Over at hosting blog 360 Degree Skeptic, Andrew Bernardin has posted the 27th Carnival of Evolution, with a fine assortment of contributions from Deep Sea News, The Tree of Life, and Greg Laden’s blog, among others. Also, there’s a nice piece from Byte-sized Biology that makes a great tie-in with today’s D&T post about the evolution of cooperation.
Tag Archives: Carnival of Evolution
Carnival of Evolution #26 at The Thoughtful Animal
I’m late to the party on this one: the 26th Carnival of Evolution is on over at this month’s host, Jason Goldman’s The Thoughtful Animal. This round of submissions is more concentrated on the “endless forms most beautiful” than directly challenging creationism, which is a welcome change if I do say so myself. Don’t get me wrong; creationists need (apparently endless) debunking. But I think the argument is made just as effectively by showing that there’s “grandeur” in the scientific view of life—which these posts do in spades.
Carnival of Evolution #17 at Adaptive Complexity
Over at Adaptive Complexity, Michael White has just compiled the 17th monthly Carnival of Evolution. Marking the 150th anniversary of the publication of The Origin of Species (November, 1859), Michael structures submitted posts into a “virtual voyage of the Beagle.” Topics range from the sexual habits of our ape-like ancestors* to a highly optimistic study predicting that the frequency of the creationist meme in the United States will drop to 0% by 2050.
* Which habits might, I think, explain why we never invite them round to tea.
Carnival of Evolution #12 at Deep Sea News
Deep Sea News has the latest issue of the Carnival of Evolution, rounding up the blogosphere’s discussion of descent with modification over the last month. Highlights include GRRL Scientist’s review of Jerry Coyne’s new book, Blag Hag’s snarky deflation of anthropocentrism, and Greg Laden’s analysis of some fossil primate of which I hadn’t previously heard.
In social courtship, it pays to be a good wingman
The search for a mate is traditionally a selfish enterprise. After all, the ultimate goal is reproduction, and — barring any effect of kin selection — natural selection only cares about how many babies you make, not how many you help to make. This is fundamentally a biological question, though, and if there’s a universal rule in biology, it’s that nature is good at making exceptions.
One such exception is the wire-tailed manakin. A study in the latest Proceedings of the Royal Society seems to show that male manakins can boost their own mating success by helping other males attract mates [$-a]. Manakins are a family of brightly-colored neotropical birds, and the males of many manakin species attract females by putting on dancing displays, as seen in this video:
(I seem to recall that there’s also some excellent footage of manakin dancing in David Attenborough’s The Life of Birds.)
To dance for females, male manakins gather at locations called “leks,” where most try to establish a small territory to perform. Among wire-tailed manakins, though, some males will team up to dance — presumably because if one brightly-colored male jumping around on a branch is attention-grabbing, two or three are even more so. But in these “coordinated displays,” one performer, the socially dominant one, is most likely to mate with the females who like the performance. So what’s in it for the other guys?
There seem to be two possible (though not mutually exclusive) explanations [$-a]: (1) that the mate-attracting dancing does double duty to establish social dominance relationships among males, and (2) that, even if it wins fewer mates than the “lead” role, being a supporting player in a successful cooperative display means better mating prospects than trying to go it alone. To try and disentangle these two possibilities, the new study’s authors followed the behavior of wire-tailed manakins at several leks for four years, building a “social network” of male-male cooperation at the leks and counting the offspring each male bird by taking DNA fingerprints of the males and of newly-hatched chicks in the nests of females who attended each lek.
Although the most reproductively successful males at each lek were all territorial, defending their own spot at the lek and dominating other males who joined in the display on that territory, non-territorial “floater” males tended to make more babies if they joined in more displays. In fact, the number of offspring produced was best predicted by the number of cooperative display interactions in which a male joined, whether he had his own territory or not. This complements an earlier study by the same group [$-a], which showed that a male’s “tenure” — how long he had been dominant in a territory within a lek — was the best predictor of mating success, but that a male’s rise through the social hierarchy at a lek was facilitated by cooperative interactions with other males.
