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Dave Black

Thinking about Pollen (again)

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This winter a report in the New Zealand Journal of Ecology reported on an emerging technique used to measure biodiversity in ecosystems, the use of DNA ‘barcoding’ or  ‘metabarcoding’. A specific region of DNA in a gene can be used to identify an organism, euphemistically referred to as it’s ‘barcode’. ‘Meta’ barcoding takes environmental bulk samples, or pooled collections of organisms (from something like an insect trap), amplifies the specific regions we are interested in, analyses the sequences in the DNA, and compares the result to a reference database of ‘barcodes’ to identify what’s there. This has now become pretty mainstream work in ecology, it’s fast, and relatively inexpensive ($200-$500 a sample I’m told, have you thought about it @JohnF?) New Zealand scientists have used the method to look at bacteria in geothermal vents, and microbial communities in grassland, pasture, vineyards, and forests, just as an example. The Journal was discussing the methodology and standards and its value in supporting the National Framework for assessing biodiversity in New Zealand.

But this is a Beekeeping forum you say; So what!

Well, in 2012 a report in PLOS One described a project by Natasha de Vere barcoding flowing plants and conifers in Wales, 1143 species. This year another paper described her follow-up which placed bee hives in the National Botanic Garden of Wales and used metabarcoding to look at pollen and nectar collection; what species appeared in the diet, where they came from, and when they appeared. The data could be used to produce exactly the kind table Trees for Bees ( @Linda Newstrom-Lloyd) recommend for identifying periods of pollen dearth, honey flows, and so on in our own bees.

 

chart.jpg.2f191d63faa0b80d3a17b422acc484ff.jpg

 

The authors conclusion confirms the value of the technique, but leaves a question open about the reasons for the bees only using a small portion (about 11%) of the flora available to them. They conclude:

“…the very close correspondence between flowering phenology and detection within the honey shows that DNA metabarcoding provides a valuable tool for investigating honey bee foraging at a landscape scale.”

 

“The results have implications for managing habitats for honey bees. They suggest that honey bees have a taxonomically diverse but small number of core plant requirements that are supplemented with lower levels of other species. Current advice on honey bee foraging suggests providing a diverse floral resource. Floral diversity is valuable in that it provides the range that honey bees may require, but in addition to this the quality and quantity of the resource is likely to be particularly important. In this study the honey bees were provided with a very high diversity of horticultural plants but their main foraging activity during the spring was not on these species. Instead it focused on native or near-native plants available within the study area, which were also very frequent within the wider agricultural landscape surrounding the study site. The foraging measured by metabarcoding honey corresponds closely both with other studies that have examined pollen use by honey bees and also the plants that provide the greatest abundance of nectar within the UK. The major plants are characteristic of native woodlands and hedgerows, suggesting that whilst gardens provide an important source of additional plants, they cannot replace diverse semi-natural habitats.”

 

The current fashion for studies about foraging frequently speculate about how bees choose their forage plants, particularly where pollen is concerned. The observation that (all) bees have clear preferences for certain kinds of pollen is not a new observation, but the complex inter-related nature of the many ‘cues’ pollen may provide that allow bees to discriminate still defies a complete analysis. Pollen has shape, colour, smell, and taste. Flowers present it in a variety of different ways in different places and different times. It isn’t made of the same ‘stuff’, and it doesn’t have the same (nutritional) reward value to the diverse creatures that collect it. And that’s without considering the effort involved in finding and transporting it, or the fact that someone else wants it too. We also have to remember that bees are clever, and we must correctly factor in learning, memory associations, and experience. We might think they are responding to the ‘smell’, but actually they could be remembering that at three o’clock  blue flowers have the right size of slightly sticky grains that will just pack nicely into their pollen baskets. Certainly the thought that ‘bees might be able pick the most ‘nutritious’, or the one type they are short of, doesn’t (yet) seem to be borne out by the evidence.

 

So most ‘bees may be stuck with collecting enough of anything and everything to make sure they have the ‘right’ stuff. It’s a pity. The more we find out about pollen and nutrition the more the ability to choose seems important. This month Michal Filipiak and his colleagues in Poland have been looking at ‘stoichiometry’ and bee pollen.

 

If you can’t remember your school chemistry, stoichiometry is an idea that has be around for a long time, maybe since the Greeks in 500BC. The Latin phrase is ex nihilo nihil fit, essentially, nothing comes from nothing. Nowadays we think of it in terms of the Law of Conservation of Mass. Since chemical reactions neither create nor destroy matter, or convert one element into another, in a closed (isolated, independent) system the amount of each element must be the same at the end of the process as it was at the beginning.

