Tag Archives: Research Blogging

Correlation and causation: Why are there so many flowering plants?

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ResearchBlogging.orgAmong the flowering plants, groups with flowers adapted to a narrower range of pollinators — the more specialized ones, like orchids or mints — tend to contain more species. Why? The classic hypothesis is that coevolution between plants and their pollinators leads to more pollinator-specialized plants, which are then more likely to become reproductively isolated, and eventually form separate species. However, I’ve just finished reading a review article that suggests an interesting alternative: that angiosperms may not be diverse because they’re specialized, but specialize because they’re diverse [$-a].

The review’s authors, Armbruster and Muchhala, first lay out a list of possible mechanisms connecting diversity and specialization. Three of them have specialization creating diversity, by (1) creating reproductive isolation, (2) enhancing isolation created by other forces, or (3) reducing extinction rates. Finally, there’s the possibility that diversity creates specialization, by (4) essentially forcing plants to divvy up the available pollinator community more and more finely.


Collinsia heterophylla, a
member of a plant genus
probably shaped by competition.
Photo by Ken-Ichi.

The first two mechanisms are, as far as I’m concerned, contained within the classic specialization-creates-diversity hypothesis classically advanced by Verne Grant, that increased floral specialization makes it easier to form new species [$-a]. The third is a bit odd — generally, ecologists think that increased specialization means an increased, not a decreased, risk of extinction [$-a]. It’s intuitive that if you rely on fewer pollinator species, you can afford to lose fewer of them, and you have fewer opportunities to colonize new sites; so on the one hand, you’re at greater risk of local extinction, and on the other, you have difficulty establishing new populations. However, as Armbruster and Muchhala point out, this process should make more-specialized plant groups less diverse, which is the opposite of what we see.

The fourth hypothesis, that competition for pollinators causes greater to create greater specialization, leads to predictions that nicely differentiate it from the classic hypothesis: that hybridization between related flowering plants should be rare, and that plants should rarely occur in the same community as their closest evolutionary relatives. The first is important because it gives a reason to specialize on one or a few available pollinators — if a plant can’t reproduce with nearby relatives, all the pollen it exchanges with them represents wasted effort, and may actually interfere with pollen transfer from members of its own species. The second is a consequence of that process; plants are most likely to be able to hybridize with their evolutionary sisters, so successful speciation will usually require geographic or ecological isolation.

The authors then evaluate the evidence for these predictions in four plant genera with which they have prior experience: Dalechampia, Collinsia (pictured above), Burmeistera, and Stylidium. For these four groups, they find good support for the diversity-causes-specialization hypothesis — few natural, or even artificial hybrids, and few co-occurring sister species. To some degree, then, the new hypothesis is an effect of a researcher’s favorite study systems influencing their perspective on the broader picture of evolution. Armbruster and Muchhala give the same treatment to orchids, and find that for the most diverse angiosperm family, natural hybrids and co-occuring sister species are not rare. This ambiguity makes the review more interesting — it overturns the causation commonly inferred from the correlation between diversity and specialization, but it doesn’t make the mistake of sweepingly assuming the opposite instead.

Correlation, and causation.
xkcd.

References

Armbruster, W., & Muchhala, N. (2008). Associations between floral specialization and species diversity: Cause, effect, or correlation? Evolutionary Ecology, 23 (1), 159-79 DOI: 10.1007/s10682-008-9259-z

V. Grant (1949). Pollination systems as isolating mechanisms in angiosperms. Evolution, 3, 82-97

Johnson, S.D., & Steiner, K.E. (2000). Generalization versus specialization in plant pollination systems Trends in Ecology & Evolution, 15 (4), 140-3 DOI: 10.1016/S0169-5347(99)01811-X

Sargent, R. (2004). Floral symmetry affects speciation rates in angiosperms Proc. R. Soc. B, 271 (1539), 603-608 DOI: 10.1098/rspb.2003.2644

No room for group selection in disease evolution?

