Mammalogy Exam 2 Study Guide
Mammalogy Exam 2 Study Guide
Topic 3: Evolution and Systematics
Definitions
Taxonomy: The process involving the naming of organisms and the classification of organisms into a hierarchical scheme.
Systematics: The scientific discipline focused on resolving the historical (or phylogenetic) relationships among organisms.
Understanding Evolution
Technical Definition of Evolution: A change in gene frequency over time.
Intuitive Definition of Evolution: A change in the characteristics of organisms over time.
Three Mechanisms of Evolution:
Drift: Resulting from chance events or sampling errors.
Example: In a population with 70% gray and 30% black individuals, a natural disaster reduces the population, resulting in a new ratio of approximately 33.3% gray and 66.7% black, purely by random chance.
Gene Flow: This refers to the exchange of genes between different populations.
Natural Selection: The mechanism wherein individuals with advantageous traits survive and reproduce more effectively than others.
Assumptions of Natural Selection:
Individuals vary in characteristics.
Variation is heritable.
Individuals with specific attributes have higher survival and/or reproductive rates.
Mechanisms of Trait Generation
New traits emerge from alterations of genes associated with pre-existing traits. Common modifications include:
Mutations: Alterations in the DNA sequence.
Changes in Gene Expression: Variability in how much or how little genes are expressed.
Gene Silencing: The process by which a gene's expression is inhibited.
Gene Duplication: The process in which segments of DNA are duplicated, leading to additional copies that may evolve new functions.
Outcomes of Natural Selection
Adaptation: The adjustment of organisms to environmental conditions over time, linked with anagenesis, which refers to changes within a lineage.
Speciation: The emergence of new species, associated with cladogenesis which pertains to lineage splitting.
Reading Evolutionary Trees
Each bifurcation (branching point) in a phylogenetic tree signifies a historical speciation event.
The axis represents relative evolutionary time.
The characters are heritable traits used for constructing the tree.
Phylogenetic Terminology
Clade: A group comprising an ancestor and all of its descendants.
Monophyletic Group: A complete clade containing all descendants with no members outside the clade.
All clades are, by definition, monophyletic.
Crown Group: The common ancestor to all modern mammals.
Stem Group: The common ancestor to amniotes.
Ancestral Trait: A trait that was present in the ancestor.
Derived Trait: A trait present in a descendant organism but absent in the common ancestor.
Understanding Phylogenies as Hypotheses
Phylogeny: A hypothesis about the evolutionary relationships among a group of organisms.
Data Types Used to Construct Phylogenies:
Morphological characteristics.
DNA sequences.
Fossils.
Embryological development insights.
Vestigial structures.
Methods for Developing Phylogenetic Trees
Phenetics: A method to construct phylogenies based on overall similarity of organisms.
Utilizes DNA sequences via DNA-DNA hybridization:
Heat the DNA from two species, mix with single-stranded DNA, cool to allow hybrids to form, separate hybrid double strands, and measure the energy required for separation, which reflects overall similarity.
Trees derived from phenetics should not be termed cladograms or phylogenetic trees due to their fundamentally differing methodologies.
Issues with Phenetics: Lack of clear evolutionary relationships, disregarding shared derived traits.
Cladistics: A method for constructing phylogenies based on shared derived characters.
Principle of Parsimony: The simplest phylogenetic tree (with the fewest incidences of convergence and reversals) is considered the correct one.
Descent vs. Convergence
Descent: The inheritance of traits from a shared ancestor.
Homology: Similarity due to shared ancestry.
Convergence: The independent evolution of similar traits in different lineages.
Homoplasy: Similar traits in organisms that arose independently, encompassing both phenotype and genotype.
Genomics in Mammalogy
Ruminant Genomics Paper (2019): Significant findings regarding ruminant genome evolution.
Zoonomia Project (2023): Notable insights into mammalian genomic research and biodiversity.
Topic 4: Speciation
Genetic Structure and Speciation
Understanding how genetic structure influences speciation, with case studies on walrus and bat populations presented in class.
Key Terms Related to Speciation
Gene Flow: The transfer of genetic material between populations; it works against speciation.
