>What helped these species to be so resilient to a devastating infection when other animals Well for starters asexual reproduction is an option for them, not t

>What helped these species to be so resilient to a devastating infection when other animals Well for starters asexual reproduction is an option for them, not the sole means of reproduction. Secondly, diseases and catastrophes strike all sorts of critters and sometimes no amount of genetic variation will save them. For example you mention snakes and their resilience: http://www.bbc.com/news/science-environment-42428528 http://www.bbc.com/news/science-environment-42428528 Thirdly, snakes, lizards, sharks, make up a huge number of species and genetic variability with global distribution. That provides some protection. And for most of history global pandemics were probably less common or were slow enough that it didn't happen at once everywhere. And if enough individuals survive for the species to recover, then that's that. Fourth, sexual reproduction isn't a guarantee of immunity to disease, it's a survival strategy to help increase the odds of surviving as a species or having individuals with immunity because of all the possible combinations of genes being tried. For example, AIDS (without treatment) is lethal for most of the human population. But there are a few Scandinavian groups that have partial or full immunity, something like less than 1% of the total human population. That's what sexual reproduction gets us as a species.