"Our results are important in developing efficient breeding schemes for better bees"

Posted by ap507 at Aug 10, 2016 03:14 PM |
Dr Eamonn Mallon discusses declining bee populations and genomic imprinting

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If you have spent a lunchtime in the University's Botanic Garden during March or April over the last few years, you've probably seen distracted-looking people with insect nets staring at the ground. That's us, the insect epigenetics lab from the University of Leicester.

We collect bumblebee queens from the Garden and allow them to start colonies in our lab, so that we can study their fascinating behaviour.

Fig. 1
The Buff-tailed Bumblebee, Bombus terrestris (Fig. 1), is one of the most ecologically and economically important pollinators. At least 25 major crops in Europe are visited by bumblebees and insect pollination services are estimated to be worth 14.2 billion euros to Europe’s economy. It is really big business: bumblebees have been reared commercially since the late 1980s for crop pollination services, and there are over 30 production companies in 19 countries, servicing 40 nations in Europe, North America, South America, New Zealand, and Asia.

Unfortunately, bees are undergoing a rapid decline in population numbers because of a combination of pesticides, habitat loss and disease. Distressingly, in the UK, 52% of surveyed areas show a decline in bee species richness since 1980; in Europe, 37-67% of bee species are on lists of conservation concern and 11% of bumblebee species are listed as ’near threatened’ or worse by the International Union for the Conservation of Nature (IUCN).

The social insects, generally, (ants, bees, wasps and termites) are an enormously successful group. This success stems from the division of labour found in their colonies. Most fundamentally this includes the division of reproductive labour. This involves the differentiation of developing females into either workers or queens. Queens carry out most of the reproduction, while workers carry out all the other tasks required of the colony, e.g. brood care, foraging and nest maintenance. Queens are bigger, live longer and have a host of behavioural and physiological specialisations compared with workers. Importantly, and this is where our interest comes in, the division of reproductive labour is not caused by inherited genetic differences. Instead, it is an example of a much more

Fig. 2
widespread phenomenon called epigenetics. In epigenetics you can have heritable changes in gene function that are not explained by changes in DNA sequence. As an example, have a look at the picture of the different forms of a leaf-cutter ant called Atta cephalotes (Fig. 2). Almost all of these are genetically identical. Epigenetics tries to explain how these variations can arise despite the absence of changes to the DNA sequence.

One facet of epigenetics that we are interested in is genomic imprinting. Let me explain. Every gene in my body has two copies. One I inherited from my mother and one from my father.  For most genes, I use both copies. But for some genes in my body this is not the case. Imagine one such gene, where only the version inherited from the mother is used. My father's copy is not used. I pass my mother's copy on to my son which, in him, now represents his father's copy and therefore is not used. Only the version inherited from his mother will work. So despite the fact that the genetic sequence of my version of the gene is identical in me and my son, in me the copy works but in my son it does not. This phenomenon is called genomic imprinting. In this example it is driven maternally.

About 200 genes in the human genome are imprinted. Some as above, favour the mother's copy whereas others favour the father's copy. Imprinting is also found in flowering plants as well as throughout the mammals. An evolutionary biologist looks at such a system and asks how it could have evolved.

Fig. 3
Bees are an excellent test of the theories for the evolution of imprinting. Bees are haplo-diploid, meaning females (queen and workers) have two copies of every gene (diploid) whereas males (drones) have only a single copy (haploid) – Fig. 3. This permits new and independent predictions for theories about evolutionary fitness, which had otherwise been based on observations from mammals. Also, the social structure of these insects (called eusociality) and sex determination are much more complicated than in most mammals (see box for explanation of the latter). This allows us to make predictions about behaviours that were never considered when mammalian theories were formulated.

This work is important both as pure research into a fascinating and fundamental natural phenomenon, but also it will provide essential baseline data as a foundation for more applied research. The new knowledge about epigenetics discovered in our lab provides a solid basis on which to understand the role that epigenetics plays in resistance to pesticides and diseases, and also, importantly, the effect pesticides may have on epigenetics itself.  Our results are also likely to be important in developing efficient breeding schemes for better bees.

By Dr Eamonn Mallon, Department of Genetics

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