REPRODUCTIVE STRATEGIES

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INTRODUCTION

What are the consequences of the major modes of reproduction in trees--
SEXUAL AND ASEXUAL REPRODUCTION

SEXUAL REPRODUCTION

Most widespread form of reproduction

Two step process:
Meiosis-- formation of sex cells (gametes)

  • cuts number of chromosomes in half
  • important feature is recombination of genes

Fertilization-- union of gametes to form 1st cell of new organism (zygote)

  • re-establishes "normal" number of chromosomes
  • results in new combinations of genes in same cell due to union of 2 different lines of inheritance (mother, father)

 

Plants represent nearly a continuum from the union of gametes coming from the same or different individuals.

Obligate outcrosser
outcross/self
Obligate selfer
dioecious
monoecious, perfect flowers
cleistogamous flowers
high heterozygosity
intermediate
high homozygosity
Examples: Salix, Populus, Juniperus, Sassafras
M- virtually all Gymnosperms, all Amentiferae

PF- most Floriferae

none
advantageous in fluctuating environments; allows production of new genotypes that might be successful

 

advantageous in stable environmnent; allows close adaptation

 

Advantages of sexual reproduction
  • Variety of progeny in the future
  • Seeds/fruits are formed- allows for effective long-distance dispersal

Disadvantages of sexual reproduction

  • Too much variation is a problem because it prevents close adaptation to any given environment
  • Seed germination and seedling stages are precarious due to high mortality rates in stressful environment

ASEXUAL REPRODUCTION

Vegetative propagation-- formation of new individual from vegetative parts of old individual

· Stump sprouts-- adventitious buds (buds formed from other meristematic tissue (such as cambium) on stem or branches (when brocken off). e.g Populus, Acer macrophyllum, Quercus, Salix, Castanea dentata.

· layering-- roots emerge from branches pressed to round. e.g., Abies lasiocarpa, Thuja plicata, Acer circinatum.

· root crown sprouts-- from top of roots e.g., Sequoia sempervirens.

· root sprouts, suckers-- upright stems emerge from lateral roots. e.g., Populus tremuloides, Populus nigra var. italica, Sassafras albidum.

Advantages of Asexual Reproduction

· well-adapted genotypes can be preserved and multiplied

· root sprouts etc take advantage of already existing root system

· no fragile seedling stage \ good for harsh environments

Disadvantages of Asexual Reproduction

· little variation to cope with fluctuating environement (high adaptation, but low adaptibility)

· root sprouts-- disease spreads from old to young individuals of clone \ susceptible for fast spread of epidemics

PRACTICAL USE OF ASEXUAL REPRODUCTION