of sensitivity requires about 20-60min. The authors point to their finding as evidence that nematocysts, rather than being independent effectors, are themselves subject to control systems operating elsewhere in the body.  Ross & Sutton 1964 J Exp Biol 41: 751.

NOTE in this case an aqueous extract of crushed scallop

NOTE  in addition to this nematocyst response, the authors confirm the findings of other researchers that Stomphia is generally insensitive to handling and other stimulation during and for some time after swimming

 

Leather star Dermasterias imbricata 0.5X

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Research study 5
 

When different tissues and/or exudations of leather stars Dermasterias imbricata are homogenised and spun down, then injected from a syringe onto Stomphia, only skin from the aboral surface, mucus, and coelomic fluid initiates swimming.  Later studies show that the effective agent is an alkaloid, given the name imbricatine, which is of a type formerly known only from plants.  Even in extremely low concentrations (e.g., 50ng) it is effective in making S. coccinea swim, but has much less effect on S. didemon and none at all on other anemones such as Urticina piscivora.  Preliminary evidence suggests that the chemical in Hippasteria spinosa that causes Stomphia to swim is actually different from imbricatine, suggesting that the prey anemones must have finely tuned chemical recognition systems.   Ward 1965 J Exper Zool 158: 357; Elliott et al. 1989 Biol Bull 176: 73.

NOTE  in a later publication, researchers at the University of British Columbia report the structure of imbricatine, a novel benzyltetrahydroisoquinoline alkaloid.  Pathirana & Andersen 1986 J Am Chem Soc 108: 8288.

NOTE  nanogram: one billionth of a gram, or 10-9 g

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Research study 6
 

Discovery of numerous secretory cells in the dermis layer of the aboral skin-surface of Dermasterias imbricata, but not on other parts of the body, photograph of close view of the aboral surface of a leather star Dermasterias imbicata
and a similar chemistry of the secretory substance contained within them with the alkaloid just described, suggests that these cells may be the source of the stimulatory substance.  Whether the secretion serves a defensive role in the sea star is not known, but the author notes that the thickened dermis is otherwise lacking in defensive spines or pedicellariae, and so the possibility exists.  Ward 1965 J Exp Zool 158: 365.


Close view of aboral surface of Dermasterias imbricata
showing clusters of dermal papulae and the madreporite 10X

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Research study 7
 
map of Barkley Sound, British Columbia showing collecting sites for sea stars used in study of swimming in the sea anemone Stomphia didemon

Studies at the Bamfield Marine Sciences Centre, British Columbiashow that a deeper-living species Stomphia didemon (seldom found shallower than 25-30m depth) will swim from sea stars, with 3 species in the Order Valvatida, Hippasteria spinosa (97%), Dermasterias imbricata (90), and Patiria table showing responses of swimming sea anemone Stomphia didemon to different species of sea stars(Asterina) miniata (90), inducing strongest responses.  Five other sea-star species produce intermediate responses: Poraniopsis inflata (26%), Mediaster aequalis (14), Solaster stimpsoni (33%), S.  dawsoni (10), and S. endeca (17). Nine other species induce no or only little response: Pycnopodia helianthoides (3), Crossaster papposus, Pteraster tesselatus, Henricia leviuscula, Evasterias troscheli, Orthasterias koehleri, Stylasterias forreri, Pisaster ochraceus, and P. brevispinus (see table of data).  Dalby et al. 1988 Can J Zool 66: 2484.

NOTE tested in the lab, 10-30 trials each, with “swimming” defined as detaching within 1-2min. "Degree of response" is an arbitrary classification ranging from 0=no response, to 5=detachment & swimming. Degree of response differs significantly between the 3 asteroid Orders, Valvatida (mean of 4.1), Spinulosida (1.8), and Forcipulatida (0.7)

NOTE more recent classification places Solaster spp., Crossaster papposus, and Pteraster tesselatus in Order VELATIDA, leaving only the blood star Henricia leviuscula in Order SPINULOSIDA. The phylogenetic affinity of the swimming response is considered later in this section

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Interestingly, out of all of these potential predators, only the leather star Dermasterias imbricata is known to prey on Stomphia.  In fact, one sea-star species inducing strong swimming response, the bat star Patiria miniata, is primarily herbivorous.   Might there be another explanation(s) for the swimming behaviour of Stomphia?  Consider these alternative ideas, then CLICK HERE for explantions.  Ideas from Mauzey et al. 1968 Ecology 49: 603; Dalby et al. 1988 Can J Zool 66: 2484.

Migration. 

Escape from predators of the organism(s) Stomphia is using to perch on. 

Escape from adverse environmental conditions. 