Panmixia: Complete mixing of genotypes across a population.
Genetic Structure: The distribution of genetic variation across populations.
Anagenesis: Change within a lineage that may lead to cladogenesis if gene flow ceases.
Clinal Variation: Gradual phenotypic changes across a species' geographical range.
Divergence Times in Vertebrates
100 years: Likely no detectable genetic changes.
1,000 years: Small, distinguishable genetic differences likely emerge.
10,000 years: Noticeable fixed genetic differences; potential slight divergence in morphology.
1 million years: Significant species-level differences; divergence of >2% in genetic makeup.
10 million years: Major divergences in ecology and body structure emerge.
~225 million years: Significant mammalian diversification observed.
~2 billion years: Eukaryotic diversity witnessed.
Allopatric Speciation
Allopatric speciation occurs when a parent population is divided by a physical barrier (e.g., bodies of water), leading to reproductive isolation over time.
This is the most common form of speciation documented.
Species Concepts
Morphological Species Concept: Focuses on physical characteristics for species designation.
Biological Species Concept: Defines a species as a group of interbreeding populations that are reproductively isolated from other such groups.
Hybrid Breakdown: The reduction of hybrid fitness is critical for species definition.
Phylogenetic Species Concept: Specifies any group of organisms bearing unique evolutionary histories as a separate species, evaluated through one or more traits.
Hybridization: Considered irrelevant to species status in this concept.
Genetic Species Concept: A species is defined as a group that is genetically distinct from others, requiring hybrid breakdown for identification.
Mitonuclear Compatibility Species Concept: A species is a genetically isolated population due to incompatibilities between mitochondrial and nuclear genes.
Hybrid fitness: Essential for species classification.
A. Species Concept Differentiation
Students should distinguish species concepts based on reproductive isolation, gene flow, geographical distribution (allopatry), and the relevance of divergence timing.
B. Mitonuclear Co-adaptation
Defined as the coordination of functional expression between mitochondrial and nuclear genomes, necessary for oxidative phosphorylation and maintained through coevolution.
Topic 5: Origin and Evolution of Mammals
Geological Timeline for Synapsids and Mammals
320 million years ago (mya): First synapsids appeared.
330 mya: First amniotes evolved.
240 mya: First mammals emerged.
260 mya: Lineage leading to mammals originated.
Major Taxonomic Groups and Characteristics
Amniota
Origin: 330 mya (Carboniferous)
Distinguishing Feature: Cleidoic egg with three extraembryonic membranes.
Synapsida
Origin: 320 mya (Carboniferous)
Feature: Single temporal fenestra aiding muscle attachment to the skull.
Pelycosauria
Origin: ~290-250 mya (Permian)
Features: Small single temporal fenestra, absence of reptilian scales, presence of some osteoderms, potential for glandular skin, and canine-like teeth in derived taxa.
Therapsida
Origin: Mid-Permian to Mid-Jurassic
Characteristics: Mammalian gait, larger temporal fenestra, heterodont teeth, lack of growth rings in bones (determinate growth), nasal turbinates, some with hair.
Cynodontia
Origin: Permian and established in the Triassic period
Features: Distinct premolar and molar structures (tricuspid molars), reduced post-dentary bones, secondary palate, and initial presence of mammary glands.
First Mammals
Origin: 200 mya
Features: Development of skull and teeth with several adaptations retained in modern mammals.
Importance of Hadrocodium Wui Fossils
Age: Approximately 195 million years old (Jurassic)
Remarkable for having well-preserved mammalian dentary and ear ossicles, indicating a larger brain compared to other contemporary species.
Key Phylogenetic Terms
Monophyletic Group: Organisms that derive from a common ancestor.
Polyphyletic Group: Organisms from multiple evolutionary ancestors; unsuitable for taxonomic classification.
Crown Group: Refers to the common ancestor shared by all mammals.
Stem Group: The common ancestor of amniotes.
Models for Mammalian Diversity Evolution
Explosive Model: All diversification occurred within approximately 10 million years post the K-Pg boundary (supported by fossil records).
