BIOL 321 (Inverts.) Flashcards
Define taxon.
Any named group of organisms distinct enough to be assigned a Linnaean category.
Define monophyletic.
A group of members of a taxon that includes all descendants of their defining common ancestor.
Define paraphyletic.
A group of taxon members that does not include all descendants of the common ancestor.
What is the defining characteristic of the current distinct phyla in invertebrate biology?
Each phylum represents a unique body plan.
Define species.
A group whose members are reproductively isolated from members of all other species.
Define Phylocode.
A rankless, hierarchical biological naming system proposed in 1998 as an alternative to Linnaean classification.
When did the last new phylum-level body plans appear?
250 million years ago(!).
Define convergent evolution.
The process whereby similar characteristics are independently evolved by different groups of organisms in response to similar selective pressures.
Define analogous characters.
Features in organisms of different species that resemble each other as a result of convergent evolution.
Define expressed sequence tags (ESTs).
DNA fragments that are complementary to expressed mRNA.
Define Protostomia.
A family consisting of triploblastic acoelomate and pseudocoelomate animals.
What are the 2 major clades of protostomes?
Ecdysozoa (molting animals) and lophotrochozoa.
What is the main purpose of phylogeny?
Understanding the evolution of specific characteristics within a group of organisms.
Which tells us more about phylogeny: homology or convergence?
Homology.
Define polarity.
The direction of evolutionary change (from ancestral to derived state).
What are the 2 main schools of thought in determining evolutionary relatedness?
Evolutionary systematics (classical taxonomy) and cladistics (phylogenetic systematics).
How are organisms classified using evolutionary systematics (classical taxonomy)?
Subjective analysis of homologous characters for degree of similarity or difference between organisms leads to classification of relatedness.
What are the main problems with evolutionary systematics (classical taxonomy)?
It is very subjective, is not well standardized, requires years of experience with the organisms in question, and often leads to paraphyletic groupings based on an intuitive sense of what is similar or different between organisms.
Define anagenesis.
Change occurring within a lineage of organisms.
Define ancestral (primitive; a.k.a. plesiomorphic) state.
The character state exhibited by the ancestor from which current members of a clade have evolved.
Define apomorphy.
Any derived or specialized character.
Define autapomorphy.
A derived character possessed by only one descendant of an ancestor, and thus of no use in discerning relationships among other descendants.
Define Bayesian inference.
A statistical technique used to infer the probability that a particular phylogenetic hypothesis is correct.
Define bootstrapping.
A technique for evaluating the reliability of a phylogenetic tree by resampling some characters from the original data set (with replacement) at random.
How does bootstrapping work?
Once a phylogenetic tree has been generated, some characters are resampled with replacement at random. Each resampling gives a new data set with some values duplicated and some omitted. The bootstrap value is the % of resamplings that recover the branch in question.
Define clade.
A group of organisms that includes the most recent common ancestor of all its members and all descendants of that ancestor; every valid clade forms a monophyletic group.
Define cladogenesis.
The splitting of a single lineage into 2 or more distinct lineages.
Define cladogram.
The pictorial representation of branching sequences characterized by particular changes in key morphological or molecular characteristics.
Define derived (apomorphic) state.
An altered state, modified from the original (ancestral) state.
Define homologous characters.
Characters that have the same evolutionary origin from a common ancestor, often coded for by the same genes.
In cladistics (phylogenetic systematics), what is the basis for all decisions about evolutionary relationships between species?
Homology.
Define homoplasy.
The independent acquisition of similar characteristics from different ancestors via convergence or parallelism, creating the illusion of homology.
Define jackknifing.
A technique for evaluating the reliability of a branch of a phylogenetic tree by deleting some % of information at random and rerunning the analysis; the jackknife value is the % of resamplings that recover the branch in question.
Define node (cladistics).
A branching point on a cladogram.
Define outgroup.
A group of taxa outside the group being studied, used to ‘root’ a phylogenetic tree and imply the direction of evolutionary changes.
Define parsimony.
A principle stating that, in the absence of other evidence, one should always accept the least complex scenario.
Define pleisiomorphy.
Any ancestral or primitive character.
Define polyphyletic grouping.
An incorrect grouping containing species that descended from 2 or more different ancestors; members do not all share the same immediate ancestor (but may resemble each other due to convergence).
Define saturation (cladistics).
A situation in which the gene sequences being compared have experienced so many base-pair substitutions that the phylogenetic signal is largely lost.
Define sister groups.
2 groups of organisms descended from the same immediate ancestor.
Define synapomorphy.
