Evolution of images of Raphus (Didus) cucullatus

E. Popping, 1841 2005 - Oxford NHMRothschild, 1907

R. Savery, 1626

1. concept - "the variety of life;" or

2. measurable entity - "a measure of biodiversity;" or

3. social/political construct - a policy is "good for biodiversity.”

Meanings of biodiversity seem to encompass a:

Sydney Canning (1990) estimates there are 35 000 insect species in BC (Phylum Arthropoda, Class Insecta), with 50% described.

But what exactly is he (or anyone else) estimating?

Cicindela parowana, the PAROWAN TIGER BEETLE (Family Cicindelidae - Tiger BeetlesOrder Coleoptera - Beetles) is considered extirpated

1. Are species real? (Answer: in a fuzzy sense)

2. If so, why do they exist? (Answer: sex and selection)

3. How do we recognize them? (Answer: statistics)

4. What causes speciation? (Answer: Evolution 300)How long does it take? (Answer: a long time! see Q. 2)

5. Why might species be the “fundamental unit” of biodiversity research? (Answer: enumeration often works at *local* scales,

and differences map onto other values)

The menu Question 1:are species real entities(or are they figments of our imagination)?

P. paniscusPan troglodytes

“Species” is a common term in biodiversity and the law

Prof. Ernst Mayr Age 96 (Feb 2001)

sciencemag.org/cgi/content/full/305/5680/46

published essay July 4, 2004,eve of his 100th birthday.Died Feb 5, 2005.

Folk taxonomies (cross-cultural common sense)

He went to Arfak Mountains(New Guinea) in 1920's

-collected 137 species of bird.Asked Arfaks for the names, and got 136 names...

(and E.O. Wilson did same for ants in the 1960s, but got one name - "ant” - for all the species)

J. Diamond (of Guns, Germs and Steel fame) did same for Fore of NG in 1966-got 80% concordance (on 120 spp)

We'll return to folk taxonomies when we do taxonomy formally...

Statistical evaluation of ‘clusters’ in sympatryin 3/4 cases I know, (pupfish, sunfish, elephantfish, not ciscoes), individuals do cluster.

pupfish sunfish

ciscoe African elephantfish...

8from Barraclough, 2010, Feulner et al., 2007

trait value (morphological, genetic, ecological)

frequency

On that somewhat flimsy primary evidence, there is consensus that for, entities with sexual reproduction, species are ‘real’ - people see, and agree on, measurable discontinuities...in sympatry at least(ie. variation in nature is “clumped”)

And statistical clumping is also how we recognize species in practice (more on that later)

Why isn't the earth covered in one (or few)

very highly variable entities (species)?

Why do we have species at all?

...one of the most important questions in evolutionary biology: (Coyne and Orr, 2004, pg. 49)

Question 2:

Are species inevitable - where there is life, there are species?

#1. species represent separate stable states of matter (like chemical elements).

#2. species are adapted to discrete ecological niches (and discreteness caused by, inter-alia, trade-offs)

#3. reproductive isolation is inevitable when sex evolves, and this means different populations evolve independently and diverge (see #2) (so sex causes species).

(Maynard Smith & Szathmary, 1995;Coyne and Orr, 2004)

Three Hypotheses:

Why might sex and reproductive isolation cause species? (i) sex mixes individuals’ genotypes, and

(ii) evolution leads to divergence

(iii) discontinuities result between mixing ‘pools’

Hypothesis:

Asexual forms should show (more) continuous variation

than sexual species.

Rarely tested hypothesis (Barraclough and Herniou ‘03)

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The Prediction

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RESEARCH ARTICLE

Independently Evolving Species in Asexual Bdelloid RotifersDiego Fontaneto Elisabeth A Herniou Chiara Boschetti,Manuela Caprioli, Giulio Melone, Claudia Ricci,àTimothy G BarracloughPLoS Biol 5(4): e87. doi:10.1371/journal.pbio.0050087

Rotaria spp. 16Fontaneto et al., PLoS Biol (2007)

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Rotifer tree looks most like this:

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Consistent with the theory that lots of sex "causes" species?

Prokaryotes (who are said to exchange DNA if < 20% divergent,and can take up wholly foreign DNA too):

According to Maynard-Smith and Szathmary (1995), "it is not clear that species [of bacteria] exist”

“The general degree of distinctness in bacteria is unclear”(Coyne and Orr, 2004).

But recent work suggests there are often discontinuities(this may be linked to hypothesis #2 (discrete niches),coupled with selective sweeps)

so...does sex + evolution cause species? Observations:

1. Asexual Bdelloids seem to show discontinuous morphologies.2. Bacteria can share large amounts of DNA across disparate"taxa,” yet remain distinct, perhaps due to very little sex.

(Explain how a little sex can cause species in bacteria)

Rest of the data seem anecdotal.

