Stickleback Evolution Lab Glossary

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This list is not meant to be comprehensive. It is a selection of terms from this lab that may be unfamiliar to new users.

Absent pelvis. There is nothing left of the pelvis: no pelvic girdle and no pelvic spines.

Anadromous. Referring to fish that ascend rivers from the sea to breed. Salmon are anadromous fish.

Ancestral/Ancestry. Pertaining to ancestors, the progenitors to an existing species or group.

Bar graph. A chart with rectangular bars; the length of the bars is proportional to the values they represent.

Bias/Left bias/Right bias. Bias refers to a deviation from an expected value. In the case of a reduced pelvis, the expectation would be that in a population there is an equal number of pelvises with vestiges larger on the left and on the right. A left bias indicates that a significantly greater number of individuals in a population have larger left vestiges; a right bias indicates more larger right vestiges.

Bilateral symmetry. Body symmetry in which a central longitudinal plane divides the body into two equal but opposite halves that are mirror images of each other. The pelvis is a bilaterally symmetrical structure.

Complete pelvis. A full pelvic girdle, without any parts missing, and two pelvic spines.

Crossbreed. To cross two varieties of organisms to produce hybrid progeny.

Deposition. The laying down of sediment over geologic time.

Diatoms. Microscopic, unicellular, photosynthetic green algae.

Ectocoracoid. A bone that forms the base of the pectoral fin. The pelvis is attached to the back end of the ectocoracoid.

Evolution. Descent with modification—the change in the inherited characteristics in a population over many generations.

Expression. Gene expression involves the production of messenger RNA and proteins from genes. This process is often referred to as the gene being "on," or expressed.

Fossil. The remains or impression of an ancient organism preserved in sedimentary rocks.

Fragmentary. When referring to the fossil record, it means that it is disconnected and incomplete.

Gene. A basic unit of heredity; a linear sequence of nucleotides along a segment of DNA that provides the coded instructions for the synthesis of RNA and protein.

Homology/homologous. Refers to traits or genes of different species that have evolved from the same common ancestor.

Lateral. The side of an organism or toward the side of an organism.

Line graph. A chart consisting of a series of data points connected by line segments.

Marine. Relating to the sea. When it comes to stickleback populations it means that the fish live exclusively in the sea or ocean.

Model organism. Nonhuman species extensively studied to understand particular biological phenomena.

Morphology. The form and structure of an organism.

Mutations. Random changes in genetic material.

Native. A species that normally lives and thrives in a particular ecosystem.

Pelvic. The region of the body where the hind limb is located.

Pelvic asymmetry. One side (left or right) of the pelvis is larger than the other.

Pelvic girdle. The part of the pelvis that supports the hind limbs. In the stickleback, the pelvic girdle connects to the pelvic spines.

Pelvic reduction. A process by which the pelvic structure becomes reduced—for example, resulting in a pelvic girdle with no spines to no pelvis at all.

Pelvic spines. Bony structures protruding from the pelvis of some fish; they serve as protection from predators.

Pelvis. The internal skeletal portion of the hind limb to which the pelvic spines of sticklebacks and the hind legs of many vertebrates are attached.

Phenotype. An organism's observable characteristics, or traits, governed by its genetic makeup (or genotype).

Pitx1. A gene with a large effect on the development of the pelvic girdle and spines of stickleback fish and the hind limbs of almost all vertebrates.

Postglacial. Anything that occurred after the glaciers that covered the Earth during the last ice age retreated.

Random sampling. Unbiased inclusion of individuals from a population into a group of specimens used to study the population's phenotypic or genetic properties. For example, random sampling is used to estimate the properties of stickleback populations in different lakes.

Reduced pelvis. A simplified pelvic girdle structure with no pelvic spines.

Sea-run. Referring to fish that ascend rivers from the sea to breed. It is synonymous with anadromous.

Sediment. Material deposited by water, wind, or glaciers.

Ventral. The lower surface or toward the lower surface of an organism.

Vestigial/vestige/vestiges Traits that are simplified and reduced in size and function compared to homologous traits in an ancestor.