How the Cobra Got Its Flesh-Eating Venom: Cytotoxicity as a Defensive Innovation and Its Co-Evolution with Hooding, Aposematic Marking, and Spitting

The cytotoxicity of the venom of 25 species of Old World elapid snake was tested and compared with the morphological and behavioural adaptations of hooding and spitting. We determined that, contrary to previous assumptions, the venoms of spitting species are not consistently more cytotoxic than those of closely related non-spitting species. While this correlation between spitting and non-spitting was found among African cobras, it was not present among Asian cobras. On the other hand, a consistent positive correlation was observed between cytotoxicity and utilisation of the defensive hooding display that cobras are famous for. Hooding and spitting are widely regarded as defensive adaptations, but it has hitherto been uncertain whether cytotoxicity serves a defensive purpose or is somehow useful in prey subjugation. The results of this study suggest that cytotoxicity evolved primarily as a defensive innovation and that it has co-evolved twice alongside hooding behavior: once in the Hemachatus + Naja and again independently in the king cobras (Ophiophagus). There was a significant increase of cytotoxicity in the Asian Naja linked to the evolution of bold aposematic hood markings, reinforcing the link between hooding and the evolution of defensive cytotoxic venoms. In parallel, lineages with increased cytotoxicity but lacking bold hood patterns evolved aposematic markers in the form of high contrast body banding. The results also indicate that, secondary to the evolution of venom rich in cytotoxins, spitting has evolved three times independently: once within the African Naja, once within the Asian Naja, and once in the Hemachatus genus. The evolution of cytotoxic venom thus appears to facilitate the evolution of defensive spitting behaviour. In contrast, a secondary loss of cytotoxicity and reduction of the hood occurred in the water cobra Naja annulata, which possesses streamlined neurotoxic venom similar to that of other aquatic elapid snakes (e.g., hydrophiine sea snakes). The results of this study make an important contribution to our growing understanding of the selection pressures shaping the evolution of snake venom and its constituent toxins. The data also aid in elucidating the relationship between these selection pressures and the medical impact of human snakebite in the developing world, as cytotoxic cobras cause considerable morbidity including loss-of-function injuries that result in economic and social burdens in the tropics of Asia and sub-Saharan Africa

Contrasting patterns of virus protection and functional incompatibility genes in two conspecific Wolbachia strains from Drosophila pandora

infections can present different phenotypes in hosts, including different forms of reproductive manipulation and antiviral protection, which may influence infection dynamics within host populations. In populations of two distinct strains co-exist, each manipulating host reproduction: PanCI, causes cytoplasmic incompatibility (CI), whereas PanMK, causes male-killing (MK). CI occurs when a -infected male mates with a female not infected with a compatible type of leading to non-viable offspring. PanMK can rescue PanCI-induced CI but is unable to induce CI. The antiviral protection phenotypes provided by the PanCI and PanMK infections were characterised; strains showed differential protection phenotypes whereby cricket paralysis virus (CrPV)-induced mortality was delayed in flies infected with PanMK but enhanced in flies with PanCI when compared to their respective -cured counterparts. Homologs of and genes involved in CI identified in PanMK and PanCI showed a high degree of conservation; however, the cifB protein in PanMK is truncated and is likely non-functional. The presence of a likely functional in PanMK, and PanMK's ability to rescue PanCI-induced CI is consistent with the recent confirmation of cifA's involvement in CI rescue; and the absence of a functional cifB protein further supports its involvement as a CI modification factor. Taken together these findings indicate that PanCI and PanMK have different relationships with their hosts in terms of their protective and CI phenotypes. It is therefore likely that different factors influence the prevalence and dynamics of these co-infections in natural hosts. strains are common endosymbionts in insects with multiple strains often coexisting in the same species. The coexistence of multiple strains is poorly understood but may rely on having diverse phenotypic effects on their hosts. As is increasingly being developed as a tool to control disease transmission and suppress pest populations, it is important to understand the ways in which multiple strains persist in natural populations and how these might then be manipulated. We have therefore investigated viral protection and the molecular basis of cytoplasmic incompatibility in two coexisting strains with contrasting effects on host reproduction