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Spontaneous speciation?

In a world without natural selection and no vast mountain ranges dividing populations, one might expect biodiversity to remain forever stagnant. But according to a study published this week in Nature, new species can arise arbitrarily and without provocation, challenging the widely held notion that physical isolation and selection are the driving forces behind speciation. Image: Wikimedia commons"So much of ecology and evolutionary biology is based on this idea of adaptive divergence leading to

By | July 15, 2009

In a world without natural selection and no vast mountain ranges dividing populations, one might expect biodiversity to remain forever stagnant. But according to a study published this week in Nature, new species can arise arbitrarily and without provocation, challenging the widely held notion that physical isolation and selection are the driving forces behind speciation.
Image: Wikimedia commons
"So much of ecology and evolutionary biology is based on this idea of adaptive divergence leading to speciation," said evolutionary biology linkurl:Charles Goodnight;http://www.uvm.edu/%7Ebiology/Faculty/Goodnight/Goodnight.html of the University of Vermont, who was not involved in the work. "What this [study] is saying is that speciation may just be a result of random processes." In 2001, linkurl:Stephen Hubbell;http://www.plantbio.uga.edu/%7Eshubbell/Webpages/Members/steve_wp.htm of the University of Georgia proposed the neutral theory of biodiversity, in which the patterns of biodiversity across the globe are explained largely by chance. The idea brought into question the traditional, niche-based view of ecological community structure, which posits that organisms diffuse across a variable environment as a result of competition for resources. Hubbell's theory, explained physicist linkurl:Amos Maritan;http://www.padova.infm.it/sezioneb/PeopleMaritan.htm of the University of Padova in Italy, who wrote an accompanying review to the current study, demonstrated that this type of species segregation can happen "in a spontaneous way." However, neutral theory described the spatial distribution of species once they form, but not how or why they arise in the first place. Complex systems biologist linkurl:Yaneer Bar-Yam;http://necsi.org/faculty/bar-yam.html of the New England Complex Systems Institute in Cambridge, Mass., and colleagues expanded this model to explain the process of speciation. They found that starting with a population of genetically identical individuals in a homogeneous environment, sexual reproduction, mutation, and limited dispersal led to the splitting of species -- as defined by a threshold genetic distance -- after just 300 generations, in the absence of physical barriers and selection. "Traditionally, it was believed that most species arise because physical barriers prevent mating for long enough for the populations to diverge," said Bar-Yam. Similarly, natural selection in a heterogeneous environment can explain species divergence, as spatially divided populations adapt to their local environments. "But what our work shows is that's not necessary," he said. "That doesn't mean that [geographic barriers and selection] are not playing a role," Bar-Yam added. It's like a spontaneous traffic jam, he explained. An accident is not necessary for traffic to back up. "It's enough just to have heavy traffic, and you'll have jams forming," he said. But if there is an accident, there's no doubt the traffic will slow. Likewise, "if there is a barrier, you expect that species will form," he said, "[but our results suggest that] the underlying process of spontaneous formation of species is so strong that it's overwhelming [such local] processes." As in previous models of neutral selection, the patterns of biodiversity estimated by this new model accurately reflected the observed patterns in nature, Bar-Yam said. From speciation rates to patterns of species richness and abundance, the model produced spatial dynamics that approximated the empirical data known for a variety of species, including plants, birds, and fish. The universality of these results raises "the possibility that something really simple could be underlying many of the patterns seen," said physicist linkurl:Jayanth Banavar;http://www.phys.psu.edu/people/display/?person_id=19 of Penn State University, who coauthored the accompanying review with Maritan. Species may arise and coexist simply as a result of spatial and genetic diffusion, he said. However, "more study is needed to assess whether the assumptions are in fact justified in real field data," Banavar cautioned, such as how genetically similar individuals must be in order to successfully produce offspring and the distance those offspring disperse after birth. Additionally, the model must be expanded to include how species interact with each other, Maritan added, as "interactions are relevant to understanding biodiversity." Still, this simplified model is "a step forward," Banavar said. It examines "speciation in a more natural way than has been done previously [while] retaining many of the patterns that [are] seen in nature. It's the next step in considering realistic speciation processes."
**__Related stories:__***linkurl:Sticky speciation;http://www.the-scientist.com/article/display/55360/
[February 2009]*linkurl:Evidence for sympatric speciation;http://www.the-scientist.com/news/display/23103/
[9th February 2006]*linkurl:Red fish, blue fish, speciation?;http://www.the-scientist.com/blog/display/55065/
[2nd October 2008]
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Comments

