Evidence For Sympatric Speciation Research Articles

Evidence for sympatric speciation in a Wallacean ancient lake.

Sympatric speciation has been demonstrated in few empirical case studies, despite intense searches, because of difficulties in testing the criteria for this mode of speciation. Here, we report a possible case of sympatric speciation in ricefishes of the genus Oryzias on Sulawesi, an island of Wallacea. Three species of Oryzias are known to be endemic to Lake Poso, an ancient tectonic lake in central Sulawesi. Phylogenetic analyses using RAD-seq-derived single nucleotide polymorphisms (SNPs) revealed that these species are monophyletic. We also found that the three species are morphologically distinguishable and clearly separated by population-structure analyses based on the SNPs, suggesting that they are reproductively isolated from each other. A mitochondrial DNA chronogram suggested that their speciation events occurred after formation of the tectonic lake, and existence of a historical allopatric phase was not supported by coalescent-based demographic inference. Demographic inference also suggested introgressive hybridization from an outgroup population. However, differential admixture among the sympatric species was not supported by any statistical tests. These results all concur with criteria necessary to demonstrate sympatric speciation. Ricefishes in this Wallacean lake provide a promising new model system for the study of sympatric speciation.

Extensive range overlap between heliconiine sister species: evidence for sympatric speciation in butterflies?

BackgroundSympatric speciation is today generally viewed as plausible, and some well-supported examples exist, but its relative contribution to biodiversity remains to be established. We here quantify geographic overlap of sister species of heliconiine butterflies, and use age-range correlations and spatial simulations of the geography of speciation to infer the frequency of sympatric speciation. We also test whether shifts in mimetic wing colour pattern, host plant use and climate niche play a role in speciation, and whether such shifts are associated with sympatry.ResultsApproximately a third of all heliconiine sister species pairs exhibit near complete range overlap, and analyses of the observed patterns of range overlap suggest that sympatric speciation contributes 32 %–95 % of speciation events. Müllerian mimicry colour patterns and host plant choice are highly labile traits that seem to be associated with speciation, but we find no association between shifts in these traits and range overlap. In contrast, climatic niches of sister species are more conserved.ConclusionsUnlike birds and mammals, sister species of heliconiines are often sympatric and our inferences using the most recent comparative methods suggest that sympatric speciation is common. However, if sister species spread rapidly into sympatry (e.g. due to their similar climatic niches), then assumptions underlying our methods would be violated. Furthermore, although we find some evidence for the role of ecology in speciation, ecological shifts did not show the associations with range overlap expected under sympatric speciation. We delimit species of heliconiines in three different ways, based on “strict and ” “relaxed” biological species concepts (BSC), as well as on a surrogate for the widely-used “diagnostic” version of the phylogenetic species concept (PSC). We show that one reason why more sympatric speciation is inferred in heliconiines than in birds may be due to a different culture of species delimitation in the two groups. To establish whether heliconiines are exceptional will require biogeographic comparative studies for a wider range of animal taxa including many more invertebrates.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0420-3) contains supplementary material, which is available to authorized users.

Evidence of Sympatric Speciation in Cyathea sinuata Hook. & Grev. from Lowland Rainforests of Sri Lanka

