Are Amazonia Rivers Biogeographic Barriers for Lizards? A Study on the Geographic Variation of the Spectacled Lizard Leposoma osvaldoi Avila-Pires (Squamata, Gymnophthalmidae)
With improvements in taxonomic resolution in recent years, the Amazon basin is increasingly recognized as containing restricted-range taxa and areas of endemism. For many of these taxa, rivers delimit their geographic distributions and separate sister species. Among most lizards the geographic pattern is not clear. We attempt to determine the existence of cryptic diversity in the Spectacled Lizard Leposoma osvaldoi by analyzing the geographic variation in its morphology. We specifically tested whether the Rio Madeira, Rio Purus, Rio Aripuanã, and Rio Roosevelt delimit differentiated lizard forms. Using multivariate analysis, we detected that males of L. osvaldoi have larger heads than females but females have longer bodies. Large rivers, such as the Rio Purus and Rio Madeira, do not play a significant role in the geographic variation of L. osvaldoi. However, specimens from two localities on opposite banks of the upper Rio Aripuanã occupy the lower and upper ranges of variation in L. osvaldoi and are distinct from all other specimens analyzed. This unusual pattern differs from one of the main river hypothesis predictions, which is that similarity between individuals on opposite river banks should increase with decreasing barrier strength. We hypothesize that the differences in river dynamics between the lower and upper Rio Aripuanã during mid-Miocene through the Pleistocene could explain our results, although phylogeographic evidence is lacking to support such a hypothesis. The elucidation of recent and ancient processes that shaped diversity in Leposoma could provide important clues to understand the formation of the megadiversity of Amazonia.Abstract
Localities included in the analysis (small caps) and hypothesized groups based on main rivers (all caps). Gray scale refers to geographic extension of groups. RBA = right bank of Rio Aripuanã; LBA = left bank of Rio Aripuanã; ARI = Aripuanã - Roosevelt interfluvium; RBAb = right bank of Rio Abacaxis; LBAb =left bank of Rio Abacaxis; MPI = Madeira - Purus interfluvium; PJI = Purus-Juruá interfluvium. Localities: (a) Itapinima; (b) Lago Cipotuba; (c) Arauazinho; (d) Igarapé Extrema; (e) Projó Left; (f) Projó Right; (g) PAREST Sucundurí; (h) Aripuanã; (i) São Sebastião; (j) Igarapé Açú; (l) Cachoeirinha; (m) Lago Ayapuá; (n) Nova Colina; (o) Cachoeira do Nazaré; (p) Ministro Andreazza – Nova Brasília.
Measurements made on specimens of Leposoma osvaldoi, represented by specimen INPA 17707. INTL = interparietal length; INTAW = anterior width of interparietal; INTPW = posterior width of interparietal; PARL = parietal length; FRPL = frontoparietal length; FRPW = frontoparietal width; FROL = frontal length; FROAW = anterior width of frontal; FROPW = posterior width of frontal; 1SUPL = length of first supraocular; 2SUPL = length of second supraocular; 3SUPL = length of third supraocular; FROPCO = contact between frontoparietals; PRECO = contact between prefrontals; CEFL = length of cephalic scales; HEAW = head width.
Scatter plot of the first two principal components of PCA performed with GLM residuals from all individuals analyzed. Points in the graphic are connected according to the biogeographic groups proposed as follows (localities that belong to each group are in parentheses): RBA = right bank of Rio Aripuanã (Lago Cipotuba, Igarapé Extrema, Projó Right, PAREST Sucundurí, Aripuanã); LBA = left bank of Rio Aripuanã (Itapinima, Arauazinho, Nova Colina, Cachoeira do Nazaré, Ministro Andreazza/Nova Brasília); ARI = Aripuanã-Roosevelt interfluvium (Projó Left); RBAb = right bank of Rio Abacaxis (Igarapé Açú); LBAb = left bank of Rio Abacaxis (São Sebastião); MPI: Madeira-Purus interfluvium (Cachoeirinha); PJI = Purus-Juruá interfluvium (Lago Ayapuá).
Measurements showing significant sexual dimorphism (SD) in Leposoma osvaldoi. Points on the graph represent the difference between average partial residuals obtained in GLM. Positive values: male-biased SD. Negative values: female-biased SD. Variables are explained in Fig. 2.
(A) Localities used in PCA performed specifically at Rio Aripuanã watershed; (B) localities used in PCA performed specifically at Rio Abacaxis watershed; (C) scatter plot of first two principal components of PCA performed with GLM residuals only from individuals of Rio Aripuanã watershed; (D) scatter plot of first two principal components of PCA performed with GLM residuals only from individuals of Rio Abacaxis watershed. Localities: (a) Itapinima; (b) Lago Cipotuba; (c) Arauazinho; (d) Igarapé Extrema; (e) Projó Left; (f) Projó Right; (g) Parque Estadual (PAREST) Sucundurí; (h) Aripuanã; (i) São Sebastião; (j) Igarapé Açú.
Mean and standard deviation of scores obtained from first principal component (PC1) of eight localities that had a sample size greater than three. Numbers next to mean dots represent the sample size of each locality. Localities are arranged in crescent latitudinal order: (h) Aripuanã; (e) Projó Left; (d) Igarapé Extrema; (c) Arauazinho; (l) Cachoeirinha; (a) Itapinima; (j) Igarapé Açú; (i) São Sebastião.
Scatter plot of pairwise geographic distances and the differences between means of PC1 scores between 15 localities included in this study.
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