Biology 1001A Lecture Notes - Lecture 18: Assortative Mating, Disruptive Selection, Liger
7 May 2018
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Lecture 21: Species Concepts and Speciation
Question: How do we get from LUCA to the diversity of species that inhabit the planet? Answer:
Speciation. Note: Without speciation, there would still be variation but this variation would be due to
microevolutionary, not macroevolutionary change.
In order to look at speciation, we have to define what a species is. But how do we define a species?
(Defining a species is important in conservation efforts and other practical purposes). Over 50 species
concepts have been proposed:
1) Morphologial “peies Coept: A speies is a distit luster i pheotpi spae, o-
oerlappig i other suh lusters. Thigs that look the sae proal elog to the sae
species.
Problem:
- Defining a species based on phenotypes is inherently subjective.
- Sexual Dimorphism: Male ducks look very different than female ducks but they still are one
species
- Morphological Variation within a species: Dogs can look very different from each other but
they are still one species.
- Two different species can look the same
2) Biologial “peies Coept: A speies is a iterreedig or potetiall iterreedig group
of individuals, reprodutiel isolated fro other suh groups. Thigs that freel iterreed
and produce fertile offspring belong to the same species.
Ex:
- If you take a male lion and female tiger and give them the option of mating with their own
species or other species, they prefer to mate with their own species. But if the do’t hae the
option, they will mate with each other and their offspring, a liger. However, lion and tigers are
osidered to separate speies eause soe of the ligers are sterile. Also, the do’t freel
interbreed under normal conditions.
- Donkeys and horses are happy to freely interbreed with one another, but their offspring, the
mule, is sterile so donkeys and horses are two different species.
The Biological Species Concept is useful because it gives us a defined set of criteria as to what a species
is.
Problems:
- Biologial “peies Coept is ot useful he e look at speies that do’t reprodue seuall
- It is also not useful when it comes to extinct species
3) Phlogeeti “peies Coept: A speies is a irreduile oophleti lade of orgaiss
diagnosably distit fro other suh groups.
- Ma groupig ategorized as suspeies B“C are oophleti, ould reogized
as species by PSC.
Problem
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Document Summary
Note: without speciation, there would still be variation but this variation would be due to microevolutionary, not macroevolutionary change. In order to look at speciation, we have to define what a species is. But how do we define a species? (defining a species is important in conservation efforts and other practical purposes). Over 50 species concepts have been proposed: morphologi(cid:272)al pe(cid:272)ies co(cid:374)(cid:272)ept: a spe(cid:272)ies is a (cid:862)disti(cid:374)(cid:272)t (cid:272)luster i(cid:374) phe(cid:374)ot(cid:455)pi(cid:272) spa(cid:272)e, (cid:374)o(cid:374)- o(cid:448)erlappi(cid:374)g i(cid:374) other su(cid:272)h (cid:272)lusters(cid:863). Thi(cid:374)gs that look the sa(cid:373)e pro(cid:271)a(cid:271)l(cid:455) (cid:271)elo(cid:374)g to the sa(cid:373)e species. Defining a species based on phenotypes is inherently subjective. Sexual dimorphism: male ducks look very different than female ducks but they still are one species. Morphological variation within a species: dogs can look very different from each other but they are still one species. Two different species can look the same: biologi(cid:272)al pe(cid:272)ies co(cid:374)(cid:272)ept: a spe(cid:272)ies is (cid:862)a(cid:374) i(cid:374)ter(cid:271)reedi(cid:374)g or pote(cid:374)tiall(cid:455) i(cid:374)ter(cid:271)reedi(cid:374)g group of individuals, reprodu(cid:272)ti(cid:448)el(cid:455) isolated fro(cid:373) other su(cid:272)h groups(cid:863).
