Abstract
Ontogenetic changes in venom composition have important ecological implications due the relevance of venom in prey acquisition and defense. Additionally, intraspecific venom variation has direct medical consequences for the treatment of snakebite. However, ontogenetic changes are not well documented in most species. The Mexican Black-tailed Rattlesnake (Crotalus molossus nigrescens) is large-bodied and broadly distributed in Mexico. To document venom variation and test for ontogenetic changes in venom composition, we obtained venom samples from twenty-seven C. m. nigrescens with different total body lengths (TBL) from eight states in Mexico. The primary components in the venom were detected by reverse-phase HPLC, western blot, and mass spectrometry. In addition, we evaluated the biochemical (proteolytic, coagulant and fibrinogenolytic activities) and biological (LD50 and hemorrhagic activity) activities of the venoms. Finally, we tested for recognition and neutralization of Mexican antivenoms against venoms of juvenile and adult snakes. We detected clear ontogenetic venom variation in C. m. nigrescens. Venoms from younger snakes contained more crotamine-like myotoxins and snake venom serine proteinases than venoms from older snakes; however, an increase of snake venom metalloproteinases was detected in venoms of larger snakes. Venoms from juvenile snakes were, in general, more toxic and procoagulant than venoms from adults; however, adult venoms were more proteolytic. Most of the venoms analyzed were hemorrhagic. Importantly, Mexican antivenoms had difficulties recognizing low molecular mass proteins (<12 kDa) of venoms from both juvenile and adult snakes. The antivenoms did not neutralize the crotamine effect caused by the venom of juveniles. Thus, we suggest that Mexican antivenoms would have difficulty neutralizing some human envenomations and, therefore, it may be necessary improve the immunization mixture in Mexican antivenoms to account for low molecular mass proteins, like myotoxins.
Highlights
Phenotypic variation as a result of ontogenetic changes during the life of an organism result from differential selection pressures through time [1]
The proportion of each of these components was variable among venoms from smaller and larger snakes, where small snakes displayed more crotamine-like myotoxins and snake venom serine proteinases (SVSPs) compared to larger snakes, but the opposite occurred with snake venom metalloproteinases (SVMPs) (Figure 6A–C; Table 1)
Similar results has been reported in species such as C. durissus cumanensis [18] and C. d. terrificus [75] where venoms from neonate or juvenile snakes had Minimum Coagulant Dose Plasma (MCD-P) lower than venoms of adult snakes. These results suggest that fibrinogenases are responsible for activity in C. m. nigrescens venoms breaking both α- and β-chains of fibrinogen, while TL-SVSPs would be responsible of the activity in venoms with affinity only for the α-chain of fibrinogen
Summary
Phenotypic variation as a result of ontogenetic changes during the life of an organism result from differential selection pressures through time [1]. Because of the different pressures, the realized niche differs through time based on size and maturity. Many species of snakes are known to change the prey composition of their diet based on their size [6,7,8,9]. Margres et al [15] reported that ontogenetic shift in venom composition of C. adamanteus occurred at 102 cm, the size at which the species reaches sexual maturity. Understanding ontogenetic venom variation is important from medical and biotechnological perspective because these phenotypic differences have direct consequences for the treatment of snake bites
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