Nurse eggs and cannibalism influence intracapsular
development and survival in a poecilogonous
spionid polychaete
OBJECTIVE
“This study examines interactions between
adelphophagic and planktotrophic larvae
and nurse egg in capsules; specifically
measures cannibalism and larval growth
rate”
FERNANDA X. OYARZUN
Department of Biology, University of Washington.
ABSTRACT
METHODS & RESULTS
Poecilogony is the ability to alternate between multiple developmental modes. Boccardia
proboscidea, a spionid polychaete, has three different types of developmental strategies, including
one in which capsules have approximately 90% nurse eggs and a mixture of planktotrophic and
adelphophagic larvae. In this study I evaluated whether larval development was influenced by the
conditions in which larvae develop inside the capsule, by manipulating combinations of larval types
and nurse egg concentrations in vitro. Both larval types ate nurse eggs inside the capsule and when
they were removed from capsules, showing an active feeding behavior from early stages. Both
larval types grew more at higher concentrations of nurse eggs, but adelphophagic larvae grew
faster. Planktotrophic larvae continued developing inside the capsule and ate nurse eggs, contrary
to predictions from previous studies. I found no significant effect of larval combination on growth rate
for either of the two developmental modes, however mortality of planktotrophic larvae was high due
to cannibalism, implying that there are big disadvantages for planktotrophic larvae inside capsules
that contain adelphophagic siblings. Mother’s capsule-opening behavior is hypothesized as a
mechanism to regulate survival of different developmental types in nature.
Original capsule
Methods:
Methods:
Two factors were used to test the effect of nurse eggs:
1. Number of nurse eggs: 0, 20 and 40
2. Larval type: adelphophagic [A] and planktotrophic [P]
1) Adelphophagic
larvae
STUDY SYSTEM
Female
Adult
II. Capsule Manipulation Experiment
I. Nurse-egg Manipulation Experiment
Manipulated capsule (start)
2) Plankton-trophic
larvae
• Two factors were used to test the effect of the
environment in each larval type:
1. Encapsulation
• encapsulated larvae
• free larvae
2. Combination of larvae
• 2 adelphophagic [AA]
• 2 planktotrophic [PP]
• 1 planktotrophic and 1 adelphophagic [AP]
• untouched capsules [U]
• open/close capsules [C]
Results:
3
Growth rate
(setigers/day)
A
A
B
2
Capsules
100μm
A
P
Larval type
Larvae
C
B
C
Manipulated capsule (end)
C
1
a
p
3
2
1
AB
0
20
40
Growth rate (setigers/day)
Results:
3
Adelphophagic
larvae
Planktotrophic
larvae
2
1
Free
Capsule
Capsule
Free
3
2
1
Nurse egg treatment
AA
Some population of B. proboscidea (Polychaeta: Spionidae deposit capsules with
90% of nurse eggs and planktotrophic (p) and adelphophagic (a) larvae
(Gibson…..).
Nurse eggs
AP
C
U
PP
AP
C
U
Presence of sibling larvae does not influence
developmental mode or growth rate, but there are high
levels of cannibalism of planktrophic larvae (71%).
Growth is faster with more nurse eggs
Planktrophic larvae eat nurse eggs too
Experimentally opened capsules does not affect the
results
Habitat
Adelphophagic larvae have a faster growth rate
FUTURE & ON-GOING
RESEARCH
ACKNOWLEGMENTS
Cannibalism rate (---)
Dispersal potential ( –– )
Richard Strathmann,
Danny Grunbaum, Bruno Pernet,
Jennifer Ruesink, Billie Swalla,
Martha Groom, Federico Brown,
Alex Primus, Eric EdsingerGonzales, Paul Bourdeau,
Caroline Faria,
Larval Ecology Class,
Friday Harbor Laboratories
CONCLUSIONS
Hatching time
0
4
8
12
16
Developmental Stage (#setigers)
1. Test interactions at earlier stages
2. Variation in timing of mother
opening of capsules and stages
and number at hatching
3. Consequence in population
dynamics (model)
• Adelphophagic larvae:
– Have an active feeding behavior, and do not
need pressure inside the capsule to eat.
– Eat plankton-feeding larvae
– Grow faster at higher nurse egg concentrations
•
Planktotrophic larvae:
– Eat nurse eggs!
– Most of them continue developing inside the
capsule
– Although growth rates do not seem to be
affected by the presence of nurse-egg
feeding larvae, they suffer of high levels of
cannibalism