Current Biology has just published what is surely among the most significant papers this year on insect evolutionary relationships:
Cladogram depicting relationships among major groups of aculeate wasps, based on analyses of 308 aligned nuclear genes. Branch color represents parasitism (=green) or predation/nest-building (=yellow). Adapted from Figure 3 of Johnson et al (2013).
The importance of the paper derives from a combination of hitting a controversial topic with a much-needed phylogeny, and doing so with a staggering amount of information. The 300 or so genes employed to create the genomic tree is orders of magnitude more data than that used in any previous effort, and the result finally brings clarity to a question that’s been nagging a lot of Hymenopterists: what are the closest relatives of ants?
Probably, bees and spheciform wasps.
That’s not necessarily the relationship I would have guessed, but it holds under multiple modes of analysis.
Here’s the abstract (emphasis mine):
Eusocial behavior has arisen in few animal groups, most notably in the aculeate Hymenoptera, a clade comprising ants, bees, and stinging wasps. Phylogeny is crucial to understanding the evolution of the salient features of these insects, including eusociality. Yet the phylogenetic relationships among the major lineages of aculeate Hymenoptera remain contentious. We address this problem here by generating and analyzing genomic data for a representative series of taxa. We obtain a single well-resolved and strongly supported tree, robust to multiple methods of phylogenetic inference. Apoidea (spheciform wasps and bees) and ants are sister groups, a novel finding that contradicts earlier views that ants are closer to ectoparasitoid wasps. Vespid wasps (paper wasps, yellow jackets, and relatives) are sister to all other aculeates except chrysidoids. Thus, all eusocial species of Hymenoptera are contained within two major groups, characterized by transport of larval provisions and nest construction, likely prerequisites for the evolution of eusociality. These two lineages are interpolated among three other clades of wasps whose species are predominantly ectoparasitoids on concealed hosts, the inferred ancestral condition for aculeates. This phylogeny provides a new framework for exploring the evolution of nesting, feeding, and social behavior within the stinging Hymenoptera.
Source: Brian R. Johnson, Marek L. Borowiec, Joanna C. Chiu, Ernest K. Lee, Joel Atallah, Philip S. Ward (2013) Phylogenomics Resolves Evolutionary Relationships among Ants, Bees, and Wasps. Current Biology, Available online 3 October 2013. http://dx.doi.org/10.1016/j.cub.2013.08.050
Leptomyrmex darlingtoni, Australia
A big day for ant evolution! The Ant Tree of Life research group (AToL) has published their dolichoderine phylogeny in the journal Systematic Biology.
Dolichoderines are one of the big ant subfamilies, comprising just under ten percent of the world’s ant species. These are dominant, conspicuous ants noted for having ditched the heavy ancestral ant sting and armor in favor of speed, agility, and refined chemical weaponry. Most dolichoderines live in large colonies with extensive trail networks, and they fuel their frenetic lifestyle through copious consumption of hemipteran honeydew.
The paper is unfortunately behind a subscription barrier, but I’ve reproduced the primary finding below. Continue reading →
A clarification, relevant the discussion below:
Tree from Brady et al 2006.
I see that the TimeTree of Life project is now public. This collaborative project draws on the research of dozens of biologists to estimate the timing of past evolutionary divergences. The work is available as a book, but the online version has an interactive section that allows the user to name two organisms and get back the date the two last shared an ancestor.
Ants vs. Bees: 163.5 million years ago
A word of caution, though. While the output is extremely precise (i.e., it gives exact dates with decimal places), precision is not necessarily accuracy. The given dates are really the midpoints across a range of estimates, and for appropriate scientific caution you’re still best off consulting the referenced papers themselves. In our insect example, the work was done by the Smithsonian Institution’s Seán Brady.
Still, it’s a fun little tool.
I saw this short video at a conference last year and was entranced. The clip shows how the ancestral arachnid body plan changed as it evolved through various descendant lineages.
Pyramica (or is it Strumigenys?) rostrata, Illinois
I’ve been thinking today about the Wikipedia edits to the Pyramica page, and my curiosity about the controversy prodded me to attempt a quick phylogenetic analysis. Before I get to the analysis, though, here is some background.
Continue reading →
Simopelta sp. nr. pergandei, Venezuela
I’ve just started a project in collaboration with Daniel Kronauer, Jack Longino, and Andy Suarez to infer the phylogeny of species in the Neotropical ponerine genus Simopelta. If you happen to have any DNA-quality specimens of these unusual ants in your keep, we’d greatly appreciate a donation.
Why Simopelta? These insects are among the “other” army ants, the barely-known lineages that have also evolved the specialized nomadic lifestyle that characterizes the well-known, photogenic, and oft-televised ecitonine and doryline army ants. Yet Simopelta are ponerines, a completely different subfamily of ants. Because they acquired their traits independently, Simopelta will add power to statistical tests of various hypotheses about how army ants came to be. That, and they’re really interesting critters in their own right.
Ideally, specimens will have been collected into strong (>90%) ethanol and stored in a cool place, but these ants are rare enough that we’ll take whatever we can get. Send to:
Department of Entomology
320 Morrill Hall
University of Illinois at Urbana-Champaign
505 S Goodwin Ave
Urbana, IL 61801 USA
Explaining the evolutionary tree of life is always a tricky proposition, as narratives are inherently linear but evolution spirals outwards in countless messy directions at once. To tell a story from the tangled bank requires picking a single thread and following it, yet it is precisely our tendency to follow single threads that causes so much misunderstanding of how evolution works.
Attenborough grapples with the problem using an animation that permeates the video, showing graphically the complexity of an ever dividing tree in the background as he traverses time from ancient to modern. Yet I don’t think he is entirely successful. The problem is that the story he tells is the same one that’s always told: the vertebrate descent from early chordates to primates. There is lip service paid to other lineages, but probably not enough. The more the same vertebrate story is repeated as the preferred exemplar of evolution, the more we reinforce the incorrect ladder-like narrative of linear evolutionary progression.
The same sort of video could be made that ends at sea cucumbers, or rotifers, or grasses, and it would be every bit as accurate as the same old primate one that we see again and again.
Argentine ants tending scale insects
Three years after finishing my Ph.D., I have finally published the last bit of work from my dissertation. It’s a multi-locus molecular phylogeny of the ant genus Linepithema, a group of mostly obscure Neotropical ants that would be overlooked if they didn’t happen to contain the infamous Argentine Ant. In less jargony language, what I’ve done is reconstruct the evolution of an ant genus using genetic data. Here’s the citation:
Continue reading →
Martialis heureka Rabeling & Verhaagh 2008
drawing by the inimitable Barrett Klein for PNAS
Most scientific discoveries these days emerge through carefully planned and controlled research programs. Every now and again, though, something unexpected just pops up in a distant tropical jungle. Martialis heureka is a fantastic discovery of that old-fashioned kind. This little ant simply walked up to myrmecologist Christian Rabeling in the Brazilian Amazon. It is not only a new species, but an entirely different sort of ant than anything known before. Continue reading →