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ResearchBlogging.orgParasites coexisting within a single host have been proposed as one of the best examples of individuals sacrificing their own reproductive fitness for the benefit of a group. A new theory paper in last week’s Nature suggests that the apparent effect of “group selection” in this case can be explained by individual-level selection instead [$-a].

Group selection posits that organisms sometimes evolve traits that hurt their individual fitness but benefit their social group. Charles Darwin originally proposed it to explain the evolution of human moral systems: in a tribal society, helping your neighbor might cost you, but it might still help your whole tribe to compete against other tribes. So natural selection on individuals within a tribe may act in one way, but be opposed by group selection arising from competition among tribes.

This process has also been proposed to explain a common phenomenon in the evolution of disease organisms: the trade-off between transmission and virulence [PDF]. Simply put, if it’s easy for a disease-causing critter to spread through a host population, it tends to do more damage to its hosts; and if it is less easy to spread, the disease tends to do less damage [$-a]. A classic case of this effect is documented in cholera, which has evolved lower virulence when good sanitation practices cut off the easy route of transmission through sewage-contaminated drinking water.

Proponents of group selection say that this occurs because, under difficult transmission conditions, disease organisms must throttle back their production of offspring lest they kill their shared host. But it’s also possible to describe a verbal model by which reduced transmission selects for lower virulence without invoking group selection, courtesy of kin selection.

Kin selection takes into account the effect of natural selection on not just the copies of an individual’s genes within that individual’s body, but also the copies borne by close relatives; if you’re a parasite that reproduces inside your host, making more offspring also means making more competitors for your offspring, and thereby reducing the fitness of the genes that you share with the next generation. So, unless it’s easy to disperse to new resources — uninfected hosts — natural selection can actually favor prudent reproduction by a parasite, which keeps the host alive longer.

The new paper in Nature puts some math behind this verbal model. The authors, Wild et al., building on a standard disease-modeling framework, assume a world of patchily-distributed hosts infected by a single parasite species. Parasites are transmitted by host-to-host contact; it’s assumed that the number of offspring a parasite produces is proportional to the chances that some of those offspring are transmitted to another host, so that more virulent parasites have a better chance of sending offspring to new, uninfected hosts.

Under this model, the authors show that the fitness of a mutant, more virulent parasite, differs from that of its less-virulent competitors in several important ways: A more virulent mutant has

  • an increased chance of killing its host;
  • an increased chance of sending offspring to another patch of hosts;
  • increased competition from the offspring it produces that do not disperse to another patch;
  • increased competition experienced by those offspring; and
  • a greater chance that, by killing its host, it will make way for an uninfected replacement host for its offspring.

When the parasites can disperse to new patches with maximum efficiency, they simply evolve to maximize their own fitness at the expense of the host — but as dispersal becomes more restricted, the costs of competition exert selection on individual parasites to evolve reduced virulence.

Wild et al. conclude that, because their model replicates the transmission-virulence trade-off without invoking group selection, they can reject the group selection hypothesis. In fact, they strongly suggest that group selection may not matter much in natural systems:

The multilevel (group) selection and kin selection (inclusive fitness) approaches to social evolution have long been known to be mathematically equivalent and, if the analyses are performed correctly, do not lead to conflicting predictions. Thus, irrespective of the relative strengths of within-group versus between-group selection, individuals are predicted to maximize their inclusive fitness. [In-text citations removed; emphasis added.]

Clearly this result shows that group selection isn’t necessary to create the transmission-virulence trade-off. On the other hand, it doesn’t provide a good comparison of group-level and individual-level selection, because (so far as I can see) it doesn’t explicitly contain an effect of group selection. It’s one thing to show that group selection isn’t necessary, but it’s another to show that its effects would be overwhelmed by individual-level selection.

