Paul R. Ehrlich and Peter H. Raven present a detailed
account of butterfly genera and the specific plant genera they feed on. The
point of the study was connect the biochemical (and mechanical) adaptations of
herbivores, with insect larva as a particular example, to the plant as a means
of diversification for the herbivores. Ehrlich and Raven also mention how radiation
of plants has been greatly affected by the development of these biochemical
defenses via secondary metabolites.
Frankly, I barely skimmed over the eight pages of genera matching,
because other than the table of butterfly taxonomy I had no frame of reference
for plenty of the plant taxonomy. A visualization of the matching would have been rather helpful. Most of what I got from those pages was how
certain compounds in the plants designated which butterfly larva would eat them.
Additionally, I did take note of the presence of angiosperms due to the
mentioning of monocotyledon and dicotyledon.
Angiosperm radiation would have provided a platform for
insect herbivore radiation based on the notion of plant diversity providing more
niches for the herbivores to occupy. There are generalists to be sure, but
there are many specialists who form tight connections with the particular plant
they feed off of. As the diversity of the plants increases, the different types
of compounds increases. Which then leads to the increase of insect diversity due
to resistance to the specific secondary metabolites of a particular plant.
When I first started reading this paper, I was expecting the
main focus to be pollination. It was interesting to find that Ehrlich and Raven
focused on the metabolic connection of butterfly and moth larva on plants. Perhaps
I am coming from a perspective that does not weigh insect herbivory all that
well? I just think that another consideration to this coevolution study is
missing.
The ability of the caterpillars to be able to coevolve
and/or adapt to certain genera of plants due to mechanical and chemical
compatibility is important, but the larva is only one stage to the insect’s
life. I’m sure the affinity of a butterfly larva to a particular plant would
then mean the adult insect would more than likely pollinate that particular
plant. However, pollination is only mentioned once, briefly, and in reference
to wind-pollination. I think about how
there are some many animals that have become finely tuned in their ability to
take advantage of a particular plant’s flowers for food and how those animals
then act as pollinators to increase genetic diversity in the angiosperms.
I feel this paper did a good job at exploring coevolution of caterpillars and their host plants. The relationship between these two organisms an antagonistic relationship, caterpillars of course benefit from this relationship at the expense of the plant. Plants would be selected for those which could produce secondary chemicals, or morphologic traits that would inhibit consumption. Any herbivore/caterpillar that can adapt novel ways of dealing with this will have a selective advantage causing families and subfamilies of Lepidoptera (lep) larva to coevolve with these plants. This would result in larva being more specialized on a these plants or group of plants. However, as adults, (If I recall, and I am not, nor claim to be a lepidopterist) leps tend to be more generalists. The relationship between leps (that are nectivorous) and the plants they associate with is a mutualistic relationship where both benefit. This may ease a lep’s need to specialize as flowers are most likely attracting as opposed to repelling nectarivores (there are many examples to the contrary I know, and in fact some plants are known to promote specialization of nectarivores to encourage fertilization, but I digress).
ReplyDeleteI found it interesting in this article, that at the time of publication (1964) five families of butterflies were recognized, this holds true today however not the same five families are recognized. I’ll briefly mention the families because I’m sure most people are familiar with them even if the family names are not familiar.
1) Papilionidae is still a valid family, these include the swallowtail butterflies
2) Pieridae still valid, these are the called “sulfurs” they come in an array of whites and pastel yellow/orange
3) Nymphalidae still valid include monarchs, mourning cloaks, and morpho butterflies
4) Libytheidae was synonymized with Nymphalidae, no surprise, even in the text it says “The tiny family Libytheidae, closely related to Nymphalidae, is obscure to everyone except butterfly taxonomists.” (Page 364) and the mention of the similar internal anatomy between libytheins and nymphalids (page596). These comments showed how the validity of this family stood on shaky ground.
5) Lycaenidae still valid, these are the hairstreaks, small brightly colored butterflies, typically blues and purples (our state butterfly is a hair streak, and why we have a state insect and a state butterfly makes no sense to me, but again I digress)
6) Riodinidae mentioned as a subfamily of lycaenid has since been elevated to family status, these are the metal-marks, and are very similar in appearance to lycaenids.