The family Cyatheaceae (tree ferns) is represented by a single genus, Cyathea, with eight taxain Sri Lanka where 75% are endemic to the island. An endemic Cyathea sinuata Hook. &Grev. is an unique species because it is the only known simple leaves tree fern among about600 Cyathea species in the world. An eco-geographic survey was conducted covering allpossible natural habitats of all Cyathea species in 12 administrative districts of Sri Lankaduring the period of two years. Morphological characters were recorded following thestandard developed by Janssen (2006) from a total of 60 individuals of Cyathea species.Twenty two morphological characters used to perform Cluster Analysis. A detailmorphological investigation was carried out on 23 individuals of C. sinuata and itsmorphotype collected from Sinharaja and Kanneliya MAB reserves, Runakanda and Beraliyaproposed forest reserves (FR) and Hiniduma FR.Results of cluster analysis and dendrogram revealed that all species were separately grouped.Interestingly, C. sinuata is clustered into two sub groups. Sub group I (usual C. sinuata) andsub group II (morphologically different form of it). Sub group II can be easily differentiatedfrom usual C. sinuata by their dentate leaf margin, irregular or global shape crown withdrooping leaves, the number of veinlets, spore arrangement and number of pair of sporangia.Since those variations and current information are not adequate to determine the correcttaxonomic status of two sub groups, it is suggested that sub group II may be a morphotype ofC. sinuata. It is also suggested that this may be an initial step of the evolutionary process,although this morphotype was observed only from the population of Sinharaja and KanneliyaMAB reserves. Sri Lankan ferns show wide range of morphological variation mainly due toisland nature of the country and long period of geological isolation from mainland India.Therefore, continuous monitoring of morphotype of C. sinuata within their natural habitatswill further reveal information on sympatric speciation.

The puzzle of sympatry

Sympatric speciation—the rise of new species in the absence of geographical barriers—remains a puzzle for evolutionary biologists. Though the evidence for sympatric speciation itself is mounting, an underlying genetic explanation remains elusive.

Evolutionary Biology: Speciation on Islands

One of the strongest rules of biological diversity - the observation that more species live on large islands than on small ones - is usually attributed to the balance between colonization and extinction. But speciation on islands cannot be ignored.

Sympatric speciation by allochrony in a seabird.

The importance of sympatric speciation (the evolution of reproductive isolation between codistributed populations) in generating biodiversity is highly controversial. Whereas potential examples of sympatric speciation exist for plants, insects, and fishes, most theoretical models suggest that it requires conditions that are probably not common in nature, and only two possible cases have been described for tetrapods. One mechanism by which it could occur is through allochronic isolation-separation of populations by breeding time. Oceanodroma castro (the Madeiran or band-rumped storm-petrel) is a small seabird that nests on tropical and subtropical islands throughout the Atlantic and Pacific Oceans. In at least five archipelagos, different individuals breed on the same islands in different seasons. We compared variation in five microsatellite loci and the mitochondrial control region among 562 O. castro from throughout the species' range. We found that sympatric seasonal populations differ genetically within all five archipelagos and have ceased to exchange genes in two. Population and gene trees all indicate that seasonal populations within four of the archipelagos are more closely related to each other than to populations from the same season from other archipelagos; divergence of the fifth sympatric pair is too ancient for reliable inference. Thus, seasonal populations appear to have arisen sympatrically at least four times. This is the first evidence for sympatric speciation by allochrony in a tetrapod, and adds to growing indications that population differentiation and speciation can occur without geographic barriers to gene flow.

Dynamics of the evolution of Batesian mimicry: molecular phylogenetic analysis of ant‐mimicking Myrmarachne (Araneae: Salticidae) species and their ant models

Batesian mimicry is seen as an example of evolution by natural selection, with predation as the main driving force. The mimic is under selective pressure to resemble its model, whereas it is disadvantageous for the model to be associated with the palatable mimic. In consequence one might expect there to be an evolutionary arms race, similar to the one involving host-parasite coevolution. In this study, the evolutionary dynamics of a Batesian mimicry system of model ants and ant-mimicking salticids is investigated by comparing the phylogenies of the two groups. Although Batesian mimics are expected to coevolve with their models, we found the phylogenetic patterns of the models and the mimics to be indicative of adaptive radiation by the mimic rather than co-speciation between the mimic and the model. This shows that there is strong selection pressure on Myrmarachne, leading to a high degree of polymorphism. There is also evidence of sympatric speciation in Myrmarachne, the reproductive isolation possibly driven by female mate choice in polymorphic species.

Evidence for sympatric speciation? (Reply)

Replying to Schliewen We reported a case of sympatric speciation in the Nicaraguan Midas cichlid species complex1. Schliewen . 2 question the interpretation of aspects of our data, but their proposed alternative scenario of multiple colonization and hybridization is considerably less parsimonious, contains some inconsistencies, and is incompatible with the available evidence.