Long Fuse Model: Interordinal diversification initiated during the Cretaceous, with most intraordinal diversification happening immediately after the K-Pg boundary (supported by genetic data).
Short Fuse Model: Orders and families originated and diversified during the Cretaceous era, preceding the K-Pg extinctions.
Molecular Clock Theory
Works on the concept that certain regions of the genome mutate at a relatively constant rate; the rate of mutations can be used for dating evolutionary divergences.
Average mutation rate: 1 base change per 25 million years.
Evolution of Flight and Echolocation
Evidence suggests that flight evolved prior to echolocation.
Students should interpret the data from Simmons et al. (2008) research presented in class.
Morphological Changes in Cetacean Evolution
First Cetaceans:
Pakicetidae: Teeth suited for piscivorous diets, high eye positioning on the skull, and a narrow mandibular joint.
Ambulocetidae: Initial marine cetaceans with a muscular tail, enhanced swimming limbs, and transition of eye placement.
Remingtonocetidae: Notable for their long snouts and adaptations for diverse diets, including directionality in hearing.
Precursors to Modern Cetacea:
Protocetidae: Showed a broad distribution, diverse features compatible with both aquatic and terrestrial environments.
Basilosauridae: Fully aquatic cetaceans with shifted nasal openings that form a blowhole and reduced hind limbs.
Modern Cetaceans: Include various species such as Odontoceti and Mysticeti.
Changes in Homininae Morphology
Hominid Evolution Timeline: 6-7 million years ago.
Sahelanthropus tchadensis: Similar brain size to chimpanzees, features of bipedalism bequeathed by the foramen magnum placement.
Orrorin tugenensis: Known from a femur fossil indicating bipedality circa 5.7-4.4 million years ago.
Ardipithecus ("Ardi"): Exhibited bipedalism with unique pelvic structure and significant arboreal adaptations, existing between 4.5-1.9 million years ago.
Australopithecus ("Lucy"): Notable for a larger body size and habitation in both terrestrial and arboreal environments over the last 3 million years.
Topic 6: Biogeography
Terminology in Biogeography
Biogeography: The study of the distribution of organisms, encompassing extant and extinct species.
Historical Biogeography: Focused on the evolutionary changes in species distributions over time.
Ecological Biogeography: Examines current species distributions through environmental contexts.
Vicariance: Geographic isolation of a previously widespread species due to barriers forming within its ancestral range.
Continental Drift: The gradual shift of landmasses due to tectonic movements.
Ice Age: A significant cooling period with widespread ecological impacts.
Refugia: Locations that serve as safe havens during ecological upheaval, allowing species to survive.
Diversification: Evolution of subpopulations accruing unique genetic alterations, potentially leading to new species.
Adaptive Radiation: The swift diversification of ancestors into new ecological niches in novel regions.
Processes Influencing Animal Distributions
Abiotic Factors:
Vicariance
Continental Drift
Climate Change
Biotic Factors:
Dispersal: Movement of organisms expanding their ranges.
Extinction: Loss of species due to environmental and ecological factors.
Mass Extinction: Sudden loss of diverse species globally across taxonomic groups.
Background Extinction: Species loss from local factors such as habitat changes and interspecific competition.
Diversification/Speciation
Adaptive Radiation
Early Synapsids and Mammal Distribution
Evolutionary positioning and distribution of early synapsids and mammals must be reviewed.
Theory of Marsupial Distribution in Australia
Review the hypotheses concerning the dispersal of marsupials to the Australian continent.
Original Clades of Eutherian Mammals
Identification of the four original clades should be done, along with an understanding of biogeographically influenced distributions.
Great American Interchange and Pleistocene Influence
Great American Interchange:
Occurred around 3 million years ago when North and South America joined, influencing species dispersal.
Initially comprised of savannah and tropical habitats shaping diverse mammalian interactions.
Pleistocene Ice Ages:
Occurred from 2.6 mya to 11,700 years ago, associated with significant shifts in large North American mammal populations due to glaciation.
Seven Zoogeographic Regions
Nearctic: North America with endemic families like Antilocapridae and Aplodontidae.
