ABSTRACT To allow analysis of the variation in circulating concentrations of glucose, a database was assembled of published concentrations of glucose in serum/plasma of vertebrates and annelids, hemolymph of mollusks and arthropods, blood of annelids, and celomic fluid of echinoderms. Within major taxa, circulating concentrations of glucose are fairly consistent with coefficients of variation of 84.3% (mollusks), 66.5% (arthropods excluding the insects) and 64.0% (chordates/vertebrates). There were lower coefficients of variation for circulating concentrations of glucose within some vertebrate classes, namely Aves (23.7%), Mammalia (33.9%) and Actinopterygii (46.5%). Circulating concentrations of glucose are very low in annelids and echinoderms [< 0.3 mM], low in mollusks [0.52 ± (n = 8 species) stardard error of the mean (S.E.M.) 0.16 mM] and arthropods excluding insects [1.00 ± (33 species) 0.12 mM] but markedly higher in insects [7.2 ± (5) 2.4 mM] and vertebrates [9.4 ± (626) 0.24 mM]. Within the vertebrates, circulating concentrations of glucose are relatively low in species in the Superclass Cyclostomata [2.6 ± (6) S.E.M. 0.59 mM], in the Super-order Batoidea in the Class Chondrichthyes [1.9 ± (4) 0.20 mM], in the Class Actinopterygii [4.3 ± (91) 0.21 mM], in the Class Sarcopterygii [3.1 ± (4) 1.12 mM], in the Class Amphibia [2.8 ± (11) 0.66 mM], Class Reptilia excluding Family Lacertidae and families in Sub-order Iguania [4.3 ± (92) 0.21 mM] and within Class Mammalia, Prototheria [3.3 ± (2) 0.85 mM], Super-order Afrotheria [4.6 ± (3) 0.53 mM] and Super-order Xenarthra [3.0 ± (4) 0.75 mM]. There is evidence of multiple events each resulting in increases in the set-point for circulating concentrations of glucose. There are elevated concentrations of glucose in the mammals in Super-orders Laurasiatheria [7.6 ± (96) 0.22 mM] and Euarchontoglires [7.2 ± (31) 0.52 mM] and in reptiles of Sub-order Iguania [9.6 ± (19) 0.77 mM] and the Family Lacertidae [11.0 ± (6) 1.15 mM] together with even larger increases in birds in the Super-order Paleognathae in Class Aves [10.9 + (4) 0.84 mM] with a further increase in birds in the Neognathae [16.0 + (226) 0.25 mM].
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