It would be interesting to take a closer look at what libytheinae are eating and compare that to nymphalids. It was interesting to see the similar feeding habits of riodinids and lycaenids, morphologically they are also very similar. Both groups are known have examples of carnivorous larva, not common in leps but also seen in other groups such as geometrid moths.
Also as mentioned many of the examples where taken from individual records so little weight to those should be given. It would however, be interesting to see a more in depth look at feeding habits of a smaller well resolved group of lep, maybe a single family or subfamily so phylogenies could be constructed and compared.
I was so persuaded by Ehrlich and Raven's description of gradual natural selection based on repellent secondary metabolites that I forgot that some plant compounds actually attract butterflies! Thank you for pointing that out.
DeleteGlad to have your insight Matthew! I thought you might appreciate this one, as our resident arthropod taxonomist.
DeleteExcellent, this helps answer a couple of the questions that I had about this paper in general like the groupings of the butterflies. At the time all of the butterflies were classified just using observation, correct? Taking a look at this study again with all of our molecular biological knowledge I think would be very interesting because we can actually see how closely related some of these different organisms (butterflies and trees) are, and then make conclusions about the coevolution from a more informed standpoint, like you are suggesting in your last paragraph.
DeleteI really liked how this paper correlated evolution and ecology, which is a synthesis that has been touched on, but not really fleshed out so far. It made me think of the idea that these butterflies are evolving to utilize other niches. And those niches have some plants that are similar to the plants that were in their old niche, but then they can change as the butterflies move into those niches. It is a cool circular pattern that shows the interconnectedness between ecology and evolution.
Good points Noah. Butterfly taxonomy probably primarily based on morphology, and even today morphology is used for species level identification. I was also curious how butterfly taxonomy has been refined using genetic methods, and I found an interesting butterfly phylogenetics paper (see link below) that includes a cool figure on Papilio mitochondrial DNA phylogeny and a distribution map for comparison (figure 2).
DeleteButterfly Phylogenetics paper:
http://www.researchgate.net/profile/Felix_Sperling/publication/252329509_Butterfly_Molecular_Systematics_From_Species_Definitions_to_Higher_Level_Phylogenies/links/0deec5226b0b5a041c000000.pdf
Thank you, Matthew, for giving us more information on the butterflies! I kinda figured you would have some insight for us. Haha. Yeah, Ehrlich and Raven were really careful about using some of the literature they reviewed for the butterfly identification and classification due to frequent errors.
DeleteThank you, Matthew, for giving us more information on the butterflies! I kinda figured you would have some insight for us. Haha. Yeah, Ehrlich and Raven were really careful about using some of the literature they reviewed for the butterfly identification and classification due to frequent errors.
DeleteButterfly taxonomy as in the case of other groups is by and large morphology driven. Where is becomes beneficial (in my opinion and others may disagree) to throw molecules at it would in cases of cryptic species. A true feat of this paper though was the use of larvae. Caterpillars are, again in my opinion, pretty generalized. It takes a pretty talented person to id a lep larva. Even the article mentions placing an emphasis on the identification of larvae that had been grown to maturity. For example many people including myself (again I’m no lepidopterist) need a microscope to distinguish a Symphta larva from a Lepidoptera larva and they are in different orders. This is where a repeat of this study, I feel, would really benefit from modern technology. Using sequencing to pair larvae with adults would be amazingly beneficial. Gut contents could also be sequence to better determine diet. I imagine a lepidopterist in the field may do a great job on the larvae IDs but the plant IDs may leave something to be desired, opposite holding true for a botanist in the field.
Delete
ReplyDeleteButterflies and plants: The authors are shedding light of the main mechanisms that allowed coexistence between a host plant and insect . I think using Lepidoptera is a challenge because of the tremendous diversification within the group and the taxonomic issues not fully resolved back in those days. I found interesting the amount of literature review in order to get a better insight of the study case. One of the common observation made was to see how certain clades of butterflies are specific for certain host plants. My personal opinion is that the specificity of the defense mechanism for each host plants against a group of insects allowed their secondary metabolites to diversify into new functions. In nowadays, I think comparative methods and phylogenies could help to resolve coevolution questions with regard to this group.