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  Research study 8
  Is it possible that repeated contact with the more shallow-living Dermasterias imbricata could force Stomphia spp. to deeper depths?  Staged interactions on rocky slopes in Barkley Sound, B.C. suggest that the answer is 'yes', at least for S. didemon.  In one experiment, investigators move 4 individuals of this species from deeper water to an area at 10m depth inhabited by Dermasterias.  At 2 intervals over the following week they touch the sea stars to the sea anemones, each time causing the anemones to swim and settle at a lower level.  Although the net displacement is only 2m, the experiment shows that it could effect considerable vertical separation over time. Dalby et al. 1988 Can J Zool 66: 2484.
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Research study 9
 

table showing % swimming responses of the sea anemone Stomphia to sea stars in different OrdersIs there any common factor about the sea stars that might explain why they induce Stomphia to swim?  Several ideas are proposed in the literature in this regard. Let’s look at the first of these, namely, phylogenetic affinity.  The 17 species in the study belong to 4 Orders of Class Asteroidea.  Note that the species that strongly induce swimming in Stomphia are VALVATIDS, while those that only moderately or don’t induce swimming in Stomphia are VELATIDS, FORCIPULATIDS, and SPINULOSIDS.  So, phylogenetic affinity looks promising. Mauzey et al. 1968 Ecology 49: 603; Dalby et al. 1988 Can J Zool 66: 2484.

 

 

NOTE  this topic is also considered elsewhere in the ODYSSEY: LEARN ABOUT KEYHOLE AND OTHER
LIMPETS: DEFENSES & PREDATORS

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Research study 10
 
Another idea is dietary affinity – i.e., escape is induced by species that eat a common dietary item, most obviously, sea anemones. The categorisation is made difficult by the wide variety of prey items consumed by the various sea-star species, but immediately we see that one of species that strongly induces swimming is Patiria (Asterina) miniata, a grazing species that consumes a variety
of bottom matter including detritus, and encrusting animals and plants, while the others are mostly carnivores. Of the species listed, only the leather star Dermasterias imbricata commonly eats sea anemones. Also, all of the FORCIPULATIDS listed are carnivores, but none regularly eats sea anemones. Mauzey et al. 1968 Ecology 49: 603; Dalby et al. 1988 Can J Zool 66: 2484.

So, the idea of dietary affinity does NOT hold promise.

MAIN DIETARY ITEMS OF THE SEA STARS:

Hippasteria spinosa: sea pens
Patiria
miniata: omnivorous scavenger
Mediaster aequalis:
sea pens, algae, sponges, hydroids
Poraniopsis inflata:
sponges?
Dermasterias imbricata:
anemones, corallimorpharians, sea cucumbers, sea urchins
Solaster stimpsoni
:
sea cucumbers
Solaster dawsoni:
sea stars
Solaster endeca:
sea cucumbers

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Research study 11
 

Another possible “commonality” among the sea stars is habitat occupied.  We would not expect Stomphia to swim from a species that it never encounters in in the field.  Stomphia didemon is a deeper-inhabiting species, occurring most commonly from about 10-20m in depth, and sporadically to depths greater than 200m. Thus, at its shallowest depth, most of the asteroids listed above would be expected to encounter Stomphia (a notable exception being the mostly intertidal-inhabiting ochre star Pisaster ochraceus). At depths of 20m or more, few sea-star species would be present. The authors of the above study specifically note that of Mediaster, Dermasterias, Patiria, and Hippasteria (from the above list), only the last, Hippasteria, would likely co-occur on "deep reefs" (20-25m) with Stomphia.  Dalby et al. 1988 Can J Zool 66: 2484.

In summary, the phylogenetic idea looks the best, even though there are parts of the pattern that don’t fit and more questions are raised than answered.  For example: what do the 5 valvatid species have in common with themselves and with the 3 velatids (all species of Solaster), and what do the 3 Solaster species have in common with themselves, but not with the other two velatids?

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Alarm pheromone

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  Research study 1
 
photo series showing behavioral responses of a sea anemone Anthopleura elegantissima to the presence of anthopleurine imn the water

When a sea anemone Anthopleura elegantissima is damaged mechanically, all nearby and downstream conspecifics exhibit a stereotypical alarm response consisting of several rapid, convulsive, radially symmetrical flexures of tentacles towards the centre of the body column. Eventually, the tentacles pull in and the marginal sphincter muscles close the disc region (see photographs on Left for an individual of 2cm basal-disc diameter).  The substance released is a quaternary ammonium ion compound termed anthopleurine by its discoverers.  It is effective in concentrations as low as 3.5 x 10-10 mole per liter of seawater.  Extracts of the compound elicit identical responses in conspecifics to that of wounding.  The authors note that anthopleurine is only the second pheromone in marine invertebrates to be described – the first being a sex pheromone crustecdysone in crabs.  Howe & Sheikh 1975 Science 189: 386

NOTE (3-carboxy-2,3-dihydroxy-N,N,N-trimethyl)-1-propanaminium


 

 



 
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Research study 2
 

Later studies in Pacific Grove, California show that anthopleurine is effective only with Anthopleura elegantissima and A. xanthogrammica, but not with A. artemisia or Metridium senile, or the corallimorpharian Corynactis californica (see table of data).

table showing effectiveness of the alarm substance anthopleurine on different sea-anemone species

The receptor cells for anthopleurine are located primarily in the tentacles. drawings showing initial behavioral responses of a sea anemone Anthopleura to the alarm substance anthopleurine The first response is contraction of the tentacles causing them to draw closer to the body column. 

