Lecture 1 - Pollination Part 1 Flashcards
Gymnosperms comprise 4 phyla?
- Cycadophyta 2 families, ~150 spp
- Gingkophyta - one living species: Ginko biloba
- Gnetophyta - 3 families, 70 spp
- Coniferophyta - 5 families, 50 genera, ~600 spp (most successful)
- Pinaceae
- Cupressaceae
- Taxaceae
- Araucariaceae
- Podocarpaceae
Life cycle of a gymnosperm
The gymnosperm life cycle has a dominant sporophyte generation. Pollination occurs when pollen is transferred from a male to female cone. Zygotes develop into embryos inside seeds, from which the next generation grows. If the seed germinates, it may grow into a mature sporophytes tree, which repeats the cycle
Life cycle of an angisoperm
The angiosperm life cycle consists of a sporophyte phase and a gametophyte phase. The cells of a sporophyte body have a full complement of chromosomes (i.e., the cells are diploid, or 2n); the sporophyte is the typical plant body that one sees when one looks at an angiosperm. The gametophyte arises when cells of the sporophyte, in preparation for reproduction, undergo meiotic division and produce reproductive cells that have only half the number of chromosomes (i.e., haploid, or n). A two-celled microgametophyte (called a pollen grain) germinates into a pollen tube and through division produces the haploid sperm. An eight-celled megagametophyte (called the embryo sac) produces the egg. Fertilization occurs with the fusion of a sperm with an egg to produce a zygote, which eventually develops into an embryo. After fertilization, the ovule develops into a seed, and the ovary develops into a fruit.
Some context about the angiosperms and their pollinators
- There are 300,000 species of angiopserms -~90% of these angiosperms are animal pollinated.
- There are ~130 000 - 300 000 species of animal that are regular flower visitors and serve as potential pollinators. (Why potential? beause how an animal manipulates a flowere determines if pollination will be successful.)
- Pollination by animal is more common and usually more effective than abiotic vectors (i.e. wind and water)
- Animal pollintaion is also associated with more rapid speciation of plants. Angiosperms and their pollinators diversified at the same time – roughly 65-60 MYRs ago.
- Hence, our focus will be on animal pollinitiated flowering plants.
What is pollen?
Pollen houses the male gametophyte - In seed plants, the male gametophyte is reduced to just two cells.
The structure of the polllen grain serves to protect and nourish the gametophyte.
Pollen grain develop a tick wall consisting of 2 layers ?
the exine and intine layer
The exine layer
The exine layer is largely composed of sporopollenin rendering the grain resistant to decay, to physical damage and to chemical attack.
The outside of the exine layer is covered with:
1. flavonoids and carotenoids to absorb UV light.
2. proteins with adehsive properties
3. proteins involves in self-incompability effects
These same proteins are what cause allergies in human.
Different plant species have morphologically distinct exine layers.
Exine layer of* zoophilous angiosperms* (pollen dispersed by animals) is usually more ornate with proteins.
Pollen grains remain on the anther by the adhesiveness of their surface proteins. When a pollinator visits the flower, the pollen **grain transfers to the body of the animal. Best pollinators are hairy. **
In a minority of flowers the pollen grains may be “launched” dynamically onto a visitor.
The intin layer
The intine consists primarily of cellulose and pectins - essentially much like a regular cell wall except it has aperture through which the pollen tube will emerge.
Inside the pollen grain is the cytoplasm of the cell rich in carbohydrates (both complex carbs and simple sugars) which serve as the fuel reserve for the gametes.
IN SHORT, pollen function both as a **reward for animals and in reproduction **
With time, pollen was replaced by nectar - a much cheaper quality reward.
Nectar - A new reward for pollinators
Nectar provides an alternative food to pollen-in the evolutionary sense it is the** flowers secondary reward.**
Nectar is** easy to produce and easy for animal to handle.
**
Nectar feeders typically have storage regions to store the nectar and mechanisms to** avoid osmotic shock f**rom sudden sugar overloads.
Nectar glands
Nectar is usually produced in specilaized glands called nectaries.
Sugar concentration varies between 10% and 75%.
The sugars are predominantly **glucose, frutcose and sucrose **in various proportions.
Given that sugars do not circulate as monosaccharide in the phloem, sucrose must be broken down within the nectaries.
Nectar viscosity
Concentration of nectar is measured **as a function of grams of sucrose per 100g of solution. **
Viscosity rises exponentially with increasing concentration: a 60% sugar solution is 28 times more viscous than a 20% surcose solution.
Viscosity of nectar can change diurnally and therfore appeal to a greater range of pollinators throughout the day.
Amino Acid in Nectar
- Nectar also contains amino acids - the essential builiding block of all proteins.
- After sugar, the most abundant component of nectar are amino acids.
- Little evidence that amino acid levels in nectar are important or even detected by most flower visitors.
Pollination is integral to ecosystem functioning-it is a key “ecosystem service”.
The following flower traits can influence ecosystem service delivery:
- accessibility
- abundance
- attrativeness
- density
- variety of nectar viscosity
- size
Flowers are incredibly diverse in size, shape, color, scent, nectar charcteristics and other features.
Primitive flower characteristics
- many parts
- unfused parts
- radial symetry (pollinators can approach the flower from many angles)
More recently evolved flower characteristics
- fewer parts
- fused parts- corolla, calyx
- bilateral symmetry (fewer parts, fused parts, pollinators can enter the flower from only 1 angle)
- odors
- spurs
- lids/hairs to conceal nectaries (protect against theft and evaporation)
- attractant - rewards, guides
- inflorescence
