Defenses
  black dot
  Alarm pheromones
 

Defenses of nudibranchs and their relatives include alarm pheromones, considered in this section, and
CAMOUFLAGE (CRYPSIS),
FAST CRAWLING & SWIMMING
,
MUCOUS COATINGS
,
CERATAL AUTOTOMY
,
NUTRITIONAL CONTENT,
SPICULES
,
NEMATOCYSTS
,
VACUOLATED SKIN WITH PROTECTIVE SPINDLES,
ACID SECRETIONS
,
INK & OPALINE SECRETIONS,
SECONDARY METABOLITES
,
APOSEMATIC (WARNING) COLORATION & BATESIAN MIMICRY
, and
NAVANAX: A SPECIAL CASE STUDY
, considered in other sections. 

  black dot
Research study 1
 

The cephalaspidean Navanax inermis occurs from northern California to the southern limits of the Gulf of California.  It is a predator of other opisthobranchs, most notably other shelled species, but may even prey upon conspecifics.  On attack, Navanax releases a yellow hydrophobic substance photograph of cephalaspidean Navanax inermis courtesy Kevin Lee, Fullerton, Californiafrom a “yellow gland” near its anus directly onto its slime trail.  The secretion does not dilute in seawater but adheres to the slime trail, which can persist for several days.  Other Navanax, perhaps searching for a meal along the slime trail, turn away. The response is well defined, consisting of contraction, turning at an angle greater than 90o, and retreat. Studies at Scripps Institution of Oceanography, La Jolla, California show that the substance is a mix of 3 related conjugated methyl ketones called navenones, synthesised de novo by Navanax.  After its release, the depleted navenone supply is topped up within 3-7d.  The authors describe the secretion as an alarm pheromone, presumably because it communicates a message to conspecifics warning them of danger.  However, if its function is to ward off potential predatory species including conspecifics looking for a meal, then its role may be dual: both a defensive chemical and an alarm pheromone.  Sleeper & Fenical 1977 J Amer Chem Soc 99: 7; Sleeper et al. 1980 J Chem Ecol 6: 57.  Photo courtesy Kevin Lee, Fullerton, California diverKevin.

Navanax inermis 1X

  black dot
Research study 2
 

Like many other gastropods, the sea hare Aplysia californica will run from predators or from the scent of alarm chemicals such as ink and opaline secretions remaining behind after a conspecific is damaged or killed.  The escape crawling can be quite quick, and often takes the form of a histogram showing frequency of running responses of sea hares Aplysia californica to various substanceslively “galloping”.  While both ink and opaline secretion willl evoke the alarm response, other conspecific fluids such as mucus or hemolymph histogram showing frequency of running responses of sea hares Aplysia californica to various substanceswill not, nor will odours from known predators such as spiny lobsters (see histogram on Left.  The active components of ink and opaline secretion have been identified by researchers in Maryland and Georgia as the base uracil and the nucleosides uridine and cytidine (see histogram on Right)  Each molecule alone will elicit a full escape response, while ink without these molecules will not.  All 3 molecules are highly polar and, of course, water soluble.  Interestingly, ink from congenor sea hares A. juliana and A. dactylomela, and ink from certain squids and octopuses, also contain uracil and uridine, and all elicit escape behaviours in A. californica.  The authors suggest a common evolutionary selection for these chemicals in these distantly related molluscan species.  Kicklighter et al. 2007 Animal Behaviour 74: 1481.

 

NOTE  other known pheromones in sea hares include 4 involved in reproduction: attractin, enticin, temptin, and seductin

NOTE  the authors seem unclear whether the octopus species they used in the study is Octopus vulgaris or O. bimaculoides

  black dot
  RETURN TO TOP