Chapter 11 (Plant Taxonomy, pp. 137-152) Species Concepts.

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1 Chapter 11 (Plant Taxonomy, pp. 137-152) Species Concepts

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4 Morphological Species Concept A species is a community, or a number of related communities, whose distinctive morphological characters are, in the opinion of a competent systematist, sufficiently definite to entitle it, or them, to a specific name (Regan 1926)

5 Layia (Asteraceae) Layia discoidea Layia glandulosa

6 Layia spp. L. chrysanthemoidesL. fremontii L. platyglossaL. munzii

7 Limitation Morphological Species Concept- variation Layia gaillardioides Leaf shape Layia glandulosa Flower color

8 Limitation Morphological Species Concept- subjectivity How many species are represented?

9 Biological Species Concept Species are groups of interbreeding natural populations that are reproductively isolated from other such groups (Mayr 1969)

10 Layia discoidea Layia glandulosa F1= 8/8, 100% fertile!

11 Layia spp. L. chrysanthemoidesL. fremontii L. platyglossaL. munzii

12 Limitations Biological Species Concept Difficult to measure the true extent of gene flow among natural populations Inapplicability of this concept to asexual species Interspecific hybridization between species of flowering plants is common What qualifies as reproductively isolated? 25%, 50%, 75%, or 100%?

13 Phylogenetic Species Concept Species are the terminals in a phylogenetic tree (Davis and Goldman 1993) The smallest diagnosable monophyletic unit with a parenteral pattern of ancestry and descent (Rosselló-Mora and Amann 2001)

14 Layia Phylogeny

15 L. chrysanthemoides L. fremontii L. munzii L. platyglossa L. discoidea L. glandulosa

16 Limitations Phylogenetic Species Concept Species are mosaics of genetic variation and often of reticulate origin Some species are monophyletic and others paraphyletic, and species are therefore not amenable to cladistic analysis It is unrealistic to assume that all species are bifurcating, completely evolved entities that form at the same evolutionary rates

17 Barcode Species Concept Identification of species is based on comparing DNA sequences of specimens to sequences in databases (Hebert et al. 2003)

18 Limitations Barcode Species Concept Many sequences in databases are based on misidentifications Interspecific and intraspecific variation exhibited by rbcL and matK varies between plant taxa Genetic variation considered intraspecific by some workers is treated as interspecific by others Species discrimination using the two locus combination rbcL + matK is successful in only 72% of cases

19 Ecological Species Concept A species is a lineage which occupies an adaptive zone minimally different from that of any other lineage in its range and which evolves separately from all lineages outside its range (Van Valen 1976) Limitations- not all species fit this model, and it is hard to confirm without extensive genetic study