Bumble and Bumble: what’s black and yellow and maybe more than one species?

During the dark afternoons of December in New England, I like to scroll through my old field photos and think of all the green, growing things I’ve measured in beautiful places during those long-ago long-lit seasons. Yesterday I flipped through a couple field photos from a friend — “Photos of younger Jon! :)” he wrote in the email — and the same sunny feelings flooded in. As a master’s student*, Dr. Jon Koch and his insect net chased bumble bees all over the western United States. He was studying bumble bee decline, but hit weird hurdle: a messy species boundary between two bumble bees.

Taxonomists and field guides were torn on whether Bombus fervidus was or was not Bombus californicus. These two “species” in the Bombus fervidus species complex were nearly morphologically identical, except for their color patterns: B. fervidus is noted as usually mostly yellow with a little black, while B. californicus sports mostly black with some yellow in variable detail. They were maybe different species, maybe hybridizing, or maybe the same thing with different color morphs. As Jon explained to me, “If we don’t know what the species are, how will we manage them? Bumble bees are differentially sensitive to land use change, disease, etc. The bumble bees in the Bombus fervidus species complex are found to be impacted by one disease, Nosema bombi, but perhaps differently. Therefore, it is important to recognize what the species boundaries are because estimates of infection prevalence might be not be done correctly due to the inability to tell the species apart.”

Jon wanted to bring some clarity to the species complex by providing some new molecular evidence with broader taxa sampling. His new PLoS ONE paper, “Phylogeny and population genetic analyses reveals cryptic speciation in the Bombus fervidus species complex (Hymenoptera: Apidae)” delivers on the broader taxa sampling — 320 specimens from 53 sites — but the clarity is a bit of a cliff hanger.

During the fieldwork, Jon and his coauthors keyed out identifications for their bees based on the setal color, and also took a tarsal clipping from the mid-leg for DNA extraction and microsatellite genotyping. When they compared field identification to the genotypes, they had an ID rate of just under 94%. Jon and I agree that that’s a pretty good record for fieldwork with cryptic species** but he adds, “it’s also cool to think that 6.2% of the time we were wrong! These bees are great at fooling us.”

The bees that were fooling Jon were B. fervidus dressed as B californicus and vice versa. In Pinnacles and Yosemite National Parks there were ten mostly black bees (the typical B. californicus look) that turned out to belong to the genetic cluster that usually wears mostly yellow. The rest of the bees with black setal coloration belonged to another clade based on genotype, though this clade also included some bees in yellow. I asked Jon, “What is going on with the bee costume parties in Pinnacles and Yosemite?” His wild speculation is that little black dress is the dominant phenotype for bees in these parks, and the typically-yellow-genotype wears black here because everyone else is doing it: “bumble bees are notorious for converging on a local phenotype, which can even make it very hard to tell distantly related species apart.” However, in the sites where both genetic clusters of the B. fervidus species complex overlap, they usually do not look alike, so they aren’t mimicking each other.

Ultimately, Jon’s team determined that the species complex comprised two lineages, but that both lineages exhibit the yellow and black phenotypes depending on geography. So while the B. fervidus species complex is not a single species, B. fervidus and B. californicus are not NOT conspecifics. Jon explains, “those names [B. fervidus and B. californicus] might not even be valid! The holotype of B. californicus happens to be where the genotype assigned to the “B. fervidus” was collected in the Sierra Nevada.” In short, the original bee that taxonomists knew as B. californicus may actually be genetically on the B. fervidus side of the lineage, and eventually one or both names might need to be thrown out. This “it’s complicated” conclusion might be depressing news for someone who dedicated so much time and energy towards disentangling the species complex, but Jon closes his email to me with a happy emoji “nature has so many surprises, and science is an ongoing process 🙂” In the meantime, this paper points out that even if we don’t have the right names in place, we know enough to recommend that managers use Jon’s non-lethal method of clipping a bit of mid-leg for genotyping, and monitor the two clades of the B. fervidus complex separately. This is a great reminder for all of us in conservation research: we need to keep the ongoing process in perspective, while also delivering our findings, however not-quite-as-clear-as-we-hoped or maybe-unnamed as they may be, to our partners in management and policy.

References:

Koch JB, Rodriguez J, Pitts JP, Strange JP (2018) Phylogeny and population genetic analyses reveals cryptic speciation in the Bombus fervidus species complex (Hymenoptera: Apidae). PLoS ONE 13(11): e0207080.

*Now, old Jon and old Caitlin are David H. Smith postdoctoral fellows together 🙂

**see McDonough MacKenzie et al. 2017 — When I was a master’s student working with volunteer-collected data I would have killed for a 93.8% identification rate. One my species, Labrador tea, was correctly identified 27.3% of the time. This is not a cryptic species; it doesn’t sometimes dress up as Diapensia.

Banner image: kenlarson, creative commons