Effects of change in environmental temperature and natural shifts in carbon dioxide and oxygen concentrations on the lungs of captive naked mole-rats(Heterocephalus glaber): a morphological and morphometric study

The lungs of the naked mole-rat Heterocephalus glaber were morphologically (qualitatively) and morphometrically (quantitatively) investigated in adult captive in-burrow body-temperature-maintained (CBTMA) and captive cold-exp osed animals (CCEA). The observations were compared with those of field (bu rrow-dwelling) animals (FA) examined in an earlier study. The lungs of the captive animals were morphologically (qualitatively) similar to those of th e field mole-rats. Conspicuous paedomorphic features, i.e. a preponderant d ouble pulmonary capillary arrangement, incomplete differentiation of alveol ar pneumocytes, and extension of a cuboidal epithelium to the immediate vic inity of the alveoli, were observed. The prevalent pulmonary underdevelopme nt was attributed to the relatively low metabolic rate of the poikilothermi c naked mole-rat, a species that has evolved in a thermally stable environm ent. Measurable differences and similarities were found between the lungs o f the captive naked mole-rats themselves (i.e. the CBTMA and the CCEA) and between the captive and the field ones. Genetic factors may help explain th e conserved pulmonary structural features while environmental (gaseous) cha nge from a hypoxic-hypercapneic (an oxygen deficient-high carbon dioxide co ncentration) to a normoxic-normocapnic atmosphere and the thermal shift res pectively may have enforced pulmonary transformations between the CBTMA and the FA and between the CCEA and the CBTMA. Paradoxically, the CCEA had a s ignificantly lower mass-specific total morphometric pulmonary diffusing cap acity of 0.024 compared with that of 0.102 mlO(2).s(-1).mbar(-1).kg(-1) in the CBTMA. The observed morphometric differences indicate that the lung of the naked mole-rat, though morphologically unchanged, is intrinsically trac table to environmental shifts in its habitat. Studies on captive naked mole -rats should not be indiscriminately taken to be representative of the spec ies.