speciation in plants example
The best-studied ecotype pair has evolved at least three times independently in Galician Spain, where the two types specialize in and prefer either the high intertidal barnacle belt or the low intertidal mussel belt and occasionally hybridize in the intermediate area between those environments [134, 135]. However, we believe that it is useful to examine parallel ecological speciation explicitly in plants given how fruitful such studies have been in animals. [46] used microsatellite data to show that four patches of resistant black grass in two neighbouring fields were independently derived from nonresistant plants. For strong evidence of reproductive compatibility we require that descendent populations show little or no barriers to reproduction when experimentally crossed and minimal ecological divergence as demonstrated by reciprocal transplant or manipulative ecological experiments. Two common morphotypes A. Sympatric divergence of the palm complex Geonoma macrostachys Mart. Researchers have been able to manipulate mating preferences in stickleback by rearing juveniles with individuals of the other ecotype, indicating that reproductive isolation is at least partly extrinsic [121]. When studying parallel ecological speciation, it is also useful to recognize that evidence of parallelism may or may not extend across multiple levels of biological organization. On the other hand, flowering time may be quite constrained because partitioning flowering time requires narrower windows of flowering, which can have strong negative fitness consequences. Thus, the frequency of an allele at one end of a distribution will be similar to the frequency of the allele at the other end. Differences of public and scientific attention to plant speciation and extinction. The cultivated forms of wheat, cotton, and tobacco plants are all allopolyploids. ", International Journal of Ecology, vol. Phylogenetic analyses show that the color morphs are not monophyletic [20, 144], indicating possible multiple origins of at least one of the morphs, although this pattern could also be explained by a single diversification event followed by ongoing local gene flow between the morphs. In fact, we believe it to be common. In one mildly tolerant population, zinc tolerance appears to be controlled by only one of the tolerance alleles, and intolerant populations in both subspecies have neither. Indeed, as discussed by researchers in this system, these walking-stick insects seem to be experiencing a heterogeneous balance of gene flow and divergent selection, and it is unclear whether this process will ultimately result in speciation between the currently weakly isolated morphs. This widespread plant grows on inland, coastal, and salt marsh habitats across North America and Europe. Other finches have long, thin beaks that can probe into cactus flower… The agricultural weed Chenopodium album has developed resistance to triazine herbicides in multiple locations [67]. The finches are isolated from one another by the ocean. In fact, none of the examples have strong evidence for compatibility. The evidence and its theoretical analysis,”, L. Wu, A. D. Bradshaw, and D. A. Thurman, “The potential for evolution of heavy metal tolerance in plants. These include (1) direct measurements of divergent ecological selection on parental genotypes (e.g., immigrant inviability) or hybrids (i.e., extrinsic postzygotic isolation) in the different environments; (2) natural selection studies showing that phenotypic differences underlying premating reproductive barriers are a consequence of divergent ecological selection; (3) molecular marker studies of selection against immigrants (i.e., isolation by adaptation); (4) molecular evolutionary studies linking intrinsic genetic incompatibilities with divergent ecological selection; and (5) tests of parallel ecological speciation, which is the process in which related lineages independently evolve similar traits that confer shared reproductive isolation from their ancestral populations [6]. Although a majority of populations are found on serpentine soil, nonserpentine populations are also present. This potential difference between plants and animals may be in part because behavior is not particularly relevant to plants. The animal cases used as a comparison are summarized in Table 2 and Appendix B. We hope our study will spur additional investigation of the promising systems identified here, as well as provide guidance regarding the kinds of studies that should be performed in each system. Changes in expression in at least two candidate genes are also replicated in the closely related European whitefish system ([115], see below). For example, 200 years ago, the ancestors of apple maggot flies laid their eggs only on hawthorns — but today, these flies lay eggs on hawthorns (which are native to America) and domestic apples (which were