Little evidence for sympatric speciation in island birds.

It has been suggested that the presence of sister species in small circumscribed areas, such as isolated lakes or islands, might imply that these species originated sympatrically. To investigate this possibility in birds, we searched for endemic, congeneric species on isolated islands in the ocean. Among 46 islands and small archipelagos chosen because they contain at least one species of endemic land bird, we identified seven pairs of endemic congeners (excluding flightless rails). Of these seven, only four pairs are potentially sister species and thus possible candidates for sympatric speciation. However, three of these four pairs have always been considered the results of double invasion from a mainland source (in two of these cases, molecular-phylogenetic work has either confirmed a double invasion or is ambiguous). The one remaining pair may have speciated allopatrically on a small archipelago. Additional phylogenetic studies are required to understand these cases, and our results should also be considered in light of the large number of island-bird extinctions in historic time. We conclude that, at present, there is little evidence for sympatric speciation in island birds.

How fast do crossbills speciate? On assortative mating and vocalizations

The question of whether sympatric speciation (i.e. reproductive isolation of populations with overlapping distributions) is a source of biodiversity has always been controversial. So far, mounting evidence from only a few species, for example African lacustrine cichlids, African widowbirds and phytophagous insects, supports the notion that it occurs in nature. In the latter two, host shifts can lead to genetic isolation of the population that has shifted.A potential new example comes from Eurasian and North American crossbills. The North American red crossbill (Loxia curvirostra) can be divided into sibling species that differ in vocalizations, with positive assortative mating between males and females of the same vocal type. Moreover, crossbills with the same vocalizations share allozyme patterns, whereas other vocal types differ in allozyme patterns and bill morphology. Worldwide, some host race formation and subsequent speciation has obviously occurred allopatrically (i.e. when geographically isolated) in island populations such as those of Hispanolia (L. megaplaga), Scotland (L. scotica) and perhaps Corsica (L. curvirostra corsicana). However, in North America, red crossbills are continental sibling species that occur sympatrically over large areas and disperse over long distances, making a sympatric origin of these sibling species probable. For sympatric speciation and subsequent species coexistence to occur, two conditions must be met: genetic isolation and ecological diversification of the incipient species. The coevolution of American crossbills and conifer species has already been demonstrated, and provides evidence for ecological diversification. The numerous conifer species in North America provide a huge variety of different cone structures, which must have been a necessary condition for host–race formation. The incipient species can coexist because specialization reduces competition. But, how do incipient species come about? Crossbills are highly social; if songs are learned (as with other finches) cultural evolution is likely to occur within cohesive groups. The preference for mates of the same vocal type (i.e. positive assortative mating) can then ultimately lead to genetic isolation.Magnus Robb1xIntroduction to vocalizations of crossbills in north-western Europe. Robb, M.S. Dutch Birding. 2000; 22: 61–107See all References1 now publishes extensive evidence that European crossbills also fall into discrete vocalization patterns. Of the six types he observed in The Netherlands alone, four were still present at the start of the breeding season, and the males and females in all the observed pairs belonged to the same vocal type. Two vocal types were found breeding sympatrically in the area. Importantly, unlike North America, there is little evidence that European crossbill populations can be divided into groups that differ in bill morphology. In addition, specialist species feeding on pine (L. scotica and L. pytyopsittacus) often occur sympatrically with L. recurvirostra in Europe, excluding the possibility of specialization on pine for the latter. Therefore, in Europe, low conifer diversity and interspecific competition might have prevented the formation of host races and morphological differentiation.In both America and Europe dialect formation has evolved in association with assortative mating. In America there is differentiation both of the feeding niche and of morphology and sibling species can be recognized. In Europe there is no such differentiation both of the feeding niches, no apparent differentiation of the morphology and no evidence of sympatric speciation. The evidence presently available suggests, thus, that cultural evolution of vocalizations and assortative mating among birds of the same vocal type facilitate the generation of new species, provided that sufficient opportunity for ecological differentiation is present.

