Species and Speciation

What is an example of a species with rapid speciation in a short evolutionary period?

Lake Malawi Cichlids; they formed ~600 species from one common ancestor in less than 600,000 years

What is a species?

A group that experiences a independent evolutionary trajectory (evolves without being influenced by gene flow from other groups)

What makes it difficult to put a boundary what defines a species?

• there is lots of variation both within groups and between groups

• phenotypes are often plastic within a species and even an individual

• there can be genetic differences present that do not correspond to any visible phenotypic differences

What is the best evidence that species are always changing?

The fact that it is so difficult to distinctly define species

What are the 3 basic concepts of species?

• Morphological

• Biological (Genetic)

• Phylogenetic

What is the morphological species concept and what are the major difficulties with it?

It defines species by differences in characters, especially morphology; this definition works well for extant and extinct organisms

Major Difficulties:

• Polymorphism → individuals in the same species can have very different morphologies; sexual dimorphism; ex. coneheaded termites look very different based on their social role (worker, soldier, etc.)

• Geographic Variation → a single species may appear different in different parts of its range due to genes or environment

• Cryptic Species → genetically distinct species might have no outward differences; ex. H. chrysoscelis frog and H. versicolor frog look the exact same

What is the biological species concept and what are its major problems?

This is the predominant thinking among biologists and it is the legal definition used; It defines species as a group of interbreeding (or potentially interbreeding) populations that is reproductively isolated from other such groups; if individuals from two separate populations cannot produce fertile offspring, they are said to be two different species

Major Problems:

• Fossils and extinct organisms → cannot look at how they breed

• Asexual lineages, bacteria → organisms that do not sexually reproduce, how do we define them?

• Geographically Isolated Groups → groups that live in different continents may be able to interbreed, but they never come into contact, are they separate species?

• How much interbreeding is too much? → are species that can form hybrids not actually separate species?

How do hybrids come into play when defining species?

Hybrids do exist; and the hard line between species is that if they produce a hybrid, it should be infertile; however, hybrids in the past have turned into new species, or they are fertile, so there isn’t really a clear line

What is the phylogenetic species concept and what are its major problems?

It defines species as the smallest possible monophyletic group, which are identifiable through phylogenetic reconstruction

Major Problems:

• There is no definition of how much difference there has to be between groups to put them on different branches in a phylogeny

What species concept could best be used to group adult and larval fossils that look different, but are from the same species, into the same species?

Phylogenetic; can’t use biological because they are fossils, and morphological wouldn’t work well because the adult and larval forms look very different

How does the Red Wolf identify the difficulties of defining a speces?

The endangered species act uses the biological species definition, which says hybrids are not species; the Red Wolf is technically a hybrid of coyote and Grey Wolf (70% coyote), so BSC does not define them as a species; MSC does define them as a species because they have distinct morphologies from modern Grey Wolves and coyotes; PSC is a grey area because there is some shared DNA and some unique DNA, so it could suggest an old, diverged lineage; Whole Genome Data and a phylogenetic approach has shown that Red Wolves have unique ancestral elements shared with Grey Wolves, giving evidence that Red Wolves are a species, so there is a lot of grey area