Abstract
Lungs of the rodent species, the African giant pouched rat (Cricetomys gambianus) and the Nigerian mole rat (Cryptomys foxi) were investigated. Significant morphometric differences exist between the two species. The volume of the lung per unit body mass was 2.7 times larger; the respiratory surface area 3.4 times greater; the volume of the pulmonary capillary blood 2 times more; the harmonic mean thickness of the blood-gas (tissue) barrier (τht) ~29% thinner and; the total pulmonary morphometric diffusing capacity (DLo2) for O2 2.3 times more in C. foxi. C. gambianus occupies open burrows that are ventilated with air while C. foxi lives in closed burrows. The less morphometrically specialized lungs of C. gambianus may be attributed to its much larger body mass (~6 times more) and possibly lower metabolic rate and its semifossorial life whereas the ‘superior’ lungs of C. foxi may largely be ascribed to the subterranean hypoxic and hypercapnic environment it occupies. Compared to other rodents species that have been investigated hitherto, the τht was mostly smaller in the lungs of the subterranean species and C. foxi has the highest mass-specific DLo2. The fossorial- and the subterranean rodents have acquired various pulmonary structural specializations that relate to habitats occupied.
Highlights
About 300 of the extant mammalian species that represent 54 genera and belong to 10 families of four orders live in moist and dark, climatically stable, hypoxic and hypercapnic underground burrows[1,2,3,4,5,6,7,8]
In the two rodent species, the lungs comprise two main structural parts, namely the parenchyma and the nonparenchyma: the former comprises respiratory bronchioles, alveolar ducts, alveolar sacs and alveoli while the later consists of the large blood vessels, i.e., those larger than blood capillaries, and large airways that bifurcate to terminate in terminal bronchioles (Fig. 2A,B)
In C. foxi, occasionally, the blood capillaries are exposed to air only on one side of the interalveolar septum (Fig. 2F - insert)
Summary
About 300 of the extant mammalian species that represent 54 genera and belong to 10 families of four orders live in moist and dark, climatically stable, hypoxic and hypercapnic underground burrows[1,2,3,4,5,6,7,8]. Comparisons of two species or populations of animals that differ in certain attributes like body mass, genetic make ups, morphological and physiological properties, lifestyles pursued and habitats occupied have been performed for a long time[64,65,66,67,68,69,70,71] Such studies have been used to explicate the consequences of the interactions between the phenotype and the environment, means and processes by which evolutionary adaptations are envisaged to occur[72,73,74,75]. If two species or populations comparisons in which relative differences are inferred to be adaptations are proven to be experimentally flawed, studies like ours will need to be re-evaluated
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