Palearctic: Europe and north Asia.
Holarctic: Greenland.
Neotropical: South America.
Ethiopian: Africa.
Oriental: India and South Asia.
Australian
Ecogeographical Rules
Allen’s Rule: Appendage size in endotherms decreases with latitude, e.g., ear length in rabbits, tail in foxes, limb lengths in humans.
Bergmann’s Rule: Larger body sizes in endotherms are found at higher latitudes, reducing surface area to volume ratios.
Foster’s (Island) Rule: Smaller mammals tend to grow larger on islands, while larger mainland mammals experience dwarfism, linked to heightened reproductive success.
Latitudinal and Elevational Diversity
Diversity often increases towards the equator, supported by various taxa such as bats and primates due to greater productivity and diversification rates throughout the tropics.
Elevation diversity often decreases with increased elevation due to lower oxygen, scarcity of water, and colder temperatures.
Topic 7: Skull, Teeth, Feeding, and Digestion
Unique Mammalian Skull Characteristics
Features like nasal turbinates, secondary palate for suckling, spacious neocortex, and well-defined dentary-squamosal jaw articulation, as well as three small ear ossicles.
Jaw Articulation Evolution
Students need to identify the jaw articulation bones and how articulation evolved through vertebrate history, influenced by body size transitions.
Jaw Muscle Anatomy in Feeding
Major muscles controlling the jaw:
Temporalis: Connects from the temporal fossa to the mandible.
Masseter: Extends from the zygomatic arch to the mandible.
Pterygoids: Connects from the underside of the skull to the mandible.
Students should recognize carnivorous versus herbivorous skull traits based on jaw muscle sizes and configurations.
Mammalian Dietary Specializations
Insectivory:
Taxa include echidnas, anteaters, and others.
Unique adaptations include the bill of the platypus with electroreceptive features, and star-nosed moles with densely packed tactile receptors.
Digestive traits often feature short intestines and high protein but limited fiber intake.
Carnivory:
Predominantly found in orders such as Carnivora and certain metatherians.
Involves unique dentition (e.g., incisors for holding, canines for piercing) and a rapid digestive-tract to handle nutrient-dense diets.
Sanguivory:
Observed in three species of bats with specialized adaptations for feeding on blood.
Piscivory:
Characteristic dentition adapted for minor modifications such as homodont dentition maximizing efficiency in swimming and capturing mobile prey.
Frugivory:
Practiced by many chiropterans and primates, playing a crucial role in seed dispersal within ecosystems.
Nectarivory:
Found within specific bats and marsupials, essential for pollination, requiring specialized elongated anatomical features.
Herbivory:
Adaptations for processing fibrous plant materials include high-crowned teeth, modified jaws for effective grinding, and complex digestive systems.
Omnivory: Exhibited by taxa such as opossums and some primates, showing a blend of adaptations from herbivory and carnivory.
Topic 8: Integument and its Derivatives
Functions of Integument
Role in protecting the internal environment, regulating water balance, insulating organisms, facilitating communication, and providing camouflage.
Mammalian Skin: Characterized by layers that constantly grow and are replaced.
Evolution of Hair
Conclusively, hair evolved independently from other integument structures, with its existence confirmed in cynodont fossils.
Hair Structure and Development
Components include:
Follicle
Shaft
Medulla
Cortex
Cuticle
Types of Hair Characteristics
Students should describe various hair types found across mammalian taxa and their distinctive features.
Pigmentation in Fur
Examination of pigment sources within mammalian fur and the significance of color patterns, focusing on adaptive functions such as camouflage and signaling as exemplified by Peromyscus from the Hoekstra lab.
Patterns of Molting
Familiarity with the processes and patterns surrounding the molting of mammalian integument.
Mammalian Integumentary Glands
Unique glandular structures present in mammals, particularly concentrating on mammary glands, their anatomy, and development.
Current Theories on Mammary Gland Origin
Understanding prevailing hypotheses regarding the evolutionary origins of mammary glands.
Derivatives of Integument
Structure and function of claws, nails, hooves, horns, antlers, and baleen, with attention paid to the taxa reflecting each derivative.