In short, male manakins seem to help each other in mating displays for essentially selfish reasons. Being a supporting dancer has a coattail effect, earning more mates than trying to go solo, and it helps young males improve their social status toward the day when they can establish their own display territory.
References
Prum, R.O. (1994). Phylogenetic analysis of the evolution of alternative social behavior in the manakins (Aves: Pipridae). Evolution, 48, 1657-75 DOI: http://www.jstor.org/stable/2410255
Ryder, T., McDonald, D., Blake, J., Parker, P., & Loiselle, B. (2008). Social networks in the lek-mating wire-tailed manakin (Pipra filicauda) Proc.R. Soc. B, 275 (1641), 1367-74 DOI: 10.1098/rspb.2008.0205
Ryder, T., Parker, P., Blake, J., & Loiselle, B. (2009). It takes two to tango: reproductive skew and social correlates of male mating success in a lek-breeding bird Proc. R. Soc. B, 276 (1666), 2377-84 DOI: 10.1098/rspb.2009.0208
Carnival of Evolution #11 at Oh, For the Love of Science
The 11th monthly Carnival of Evolution is up at Oh, For the Love of Science. Following Miriam Goldstein’s lead from last month, there’s a cute narrative framing for a long list of interesting posts, ranging from natural history to science education strategies. Lots to read in between undergrad research papers this weekend!
Ants trim trees for more living space
In the natural world, cooperative interactions evolve not as expressions of altruism, but as careful “negotiations” between interacting species. Each player may benefit from the relationship, but each stands to benefit from trying to cheat the other. In this month’s issue of The American Naturalist, we see a prime example: mutualistic ants sterilize their host plants [$-a] to get the most out of the interaction.
The ant species Allomerus octoarticulatus is part of a classic protection mutualism with the tropical tree Cordia nodosa, in which the plant grows structures called domatia that provide shelter for a colony of ants, and nutrient rich “food bodies” for the ants to feed on. The ants, in turn, patrol the plant and drive off herbivores. This mutually beneficial relationship also sets up a conflict of interest. The tree must divide its resources between providing food and shelter for its resident ant colony — growing new domatia and fruiting bodies — and its own reproductive efforts — growing flowers and fruit. The ants, naturally, would prefer for the host tree to spend as much energy as possible on them.
Indeed, Allomerus octoarticulatus has been observed killing the flowers of its host trees. This is what led the new paper’s author, Megan Frederickson, to conduct a simple experiment on C. nodosa, asking whether such pruning prompts the tree to grow more domatia. She experimentally removed flowers from trees occupied by a species of ants that don’t engage in flower pruning to see if pruned trees grew more domatia — and pruned trees grew more domatia over the course of four months than trees that were allowed to flower and produce fruit.
Ant-hosting plants need not be totally subject to the whims of their protectors, however — this kind of regulation works both ways. A study published last year in Science found that ant-hosting Acacia trees cut back on support for their resident ant colonies [$-a] when herbivores are removed and ant protection is no longer needed. (I wrote about this study back when it was released.) It seems likely that flower-pruning ants are exerting strong selection on Cordia nodosa to circumvent this behavior — a new tree variant that can overcome pruning, or make life uncomfortable for pruning ants, should have a large selective advantage.
In the absence of such a mutation, as Frederickson points out, Allomerus octoarticulatus is creating a tragedy of the commons by reducing the long-term viability of its host tree’s populations in exchange for the short-term benefit of more living space. As it stands, Cordia nodosa can only reproduce when it hosts non-pruning ant species, which are a minority in the populations Frederickson studied. Only time, and further study, can determine whether this mutualism might break down altogether.
