Biodiversity, Microbial Life, and Phylogenetic Systematics

Comprehensive vocabulary flashcards covering biodiversity metrics, bacterial biology, horizontal gene transfer, and phylogenetic systematics based on lecture notes.

Biological Diversity (Biodiversity)

The variety of all living things on Earth, encompassing genetic differences within species, individual species richness and abundance, and entire ecosystems across the biosphere.

Levels of Biodiversity

The three hierarchical tiers of biological variety: genetic diversity (variety of genes and alleles within species), species diversity (number of species and relative abundance), and ecosystem diversity (variety of habitats, biological communities, and ecological processes).

Genetic Diversity

The variety of genes and alleles within individual species, providing the variation necessary for natural selection, environmental adaptation, and resilience against disease.

Species Diversity

A measurement of biological variety that accounts for both the total number of distinct species (richness) and their relative numerical distribution (evenness) in a given biological community.

Species Richness

The total number of different biological species present within a defined geographic area or sampling community.

Species Evenness

The measure of how equally individuals are distributed among the different species present in a community, contrasting communities dominated by a single species with those where abundances are balanced.

Simpson’s Diversity Index

A mathematical diversity metric combining species richness and evenness that places greater emphasis on the dominance of common species.

Shannon Index

A mathematical diversity metric combining richness and evenness that gives greater weight to the diversity contributed by less common or rare species.

Alpha ($\alpha$) Diversity

The localized species diversity measured within a single, specific site or biological community (e.g., the species count within one pond).

Beta ($\beta$) Diversity

The change or turnover in species composition between two different ecosystems or communities, often calculated additively as $\beta = (S_1 - c) + (S_2 - c)$ or by Whittaker's ratio method comparing regional to local diversity.

Gamma ($\gamma$) Diversity

The overall regional biodiversity calculated across an entire geographic landscape containing multiple distinct ecosystems.

Environmental DNA (eDNA)

Microscopic genetic material collected directly from environmental substrates (such as water, soil, or snow) and sequenced to detect the presence of local organisms without direct physical observation.

Biodiversity Hotspot

A biogeographic region characterized by exceptionally high biodiversity and endemism; 36 hotspots exist globally, supporting nearly $60\%$ of the world’s plant, bird, mammal, reptile, and amphibian species.

Mass Extinction

A catastrophic event characterized by the loss of at least $75\%$ of Earth's species within a geologically brief interval (approximately $2\text{ million years}$).

The 'Big Five' Mass Extinctions

The five major extinction pulses in Earth's history: End Ordovician ($444\text{ Mya}$, $86\%$ species lost), Late Devonian ($360\text{ Mya}$, $75\%$ species lost), End Permian ($250\text{ Mya}$, $96\%$ species lost), End Triassic ($200\text{ Mya}$, $80\%$ species lost), and End Cretaceous ($65\text{ Mya}$, $76\%$ species lost).

Three-Domain System

A molecular evolutionary classification framework based on molecular systematics that divides all cellular life into Bacteria, Archaea, and Eukarya.

Horizontal Gene Transfer (HGT)

The transfer of genetic material between organisms other than via vertical parent-to-offspring inheritance, converting the evolutionary tree into an interconnected 'web of life.'

Transformation

A mechanism of horizontal gene transfer in which a competent bacterial cell takes up naked, cell-free foreign DNA released by dead donor cells from the environment and incorporates it into its genome.

Transduction

A vector-mediated horizontal gene transfer pathway in which a bacteriophage accidentally packages donor bacterial DNA and injects it into a recipient bacterium.

Bacterial Conjugation

The direct transfer of genetic material between two temporarily joined bacterial cells via a specialized mating pilus, regulated by the fertility ($\text{F}$) plasmid.

F Factor (Fertility Plasmid)

A specific plasmid that confers the ability to form a sex pilus and initiate bacterial conjugation, converting an $\text{F}^-$ recipient cell into an $\text{F}^+$ cell upon transfer.

Prokaryotic Appendages

Specialized surface projections in prokaryotes, comprising fimbriae (short fibers used for surface attachment), pili (structures mediating DNA transfer during conjugation), and flagella (tail-like organelles for locomotion).

Peptidoglycan

A tough, mesh-like structural macromolecule composed of long carbohydrate chains cross-linked by short peptides that forms the bacterial cell wall (absent in Archaea).

