lecture 14 - chemical defense Flashcards
what started the field of chemical ecology and why did it take so long ?
1959 - female sex attractant of the silk moth was identified
humans aren’t part of the chemical world in this way due to our underwhelming olfactory sensory system
two components of chemical signals
producer of chemical signal
receiver of chemical signal
RESULT:
Some aspect of receiver’s phenotype changes
e.g. behaviour morphology
physiology
3 types of chemical signals and explanation
Pheromones
- producer and receiver are same species (intraspecific)
– like attracting a mate
– ex// snails hv pheromones in mucus
Kairomones
- producer and receiver are different species
– benefits RECEIVER
Allomones
- producer and receiver are different species
– benefits PRODUCER
what are the minimal criteria for proving a chemical entity is a selected adaptation for defense?
1) isolated chemical deters predator when applied to otherwise palatable substance
2) effective at native concentration
3) effective against sympatric predators
4) appropriate anatomical distribution (to repel before attack is fatal)
5) survival after attack
experiment on spanish dancer nudibranch
lay egg masses in ribbons
this nudibranch (Hexabranchus) feeds on sponge (Halichondria)
Halichondria contains secondary metabolite (a macrolide called halichodramide)
when ingested, the halichodramide gets a double bond added and turns into dihyrohalichondrimide
conclusion:
- nudibranch probably acquiring secondary metabolite from sponge prey
follow up spanish dancer nudibranch (concentrations)
Hexabranchus (nudibranch) and Halichondria (sponge)
this macrolide was extracted and added to food pellets (at diff concentrations)
effective at 0.05% - 1%
another follow up on Hexabranchus and Halichondria (locations)
found at effective concs in:
- dorsal mantle
- digestive gland & gonad
- egg mass
***mostly in egg mass
NOT found enough in:
- foot
- accessory reproductive organs
*** bc these places dont come in contact w predator
what is the relationship between the loss of the shell and defensive chemicals?
chemical defense has allowed for the loss of the shell as it can work as protection instead
what are defensive allomones mostly present in?
sessile marine invertebrates or organisms that are particularly vulnerable to predation (soft body and sessile)
- sponges (Porifera)
- ascidiacea (tunicates)
- bryozoans
- cnidarians
multiple potential roles for defensive allomones (4)
defense against:
1) predators
- against subjugation phase
2) space competitors
- things encroaching on you
3) settling larvae of other species (fouling deterrent)
4) pathogens (things leading to disease)
example of secondary metabolites with multiple defensive roles (and first part of study)
porifera
Caribbean sponges - 2 species have this secondary metabolite (triterpene glycoside)
testing predator deterrent-
study:
- strips of phytagel on thing like clothes line
- some had crude extract from sponge and some had purified triterpene glycoside
***ones with just squid paste and no treatment were eaten more often
example of secondary metabolites with multiple defensive roles –> follow up study
testing antifouling activity
study:
- some w just phytagel, some w phytagel and glycoside (secondary metabolite or chemical deterrent)
- measured how much coverage of petridish of settled larvae
** found that glycoside has antifouling properties
** few larvae settles on dish treated w glycoside
example of secondary metabolites with multiple defensive roles –> another follow up study
testing repel space competitors
- sponge overgrowth assay
study:
- middle circle of rapid growth sponge species (competitor)
- other areas around with different treatments (some w phytagel and treated, some not)
*** found the control (non-treated) had a lot more encroaching competitor sponge than ones with added glycoside
2 sources of defensive allomones
- and quick mention of organisms for each
- direct acquisition
(manufacture it themselves)
(de novo synthesis) - indirect acquisition
a) Food
b) Microbialsymbionts
c) Other
2 examples of de novo synthesis
1) melibe leonine (lion nudibranch)
has hood w tentacles and captures zoop like a slow Venus fly trap
doesnt get chemical defense from food source, makes it themselves
‘repugnatorial glands’
look like white specks on dorsal mantle and smells like citrus
deterrent for sea stars
2) echinodermata
de novo synthesis of saponins
saponins are a detergent that disrupt cholesterol molecules within biological membranes (like having your hands in soap for way too long)
and taste bad –> like eating soap (detergent)
what are ‘repugnatorial glands’
apparatus’ on organisms that produce or expel chemical deterrent
what are saponins?
echinoderms produce these using de novo synthesis
used as a chemical deterrent
saponins are a detergent that disrupt cholesterol molecules within biological membranes
sources of defensive allomones:
indirect acquisition through MICROBIAL symbionts example
sponges have secondary metabolites often from microbes since prokaryotes can make them more easily
up to 40% of sponge volume is microbial (huge amt of body composed of these)
sources of defensive allomones:
indirect acquisition through FOOD example
Bryozoans use bryostatins as a chemical deterrent
these help adults and protect larvae and young juveniles
mothers provision these bryozoans yolk but also chemical deterrent
a species of nudibranch also feeds on these and uses for defense
sources of defensive allomones:
indirect acquisition through “OTHER” example
some organisms use other organisms for protection, without eating them
1) amphipods select species of algae that have chemical defense for their domiciles
2) Clione (pteropod) are held onto by amphipod bc predators didn’t consume any Clione during study (chemical defense)
how does Aposematic Colouration work as chemical defense? (give an example organism)
Response of pinfish (Logodon rhomboides) with different experience levels to larvae of Ecteinascidia turbinata and to dyed and undyed larvae of Clavelina oblonga.
tadpole larvae of this species is toxic and bright orange (whereas adults are not)
labelled fish being inexperienced or experienced - if fish had prior interactions w chemically defended larvae
experienced them already so knew colour meant bad = ignored
- when added dyed good ones w inexperienced, most were eaten —> bc more noticable and tasty
