1B (Animal) Notes - Bio 10B PDF
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Pasadena City College
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These notes provide a summary of animal evolution and diversification, covering topics such as initial animal characteristics, the Cambrian explosion, and the role of Hox genes. The information is organized into sections with sub-sections, including a section on the evolution of animals, a discussion of the Hox genes, and additional notes on the creation and development of phenotypes.
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1B. Explain how various mechanisms have caused diversification of life on earth (Animals) Animal Evolution and Diversification What is an Animal? ○ Eukaryotic, multicellular, heterotrophic organisms that obtain nutrients by ingestion...
1B. Explain how various mechanisms have caused diversification of life on earth (Animals) Animal Evolution and Diversification What is an Animal? ○ Eukaryotic, multicellular, heterotrophic organisms that obtain nutrients by ingestion ○ Digest their food within their bodies ○ Nervous & muscle tissue ○ Evolved from a colonial protist called a choanoflagellate Choanoflagellates are colonial - individuals aggravate together - but are not multicellular Shows evidence for multicellularity Cambrian explosion (545 mya) ○ First thing was a squishy simple thing in the ocean ○ May have developed things like armor ○ The fossil record reveals all of the phyla we have today Although fossils look familiar, they are not the same with what we have today All of the phyla had already evolved Phylogeny of animals ○ The big 9 - more diverse Arthropoda, nematoda, platyhelminthes, annelida, mollusca, chordata, echinodermata, cnidaria, porifera(sponges) More simple on bottom Cambrian explosion Cambrian explosion ○ What ignited the Cambrian explosion? H1: New predator-prey relationships generated diversity through NS Trilobites; ex: selection pressures - different ways to defend yourself and that shows as a phenotypic characteristic H2: Increase in oxygen levels enabled animals to develop higher metabolic rates & larger body size And achieve more complexity Oxidative phosphorylation - using more oxygen in as an electronic sector in the electron transport chain that yields many, many more ATP molecules, which are the molecules that we use to generate energy H3: The evolution of the Hox genes enabled developmental flexibility Hox genes ○ Transcription factors that regulate gene expression during development T his protein actually moves to the DNA and binds to the DNA sequence to act as a switch that either switches on the expression of a gene that it’s attached to or switches it off Hox genes are ordered in the same way as they are ○ expressed in the body More on Homeobox Genes and Development How were HOX genes discovered ○ Scientists will zap them with radiation and see if their genes mutate and lead to phenotypic change Grew legs in their head where antennae should be Found HOX genes that control limb development Different animals possess the same HOX gene ○ Humans, mouse, and fruit flies all have the pax6 genes which control eye Mutations may lead to innovation ○ animal s have hox genes ○ These genes are lined up along the chromosome in the same order in which they express body parts along the body plan ○ Similarly related organisms have similar hox genes ○ Mutations are common in animals ○ Duplications of hox genes or duplications of whole hox clusters Which are the suite of hox genes down on chromosome Mice have at least 4 hox clusters V ariations in HOX genes are instrumental in the variation of body plans in arthropods ○ Arthropods are from different classes S ○ imilarities in overall body plan ○ Always have most of the different body regions but the details of each of those body regions looks different Hox gene evolution: macroevolutionary change ○ Evolution rarely creates a new gene, rather it “tinkers” with existing parts in new ways Heterotopy: change in location BMP causes apoptosis In ducks, gremlin inhibits BMP and they come out with webbed feet Heterochrony: change in time Bones are different length because they grew for longer or shorter times during development Heterometry: change in amount Change in amount of particular transcription factor/HOX genes ○ Cal module and BMP Both have shown to influence beak sizes Cal module influences how short or long BMP influences how deep or wide Heterotypy: change in kind Change in the function of a particular protein Ex: Change in Ubx protein structure ○ Before, Ubx did not inhibit Distal-less (influences number and structure of legs) - centipedes have many legs. Now, Ubx inhibits Distal-less - insects have only 6 legs. The evolution of invertebrates the evolution of vertebrates ○ origin from invertebrates ○ distinguishing characteristics of chordates all vertebrates belong to the phylum Chordata ○ which also includes two groups of invertebrates cephalochordata and urochordata 5 key traits shared by organisms classified as chordates are ○ A notochord, dorsal hollow nerve cord, pharyngeal gill slits, a postanal tail, and an endostyle or thyroid gland evolutionary relationships and the development of key traits among vertebrates ○ role of Hox genes in controlling the development of animal body plans ○ differences between invertebrate and vertebrate homeobox gene clusters Vertebrates evolved from invertebrates and possess a vertebral column, unlike invertebrates. The phylum Chordata includes both vertebrates and invertebrates, such as cephalochordata and urochordata. Organisms classified as chordates share five distinguishing characteristics. Urochordates exhibit chordate traits in the larval stage but lose them in adulthood. V ertebrates are differentiated from invertebrates by their internal skeletons, vertebral columns, and the presence of a brain. Homeobox genes play a crucial role in controlling the development of animal body plans. Vertebrates have multiple copies of the homeobox gene cluster, unlike invertebrates. The duplication of homeobox gene clusters and the subsequent mutations and losses of individual genes contributed to the evolution of vertebrate traits. Meet the Family Cichlida phenomenon of speciation and reproductive isolation in the Cichlidae family of fish, particularly in lakes of East Africa such as Lake Victoria and Lake Malawi cichlid fish represent the largest family of species in vertebrates ○ over 3000 known species worldwide explosive speciation of cichlid fish in Lake Victoria ○ more than 500 endemic species exist, is exceptional and unexplainable by traditional neo-Darwinian views of speciation ○ suggests that no recent genetic bottlenecks or changes in alleles have occurred, and interbreeding between endemic forms still produces viable and fertile hybrids ○ For a long time, allopatric speciation has been considered to be the most important, if not the only, mechanism of speciation in Lake Malawi ○ OR arose via “intralacustrine microallopatric speciation” as a result of differential preferences in diet or microhabitat specialization Interbreeding between endemic cichlid fish forms in Lake Victoria still produces viable and fertile hybrids. In Lake Malawi, over 500 endemic cichlid fish species have evolved from a common ancestor within the last 700,000 years ○ sexual selection potentially playing a role in their speciation Laboratory experiments have shown that reproductive isolation of three morphologically similar species of rock-dwelling cichlid fish, living sympatrically in the lake, relies not on postzygotic but on prezygotic (sexual behavior) barriers between them Speciation through sensory drive in cichlid fish Sensory drive refers to the idea that an animal’s sensory system and its ability to perceive signals from others in the population can be a selection pressure in the context of mate choice, if a male cichlid fish develops coloration that is appealing to females’ sensory systems, it may attract more attention and have more offspring, leading to the spread of this trait throughout the population importance of the environment in shaping perception and preferences, as the most effective visual signals are likely to be those that match the local light conditions speciation processes observed in cichlid fish, where hundreds of species have evolved rapidly within lakes, even in the absence of geographical barriers. Speciation through sensory drive: Empirical evidence hypothesized that speciation through sensory drive in cichlids would be supported by variations in the long wavelength sensitive (LWS) opsin sequence, an association of
