BIO112 Lec10 Speciation 2025
Speciation Overview
Speciation involves the process through which populations diverge and develop distinct characteristics over time.
Example: The divergence of the large ground finch and the medium ground finch from an ancestral population to distinct species on separate islands.
Importance of Speciation
Energy Sources:
Primary energy input comes from the sun.
Various organisms such as spiders, geckos, and mud wasps are part of a biodiverse web supported by solar energy.
Ecological Interactions:
Pollination and interactions among species, including palms, sunbirds, and insects, show the interconnectedness of biodiversity.
Nutrient Cycling:
Decomposers like fungi and organisms that break down organic matter contribute to nutrient release vital for plant growth like cassava.
Understanding Species
Definition of Species:
A species is often defined as a group of organisms that can interbreed and produce viable, fertile offspring.
Examples of Species:
Southern giant pouched rat, fruit bats, and various types of doves and skinks show the diversity of species.
Concepts of Speciation
Biological Species Concept
Species are reproductively isolated from one another, meaning they do not interbreed, or if they do, they produce no viable offspring.
Types of Isolation:
Prezygotic Isolation: Mechanisms that prevent mating or fertilization between species.
Postzygotic Isolation: Mechanisms that occur after fertilization that prevent the hybrid from developing into a viable, fertile adult.
Limitations:
Cannot be used for fossils or asexual organisms.
Limited applicability if populations do not overlap geographically.
Morphospecies Concept
Species identification based on physical traits, such as size and shape.
Advantages:
It does not require knowledge of gene flow and can be applied widely, including to fossils.
Limitations:
Issues with polymorphic (varying forms) and cryptic species, and subjectivity in determining morphological characteristics.
Phylogenetic Species Concept
Species identified based on evolutionary history, focusing on monophyletic groups (ancestral population plus all descendants).
Key Terms:
Monophyletic Group: All descendants from a common ancestor.
Synapomorphy: Traits unique to a monophyletic group, which can be morphological, behavioral, or genetic.
Advantages:
Applicable to any population and offers testable criteria.
Limitations:
Limited phylogenetic trees available; can identify more species than other concepts might suggest.
Mechanisms of Speciation
Allopatric Speciation
Occurs when populations are geographically isolated.
Steps:
Geographic isolation leads to separate environments for populations.
Divergence occurs through genetic drift and natural selection.
Ultimately leads to reproductive isolation.
Example: Snapping shrimp on either side of the Isthmus of Panama show clear separation and species divergence.
Sympatric Speciation
No geographic separation; populations coexist and diverge through other means, like behavioral differences or polyploidy.
Example: Apple and hawthorn flies exhibit preferences for different scents, leading to potential divergence.
Polyploidy in Speciation
Definition: A condition where a cell has more than two paired (homologous) sets of chromosomes.
Formation Process:
Autopolyploid: Results from errors during mitosis or meiosis, leading to increased chromosome numbers in offspring.
Allopolyploid: Hybrid offspring that are fertile and capable of subsequent generations, contributing to speciation in plants like wheat and cotton.
Advantages of polyploidy include higher genetic variation and the ability to adapt to new environments.
Secondary Contact Between Species
When two previously isolated populations come into contact again, several outcomes are possible:
Reinforcement: Natural selection favors traits preventing interbreeding.
Hybrid Zone Formation: A defined area where hybridization occurs.
Extinction of One Population: One population may outcompete the other.
Formation of New Species: Hybrids may occupy new ecological niches and adapt over time.