Biofilm

A surface-attached microbial community encased in a self-secreted polysaccharide matrix where cells coordinate collective metabolic activities using chemical signaling.

Human Microbiota

The ecological community of commensal, symbiotic, and pathogenic microorganisms living on and in the human body, numbering approximately $100\text{ trillion}$ cells ($70\text{--}90\%$ of total body cells) and comprising $99\%$ of the unique genes.

Borrelia burgdorferi

A spiral-shaped bacterium (spirochete) and obligate parasite that is transmitted by the blacklegged (deer) tick to cause Lyme disease in mammalian hosts.

Rhizobia

Nitrogen-fixing bacteria (including genera Rhizobium, Bradyrhizobium, and Sinorhizobium) that inhabit the root nodules of legumes to convert atmospheric nitrogen into plant-absorbable ammonium.

Cyanobacteria

Photosynthetic, oxygen-producing aquatic prokaryotes that serve as major primary producers; ancestral forms generated Earth's oxygen-rich atmosphere and gave rise to eukaryotic chloroplasts.

Myxobacteria

Soil-dwelling bacteria exhibiting gliding motility that hunt cooperatively in swarms and aggregate to form macroscopic fruiting bodies with elevated spores when nutrients are depleted.

Streptomyces

Filamentous, soil-dwelling bacteria that produce geosmin (petrichor odor) and synthesize over two-thirds of all clinically utilized natural human antibiotics.

Magnetosomes

Membrane-bound intracellular iron crystals (magnetite) found in magnetotactic bacteria that align the cell with Earth's geomagnetic field lines for vertical orientation in water columns.

Bioremediation

The application of microbial metabolic processes to break down, neutralize, or remove environmental contaminants such as petroleum hydrocarbons and industrial chemicals.

Bioleaching (Biomining)

The industrial use of chemolithotrophic bacteria to oxidize iron and sulfur compounds in low-grade ores, dissolving trapped metals (such as copper and gold) into solution for extraction.

Systematics

The overarching scientific discipline focused on analyzing the evolutionary relationships and diversification of biological organisms through time.

Taxonomy

The science of naming, describing, and classifying organisms into ordered hierarchical categories for identification, communication, and evolutionary illustration.

Careproctus colliculi

The bumpy snailfish, a newly described marine fish species named in 2025 according to the International Code of Zoological Nomenclature.

Holotype

The single physical specimen designated as the official name-bearing, benchmark representative for a species when its description is validly published.

Principle of Priority

The foundational rule of biological nomenclature establishing that the earliest validly published scientific name applied to a taxon is the correct name that takes precedence.

Biological Species Concept

The species definition proposed by Ernst Mayr (1942) characterizing a species as an array of natural populations that are actually or potentially interbreeding and reproductively isolated from other such groups.

Phenetic Taxonomy

An approach to biological classification that clusters organisms based purely on overall phenotypic and morphological similarity, frequently employing statistical regression or cluster analysis.

Cladistic Taxonomy

A classification methodology that reconstructs evolutionary relationships based strictly on evolutionary branching points and shared derived characters (synapomorphies).

Monophyletic Clade

A natural phylogenetic group consisting of an immediate common ancestor and all of its evolutionary descendants.

Paraphyletic Group

A taxonomic grouping consisting of a common ancestor and some, but not all, of its descendants (for example, class Reptilia excluding birds).

Polyphyletic Group

An artificial taxonomic assemblage derived from more than one ancestral lineage that does not include the common ancestor of all members (e.g., pachyderms).

Homologous Structures

Anatomical traits or organs in different organisms that share a common ancestral origin, regardless of whether they have diverged to perform different functions.

Analogous Structures

Anatomical traits in different lineages that perform similar functions but evolved independently from distinct ancestral origins due to convergent evolution.

Synapomorphy

A shared derived character state that evolved in a recent common ancestor and is shared exclusively by its descendant lineages, serving as evidence of monophyly in cladistics.

Plesiomorphic Character

An ancestral, primitive character state retained in a relatively unmodified form from the original ancestor of a group (such as the ancestral post-anal tail in vertebrates).

Apomorphic Character

A modified or derived evolutionary trait that represents an evolutionary novelty relative to the ancestral condition (such as the loss of an external tail in great apes).

Parsimony

The cladistic optimality criterion (analogous to Occam’s razor) asserting that among competing phylogenetic hypotheses, the tree requiring the fewest evolutionary character transitions is favored.