References

Cochran G.M., Ewald P.W., & Cochran K.D. (2000). Infectious causation of disease: An evolutionary perspective Persp. Biol. Medecine, 43 (3), 406-48 DOI: 10.1353/pbm.2000.0016

Day, T., & Gandon, S. (2007). Applying population-genetic models in theoretical evolutionary epidemiology Ecology Letters, 10 (10), 876-88 DOI: 10.1111/j.1461-0248.2007.01091.x

Frank, S.A. (1996). Models of parasite virulence Quarterly Rev. Biol., 71 (1), 37-78 DOI: http://www.jstor.org/stable/3037829

Wild, G., Gardner, A., & West, S. (2009). Adaptation and the evolution of parasite virulence in a connected world Nature, 459 (7249), 983-6 DOI: 10.1038/nature08071

Wilson, D., & Wilson, E. (2007). Rethinking the theoretical foundation of sociobiology Quarterly Rev. Biol., 82 (4), 327-48 DOI: 10.1086/522809

For wasps’ pheromones, quantity predicts quality

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ResearchBlogging.orgDon’t tell the people behind Axe body spray, but entomologists have shown that the fertility of male Nasonia vitripennis wasps is predicted by how much sex pheromone they produce [$-a].

How many sperm a male wasp can produce turns out to be a big deal for female Nasonia wasps, because the species is haplodiploid — fertilized eggs become females, and unfertilized eggs become males. Because females are the only sex that can fly off to lay more eggs, the number of female offspring a wasp produces strongly determines her reproductive fitness. She wants, therefore, to mate with a male who can fertilize a lot of eggs, and determines who that is by smelling prospective mates.

Reference

Ruther, J., Matschke, M., Garbe, L., & Steiner, S. (2009). Quantity matters: male sex pheromone signals mate quality in the parasitic wasp Nasonia vitripennis. Proc. R. Soc. B DOI: 10.1098/rspb.2009.0738

Evolution 2009: Day three

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Evolution 2009
ResearchBlogging.orgOn the third day of Evolution 2009, things are winding down already. I’ve been up late saying goodbye to folks leaving tomorrow.


A bog turtle
Photo by Wall Tea.

The most entertaining talk of the day was more about physics than evolution as such: specifically, an analysis of turtle shell architecture. C.T. Stayton discussed work he published in the May issue of Evolution, showing that turtle shell shapes are a compromise between streamlining for efficient swimming and ability to resist crushing attacks from predators [$-a]. He referenced Terry Pratchett in his introductory slides, but I didn’t have the presence of mind to ask afterward what the optimal shell shape is to support the weight of four elephants and a Discworld.

Other highlights:

  • Simone Des Roches presented more results from experiments that showed how the adaptive divergence of sticklebacks can alter ecosystem dynamics. (I discussed the original publication back in April.)
  • The amoeba Dictostelium discoideum responds to stress by forming spore-making fruiting bodies. Some cells “cheat” by taking the beneficial spots in the fruiting body and leaving others to form its non-reproductive stalk — and it seems that the cheaters do this by getting there first.
  • Live-bearing guppies are able to compensate for a reduced food supply by restricting the size of their developing babies.
  • Although whaling nations argue that Minke whales have become much more abundant due to lack of competition from species hunted to near extinction in the early 20th century, population genetic data suggest that Minke whales are about as numerous as they were prior to that time.
  • It’s actually proving pretty tricky to determine the evolutionary relationships of chipmunks in Western North America, both because they hybridize frequently and because they speciated rapidly.
  • Boundaries between related species’s geographic distributions may be maintained by locally-adapted pathogens.

And, finally, video of Eugenie Scott’s Gould Award lecture is now online for streaming in Real Video format here.

