Download The Co-evolution of Fig Trees and Fig Wasps

The Co-evolution of
Fig Trees
and
Fig Wasps
A Unique Symbiotic Relationship

The flowers of fig trees are unique
because they are completely concealed
inside the fig

This results in the pollination of this
species to be carried out by a very
specialized organism…the fig wasp.

Fig wasps are just as dependent on the
fig tree as there is nowhere else that the
wasp can breed but inside the fig itself.
http://www.figweb.org
Ceratosolen capensis

Neither can survive without the help of
the other, a relationship that has thought
to evolved over millions of years.
The Definition of Co-evolution

“In biology, co-evolution is the mutual
evolutionary influence between two species.
Each party in a co-evolutionary relationship
exerts selective pressure on the other, thereby
affecting each others' evolution. Co-evolution
includes the evolution of a host species and its
parasites, in examples of mutualism evolving
through time”
(http://en.wikipedia.org).
The importance of the interaction

Fig wasps are the
only pollinators of
fig trees

Each female
wasp is species
specific and are
attracted to
receptive figs of
“their” host tree.
Cook, 2004
1
The cycle





1) Fig wasps are species
specific and so to begin with they
must find their “host” fig tree.
2) They enter through the Bractlined ostiole.
3) Once inside they pollinate the
flowers
4) Also during this time they lay
eggs in some of the flowers
and leave the rest of the flowers
to produce only seeds
5) The larvae eat a portion of the
seeds
Finding their host tree
http://www.figweb.org

After leaving the fig in
which they have bred
the fig wasp must go in
search of “their” host tree

Few individuals make it!!
Philocaenus rotundus depositing eggs
Jones, 2002
Laying their eggs



The offspring
The foundress must now
enter the fig through the
ostiole

The larvae feed of a small portion
of the seeds

Once the wasp larvae reached
maturity, they mate.
They pollinate the flower
and also lay their eggs
(one egg per flower)

The wingless male then chews
through the fig wall and dies shortly
afterward

This allows the female to escape

The females, loaded with pollen
from the mature stamenate
flowers, go in search of young
receptive figs to complete the cycle
This small deposition of
eggs leave the rest of the
flower to produce seeds
http://www.figweb.org
Anthers of the male flowers of a Ficus pumila
2
A sacrifice or a win-win situation?


Although the fig tree is
allowed to reproduce it
must give up some of
its seed production to
feed the wasp larvae
Conversely the fig
wasp receives the
essential food source
for its progeny
http://www.figweb.org
The length of the wasp’s
ovipositors cannot penetrate all
styles of flowers.

This allows for the longer style
flowers to avoid destruction by
the larvae and produce only
seeds.

It is still unknown why the fig
wasp has not evolved longer
ovipositors or produced greater
numbers of offspring


Short – ovipositor – length hypothesis

Unbeatable seeds hypothesis

Insufficient – egg – supply hypothesis
The emergence of a fig wasps from a
Ficus sur
Short – ovipositor – length
hypothesis

Three hypothesis for Mutual
Stability
Arguments against this
hypothesis

Wasps can reach the
majority of ovaries but they
prefer to oviposit in shorter
styled flowers:

Penetration may be more difficult

Longer probing time is required
Rasplus, 2003
Apocrypta robusta

Increased friction between the
ovipositor and the stylar canal
http://www.figweb.org
3
Insufficient-egg-supply hypothesis
Unbeatable seeds hypothesis



A portion of the flower is
inaccessible because some
ovaries are untouchable to all
fig wasps, both pollinating
and un-pollinating.

This study shows that 20% to
65% of the sites were unused


Unused and/or insufficient
egg supply
http://www.figweb.org
Restrictions and Controls

Competition for the oviposition
sites

Length of the ovipositor

If the pollinators do not find the
host the fig aborts

If the pollinators do enter the
ostiole closes within 24-48 hours
The number of flowers that
are not destroyed by the
wasp larvae depends on a
combination of:

Total number of eggs
produced by one individual
Number of ovaries within each
fig
The number of female wasps
that can enter before the
closure of the ostiole
Why choose short style flowers?


http://www.figweg.org
Ceratosolen capensis

The fig’s ostiole size may be
limiting to entry
http://www.figweg.org

It seems to be more efficient
to oviposit in shorter styles
lengths
Once the flowers are
pollinated they wither making
it more difficult for the wasps
to penetrate the stylar canals
Predation of the larvae
www.argnet.org
Parasitoid wasp (Torymus sinensis)
4
Predation on fig wasp and larvae

The conclusion
Larvae are killed by
parasitoid wasps as
they penetrate
though the fig walls

The successive interaction
of female wasps and fig
seeds mutualism is
influenced by:

The number of pollinators

Their successive entry into
the fig allowing for the
deposition of their egg
supply
Rasplus, 2003

Predation by ants
Philotrypesis caricae
Weiblen, 2003

Questions
+
Deeble, 2007
References
Author unknown. 2006. Retrieved January 5, 2007 from http://en.wikipedia.org/wiki/Co-evolution

Author unknown. Retrieved January 6, 2007 from http://www.arbolesornamentales.com

Author unknown. Retrieved January 7, 2007 from http://www.agnet.org/library/image/ac1997g2.html

Bolstad, P. 2004. Retrieved January 6, 2007 from http://www.forestryimages.org

Butchart, D. 2003. Retrieved January 5, 2007 from http://www.wildwatch.com

Cook, J. 2004. Retrieved January 5, 2007 from http://www3.imperial.ac

Cook, J. M . and J. Y. Rasplus. 2003. M utualist with attitude: coevolving fig wasps and figs. Trends in Ecology and Evolution.
18, 241-248.

Deeble, M . 2007. Retrieved January 7, 2007 from http://www.bbc.co.uk/cornwall

Fagg, M . Retrieved January 5, 2007 from http://www.anbg.gov.

Jones, M . 2002. Retrieved January 5, 2007 from http://www.blackbeltjones.com

Linney, G. Retrieved January 7, 2007 from http://www.botany.hawaii.edu/FACULTY/CARR/mor.htm

Van Noort, S. 2004 – 2006. Retrieved January 5, 2007 from http://www.figweb.org

Weiblen, G. 2003. Retrieved January 5, 2007 from http://www.cbs.umn.edu
Deeble, 2007
5