Saturday, 9 May 2020

Evolution News - Another Beneficial Mutation

Cape honey bee workers laying parasitic eggs on a queen cell.

Photo credit: Benjamin Oldroyd
Virgin birth has scientists buzzing - The University of Sydney

I have often commented in this blog about how science without any effort or intent, casually refutes creationism by falsifying another of it's articles of faith, or sacred dogmas.

This paper on parthenogenic bees is yet another of these, as was the recent one on the transitional plant fossil. It illustrates how a mutation can be highly beneficial in the right environment. Creationist dogma says it can't be, of course, because all mutations are harmful and increase 'genetic entropy' - an argument made popular by Michael J Behe in his failed attempt to show that evolution is consistent with the Christian notion of 'the fall' because all evolution is really 'devolution' [sic].

Yet here we have a mutation in a subspecies of honeybee - the Cape honeybee (Apis mellifera capensis) which is highly advantageous, enabling this subspecies to parasitise other honeybee colonies, to the extent that they present a serious threat to other honeybee populations.

We already have the example of parthenogenetically-reproducing marbled crayfish but that was due to an accidental duplication of the entire genome, giving rise to a new species. This example is due to a mutation in a single gene.

As the press release from the University of Sydney, Australia, where the research team were based, explains:

In the Cape honey bee, found in South Africa, the gene has allowed worker bees to lay eggs that only produce females instead of the normal males that other honey bees do. “Males are mostly useless,” Professor Oldroyd said. “But Cape workers can become genetically reincarnated as a female queen and that prospect changes everything.”

But it also causes problems. “Instead of being a cooperative society, Cape honey bee colonies are riven with conflict because any worker can be genetically reincarnated as the next queen. When a colony loses its queen the workers fight and compete to be the mother of the next queen,” Professor Oldroyd said.

The ability to produce daughters asexually, known as “thelytokous parthenogenesis”, is restricted to a single subspecies inhabiting the Cape region of South Africa, the Cape honey bee or Apis mellifera capensis.

Several other traits distinguish the Cape honey bee from other honey bee subspecies. In particular, the ovaries of worker bees are larger and more readily activated and they are able to produce queen pheromones, allowing them to assert reproductive dominance in a colony.

These traits also lead to a propensity for social parasitism, a behaviour where Cape bee workers invade foreign colonies, reproduce and persuade the host colony workers to feed their larvae. Every year in South Africa, 10,000 colonies of commercial beehives die because of the social parasite behaviour in Cape honey bees.
The existence of Cape bees with these characters has been known for over a hundred years, but it is only recently, using modern genomic tools, that we have been able to understand the actual gene that gives rise to virgin birth.

“Further study of Cape bees could give us insight into two major evolutionary transitions: the origin of sex and the origin of animal societies,” Professor Oldroyd said.

Perhaps the most exciting prospect arising from this study is the possibility to understand how the gene actually works functionally. “If we could control a switch that allows animals to reproduce asexually, that would have important applications in agriculture, biotechnology and many other fields,” Professor Oldroyd said. For instance, many pest ant species like fire ants are thelytokous, though unfortunately it seems to be a different gene to the one found in Capensis."

The team have identified the gene responsible on chromosome 11. It is a varient of GB45239 which is a derivative of that found in the related subspecies. In other words, during the divergence of these subspecies, a mutation in GB45239, produced the asexual subspecies, A. m. capensis

Highlights
  • Gene GB45239 causes thelytoky (virgin birth) in A. m. capensis honeybees
  • Variants in GB45239 consistently co-segregate with thelytoky across populations
  • GB45239 is downregulated in the ovaries of thelytokous bees
  • GB45239 likely affects chromosome segregation, which results in a faulty meiosis

Summary
In honeybees, the ability of workers to produce daughters asexually, i.e., thelytokous parthenogenesis, is restricted to a single subspecies inhabiting the Cape region of South Africa, Apis mellifera capensis. Thelytoky has unleashed new selective pressures and the evolution of traits such as social parasitism, invasiveness, and social cancer. Thelytoky arises from an abnormal meiosis that results in the fusion of two maternal pronuclei, restoring diploidy in newly laid eggs. The genetic basis underlying thelytoky is disputed. To resolve this controversy, we generated a backcross between thelytokous A. m. capensis and non-thelytokous A. m. scutellata from the neighboring population and looked for evidence of genetic markers that co-segregated with thelytokous reproduction in 49 backcross females. We found that markers associated with the gene GB45239 on chromosome 11, including non-synonymous variants, showed consistent co-segregation with thelytoky, whereas no other region did so. Alleles associated with thelytoky were present in all A. m. capensis genomes examined but were absent from all other honeybees worldwide including A. m. scutellata. GB45239 is derived in A. m. capensis and has a putative role in chromosome segregation. It is expressed in ovaries and is downregulated in thelytokous bees, likely because of polymorphisms in the promoter region. Our study reveals how mutations affecting the sequence and/or expression of a single gene can change the reproductive mode of a population.


Very clearly, in this subspecies of the honeybee, a single mutation on a single gene, in the presence of sexually-reproducing related populations of honeybee was hugely beneficial, and led to the evolution of this novel population. This is not a problem at all for evolutionary biology to understand and explain. However, it represents a major rebuttal of creationist claims that all mutations are harmful and deleterious. The religious notion of 'genetic entropy' is a desperate attempt to refresh the flagging fortunes of the Discovery Institute's failing Wedge Strategy with the biologically nonsensical idea that a deleterious allele can increase within a gene pool, so leading to 'devolution' of the species.







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