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Unformatted text preview: EVOLUTIONARY TRENDS EVOLUTIONARY TRENDS
SPECIATION CHAPTER 19 . WHAT IS A SPECIES WHAT IS A SPECIES SPECIES CAN NOT BE IDENTIFIED BY APPEARANCE ALONE. THE “BIOLOGICAL SPECIES CONCEPT” DEFINES SPECIES AS : “ONE OR MORE GROUPS OF INDIVIDUALS THAT INTERBREED AND PRODUCE VIABLE, FERTILE OFFSPRING, AND ARE REPRODUCTIVELY ISOLATED FROM OTHER SUCH GROUPS” LIMITS TO THE BIOLOGICAL LIMITS TO THE BIOLOGICAL SPECIES DEFINITION CAN NOT APPLY TO ORGANISMS THAT DO NOT REPRODUCE SEXUALLY CAN NOT BE APPLIED TO THE FOSSIL RECORD A MORE RECENT DEFINITION A MORE RECENT DEFINITION “A SPECIES IS ONE OR MORE POPULATIONS OF INDIVIDUALS THAT SHARE AT LEAST ONE STRUCTURAL,FUNCTIONAL, OR BEHAVIORAL TRAIT—THE LEGACY OF A COMMON ANCESTOR—THAT SETS THEM APART FROM OTHER SPECIES.” The definition “A species is a group of individual that share the same gene pool and can breed producing viable, fertile offspring” is the definition that will be used in this course. Simplified diagram of genetic divergence SPECIATION IS THE FORMATION OF A DAUGHTER POPULATION OR A SUB POPULATION FROM A PARENT POPULATION. THE NEW POPULATIONS CAN NO LONGER INTERBREED WITH THE PARENT POPULATION OR WITH OTHER DAUGHTER POPULATIONS. “Reproductive isolation” time A time B time C time D parent species time daughter species REPRODUCTIVE ISOLATING REPRODUCTIVE ISOLATING MECHANISMS THAT LEAD TO GENETIC DIVERGENCE PREZYGOTIC MECHANISMS GAMETE MORTALITY TEMPORAL ISOLATION BEHAVIORAL ISOLATION ECOLOGICAL ISOLATION MECHANICAL ISOLATION POST ZYGOTIC ISOLATING MECHANISMS EARLY DEATH STERILITY WEAK HYBRIDS . TEMPORAL ISOLATION POPULATIONS CAN NOT INTERBREED WHEN THEIR TIMING OF REPRODUCTION DIFFERS. Fig. 19-4b, p.302 Behavioral Isolation Behavioral Isolation IN MANY SPECIES FEMALES ARE GENETICALLY “PREWIRED” TO RECOGNIZE SPECIFIC COURTSHIP PATTERNS. IF THE CORRECT COURTSHIP PATTERN DOES NOT OCCUR, MATING WILL NOT PROCEDE. ie: Courtship displays of the Albotross Fig. 19-4d, p.302 Fig. 19-4e, p.302 Fig. 19-4c, p.302 ECOLOGICAL ISOLATION ECOLOGICAL ISOLATION
EVEN WITHIN THE SAME GIVEN AREA THERE MAY BE SLIGHT VARIATIONS IN THE ENVIRONMENT EXAMPLES MIGHT BE DIFFERENT ALTITUDES, AVAILABILITY OF WATER OR SUNLIGHT, SALINITY OF SOIL OR OTHER VARIATIONS IN NUTRIENTS. POPULATIONS ADAPTED TO ONE TYPE OF ENVIRONMENT ARE LESS LIKELY TO INTERACT (OR BREED) WITH POPULATIONS ADAPTED TO A DIFFERENT ENVIRONMENT ie: the Manzanita plant in the Sierra Nevada foothills .MECHANICAL ISOLATION THE BODY PARTS OF A SPECIES ARE NOT A PHYSICAL MATCH WITH THOSE OF A SPECIES THAT COULD OTHERWISE SERVE AS A MATE OR POLLINATOR. Fig. 19-4a, p.302 Fig. 19-5, p.303 Types of Speciation Types of Speciation Allopatric speciation Sympatric speciation Parapatric speciation Allopatric Speciation Allopatric Speciation “different lands” Speciation in geographically isolated populations Some sort of barrier arises and prevents gene flow Effectiveness of barrier varies with species Extensive Divergence Extensive Divergence Prevents Inbreeding Species separated by geographic barriers will diverge genetically If divergence is great enough it will prevent inbreeding even if the barrier later disappears Archipelagos Archipelagos (an example of allopatric speciation) Island chains some distance from continents
– Galapagos Islands – Hawaiian Islands Colonization of islands followed by genetic divergence sets the stage for speciation Speciation Speciation on an Archipelag o A few individuals of a species on the mainland reach isolated island 1. Speciation follows genetic divergence in a new habitat. 1 2 3 4 Later in time, a few 1 individuals of the new species colonize nearby island 2. In this new habitat, speciation follows genetic divergence. 2 Fig 19-7, p. 305 Speciation may also follow colonization of islands 3 and 4. And it may follow invasion of island 1 by genetically different descendents of the ancestral species. 1 2 3 4 Hawaiian Islands Hawaiian Islands Volcanic origins, variety of habitats Adaptive radiations:
