There has been a flurry of news in the bee conservation world lately. A couple of big papers have been published, one by Laura Burkle et al. in Science and one by Ignasi Bartomeus et al. in PNAS. Laura Burkle’s paper looks at a famous historical dataset from Carlinville Illinois, and adds present day collections and collections from the 1970s to look for declines in bees. They find rather drastic declines in bee species, and while the pollination networks appear stable for now, the loss of pollinator species doesn’t bode well for the future. The tough thing about these data is that the old dataset had no record of sampling intensity or bee abundances besides broad classifications. So comparing to present day data is tough, but the findings of Burkle et al. are still a red light.
The paper by Bartomeus uses museum collections to look at bee populations across the northeastern US, and comes to a different conclusion. While the museum collections agree with other studies (including mine from San Francisco) finding declines in bumble bee species, other bee species are fluctuating, but overall species richness does not appear to be significantly declining. They cite a study stating that human land use has increased in the study area, but there has also been shifts away from farming in the Northeast. Quantifying land use change in their study area would have been very interesting. Perhaps land use change can explain some of the turnover in bee species over time, or perhaps the turn over is just part of the natural variation in bee communities. Bee biologists have known for a long time that bee communities vary greatly from year to year. But perhaps the northeast bee community is not in decline because land use change has not been as drastic in the northeast as in other areas.
The third bit of news is not published, but there have been early media reports of heavy winter losses in honey bee colonies. Colony Collapse Disorder (CCD) attributed colony losses have declined over the previous 2 winters to levels around 20% losses, but it sounds like this winter may have been the worst year yet. There is still no smoking gun as to the cause, but these losses should be another red light. We need to act fast to figure out what we can do, and we need to continue to research the other pollinators out there, as a sort of insurance if commercial honey bee cultivation continues to face these challenges. For CCD, we need more research looking at the newer pesticides out there, especially looking at combinations of pesticides, pathogens and other factors and how that affects bee health. The pesticides undergo some testing on their own, but very little testing for combined effects is done.
Finally, to add to the mostly dreary news, there are alarming reports that monarch butterfly populations at the overwintering grounds in Mexico were at record lows this year. And this loss is being attributed not to logging in Mexico (which has been halted), but to changes in farming practices in the US that has led to fewer milkweed plants, which is the larval food source for monarchs and to harsh weather (also likely our fault). These reports are again in the media and not yet published in peer reviewed journals, but the decline appears to be real. So if you are doing any gardening this year, why not add some native milkweed plants? Milkweed flowers are pretty, they will attract monarchs, and perhaps you will help save one of the marvels of the natural world (the monarch migration). Mexico is doing its part to save the monarchs, and we need to step up as well.
I haven’t had time to post much lately, but field season has started here in Texas and I will be posting pictures from this year’s field work. This will be my last season in Texas, and I’m hoping to make the most of it!
In the meantime, I’ve published another paper (Insectes Sociaux 2013 McFrederick) from my dissertation work with sweat bees and nematodes. I had a lot of fun doing this project several years ago, and finally got the work written up for publication. I reared lab nests of a social and a solitary sweat bee, both species that associate with host specific nematodes. Here is apicture of an infected brood cell, from the paper. The dashed arrow points to pollen, while the solid arrow points to a mass of nematodes:
Rearing the lab nests is what got me interested in how microbes affect bee health. But the point of the project was twofold: to figure out if the nematodes affect bee health, and if so, if associating with a social host creates natural selection for more benevolent nematode strains when compared to nematodes that associate with a solitary host. The influence of social structure on symbiont evolution has been posited before, most notably by David Hughes in this TREE article. But David suggested that associating with large insect colonies should influence symbiont evolution, while social halictids live in small colonies, with a couple of exceptions. My data agreed with this suggestion, because I found that both nematodes had small or no effects on host fitness (number of offspring produced):
Augochlora pura is the solitary host, while Halictus ligatus is primitively eusocial. There was a slight trend towards the opposite effect than what I hypothesized, that is that infected solitary hosts had greater fitness than uninfected solitary hosts and vice versa for the social host. But these effects weren’t significant. So either social structure does not influence symbiont evolution in this case, or there are effects that I was not able to detect in the lab.
Raising these nests was a great experience, just looking into the nests every day was really interesting. But it was a lot of work, and I’m not sure I will try to rear halictids again. I’m more likely to rear bees that take well to it, like leafcutting bees!