introduced to America by immigrants and bred). Yet in lighted conditions in the laboratory, surface fish outcompete cave fish for food. In particular, parallel ecological speciation indicates that all of the new barriers present are predominantly if not entirely due to natural selection, whereas in the other cases, other forces may have been at play along with natural selection. The black-grass Alopecurus myosuroides is an agricultural weed that has evolved resistance to herbicides in many locations, possibly independently [45]. Early work showed that different resistant populations have distinct isozyme patterns in France [68] with at least two resistant genotypes in Canada [69]. Another well-known example is domestic sheep. Potential explanations for the lack of convincing examples include a lack of rigorous testing and the possibility that plants are less prone to parallel ecological speciation than animals. The two taxa are rarely found growing sympatrically despite overlapping elevational ranges (with S. grahamii generally at higher elevations). Further research has demonstrated parallel changes in gene expression among independent sympatric ecotype pairs [113], while changes at the genetic level between normal and dwarf populations are more weakly correlated among lakes [112, 114]. The third pattern (Figure 1(c)) has been called “replicated ecological speciation” [39] and is made up of multiple distinct speciation events. Therefore, reciprocal transplants between the new habitat types (as a test of isolation) and among sites in a single habitat type (as a test of compatibility) are crucial. When there is an evolution of new species, even though there has been no geographical isolation of the species, it is called Sympatric Speciation. The authors would like to thank Andrew Hendry, Dolph Schluter, Kieran Samuk, Gina Conte, Sébastien Renaut, and two anonymous reviewers for helpful comments and discussions. Although such hybridization may be a common mode of speciation in plants, it is rare in animals. A. Mouemar, and H. Darmency, “Triazine herbicide resistance in Chenopodium album L.: occurrence and characteristics of an intermediate biotype,”, J. Gasquez and J. P. Compoint, “Isoenzymatic variations in populations of, S. I. Warwick and P. B. Evidence that an example failed to meet any of the four criteria resulted in its exclusion. We use four explicit criteria (independence, isolation, compatibility, and selection) to judge the strength of evidence for each potential case. Leptocladus has no evidence of isolating traits. We used explicit criteria to determine the strength of evidence for parallel ecological speciation. As a result, several promising systems were not included in our table or appendix (e.g., Frankenia ericifolia [41] and Heteropappus hispidus ssp. Estimating phylogenetic independence can be difficult for recently diverged taxa because of inadequate resolution, hybridization and introgression, and deep coalescence. Although these traits appear to have evolved independently and in parallel on two different continents, little is known about the genetic basis of these traits or their effects on reproductive isolation or local adaptation. The following sections discuss each criterion and the types and strengths of evidence we considered. Two matings are necessary to produce viable offspring. The best known example of sympatric speciation is that of the cichlids of East Africa inhabiting the Rift Valley lakes, particularly Lake Victoria, Lake Malawi and Lake Tanganyika. Metal refining in Prescot, UK, caused considerable copper contamination to surrounding soil, and the grass Agrostis stolonifera has since then colonized a number of contaminated sites. On the other hand, the criterion with the most evidence is the independent evolution of lineages that appear to be diverging in parallel. This does not imply that ecological speciation is uncommon in plants. Crossing experiments in this complex found that hybrid fertility is inversely related to geographic distance, suggesting that nonserpentine populations would be more compatible with neighbouring serpentine populations than distant nonserpentine ones [107]. When that separation lasts for a peri… Later studies used cpDNA restriction site data and ITS sequence to show that the species is structured into several roughly geographically based subspecies [104–106]. Phylogenetic analyses using ribosomal and chloroplast sequences along with allozyme variation indicate two cryptic clades within the species with representatives of both races in each [81–84], suggesting a parallel origin of each race. A. J. Breeuwer, and K. Bachmann, “Incipient adaptive radiation of New Zealand and Australian, F. Quattrocchio, J. Floral morphology may adapt to attract different pollinators and, consequently, lead to pollinator isolation. One such possible example, described by Bullini (1994), is the