Molecules, Morphology and Species Concepts. Speciation Occurs at Widely Differing Rates. Speciation Rates

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1 Molecules, Morphology and Species Concepts Speciation Occurs at Widely Differing Rates Horseshoe crabs (Limulus), the same as fossils 300 Mya Darwin s Finches: 13 species within 100,000 years. Speciation Rates Generalists, like the horseshoe crab, tend to remain as stable species. Specialists, like the Galapagos finch, tend to be unstable as species. Speciation also becomes rapid when, as occurred with Galapagos finches, new niches become available. 1

2 Process-oriented taxonomy Speciation is a universal process. Speciation is the core of taxonomy because speciation processes provide the most plausible criteria for species definition. Microevolution Macroevolution leads to changes within populations (often genotypic) leads to phenotypic changes resulting in distinctive lineages (e.g. species) Evolution creates (and destroys) new species, but What is a species? Its not as straightforward a question as most believe. Eastern Meadowlark Western Meadowlark 2

3 Determining what is and what isn t a distinct species has big consequences ENDANGERED Not endangered Northern spotted owl Barred Owl What is a Species? And these are all members of a single species. What is a Species? There is only one extant (existing) human species. 3

4 Diversity of Life 1.4 million species described ca. 10 million estimated many extinct species: >90% of all species that every lived! Large diversity of species - speciation must be a common event Understanding how this diversity arose is a central question in evolutionary biology Diversity of Life All cultures recognize different forms (species) and name them But what are species? The challenge to scientists is to name and classify species in a testable, replicable way Taxon units are working hypotheses Systematics depends on species Species may be flawed 4

5 Species A Genetic Divergence Two species of Tuna! Diversity of Life Species = basic unit Continuous lineage - information passed through genes Speciation - rise of new species 5

6 A flock of species concepts Species Smallest independently evolving unit Independent evolution occurs when mutation, selection, gene flow, and drift operate independently in different populations Therefore, these species will follow independent evolutionary trajectories The essence of speciation is lack of gene flow All modern species concepts really fall under a lineage concept The different species concepts are really criterion for determining when you have lineage formation Defining species is extraordinarily contentious Potentially 23 different species concepts Species concepts Biological species concept Phenetic (morphological) species concept Ecological species concept Phylogenetic species concept Of course there are many more! 6

7 Biological species concept Species are groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups. (Mayr, 1942) Problems with Biological Species Fossils - how do we know if they interbreed? Good species can sometimes produce viable hybrids hummingbirds Asexual organisms? Parthenogenic organisms?? Morphological species Species defined by measurable morphological characteristics (quantitative morphometric evidence, statistically tested) 7

8 Morphological Species Concept - sometimes gets it wrong New Zealand moa (extinct): females much bigger than males! Ecological species concept A species is a lineage (or closely related set of lineages) which occupies an adaptive zone [ecological niche] minimally different from that of any other lineages in its range and which evolves separately from all lineages outside its range. (Van Valen, 1976) Problems with Ecological Species Niches are very hard to define in a testable way Most species don t respect scientists ideas about niches!! (e.g. invasive species) If a species exploits a new niche, it does not necessarily become a new species, or become isolated from populations in the original niche 8

9 Evolutionary species concept Evolutionary species concept: A species is a single lineage of ancestor-descendant populations which maintain its identity from other such lineages and which has it own evolutionary tendencies and historical fate (Simpson, 1961; Wiley, 1981). Difficult to apply, so we use the following: Phylogenetic species concept A species is the smallest diagnosable cluster of individual organisms within which there is a parental pattern of ancestry and descent (Cracraft 1983). Phylogenetic Species Concept Species = lineage between successive speciation events 9

10 Phylogenetic Species Concept Two-step process to define species 1. Grouping taxa (regardless of rank) using the criterion of monophyly, or at least potential monophyly I.e. build a tree 2. Ranking groups by the criterion of smallest diagnosable monophyletic groups Problems: Almost any population could be diagnosed Not all monophyletic groups are species! But wait, there s more 10

11 Recognition Species Concept Two individuals that recognise each other as potential mates are the same species! The Leave them to themselves approach to biology To each its own? Each of the species concepts has certain advantages and disadvantages which makes it the favourite of one or the other discipline of biology. Even more important some concepts have features which prevent their use in some disciplines. What they can t do Biological SC: asexual, fossils Ecological SC: much (esp. botany) Morphological SC: things without whole populations Recognition SC: farmers 11

12 Speciation The species concept problem arises, because the species is not the central issue The central issue of interest is speciation Speciation The process of speciation combines micromacroevolution; molecules and morphology All data is important Taxon Sampling Dependent on preservation and specimen availability Dependent on access to specimen material 12

13 Conclusions The pattern (sum, end result) of all speciation processes identify a species A fixed definition of a species is only possible after it ceased to exist (??) Species are hypotheses about relatedness and relationships 13