Chapter 14: How Biological Diversity Evolves Flashcards
Variation and the Evolution of Biological Diversity
Genetic Basis of Variation: Variation in shared traits among individuals is primarily the result of variations in alleles that influence those specific traits.
Defining Species
Etymology: The word "species" is derived from Latin, meaning "kind" or "appearance."
The Biological Species Concept: This concept defines a species as a group of populations whose members possess the potential to interbreed with one another in nature to produce fertile offspring.
Fertile Offspring: Defined as offspring that are themselves capable of reproduction.
The Speciation Process
Speciation: The biological process by which new species arise.
Reproductive Isolation: The cessation of gene flow between populations. Reproductive isolation is a fundamental and mandatory component of the speciation process.
Types of Isolation: Mechanisms for reproductive isolation are categorized as either prezygotic or postzygotic.
Prezygotic Barriers to Interbreeding
Prezygotic barriers are reproductive isolating mechanisms that prevent mating or fertilization between individuals of different species.
Temporal Isolation: This occurs when mating or fertilization happens at different seasons or different times of the day.
Example: The eastern spotted skunk and the western spotted skunk exhibit temporal isolation because they have different breeding seasons.
Habitat Isolation (Ecological Isolation): Populations live in different habitats within the same general area and therefore do not meet to mate.
Example: Two different species of garter snakes are isolated because one species lives primarily in water while the other lives on land.
Behavioral Isolation: There is little or no sexual attraction between populations due to specific behaviors.
Courtship Rituals: Many species use elaborate courtship rituals that are specific to their species, such as specific songs or visual displays.
Mechanical Isolation: Structural or anatomical differences in reproductive organs prevent successful fertilization.
Plant Examples: Differences in flower size or structure can require different pollinators, preventing cross-species fertilization.
Gametic Isolation (Gametic Incompatibility): Female and male gametes fail to unite during fertilization. The gametes may meet, but they are molecularly incompatible.
Example: The gametes of red sea urchins and purple sea urchins do not fuse because of the incompatibility of their surface proteins. A similar mechanism is found in various plant species.
Postzygotic Barriers to Interbreeding
Postzygotic barriers are reproductive isolating mechanisms that take effect after a hybrid zygote has formed.
Reduced Hybrid Viability: Hybrid zygotes fail to develop properly or fail to reach sexual maturity.
Example: Crosses between lions and tigers often result in reduced viability.
Reduced Hybrid Fertility: Hybrids are physically healthy but fail to produce functional gametes, rendering them sterile.
Example: A mule is the sterile offspring of a cross between a horse and a donkey.
Hybrid Breakdown: The first-generation hybrids are viable and fertile, but when they mate with each other or with either parent species, the offspring of the next generation are feeble or sterile.
Modes of Speciation
Allopatric Speciation: Speciation that occurs due to geographic isolation.
Mechanisms of Isolation: This can result from great physical distances or physical barriers such as deserts or rivers.
Examples: Ancestral housefinches and Hawaiian honeycreepers.
Galápagos Finches: These birds evolved different beak shapes adapted for specific diets:
Cactus-seed-eaters (cactus finch).
Tool-using insect-eaters (woodpecker finch).
Insect-eaters (warbler finch).
Sympatric Speciation: The emergence of new species without geographic isolation.
Polyploidy in Plants: This is a common mechanism for sympatric speciation in plants where chromosome numbers double or change, creating immediate reproductive isolation.
Evolution of Bread Wheat (Triticum aestivum):
Approximately years ago, a diploid wheat species (wild einkorn, Triticum urartu, ) hybridized with a diploid species of wild goatgrass (Aegilops species, ).
The resulting hybrid was Triticum ().
The chromosome number doubled to create the tetraploid () emmer wheat (Triticum turgidum, ).
Emmer wheat hybridized with another diploid goatgrass (Aegilops tauschii, ).
This resulted in common bread wheat (Triticum aestivum, ).
Parapatric Speciation: Speciation occurring when populations maintain contact along a common border but still evolve into distinct species.
Hybrid Zones: These are regions where members of different species meet and mate, producing at least some offspring of mixed ancestry.
Characteristics: Often involves reproductive isolation or the sterility of hybrids.
Example: The walking velvet worm.
Macroevolution and the Geologic Time Scale
Macroevolution: Refers to evolutionary changes at or above the species level, encompassing the major events in the history of life on Earth.
Taxonomic Groups: It involves the origin of new taxonomic groups.
Geologic Time Scale: This scale divides Earth's history into a consistent sequence of geologic periods.
Measuring Age:
Radiometric Dating: A method used to measure the age of rocks and fossils based on the decay of radioactive isotopes.
Half-life: The specific duration of time it takes for half of the atoms in a sample of a radioisotope to decay.
Continental Drift and Plate Tectonics
Continental Drift: Proposed in the early , this is the movement of Earth's continents relative to each other by appearing to drift across the ocean bed.
Pangaea: Approximately million years ago, plate movements brought all land masses together into a single supercontinent named Pangaea.
Breakup: Approximately million years after its formation, Pangaea began to break apart.
Plate Tectonics Theory: Developed in the , this theory explains how continents move. Earth’s crust is divided into giant, irregularly shaped plates that float on the mantle.
Plate Interactions:
Plates can move away from each other.
Plates can slide past each other, which often causes earthquakes.
Plates can collide, leading to the formation of mountain ranges.
Biological and Environmental Impacts:
Fossil Evidence: Explains why similar animal and plant fossils are found on different continents.
Environmental Reshaping: Alters the physical environment, climate, and habitats in which organisms live.
Evolutionary Consequences: Leads to species extinction while simultaneously providing new evolutionary opportunities.
Biogeography
Definition: The study of patterns in the geographic distribution of species.
Example: Large Flightless Birds: The distribution of specific flightless birds across different continents illustrates biogeographical patterns:
Emu: Found in Australia.
Rhea: Found in South America.
Ostrich: Found in Africa.
Patterns of Macroevolution
Stasis: A lineage that persists for millions of years with little or no observable change.
Exaptation: The adaptation of an existing biological structure for a completely different purpose (e.g., feathers originally for insulation later used for flight).
Mass Extinction: The permanent loss of a species or an entire group of species.
Adaptive Radiation: A process in which a lineage rapidly diversifies into several new species to exploit new resources or habitats.
Coevolution: The joint evolution of two closely interacting species, where each species exerts selective pressure on the other.
Specific Example of Coevolution (Ants and Caterpillars):
The caterpillar of the Maculinea arion butterfly exudes a honey-like substance and appears hunched up, mimicking an ant larva to the Myrmica sabuleti ant.
The deceived ant carries the caterpillar back to its nest.
Inside the nest, the caterpillar predates on ant larvae for the next months until it reaches the pupa stage.
The butterfly eventually emerges from the pupa and lays eggs on wild thyme flowers.
The larvae that emerge from these eggs will only survive if they are adopted by a colony of Myrmica sabuleti ants.