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The tempo and mode of evolution: a neontological reappraisal
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The theory of “punctuated equilibrium” suggests that species evolve rapidly during or immediately upon speciation, “punctuating” long periods of little or no morphological evolution. Here I confirm that body size differences within clades of birds and mammals are best explained using a model of punctuated evolution. This allows me to suggest that rates of speciation and extinction are responsible for why there are more small mammals than large, as large mammals likely speciate and go extinct at a higher rate than small mammals, and hence undergo cladogenetic change more often. Likewise, mammals appear to evolve at a higher rate than birds, because mammals, as a whole, speciate and go extinct at a higher rate than birds. Furthermore I show that mass extinctions and competition, i.e. forms of natural selection, do not seem to explain differences in body size between species on a macroevolutionary scale. Taken together, these findings not only contradict the idea that apparently different rates of evolution are due to differential selection intensities, and emphasize the importance of the speciation process in evolution, but raise the intriguing question as to what limits evolution in established species. Here I suggest that phenotypic traits, dependent on one another for development and/or function may constrain evolution by exerting stabilizing selection from within the organism, as opposed to external environmental selection, which has been the main focus of evolutionary studies thus far.

Abstract [sv]

Teorin om "punkterad jämvikt" säger att arter utvecklas snabbt under och omedelbart efter artbildning, vilket "punkterar" långa perioder med lite eller ingen morfologisk föränding. I den här avhandlingen visar jag att skillnader i kroppsstorlek inom klader (grupp med gemensam förfader) hos fåglar och däggdjur förklaras bäst när man använder en modell med punkterad evolution. Detta gör i sin tur att jag kan föreslå att hastigheten var med artbildning och utdöende sker, förklarar varför det finns fler små däggdjur än stora, eftersom stora däggdjur sannolikt bildar nya arter och dör ut med en högre hastighet än små däggdjur. Likaså förefaller däggdjur i sin helhet att evolvera med en högre hastighet än fåglar, detta eftersom däggdjur bildar nya arter och dör ut med en högre hastighet än fåglar. Dessutom visar jag att massutdöenden och konkurrens (naturlig selektion) inte verkar förklara skillnader mellan arter över makroevolutionära skalor (över geologisk tid). Sammantaget motsäger dessa resultat inte bara idén om att skenbart olika hastighet på evolution främst beror på skillnader i selektionstryck utan understryker också vikten av artbildningsprocessen som en viktig faktor som styr evolutionens hastighet. Dessutom leder dessa resultat till frågan om vad som begränsar evolutionen hos redan etablerade arter. Här föreslår jag att fenotypiska karaktärsdrag som är beroende av varandra för sin funktion och utveckling kan begränsa evolutionen genom att utöva stabiliserande selektion inifrån organismen, i motsats till selektion från den omgivande miljön vilket har varit fokus för de flesta evolutionära studier hittills.

Place, publisher, year, edition, pages
Umeå: Institutionen för ekologi, miljö och geovetenskap, Umeå Universitet , 2011. , 38 p.
Keyword [en]
birds, extinction, macroevolution, mammals, microevolution, punctuated equilibrium, speciation
National Category
Evolutionary Biology
Identifiers
URN: urn:nbn:se:umu:diva-49761ISBN: 978-91-7459-306-8 (print)OAI: oai:DiVA.org:umu-49761DiVA: diva2:457287
Public defence
2011-12-09, KBC-huset, KB3A9, Umeå Universitet, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2011-11-18 Created: 2011-11-17 Last updated: 2011-11-17Bibliographically approved
List of papers
1. Punctuated equilibrium in a neontological context
Open this publication in new window or tab >>Punctuated equilibrium in a neontological context
2010 (English)In: Theory in biosciences, ISSN 1431-7613, E-ISSN 1611-7530, Vol. 129, no 2-3, 103-111 p.Article in journal (Refereed) Published
Abstract [en]

The theory of punctuated equilibrium, which proposes that biological species evolve rapidly when they originate rather than gradually over time, has sparked intense debate between palaeontologists and evolutionary biologists about the mode of character evolution and the importance of natural selection. Difficulty in interpreting the fossil record prevented consensus, and it remains disputed as to what extent gradual change in established species is responsible for phenotypic differences between species. Against the historical background of the concept of evolution concentrated in speciation events, we review attempts to investigate tempo and mode of evolution using present-day species since the introduction of the theory of punctuated equilibrium in 1972. We discuss advantages, disadvantages, and prospects of using neontological data, methodological advances, and the findings of some recent studies.

