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Robert E. Ricklefs - One of the best experts on this subject based on the ideXlab platform.
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Host–pathogen coevolution, secondary Sympatry and species diversification
Philosophical transactions of the Royal Society of London. Series B Biological sciences, 2010Co-Authors: Robert E. RicklefsAbstract:The build-up of species locally within a region by allopatric speciation depends on geographically separated (allopatric) sister populations becoming reproductively incompatible followed by secondary Sympatry. Among birds, this has happened frequently in remote archipelagos, spectacular cases including the Darwin's finches (Geospizinae) and Hawaiian honeycreepers (Drepanidinae), but similar examples are lacking in archipelagos nearer to continental landmasses. Of the required steps in the speciation cycle, achievement of secondary Sympatry appears to be limiting in near archipelagos and, by extension, in continental regions. Here, I suggest that secondary Sympatry might be prevented by apparent competition mediated through pathogens that are locally coevolved with one population of host and are pathogenic in sister populations. The absence of numerous pathogens in remote archipelagos might, therefore, allow sister populations to achieve secondary Sympatry more readily and thereby accelerate diversification. By similar reasoning, species should accumulate relatively slowly within continental regions. In this essay, I explore the assumptions and some implications of this model for species diversification.
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host pathogen coevolution secondary Sympatry and species diversification
Philosophical Transactions of the Royal Society B, 2010Co-Authors: Robert E. RicklefsAbstract:The build-up of species locally within a region by allopatric speciation depends on geographically separated (allopatric) sister populations becoming reproductively incompatible followed by secondary Sympatry. Among birds, this has happened frequently in remote archipelagos, spectacular cases including the Darwin's finches (Geospizinae) and Hawaiian honeycreepers (Drepanidinae), but similar examples are lacking in archipelagos nearer to continental landmasses. Of the required steps in the speciation cycle, achievement of secondary Sympatry appears to be limiting in near archipelagos and, by extension, in continental regions. Here, I suggest that secondary Sympatry might be prevented by apparent competition mediated through pathogens that are locally coevolved with one population of host and are pathogenic in sister populations. The absence of numerous pathogens in remote archipelagos might, therefore, allow sister populations to achieve secondary Sympatry more readily and thereby accelerate diversification. By similar reasoning, species should accumulate relatively slowly within continental regions. In this essay, I explore the assumptions and some implications of this model for species diversification.
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The causes of evolutionary radiations in archipelagoes: passerine birds in the Lesser Antilles.
The American Naturalist, 2007Co-Authors: Robert E. Ricklefs, Eldredge BerminghamAbstract:To investigate why some lineages undergo evolutionary radiation, we compare the passerine avifaunas of the Hawaiian and Galapagos archipelagoes, which have supported well-known radia- tions of birds, with those of the Lesser Antilles, which have not. We focus on four steps required for the buildup of diversity through allopatric speciation and secondary Sympatry: genetic divergence in isolation, persistence of island populations, recolonization of source islands, and ecological compatibility in secondary Sympatry. Analysis of genetic divergence among island populations in the Lesser Antilles reveals evidence of both prolonged independent evolution and re- expansion of differentiated island populations through the archi- pelago but little evidence of secondary Sympatry of divergent genetic lineages. Archipelagoes with high rates of colonization from conti- nental or nearby large-island sources might fail to promote evolu- tionary radiations because colonists fill ecological space and constrain diversification through competition. However, morphological anal- ysis demonstrated similar divergence between allopatric populations in species in Hawaii, Galapagos, and the Lesser Antilles, although the rate of divergence between secondarily sympatric species evidently is more rapid in Hawaii and the Galapagos. Alternatively, endemic buildup of diversity might be facilitated by the relative absence of pathogens in Hawaii and Galapagos that otherwise could prevent the secondary Sympatry of populations owing to disease-mediated com- petition.
Karen D. Mccoy - One of the best experts on this subject based on the ideXlab platform.
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sympatric speciation in parasites what is Sympatry
Trends in Parasitology, 2003Co-Authors: Karen D. MccoyAbstract:Parasites account for a large part of known species diversity and are considered to have a high potential for sympatric speciation. However, the frequency of sympatric divergence in these organisms will depend on the definition of Sympatry that one uses. Like many of our current species concepts, the typical definition of Sympatry is not widely applicable to parasites. Revisiting the historically defined conditions for sympatric speciation and considering the situations in which we might regard parasites as being sympatric leads us to question the classic prediction that parasites have a greater tendency to speciate in Sympatry than do free-living organisms.
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Sympatric speciation in parasites – what is Sympatry?
