Evolutionary implications of the analysis of feulgen hydrolysis curves in mammalian species with a different nuclear DNA content

Abstract

The nuclear DNA or DNP differences in hydrolysis resistance are utilized here as an indication of the greater or lesser complexity of DNA-protein bindings, possibly related to the degree of heterochromatinization. They have been studied with the Feulgen reaction in lymphocytes of peripheral blood smears of Cercopithecus aethiops aethiops (Primates) (a species in which adaptive evolution still appears to be under way) and of Rhinolophus ferrumequinum (Microchiroptera), a representative of an older group of Mammals, Chiroptera, which is considered as evolutionarily established at least since the Eocene period (Simpson, 1945). These species have a very different “genome size” (recorded as Feulgen-DNA nuclear content): the percent ratio is at least 130:100 (Capanna & Manfredi Romanini, 1971) . From the comparison between the two hydrolysis curves it appears that their general shape is similar and that the height differences are constant for each hydrolysis time, with the exception of the first peak which is operationally defined as the acid labile fraction of DNA. This peak is higher in C. aethiops aethiops than in R. ferrumequinum. Both curves fall short of characteristic platform (120 min — 360 min) of “acid resistant” DNA, which is constantly recorded in Homo and tentatively attributed to some particular DNA-protein link (depolymerization peak of Anderson et al., 1971, 1975). No qualitative difference is remarkable in the DNA protein ratio, which could be relied to heterochromatinization materials, or to a selective loss of heterochromatic fractions of chromatin. We are therefore lead to interpret the present data as a verisimilar indication that Chiroptera ancient specialization is ascribable to a mechanism of evolutionary loss which, unlike the actual microevolution of some species of Mammals, could not be preceded by a selective heterochromatinization.