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| speciation_and_plasticity [2013/02/14 12:31] – [Background and general question] mkopp | speciation_and_plasticity [2019/03/21 10:21] (current) – external edit 127.0.0.1 |
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| ===== Background and general question ===== | ===== Background and general question ===== |
| * Speciation -- the splitting of one evolutionary lineage in two descendant lineages -- is a central topic in evolutionary biology (e.g. Coyne and Orr 2004), and one in which mathematical modeling has for a long time played a prominent role (Gavrilets 2004). | * Speciation -- the splitting of an evolutionary lineage into two descendant lineages -- is a central topic in evolutionary biology (e.g. Coyne and Orr 2004), and one in which mathematical modeling has traditionally played a prominent role (Gavrilets 2004). |
| * The reasons are the complexity of the process, which involves interactions of several deterministic and stochastic forces, and the typical long time-scales, which make direct observation difficult. Mathematical theory has been instrumental in determining the conditions for key aspects of the speciation process, such as adaptive divergence, accumulation of genetic incompatibilities, and species-specific mate choice. | * The reason is that speciation is a complex process that usually unfolds over long timescales, so that direct observations are difficult. Mathematical theory has been instrumental in determining the conditions for key components of speciation, such as adaptive divergence (e.g. Geritz et al. 1998), accumulation of genetic incompatibilities (e.g. Gavrilets ...) and species-specific mate choice (e.g. Dieckmann and Doebeli 1999). |
| * Here, we propose to use mathematical modeling to shed light on a topic of much recent interest: Whether speciation can be facilitated by phenotypic plasticity. | * Here, we propose to develop mathematical models that will shed light on a topic of much recent interest: Whether speciation -- and, in particular, speciation with gene-flow, can be facilitated by phenotypic plasticity. |
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| * According to the most wide-spread definition, a species is a group inter-fertile individuals that cannot reproduce with members of other species (Mayr ...). In this context, understanding speciation requires understanding of reproductive isolation. | * A **species** is most commonly defined as a group inter-fertile individuals that cannot reproduce with members of other species (Mayr 1942). Thus, understanding speciation requires understanding the evolution of reproductive isolation. |
| * According to the traditional view, almost all speciation processes are initiated by the formation of a geographic barrier between two populations. After a sufficiently long time if independent evolution, these subpopulations will have become sufficiently incompatible to be recognized as separate species. | * According to the traditional view, speciation almost always requires a geographic barrier separating the range of an ancestral species (allopatric speciation). Two independently evolving subpopulations will then diverge between the nascent species (allopatric speciation) and become more and more incompatible, until they are recognized as separate species. |
| * However, there is mounting evidence for that speciation is also possible in the presence of continuous gene-flow (parapatric or even sympatric). Speciation with gene flow is theoretically challenging because migration and hybridisation will counter-act divergence, and because genetic recombination tends to destroy co-adapted sets of genes/traits. | * However, there is mounting evidence for the opposing view that speciation is also without a strict geographic barrier (parapatric or sympatric speciation). Such "speciation with gene-flow" (Smadja and Butlin 2011?) is theoretically challenging, because migration and hybridisation will counter-act genetic divergence, and because genetic recombination tends to destroy associations between sets of genes or characters. Most models of speciation with gene-flow assume a prominent role for divergent ecological selection pressures (Nosil 2012). |
| * Another recent development: allegedly important role for phenotypic plasticity | |
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| * Phenotypic plasticity is the ability of organisms with identical genotype to produce different phenotypes in different environments. It is a general feature of all living beings, and in many cases is adaptive, because it helps organisms to cope with variable environments. | * **Phenotypic plasticity** is the ability of organisms with identical genotype to produce different phenotypes in response to different environments (e.g. West-Eberhard 2003). It is pervasive in nature, and often is crucial in helping organisms cope with variable environments. |
| * Recently, plasticity has been advertised by some as a centerpiece of an "extended evolutionary synthesis" (West-Eberhard 2003, Piggliucci and Müller 2009?), which aims to unify traditional population genetics with evolutionary developmental biology. | * Recently, plasticity has been advertised by some as a centerpiece of an "extended evolutionary synthesis" (West-Eberhard 2003, Piggliucci and Müller 2009?), which aims to unify traditional population genetics with evolutionary developmental biology. |
| * General thrust: Plasticity plays a leading role in (guiding) phenotypic evolution, including "evolutionary novelties" and diversification ("genes follow development") | * The main argument is that plasticity plays a leading role evolution ("genes follow development"), including diversification and evolutionary novelties (West-Eberhard 2003). |
| * In the context speciation, plasticity is thought to facilitate phenotypic/ecological divergence as well as evolution of RI. Suggested mechanisms include ... In particular, several of the proposed empirical examples (arctic charr etc.) imply speciation with gene flow. | * In the context speciation, plasticity is thought to facilitate phenotypic/ecological divergence as well as the evolution of reproductive isolation (West-Eberhard 2003, Pfennig et al. 2010, Pfenning and McGhee 2010, Fitzpatrick 2012). [Suggested mechanisms include ...] In particular, several of the proposed examples imply speciation with gene flow (e.g., ...). |
| * However, many proposed scenarios rely on verbal models, and many details remain unclear. This is particularly true for scenarios involving plasticity in an ecological adaptation trait (but see Thibert-Plante and Hendry 2011). | * However, many proposed scenarios rely on verbal models, and many details remain unclear. This is particularly true for scenarios involving plasticity in an ecological adaptation trait (but see Thibert-Plante and Hendry 2011). |
| * Open questions include: | * Open questions include: |
| * Under what conditions does plasticity facilitate or impede the evolution of reproductive isolation in the presence of gene flow? | * Under what conditions does plasticity facilitate or impede the evolution of reproductive isolation in the presence of gene flow? |
| * If plastic traits themselves contribute to RI, what are the interactions between the evolution of environmentally and genetically induced reproductive barriers (see Fitzpatrick 2012)? | * If plastic traits themselves contribute to RI, what are the interactions between the evolution of environmentally and genetically induced reproductive barriers (see Fitzpatrick 2012)? |
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| ===== Outline of project ===== | ===== Outline of project ===== |
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