minnow, Gila seminuda, of Western North America. The adaptation to copper-contaminated soil at multiple sites may be parallel, or may be the result of the transmission of tolerant genotypes between mines. This case is quite promising, as it has strong evidence for both independence and isolation from ancestral populations. This is unsurprising given the widespread application of molecular phylogenetic methods in plants. Similarly, British coastal plants also have lax spikes relative to inland populations, although in this case the spikes are less dense than North American salt march plants [93]. Here we use explicit criteria to evaluate the strength of evidence for parallel ecological speciation in plants. Additional populations of S. vulgaris have colonized naturally metalliferous (serpentine) soils in Switzerland and differently contaminated mine sites in Canada and Europe [101, 102], which may indicate the ease of evolving metal tolerance in this species. Similarly, copper tolerance is controlled at two loci: one common across all tolerant populations and a second found only in Imsbach, Germany where plants are extremely tolerant [100]. In a series of Northern European lakes, European whitefish (C. lavaretus) has differentiated into two ecotypes: a “sparsely rakered”, larger-bodied, benthic form, and a “densely rakered” smaller limnetic form. Although polyploidy occurs occasionally in animals, it takes place most commonly in plants. Alternate hypotheses of a history of local gene flow among subspecies or phenotypic plasticity must be ruled out before this case can be considered parallel speciation, and further work on reproductive isolation and the mechanisms of microhabitat adaptation is warranted. As we briefly discuss above, the lack of reproductive barriers between descendent populations is a key criterion distinguishing true parallel ecological speciation from other forms of replicated ecological speciation (Figure 1). Most plant species appear to be able to reduce As (V) to As (III) rapidly, resulting in the dominance of trivalent As inside plant cells. Furthermore, the signature of parallel speciation is easily lost. Often-cited examples of sympatric speciation are found in insects that become dependent on different host plants in the same area. Peripatric speciation: It occurs when the individuals lying on the periphery, or border … However, evidence of parallel ecological speciation in plants is not yet as convincing as it is for animal examples. The most striking result of this survey is that very few plant cases have strong evidence for two or more criteria of parallel ecological speciation, and most have only weak or indirect evidence for any of the criteria (Table 1; Appendix A). A specific type of parallel speciation, known as parallel ecological speciation, is one of several forms of evidence for ecology's role in speciation. Note that we consider genetic information from completely linked markers (e.g., multiple genes sequenced from the chloroplast genome) as information from one locus. We do not intend to imply that ecological speciation does not happen in plants. Within one sympatric population, experimental interspecific crosses produced no seed set, while intraspecific seed set was 63–72% [96]. Annual bluegrass (Poa annua) is an agricultural weed with populations known to be resistant to the triazine herbicides [94]. A specific type of parallel speciation, known as parallel ecological speciation, is one of several forms of evidence for ecology's role in speciation. With this type of speciation, though, one of the groups that split from the original group is significantly smaller than the other. Although phenotypic and genetic differences in both the North American and European species complex are well characterized, evolving in parallel, and show signatures of divergent selection, comparatively little is known about the strength and nature of reproductive barriers in both systems. However, one can also envision several other patterns, in which either the ancestral or descendent groups (or both) represent multiple compatibility groups (Figures 1(b)–1(d)). When populations become geographically discontinuous, that free-flow of alleles is prevented. Numerous other strong candidates for parallel ecological speciation are found in animals, including but not limited to lake whitefish [26], cave fish [27], walking sticks [20], scincid lizards [21], lamprey [28], electric fish [29], horseshoe bats [30], and possibly even in the genetic model organism Drosophila melanogaster [31], though not all of these examples are fully validated with the criteria described below. vespertina, Lasthenia californica, Petunia axillaris, Schizanthus grahamii, and Streptanthus glandulosus. While this type of speciation may not be as common as the other types, it does occur, as evidenced by the sympatric speciation of cichlid fish in Africa and