> >While the bees are slowly evolving, varroa is evolving faster and even faster are the viruses.

> Pete, that appears to be an off-the-cuff claim.  Do you have evidence to offer in support? It's obvious that viruses and mites, due to their far more rapid reproductive cycles have the *ability* to evolve at a greater rate than do bees.  Despite that fact, the evidence from South Africa suggests that bees got the upper hand.

¶

So, you agree that mites and viruses adapt more quickly than their host? Except the African bees. There are several reasons for this, in my view. One, a very large population of wild bees. In such a wild population, there would be rapid loss of susceptible strains, due to the lack of intervention by beekeepers, and resistance would become the dominant trait in the population. So, yes, we have prevented such radical natural selection from occurring in our stocks (with some exceptions). 

But the reason may have more to do with behavior: tropical bees abscond and migrate, abandoning their nests, which European bees do not do. In fact, Seeley theorizes if we let our bees swarm, the colonies would suffer less from parasites. In a sense, swarming is similar to absconding as a behavioral trait with many benefits to the species as a whole, while risky to the individual and useless to modern beekeepers. 

The honey bee superorganism resembles an individual in many ways, particular in its use of behavioral strategies for survival. For example, Harpur and Zayed state: "The genomes of eusocial insects have a reduced complement of immune genes—an unusual finding considering that sociality provides ideal conditions for disease transmission. The following [may] explain this finding: ... social insects have effective behavioral ... mechanisms for combating pathogens."

The following refers to mammals but may apply to bee colonies, as well.

¶

The costs of mutation may be higher for large, slow-maturing, long-lived mammal species. There is more opportunity for mutations to occur in a large organism which has more cells (and therefore more genome copies), takes more cell generations to produce gametes, and must maintain its body through a prolonged period of immaturity and long reproductive lifespan. And each mutation may have a higher cost. 

Therefore, there should be stronger selection pressure to reduce mutation rates in larger species, so they may invest more in DNA copy fidelity and repair mechanisms, despite the metabolic and time costs involved. Like any other life-history trait, the rate of molecular evolution represents a balance between competing needs that vary according to a species size, reproductive strategies and lifestyle.

We need to recognize that the genome is the central adaptation of any organism. As with any adaptation, it is shaped by trade-offs between competing needs and processes. While analytical methods are increasingly taking lineage-specific rate variation into account, many assume that rates are drawn randomly from a distribution, or evolve by a purely stochastic process. But rates can evolve in concert with species characteristics, which may create complex patterns of changing rates along phylogenies.

Lindell Bromham. Centre for Macroevolution and Macroecology, Botany and Zoology, School of Biology, Australian National University, Canberra, Australian Capital Territory 0200, Australia 

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