Biological basis of life and Mendel 1
Take home quiz How it works -Friday, June 30 at 5pm the quiz will be emailed and available on the course website DUE DATE: Sunday, July 2 at midnight -students must email their answers (in the email body or as an attachment) before the date above Format 20 questions total - 15 multiple choice and 5 short answer (must answer all five) Content Chapters 3 and 4 2
Modern Evolutionary Theory 5. Natural selection - acts on the variation produced and distributed by 1-4 -Directs change in the allele frequencies of a population relative to environmental factors Microevolution - small genetic changes that occur w/in a species Macroevolution - large-scale changes that occur in populations over many generations -result in speciation 3
Current theory of natural selection Natural selection provides directional change in allele frequencies relative to specific environmental factors If the environment changes, then selective pressures change too If there's long-term directional change, then allele frequencies will shift gradually each generation 4
Ch 5 Macroevolution 5
Taxonomy and Species Concepts Biological Species Concept (BSC) - isolated populations gradually change over time and become distinct taxonomic groups -Taxonomic grouping heavily influenced by genetic drift and natural selection Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Primates Family: Hominidae Genus: Homo Species: sapiens We are Homo sapiens (also H. sapiens for short). 6
Macroevolution aka speciation Macroevolution - synonymous with speciation Focus: large-scale evolutionary processes Synthesize our understanding of modes of evolutionary change, geologic time, and taxonomic classification 7
Homologies Homologies - Structures shared by species due to common descent E.g., Humans, birds, and bats: same basic bone structure but modified 8
Analogies Analogies - similar structures arise in other lineages in response to different functional demands 9
Classification schemes: Systematics and Cladistics Evolutionary Systematics: -use homologous traits to trace evolutionary relationships over time -focus: identify common ancestry between groups Cladistics: -uses homologous traits to separate organisms into taxonomic groups 10
Classification schemes: Systematics and Cladistics Similar: Both use homologies to trace evolutionary relationships Differ: Systematics uses homologies to trace common ancestry over time vs. Cladistics uses homologies to separate organisms into groups 11
Overview Slide (will be on site) Mendelian = discrete categories of variation Polygenic = continuous Both -determined by Mendelian principles at specific loci -Dominance and recessiveness still a factor Evolution now defined in two stages 1. Variation - inherited differences among organisms is produced and redistributed through various processes 2. Natural selection acts on variation resulting in differential reproductive success (85p). -Both mutations and natural selection contribute to evolution Current definition of Evolution - Change in allele frequency from one generation to the next. Allele frequencies = indicators of a group/population's genetic composition -Described as proportions or percentages of a total 12
Cladistics more explicit and rigorous Ancestral traits - similarities shared by many distantly-related groups that are inherited from a remote ancestor E.g., Grasping hand in humans -Mice, bears, and lizards all have lungs -Remember the similar bone structures between whales, bats, and humans? Derived traits - reflect specific evolutionary lineages -modified traits from last common ancestor unique to a given group 13
Adaptive radiation and ecological niche Adaptive radiation - rapid expansion and diversification of new life forms into open ecological niches. Speciation results in as many variations as allowed by (1) its adaptive potential; and (2) adaptive opportunities E.g., reptilian egg evolution spawned an adaptive radiation event by opening new adaptive niches on land. 14
Processes of Macroevolution Adaptive Radiation - rapid expansion and diversification of organisms into other ecological niches -Individuals of a species become diverse due to the differing environmental factors associated with a given ecosystem Generalized and Specialized Characteristics - adaptive radiation results in generalized characteristics *Generalized traits - adapted for multiple functions *Specialized species have more adaptive potential 15
Identifying paleospecies -grouped by the clusters of derived traits -use living species as proxy Concerns -variation spatially (over space) and temporally (through time) -fossils separated by millions of years. -expanded time frame = more dynamic image of species morphology -blurs taxonomic boundaries -Still a disputed process because of the concern with homoplasy 16
Variation in the fossil record Cladistics and the fossil record Individual variation - the variation seen in an individual's phenotype due to recombination Age change variation - some fossil forms have deciduous teeth (20) while others are matured to having permanent teeth (32) Sexual dimorphism - physical characteristics differ between males and females Remember these variables to avoid errors. 17
Types of variation continued Intraspecific - variation = individual, age, sex differences within species -If variation in fossils compares to related extant organisms, then disignate single species Interspecific - such variation represents differences between species Splitters - speciation occurred more often Lumpers - more likely intraspecific variability 18
Fossil Genera -a genus has at least 2 species that are distinct from each other Extinct genera -share adaptative zone. Adaptive zone = broader than ecological niche or econiche which are used to identify individual species. Ecological niche = position of a species in a physical/environmental context -diet, terrain, vegetation, predation, interaction with other species, etc. Anthro e.g., Fossilized primate teeth 19
Fossils preservation Mineralization - hard tissues are impregnated with other minerals and eventually solidify Insects encased in tree sap - No oxygen = well preserved insects (we can extract DNA from them!). 20
Fossils preservation Impressions of leafs/things - clay hardens into stone Anthr e.g., 47 mya well preserved primate skeleton with soft-body imprint and fossilized remains associated with the digestive tract (Franzen et al 2009). Footprints from dinosaurs and early Hominins Teeth: hardest, most durable portion of vertebrate skeleton and so most likely to mineralize Most available fossil data is inferred from teeth including primates 21
Fossils preservation -depends on how and where individual died Marine fossils are more frequent than land fossil organisms -circle of life leaves nothing left of the individual to fossilize -Need rapid sedimentation to cover up the individual or volcanic ash Taphonomy: studies how fossils are preserved - look at bone preservation and sedimentary processes 22
Vertebrate Evolutionary history Geographical changes in Paleozoic and Mesozoic influenced vertebrate evolution Continental drift - continents move like sliding plates on the Earth's surface (still happening today - slow process) -Large landmasses shifted dramatically throughout geologic time -Induces volcanic activity (Pacific Rim); mountain building (Himalayas); earthquakes Pangea - singular land mass during the late Paleozoic -large chunks split to the north and south in the early Mesozoic ~65 mya Isolation - isolated by oceans => distributed mammals and other land vertebrates 23
Vertebrate evolution -spans Paleozoic, Mesozoic, and the Cenozoic eras Fish ~500 mya in the Paleozoic (earliest out of reptiles, mammals, and birds) Continental drift = continents move like sliding plates on the Earth's surface -Large land masses move in geologic time Pangea - late Paleozoic singular land mass -Large chunks split to the north and south in the early Mesozoic ~65 my Mammal-like reptiles ~250 mya - diversify in Late Paleozoic Reptiles/dinosaurs ~252 mya = most dominant land vertebrates cf Mesozoic -expanded into a wide array of econiches 24
Cretaceous-Tertiary Mass Extinction ~66 mya = Cretaceous-Tertiary or K-T boundary -Large asteroid impacted the Earth caused dramatic changes in the global environment Ex: Plants and plankton could not photosynthesis 75% of plants and animals went extinct -Dinosaurs died off = empty ecological niches 25
Mammalian Evolution ~75 mya diverged -became dominant land-living vertebrates -rapid growth starting the Cenozoic Era Major Mammal Groups *Monotremes - egg-laying = most ancestral *Marsupials - pouched = immature young complete development in external pouch *Placental - long development period in utero and placental tissue specialized to provide nourishment 26
Distinctive mammalian features Large brains - complex information processing E.g., cerebrum enlarged - trend continued to increase in primates Placental - give live birth Heterodont - ancestral mammalian teeth patterns -generalized Endothermic - maintained constant internal temperature thru metabolic activities 27