References

Harmon, L., Matthews, B., Des Roches, S., Chase, J., Shurin, J., & Schluter, D. (2009). Evolutionary diversification in stickleback affects ecosystem functioning Nature, 458 (7242), 1167-70 DOI: 10.1038/nature07974

Stayton, C. (2009). Application of thin-plate spline transformations to finite element models, or, how to turn a bog turtle into a spotted turtle to analyze both. Evolution, 63 (5), 1348-55 DOI: 10.1111/j.1558-5646.2009.00655.x

Evolution 2009: Day two

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Evolution 2009
ResearchBlogging.orgAfter a late (early) night yesterday, I started my day at the R.A. Fisher Award talk, a presentation of results from “an outstanding Ph.D. dissertation paper published in the journal Evolution.” This year’s winner turned out to be a paper I remember reading when it was first published, in which Megan Higgie and Mark Blows showed that sexual selection for mate-signaling hydrocarbons in Drosophila serrata is opposed by selection to avoid mating with the closely related D. birchii. Populations of D. serrata that occur with D. birchii have been selected for different hydrocarbon profiles [$-a] than populations that don’t occur with D. birchii — so that adaptive speciation could result from the opposing selective regimes.


Photo by Jo Mur.

On a more natural history-oriented note, today I learned that honeyguides, the African birds known for their habit of guiding badgers (or humans) to bees’ nests, are also particularly vicious brood parasites. Like cuckoos and cowbirds, honeyguides lay their eggs in the nests of other bird species, and let the parasitized parents raise ’em. Apparently the Greater Honeyguide (the chick in the figure provided) has had its eggs selected to more closely match a variety of host species.

Other highlights:

  • Flowers of the genus Pedicularis are more different in co-occuring species than would be expected by chance, possibly to minimize the chance that their shared pollinators, bumblebees, transfer pollen between different species.
  • When female Hadena bircuris moths pollinate their host plant Silene latifolia, they lay eggs on the flower so that their larvae can eat some of the seeds produced — much like yucca moths — but male moths of the same species also pollinate, and this may help offset the cost of female pollination.
  • Host-parasite coevolution may actually drive the evolution of mutation rates in the host and the parasite, much like yesterday’s demonstration that coevolution can alter migration rates.

Finished the day much more quietly than yesterday, with a handful of folks at my place for burgers and beer. And, hey, I’m getting to bed before 4 a.m.!

References

Higgie, M., & Blows, M. (2008). The evolution of reproductive character displacement conflicts with how sexual selection operates within a species. Evolution, 62 (5), 1192-203 DOI: 10.1111/j.1558-5646.2008.00357.x

Evolution 2009: Day one

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Evolution 2009
ResearchBlogging.orgIn this morning’s session on species interactions and coevolution, everyone was talking about these videos of snakes attacking snails. Turns out that snail shell chirality (the direction the shell spirals) can determine how easy it is for a snake to attack. Very, very cool. Detailed discussion by John Dennehy is here. [Edit, 14 June 2009: link to the video originally found by Matt Labrum.]

I presented today, and survived another twelve-minute talk. Immediately after I finished describing my preliminary conclusion that coevolution between species only generates evolutionary diversity if it exerts disruptive selection on one or the other interactor — the best example of which may be competitive exclusion — Jeremy Fox described a model in which competitor species converge on a single set of traits [$-a]. It’s a cool result, and one I’ll need to consider carefully.

I also learned today that

  • A bacterial endosymbiont helps fruit flies fight off parasitic worms;
  • It might not “cost” anything for some specialist herbivores to sequester the toxins produced by the plants they eat;
  • Coevolution can actually change the migration rates of interacting species; and
  • Bacteria and phage living inside horse chestnut leaves are locally adapted within individual trees, but not within individual leaves.

Was out way too late, as the timing of this post may indicate. Don’t think I’ll make the morning sessions. Not that the love-in-a-canoe coffee provided by campus catering will help. Ugh.

References

Fox, J., & Vasseur, D. (2008). Character Convergence under Competition for Nutritionally Essential Resources The American Naturalist, 172 (5), 667-80 DOI: 10.1086/591689

When plant siblings play nice, everyone loses

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ResearchBlogging.orgA couple years ago, scientists studying the wildflower American searocket, noticed something funny: when grown in the same pot with sibling seeds, searocket plants grew smaller roots than they did when sharing a pot with unrelated plants. It looked as though searocket plants recognized their siblings, and tried not to compete with them.