I’ve just published a paper (link here)(pdf) looking at host-specificity between Hymenoptera and Lactobacillus in Applied and Environmental Microbiology. This paper is a follow up to my earlier paper where I found that sweat bees associate with Lactobacillus species that have also been isolated from flowers (link here). Other researchers (mostly in Nancy Moran’s lab) have found that honey- and bumble-bees, which have larger colonies than my sweat bees, associate with host specific lactobacilli. So I wanted to determine if other Hymenoptera that form large colonies also have host specific lactobacilli. To answer that question, I collaborated with ant researchers that have found lactobacilli in their ants and built a phylogeny representing all publicly available Lactobacillus sequences along with our ant and bee sequences. To make the phylogeny as accurate as possible, I collaborated with Robin Gutell and Jamie Cannone, who study the secondary structure of 16S rRNA (check out their work here). They built models of the 16S rRNA secondary structure, and used those models to create the most accurate alignment possible (thanks for the awesome work Robin and Jamie!). I used this alignment to reconstruct the phylogenetic history of the genus Lactobacillus, and found that host specificity is only found in corbiculate apids and not ants that live in colonies with up to hundreds of thousands of individuals. Host specificity is therefore not related to large colony size, but instead is either a relic of a shared evolutionary history of bumble bees and honey bees or related to something special about corbiculate apid ecology. This was a really fun project because I collaborated with people from several different fields. Here is one of the phylogenies from our paper:
This time I have have a more bee-focused paper that has just been posted online early here in Molecular Phylogenetics and Evolution. The pdf of the paper is here. This paper is on the evolutionary history of nematode associates of sweat bees. I found six species of halictids in Virginia that associate with nematodes, and when I reconstructed the nematode’s phylogenetic history it was very similar to the host’s phylogenetic history. This suggests a pattern of cospeciation, where the host and associate speciate in tandem. Tests for cospeciation were significant, but the biogeography of the hosts suggests that cospeciation is not the only evolutionary force acting. One of the lineages of hosts radiated in the old world, where the nematodes do not exist. So there had to be at least one host switch to colonize the bees that migrated from the old world. Another interesting bit is that all of the hosts come from social or socially polymorphic lineages of bees, although one host Augochlora pura, has reverted to a solitary lifestyle. This suggests that social hosts may be more suitable than solitary hosts. Here is the main figure from the paper:
This is a bit off topic for the melittology focus of the blog, but my paper on Onchocerca just came out online in Parasitology (pdf here). Onchocerca is a genus of nematodes which parasitizes mammals. One species causes river blindness, which is the second leading cause of infective blindness in humans. While I was in Rochester working in John Jaenike’s lab, we studied Onchocerca in deer in Upstate New York. We built a molecular phylogeny using Onchocerca that we found in New York, publicly available DNA sequences and samples from moose in the Northwest Territories in Canada that our collaborator isolated. We found that the moose and deer worms were distantly related, which was a surprise as it was thought that only one Onchocerca species occurred in cervids (the family that includes moose and deer) in North America. We recently obtained some adult specimens, and will hopefully be formally describing the new species soon. We also did a reconstruction of the ancestral hosts of Onchocerca, and showed that the worms readily switch hosts. Deer and cattle appeared to be particularly important ancestral hosts. Zoonotic infections (that is, infections of humans arising from other animals) are on the rise, in fact there was a new report of a zoonotic infection in Oregon that was published last week. It is not known what host the worm came from, but our analysis suggests that deer are a likely source. Here is the phylogeny that we produced, with hosts (both current hosts (on the right) and ancestral hosts (on the left)) indicated as pictures.
I did a lot of dissections this summer, to look at the bacteria in bee intestines. I find the intestinal tract beautiful; the pollen is a striking color. The intestines are separated into three major parts: the crop first, the midgut, and the hindgut. The crop is not developed in larvae, but you can see the midgut and hindgut here:
The midgut is the large bit that starts on the right. In the larva this starts right after the mouth. The part with the twist is the hindgut.
I have wrapped up the experiments for the summer, and the fall will consist of lab work, analyzing data, and writing up results. One of the nice things about biology is the variety of work that you do. During field season it is a physical job, while the lab work requires organizational skills and good hands, and the analysis and writing require clear thinking and creativity.