A derived character shared by the most recent common ancestor and 2 or more descendants, used to define which species/groups are most closely related to each other.
In cladistics, which characters are the most important to establish evolutionary relationships?
Synapomorphies (homologous derived characters) - and these are the -only- characters used!
How does cladistics (phylogenetic systematics) work?
Compare organisms from one group to a closely related taxon (the outgroup) that lies outside the taxa being studied, assuming the outgroup’s characteristics represent the ancestral condition, then create a branched cladogram with the least complex (parsimonious) pathway.
How does convergent evolution affect cladistics?
Convergence can create the illusion of false homologies, so that even the most parsimonious tree standing up to statistical analysis can be completely wrong.
What is the difference between cladistics and classical taxonomy w.r.t. molecular data?
Cladistics takes molecular data into account; classical taxonomy does not.
In cladistics, what do differences in base pair sequence represent?
Evolutionary events by mutation (change, insertion, or deletion) of base pairs.
In cladistics, what do base pairs represent w.r.t. ancestral/derived characters?
Each base is a distinct character, so genome comparison compares 100s to 1000s of characters.
What are the problems with cladistics?
Relationships defined depend on the methodology (equipment, stats tests, etc.) used and can be hard to replicate; assumptions of outgroups as ancestral can be wrong; evolution is rarely parsimonious; and molecular data is another realm of problems!
What are the problems with using molecular data in cladistics?
Molecular change/evolution is not uniform even within the same organism, and sequence addition/deletion events can mess up sequence alignment, making comparisons between organisms inaccurate.
What kind of phylogenetic trees are generated from organisms with gene sequences that evolve unusually quickly?
Trees have longer branches that are grouped more closely together - not because the animals are closely related, but because of the rapid evolution of those sequences.
In cladistics, how can base pair comparisons lead to false homologies?
There are only 4 bases to choose from, so molecules from unrelated organisms are very likely to resemble each other by convergence.
What are the benefits of cladistics over classical taxonomy?
Its clear methodology is easy to analyze and duplicate, and less specialized experience with the organisms in question is needed.
What is the limitation of the fossil record in terms of defining evolutionary relationships between organisms?
Issues resolvable by fossils are usually limited to questions within phyla, not among them.
Which is better for understanding evolutionary relationships between different phyla: molecular data or the fossil record?
Molecular data: changes in DNA sequences provide the best chance of understanding relationships among phyla, while the fossil record is limited to relationships within phyla.
Define terrestrial.
Living on land.
Define marine.
Living in the ocean.
Define intertidal.
Marine organisms living between the physical limits of high and low tides, and thus exposed to air periodically.
Define subtidal.
Marine organisms living below the low-tide line and thus exposed to air only under extreme conditions, if ever.
Define mobile.
Organisms capable of locomotion.
Define sessile.
Organisms that are immobile.
Define sedentary.
Organisms exhibiting only limited locomotory capabilities.
Define planktonic.
Aquatic organisms with negligible locomotory powers w.r.t. the movement of the medium they live in, and are thus forced to drift or wander.
Define suspension feeders.
Organisms that feed by removing small food particles from the surrounding medium.
Define deposit feeders.
Orgnisms that feed by ingesting sediment, digesting the organic component as the sediment moves through the digestive tract.
Define ectosymbionts.
Symbionts living near or on the body of the other participant.
Define endosymbionts.
Symbionts living within the body of the other participant.
Define mutualism.
A symbiotic relationship in which both symbionts benefit.
Define commensalism.
A symbiotic relationship in which only 1 symbiont benefits, but the other is neither benefited nor harmed.
Define parasitism.
A symbiotic relationship in which the parasite is absolutely metabolically dependent on the host; a parasite may or may not substantially impair the host.
What are the 3 types of symbiotic relationships?
Mutualism, commensalism, and parasitism.
Define transitional forms (w.r.t. symbiotic relationships).
Stages in the evolution of relationships between organisms (e.g. from parasite to predator when the host is killed).
Define embryogenesis.
The process of producing many different cells of different types to form an embryo.
What are the 4 basic types of metazoan tissues?
Epithelial, connective, muscle, and nervous tissue.
Which is the most important type of metazoan tissue?
Epithelial.
What is the function of epithelial tissue?
It forms the lining of outer surfaces and internal compartments, acting as an interface between compartments and between the organism and its environment.
What are the 3 key features of epithelial tissue?
Intercellular junctions, basal lamina, and apico-basal polarity.
What is the function of intercellular junctions in epithelial tissue?
To control the exchange of material between epithelial cells.
