The New York Times published on article titled “Think You’re Smarter Than Animals? Maybe Not” in the Sunday Review section on August 21, 2011. In addition to offering insights on chimp and bird cognition, the authors, Alexandra Horowitz and Ammon Shea recap an article, “Do sheep (Ovis aries) categorize plant species according to botanical family?” by researchers Cecile Ginane and Bertrand Dumont, which appeared in the journal Animal Cognition (2011). The researchers fed 12 lambs a legume (followed by an adulterant, lithium chloride) and a grass (with no such adulterant). To quote the Times:
“After learning that eating sainfoin [Onobrychis vicifolia, the legume], but not fescue [Festuca arundinacea, the grass], was followed by a stomachache, the lambs knew to pick cocksfoot [another grass] over alfalfa [another legume] when given the choice in the future. Have no idea what this means? In non-lamb terms, if a pasture legume caused indigestion… but a grass found in pastures did not, the lambs, when facing a later choice between a different legume and a different grass, opted for the grass over the legume. In other words, the lambs demonstrated an ability to form a generalization about the relative digestibility of families of plants.”
Wow.
Pavlov’s dog taught us that animals (at least canids) learn to modify their behavior (well, maybe not my dogs…) as a result of the positive or negative results of that behavior. In other words, push the lever with your nose and get a treat? Keep pushing! Or, press the lever and get an electric shock? Well, shoot, let’s not do that again! But this lamb result is much more interesting. Here, a bad outcome resulting from a particular behavior is learned and generalized: that plant gave me a stomachache; therefore, I will not eat that plant or plants like it. How do they know that plant species B (alfalfa) is “like” that disgusting plant species A (sainfoin)? What does “like” mean to a lamb, anyway?
Well, Ginane and Dumont do pose thusly this very question in the abstract of their paper: “…the question now is to identify which specific plant characteristics or functional traits the animals rely on in order to form categories.”
A little historical perspective…
Human beings excel at naming things. For thousands of years, people have named stars and constellations and wild edible plants and prey species and the types of rocks good for arrow and spear-tip making and who knows what else. This is about the thing. We also discriminate. This prey species tastes better or is more nutritious than that prey species. This is a comparison between or among things. We also bucketize or classify. This prey species and that prey species are pretty much the same in some way that is important to us. Let’s call these two species and others like them “antelope”. This is about groups of things.
In our never-ending quest to intellectually organize our natural world in ways that are useful to us, we ask ourselves, “How do we place newly seen or discovered species in the right buckets?” This is the question that led to the development of modern taxonomic science. I offer that the broad application and refinement of binomial nomenclature (i.e. Genus species) and dichotomous keys (“if it has heart-shaped leaves, then it is a so-and-so and, if not, then it is not a so-and-so” and so on until a unique species is revealed by the key in a process called identification) was propelled vastly forward by the discovery of thousands upon thousands of new species in the 16th through 18th centuries by expeditions under sovereign sponsorship. This rapid evolution in the tools we employed to assist us in categorizing the avalanche of newly discovered living things culminated in a veritable orgy of taxonomic classification in the mid-18th century by Carl Linnaeus (1707 – 1778) and others.
SIDEBAR: Linnaeus, in fact, was so prolific in his taxonomic assignations that his full name is rarely used after a scientific binomial. A simple “L” suffices to let us know that Linnaeus named it. Indeed, several species of the alfalfa genus, Medicago, were originally described by Linnaeus, including Medicago sativa, which is the very species avoided in the Ginane-Dumont study by lambs upset by their prior encounter with “tainted” sainfoin.
OK. But how did Linnaeus – or anyone else — know what name to give a plant or animal?
At first, taxonomists looked at gross morphological characteristics. In a pre-Mendelian (see below) world where genes were unknown, the number of petals and flower symmetry and type of leaf and a very long list of other factors were used to differentiate plant species on the basis of their expressed physical traits.
SIDEBAR: At the end of the day, this phenotypic approach proved a not-too-shabby way to classify plants and animals: a remarkably high degree of correlation exists between the organization of taxa 250 years ago and the organization of taxa today, the latter based on inexpressably more sophisticated biochemical and genetic analyses. After all, an oak is observably a member of the genus Quercus — however much various oak species may hybridize — and a larkspur species is, by and large, observably a member of the genus Delphinium. This was true in 1750 and is true today.
Then, with improvements in the microscope, invented and first used to study single-celled organisms by Antonie Philips van Leeuwenhoek (1632 – 1723), cyto-morphological factors were added to the list of traits used to differentiate and classify living things.
A number of analytical techniques important to taxonomy were first developed in the mid- to late-19th century and refined in the early 20th. These included chromatography techniques used to separate various biochemicals, thus aiding the identification of compounds specific to or in concentrations indicative of particular taxa, and karyotyping, or the creation and examination of photomicrographs which show an organism’s complement of chromosomes and display differences in length, banding patterns and other morphological characteristics which are useful in distinguishing taxa. The application of these tools helped us change, refine or confirm our prior assessments of biological “closeness”.
Although the field of genetics began with the classic inheritance experiments conducted by Gregor Johann Mendel (1822 – 1884) on his celebrated pea plants (nota bene: peas are legumes), it was not until Watson and Crick published their seminal paper elucidating the structure of DNA (in the journal Nature on April 25th, 1953) that the stage was set for the development over the next several decades of an arsenal of very powerful analytical technologies, including gene sequencing. At this point, phylogeneticists were able to get to the crux of the matter and evaluate the core material of heredity — even down to a level of base pair by base pair precision. Scientists found that mitochondrial DNA, in particular, was useful in assessing evolutionary relationships. Taxonomy, or the classification of living things from Kingdom to species, became much less speculative; scientists could reproducibly demonstrate evolutionary relationships and estimate the time of evolutionary divergence based on genetic isolation.
