Altruism: Even Plants Can Do It

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A recent paper (free access) by Associate Professor Susan Dudley, published in the Royal Society journal Biology Letters argues that some plants recognize their kin.

Kin recognition is important in animal social systems. However, though plants often compete with kin, there has been as yet no direct evidence that plants recognize kin in competitive interactions. Here we show in the annual plant Cakile edentula, allocation to roots increased when groups of strangers shared a common pot, but not when groups of siblings shared a pot. Our results demonstrate that plants can discriminate kin in competitive interactions and indicate that the root interactions may provide the cue for kin recognition. Because greater root allocation is argued to increase below-ground competitive ability, the results are consistent with kin selection.

Although it were gardeners who knew this all along:

Gardeners have known for a long time that some pairs of species get along better than others, and scientists are starting to catch up with why that happens,” says Dudley. “What I’ve found is that plants from the same mother may be more compatible with each other than with plants of the same species that had different mothers. The more we know about plants, the more complex their interactions seem to be, so it may be as hard to predict the outcome as when you mix different people at a party.”

Source: Plants recognize their siblings, biologists discover at PhysOrgForum

22 Comments

Although it were gardeners who knew this all along:

yeah, that last quote was probably a bit of colloquialism for the press article.

botanists have known about allelopathy beteen heterospecifics for decades, at least.

I find it very strange that a simple experiment to test for kin selection in plants like this had never been done before.

if correct, it’s definetly one of those “Doh! why didn’t I think of that!” moments.

I’m hoping someone more up to date with the botanical lit. can shed more light on this.

That *proves* Dr. Egnor assertion that altruism is NOT in the brain !

I realize that is a joke (and it’s not bad), but it got me thinking…

In fact what things like this SHOULD do is make people think twice that behavior itself requires some sort of brain for processing feedback.

that plants have behaviors has been known for many decades.

Of course, the definition of altruism as kin selection only is a subset of the whole.

Hamilton logically predicted altruism in systems where there physically would be mechanisms for kin recognition, and where kin were in common contact, and lo and behold, that’s what we’ve found for the most part in the intervening years.

the argument extends from there to consider whether altruism in cases where there is demonstrably no kin relationship is really just a hold-over from kin-selection, where there have been no significant counter selective pressures, or whether there are reasonable expectations in any given system of a “return on investment”, or whether there is yet another explanation for it in these cases.

taking a look at social interactions and apparent altruism in vampire bats tends to help one think through the various possibilities.

bottom line though, especially when kin selection is demonstrated, is that it’s obvious that supernatural influences are simply not needed to explain the behavior.

Pim-

this is actually a question that really needs to be resolved:

Is this REALLY the first instance of Kin Selection demonstrated in plants?

you have access to the lit.

can you do a quick search in the bot lit to see if “kin selection” comes up with any hits?

thanks

Is this REALLY the first instance of Kin Selection demonstrated in plants?

Nope, what is first is Kin Recognition

Kin recognition is important in animal social systems. However, though plants often compete with kin, there has been as yet no direct evidence that plants recognize kin in competitive interactions.

and

Kin and other multilevel selection has been demonstrated in plants (Donohue 2003, 2004; Goodnight 1985; Stevens et al. 1995; Kelly 1996), and self-incompatibility systems allow plants to discriminate against relatives in mating (Waldman 1988). To our knowledge, however, no studies have yet tested directly for kin recognition in plants.

Donohue, K. 2003 The influence of neighbor relatedness on multilevel selection in the Great Lakes sea rocket. Am. Nat. 162, 77-92 (doi:10.1086/375299).

Donohue, K. 2004 Density-dependent multilevel selection in the Great Lakes sea rocket. Ecology 85, 180-191.

Goodnight, C.J. 1985 The influence of environmental variation on group and individual selection in a cress. Evolution 39, 545-558 (doi:10.2307/2408652).

Kelly, J.K. 1996 Kin selection in the annual plant Impatiens capensis. Am. Nat. 147, 899-918

Stevens, L., Goodnight, C.J. & Kalisz, S. 1995 Multilevel selection in natural populations of Impatiens capensis. Am. Nat. 145, 513-526 (doi:10.1086/285753).

Waldman, B. 1988 The ecology of kin recognition. Annu. Rev. Ecol. Syst. 19, 543-571 (doi:10.1146/annurev.es.19.110188.002551).

Remember this is but a first study, 4 pages long, of kin recognition in plants. Still a cool experiment.

More recent, still unpublished research by Dudley’s team suggests other plants besides sea rocket show similar behavior.

In addition to restraining root growth, such plants may also develop different stem lengths in the presence of siblings, she said.

But how the plants determine which of their neighbors are siblings remains a mystery, Dudley said.

Learning and memory appear to be important for kin recognition in animals, but this isn’t an option for plants, she noted.

Some researchers speculate that plants communicate through their roots, identifying themselves using tiny chemical signatures specific to each plant’s family.

Source: Plants Can Recognize, Communicate With Relatives, Studies Find, National Geographics.com

Learning and memory appear to be important for kin recognition in animals, but this isn’t an option for plants, she noted.

