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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