Introduction Biology 351 Comparative Anatomy Dr Tony Serino

Introduction Biology 351 Comparative Anatomy Dr. Tony Serino Misericordia Univ.

Comparative Anatomy • The study of morphology between species to understand evolutionary trends. • Evolutionary Morphology • Uses both living and extinct species • Can be combined with Comparative Physiology

Darwin’s Theory (1859)

Darwin’s Observations • All species over produce • Most populations are normally stable • Natural resources are limited

Darwin’s Observations Individuals of a population vary from one another Much of this variation is inheritable

Darwin’s Inferences • Over reproduction leads to a struggle (competition) for resources and survival with only a fraction surviving to reproduce successfully • Those who are better fitted (adapted) to their environment more often succeed to survive and reproduce • This results in the population changing to increase the frequency of those alleles which increase the survival rate.

Evolution- Descent with modification by means of natural selection to better adapt to their environment • Differential success in the survival and reproduction of individuals in a population changes the frequency of alleles in the gene pool such that the population adapts to its environment (increases its fitness)

Descent with Modification

Evidence of Evolution • Biogeography – study of the geographic distribution of populations

Evidence of Evolution • Comparative Anatomy & Physiology – study of common characteristics, processes, and/or behaviors • Homologous Structures • Vestigial organs

Evidence of Evolution • Fossil Record

Fossils

Evidence of Evolution • Comparative Embryology –study of animal development

Evidence of Evolution • Molecular Biology study of important molecules in living cells; degree of conservation of molecular structure indicates relatedness between species

Microevolution • Generational changes in allele frequency in a population over time. • May lead to formation of new species Darwin in 1874

Mechanisms for Microevolution • Genetic drift –random changes in small gene pool survival based on random chance (seeds happen to fall on fertile ground)

Genetic Drift: Founder Effect • Small random number of individuals move to a new location • Chance alone dictates what alleles moved to start new population • Ex. Galapagos finches – a storm blew a completely random number of birds from the main land to the islands.

Genetic Drift: Bottleneck Effect • Large environmental change that randomly kills off most of the population

Other Mechanisms for Microevolution • Gene flow –change in gene pool frequencies due to migration of individuals between populations • Mutation –change in gene structure changes allele frequency (only mechanism that can create new alleles) • Non-random mating –changes allele frequency due to choices in mating; ex. Inbreeding, assortative mating, sexual selection • Natural Selection –change in allele that adapts the population better to its environment

Types of Natural Selection

Speciation –generation of new species • Two types: – Anagenesis –one species evolves into another – Cladogenesis –one species evolves into several new species (like, in adaptive radiations); forms a lineage or clade

Cladogenesis • Requires reproductive isolation to occur – Behavior, Temporal, Mechanical, Gametic, etc. Main modes for reprod. isolation: • Allopatry –geographical isolation leading to reproductive isolation • Sympatry –reproductive isolation arising within the parent’s population habitat

Grand Canyon Ground Squirrels The formation of the Grand Canyon 10, 000 ya led to allopatric isolation of the rims squirrel populations eventually forming new species

Macroevolution –refers to large scale patterns, trends and rates of change in groups of species over time • Two theories on rate of evolution: Gradualism and Punctuated Equilibrium • Related concepts: – Pre-adaptation –pre-existing structures used to fulfill new role (biological role vs. function) • Ex: feathers (as insulator and later flight), • Some fish fins tetrapod limbs for walking

Heterochrony –evolutionary changes in the timing or rate of developmental growth Tree dwelling salamanders have shorter more webbed feet; growth of the foot ends sooner.

Heterochrony –change in timing of developmental development; may result in: Allometric Growth –differential growth of body regions results in the adults shape

Heterochrony –change in timing of sexual development; may result in: Paedomorphosis (Neoteny) Retention of juvenile characteristics in the adult

Plate tectonics

Continental Drift

Adaptive Radiations

Geological Time Scale

Geologic Timeline of Earth *mya – millions of years ago Era Cenozoic (Age of Mammals) Period Quaternary Time (mya)* 1. 8 Tertiary 65 Cretaceous 144 Mesozoic (Age of Dinosaurs) Jurassic 206 Triassic Important Events Historical time; Ice age, Humans appear Mammals, Teleosts, Birds, Insects and angiosperms undergo major radiation Cretaceous extinction (includes dinosaurs), angiosperms appear Dinosaur and gymnosperms dominate Major radiation of dinosaurs and gymnosperms; extinction near end of period of many early dinosaur groups 245 Permian 290 Paleozoic (Age of Fish) Carboniferous (Pennsylvanian and Mississipian periods) (Age of Amphibians) Devonian (Age of Teleosts) Permian Mass Extinction (half of all life forms become extinct); radiation of reptiles Amphibians and vascular plants dominate, first reptiles and seed plants appear 363 Radiation of bony fish, first amphibians and insects appear; extinction of many jawless fish 409 Silurian 439 Ordovician Diversity of jawless fish and early vascular plants; first jawed fish appear 510 Marine alga abundant, colonization of land by arthropods and plants 543 Radiation of most modern animal phyla (Cambrian Explosion) Cambrian Precambrian Formation of Earth and its biosphere, Life begins (Archaebacteria) about 3800 mya; Oxygen begins to dominate atmosphere about 2700 mya; 600 mya soft-bodied invertebrates and algae thrive (Pre-cambrium Explosion) 4600

Types of Macroevolution: Convergent Evolution

Types of Macroevolution: Co-evolution -ants and acacia tree -lions, prey, and scavengers

Types of Macroevolution: Divergent Evolution

Phylogeny –course of evolution • Dendrograms –branching “tree” diagrams depicting possible phylogeny usually by assorting organism by their similarities or common features • Systematics –study of biological diversity in an evolutionary context; links groups together is some logical pattern – Traditional systematics –places organisms in same taxon (group) if they share homologous structures – Phylogenetic systematics (cladistics) –places organisms in the same clade (lineage) (all the organisms in that lineage plus their common ancestor) Example of Lungfish –traditional may put with other organisms with lung; Cladistics would group only with fish

Hierarchal Classification -usually only group organisms together by morphological structures Binomial system for naming species

Cladistics –uses multiple characters to group organisms -may include morphology, fossils, molecular data, etc. Cladograms allow us to explore relationships easily, but can lead to redundant terminology

Cladistic Relationships Monophyletic taxons include an ancestor and all of its descendants Paraphyletic taxons include a common ancestor but only some (not all) of its descendents (an artificial grouping) Polyphyletic taxons place animals together for non-homologous similarities (an artificial grouping)

Other Important Anatomical Concepts Similarity Comparisons • Homology –structures in two different species are homologous if they can be traced back to a feature in a common ancestor • Analogy –structures which share a common function • Homoplasy –structures with similar appearance Note: primitive vs. derived

Symmetry

Body Planes

Anatomical Directions

Segmentation (metamerism)