CONICET | Buscador de Institutos y Recursos Humanos

D. buzzatii is a cactophilic sucosmopolitan species originated in the Argentininan arid regions. Natural populations are polymorphic for several inversion arrangements of its second chromosome. Inversion frequencies are extensively differentiated among populations located in different phytogeographic regions and vary clinally along latitudinal and altitudinal gradients. Although these evidences are suggestive of selective differentiation, alternative mechanisms such as genetic drift, gene flow and historical factors can also account for the population strucute observed. The objective of the present study was to test the role of selective vs. historical events, using the comparative approach between population genetic structures determined with different genetic markers: the inversion polymorphism and seven allozyme loci. The electrophoretic loci assayed: Esterase 1 and 2 (Est-1 and Est-2), Peptidase 1 and 2 (Pep-1 and Pep-2), Leucy aminopeptidase (Lap), Aldehyde oxidase (Aldox) and Xanthine dehydrogense show different degrees of association with the segments involved in the inversions. The analysis of the population structure by means of Wright´s F-statistics showe that differentiation of inversion frequencies was on average an order of magnitude higher than for allozymes. However, among populations differentiation varied greately among electrophoretic locy. Allele frequencies did not significantly differ for Lap and Pep-2, differentiation was low to moderate for Pep-1, Est-1 and Aldox, and high for Est-2 and Xdh. These contrasting patterns of variation suggest that selective differentiation is the most likely explanation for the inversion polymorphism, and for Est-2 and Xdh, while for Est-1 and Aldox differentiation might be the result of hitchhiking with the inversions. Finally the lack of differentiation for Pep-2 could be interpreted as result of balancing selection.

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