Nicaragua. Each ecotype is more likely to spawn with fish of the same ecotype than of the other ecotype, regardless of lake of origin [15]. They are different food plants that taste different when eaten, but they all belong to the Brassica oleracea species. In the Baltic region, populations vary in leaf shape, with two island populations exhibiting more deeply lobed leaves than those from the mainland. When added to the suffix -patric, it translates to "near place. A second essential set of tests that should be conducted is crosses between ancestral and descendent populations and crosses among populations in each habitat. The isthmus of Panama is a prime example of a geographical barrier and it … The mechanisms of reproductive isolation are a collection of evolutionary mechanisms, behaviors and physiological processes critical for speciation.They prevent members of different species from producing offspring, or ensure that any offspring are sterile.These barriers maintain the integrity of a species by reducing gene flow between related species. However, the genetic basis of isolation, compatibility among dwarfed populations, and the selective advantage of being dwarfed still need to be confirmed in this example. Marriage, “Geographical variation in populations of, P. Bettini, S. McNally, M. Sevignac et al., “Atrazine resistance in, S. Andersson, “Phenotypic selection in a population of, S. Andersson, “Differences in the genetic basis of leaf dissection between two populations of, E. J. Bush and S. C. H. Barrett, “Genetics of mine invasions by, K. K. Nkongolo, A. Deck, and P. Michael, “Molecular and cytological analyses of, S. A. This type of speciation is also referred to as geographic speciation. Other promising cases include Lasthenia californica [81] (Appendix A) and Schizanthus grahamii [96] (Appendix A). Because of this, we searched for evidence of the adaptive mechanism(s) underlying parallel isolation. Some Examples of Speciation. A number of quantitative trait loci for growth rate and morphology have been identified as under divergent selection between the ecotypes [111, 112]. Herbicide resistance occurs either through plant metabolism, often polygenic, or via mutant ACCase alleles, and seven mutant resistance alleles have been identified [47–49]. "Peripatric speciation is actually a special type of allopatric speciation. We choose to use the term “parallel” over the alternative term “convergent” because of the initial similarity of the independent lineages [32–34] and because this vocabulary is consistent with the original description of the process [6]. Specifically, we judged the strength of evidence for each of the aforementioned four criteria: independence, isolation, compatibility, and selection. This is because replicate populations of selfers are likely to be as strongly isolated from one another as they are from the ancestral outcrossing populations. The red campion, Silene dioica, has the ability to colonize both serpentine and nonserpentine habitats. To more critically evaluate the importance of ecological speciation in nature, several authors have suggested methods for reliably inferring ecological speciation [2–5]. This variability indicates that multiple genes or alleles are responsible for copper tolerance in different populations, although crossing experiments could further support this inference. C. glabriuscula is found in mesic habitat, has yellow flowers, and has Finally, indirect evidence for independence could include the improbability of long-distance colonization or gene flow between geographically separated but ecologically similar habitats, or phenotypes that are similar but not identical suggesting different genetic bases. There are numerous examples of using XAS to investigate the chemical speciation of elements in plant tissues; some examples are described below. Each type of speciation is an important part of the process of evolution within plant and animal kingdoms. Also, few studies have explicitly tested for isolation by adaptation in plants [1] or for ecological causes of hybrid incompatibilities (reviewed in [11]). The two color morphs are found in higher proportions on the host plant species on which they are most cryptic, although this is quite variable for individual plants, and crypsis helps the insects to avoid strong predation pressure by birds and lizards [142, 143]. Example of Speciation Speciation is a term used to describe the process of creation of sub species of plants and animals, usually through changes in habitat or environment. Additionally, at least one independent case of “benthic” and “limnetic” ecotypes has collapsed back into a single panmictic pool, possibly due to the human-mediated introduction of an exotic crayfish [122]. Future work should use molecular tools to verify the cytological data and quantify gene flow between species. Copyright © 2020 LoveToKnow. Additionally, the