Transcript “SPECIES”
“SPECIES” What sort of Biological Entity is it? What is a “Species”? • Biological Species Concept: – 1 or more populations of individuals that can interbreed and produce fertile offspring, and are reproductively isolated form other such groups. – Members of a species have a shared gene pool. – Different populations can mate and produce fertile offspring. What is a “Species”? • But…what about asexual organisms? • Morphological Species Concept: – Groups of organisms that share certain morphological or biochemical traits. • This is rather subjective. • Phylogenetic Species Concept: – Groups of organisms (or lineages) that share recent common ancestry. Speciation • • • • How do species arise? Microevolution Pre-existing organisms (ancestors). Divergent Evolution – Adaptation to specific environmental cues. • (This contrasts Convergent Evolution) – Similar adaptations in organisms from very different lineages. Speciation • Biological Species Concept: – 1 or more populations of individuals that can interbreed and produce fertile offspring, and are reproductively isolated form other such groups. • Reproductive Isolation – Prevents Gene Flow. – If no gene flow, then populations can develop into more and more different subpopulations…perhaps eventually forming species. Reproductive Isolating Mechanisms 1. Pre-Zygotic Isolating Mechanisms 2. Post-Zygotic Isolating Mechanisms Pre-Zygotic Isolating Mechanisms • Prevent Reproduction Attempts • Habitat Isolation – Isolated in space/habitat. • Temporal Isolation – Mating occurs at different times • Behavioral Isolation – Differences in mating displays, calls, chemicals… • Mechanical Isolation – Incompatibility of reproductive organs … (“the key doesn’t fit the lock”) Post-Zygotic Isolating Mechanisms • Copulation occurs, but offspring are kept from developing & breeding. • Gamete Isolation – sperm & egg don’t fuse. • Zygote Mortality – Zygote dies, unable to function. • Hybrid Inviability – Hybrid is produced, but does not survive to adulthood. • Hybrid Sterility – Hybrid is produced, but is unable to produce viable gametes. Speciation • Formation of new species via reproductive isolation. 1. Allopatric Speciation – 2 populations become reproductivelyisolated while separated from each other (geographic barrier). Speciation 2. Sympatric Speciation – 2 populations become reproductivelyisolated while occupying the same geographic area. How Fast? • Gradualist Model • Punctuated Equilibrium Model Systematics • Science of organizing the diversity of life. 1. Taxonomy – Identification & Naming 2. Phylogeny – Analyzing evolutionary relationships among groups. 3. Classification – Placing organisms into an organized categorization scheme. Taxonomy • Identification & Naming • Taxon: a group of organisms (Taxa) • “Species” – the most fundamental group. – Group of interbreeding populations that are reproductively isolated from other such groups (and evolving independently of other such groups). Taxonomy • New species each given a “Scientific Name” – Carolus Linnaeus – Binomial Nomenclature – 2-word Latin name. • Pinus strobus • Dictyostelium discoideum • Bubo virginianus • “Common Names” also… – Can be misleading Taxonomy • Pinus strobus • 1st word = Genus – A generalized name • 2nd word = specific epithet – A descriptive name • Always in italics or underlined. • Genus is capitalized, epithet is lower case. • Specific epithet never used alone! Phylogeny • Grouping new species/taxa with closelyrelated taxa from an evolutionary perspective. • Phylogenetic Trees: Phylogeny • Outgroups: Classification • Categorizing organisms into a hierarchy of names (hopefully) according to their relatedness. • Historically – based on convenience. • Starting at Species (the most exclusive group), organisms are grouped into more and more broad & inclusive Taxa. • “Species” is the only level that really exists as an true single entity. Classification Kingdom Animalia Phylum/Division Chordata Class Mammalia Order Primates Family Hominidae Genus Homo Species Homo sapiens Classification Homo sapiens Tyto alba Homo Tyto Hominidae Tytonidae Primates Strigiformes Mammalia Aves Chordata Animalia Systematics • Tree of Life: http://tolweb.org/tree/phylogeny.html