Are tropical urchins more tolerant of tropical chemically-defended seaweeds than temperate urchins? A comparison of populations of Arbacia punctulata

Alyssa M. Demko1, Valerie J. Paul2, and Erik E. Sotka1 1College of Charleston, Grice Marine Lab

2Smithsonian Marine Station at Fort Pierce

Introduction

Chemical Extractions and Feeding Assays

Future Research and Significance

References

Bolser RC and Hay ME. 1996. Are tropical plants better defended? Palatability and chemical defenses of

temperate vs. tropical seaweeds. Ecology 77:2269–2286.

Craft, JD, Paul, VJ and Sotka, EE. 2013. Biogeographic and phylogenetic effects on feeding resistance of

generalist herbivores toward plant chemical defenses. Ecology 94:18-24.

Fitness Effects

Acknowledgements

• It has been hypothesized that a co-evolutionary arms race is

occurring between marine herbivores and seaweeds.

• In comparison to temperate seaweeds, tropical seaweeds produce

more lipophilic metabolites which can act as herbivore deterrents

(Bolser and Hay 1996).

• Tropical urchin lineages have shown increased tolerance to whole

lipophilic extracts from tropical seaweeds (Craft 2013).

• Even within the single species Arbacia punctulata, there appears to

be differences in tolerance to secondary metabolites (Craft 2013).

Future Research

• Examine the transcriptomic response to the differentially deterrent

compound or compounds.

• Test seaweeds from temperate and polar regions to evaluate

evolution of seaweed offense.

Significance

• This project will facilitate our understanding of latitudinal

variation in the co-evolution of herbivores and their seaweeds.

• Additionally, insight will be gained into the effects of algal-

herbivore interactions on community structure and marine

ecosystems.

1. Extract non-polar organic, polar organic, and water soluble

compounds from D. ciliolata and D. pulchella.

2. Isolate and purify primary secondary metabolites in non-polar

fractions.

3. Perform feeding assays using A. punctulata populations to

determine the differentially deterrent compound or compounds.

4. Conduct a long term feeding assay to examine the fitness effects of

a chemically rich diet.

Study System

Objectives

Feeding Assays

Urchin populations are offered feeding strips of the various extracts at

the following dosages: 0, 0.25, 0.50, 1.0 (natural concentration), and

2.0.

After 12 hours, the number of completely empty squares are counted

to determine the amount of food consumed.

Seaweed Extractions

1) Seaweeds are

collected, lyophilized

and extracted in a 1:1

MeOH: EtoAC

followed by a 1:1

H2O:EtOH solvent.

2) Whole extracts are then

separated into nonpolar

organic, polar organic, and

water soluble layers and dried.

3) Thin layer

chromatography

(TLC) and nuclear

magnetic

resonance (NMR)

are performed.

4) Open columns are utilized

to separate the extracts

based on polarity into

fractions of compounds.

5) Fractions of compounds can

be dried and stored until feeding

assays are performed.

The purple-spined sea urchin,

Arbacia punctulata, spans from MA,

USA to the West Indies. Few urchin

species span temperate and tropical

regions, making this urchin a good

species for comparing temperate

and tropical populations.

Dictyota ciliolata is a

circumtropical brown seaweed.

In the USA, it is found from NC

to Florida. Previous work by

Craft (2013) found that both D.

ciliolata and D. pulchella caused

differential deterrence in

populations of A. punctulata.

Figure 1. Relative consumption of Dictyota pulchella extract to

controls in no choice feeding assays with FL and MA Arbacia

punctulata. Extract was applied to Gracilaria tikvahiae while the

control consisted of G. tikvahiae without additional extracts. Error

bars represent standard error (Craft 2013).

An algae dominated

ecosystem. This can

occur in areas devoid of

urchins.

A healthy coral reef. If urchin populations

“boom,” they can create

barrens devoid of any

algae.

We would like to thank everyone at the College of Charleston Grice Marine

Laboratory and the Smithsonian Marine Station at Fort Pierce for their help and

support. Special thanks to my committee: Allan Strand, Christine Byrum, & Gavin

Naylor.

Smithsonian Marine Station

at Fort Pierce

Recirculating tanks hold

separate populations of A.

punctulata at Grice Marine

Lab.

Individual urchins are maintained in separate

perforated containers. Feeding

strips post

assay.

0

25

50

75

100

125

0 0.5 1

Re

lati

ve

Co

nsu

mp

tio

n

Concentration

FL

MA

Question How do algal secondary metabolites influence feeding tolerance and

fitness in tropical and temperate populations of the purple-spined sea

urchin, Arbacia punctulata?

Urchins will be fed diets of lyophilized G. tikvahiae, D. ciliolata, or a

50/50 mixture for a period of 3-6 months. Both mortality and serious

stress signified by loss of spines will be documented. Additional proxies

for fitness have yet to be determined, but some potential options

include measuring test and spine lengths, examining fecundity and

quantifying fertilization success.

Subsequent feeding assays will also be conducted to see if secondary

metabolite tolerance changes after prolonged exposure to a chemically

rich diet.

1 cm

Adult Arbacia punctulata exhibit different morphologies

depending on latitude. The southern (FL) urchins have larger

tests and longer spines compared to their northern (MA)

counterparts.