 

Metabolic processes are nothing but chemical reactions. Filipiak puts it like this:

 

“According to the law of conservation of mass, specific atoms (in contrast to organic compounds) are not converted to other elements during processing of the consumed matter. Thus, a stoichiometric mismatch can occur between the elemental composition of the consumer's body and that of its food, thereby limiting the consumer's growth and development”

 

 

“…The vast majority of the non-carbon elements used to build the tissues of growing bee larvae originate from pollen...nectar is the source of C, H and O, and pollen is the source of other elements composing organic molecules... Considering the possible sources of chemical elements gathered by bees (nectar, pollen, water), it can be assumed that the stoichiometry of pollen is the key factor influencing the nutritional balance of larval food, since (1) energy is readily available from nectar; (2) pollen is almost the exclusive source of non-carbon elements for bees; (3) elements are conserved, i.e., they cannot be converted into other elements; and (4) organic compounds are processed and recycled by jelly-producing nurse bees”

 

 

“Considering ‘nutritional quality’ in the framework of ecological stoichiometry suggests that the mixing of pollen that differs in multi-elemental composition permits a stoichiometric balancing of the diet, thus avoiding limiting stoichiometric mismatches that constrain honeybee development.”

 

In stoichiometry Filipiak sees a short-cut. Rather than exhaustive (and exhausting) dietary studies we can learn quite a lot by comparing the composition of the body with the composition of the food – if the body is built with zinc there must be zinc in its food. This is a lengthy and comprehensive study full of charts, tables, and supplementary data that you can read in your own time. One of the suggestions that struck me reading through it was this one, I’ve written about it before;

 

“The Na [sodium] concentration in pollen is low and insufficient for bee development. However, Na concentrations in jelly reach values that meet or exceed the highest values reported in pollen pellets. Even if 100% Na assimilation is considered, it is unlikely that bees concentrate the scarce Na available in pollen to a great extent, and nectar cannot serve as a source of nutritional elements other than C [carbon]. Thus, it is likely that the bees supplement Na from sources other than pollen and nectar. For bees, the source of non-C elements may be ‘dirty water’, as honeybees are known to willingly utilize liquid waste and ‘dirty water’, which are rich in decomposing matter and salts. We hypothesize that bees are able to produce stoichiometrically balanced jelly for the reared larvae by supplementing Na deficiencies with ‘dirty water’. Such supplementation has been suggested by Bonoan et al. Supplementation from the sweat, urine and excrement of animals is also possible”

 

and;

 

“We calculated the cost of production for each caste… Drones are the ‘most expensive’ to produce, as the highest masses of elements must be incorporated into their bodies (especially Cu, C, K and N), whereas individual workers are the ‘cheapest’ to build. Considering the invested amounts of C, N, S and Mn, one worker is 3 times less expensive than a drone and 2.5 to 3 times less expensive than a queen. Considering K and Na, a worker is 2.7 and 2.5 times less expensive, respectively, than a drone and 2 and 3 times less expensive, respectively, than a queen."

 

Helpfully, the conclusions of this engaging paper are all set our rather neatly, and I’ve underlined what I think the important bits are;

 

“1. The feeding strategy of a pollen eater contrasts with the strategies of other herbivores due to the exceptional nutritional richness of pollen.

2. Particular honeybee castes and sexes differ in stoichiometry and need to incorporate various proportions of elements during development; therefore, different castes and sexes experience different stoichiometric mismatches and must be provided with appropriate and balanced combinations of nutrients in their food.

3. The nutritional elements that limit honeybee development to the highest degree due to their scarcity in pollen are Na, S, Cu, P and K. Zn and N were determined to be possibly limiting for bees.

4. Not all plants produce pollen that satisfies the nutritional requirements of bees with respect to the required proportions of elements. Pollen eaters may not be able to stoichiometrically balance their diets without access to pollen species that are rich in limiting elements. Floral diversity may allow all of the necessary nutritional elements to be gathered in the appropriate proportions. Thus, a diverse flora is needed for bee development.

5. Particular plant species that satisfy the nutritional requirements of bees may play greater roles than other species in stoichiometrically balancing the diets of pollen eaters. These taxa should be promoted in intervention strategies aimed at improving the nutritional base for pollen eaters, regardless of the amounts of nectar and pollen produced. We propose clover as such a stoichiometrically balanced taxon for bees.

6. Single-species crop plantations might limit bee development even if the crops are rich in nectar and pollen. Sunflower may negatively affect bees' growth and development because of the scarcity of P in its pollen.

