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Vol 9 February doi Sympatric speciation, the formation of species in the absence of geographical barriers, remains one of the most contentious concepts in evolutionary biology. Although speciation under sympatric conditions seems theoretically possible 1 — 5 , empirical studies are scarce and only a few credible examples of sympatric speciation exist 6. Here we present a convincing case of sympatric speciation in the Midas cichlid species complex Amphilophus sp.
To examine whether the endemic Arrow cichlid emerged in Lake Apoyo from an ancestral stock of Midas cichlids under fully sympatric circumstances, we adopted a comprehensive approach including phylogeographic, population- genetic, morphometric and ecological analyses.
We included about specimens from Lake Apoyo and over individuals from six other lakes of Nicaragua outgroup sample; see Supplementary Table 1. Analysis of the mitochondrial control region bp showed that the two Amphilophus species from Lake Apoyo form a monophyletic assemblage Fig. Notably, not a single mtDNA haplotype is. Figure 1 The study area. Ever since Darwin proposed the concept in The Origin 7 , the issue of whether sympatric speciation is common or even possible in nature has received much attention from evolutionary biologists.
Despite current enthusiasm in favour of sympatric speciation and models espousing that it is theoretically possible 1 — 5 , the empirical evidence for it remains scant and many of the proposed cases are equally compatible with allopatric schemes. Crater Lake Apoyo in Nicaragua Fig. It is small diameter, , 5 km; max. These, together with Amphilophus labiatus from the large Nicaraguan lakes 1 3 — 1 5 , and possibly more species from some of the crater lakes 1 6 , make up the Midas cichlid species complex that is restricted to Nicaragua and the.
Roman numerals indicate the four sampling localities. Figure 2 Phylogeography of the Lake Apoyo Amphilophus species. The genetic diversity and the number of mtDNA haplotypes are low in Lake Apoyo 22 versus in the outgroup sample , in line with the young age of the species assemblage 1 5. A mitochondrial mismatch analysis indicates a single demographic expansion of A. A plot of the microsatellite distances Fig.
Similarly, microsatellite-based bayesian population assignment tests Fig. Reproductive isolation is further suggested by mate-choice experi- ments that demonstrate strong assortative mating between both species 1 7. The two Amphilophus species in Lake Apoyo are morphologically clearly distinct 1 3 , 1 4 Fig. Morphometric analysis uncovered two discrete body types corresponding to the two species, with body height explaining most of the differences Fig.
The two species also differ in the shape of a trophically relevant structure that is tightly linked to the ability of cichlids to process alternative food types 1 8 : the pharyngeal jaw Fig. Morphometric analyses show clear differences between the two species Fig.
Our eco-morphological inferences characterize A. Taken together, we present a strong case where only sympatric speciation can account for the origin of a new species from a more widespread one in Lake Apoyo in , 10, yr Supplementary Table 2. The Lake Apoyo population of the Midas cichlid and the Arrow cichlid form a monophyletic assemblage Fig.
Table 1 Genetic distance between the two Amphilophus species from. Haplotypes are coloured according to species and geographic origin:. The recent volcanic origin of Lake Apoyo, its small size, its degree of.
The framed haplotype network is taken from ref. Lake Apoyo representatives, albeit belonging to two species, form a monophyletic assemblage showing a characteristic mutation in alignment position The central haplotype in Lake Apoyo 1 is connected by this characteristic mutation to the central haplotype C. Lake Apoyo. F -statistics. Individuals are colour-coded as described above. Figure 3 Bayesian population assignment test. A population assignment. However, most theoretical models predict that the completion of speciation requires the evolution of other forms of pre- or post- zygotic isolation 5 , such as assortative mating, and a linkage disequi- librium between loci involved in disruptive natural selection and those involved in mate choice 1 , 3.
Therefore, both ecological speciation mechanisms through divergent habitat preferences and resource partitioning, and assortative mating through behavioural isolation separate the two Amphilophus species in Lake Apoyo.
For Lake Apoyo, it seems likely that a new ecological dimension—the open water column over greater depths, which is absent in the shallow large Nicaraguan lakes—facilitated the emergence of a limnetic morphotype and, ultimately, of the new species A.
The outstanding species richness of cichlids in the East African Great Lakes, which alone contain more than 1, endemic species 2 0 , 2 1 , has repeatedly been suggested to be caused by sympatric speciation through sexual selection, as most cichlid species differ more strongly in body coloration than in morphology 2 2 , 2 3. But one of the few possible cases of sympatric speciation involves cichlids, namely tilapiine cichlids in crater lakes in Cameroon 6 , 8 , 2 4 , where, as in Lake Apoyo, disruptive natural selection seems to be the driving force of the formation of new species.
This is in line with data showing that sympatric speciation by sexual selection alone is rather unlikely 2 5 , 2 6. Fish were collected in the fall of with gill nets and photographed. Both Lake Apoyo species co-occurred at all sampling sites Fig. Fish heads were taken as voucher specimens and to dissect the lower pharyngeal jaws. In addition, full stomachs of some sampled individuals were taken for dietary analyses.
Stomach content analysis. Morphometric analyses. Species were discriminated on the basis of established meristic measurements 1 3. A coalescence-based mismatch analysis was done with Arlequin 2. Microsatellite genotyping. Individuals were genotyped with ten unlinked microsatellite loci those in ref. Fragment visualization and scoring were done as previously described 1 5.
Visualization and scoring of fragments were done as described for microsatellites. The presence or absence of fragments was binary coded 1 or 0 ,. Population genetic parameters and phylogenetic reconstruction. Allelic diversity, genetic variation, deviation from Hardy—Weinberg equilibrium, and genetic differentiation were calculated with Arlequin.
F -statistics were calculated for all molecular markers as implemented in Arlequin. Using microsatellite data, we applied a bayesian model-based clustering algorithm implemented in Structure 2. We used the admixture model and determined the number of ancestral clusters, K , by comparing log-likelihood ratios in multiple runs for values of K between 1 and 5.
Each run consisted of 1,, iterations with a burn-in period of 50,; multiple runs with the same value of K led to virtually identical results.
To detect the degree of similarity of the Midas cichlids in Lake Apoyo to those outside the lake, a factorial correspondence analysis of the microsatellite data was done with Genetix 4. For both analyses individ- uals were grouped according to species and lake of origin. In addition, we did a bayesian analysis of population structure with Structure for each species.
Received 13 September; accepted 10 October Dieckmann, U. On the origin of species by sympatric speciation. Nature , — Higashi, M. Sympatric speciation by sexual. Kondrashov, A. Interactions among quantitative traits in.
Gavrilets, S. Fitness Landscapes and the Origin of Species: Monographs in. Population Biology vol. Press, Princeton, NJ, Kawecki, T. Cambridge Univ. Press, Cambridge, UK, Coyne, J. Darwin, C. Murray, London,. Schliewen, U.
Sympatric speciation suggested by. Weiblen, G. Arrow cichlid A. The transformation grid based on principal. Rapid and coupled phenotypic differentiation in Icelandic Arctic charr Salvelinus alpinus. McKaye, K. Behavioral, morphological and genetic evidence of. Fish Aquat. Bice, D. Quaternary volcanic stratigraphy of Managua, Nicaragua: Correlation. Barlow, G. The corresponding transformation grid right; scaling factor 2. Thorson, T.
Fruit Flies pp Cite as. In the past two decades, alternative models, besides the classic model of allopatric speciation, have been proposed. Among them is one published by White , with semigeographic speciation. It is based on negative heterosis, and the sympatric speciation model of Maynard-Smith These are probably the two most outstanding.