There’s that pervasive cephalocentrism rearing its ugly … erm … head again.

Nope, what is first is Kin Recognition

then here’s a question for you Pim:

how would kin selection proceed without kin recognition?

IOW, the question just moves a level lower, but is still just as perplexing as to why this is apparently the first study to look at this issue.

I’m still skeptical, not of the study, but that it is in fact the first of its kind.

Kin selection is HUGELY well studied topic in animal behavior, so I’m still a bit skeptical that the issue of kin recognition hasn’t been looked at in plants before now.

for example, the 88 waldman paper likely touches on previous studies looking at this issue in plants.

do you have access to that?

I believe that we need to distinguish between detecting kin selection which can be detected using statistical methods, and direct detection of kin recognition by including relatedness into the equation.

Kin selection is facilitated by kin recognition, which allows organisms to favour relatives preferentially over strangers, reducing the costs of positive interactions

and

4. Discussion

We found that kin groups allocated less to their fine root mass than did stranger groups when they competed below ground, indicating that these plants could discriminate relatives. Root allocation did not differ between kin and stranger groups grown in isolated pots, indicating that the cues for kin recognition lie in root interactions. Siblings were less competitive than strangers, which is consistent with kin selection.

and the discussion part

If kin discrimination via root-root interactions proves widespread, it will profoundly change how we view competition in plants. Our results, because we used maternal sibships, indicate a genetic or maternally derived mechanism for kin recognition involving root communication. However, the mechanism is probably different from the self/non-self mechanism, because plants recognize genetically identical individuals as non-self (Falik et al. 2003; Gruntman & Novoplansky 2004). Having found kin discrimination once, we expect to find kin discrimination elsewhere in plants, since variable dispersal, variable competitive situations, and increases in fitness when competing with kin, are found in other plants. Other competitive traits, such as stem elongation and apical dominance, are the most probable candidates to exhibit plastic responses contingent on kinship of neighbours.

No, pim, you are confusing proximal mechanism with ultimate explanations, rather than looking at whether the issue of kin recognition (as a proximal mechanism required for the evolution of kin selection) has been found in plants before.

again, although the question has become more specific, it still remains:

is this really the first time kin recognition has been demonstrated in plants?

I realize you aren’t an expert in animal behavior, but to compare, if someone released a study that claimed to be the first to analyze kin recognition in animals, everyone in my field would have had a hearty laugh.

so the question is, is this really the first, and if so, what the hell took so long, as it seems a pretty obvious issue to be testing for.

I don’t see how I can be much clearer than that, but if you can figure out what might make it so, please ask.

I’ll guess that gardiners have kinda known about this for hundreds, if not thousands, of years.

How much clearer than

Kin and other multilevel selection has been demonstrated in plants (Donohue 2003, 2004; Goodnight 1985; Stevens et al. 1995; Kelly 1996), and self-incompatibility systems allow plants to discriminate against relatives in mating (Waldman 1988). To our knowledge, however, no studies have yet tested directly for kin recognition in plants.

please note:

To our knowledge, however,

we seem to be missing each other. I’m getting the impression you think I am personally attacking this paper.

I’m not. I’m merely curious as to the veracity of this statement:

no studies have yet tested directly for kin recognition in plants.

since I know quite a bit about the the study of altruism and kin selection in animals, and it surprises the hell out of me, given the vast amount of literature on this on the animal side.

If verified, the next obvious question would be:

why not?

was it just overlooked?

were there technical issues in the way (the 88 paper suggests not, but I haven’t read it)?

maybe it’s just a perspective difference between the two of us, but aren’t you even the slightest bit curious about whether if this is the case, how the study of kin selection got so far separated between animals and plants?

Research on kin recognition also may have practical uses. Mary V. Price and Nickolas M. Waser of the University of California at Riverside have discovered that mountain delphinium (Delphinium nelsonii ) can recognize pollen of related plants. Also, Stephen J. Tonsor of Michigan State University and Mary F. Wilson of the Forestry Sciences Laboratory in Juneau, Alaska, found that some flowering plants, such as pokeweeds (Phytolacca americana) and English plantains (Plantago lanceolata), grow faster when potted with full or half sib lings than when potted with nonrelatives. If these kinship effects are wide spread, they could be used to advantage in planting crops.

Source

No publications found so far for Tonsor and Phytolacca should be 1989 Ah there we are

Under intraspecific competition in the glass house, the number of Plantago lanceolata plants flowering per pot increased with the genetic relatedness from nonsibs to half sibs to full sibs (Tonsor, 1989 ).

