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Key Features

LECTURE OVERVIEW (web,ppt)

Basic statement:

Pollen grains and seeds are the mobile life stages of trees. Both stages have very high mortality rates. However, rather than being the weak link in the chain of survival, pollen grains and seeds serve vital functions that cannot be accomplished during the longer, dominant adult stage of trees.

Key ideas:

Pollen grains are produced in the anthers and transported to the surface of the stigma by air, animals or water. Pollen grains are small compact structures made up of several cells, one of which is the sperm cell. The sperm cell is delivered to the ovary, where it fertilizes the egg cell, contained within the ovule. The wide array of flower structures, sizes, and color reflects different adaptations to pollinating agents. Wind-pollinated flowers are typically small and have large anthers and stigmas. They often lack petals, which interfere with the wind. By contrast, insect-pollinated plants have prominent petals, which function to attract insects and direct them to the reproductive structures. Insect-pollinated plants often have other attractants, such as aroma, and "rewards," such as nectar. All of these features enhance the potential for successful movement of genes (contained in sperm) between individuals in the process of sexual reproduction.

Seeds consist of an embryo surrounded by nutritive material and enclosed in a protective covering. They are the primary mode of dispersal in tree species. Seed dispersal allows trees to expand into favorable environments. Over short time periods (decades) this includes the ability of early successional species to find open ground for establishment. Over very long time periods (centuries to thousands of years), seed dispersal allows trees to migrate in response to changing climate. Seed dispersal has genetic consequences, as wide dispersal enhances the chance that mating will occur between genetically unrelated individuals. Seed dispersal is also an important agent of gene flow between neighboring populations. As with other types of adaptations, seed adaptations in trees include a variety of traits (biochemical, structural, developmental).

Important terms:

nectar guides	inflorescence
pollination	fruit

LECTURE OUTLINE

Introduction

Pollination

1. Wind

2. Animals (primarily insects)

• many parts
• unfused parts
• radial symmetry

• fewer # of parts
• fusion of parts
• attractants, guides and awards
• aroma, size and color (including rotting meat)
• marking on petals to direct insects (honey guides)
• nectar and pollen
• bilateral symmetry
• forces movement of insect through flower
• inflorescence (including "division of labor")
• greater efficiency—more reproductive parts/area

SEEDS AND FRUITS

• We’ve discussed seeds and fruits before (Species descriptions, discussion of life history strategies
• Today we will discuss characteristics in more detail, with real examples

SEEDS-- completely matured and modified ovule containing an embryo

FRUITS—Mature ovary containing seeds

PROTECTION:

Morphological defenses: Structures that defend

• spines of pine cones
• large burs of chestnut
• very dense pubescence

Chemical defenses: toxic chemicals in seed coats, food material, or embryo

• pea family
• horse chestnut
• Ginkgo biloba
• tanins in oaks
• immature fruit: sour, bitter

Animal body guards: animals fight off predators

e.g., ants defend some legumes

Plant rewards ants with nectar (at base of fruit) and ants attack flies trying to lay eggs in fruit. Plant also supplies proteins/fats and lodging to ants.

Escape in time

predator satiation

DISPERSAL

Balistic—explosive release

• scotch broom
• dwarf mistletoe

Wind

• very small seeds (Salix, Populus, Liquidambar—fruits are capsules here)
• hairs, plumes (Salix, Populus, Platanus)
• wings

samaras: Acer, Liriodendron,

winged seeds: most Gymnosperms, Liquidambar

• plant swaying: poppies
• plant dispersed: tumble weeds

Water

• coconut

Animals

unintentional carrying

• burs, barbs
• stickum—dwarf mistletoe

harvesting and caching

• birds: jays, nutcrackers, passenger pigeons

  carry 70-100 seeds 10s of miles
  several pines (e.g. white bark pines, pinyon pines [pine nuts], Pinus pumila)

• mammals: squirrels

big seeds: Aesculus, Quercus, Juglans, Carya, Fagus, Castanea

• predator satiation

eating

• seed enclosed or attached to a edible material (food is reward for consumer)
• fate of seed: (note: need to lighten balast)
  • discarded (we do that)-- fastest
  • regurgitated
  • passed through gut—slowest
• characteristics of fruit
• prominent display position
• prominent color when ripe
• protection

green when immature
bitter when immature

• high energy cost to produce

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