There is more work to be done here

Question 3. How do we recognize species?

One could define 'species' as sets of populations that aredecidedly different from other populations. Such sets may interbreed (occasionally), but ecologically-relevant traits do not mix. (Mating propensity is an important difference.)

This idea marries the niche-based explanation forthe reality of species (#2) with phenotypic definitions for their identification.

Perhaps this is also a helpful way to conceptualize bits of biodiversity: are the species interchangeable on the landscape - e.g, could we move Sumatran Orang-utans to Borneo and no one would be the wiser? This also works in theory - statistical clumping also requires irreplaceability.

-According to Darwin (1859) , species are no more than“well-marked varieties”- i.e., there is nothing special about them.

Observations on “Species”

Purely empirical definition

This speaks to the readings for discussion in class on Monday

~1930: T. Dobzhansky discovered the cryptic speciesDrosophila pseudoobscura and D. persimilis

Look ‘exactly’ alike, but don’t interbreed

1943

...70 years of confusion ensue...

Two approaches take hold...

First approach:E. Mayr decides we need a species conceptthat can allow for look-alikes:

The Biological Species Concept (BSC):

-- a group of interbreeding natural populations unable to successfully mateor reproduce with other such groups. (1930’s)

-- a group of interbreeding natural populations unable to successfully mateor reproduce with other such groups, and which occupies a specific niche in nature(gets around,eg. instant species due to infection...) (1982)

concepts tend to be

-process-based -prospective

definitions tend to be

-pattern-based -retrospective

...however a species concept = species definition

Phyloscopus trochiloides,a better ring species

Irwin et al., 2005 Irwin et al., 2001

Difficult cases...

(b) Note, ~all of the 250 000 angiosperm speciesare "morphospecies"-

so cryptic species don't exist by definition...

EElle's blue-eyed mary

Difficult cases...

(c) Fossils--BSC can say little about fossils: “process doesn’t fossilize”

Finally (but importantly),

(d) All asexual taxa! -- Pattern-based definitions are needed.

(Pattern-based) definitions are more operational2. Use a pattern-based definition (Darwin’s):

Two approaches take hold...

1. Use a concept-based definition (Mayr)

Genotypic cluster (Mallet, 1995) --distinguishable groups of individuals based on identifiable genotypicclusters (i.e. distinct genetic discontinuity).

And that is pretty much what Tim Barraclough used totest whether sex caused species...

Buckley-Beason et al., 2006, Current Biology

www.felineconservation.org

Molecular evidence for species-level distinctions in clouded leopards

Along with fixed subspecies-specific chromosomal differences, this degree of differentiation is equivalent to, or greater than, comparable measures among five recognized Panthera species (lion, tiger, leopard, jaguar, and snow leopard). These distinctions increase the urgency of clouded leopard conservation efforts, and if affirmed by morphological analysis and wider sampling of N. n. diardi in Borneo and Sumatra, would support reclassification of N. n. diardi as a new species (Neofelis diardi).

Neofelis nebulosa

ATP-8 (139 bp) mtDNA gene segment

N. n. diardiN. n. brachyurus

N. n. macrosceloides

N. n. nebulosa

SFU debate from 1990’s - is there one speciesof Orangutan (Pongo pygmaeus) or are there two?

(exactly the same argument as for the leopards)

Three short papers I could post if you want:Original: Xu96; Response: Muir98;More data: Muir00.

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1965 1975 1985 1995 2005

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Groves' Primate TaxonomyEncyclopaedia of MammalsWalker's Mammals of the WorldA World List of Mammalian SpeciesMammal Species of the WorldPrimate Adaptation and EvolutionIUCN Red ListIndependent

Isaac et al. (2004) Trends. Ecol. Evol. 19: 464-469

“Taxonomic inflation” of primate species

And competing estimates of bird diversity differ by up to a factor of two.(sympatry or allopatry?)

The Economist, May 17th 2007

“Hail Linnaeus, the Economist “ Conservationists—and polar bears—should heed the lessons of economics

One reason for this taxonomic inflation is that the idea of a species becoming extinct is easy to grasp, and thus easy to make laws about. Subspecies just do not carry as much political clout. The other is that upgrading subspecies into species simultaneously increases the number of rare species (by fragmenting populations) and augments the biodiversity of a piece of habitat and thus its claim for protection!.

Evolution often fails to produce the clear divisions that human thought in general, and the law in particular, prefers to work with. It therefore behoves taxonomists to be honest. If they debase their currency, it will ultimately become valueless. Linnaeus the economist would have known that instinctively.

(2007 was the 300th Anniversary of Linnaeus's birth) (2009 was the 200th Anniversary of Darwin's)

http://www.linnaeus2007.se/

Naming a species is perhaps the most important thingone can do from the point of view of biodiversity-

No name, not counted