lecture 14 - chemical defense

Question 1

what started the field of chemical ecology and why did it take so long ?

Answer 1

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

Question 2

two components of chemical signals

Answer 2

producer of chemical signal

receiver of chemical signal

RESULT:
Some aspect of receiver’s phenotype changes
e.g. behaviour morphology
physiology

Question 3

3 types of chemical signals and explanation

Answer 3

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

Question 4

what are the minimal criteria for proving a chemical entity is a selected adaptation for defense?

Answer 4

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

Question 5

experiment on spanish dancer nudibranch

Answer 5

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

Question 6

follow up spanish dancer nudibranch (concentrations)

Answer 6

Hexabranchus (nudibranch) and Halichondria (sponge)

this macrolide was extracted and added to food pellets (at diff concentrations)

effective at 0.05% - 1%

Question 7

another follow up on Hexabranchus and Halichondria (locations)

Answer 7

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

Question 8

what is the relationship between the loss of the shell and defensive chemicals?

Answer 8

chemical defense has allowed for the loss of the shell as it can work as protection instead

Question 9

what are defensive allomones mostly present in?

Answer 9

sessile marine invertebrates or organisms that are particularly vulnerable to predation (soft body and sessile)

• sponges (Porifera)
• ascidiacea (tunicates)
• bryozoans
• cnidarians

Question 10

multiple potential roles for defensive allomones (4)

Answer 10

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)

Question 11

example of secondary metabolites with multiple defensive roles (and first part of study)

Answer 11

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

Question 12

example of secondary metabolites with multiple defensive roles –> follow up study

Answer 12

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

Question 13

example of secondary metabolites with multiple defensive roles –> another follow up study

Answer 13

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

Question 14

2 sources of defensive allomones
- and quick mention of organisms for each

Answer 14

• direct acquisition
  (manufacture it themselves)
  (de novo synthesis)
• indirect acquisition
  a) Food
  b) Microbialsymbionts
  c) Other

Question 15

2 examples of de novo synthesis

Answer 15

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)

Question 16

what are ‘repugnatorial glands’

Answer 16

apparatus’ on organisms that produce or expel chemical deterrent

Question 17

what are saponins?

Answer 17

echinoderms produce these using de novo synthesis

used as a chemical deterrent

saponins are a detergent that disrupt cholesterol molecules within biological membranes

Question 18

sources of defensive allomones:
indirect acquisition through MICROBIAL symbionts example

Answer 18

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)

Question 19

sources of defensive allomones:
indirect acquisition through FOOD example

Answer 19

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

Question 20

sources of defensive allomones:
indirect acquisition through “OTHER” example

Answer 20

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)

Question 21

how does Aposematic Colouration work as chemical defense? (give an example organism)

Answer 21

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