If this were a widespread phenomenon, it could dramatically change how biologists think about plant’s evolution and ecology. Right now, we think that the huge diversity of seed dispersal mechanisms — from fruit, to ballistics, to ants — evolved at least in part to minimize competition between sibling plants. But if plants can recognize and preferentially accommodate their siblings, clusters of related plants might actually improve their collective fitness — or rather the fitness of the genes they share.


Lupinus angustifolius
Photo by enbodenumer.

A new paper in Proc. R. Soc. aims to test the hypothesis that sibling recognition boosts plants’ collective fitness. The authors conducted a more precise version of the original kin recognition experiment, planting seeds from common European lupines (Lupinus angustifolius, pictured) alongside their siblings, unrelated seeds from the same source population, or unrelated seeds from a distant population. They then measured a variety of fitness traits to determine whether individual plants benefited from growing near siblings, or whether sibling groups performed better collectively than groups of unrelated competitors.

The results were pretty clear — in staying out of each other’s way, sibling plants had lower individual and group fitness. Plants growing near siblings produced fewer fruits and seeds than those growing near non-relatives, and groups of siblings collectively produced fewer fruits and seeds than groups of unrelated plants. This suggests that the kin recognition effect may actually contribute to selection for better seed dispersal, rather than provide a benefit for growing together.

References

Dudley, S., & File, A. (2007). Kin recognition in an annual plant. Biology Letters, 3 (4), 435-8 DOI: 10.1098/rsbl.2007.0232

Milla, R., Forero, D., Escudero, A., & Iriondo, J. (2009). Growing with siblings: A common ground for cooperation or for fiercer competition among plants? Proc. R. Soc. B, 276 (1667), 2531-40 DOI: 10.1098/rspb.2009.0369

Familiarity breeds contempt: Mockingbirds recognize and react to repeat intruders

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ResearchBlogging.orgHumans are a fact of life for many, many parts of the natural world. This doesn’t always have to be a bad thing — some critters adapt to human-dominated landscapes pretty well. A paper in this week’s PNAS, for instance, shows that Northern Mockingbirds nesting on a busy university campus learn to differentiate between uninterested passers-by and people who repeatedly disturb the nest site [$-a].


Northern Mockingbird with fledglings
Photo by mjmyap.

When potential predators come too close to a nest, wild birds try to distract the threat with harassing alarm calls, diving attack flights, or “flushing” to draw attention away. This doesn’t work so well if you’re nesting near a busy sidewalk; you’d spend all you time trying to drive off passers-by who pose no real threat. And, as Levey et al. show in the new paper, mockingbirds seem to have solved this problem by reacting more strongly to people who approach the nest repeatedly.

The experimental evidence is elegant: Individual researchers approached occupied mockingbird nests on four consecutive days, and recorded the birds’ reactions. The birds flushed farther, gave more alarm calls, and attacked more often with each repeat visit. When a new person approached the nest on a fifth day, though, the birds’ reactions were equivalent to their behavior on the first day. Furthermore, nesting mockingbirds flushed farther if their nests were near less-busy sidewalks. This isn’t evidence for an evolved response, but for learning; and it suggests that mockingbirds are able to recognize individual humans, and apply that familiarity in assessing the danger posed when someone approaches the nest.

This is just one example of the evolved and learned adaptations the living world has made in response to human activity. Last year, for instance, a study showed that a French wildflower has evolved wingless seeds in response to urban growing conditions — although winged, wind-dispersed seeds do better in the wild because they’re less likely to compete with their siblings, in a heavily paved environment the best spot to germinate is more likely to be close to the parent plant. And perhaps one of the best-known examples of natural selection in action is the increased frequency of dark-colored peppered moths in response to industrial pollution. Nature is nothing if not flexible.

