speciation
DESCRIPTION
Speciation. Introduction. Species continue to evolve Changes that occur within species (microevolution) are easy to understand F aster-running cheetahs Colourful male songbirds Larger brains in humans But what factors lead to speciation - the evolution of an entirely new species?. - PowerPoint PPT PresentationTRANSCRIPT
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Speciation
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Introduction
• Species continue to evolve• Changes that occur within species
(microevolution) are easy to understand– Faster-running cheetahs– Colourful male songbirds– Larger brains in humans
• But what factors lead to speciation- the evolution of an entirely new species?
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What is a Species?
• A species includes all members of a population that can interbreed under natural conditions
• Some species are quite distinct based on their morphology but some species are only distinguished by genetic comparisons
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Modes of Speciation
• New species can evolve many ways
• Always includes the evolution of distinct features that isolate the new species reproductively, therefore genetically, from other species
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Mechanisms of Reproductive Isolation• any biological factor that prevents the two
populations from interbreeding when living in the same region.
• Prezygotic mechanisms: prevents interspecies mating and fertilization– Different breeding seasons, physical or
behavioural traits, habitat preferences or the incompatibility of gametes
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Mechanisms of Reproductive Isolation• any biological factor that prevents the two
populations from interbreeding when living in the same region.
• Postzygotic mechanisms: prevents maturation and reproduction in offspring from interspecies reproduction
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Mechanisms of Reproductive IsolationPrezygoticTemporal Isolation: Species have different breeding
seasons.
Example: Western spotted skunks breed in the fall but the Eastern species breeds in late winter
Western Eastern
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Eastern Western
Mechanisms of Reproductive IsolationPrezygoticBehavioural Isolation: Species may have different
courtship or mating behaviours.
Example: Eastern meadowlark and western meadowlark are almost identical in everything, except their courtship rituals and songs
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Mechanisms of Reproductive IsolationPrezygotic Mechanical Isolation: Species may have reproductive
structures that are physically incompatible.
Example: Snails of the same species have reproductive structures that align, but snails from two different species part the other species
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Mechanisms of Reproductive IsolationPrezygotic Ecological Isolation: very similar species may occupy
different habitats within a region
Example: The mountain bluebird lives at high elevations, while the eastern bluebird prefers lower elevations. The mountain bluebird and eastern blue bird do not encounter each other
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Mechanisms of Reproductive IsolationPrezygoticGametic isolation: male gametes may not be able to
recognize and fertilize an egg of a different species
Example: corals, clams and sea cucumbers release their sperm and eggs into open water. The sperm recognize the egg of their own species through chemical markers on the egg surface.
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Mechanisms of Reproductive IsolationPostzygoticZygotic Mortality: mating and fertilization are possible,
but genetic differences result in a zygote that is unable to develop properly
Example: If you have sheep and goats on a farm, some species of sheep and goat are able to mate, but the zygote is not viable.
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Mechanisms of Reproductive IsolationPostzygoticHybrid Inviability: a hybrid dies early in development,
or lives to maturity but is not healthy and suffers an early death.
Example: Some salamanders species may mate with each other, but most of the offspring do not live to adulthood, or if they do they are weak.
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Mechanisms of Reproductive IsolationPostzygoticHybrid Infertility: The hybrid offspring mature into
adults but are infertile.
• Example: A mule is bred from a female horse (left) and a male donkey (centre). Mules are physically healthy but they are infertile.
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Allopatric Speciation• Most new species form when a
single species is separated into two geographically isolated populations
• Once physically separated, populations cannot share genetic information
• Over many generations the populations will gradually become less alike
• Mutations and genetic drift may have caused populations to change
• Reproductive isolating mechanisms may have developed
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Allopatric Speciation
Harris’s antelope squirrelWhite-tailed antelope squirrel
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Sympatric Speciation• The evolution of populations
within the same geographic area into separate species
• Individuals within a population become genetically isolated from the larger population