Cranial phenotypic evolution in Proechimys iheringi Thomas (Rodentia: Echimyidae)

Models of evolutionary quantitative genetics were employed to analyze cranial phenotypic evolution in the echimyid rodent Proechimys iheringi Thomas. The hypothesis that cranial differentiation among populations and subspecies of P. iheringi resulted from random drift was rejected. The completely selective model was then used to reconstruct the forces of selection that might have acted to produce the observed differences in cranial morphometric traits in P. iheringi . The net gradient of selection indicates that some cranial traits evolved in the direction contrary to the forces of selection, acting to increase mean values for cranial traits in the evolutionary transitions between populations of P. iheringi . Minimum intensities of selection were calculated and showed that selective mortality per generation was low, of the order of l0^-3, suggesting that weak selection can explain the observed cranial morphometric differences among the populations of P. iheringi .