 

 

The retractors in the mesenteries then contract quickly,followed by slower contraction of the sphincter tissues in the upper column region. Within a few seconds the anemone is fully contracted. Howe 1976 J Comp Physiol 107: 67.

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Research study 3
 
photograph of head of a nudibranch Aeolidia papillosa

Defenses of the aggregating anemone Anthopleura elegantissima to attack by the nudibranch Aeolidia papillosa include crawling away, releasing attachment to the substratum (and then floating off, probably later to die), raising the tentacles, bulging the column and, if wounded by the predator, releasing the pheromone anthopleurine.  Bulging seems to prevent the predator from reaching up and biting the tastier tentacles.  The anemone apparently never defends with its attack tentacles (acrorhagi), yet these are used effectively in interclonal aggression.  Harris & Howe 1979 Biol Bull 157: 138.

NOTE  a chemical released by one individual that affects other individuals of the same species. Known pheromones (most from studies of insects, crustaceans, and fishes) are mainly of alarm or sexual types. In the present case, the pheromone causes rapid bending and shortening of the tentacles in neighbouring anemones, as well as constriction of upper margins of the oral discs and raising of the tentacles, thus preventing the predator from biting at them from below

Close view of head of nudibranch Aeolidia papillosa showing rhinophores (darker in colour: long-distance chemical perception), oral tentacles (lighter in colour: close-in contact chemoreception), and many cerata 2X

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Research study 4
 

Studies at Hopkins Marine Station, California show that the alarm pheromone anthopleurine in the sea anemone Anthopleura elegantissima is distibuted throughout the body, but with highest concentrations in the lower column wall and pedal disc regions (see table on Right).

 

 

 

 


When a predatory snail Aeolidia papillosa eats A. elegantissima it takes up the anthopleurine into its tissues, especially those of the cerata.  The cerata contain extensions of the digestive gland within which the anemone’s tissues are digested and absorbed. A single meal of Anthopleura after a few days starvation raises the level of anthopleurine in the cerata to peak level within 24h, then concentrations decrease over the next few days presumably as the anthopleurine diffuses out, is metabolised, and/or excreted.  The results show that the anthopleurine is not synthesised by Aeolidia.

 

 

 

More interestingly, if Aeolidia now approaches an Anthopleura to within about 1cm distance, the anthopleurine (either from the snail’s urine or diffusing from the certata tissues) evokes alarm responses in its potential prey. The anemone raises its column, and the tentacles and oral disc, the regions containing least concentrations of anthopleurine, are partially enclosed.  The lower column and pedal disc, containing highest concentrations of anthopleurine, are the parts now left open to contact by the predator.  On these bases, the authors speculate that anthopleurine may be functioning both as an alarm pheromone and as a chemical feeding deterrent.  Howe & Harris 1978 J Chem Ecol 4: 551. 

table showing distribution of the alarm chemical anthopleurine in different pars of the body of a sea anemone Anthopleura elegantissima

 

graph showing rate of uptake of alarm substance anthopleurine into the cerata of a predatory nudibranch Aeolidia papillosa when feeding on the sea anemone Anthopleura elegantissimacut-out photo of an aeolid nudibranch Aeolidia papillosa


graph showing response of sea anemones to an approaching nudibranch Aeolidia papillosa that has previously fed on the same anemone species

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Research study 5
 

schematic showing interactive effecs of alarm substance anthopleurine on a nudibranch and sculpinAn interesting predator-prey interaction involving the alarm pheromone anthopleurine is explored in studies at the Bodega Marine Laboratory, California. It involves the anemone-eating Aeolidia papillosa, the anemone-eating sculpin Clinocottus globiceps, and several sea-anemone species including Anthopleura xanthogrammica and A. elegantissima. First, if Aeolidia eats A. xanthogrammica (1) the nudibranch later gives off a substance (likely anthopleurine) that induces an alarm response in downstream A. elegantissima, causing them to close up (2) but not A. xanthogrammica.  Second, when a sculpin attacks A. xanthogrammica the anemone releases anthopleurine (3), which could be both alarm-inducing and defensive.  Now, the question is: given the chemical signature being released by Aeolidia, is the sculpin confused into attacking the nudibranch thinking it to be food?  The answer is 'yes', the sculpin does attack the nudibranch (4), but immediately rejects it (5).  The author thinks the rejection is based not on any defensive properties of Aeolidia’s sequestered nematocysts, because the sculpin readily eats the anemones from which Aeolidia gets its nematocysts, but rather from defensive secretions from epidermal glands in AeolidiaHand 1994-96 The Wasmann J Biol 51: 9.

NOTE  it is not clear from the study whether the sculpin is simply attacking something (the nudibranch) that may be good to eat, or whether it is attacking what it perceives to be an anemone that it knows from past experience is good to eat.  To answer this we need to know whether the sculpin will attack an Aeolidia that has been feeding on a non-anthopleurine-bearing anemone, such as Metridium spp., which should be an interesting project for someone

NOTE  the topic of secondarily-derived nematocyst defenses in aeolid nudibranchs is considered in detail elsewhere in the ODYSSEY: LEARN ABOUT NUDIBRANCHS & RELATIVES: DEFENSES AGAINST PREDATORS: NEMATOCYSTS

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