An evolutionary lineage is a temporal series of populations, organisms, cells, or genes connected by a continuous line of descent from ancestor to descendant. Lineages are subsets of the evolutionary tree of life . Lineages are often determined by the techniques of molecular systematics .
8-430: A number of lineages of crabs have evolved to live predominantly on land. Examples of terrestrial crabs are found in the families Gecarcinidae and Gecarcinucidae , as well as in selected genera from other families, such as Sesarma , although the term "land crab" is often used to mean solely the family Gecarcinidae. No clear distinction is made between "terrestrial", "semiterrestrial", and "aquatic" crabs. Rather,
16-509: A "living carpet" of crabs. The crabs can travel up to 1.46 km (0.91 mi) in a day, and up to 4 km (2.5 mi) in total. Only a few land crabs, including certain Geosesarma species, have direct development (the mother carries the eggs until they have become tiny, fully developed crabs), and these do not need access to water to breed. Many crabs belonging to the family Potamidae , which contains mostly freshwater crabs, have developed
24-534: A continuum of terrestriality is displayed among the true crabs, although most land-adapted crabs must still return to water to release their eggs . Some species of terrestrial crabs can be found many kilometres from the sea, but have to complete annual migrations to the sea. For example, following the Indian Ocean monsoon , the Christmas Island red crab ( Gecarcoidea natalis ) migrates en masse , forming
32-519: A new distinct descendant clade. Just as a map is a scaled approximation of true geography , a phylogenetic tree is an approximation of the true complete evolutionary relationships. For example, in a full tree of life, the entire clade of animals can be collapsed to a single branch of the tree. However, this is merely a limitation of rendering space. In theory, a true and complete tree for all living organisms or for any DNA sequence could be generated. Nevertheless, phylogenies can sometimes appear in
40-440: A non-treelike form. Branches on the tree of life may grow together, a phenomenon called reticulation , which occurs due to different biological processes. Another process, introgression , occurs when hybrids between distinct lineages transfer novel genetic material through subsequent crossing. In other cases, hybrid speciation takes place when lineages hybridize to form a new, distinct lineage. Horizontal gene transfer, involving
48-422: A semiterrestrial (for instance the genus Nanhaipotamon ) to terrestrial life history, and are sometimes independent of fresh water for reproduction (for instance the genus Tiwaripotamon ). Terrestrial crabs are often similar to freshwater crabs , since the physiological changes needed for living in fresh water are preadaptations for terrestrial living. On some oceanic islands , terrestrial crabs occupy
56-480: Is quantified. Mathematical procedures are used to cluster individuals by similarity. Members of a species are considered to evolve as a single unit (or lineage) when they repeatedly share the same genes. The nodes would represent a split in lineage due to a breaking of genetic connections: when a single lineage is divided into two subsets, with the individuals not exchanging genes, they will accumulate differences in genes. If they do not fuse back again, it will create
64-602: The top of the energy pyramid . Lineage (evolution) Lineages are typically visualized as subsets of a phylogenetic tree . A lineage is a single line of descent or linear chain within the tree, while a clade is a (usually branched) monophyletic group, containing a single ancestor and all its descendants. Phylogenetic trees are typically created from DNA , RNA or protein sequence data. Apart from this, morphological differences and similarities have been, and still are used to create phylogenetic trees. Sequences from different individuals are collected and their similarity
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