Avatar of: null null

null null

Posts: 18

July 15, 2009

One wonders where the data fos usch species can be found? Where are these spontaneously arisen species, especially since the claim is that the process would overwhelm isolation and other barriers. Then too, I wonder how natural selection is not or would not be a factor, no matter how such spontaneously arisen species predominate, or do they just "spontaneously" survive.
Avatar of: anonymous poster

anonymous poster

Posts: 107

July 15, 2009

I'm a little confused about the definition of a species. I always thought that speciation required some mechanism of reproductive isolation, not just "a threshold genetic distance". (Admittedly, I am a naive non-expert.) What of Homo sapiens? Most interpretations of DNA diversity lead to the conclusion that human populations derive from a common ancestor who lived around 100,000 years ago, which is conservatively 3,000 generations. Why haven't we split into multiple species? Or have we....?
Avatar of: Camilo Colaco

Camilo Colaco

Posts: 10

July 16, 2009

New individuals arise by genetic changes (mutations) that have phenotypic consequences. \nMutations are a result of (uncorrected) errors in the replication of genetic material.\nWhy then is it thought that any (force) drives the generation of species?\n\n
Avatar of: Steven Anderson

Steven Anderson

Posts: 9

July 16, 2009

Show me the math! Show me some evidence!
Avatar of: Matthew Grossman

Matthew Grossman

Posts: 27

July 17, 2009

Seems perfectly natural to me. I'm a molecular biologist not a evolutionary biologist, but I can't see any other way for the process to get started. It's DNA sequence changes and as more recently shown, inherited DNA expression patterns and probably other inherited structural changes that initiate the process. If the change is viable and able to reproduce in its environment it succeeds,; having a good niche helps obtain this success, I'd say a lot. Isolation, e.g. on islands, does clearly provide for unusual opportunities and drivers for success, as shown be many cases of gigantism and miniaturism and all the rest.
Avatar of: Thomas Liggett

Thomas Liggett

Posts: 7

July 20, 2009

I also am a molecular biologist. DNA mutation may the impetus for the alteration of one species to form another, but what stops the interaction of organisms in the same population from interbreeding? A single mutation is just not a plausible "THEORY" to produce speciation as it takes multiple mutations over time to inhibit one organism from producing viable offspring with another organism (the accepted definition of a species). There must be another force (or barrier) to inhibit the population from interbreeding over the period of time to produce multiple mutations that will inhibit interbreeding during mutation formation. Natural selection is this second component needed for speciation to occur.\nIt is ironic that a majority of the work on spontaneous speciation is done in the lab of a physicist, and from reviewing the journals about the topic, I have found that their "THEORY" is just a computerized model without regard for experimentation or scientific data. For a scientific hypothesis to be accepted, this is the minimum required. As posted previously, "Show me the Data!"\n
Avatar of: null null

null null

Posts: 44

July 20, 2009

I have read the paper, so here is a sensible critique from an old population genetics perspective. First, what I think the model is doing, and secondly how far it falls short of most reality.\n\nThis model is not free of geographical reproductive barriers, in fact it simulates geographical distance as a reproductive barrier. Distance is relative to the migration which is the ability for gene flow, which in this model is the distance S (array cells) over which a gamete can be collected. In Fig 2 it is clear that speciation is rapid when S is 4 and noise accumulates, and speciation does not occur when S is greater than 6. This will be because the smoothing effect of migration at 7 exceeds the accumulation of local noise from genetic drift (chance). The choice of mates was from about 8 neighbours. \n\nIn effect it generates linear variants then removes the intermediates by genetic drift. This is easy because the numbers in the local population-cum-species are small. There is a clear equivalent in ring species. These follow a linear habitat around a geographic obstacle. Populations within the line interbreed with those to left and right, but the extreme ends are so different that, when compared, they are different species, and this becomes apparent where the ends of the habitat overlap to close the ring. Removing the middle and leaving the populations at both ends of a ring species would exactly copy this model. See http://www.actionbioscience.org/evolution/irwin.html for more details of ring species. This model simplistically reproduces one factor of speciation in a very widely dispersed and very sparse population of sedentary individuals. \n\nThe requirement to remove intermediates explains why there is much more speciation in a linear 1D simulation than in an area 2D simulation. In the 1D simulation there is only need to lose the tiny intermediate populations to right and left to isolate a variant group as a new species. In a 2D simulation the intermediates must be lost in all directions. Equally, it explains why number of species increases with area, speciation is a function of isolation, that is distance, and so a species patch has particular size range, too small and it is lost, too large and the opposite edges are isolated and can form new species.\n\nSpeciation happens when the rate of geneflow between two populations is less than the rate of genetic change within them. This model generates a random vertical genotypic walk in a flat genetic surface, like random disturbances on a water surface. When the sides of a peak or trough exceed an arbitrary slope related to G/S the peak or trough becomes a new species which no longer interacts with neighbours, preventing any more smoothing. The model is just multidimensional, rather than the 3D of a water surface.\n\nThis model may well have relevance for populations of widely dispersed, sedentary species with limited gene flow. It was taught to me about 40 years ago as being a factor of unknown importance in explaining local variation in snails and possibly in speciation. It is nice to have it modelled now.\n\nReality differs both genetically and environmentally. In reality, the environment is not homogeneous. If heterogeneity (habitat barriers) is added to the model it will decrease gene flow so speciation will be faster. If instability is added, some patches being periodically uninhabitable, there is more chance of extremes losing their mutual intermediates and becoming new species, as happens when a habitat is fragmented ? island speciation. Genetically, reality distinguishes between premating isolation, where genes (or learned behaviour) prevents mating between types (as in this model) and postmating isolation, where some genetic combinations are not viable. These tend to remove rare (equals new) variants and reduce genetic variation. There is also ecological adaptation to consider. In a homogeneous environment, the species which uses the resources most efficiently will replace the less efficient species. This also seems to be a problem with Hubbells neutral speciation model. In a homogeneous environment there would only be one species at each trophic level, and one could question why there should be more than one trophic level. The simulation was quite unrealistic in assuming that all the mutations considered had no effect on fitness beyond the ability to find a mate.\n\nHugh Fletcher.\n
Avatar of: Matthew Grossman