– Honeycreepers In absence of other bird species, they radiated to fill numerous niches – Fruit flies (Drosophila) 40% of fruit fly species are found in Hawaii Hawaiian Honeycreepers Hawaiian Honeycreepers FOUNDER SPECIES
Fig.18-7, p. 297 . Allopatric Speciations
DUE TO THE MOVEMENT OF THE EARTH’S CRUST OCCASIONALLY A LAND BRIDGE WILL FORM EARLY “CAMELIDS” CROSSED THIS BARRIER INTO S.AMERICA Fig. 19-6c, p.304 Allopatric Speciations Fig. 19-6b, p.304 Allopatric Speciations Fig. 19-6a, p.304 ALLOPATRIC SPECIATION AND ALLOPATRIC SPECIATION AND SNAILS Snails were brought to an area in Texas Roads were built as neighborhoods were established A road is as inviting to a snail as a desert is to a catfish The road was an effective barrier separating the snail populations ALLOPATRIC SPECIATION ALLOPATRIC SPECIATION snail populations divided by barriers Speciation without a Speciation without a Barrier Sympatric speciation
– Species forms within the home range of the parent species Parapatric speciation
– Neighboring populations become distinct species while maintaining contact along a common border Sympatric Speciation in Sympatric Speciation in African Cichlids Studied fish species in two lakes No barriers within either lake Some ecological separation but species in each lake breed in sympatry – Species in each lake are most likely descended from single ancestor Sympatric Speciation in African Cichlids Fig. 19-8a, p.306 Sympatric Speciation in African Cichlids Fig. 19-8c, p.306 Sympatric Speciation in African Cichlids Fig. 19-8b, p.306 Speciation by Polyploidy Speciation by Polyploidy Change in chromosome number (3n, 4n, etc.) Offspring with altered chromosome number cannot breed with parent population Common mechanism of speciation in flowering plants Speciation by Polyploidy Fig. 19-9, p.306 Parapatric Speciation Parapatric Speciation
Adjacent populations evolve into distinct species while maintaining contact along a common border BULLOCK’S ORIOLE BALTIMORE ORIOLE EXAMPLES: ORIOLES, VELVET WORM HYBRID ZONE . Parapatric Speciation
T. barretti THE TWO HABITATS OF THE GIANT VELVET hybrid zone WORM AND THE BLIND T. anophthalmus VELVET WORM OVERLAP IN A HYBRID ZONE, BUT, WHEN THE DIFFERENT SPECIES MATE, THEIR HYBRID OFFSPRING ARE STERILE. Fig. 19-11c, p.307 Parapatric Speciation Fig. 19-11b, p.307 Parapatric Speciation Fig. 19-11a, p.307 PATTERNS OF SPECIATION PATTERNS OF SPECIATION
*(THE EVOLUTIONARY TREE) EVOLUTIONARY TREEsummary ofthe relationships among groups GENETIC DIVERGENCEa branch point in the evolutionary tree ADAPTIVE RADIATIONa burst of divergences from a single lineage, that fill “niches” or ADAPTIVE ZONES EXTINCTIONthe end of the line PATTERNS OF SPECIATION PATTERNS OF SPECIATION *RATES OF CHANGE GRADUAL MODEL rate of change happens over a very long period of time. PUNCTUATION MODELrate of change happens rapidly , over a “brief geological period of time”. Evolutionary tree designs
new species branch point (a time of divergence, speciation) extinction (branch ended before present) branch point (a time of divergence, speciation) a new species dashed line (only sketchy evidence of presumed evolutionary relationship) a single lineage a single lineage Fig. 19-14a, p.309 Fig. 19-19, p.314 MADELINE’S LIMBS . OUR FAMILY TREE IS A RECORD OF CONSERVED AND DERIVED TRAITS Fig. 19-20b, p.315 ...
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