Tonsor S. J. 1989 Relatedness and intraspecific competition in Plantago lanceolata. American Naturalist 134: 897-906

Tonsor, S.J. (1989) Relatedness and intraspecific competition in Plantago lanceolata. Am. Nat. 134:897-906

This experiment looked for an effect of relatedness on plant performance under competitive conditions in the perennial weed Plantago lanceolata L. (Plantaginaceae). Seeds from a diallel breeding design were used to establish green-house pots containing three competing individuals. Three groups of pots were set up: those with full-sib, half-sib, and unrelated plants. Plants were not given nutrients after the first 5 wk and were watered only when wilting. At the end of the growing season, all plants were harvested and their parts counted, dried, and weighed. Relatedness among competitors did not affect aboveground dry weight. There was, however, a significant decrease in the within-pot variance of vegetative and total dry weights. There was also an increase in the number of plants flowering per pot with an increase in relatedness. The differences in within-pot dry-weight variances and the propensity for reproduction among relatedness treatments are at least partially explained by the differences among relatedness treatments in the contribution of maternally inherited variation in performance to the within-pot variances of performance. The contribution of inherited variation in performance to the fitness effects of local relatedness can strongly reflect environmental variation. Inherited variation is likely to be a major determinant of the differences in the fitness effects of relatedness seen in existing empirical studies.

Tonsor, S.J. (1989) Relatedness and intraspecific competition in Plantago lanceolata. Am. Nat. 134:897-906

And then

Genetic Relatedness and Competition in Triplasis purpurea (Poaceae): Resource Partitioning or Kin Selection? Author(s) Gregory P. Cheplick and Kristin H. Kane Identifiers International Journal of Plant Sciences, volume 165 (2004), pages 623—630

Abstract In annual plants where dispersal is limited, the nearest neighbors of an individual are often genetic relatives. The negative effects on growth and reproduction that result from intraspecific competition can be greatest when genetic relatives, rather than unrelated individuals, are competing. This is because resource partitioning among genetically different, unrelated individuals might result in improved growth and reproduction when they compete. Alternatively, kin selection is hypothesized to have occurred when growth and reproduction are greatest for an individual competing with relatives compared with one competing with unrelated plants. To determine whether resource partitioning or kin selection is more likely to describe the dynamics of local competition, a greenhouse experiment was conducted with Triplasis purpurea, a cleistogamous annual with restricted dispersal. Five pairs of families were subjected to intrafamily and interfamily competition and compared with noncompeting controls. There were highly significant effects of competition on shoot mass and number of seeds matured in cleistogamous (CL) spikelets. Families showed significant variation in shoot mass, number of seeds set in chasmogamous (CH) spikelets, and mean mass of CL and CH seeds. Shoot mass and mean CH seed mass were significantly greater for target plants in interfamily competition, while the mass of competitors was lower in intrafamily competition. There was no consistent tendency for target individuals competing with kin to outperform those competing with an unrelated family. Hence, there was no support for the kin selection hypothesis. Rather, the sibling competition that results from the restricted dispersibility of CL seeds reduces growth more than competition between unrelated plants, in accordance with the resource-partitioning hypothesis.

Tonsor S. J. 1989 Relatedness and intraspecific competition in Plantago lanceolata. American Naturalist 134: 897-906

yes, I think I see what you’re getting at. for example, this paper concluded that there was kin selection, but didn’t investigate the actual mechanism used in kin recognition.

correct?

similar pattern in the latter papers suggests increasing recognition of what the mechanisms might be, without actually testing for them.

Is this what you’re finding?

like I said, I’m not familiar with the bot lit, only the animal lit, and the various mechanisms of kin recognition in animals has a decent body of publications associated with it.

I do not believe that the recent paper has determined the kin recognition method either. Both planted related and less related plants together in pots to determine growth and other variables. Both found more competition the less kin relationship. So far the only new aspect is the root part.In the older paper, the root mass was discarded since it was to entangled.

I’ve been on the periphery for quite a while, but my impression is that whole plant studies involving the weight of roots and shoots were mainly carried out in the 50s and 60s. The emphasis then moved on to allelopathy and biochemistry. Root studies are difficult. Washing the soil out of roots is both messy and tedious, and virtually impossible if there is macroscopic organic matter in the soil (when I did it, we used a nearby stream) and publications tend to comes slowly so the area seems to have been selected against. But I agree, now it’s been done it is obvious that there was a large gap.

I only read through the followup comments quickly, so forgive me if I restate someone else’s argument.

It seems to me that “kin recognition” is not the same as “producing an effect which is more pronounced versus non-kin”. I might hypothesize that, in this study, all plants in the study produce allelochemics. The genes for production are linked (perhaps functionally as well) to the genes for “dealing with” allelochemicals. And thus, allelochemics have little, or less, or no, effect on closely related plants (who share the genes for production/dismantling), and more effect on less related plants.

One might examine, say, mixed plantings of related plants with a mixture of related and non-related plants, compared to plants mixed solely with non-related plants. If “recognition” is involved, one would predict something like this:

B planted with B –> baseline growth rate for B A planted with B –> B’s growth reduced by X A planted with A & B –> B’s growth reduced by between 0 and X A planted with A –> baseline growth rate for A

One would want to fill out the table the other way as well: B planted with A around it, and B planted with mixed A and B around it.

This completely mechanistic and, to my mind, lacking in “recognition” hypothesis is worth considering and eliminating.

-Josh

is this really the first time kin recognition has been demonstrated in plants?

The key here is the difference between demonstration, which is inferential, and direct detection. It’s sort of like the difference between demonstrating that humans and chimps have a common ancestor and, as the creonuts put it, “being there”.

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This page contains a single entry by PvM published on June 15, 2007 10:58 PM.

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