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| Author(s): |
Leila Teruko Shirai
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB) |
| Defense date: | 2008-12-12 |
| Examining board members: |
Gabriel Henrique Marroig Zambonato;
Leonora Pires Costa;
Mario de Vivo
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| Advisor: | Gabriel Henrique Marroig Zambonato |
| Abstract | |
How can the tropics present such diversity? This question lies at the very core of this work. While for the origins of diversity, numerous hypotheses have been put forward over time, the pursuit of empirical proofs for them is almost as old as the hypotheses themselves. One of the better known such hypothesis, and at the same time one of the most controversial, is the Refugee Hypothesis. In this context, the main goal of this thesis has been to test the Refugee Hypothesis in the Atlantic Forest by means of a study case. Initially, the morphologic and genetic distribution patterns of Didelphis aurita Wied, 1826 marsupial have been investigated using the grids method. Cranial measurements revealed a longitudinal correlation for the females and, at the same time, the absence of any geographic correlation in the variation of male skulls. By means of a Principal Component Analysis, the latitudinal and longitudinal variations have been reduced to a geographical variation dependent on one variable only _ a diagonal that follows the extension of the Atlantic Forest along the Brazilian coast. Groups have been formed if they presented significant differences along this diagonal, thus allowing distinct, but geographically close populations, to be differentiated. It could hereby be proven that the longitudinal correlation for females reflects mainly the differentiation between populations from Bahia state, and even more, that this differentiation affects the males as well. The signature does not appear in the grid criterium for the males since they also present lower levels of differentiation in the south of Bahia, possibly due to the presence of the ecotone of the Atlantic Forest with the cerrado latu sensu biome. There is, nevertheless, a break in Bahia for both males and females. As for the geographic variation of the molecular mitochondrial marker cytochrome B, it also presented a longitudinal variation, and a clear differentiation between the two extremes of the analyzed distribution. Here, not only a similar break could be seen in Bahia, but another one further north in the specimens from Alagoas state. For both the morphological and the molecular data, while there is isolation by distance effect for the opossum, all the distribution south of Bahia behaves as a large panmitic population. This lack of geographical structuring, also apparent in differentiation analyzes (Fst), together with neutrality tests (Tajima\'s D and Fu\'s F) which point towards recent geographic expansion, show the signatures expected by the Refugee Hypothesis. Since, however, the data indicates that the divergence of southern populations occurred approximately 140,000≅60,000 years ago, the diversification cannot be due to the last inter-glacial period from 20,000 years ago. To understand this seeming contradiction, further in-depth investigations of the Fst analyzes and the neutrality tests revealed that the estimations had been highly influenced by the heterogeneity in the number of samples, as well as by the low representability of some localities and also inadequate grouping of specimens, which mixed distinct biological populations. The apparent refugee signatures have thus been the misleading consequence of three well-sampled populations from Rio de Janeiro state. Therefore, the Refugee Hypothesis cannot be regarded as an explanation for the existing diversity of the species D. aurita. (AU) | |