More of a problem than you care to know about. Species. Paul Reilly

Discuss the reality of species. Learn about the most used species concept. Learn about alternative species concepts. Discuss operational criteria and it’s importance to species delimitation. Discuss the implications of using different concepts. Objectives.

“A species is what a good taxonomist says it is” -Huxley 1942 Are species discrete, objective entities, or constructs of the human mind? The Reality of Species

Three methods to determine if species are real: ◦ Arguments from Common Sense ◦ Concordance between “folk” and “scientific" species ◦ Statistical identification of clusters In Sexually Reproducing Taxa

Asexual taxa seem to form clusters Mixed mating systems ◦ Some Prokaryotes (horizontal transfer, conjugation) ◦ Agamic complexes In Asexual or Mixed Mating Systems

Mixed Mating Systems

Most biologists agree species are real, yet we lack rigorous testing to convince skeptics nature is discontinuous Sexually reproducing eukaryotes and asexual prokaryotes seem to form discrete clusters Mixed mating systems (agamic complexes in plants, many prokaryotes) do not seem to form clusters Are Species Real? Conclusions

How do we define them? If species are real…

Common Names Conrad Gesner (1559) Genera and Species John Ray (1686) Introduces the idea that species produce the same species, though variation is possible Morison (1655), Ray (1682), Tournefort (1694) Start arguing about classify genera and species Carl Linneaus (1735)”borrows” Binomial nomeclature from the Bauhin Brothers Before Darwin

Type Specimens

Jointly present “On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection” People start to wonder about the nature of a species without and independent human observer Darwin and Wallace

Theodosius Dobzhansky(1937) describes reproductive isolation as critical to the development of new species Ernst Mayr (1942) introduces the Biological Species Concept (BSC) Bring in the Modern Synthesis

Species are groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups (Mayr 1942) Dobzhansky (1951) contributed the classification isolating barriers The Biological Species Concept

Premating ◦ Behavioral ◦ Ecological (Temporal, Pollinator) ◦ Mechanical Postmating, Prezygotic ◦ Copulatory ◦ Gametic Isolation Postzygotic isolation (Hybrid sterility or inviability) ◦ Extrinsic (no niche, can’t find mates) ◦ Intrinsic (developmental problems, sterility) BSC Reproductive Barriers

Allopatric Taxa Problems with the BSC Red deer Elk

Asexual Taxa Problems with the BSC Bdelloids Bonnethead Genus Timema

Potentially inbreeding Problems with the BSC

Ring Species

Problems with the BSC Chronospecies

Problems with the BSC Worst Case Scenario – White Oaks ◦ Subgenus Quercus ◦ 16 “species” distinguished by morphology ◦ 14 hybridize with other species ◦ Hybridize at some locations, but not others ◦ Many form environmental variants (Different morphologically, same genetically)

The main contenders generally grouped by basis of concept ◦ Interbreeding ◦ Genetic or Phenotypic Cohesion ◦ Evolutionary Cohesion ◦ Evolutionary History Contenders to the BSC

Genetic and Phenotypic Cohesion Species defined by factors that hold populations together rather than those that isolate them Recognition Species Concept(RSC) ◦ Species are the most inclusive population of individual biparental organisms which share a common fertilization system ◦ Pros : Remedies the “isolation concept” ◦ Cons : Problems with the BSC are equally problematic with the RSC and the RSC faces additionally problems such as some hybridization but no introgression Contenders to the BSC

Evolutionary Cohesion Species examined in an evolutionary context Evolutionary Species Concept (EvSC) ◦ A species is a single lineage of ancestral developmental population, which maintain identity and have their own historical fate (Wiley 1978) ◦ Pros: Deals with sexual and asexual taxa. Capable of dealing with entities as “spatial, temporal, genetic, phenetic, ecological, and behavioral” entities ◦ Cons: Not Testable e.g. Allopatric populations (when are fates different?); Two species that hybridize might be evolutionarily connected Contenders to the BSC

Evolutionary history Takes the approach of identifying historically related groups. (i.e. group members are more related to each other than anyone else) Phylogenetic Species Concept 1 (PSC1) ◦ A species is a basal cluster of organisms that is diagnosably distinct from other such clusters and has a parental pattern of ancestry and descent Contenders to the BSC

PSC1 Contenders to the BSC

Approximately 26 species concepts used today in scientific literature No concept is free from ambiguities, each has it’s own set of problems and benefits The BSC is still the most widely accepted definition with some (extremely vocal) dissenters The Reality of Species Concepts

Used in conjunction with a primary species concept (ontological definition) Eliminates subjective judgments, allows for empirical methods of delimitation ◦ Generally uses molecular markers Adding Operational Criteria

Operational Methods Numerous methods, generally fall into 2 categories: ◦ Tree-based : use assumptions about lineage and reproductive isolation ◦ Nontree-based: use assumptions about gene flow

Operational Methods Tree-based: Use assumptions about lineage and reproductive isolation Templeton’s Test of Cohesion ◦ Hypothesized species boundaries tested through a series of null hypothesizes structured to evaluate the correlation of genotypes with geographic location ◦ Nested clade analysis (NCA) with inferences key used to derive most likely cause for observed patterns. Then tests if  H1: all from the same evolutionary lineage  H2: populations are genetically or ecologically interchangeable If both null hypotheses are rejected, the species is recognized

Operational Methods Nontree-based: use assumptions about gene flow Genetic Distance : Good and Wake ◦ Plot genetic distance (e.g. distance summed over allozyme loci) against geographic distance ◦ Formulate regression line, if it passes through the origin, entities are not separate species ◦ If they are species, the line will deviate from the origin because genetic divergence is independent of geographical separation

Operational Methods Nontree-based: use assumptions about gene flow Genetic Distance : Highton ◦ Multilocus allozyme data is used to calculate genetic distances (D of Nei, 1972) ◦ Plot histogram of D values ◦ If the distribution is bimodal, delimit species ◦ Highton recommends using in conjunction with morphological and distributional data

Empirical methods (like species definitions) have variable outcomes ◦ Different empirical methods used on the E. escholtzii complex salamanders, concluded they were in actuality, 1, 2, 7, or 11 species All methods will require qualitative judgments Detailed comparative studies needed Operation Methods: Concerns

Essential unit of analysis for biogeography, ecology and macroevolution Implications for conserving biodiversity (Frankham et al. 2012) ◦ Each definition yields different numbers of species and separate financial, legal, biological and conservation implications This is a mess. Why does it matter?

Why does it matter?

Species seem to be real based on mating system. The BSC is the prominent species concept. 26 other concepts exist, all with varying pros and cons. Operational criterion is important, but more testing is needed. Biodiversity studies and Conservation are greatly affected by use of varying species concepts. Review.

Questions and Comments?