Trends in parasitology, 2003Co-Authors: Karen D. MccoyAbstract:Parasites account for a large part of known species diversity and are considered to have a high potential for sympatric speciation. However, the frequency of sympatric divergence in these organisms will depend on the definition of Sympatry that one uses. Like many of our current species concepts, the typical definition of Sympatry is not widely applicable to parasites. Revisiting the historically defined conditions for sympatric speciation and considering the situations in which we might regard parasites as being sympatric leads us to question the classic prediction that parasites have a greater tendency to speciate in Sympatry than do free-living organisms.
Jeffrey L. Feder - One of the best experts on this subject based on the ideXlab platform.
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Sympatry and Patterns of Genetic Differentiation in Sympatry
Brenner's Encyclopedia of Genetics, 2013Co-Authors: Jeffrey L. Feder, Scott P. EganAbstract:Populations are sympatric when they overlap completely in where they occur and parapatric when they co-occur in part, but not all, of their geographic ranges. In contrast, allopatric populations are completely geographically separated. The geographic distribution of populations has important consequences for the genetic divergence of populations and speciation. In allopatry, physical and environmental barriers to migration between populations allow genetic differences to independently evolve throughout the genome due to natural selection, sexual selection, and genetic drift. These differences can inadvertently cause reproductive isolation, resulting in the formation of new species. When populations diverge in Sympatry or parapatry, they must overcome the exchange of genes due to migration and hybridization (interbreeding) if speciation is to proceed. In contrast to allopatry, the physical position of genes relative to each other in the genome could have important consequences for natural selection to act to allow sympatric and parapatric populations to differentially adapt to variation in local conditions and evolve ecologically based reproductive isolation. Current theoretical and empirical studies are discussed describing how processes such as divergence and genomic hitchhiking that depend upon the architecture of diverged genes in the genome may increase the effectiveness of natural selection to facilitate speciation-with-gene-flow.
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Space, Sympatry and speciation
Journal of evolutionary biology, 2009Co-Authors: James Mallet, Patrik Nosil, Axel Meyer, Jeffrey L. FederAbstract:Sympatric speciation remains controversial. ‘Sympatry’ originally meant ‘‘in the same geographical area’’. Recently, evolutionists have redefined ‘sympatric speciation’ non-spatially to require panmixia (m = 0.5) between a pair of demes before onset of reproductive isolation. Although panmixia is a suitable starting point in models of speciation, it is not a useful definition of Sympatry in natural populations, because it becomes virtually impossible to find or demonstrate Sympatry in nature. The newer, non-spatial definition fails to address the classical debate about whether natural selection within a geographic overlap regularly causes speciation in nature, or whether complete geographic isolation is usually required. We therefore propose a more precise spatial definition by incorporating the population genetics of dispersal (or ‘cruising range’). Sympatric speciation is considerably more likely under this spatial definition than under the demic definition, because distance itself has a powerful structuring effect, even over small spatial scales comparable to dispersal. Ecological adaptation in two-dimensional space often acts as a ‘magic trait’ that causes pleiotropic reductions of gene flow. We provide examples from our own research.
Karin S. Pfennig - One of the best experts on this subject based on the ideXlab platform.
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Why do species co-occur? A test of alternative hypotheses describing abiotic differences in Sympatry versus allopatry using spadefoot toads.
PloS one, 2012Co-Authors: Amanda J. Chunco, Todd Jobe, Karin S. PfennigAbstract:Areas of co-occurrence between two species (Sympatry) are often thought to arise in regions where abiotic conditions are conducive to both species and are therefore intermediate between regions where either species occurs alone (allopatry). Depending on historical factors or interactions between species, however, Sympatry might not differ from allopatry, or, alternatively, Sympatry might actually be more extreme in abiotic conditions relative to allopatry. Here, we evaluate these three hypothesized patterns for how Sympatry compares to allopatry in abiotic conditions. We use two species of congeneric spadefoot toads, Spea multiplicata and S. bombifrons, as our study system. To test these hypotheses, we created ecological niche models (specifically using Maxent) for both species to create a map of the joint probability of occurrence of both species. Using the results of these models, we identified three types of locations: two where either species was predicted to occur alone (i.e., allopatry for S. multiplicata and allopatry for S. bombifrons) and one where both species were predicted to co-occur (i.e., Sympatry). We then compared the abiotic environment between these three location types and found that Sympatry was significantly hotter and drier than the allopatric regions. Thus, Sympatry was not intermediate between the alternative allopatric sites. Instead, Sympatry occurred at one extreme of the conditions occupied by both species. We hypothesize that biotic interactions in these extreme environments facilitate co-occurrence. Specifically, hybridization between S. bombifrons females and S. multiplicata males may facilitate co-occurrence by decreasing development time of tadpoles. Additionally, the presence of alternative food resources in more extreme conditions may preclude competitive exclusion of one species by the other. This work has implications for predicting how interacting species will respond to climate change, because species interactions may facilitate survival in extreme habitats.