serpentine intolerance of nonserpentine populations should be reevaluated in a more quantitative manner. Frequent natural hybrids between the species indicate that gene flow is possible although it may be limited by differences in edaphic preference. In nature, there are four different means of speciation: allopatric, parapatric, sympatric and peripatric. This is unfortunate given the effectiveness of this criterion for demonstrating that ecological selection was the main cause of reproductive isolation in these systems—the primary reason for studying parallel ecological speciation in the first place. Together, these four conditions are the evidence necessary to demonstrate the process we refer to as parallel ecological speciation. Populations that have independently evolved reproductive isolation from their ancestors while remaining reproductively cohesive have undergone parallel speciation. Genetic constraints on selection for zinc tolerance,”, S. K. Jain and A. D. Bradshaw, “Evolutionary divergence among adjacent plant populations I. Furthermore, there are two lines of evidence for isolation. Another well-studied system is the marine snail Littorina saxatilis, which has repeatedly evolved pairs of ecotypes on the rocky coasts of Northwestern Europe [25]. First, the dwarfed populations flower earlier than the tall populations. Morphological and isozyme analyses suggest, counterintuitively, that there is a reduction in clone number in uncontaminated sites compared to contaminated ones. Two closely related Andean butterfly flowers are taxonomically differentiated by pollination syndrome, floral morphology, and mating system: Schizanthus hookeri is purple flowered, bee pollinated, and highly outcrossing, as are other species in the genus, while S. grahamii is capable of self-fertilization, primarily hummingbird pollinated, and exhibits several color morphs. Older sites were found to have more complete ground cover and a greater proportion of resistant individuals [55], suggesting that the evolution of tolerance is ongoing at younger sites. Conversely, there are clear reproductive barriers between Schizanthus grahamii and Schizanthus hookeri as they have different primary pollinators and experimental interspecific crosses produced no seeds [96]. However, it is not certain that these barriers arose multiple times independently because only chloroplast sequence data has been analyzed. Further work is needed to confirm this independence, to elaborate the adaptive value of leaf dissection in this system and to establish if there is any reproductive isolation other than geographic between the deeply lobed and less lobed forms. Foster, G. E. McKinnon, D. A. Steane, B. M. Potts, and R. E. Vaillancourt, “Parallel evolution of dwarf ecotypes in the forest tree, J. Roncal, “Habitat differentiation of sympatric, J. Noguchi and H. De-yuan, “Multiple origins of the Japanese nocturnal, G. Turesson, “The genotypical response of the plant species to the habitat,”, N. Rajakaruna, B. G. Baldwin, R. Chan, A. M. Desrochers, B. Furthermore, because explicitly testing that isolation is genetically based was rare in our candidate studies, we only required the genetic basis of isolation to be confirmed for cases to have strong direct evidence. The existence of sympatric speciation as a mechanism of speciation was hotly contested. In contrast, several candidate loci discovered in an FST outlier screen appear to be under divergent selection between ecotypes in multiple populations [139]. In many of the candidate systems ancestral and descendent forms have evolved particular edaphic tolerances and/or specific changes in reproductive phenotype or mating system. Nevertheless, all cave populations will interbreed in the laboratory and share many adaptations to a subterranean environment, including an increase in taste bud number, improved lateral line sense, and greater fat storage ability as well as reduced pigmentation and eyes. It is also possible that parallel ecological speciation is truly rare in plants. In this survey, however, we are only interested in parallel ecological speciation (Figure 1(a)), which tells us something more specific than other patterns. These issues are exacerbated when phylogenies are based on a small number of loci or if the loci employed have little phylogenetic information content (e.g., isozymes). Nonserpentine populations occur in multiple subspecies and are more closely related to nearby serpentine populations rather than further nonserpentine populations. In the case of pelvic loss, these populations exhibit at least three different mutations at the same locus—incontrovertible evidence for the independent origin of this adaptation [133]. This suggests that there have been at least three independent transitions to dwarfism in the novel exposed granite headland habitat (barring, of course, a long history of introgression after a single origin