Ecological Speciation (Oxford Series in Ecology and Evolution)

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the evolution of reproductive isolation between populations or subsets of a single population by adaptation to different environments or ecological niches ( Schluter 2009, p. 737). Darwin, C. On The Origin of Species by Means of Natural Selection, or The Preservation of Favoured Races in the Struggle for Life. London, UK: John Murray, 1859. ( link) We consider speciation to be ecological when externally imposed selection results in reproductive isolation; therefore, speciation by drift is nonecological. Although factors that influence the magnitude of genetic drift, such as variation in population size or mating success, may often have an ecological basis, this does not imply that speciation mediated by genetic drift is also “ecological.”

Mayr (1942, 1947) judged ecological factors as the major drivers of speciation. In his classic paper “Ecological factors in speciation,” Mayr (1947) concluded that geographic isolation leads to the formation of segregated populations that experience different ecological conditions, leading to evolutionary divergence. In Animal Species and Evolution, Mayr (1963, p. 556) devoted an entire chapter to the role of ecology in speciation, and began the second paragraph as follows: “An exhaustive treatment of the indicated subject matter would require an entire book, for there is hardly an ecological factor that does not affect speciation directly or indirectly, actually or potentially.” Many other evolutionary biologists have also supported the notion that ecological divergence of populations is typically required for speciation. Simpson (1953, p. 234n) concluded “… speciation, the basic process of radiation, is normally adaptive,” and Grant (1981) provided numerous examples in which ecological factors are the primary isolating barriers between species. D. santomea and D. yakuba inhabit distinct habitats based on ecological conditions associated with elevation. Both species exhibit reduced survival to adulthood and fertility when reared at nonnative temperatures, and each species chooses its native temperature range when placed on a temperature cline.The role of ecology in the establishment of polyploids. Autopolyploidy is presented for simplicity, but equivalent processes function with allopolyploidy. Circles represent topology of a simple two-trait adaptive landscape with darker circles representing trait combinations of higher fitness. A diploid progenitor (2N) sits upon an adaptive peak. There are two potential outcomes of neopolyploid formation: (A) The neopolyploid (neo 4N) could reside at a lower elevation of the same adaptive peak occupied by the progenitor. In this case, the neopolyploid faces both competitive disadvantage and minority cytotype exclusion, and will likely not establish. (B) The neopolyploid could initially reside at the base of a new adaptive peak, and adapt to this new niche (dashed line, neo 4N → established 4N). In this case, speciation can be considered ecological because polyploidy causes an initial change in ecology followed by subsequent adaptation as the neopolyploid climbs the new adaptive peak.

van Doorn, S., Edelaar, P. & Weissing, F. J. On the origin of species by natural and sexual selection. Science 326, 1704–1707 (2009). To resolve this paradox, we propose that differences in geographic distribution caused by adaptation to different habitats be treated like any other form of reproductive isolation, as a quantitative estimate of how much gene flow is reduced by intrinsic differences between taxa. To distinguish the independent contributions of genetic and historical processes, we separate geographic factors into ecogeographic isolation and effective geographic isolation. We define “ecogeographic isolation” as the degree to which differences in geographic distribution are based on genetic differences between taxa. “Effective geographic isolation” is the actual spatial separation experienced by populations, and includes both ecogeographic isolation and differences in distribution based solely on historical factors. Therefore, effective geographic isolation will sometimes be greater than ecogeographic isolation between populations such as the case of populations separated solely by geologic features. However, only ecogeographic isolation is relevant to speciation under the BSC, because it represents the portion of effective geographic isolation due to genetic differences between populations. This distinction sets up the possibility of discordance between status assigned under the BSC and other species concepts, as populations may diverge morphologically and/or phylogentically in allopatry without complete reproductive isolation. Levin (1975) described this frequency-dependent mating success in polyploid systems as the “minority cytotype disadvantage.” The minority disadvantage experienced by neopolyploids can be overcome in a number of ways, including (1) demographic stochasticity that drives neopolyploids from the minority to the majority cytotype, (2) reduced gene flow via increased self-fertilization or asexual reproduction, (3) migration to a new geographic region so as to eliminate gene flow with progenitors, and (4) the expression of ecological attributes in neopolyploids allowing them to coexist with their progenitors, or to replace them ( Ramsey and Schemske 2002). Unless one or more of these conditions are realized, a neopolyploid will become extinct despite the presence of strong postzygotic barriers. This framework for investigating reproductive isolation has serious consequences for how we view the importance of different forms of isolation. For example, if ecogeographic isolation between two taxa is complete at the time of speciation, there is no opportunity for barriers that operate only in sympatry to contribute to the total isolation. Even if later acting barriers are strong, the potential isolation is not realized unless it prevents gene flow in nature. It therefore seems irrelevant to assess the contribution of later acting barriers if hybrids are never formed. Using the multiplicative approach of Coyne and Orr to assess reproductive isolation solves this problem by scaling the strength of isolation by how much gene flow remains.

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Divergent pollinator-selected style lengths in Mimulus cardinalis and M. lewisii lead to differentiated pollen tube lengths, reducing the amount of expected hybridization in mixed pollinations.

After epistaxis.After a nose bleed crusts can form. Nasal douching can keep these soft and prevent further bleeding Evaluate the role of chromosomal rearrangements in speciation. Stochastic forces may sometimes interact with adaptive processes to affect the resulting reproductive isolation. Chromosomal inversions, for example, may enhance isolation by building complexes of genes that are protected from recombination (e.g., Brown et al. 2004). virtually all barriers can be considered ecological in the sense that they arise from environmentally imposed selection. ( Coyne and Orr 2004, p. 179) Niche modeling can be employed equally well with taxa exhibiting some degree of sympatry. While sympatry indicates that a portion of the geographic range is suitable for both species, an ecological niche model represents an average niche across all samples used to generate the model. Therefore, despite coexistence in some regions, two taxa can show significant niche differences, and achieve some ecogeographic isolation as a result. As mentioned above, in cases with partial sympatry, we would predict a higher correlation between effective and ecogeographic isolation because dispersal limitation is unlikely to be the cause of differences in geographic range.

A nasal douche washes the nose and removes crusts and debris, keeping the nose clean and healthy. Reasons for douching Mimicry in H. cydno and H. melpomene is disrupted in hybrids, causing increased predation on hybrids and reduced mating success. M. lewisii and M. cardinalis show considerable allopatric separation based primarily on differences in altitude inhabited. Reciprocal transplants demonstrate that each species is most fit in its native range. Print head cleaning consumes some ink. To avoid wasting ink, clean the print head only if print quality declines; for example, if the printout is blurry or the color is incorrect or missing. Divergent natural selection causes low fitness in G. aculeatus benthic–limnetic hybrids, despite the absence of intrinsic postzygotic isolation.

Panhuis, T. M. et al. Sexual selection and speciation. Trends in Ecology & Evolution 16, 364–371 (2001). Sexual selection: Differential reproductive success of classes of entities (such as alleles) which differ in some characteristic(s). Flo Nozoil is not recommended for children under 4 years of age, unless advised by a healthcare practitioner. Precautions

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Natural selection: Differential survival of classes of entities (such as alleles) which differ in some characteristic(s). You can clean the print head from your computer using the Head Cleaning utility in the printer software, or from the printer itself by using the printer's control panel buttons. Evolutionary genetics of the phenotypic response to environmental change in the North American red squirrel Nosil, P., Harmon, L. J. & Seehausen, O. Ecological explanations for (incomplete) speciation. Trends in Ecology & Evolution 24, 145–156 (2009).