LITTLE EVIDENCE FOR SYMPATRIC SPECIATIONIN ISLAND BIRDS

It has been suggested that the presence of sister species in small circumscribed areas, such as isolated lakes or islands, might imply that these species originated sympatrically. To investigate this possibility in birds, we searched for endemic, congeneric species on isolated islands in the ocean. Among 46 islands and small archipelagos chosen because they contain at least one species of endemic land bird, we identified seven pairs of endemic congeners (excluding flightless rails). Of these seven, only four pairs are potentially sister species and thus possible candidates for sympatric speciation. However, three of these four pairs have always been considered the results of double invasion from a mainland source (in two of these cases, molecular-phylogenetic work has either confirmed a double invasion or is ambiguous). The one remaining pair may have speciated allopatrically on a small archipelago. Additional phylogenetic studies are required to understand these cases, and our results should also be considered in light of the large number of island-bird extinctions in historic time. We conclude that, at present, there is little evidence for sympatric speciation in island birds.Editor: S. Edwards

Speciation in black flies

In many Simuliidae, patterns of spatial and temporal relationships among the most closely related species are more readily interpreted in terms of sympatric speciation than of allopatric speciation. Specific examples are (i) the allotriploid taxa in Gymnopais and other genera, (ii) the black fly faunas of geologically recent islands (Tahiti), and (iii) species in Prosimulium onychodactylum, a prototype of a continental multisibling species complex. A model of sympatric speciation is presented based on coadaptation of polymorphic sex chromosomes in pairs reinforced by progressive development of assortative mating. This model predicts that (i) populations should frequently exhibit sex-chromosome polymorphism, (ii) these sex-chromosome polymorphisms, and autosomal ones, should in some cases display linkage or association disequilibria, (iii) species pairs or complexes should be incurred that differ only in sex chromosomes and that share extensive ancestral autosomal polymorphisms, and (iv) such species should differ in their biology and perhaps their present-day distribution. Recent publications and observations are in accordance, in general, with predictions from the model. Genetic control, e.g., of diapause, larval developmental timing, and niche preference or ethology, could substitute as a basis of incipient cleavage. The evidence for sympatric speciation is purely inferential, but this is equally true for the allopatric interpretation, and in black flies the circumstantial evidence for prevalence of sympatric speciation appears more compelling. This is not to deny the efficacy of allopatry and founder effect in the origin of some species complexes.Key words: sympatric speciation, black fly, evolution.

The taxonomy of some British Littorina species, with notes on their reproduction (Mollusca: Prosobranchia)

The rough periwinkle Littorina saxatilis is considered, in current literature, to consist of various sympatric “subspecies” and “varieties”. These, it has been suggested, are incipient species and are evidence for sympatric speciation. This paper shows that in Wales the “saxatilis” aggregate consists of four separate, fully sympatric species: L. rudis, patula, nigrolineata and neglecta. Differences between these species include proportions, sculpture and size of the shell, range of colour patterns, the anatomy of the genitalia, and isozyme patterns. The possible evidence for incipient species is discussed and rejected. The diversity of penis form amongst the British winkles is remarkable, and it is suggested that in these sympatric species the structure of the penis could be of importance in species recognition. The four species occupy different zones on the shore and three certainly differ also in their methods of reproduction: L. rudis is ovoviviparous and contains embryos throughout the year, patula is ovoviviparous but contains embryos only in winter, nigrolineata is oviparous. The reproduction and dispersal methods of all British winkles are reviewed. The evidence available supports the view that non-planktonic dispersal is an adaptation which, in species whose shell colour varies considerably from one locality to another, enables each population to become adapted to its local environmental conditions. Ovoviviparity occurs in high-shore non-planktonic species, and may be an adaptation to avoid the dangers of egg desiccation. Planktonic dispersal is found in species whose shell colour does not vary as much as in non-planktonic ones. In these species, it is argued that a common planktonic pool enables a rapid re-colonization in the case of local decrease in population numbers, and also the rapid dispersal of successful mutations.