You're right Carlos. Butterflies are a fairly diverse group with 20,000 species worldwide, but there are only 725 species in North America according to the North American Butterfly Association! But it's important to remember that butterflies are a flashy species with many professional and amateur Lepidopterists. Researching Lepidoptera and plant associations was probably easier than a lesser known orders.
DeleteI agree, Carlos, that many of the questions Ehrlich and Raven viewed as unanswerable can now be addressed with modern methods.
DeleteErlich & Raven: I am amazed at the scope of the study this paper discusses. The authors go over so many groups and sub-groups with the Lepidoptera order, and it's amazing at how well they can describe the food sources and changes in those for each sub-groups. I agree with Carlos in saying that this was not only a large project, but so much literature review had to be done in order to find all of the information they were wanting. While I'm not a specialist on butterflies, I do love plants and I appreciate the concept of coevolution between two species. It is amazing to me how some of the "secondary plant substances" control the evolutionary steps a butterfly can take, while at the same time the steps they take limit the amount of evolution that can happen in the plant. Such a symbiotic process definitely deserves study, and I think the authors completed that as far as scope. As has been said above, some phylogenies would have ultimately been helpful to visualize the connections discussed in the paper.
ReplyDeleteThis paper points out the importance of investigating and understanding the coevolution of species in order to better understand the behavior and ecology of a given organism. The interaction between groups drives the evolution of each and often times these interactions are overlooked or not given enough attention. This also relates to trophic level dynamics and the behaviors and/or characteristics that organisms evolve in order to become more efficient or evade predation.
ReplyDeleteButterflies are an exceptionally well studied group. Ranging from academic to amateurs- Lepidopterists observe, pin and collect Lepidoptera around the world. Elrich and Raven synthesized the work of many Lepidopterists to make generalizations between butterflies, host plants, and secondary compounds. Elrich and Raven concluded the reciprocal interactions between secondary compounds in plants and butterflies directly led to the coevolution and diversification of plants (and butterflies!). Compared to Hutchinson and MacArthur, Elrich and Raven’s examples of coevolution between plants and butterflies as dynamic systems whose relationships are intertwined in an “arms race” and defined by more than available niche space. Caterpillars and adult butterflies that evolve to under-utilized plants have a distinct niche advantage. Although, caterpillars and adults have different strategies for utilizing plants. Caterpillars either have a negative or null affect (parasitism or commensalism) on their respective host plant. The adults typically have a mutualistic relationship by pollenating the plant while feeding on the nectar. There is a distinct evolutionary advantage for caterpillars host plant to be different than the adult because it reduces intraspecific competition through niche partitioning.
ReplyDeleteRe Lepidotera being so-well studied, I hadn't really thought of that, but I guess they could be considered "charasmatic micro-fauna" - the arthropod equivalent of birds and big fuzzy animals among vertebrates.
DeleteI personally thought this aspect of the paper was really interesting to think about. They spent a lot of time talking about how plants evolved compounds to avoid herbivory by caterpillars, but seemed to kind of gloss over the mutualistic relationship between the adult butterflies and these plants. They mentioned briefly in the beginning that (if i read it correctly) that for some species they have to lay their eggs on plants other than those that they feed upon and then pollinate because their host plant is not hospitable for their larva. The idea that the plants evolve a mutualistic relationship with the adults but an antagonistic relationship with the larva is kind of neat. It would be interesting to compare the coevolution of plants and butterflies to that of certain plants and ants, like cecropia in the tropics which, as far as I know, is mutualistic to both parties for all life cycles.
DeleteEhrlich*** oops
DeleteThis was a nice read in that it felt like the first in depth case study/review we have seen on a focused but important topic like coevolution. I like how the authors start with the 4 questions they will address and move from there to discuss some of there “methods” and rationale for looking at coevolution and plants-butterflies in particular. The results of their analysis were pretty dense but probably an easy read for a plant taxonomist. The conclusions were most insightful .The role of secondary compounds in grouping butterflies is remarkable, but not surprising considering the role these compounds play. I had never thought that these compounds could be the reason for the diversity of angiosperms, but this paper lays out a powerful case for just that. The suggestion for the diversity of both plants and insects in the tropics brought this point home for me in realizing just how big of a driver this arms race might be in shaping evolution and present day communities.