References
Frederickson, M. (2009). Conflict over reproduction in an ant-plant symbiosis: Why Allomerus octoarticulatus ants sterilize Cordia nodosa trees. The American Naturalist, 173 (5), 675-81 DOI: 10.1086/597608
Palmer, T., Stanton, M., Young, T., Goheen, J., Pringle, R., & Karban, R. (2008). Breakdown of an ant-plant mutualism follows the loss of large herbivores from an African savanna Science, 319 (5860), 192-5 DOI: 10.1126/science.1151579
Carnival of Evolution #10 at The Oyster’s Garter
The tenth issue of the The Carnival of Evolution is now live at The Oyster’s Garter, complete with a whimsical framing narrative. Topics range from the relationship between stress and testosterone levels to an essay on the species problem that complements my own contribution, to the suprising usefulness of half a wing.
That “mystery of mysteries”: What makes a species?
In a special issue of Philosophical Transactions of the Royal Society on speciation, James Mallet argues that the Biological Species Concept is at odds with Charles Darwin’s original ideas about what a species is – and that current research supports Darwin [$-a].
When The Origin of Species was first published, biologists mostly thought species were easy to recognize – they looked different from each other, and they couldn’t successfully interbreed with each other. This view was a problem for Darwin’s ideas about gradual evolution by natural selection, since gradual divergence shouldn’t give rise to nice, discrete species. In fact, as Darwin argued, different groups of organisms exhibit a whole spectrum of reproductive isolation, from complete interfertility to total isolation – and the degree of isolation is not easy to predict based on how similar organisms look. In Darwin’s description, species are just labels that humans put on clusters of similar-looking organisms.
By the mid-Twentieth Century, evolutionary biologists favored what is commonly called the Biological Species Concept (BSC), defining species as non-interbreeding populations of living things. Research on speciation has accordingly focused on the ways that evolution creates reproductive isolation between populations. Mallet argues that this amounts to an abandonment of Darwin’s insights, and that by focusing on isolating mechanisms, biologists have returned to viewing species as distinct, “real” entities, missing much of the evolutionary process as a result.
I’m not sure I believe the distinction that Mallet makes between Darwin’s description of species and the BSC; they seem to me more different in their emphasis than in their fundamentals. Darwin was interested in demonstrating that species arise gradually, as accidents of adaptation to different environments – and, as Mallet says, he was trying to overcome the then-predominant view that species were real, discrete entities instead of the names that humans assign to clusters of similar organisms. Research motivated by the BSC generally takes this view as well, but it’s interested in the processes that create such clusters, and can prevent them from merging into nearby clusters by interbreeding.
Research on the evolution of isolating mechanisms necessarily focuses on cases where isolation is incomplete, somewhere between complete speciation and free interbreeding. A prime example is my lab’s research on the two pollinator-associated types of Joshua tree, Yucca brevifolia. It’s not clear that the two types are reproductively isolated – preliminary genetic data suggests they’re not [PDF] – even though they’re pollinated by different moth species, and classified as separate subspecies, the taller Y. brevifolia brevifolia and the short, bushy Y. brevifolia jaegeriana. They may be on the way to becoming different species, but they’re not there yet. Two other examples out of the endless forms available: marine snails that choose mates by their slime trails, and wildflowers that would interbreed if only they could survive each other’s habitat.
As Mallet concludes in the more empirical part of his review, this is what we see across the diversity of life: a continuum of reproductive isolation between populations, not a granular world of neatly divided, obviously different species. Rather than over-simplifying this reality, the Biological Species Concept gives us a framework through which to understand it.
References
Darwin, C. 1859. On the Origin of Species by Means of Natural Selection. First ed. London: John Murray. Full text on Google Books.
Mallet, J. (2008). Hybridization, ecological races and the nature of species: empirical evidence for the ease of speciation Phil. Trans. R. Soc. B, 363 (1506), 2971-86 DOI: 10.1098/rstb.2008.0081
Smith, C., W. Godsoe, S. Tank, J. Yoder, & O. Pellmyr (2008). Distinguishing coevolution from covicariance in an obligate pollination mutualism: asynchronous divergence in Joshua tree and its pollinators. Evolution, 62 (10), 2676-87 DOI: 10.1111/j.1558-5646.2008.00500.x