Unit II: Speciation Flashcards
Species
group of populations that interbreed and produce fertile offspring
Speciation
formation of a new species; a splitting event that creates two or more distinct species from a single ancestral species
Gene flow
Transfer of alleles from one population to another
- migration
- makes populations smaller
Reproductive isolation
Behaviors or processes that prevent gene flow between populations
- created opportunity for divergence
Allopatry
(occurring in different geographical areas) is an effective way to hinder gene flow between populations
Allopatric speciation
speciation that occurs via geographical separation
- most common mode of speciation
Without gene flow, there is opportunity for populations to _____ and become reproductively isolated.
diverge
What are 2 routes to allopatry?
- dispersal to a new habitat
- vicariance
With dispersal, the likelihood of speciation is ______ correlated with connectively between patches
negatively, high connectivity = low chance of speciation
What is Vicariance?
the physical splitting of a population into smaller, isolated populations by a physical barrier
With vicariance, the likelihood of speciation is _____ correlated with the strength of the barrier.
positively
Isolating mechanisms can be _______ (before zygote formation) or ________ (after zygote formation)
prezygotic, postzygotic
What are the types of mechanism that prevent the formation of a zygote?
- temporal
- habitat
- behavioral
- mechanical
- gametic
What is Temporal Isolation?
differences in breeding schedules that can act as a form of pre zygotic barrier leading to reproductive isolation
What is Habitat Isolation?
reproductive isolation resulting when species’ populations move or are moved to a new habitat, taking up residence in a place that no longer overlaps with the same species’ other populations; may never come into contact during mating periods = no hybridization
What is Behavioral Isolation?
type of reproductive isolation that occurs when a specific behavior or lack of one prevents reproduction from taking place (e.g. sound frequencies in mating calls are unattractive)
Does behavioral isolation extend to plants?
Yes, pollinators may favor different floral shapes or food (nectar)
What is Mechanical Isolation?
differences in size and shape of reproductive organs, making mating impossible (e.g. genital lock & key)
What is Gametic Isolation?
prezygotic barrier occurring when closely related individuals of different species mate, but differences in their gamete cells (eggs & sperm) prevent fertilization from happening
What are types of mechanisms that prevent zygotes from passing on alleles?
- Hybrid Inviability
- Hybrid Biological Sterility
- Hybrid Ecological Sterility
What is Hybrid Inviability?
hybrids do not survive to sexual maturity, instead they die during development or soon after birth
What is Hybrid Biological Sterility?
hybrids survive to maturity but do not produce gametes or are not fertile
What is Hybrid Ecological Sterility?
hybrids survive to maturity and are fertile, but have an intermediate phenotype that keeps them from reproducing (e.g. don’t attract mates or are not adapted to environment)
What is Reinforcement?
continued speciation divergence between 2 species due to low fitness of hybrids between them
Since producing hybrids decreased fitness, natural selection results in _____
reinforcement
