This event usually occurs when a few organisms end up in new, often distant areas or when environmental changes cause several extinctions, opening up ecological niches for the survivors. The events that cause these species to originally separate from each other over distant areas may still allow both of the species to have equal chances of surviving, reproducing, and even evolving to better suit their environments while still being two distinct species.
Cladogenesis is in contrast to anagenesis, in which an ancestral species gradually accumulates change, and eventually, when enough is accumulated, the species is sufficiently distinct and different enough from its original starting form that it can be labeled as a new form - a new species. Note that here the lineage in a phylogenetic tree does not separate.
There are many different methods and forms of evidence that can be used when it comes to determining whether a speciation event falls under cladogenesis. Below are a few different methods used by scientists, with a quick explanation or example for each:
- Simulations: This involves the process of taking already known information (such as mitochondrial information) about a species and running the information through a computer to see if a cladogenetic event is the most probable explanation for a species existence. This way of studying species is the most practical. A lot of times, case studies and constructing experiments can cost a lot of money and takes time, so it is easier to plug information into a computer and allow the computer to run different scenarios to test for accuracy.
- Morphological/Paleontological Evidence: Using fossil evidence can determine whether two species were alive at the same time. However, there are some drawbacks to using just fossil evidence since fossil evidence can only differentiate species on an assemblage level.
- Molecular Evidence: Molecular data can be used to see how the genome or DNA of specific species has diverged. This, along with the fossil evidence, can be a good basis for seeing if two distinct species came from a similar ancestral species and if they were both alive at the same time.
- Models: This involves taking already-alive species and running experiments (simulating possible environments for example) to see if speciation occurs in order to explain the presence of different species or if there is an alternate explanation for the species. This is sometimes the most accurate way of measuring speciation because it gives actual life results, as opposed to computer generated data.
These are just a few examples of ways to distinguish a speciation event as either cladogenetic or anagenetic. Alternatively it has been questioned whether the distinction is necessary at all in evolutionary theory, and scientists are constantly considering how speciation occurs and how it can be studied.
- Gould, Stephen Jay; Eldredge, Niles (1977). "Punctuated equilibria: the tempo and mode of evolution reconsidered" (PDF). Paleobiology 3 (2): 115–151 . doi:10.1017/s0094837300005224.
- Strotz, LC; Allen, AP (2013). "Assessing the role of cladogenesis in macroevolution by integrating fossil and molecular evidence". Proc Natl Acad Sci U S A. 110 (8): 2904–9. doi:10.1073/pnas.1208302110.
- Vaux, F; Trewick, SA; Morgan-Richards, M (2016). "Lineages, splits and divergence challenge whether the terms anagenesis and cladogenesis are necessary". Biol J Linnean Soc 117 (2): 165–176. doi:10.1111/bij.12665.