7. There is a need for data that allow the comparison of taxonomic, environmental, and soil nutritional status factors that may influence the elemental composition and stoichiometry of pollen.”

 

Using DNA metabarcoding to assess New Zealand’s terrestrial biodiversity (2017) Robert J. Holdaway, et al.New Zealand Journal of Ecology 41(2): 251-262. DOI: 10.20417/nzjecol.41.28

 

de Vere N, Rich TCG, Ford CR, Trinder SA, Long C, et al. (2012) DNA Barcoding the Native Flowering Plants and Conifers of Wales. PLoS ONE 7(6): e37945.

doi:10.1371/journal.pone.0037945

 

de Vere, N. et al. Using DNA metabarcoding to investigate honey bee foraging reveals limited flower use despite high floral availability. Sci. Rep. 7, 42838; doi: 10.1038/srep42838 (2017).

 

Plant Pollinator interactions from flower to landscape; Assessment of pollen rewards by foraging bees (2016). Elizabeth Nicholls and Natalie Hempel de Ibarra. Functional Ecology doi: 10.1111/1365-2435.12778

 

Filipiak M, Kuszewska K, Asselman M, Denisow B, Stawiarz E, Woyciechowski M, et al. (2017) Ecological stoichiometry of the honeybee: Pollen diversity and adequate species composition are needed to mitigate limitations imposed on the growth and development of bees by pollen quality. PLoS ONE 12(8): e0183236. https://doi.org/10.1371/journal.pone.0183236

 

 

 

 

Edited by Dave Black
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@Dave Black if a domestic  garden does not satisfy the bees requirements it must be because ornamental flowers have been  hybridised and line bred for characteristics, colour, smell etc, that the bees do not find useful.

A domestic garden with the wild species of flower should supply the bees needs.

If the bees get other elements from dirty water hives on animal farms should be healthier.

My strongest hive is next to my chook house .

But my bees prefer to get their water  from my large goldfish pond, which has snails and frogs and is often murky .

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A New Zealand group has used this approach to look at pollen diversity @Dave Black . . . it was done at Lincoln University.

https://www.ncbi.nlm.nih.gov/pubmed/27896027

While its a few hundred dollars per sample when maximised, it requires a lot of samples to make the most of the sequencing instrument run . . . and also involves a fair bit of bioinformatics (ie grunty computers and software that can separate out all the different sequences and match them to databases).

 

We have used this metabarcoding approach to look at the diversity of bacteria . . . through a wastewater system.

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That’s a compact little study @JohnF. I don’t have any argument with their discussion about the value of AES assessments [Agri-Environment Schemes], but I’m not sure their result with Phacelia is robust enough to hinge it all on! That aside, it’s an example of exactly the kind of work I think we need more of, and the sort of practical thing I think metabarcoding is good for.

This bit caught my eye: By 2009, about 66% of England’s agricultural land was managed as part of AES agreements. Wow. They’re currently around 20% of farmers’ payment through CAP I think, so that must be why, but I’m guessing Brexit is about to kill that off!

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It is so great to see that our study may be put into practice and that we managed to write the paper in accessible and comprehensible way (and this is is really difficult, especially for non native English speaker). Thank you!.

Please take a look at the Table 7 ( http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0183236#pone-0183236-t007 ) in our paper ( http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0183236#pone-0183236-t007 ), where we presented 85 plants, that were investigated during last 75 years of bee research and we calculated which plants may limit bee growth and development (negatively influencing health and condition, resulting in underdevelopment or even in death) and which plants produce pollen nutritionally balanced for bees, therefore promoting their development and health. In case of Europe, clover, producing pollen nutritionally balanced for bees, is a good choice as bee-friendly plant. You may find something else for yourself. We found that lavender produce highly nutritionally imbalanced pollen, therefore even if considered as bee-friendly, because of nectar production (source of energy but not physiologically important nutrients) and even if lavender attracts pollinators to a high degree, its good to provide the insects with another source of pollen that is nutritionally balanced and enables gathering of important nutrients in needed proportions. In general we suggest that plants should not be evaluated as adequate sources of bee food based solely on the quantity of pollen produced. The nutritional quality of pollen should also be taken into consideration.

Kind regards!
Michał Filipiak

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Hi @Michal,

I'm grateful for your kind response. Perhaps it supports your decision to publish in an Open Access journal - long may that continue.

 

NZ has many imported European plants that form a significant part of the bee forage, so that table is indeed quite useful. Ironically what we have little data is in the case of our own native flora. The country was never 'designed' for honey bees, if I can put it like that.

 

Nice to have you as a member for a while! It will take me some time to fully absorb your paper. :)

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