Is it the same bee or is not?

They are just bees, they all the same… nothing more wrong than that. A large number of bees has been described so far as belonging to different species, with large differences in morphology, nesting, foraging for acquiring resources and so on. On the other hand, even within a single species, some degree of (reasonably small) variation in morphology, behaviour, ecology and in genetics can take place.

The studied bee

This is true not only for bees and, for example, consider humans, as different people could have different eye shape, or people of an ordinary village could be sorted into diverse family trees, although these people all belong to the same entity of being humans. In a recent study, some colleagues and I have discovered that the populations of a bee species from Europe, quite widespread all over the continent, and with negligible morphological variation (for what we know), is actually structured in a western and an eastern genetic lineage. This means that at some point during the history of the bee and of the continent, a common entity ended up as separated in two spatially isolated clusters. This isolation allowed some genetic difference between these clusters to sediment in the DNA, and nowadays the apparently continuous bee range is actually divided into two adjacent genetic sections. This is quite surprising, because what superficially seemed homogeneous, in fact was an heterogenous structure. Here is the link the published study this blog is reffering to: http://fragmentaentomol.org/index.php/fragmenta/article/view/414. Similar studies have piled up over time, especially in the last 20 years, with case studies from other animals and plants.

Although not discussed in the bee study itself, the authors and I have later brainstormed that the root factor causing the observed genetic structuring of this bee might be connected with the turbulent climatic history of Europe. During the most recent ice ages, the cooling of most Europe lead organisms to seek refugium in southern Europe, where populations remained isolated by the E-W distribution of mountains that worked as geographical barriers. This likely contributed to what we have observed in the bee we studied.

It would be very interisting to know if other bee species hide patterns of variation across their range.

We should love field experiments

A study that some colleagues and I published in 2019 is currently listed in the top 100 Ecology papers published by Scientific Reports that year (ranked 54th out of 550 ones based on download rates). This rank is quite remarkable and the idea of this study came from a visit to an acquaintance. It was 2014 when on a trip to UK for attending a conference, Jan (my PhD supervisor that time) and I stopped at Jeff Ollerton’s lab in Northampton for a hello. We chatted about my PhD degree about to start in Czech Republic and set a meeting for a brainstorming. This event provided us an exciting working hypothesis about plants and pollinator interactions. Once back to Czech Republic, we decided to test how the pollinator guild would react to the sudden loss of the most favored plant species. We choose to test this with field manipulations, rather than by computer simulations. In particular, we planned to remove 4 plant species from natural communities, one plant species at a time, based on the amount of pollinators they previously received. We discovered a few but important aspects of how a pollinator guild depends on the scenario set by the plant assemblage. We found that knocking out the most visited plants caused sudden decreases of pollinator abundances. On top of that, we discovered that those pollinators who did not disappear after plant removal, redirected the visitation towards particular flowers instead of redistributing equally to the remaining plants. Specifically, our data suggested that flowers that were smaller than or with more sugar in the nectar than the removed flowers received more visitors.

These findings supported the idea that generalist flowers (i.e. higly visited) play a key role in sustaining local pollinator abundances, and that pollinator can somehow find alternative resources but according to specific flower features. It was an exciting study, which helped understanding how pollinators redirect their foraging choices after perturbations and that could also bear some implications even for ecosystem conservation. For a full view, the study is here: https://www.nature.com/articles/s41598-019-43553-4.

We did also explore what impacts this removal caused on the structures of plant-pollinator interaction networks, but I will not reveal too much about that now (but see here: https://www.biorxiv.org/content/10.1101/2020.01.28.923177v1)

Towards new, uncolonized areas

Bombus haematurus in Zlin, CZ

Organisms have the amazing ability of quickly colonize new areas, if they constitute the appropriate environment. A typical example is represented by the invasive species, imported voluntarily or involuntarily into new (but suitable) parts of the world by human activities and globalization, e.g. the agricultural pests. These are usually well studied cases because of the great negative impact on the ecosystems health and the economy.

Totally different story is for those species that are naturally spreading into new areas. These would be species that adapt to a new environment or that spread because the environment changes (from previously inhospitable to suitable), without humans carring them around. These cases are documented, but why these spreads occur is a topic somehow less frequently studied, I don't really know why! In this study, some colleagues and I have looked at a bumblebee that is protagnist of an astonishingly quick spread from the Balkan into Central Europe. Did you know that its spread started in the 80s? and do you know why the 80s is a very meaningful time for range spread? Did you know that this bumblebee is a forest-lover but that actually it also loves cities? See here for the study

https://www.biorxiv.org/content/10.1101/2020.02.15.950931v1 and the published version is here https://onlinelibrary.wiley.com/doi/full/10.1111/1744-7917.12800

The figure above is a queen of this beautiful bumblebee pictured in Zlin (Czech Republic!) by me in May 2017, the northernmost known locality in Europe (at the moment), only 70 KM from the Moravian Gate (and Poland!)