Back to our lambs…
Did they know that alfalfa is in the same family as sainfoin because of morphological similarity? Was it that the two plants “look” similar and therefore this new one is likely to be as upsetting to me as that last one? This would imply some ability to recognize patterns such as leaf shape. Well, both have purplish flowers, although the morphology of the flowering heads is different. Sainfoin has pinnate leaves with many leaflets on each side of the leaf’s rachis or stem. Alfalfa’s leaves have but three leaflets. Nevertheless, these two members of the Fabaceae or pea family are morphologically more similar to each other than either is to the grasses used in the study.
Is it possible, however, that the lambs were able to throw the two leguminous species into the same bucket on the basis of some ability to assess biochemical similarity? Did the species taste similar? Taste and smell of course are biochemical and neurological phenomena. Or were they able to discern higher protein concentrations in these nitrogen-fixing species, both of which are used as high-quality forage for livestock? And if the latter, how was this protein “assay” accomplished?
SIDEBAR: Sheep love alfalfa. Indeed, at Lava Lake, we have to be careful not to allow too much consumption of lush alfalfa in our pastures to avoid bloat which can be fatal. Even alfalfa aftermath, dry and yellow-brown in the fields in October, has the potential to induce pregnancy toxemia in bred ewes, which is a serious matter. Sheep also like the new tender leaves of native browse species. In a wide-ranging conversation with Kurt Pregitzer, Dean of the College of Natural Resources and Thomas L. Reveley Professor of Forest Ecology at the University of Idaho last month at Lava lake Ranch, we discussed the propensity of wild ungulates to eat these young leaves preferentially in season. Scientists have shown that young leaves have higher nitrogen concentrations; that they would makes sense, of course, since these leaves are growing and need nitrogen to synthesize proteins to build out the cellular infrastructure required for photosynthesis. Lambs need nitrogen, too. At the end of six or eight months of life they can weigh in excess of 150 pounds. In a lean, grass-fed lamb, that’s a lot of protein.
Are the study lambs members of the Linnaean school of morphological classification or are they biochemical taxonomists that assess the chemical products of gene expression by taste or other biological assay? Or is their ability to classify plants, at the family level, due to some other unknown capability?
I do not know the answers to these questions. I do know that my appreciation of our ovine friends is enhanced by the results of this most interesting study. The list of possible follow-on investigations is long and intriguing. I’d really like to know, for example, if elk, subjected to the same experimental protocol, would behave in the same manner. Perhaps our wild ungulate friends are similarly endowed with what I had thought until I read the article was a peculiarly human ability.
Thanks to Kelly Cash for calling my attention to the article in the New York Times and to Pete Cenarrusa for another engaging discussion of sheep herbivory.
Brian Bean
POSTSCRIPT:
Avoiding toxic browse species…
Sheep will typically but not unerringly avoid toxic browse species in a rangeland environment.
On the range, one species of concern is California false hellebore (Veratrum californicum var. californicum). I note that the ubiquitous Linnaeus is credited with naming the Veratrum genus. This species and its congener, green false hellebore (Veratrum viride), with which it appears to hybridize, are known by a number of other common names such as skunk cabbage, cow cabbage, Indian poke, corn lily and wild corn (by Basques in Idaho). The genus Veratrum, which until recently was comfortably ensconced in the Lily (Liliaceae) family, was recently re-assigned to the Melanthiaceae, suggesting that lambs may not doubt their own taxonomic determinations, but we doubt ours.
If ingested in sufficient quantity by a pregnant ewe at precisely the right point in gestation (14 days), California false hellebore, at least, may cause developmental defects in the lamb fetus resulting in a condition known as Monkey Faced Lamb Syndrome. I note that the principal consequences of ingestion are borne by the offspring, not the mother. I also note that one of the more potent teratogenic alkaloids present in false hellebore, the aptly named cyclopamine, is under consideration as a cancer-fighting agent for humans. This is indeed interesting, as one of the many, many uses to which the plant was put by First Nations peoples was to commit suicide.
Monkey Faced Lamb Syndrome is very rare at Lava Lake – even though false hellebore is found in some of our riparian areas, the ewes appear to avoid it.
Finally, although both California false hellebore and green false hellebore occur in Idaho, the latter in the northern part of the Gem State and the former in the south, the distribution map for California false hellebore published by the Natural Resources Conservation Service of the U.S. Department of Agriculture does not show the plant to exist in Blaine or Butte counties in the heart of Lava Lake’s operating area. This despite the fact that I and two dozen others saw it at Old Pete’s Corral in upper Fish Creek on the Idaho Wool Growers Association Range Tour hosted by Lava Lake in July. I must send a note to amend the database.
Gustatory preferences…
Sheep exhibit distinct gustatory preferences. They will preferentially consume “ice cream” species like yellow lupine, filaree and certain species of sunflowers.
Indeed, years of overgrazing will first affect the percentage representation of preferred species in the mix of species comprising a vegetation type and then, with significant continuing pressure, eradicate one or more of these preferred browse species in a grazing area or nearly so.
Healthy rangelands require not only representation but mix.
Clearly, sheep possess discriminating palates.
SIDEBAR: Sheep and mule deer are browsers, focusing their attention on forbs and shrubs, while elk and cattle share a similar regard for grasses – although elk are quite delighted to eat alfalfa, doubtless due to the protein concentration, and will certainly hedge willows and eat aspen leaves.