ReplyDeleteI liked their section about angiosperms also. It is an intriguing idea--that the ancestor(s) of angiosperms may have produced insect repellants which enabled them to occupy a new niche, followed by adaptive radiation.
DeleteI also found that hypothesis for angiosperm radiation fascinating, and wondered if it's been substantiated (or that's even possible).
DeleteAt the end there is a bit about the latitudinal diversity gradient, how many lepidoptera and insects hadn't figured out a way to do very well in colder environments, and how their relative diversity and ability to thrive in the tropics could've driven plant diversity, or vice versa. They seemed to give more attention to the insect diversity driving plant diversity (of course, as lepidopterists), but intuitively I would expect it to be the other way around, with the diversification of primary producers leading that of consumers (maybe my plant bias!). Has this been resolved? Or is the reciprocal coevolution so tight that it makes little sense to say one or the other "leads"?
I don't think about evolution much, and even though the taxonomy makes my eyes glaze over, I certainly appreciate the evolutionary perspective these guys provide.
Wow! What an exciting paper! How could we do evolution without ecology? How could we do ecology without evolution? Ehrlich and Raven answered in 1964 with a resounding “No!” Before next-gen sequencing, before coalescence calculations, before the application of Bayesian inference to phylogenetics, they were able to compare patterns of butterfly family feeding with the patterns of secondary metabolites in plants, to see evidence of coevolution.
ReplyDeleteEhrlich and Raven were so confident of their ability to predict relatedness based on these patterns, that in the case of two families of butterflies, Heliconiini and Argynnini, that feed on four phonetically related groups of plants for which no similarities in secondary metabolites have been established, they stated that a biochemical basis would eventually be found.
Their summary of Merz's 1959 experiment, which showed young Pterogon prosperpina larva were able to feed between the sharp raphides in Sphingidpflazen, while the older larva could not, was fascinating. If nothing else, it showed that secondary metabolites can prevent plants from being eaten, thus providing selective pressure for the insects.
Phenetically, not phonetically.
DeleteThere was a lot going on in this paper, and I feel that the authors used a very broad approach. I think that sometimes there was too much information being presented and this caused a loss of focus. However, this paper was very interesting for me in the way authors Ehrlich and Raven described co-evolution caused by complex biochemical feeding structures. In the paper they are already figuring out the chemical composition of many secondary structures found in plants that either attract or deter the butterflies. This seems to be a more thorough investigation of the same question: Why is the earth green? The authors just delve deeper and put it into another context. The earth is green because many plants have these secondary compounds that protect them from herbivores, allowing for plants to keep persisting. In combination with predators limiting herbivores, this adds yet another factor.
ReplyDeleteI thought this paper nearly too informative and consequently, a bit long getting to the point. I'm also a bit surprised that this paper didn't come along earlier, it seems to me that this should have come shortly after Darwin published the Origin of Species. At that time, lepidopterists and botanists had been around for centuries, did they just avoid each other on the street of what?
ReplyDeleteDon't get me wrong, this was a good read and an interesting topic. The authors clearly have covered (or at least tried to cover) all of the drivers of coevolution in this model and found an interesting although not unexpected relationship between angiosperms and lepidopteran radiation that seems to be driven by an arms race with plants evolving defenses and lepidopterans evolving a way to exploit them. I would be interested to see what happens if one were to look closely at the evolution of one of the widespread families or the evolution of a leapidopteran family on one continent (Australia seems like a good one) and applied modern molecular methods. Perhaps it would be possible to date the divergence of major groups based on the divergence of food plants and the subsequent evolution of novel secondary compounds.
I too was surprised by the omission of the influence of pollinators. It seems that pollinators may contribute equally or perhaps even more than herbivorous larvae to the evolution of plants. Although many pollinators are specialists, many are not and incidental cross arthropod-mediated pollination has, I'm sure, contributed greatly to the evolution of new (particularly polyploid) plant species. Moreover, there are so many specialist pollinators that plants have obviously been driving the evolution of many insects and other groups.