Lecture 25: Macroevolution part 2 : Diversification Flashcards
- Radiation & Extinction influenced by. (3)
- Biotic factors – mutation, selection, drift, migration, mating patterns
- Abiotic factors (climate, composition of atmosphere & oceans, habitat).
- Continental movement, asteroid impact
The ediacaran biota (5)
-The Ediacaran Biota took place in the precambrian
-565-544 MYA
-discovered in the 1940s when Compression and impression Fossils found in Australia of organisms without shells.
-these fossils were of sponges, jellyfish , and comb jellies all with radial symmetry
-First unequivocal evidence for macroscopic animal life
Burgess Shale Fauna (4)
-Discovery of large, complex and bilaterally symmetrical fossils
-Dated to 505 MYA
-These animals were similar to those found in the Chenjiang Biota (520 MYA)
-Showcased that A LOT happened between 544 (edicaran biota) and 520 (Chenjiang Biota)
Problematica (4)
-The Burgess shale fauna also contained many organisms not obviously related to any extant (still alive) phyla
-These are sometimes grouped together as “problematica” bc they’re problematic
-some studies suggest that these orgs are actually members or close relatives of existing living phlya
-ex: Opabinia as lateral plates, dorsal eyes and a “Nozzle” is now thought to belong to arthropods
Cambrian explosion
-Something CRAZY happened during the Cambrian
-Appearance of the earlies members of Virtually all major animal lineages appeared relatively suddenly at the same time in may parts of the world
-The Cambrian explosion only accounts for 1% of earth’s history!
Diversification in the Cambrian explosion (3)
There was great diversification in terms of:
- Morphological innovations: large body size, segmentation, limbs, antennae, shells, external skeletons, notochords
- Locomotion: swimming, burrowing, crawling, floating, walking
- Feeding: filter feeders, benthic and pelagic predators, grazer, scavengers, detritivores
Macroevolution definition
Macroevolution: evolution at or above the species level. Process the same as microevolution but thinking at different timescales
What “Lit the fuse” (5)
-Lineages existed long before they diversified and produced large-bodied forms
-Size increase accompanied by appearance of hard shells in many taxa
-Better fossilized structures (Size/hard structures) lead to an apparent explosion of animal morphologies in Cambrian
-Increased sizes have been connected with ecological changes (e.g., in atmosphere or oceanic geochemistry) Especially rising oxygen concentrations in sea water due to increase in photosynthetic algae during Proterozoic
-Makes larger size and higher metabolic rate possible and thus, evolution of tissues and powered movement
Macro vs Micro evolution
Microevolution = changes in gene frequencies and trait distributions within species and populations
Macroevolution = large evolutionary change, results from micoevolutionary processes but patterns are among species and on a larger scale
Adaptive radiation (3)
-Single or small group of ancestral species rapidly diversifies into large number of descendant species
-“Great deal of evolution” in a “relatively short amount of time”
-Usually occupy wide variety of niches
What triggers adaptive radiation (3)
- Ecological opportunity: Lack of competitors permits diversification to fill unoccupied niches, usually following colonization of an depauperate environment (lacking in numbers of individuals or number of species)
2). Extinction of other taxa. EX diversification of mammals after the dinosaurs went extinct. Same idea as ecological opportunity
3). Morphological innovation. EX jointed limbs developing in arthropods allowed them to take advantage of a variety of niches
Radiation of terrestrial plants from aquatic ancestors (4)
-440 MYA
-Land had Biologically accessible minerals in substrate, moist cool climate (ecological opportunity)
- Key features were waxy cuticles, stomata, roots (morphological innovation)
-Lead to radiation of angiosperms as well, who innovated the flower resulting in 250,000 species today
Hypothesis for angiosperm success (3)
- Co-evolution with insect pollinators
- increased global temps and CO2 levels favored angiosperms
- Dinosaur grazing habits reduced gymnosperm success and created habitats for the angiosperms to move into
Stasis (2)
-Absence of evo change in one or more characters for some period of time
-Goes hand and hand with radiation
Phyletic gradualism (4)
-Evolution by creeps
-Darwin emphasized the gradual nature of evolution by natural selection to contrast the instantaneous creation of new forms presented in the Theory of Special creation (god)
-He considered the lack of transitional forms to be a problem in his theory, but attributed it to the fossil record being incomplete
-Was accepted for the next 1000 years
Punctuated equilibrium (4)
-evolution by jerks
-Opposed gradualism in 1972
-claimed stasis is real pattern in fossil record
-Morphology is static within a species and variation occurs at the time of speciation
Testing stasis (4)
-tested in bryozoans (moss animals) that resemble coral.
-They are abundant in the fossil record and their phylogeny is well known
-None of the populations showed traits intermediate between species and Characteristics of species were stable through time
-Shows unequivocal pattern of stasis punctuated by rapid morphological change = Variation among species is discontinuous
Stasis vs gradualism (3)
-Paleontological evidence overwhelmingly supports a view that speciation is sometimes gradual and sometimes punctuated, and that no one mode characterizes this very complicated process in the history of life.
-gradualist patterns seem to predominate in many microscopic marine taxa
-stasis appears more common in macroscopic fossils e.g., arthropods, bivalves, corals, bryozoans
Living fossils (2)
-Species or clades that show little or no measurable change over millions of years
-includes horsetail and ginkgo plants as well as coelacanths and horseshoe crabs
Why does stasis happen? (4)
-tested genetic variation between king and horseshoe crabs
-found that variation in both species was the same even though the horseshoe crabs had little morphological differentiation
-likely due to relatively stable environment, where stabilizing selection occurs around an optimal phenotype
-If it aint broke dont fix it