Peter R. Grant - One of the best experts on this subject based on the ideXlab platform.
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inaugural article by a recently elected academy member the secondary contact phase of allopatric speciation in darwin s finches
Proceedings of the National Academy of Sciences of the United States of America, 2009Co-Authors: Peter R. Grant, Rosemary B GrantAbstract:One hundred and fifty years ago, Charles Darwin (1859) offered an explanation for the process of speciation by which an ancestral species gives rise to one or more derived species through adaptive evolutionary divergence (1). The explanation involved colonization of a new area, adaptive divergence in allopatry, and a barrier to interbreeding when differentiated populations encountered each other in Sympatry. Darwin was much clearer on the early stages of speciation than on the later ones. He wrote to one of his many correspondents “…those cases in which a species splits into two or three or more new species … I should think near perfect separation would greatly aid in the ‘specification’ to coin a new word” (2). Fortunately “specification” did not catch on, and we use the term “speciation” instead, but the fundamental importance of spatial (geographical) isolation for population divergence has persisted and is incorporated in most, although not all, current models of speciation (3–6). When divergent populations subsequently meet, their respective members do not breed with each other, or if they interbreed, they do so rarely. Differences in signaling and in response systems that function when mates are chosen arise in allopatry and constitute a premating barrier to interbreeding in Sympatry. The barrier may be fully formed in allopatry, in which case no interbreeding occurs in Sympatry, or it may be strengthened by natural selection that causes further divergence in Sympatry, in two ways. Offspring produced by interbreeding may be relatively unfit, either because the genomes of their parents are incompatible to some degree or because they are at an ecologically competitive disadvantage in relation to the parental populations. Discriminating among these three alternatives has been difficult, because it requires observations to be made in nature on patterns of mating at the time secondary contact is established and in subsequent generations. We have been fortunate to witness such a secondary contact. Here, we report the origin and persistence for three generations of a premating barrier to interbreeding between two groups of Darwin's finches on one of the Galapagos islands. The barrier arose as a consequence of allopatric divergence in morphology, introgressive hybridization, and divergence of song in Sympatry. The barrier has genetic and learned components. Morphology is genetically inherited, whereas song is culturally inherited. Especially noteworthy is the absence of evolutionary change in Sympatry in one group in response to the other or to the ecological environment. Our example highlights a stochastic element in the process of speciation.
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Inaugural Article: The secondary contact phase of allopatric speciation in Darwin's finches
Proceedings of the National Academy of Sciences of the United States of America, 2009Co-Authors: Peter R. Grant, B. Rosemary GrantAbstract:One hundred and fifty years ago, Charles Darwin (1859) offered an explanation for the process of speciation by which an ancestral species gives rise to one or more derived species through adaptive evolutionary divergence (1). The explanation involved colonization of a new area, adaptive divergence in allopatry, and a barrier to interbreeding when differentiated populations encountered each other in Sympatry. Darwin was much clearer on the early stages of speciation than on the later ones. He wrote to one of his many correspondents “…those cases in which a species splits into two or three or more new species … I should think near perfect separation would greatly aid in the ‘specification’ to coin a new word” (2). Fortunately “specification” did not catch on, and we use the term “speciation” instead, but the fundamental importance of spatial (geographical) isolation for population divergence has persisted and is incorporated in most, although not all, current models of speciation (3–6). When divergent populations subsequently meet, their respective members do not breed with each other, or if they interbreed, they do so rarely. Differences in signaling and in response systems that function when mates are chosen arise in allopatry and constitute a premating barrier to interbreeding in Sympatry. The barrier may be fully formed in allopatry, in which case no interbreeding occurs in Sympatry, or it may be strengthened by natural selection that causes further divergence in Sympatry, in two ways. Offspring produced by interbreeding may be relatively unfit, either because the genomes of their parents are incompatible to some degree or because they are at an ecologically competitive disadvantage in relation to the parental populations. Discriminating among these three alternatives has been difficult, because it requires observations to be made in nature on patterns of mating at the time secondary contact is established and in subsequent generations. We have been fortunate to witness such a secondary contact. Here, we report the origin and persistence for three generations of a premating barrier to interbreeding between two groups of Darwin's finches on one of the Galapagos islands. The barrier arose as a consequence of allopatric divergence in morphology, introgressive hybridization, and divergence of song in Sympatry. The barrier has genetic and learned components. Morphology is genetically inherited, whereas song is culturally inherited. Especially noteworthy is the absence of evolutionary change in Sympatry in one group in response to the other or to the ecological environment. Our example highlights a stochastic element in the process of speciation.
