Plant Reproduction

Chapter 38: Plant Reproduction

Overview

  • Variation in plant reproduction involves several tradeoffs including:

    • Pollination biology

    • Self vs. outcross pollination

    • Seed production and dispersal

    • Asexual reproduction

Size / Number Trade-offs

  • Reproductive Structures:

    • (a) Small reproductive structures:

    • Example: A plant with flowers measuring 1 mm.

    • (b) Large reproductive structures:

    • Example: A plant with seeds up to 10 cm in size.

  • Trade-offs Explained:

    • Making Many Small Offspring:

    • Producing many seeds results in each seed having limited resources.

    • Making Few Large Offspring:

    • Fewer seeds but are better provisioned, leading to a higher chance of survival.

Effort Distribution in Flowers

  • Considerations:

    • Should a plant invest all its reproductive effort into a few flowers with many attractants?

    • Or should it produce many small flowers but with less effort per flower?

Plant Lifecycle Strategies

  • Annual Plants:

    • Grow, flower, and reproduce within a single growing season.

  • Biennial Plants:

    • Grow a vegetative rosette in the first year, then flower in the second year.

  • Perennial Plants:

    • Live for multiple years with the potential to flower many times or only once.

Types of Plants and Their Reproductive Strategies

  • Liverworts:

    • Pollination mechanism has removed dependence on water to move gametes.

  • Hornworts, Mosses, Lycophytes, Whisk Ferns, Horsetails, Ferns, Cycads:

    • Sperm swim to reach the egg.

  • Ginkgo, Redwoods, Junipers, Yews, Gnetophytes, Pines, Spruces, Firs:

    • Use pollen that is transferred by wind or animals.

  • Angiosperms:

    • Majority of angiosperms have evolved pollen, which has allowed them to forsake the necessity of water in sexual reproduction.

Pollination Biology

  • General Pollinators:

    • Generalist pollinators typically favor round, radially symmetric flowers.

    • Common pollinators include bees, beetles, and flies.

Angiosperm Flower Structures

  • Components of an angiosperm flower:

    • Carpel: Major reproductive part.

    • Stigma

    • Style

    • Ovary

    • Stamen: Male reproductive part.

    • Anther

    • Filament

    • Other Parts:

    • Petals and sepals which can be fused, lost, or adapted for new functions.

Flower Symmetry

  • Types of symmetry in flowers:

    • Radial Symmetry: Often preferred by generalist pollinators.

    • Bilateral Symmetry: Often favored by specialist pollinators.

Flower Color and Visual Adaptations

  • Many pollinators can perceive UV light, influencing flower color evolution:

    • Visible light and UV light adaptation.

Wind Pollination

  • Characteristics:

    • Common in grasses and various trees.

    • Wind-pollinated plants often produce large amounts of small, greenish, odorless flowers, which are frequently grouped in quantity and hang in tassels.

Rare Water Pollination Example

  • Vallisneria americana:

    • Female flowers on underwater springs with floating male flowers on the surface.

Pollination by Bees

  • Role of Bees:

    • Major crop pollinators essential for various fruits, vegetables, and nuts.

  • Bee Disappearance:

    • Specific states reported loss of honeybee populations affecting crop values:

    • Example Crop Values:

      • Soybeans: $19.7 billion (5% pollinated by honeybees)

      • Almonds: $2.2 billion (100% pollinated by honeybees)

  • Colony Collapse Disorder:

    • A significant issue reported affecting bee populations in various states in 2014-2015.

Hummingbird Pollination

  • Key traits:

    • Red, tubular flowers producing plenty of dilute nectar with no scent.

Moth and Bat Pollination

  • Moth Pollination:

    • Features light-colored flowers with musky scent produced at night and long nectar spurs.

  • Bat Pollination:

    • Similar traits as moths but also includes light-colored flowers with nectar close to the floral surface.

    • Example of co-evolution between bat tongue length and flower structure:

    • Discovery of a bat with an exceedingly long tongue aligned with long corolla tubes.

Deceptive Pollination Mechanisms

  • Orchid Mimicry:

    • Some orchid flowers mimic female wasps to attract males, leading to the transfer of pollinia.

  • Carrion Flies and Beetles:

    • Some plants mimic the scent and appearance of decaying flesh, utilizing compounds like putrescine and cadaverine for attraction.

Co-evolution and Speciation

  • Plants may co-evolve with different pollinators across regions, contributing to reproductive isolation and potentially leading to speciation.

Self-Pollination Mechanisms

  • Benefits & Costs:

    • Benefits: Reproductive assurance when pollinators are scarce.

    • Costs: Risk of inbreeding and reduced genetic variability.

  • Concepts related to self-incompatibility include:

    • Herkogamy: Spatial separation of anthers and stigmas.

    • Dichogamy: Temporal separation of anthers and stigmas maturity.

Fruit Production and Seed Dispersal

  • Types of Fruits:

    • Simple Fruits: Derived from a single ovary. E.g., apricot.

    • Aggregate Fruits: Derived from multiple ovaries. E.g., raspberry.

    • Multiple Fruits: Derived from multiple flowers. E.g., pineapple.

  • Animal Attraction for Seed Dispersal:

    • Fruits attract animals, facilitating seed dispersal.

Asexual Reproduction Methods

  • Apomixis:

    • Embryos formed asexually producing seedlings genetically identical to the parent.

  • Vegetative Reproduction:

    • Cloning new plants from adult parts via stolons, rhizomes, or suckers.

  • Example: Quaking Aspen reproduces clonally from roots forming a clone named ‘Pando’, which contains 47,000 stems and may range up to 80,000 years in age.

Summary

  • The chapter concludes with insights into:

    • The diversity and trade-offs in plant reproduction mechanisms.

    • Comparative analysis of self and outcross pollination.

    • Importance of seed production and dispersal strategies.

    • Overview of asexual reproduction methods within plant species.