Matthew Grossman

Posts: 27

July 22, 2009

I felt that a single mutation could result in speciation without physical separation. Here is an abstract of a paper that skillfully describes this possibility. I would also suggest that a mutation or mutations that causes the mutants to not mate by choice (behavior) could achieve biological separation sufficient to allow speciation over time even if there was no physical separation.\n\n\nHans-Rolf Gregorius(1). A single-locus model of speciation. Acta Biotheoretica. Volume 40, Number 4 / December, 1992.\n\n(1) Abteilung für Forstgenetik und Forstpflanzenzüchtung, Universität Gottingen, Büsgenweg 2, 3400 Gottingen, Fed. Rep. Germany \n\nAbstract: The crucial phase of speciation is argued to be the evolution of mating cross-incompatibility (prezygotic incompatibility) between the genotypes distinguishing the prospective species populations. Based on this idea, a single-locus model of speciation is presented, which is shown to be biologically plausible and may help to settle the controversy as to the biological significance of single-locus modes of speciation. The model involves three alleles, two of which characterize in homozygous state the prospective species populations and in heterozygous state their hybrids. The third allele represents a mutant which is equivalent to one of the first two alleles with the exception that it inhibits mating with carriers of the third allele. This third allele is fixed in one population and immigrates into a second population which contains the mutant inhibiting matings with members of the former population. Migration in the reverse direction does not occur. Proceeding from a widely applicable concept of fitness and mating preference it is shown that postzygotic incompatibility (hybrid or heterozygote disadvantage) alone suffices to trigger evolutionary replacement of the extant mating relations in the population receiving immigrants by any arbitrary degree of prezygotic incompatibility. This corroborates Wallace's hypothesis and emphasizes the potential biological relevance of speciation by reinforcement (parapatric speciation) at single gene loci.

July 22, 2009

This article is a model trial, it is based on assumptions and the way the computers were programmed. The idea of spontaneous speciation has one essential problem, while single cell organisms can undergo simple asexual cell division to create new organisms, complex organisms have to be able to engage in fertilization that is quite complicated. Changes in genetic functions so comprehensive as to produce a new species would, by definition, eliminate their ability to produce viable offspring with any of the species they spontaneously speciated from.\n What is defined here is a failure to understand what constitutes a species. This is also shown in an embarrassing report in Naturwissenschaften by Knerer in 1991 (v. 78, pp328-330) where had he read E.O Wilson's Sociobiology, the article would never have been published (this says something about the state of confusion among the editors as well). Animals undergo quite significant changes in physiology and behavior due to environmental changes, heat for example, often the changed organisms are found and determined to be a new species. In Knerer's example variations in N. maurus and pratti are simply responses to environmental changes in their range and Knerer reports full fertilization among members of the variants and viable young. Knerer calls these fertile offspring hybrids, which is unfortunate.
Avatar of: RON HANSING

RON HANSING

Posts: 20

July 24, 2009

Interesting idea. I think this is plausible. Why not?, what is needed is some evidence and data, to make this a theory.\n\nI am always reminded of Baltimore and Temins Nobel prize, started with a crazy idea, using 100 year old technology. And the same can be said for the cloning of Dolly, the sheep. Not to mention Helicobacter pylori. \n\nIt all starts with a crazy idea that challenges orthodoxy. The history of science, is replete with numerous examples, with just the out of the box thinking.\n\nI always had this idea that prion replication is due to a reverse translylase and a reverse transcriptase. \n\nOK, you bight young guys, go for it. prove me wrong ... or right and get the big prize. \n\nAgain, it would be a simple experiment based on 100 year old technology. Simple substrate substitution and looking for a radio labeled product. And I don't even care if I get credit. I am only interested in this, but an old guy, and cannot do it myself.\n\nSo often orthodoxy, have inhibited science, not progressed it.\n\nron hansing, md. 7.24.9\n\n\n\n

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