References

Cheptou, P., Carrue, O., Rouifed, S., & Cantarel, A. (2008). Rapid evolution of seed dispersal in an urban environment in the weed Crepis sancta Proc. Nat. Acad. Sci. USA, 105 (10), 3796-9 DOI: 10.1073/pnas.0708446105

Grant, B.S., Owen, D.F., & Clarke, C.A. (1996). Parallel rise and fall of melanic peppered moths in America and Britain Journal of Heredity, 87, 351-7 DOI: http://jhered.oxfordjournals.org/cgi/content/abstract/87/5/351

Levey, D., Londono, G., Ungvari-Martin, J., Hiersoux, M., Jankowski, J., Poulsen, J., Stracey, C., & Robinson, S. (2009). Urban mockingbirds quickly learn to identify individual humans Proc. Nat. Acad. Sci. USA, 106 (22), 8959-62 DOI: 10.1073/pnas.0811422106

How fast do ecosystems recover from disturbance? It’s complicated.

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ResearchBlogging.orgIn the 21st century, human activity promises to impact the natural world on an unprecedented scale. In order to decide where to focus conservation effort, one thing we need to know is how permanent the damage from a forest clear-cut or a collapsed fishery actually is. A paper in this week’s PLoS ONE looks at natural systems’ ability to recover after human and natural disturbances, and the authors say the results are hopeful. I’m not so sure.


A clearcut.
Photo by : Damien.

The authors, Jones and Schmitz, assemble a meta-dataset of ecological studies published from 1910 to 2008, all examining the recovery of either ecosytem functions (like total nutrient cycling rates) or plant or animal diversity following disturbances as diverse as hurricanes and oil spills. They then calculated the proportion of measured variables that recovered, or failed to, within the period studied by each paper in the dataset, how much the measured variables had been altered by the disturbance, and how long it took before they returned to their pre-disturbance state.

The results are complicated, to say the least. For example, here’s Figure 2, which charts the times to recovery for variables measuring animal community recovery (black bars), ecosystem function (white bars) or plant community (gray bars), broken down by ecosystem type in the top panel, and by disturbance type in the bottom panel:

The authors’ conclusion? There is “no discernable pattern.” Which I can’t really dispute — recovery times look highly idiosyncratic. An ANOVA performed on the data finds significant effects of ecosystem type and disturbance type, but what does that tell us? Different ecosystems recover differently. Forests take the longest to recover, which makes sense given that trees grow slowly, and succession from clearcut to mature forest can take centuries. Similarly, ecosystems experiencing multiple types of disturbance took the longest to recover.

Of the ecosystems that do recover, the authors point out, recovery occurs comparatively rapidly:

Among studies reporting recovery for any variable, the average recovery time was at most 42 years (for forest ecosystems) and typically much less (on the order of 10 years) when recovery was examined by ecosystem. When examined by perturbation type, the average recovery time was no more than 56 years (for systems undergoing multiple interacting perturbations) and typically was 20 years or less …

The authors then perform a regression of the strength of disturbance (i.e., how much the measured variables changed due to disturbance) against the time needed for recovery. The data set is necessarily small, because not many studies follow an ecosystem all the way from disturbance to complete recovery, and they find a significant effect of disturbance strength on recovery time mostly because of a single data point.

Jones and Schmitz conclude from this dataset that ecosystem recovery from human disturbance is frequently possible within human lifetimes, especially if we put in the effort for restoration. I’ll buy that; but I think the more important lesson to draw from this paper is that, after a century of watching the natural world respond to human activity, we still can’t predict what the results of our actions will be. It shouldn’t need saying, but when we fiddle with our life-support systems, we must proceed cautiously.

Reference

Jones, H., & Schmitz, O. (2009). Rapid recovery of damaged ecosystems PLoS ONE, 4 (5) DOI: 10.1371/journal.pone.0005653

In social courtship, it pays to be a good wingman

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ResearchBlogging.orgThe 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