Pollination Of Specialized Inflorescences Arum And Ficus

Biol 324 Introduction To Seed Plant Taxonomy
Biol 324 Course topics

Pollination of specialized inflorescences, (1) Arum (monoecious example)

Example: Arum maculatum

Day 1 – Appendix (sterile tip of the raceme) is thermogenic and volatilizes odor compounds that smell like rotting flesh or faeces. Flies enter with pollen on their bodies and fall down the slippery "spathe" (a bract, with smooth surface covered with oil and downward pointing hairs) to the female flowers at the bottom of trap. A ring of sterile flowers blocks exit so they remain trapped overnight.

Day 2 - male flowers (single stamens) higher up the inflorescence axis mature and shed pollen onto the trapped flies. The spathe ceases to be slippery and the sterile flowers wither allowing flies out of the trap. The inflorescence ceases to be hot and foetid. Flies depart, dusted in pollen, to seek another foetid inflorescence.

Pollination of specialised inflorescences, (2) Figs (Ficus)

Monoecious Ficus
- Most species of figs are monoecious, with each fig (a specialised inflorescence called a syconium) containing:
(1) male flowers,
(2) short-styled female flowers (wasp producing, sacrificial), and
(3) long-styled female flowers (seed producing).

- A fertilized female wasp, carrying pollen, successfully parasitizes short-styled female flowers, and in attempting to parasitize long-styled flowers, pollinates them.

- The young wasps hatch and mate in the fig. Males die in the fig after mating. Female wasps pick up pollen from male flowers, which are now shedding, and go off to parasitize and pollinate another fig.

- The fig continues to ripen its seeds (from the long styled flowers).

Dioecious Ficus
- Functionally dioecious (gynodioecious) figs - originated by mutations, which produced figs with female flowers of only one type (in addition to male flowers). The female flowers are either all long-styled or all short-styled.

- Tree with long-styled flowers is functionally female because flowers produce seed but no wasps. With no wasps, no pollen gets carried out, so tree has no male function.

- Tree with short-styled flowers is functionally male because flowers produce wasps but no seeds. But the wasps carry pollen out, so tree is functionally male.

Domestic fig (Ficus carica)
The domestic fig is one of the most complicated types

- It is dioecious and has female trees (figs) and hermaphrodites (caprifigs - functionally male as they produce wasps not seeds). Need both to get a fig crop, except now we have parthenogenetic varieties.

- Female tree - Wasp enters with pollen, can't oviposit in long styles, but pollinates them. Wasp can't escape from fig, and dies, fig ripens hundreds of seeds. In eating a non-parthenogenetic fig (i.e. a wild-type fig) you are eating the entombed bodies of the dead females that originally brought the pollen for fertilisation. They are therefore not suitable for vegans.

- Caprifig (male) tree - Wasp enters with pollen, oviposits in virtually all short styles, so no seed is produced, just wasps. Wasps hatch out later when male flowers shed pollen, and female wasps carry it out to another fig or caprifig

Wasp-fig coevolution in domestic fig
- To keep wasps alive all year, caprifig produces 3 crops of caprifigs in succession.

- the autumn crop overwinters between the female receptive stage and the pollen donor stage with developing wasps inside. Reproductive cycle of the plant has evolved in conjunction with wasp behaviour.

- The pollen donor stage of a crop of caprifigs coincides with the receptive stage of the
later crop of caprifigs, and, once a year, with the receptive stage of the female fig.

- The three caprifig crops have separate Italian names, mamme, profichi, and mammoni

What are the best figs for eating?
Calimyrna (Smyrna = Izmir) fig, grown in California. Fabulous figs!
- need to caprify them by taking caprifigs in bags and hanging them on trees to let the wasps hatch out and take pollen to the female figs, so seeds will develop, which gives them a nice crunch and texture…..and the wasps to add a little extra protein.

Evolution of the fig inflorescence (syconium)
This forms a morphological series in the family Moraceae:

(1) Mulberry (Morus) - inflorescence a catkin - flowers on an elongated peduncle
(2) Breadfruit (Artocarpus) - flowers on a globose peduncle
(3) Dorstenia - flowers on a flat peduncle
(4) Fig (Ficus) flowers inside a sack-like peduncle

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