Place, publisher, year, edition, pages
Springer, 2010
Keyword
extinction, macroevolution, microevolution, speciation
National Category
Ecology Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:umu:diva-35396 (URN)10.1007/s12064-010-0087-7 (DOI)000283360400004 ()20514523 (PubMedID)
Available from: 2010-08-17 Created: 2010-08-17 Last updated: 2017-12-12Bibliographically approved
2. Little evidence for Cope’s rule from Bayesian phylogenetic analysis of extant mammals
Open this publication in new window or tab >>Little evidence for Cope’s rule from Bayesian phylogenetic analysis of extant mammals
2010 (English)In: Journal of Evolutionary Biology, ISSN 1010-061X, E-ISSN 1420-9101, Vol. 23, no 9, 2017-2021 p.Article in journal (Refereed) Published
Abstract [en]

According to Cope’s rule, lineages tend to evolve towards larger body size, possibly because of selective advantages of being large. The status of Cope’s ‘rule’ remains controversial as it is supported in some but not all large-scale fossil studies. Here, we test for Cope’s rule by Bayesian analyses of average body masses of 3253 extant mammal species on a dated phylogenetic tree. The data favour a model that does not assume Cope’s rule. When Cope’s rule is assumed, the best estimate of its strength is an average ancestor-descendant increase in body size of only 0.4%, which sharply contrasts with the 9% bias estimated from fossil mammals. Thus, we find no evidence for Cope’s rule from extant mammals, in agreement with earlier analyses of existing species, which also did not find support for Cope’s rule.

Keyword
bayesian models, body size, macroevolution, phylogenetics, present-day species
National Category
Ecology Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:umu:diva-35850 (URN)10.1111/j.1420-9101.2010.02051.x (DOI)000281141800020 ()
Note
Short Communication:Available from: 2010-09-08 Created: 2010-09-08 Last updated: 2017-12-12Bibliographically approved
3. Mass extinctions do not explain skew in interspecific body size distributions
Open this publication in new window or tab >>Mass extinctions do not explain skew in interspecific body size distributions
2013 (English)In: Journal of Zoological Systematics and Evolutionary Research, ISSN 0947-5745, E-ISSN 1439-0469, Vol. 51, no 1, 13-18 p.Article in journal (Other academic) Published
Abstract [en]

In several higher animal taxa, such as mammals and birds, the distribution of species’ body sizes is heavily skewed towards small size. Previous studies have suggested that small-bodied organisms are less prone to extinction than large-bodied species. If small body size is favorable during mass extinction events, a post mass extinction excess of small-bodied species may proliferate and maintain skewed body size distributions afterwards. Here, we modeled mass extinctions, and found that even unrealistically strong body mass selection has little effect on the skew of interspecific body size distributions. Counter intuitively, selection against large body size may skew size distributions towards large body size. Subsequent evolutionary diversification rapidly erases the rather small effects mass extinctions may have on size distributions. Next, we tested whether skewed body size distributions in mammals and birds can be due to mass extinctions at the transition from Cretaceous to Paleogene, approximately 65 million years ago. Body size distributions of clades that originated during the Cretaceous are on average more skewed than their subclades that originated during the Paleogene, but the difference is only minor in mammals, and in birds it can be explained by a positive relationship between species richness and skewness that is also present in clades that originated after the transition. Hence, we cannot infer from extant species whether the K-Pg mass extinctions were size-selective, but they are not the reason why most extant bird and mammal species are small-bodied.

Keyword
body-size skew, Cretaceous-Paleogene, extant species, macroevolution, phylogeny
National Category
Natural Sciences
Identifiers
urn:nbn:se:umu:diva-49755 (URN)10.1111/jzs.12002 (DOI)000313753400002 ()
Available from: 2011-11-17 Created: 2011-11-16 Last updated: 2017-12-08Bibliographically approved
4. Do speciation rates drive rates of body size evolution in mammals?
Open this publication in new window or tab >>Do speciation rates drive rates of body size evolution in mammals?
2009 (English)In: American Naturalist, ISSN 0003-0147, E-ISSN 1537-5323, Vol. 174, no 6, 912-918 p.Article in journal (Refereed) Published
Abstract [en]

Recently, it has been shown with large data sets of extinct mammals that large‐bodied lineages experienced higher speciation and extinction rates; with extant mammals, it has been shown that body size evolution is accelerated during speciation. Therefore, it is interesting to investigate whether mammalian body size evolution is faster in large‐bodied lineages. Phylogenetic analysis assuming size‐independent speciation rates suggested that the rate of body size evolution increases with body size, whereas size differences in recent sister species (that are little affected by species turnover) appear to be independent of size. This supports the hypothesis that high rates of species turnover increase the rate at which interspecific differences accumulate in large‐bodied clades, whereas rates of evolution in single lineages are approximately size invariant. Similarly, these findings support the notion that mammalian body size evolution is indeed concentrated in speciation events.

Keyword
diversification, ecological speciation, extinction, macroevolution, natural selection, punctuated equilibrium
National Category
Earth and Related Environmental Sciences Ecology
Identifiers
urn:nbn:se:umu:diva-30403 (URN)10.1086/646606 (DOI)
Available from: 2009-12-21 Created: 2009-12-21 Last updated: 2017-12-12Bibliographically approved

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