and dispersal). Although we would not consider isolation that has no genetic basis as evidence for parallel ecological speciation, we acknowledge that phenotypic plasticity can facilitate or impede the evolution of reproductive barriers and is an important consideration for studies of ecological speciation [43] (e.g., [44]). An example of this is when a species of grass becomes tolerant to heavy metals in the soil near a contamination source, such as a mine, even though such tolerance does not exist in other grass of the same species that is not in a contaminated area. Sympatric Speciation. Complementation tests between sites indicate that zinc tolerance is governed by two loci, both acting in highly tolerant populations of both subspecies [99]. However, flowering time could be such a trait, and there are many examples of flowering time changing in new edaphic environments (e.g., Lord Howe Island palms [146]). Preliminary data shows reduced seed set between different races of the same clade and greater pollination success between populations of the same race during interclade crossing, although these data have not been formally published after being presented in Rajakaruna and Whitton [87]. For example, when dogs are bred together to create a hybrid or new breed, the new breed is not considered a new species. For strong evidence, we include reciprocal transplants showing strong local adaptation, manipulative experiments relating adaptive traits to extrinsic fitness, and/or signatures of selective sweeps at loci underlying putatively adaptive traits. At mine sites across Europe, Silene vulgaris from two subspecies (ssp. In the lab, stream-resident fish are more than twice as likely to mate with other stream-resident fish than with anadromous fish (and vice versa), even when from populations as distant as Iceland and Japan [17]. The list of animal examples is not exhaustive and does not necessarily include all of the best cases. [125, 127]). While independent genetic changes simplify the task of reconstructing population and trait histories, parallel changes from standing genetic variation can be useful for pinpointing regions of the genome responsible for ecological selection and reproductive isolation [40]. vulgaris in continental Europe) has acquired tolerance to high levels of zinc and copper. They add that an adaptive mechanism must be identified to show that natural selection drove the evolution of reproductive isolation [6]. A new species is not able to reproduce with members of the original population. For example, in British Columbia speciation of 3-spined sticklebacks, freshwater fishes. Studying similarities and differences between these replicate speciation events can help identify general patterns of speciation [39]. In one location, surface fish are even regularly swept into a cave by flooding—yet this cave population shows very little genetic admixture, and only two intermediate forms have ever been found despite repeated sampling [27]. Tolerance appears to be polygenic and dependent on standing genetic variation [53]. Isozyme analysis of the populations at both contaminated sites, as well as uncontaminated sites to the south, found reduced variability in the metal-contaminated populations [73]. This was because Frankenia ericifolia has only indirect evidence of both independence and isolation and Heteropappus hispidus ssp. Boberg et al., 2014; Cosacov et al., 2014; Newman et al., 2014; Peter and Johnson, 2014; Van der Niet et al., 2014). Cytological analysis indicated that C. stevioides and C. fremontii arose from independent aneuploid reductions [66]. For example, the threespine stickleback has undergone several well-documented parallel transitions between environments. What remains is to demonstrate the compatibility of the dwarf populations with each other, and to more clearly elucidate the adaptive value of dwarfism in this system. Each group adapts to its specific habitat. Nuclear AFLP markers also support this hypothesis, as genetic distance among populations correlates strongly with geographic distance rather than ecotype identity [90]. Although adult plants from mine sites showed high degrees of tolerance, seeds were not tested, so it is unknown if gene flow from nontolerant populations is reduced pre- or postzygotically. The strength of evidence for independent or parallel evolution in either of these cases is quite weak. The lack of strong examples of parallel ecological speciation in plants is probably because botanists typically do not do the necessary tests. No work has been done on reproductive barriers between resistant and nonresistant plants, although AFLP analysis shows little differentiation between resistant and nonresistant populations [51]. Lowland forests in Peru are home to two subspecies of the palm Geonoma macrostachys that are alternately more abundant in flood plain versus tierra firme habitat [76].