Author Archives: Studio Schilthuizen

About Studio Schilthuizen

Ecology and Evolution for Everyone. I blog, write, and speak about biodiversity and the science of life on earth.

Invasive species and the perils of terminology

exotic_species_alert_for_mississippi_river_from_minnesota_department_of_natural_resourcesIn an opinion paper in Trends in Ecology and Evolution, James Russell and Tim Blackburn signal a rise in what they perceive as “invasive species denialism”. They state that more and more publications, including some in leading scientific and popular science media (e.g., Fred Pearce’s New Scientist article and the book Where Do Camels Belong? of Ken Thompson) “have challenged the existing scientific consensus” on invasive alien species (IAS). That scientific consensus, say Russell and Blackburn, is that invasive alien species cause serious damage by their global change of ecosystems. And, the authors argue, this rising trend of “IAS denialism” among scientists and science reporters is fuelled by political motives and employs selective use of research data. The parallel with denialism in global climate change is obvious, and alarming.

Russell and Blackburn then go on to show how to recognise and deal with IAS denialism. They first explain that legitimate scientific debate may exist over whether a species may classify as “invasive” and that there is the non-scientific assessment of value in deciding what is “damage”. Having said that, Russell and Blackburn then state that “[i]n some cases the rejection of scientific evidence of the negative impacts of IAS takes the form of a type of science denialism.” That is, “to manufacture uncertainty in the scientific consensus on an otherwise undisputed topic”. The political motives that lie behind this denialism are said to be those idealising free trade, the very enterprise that causes many of the harmful species introductions in the first place.

I have read Russell and Blackburn’s paper with increasing alarm. Because what do they really say? First, that species invade and that such invasives may be perceived as harmful. Second, that the assessment of “harm” can be subjective. And finally, that scientists should not cast undue doubt on undisputed scientific facts that invasive species cause harm and thus play in the hands of those grinding a political axe. However, the parallel with climate change, appealing though it may be, is not warranted. Denialism in climate change takes the form of casting aside scientific evidence that the global climate is changing. Similar denialism in the field of IAS would be a denial that more and more alien species are invading ecosystems, and nobody is denying this fact. What is debated  is whether these invasions cause harm and, if so, on what time-scale. Since “harm” (unlike global temperature) cannot be objectively defined, the so-called “IAS denialism” lies outside of the realm of science and cannot be pinned on ecologists that happen to take a different view on invasive species than Russell and Blackburn.

What does lie within the realm of science are discussions on how energy flows within ecosystems are affected by species invasions, and how invasive species and the native species they interact with may evolve, and at what temporal scales. By casting such debates as “denialism”, Russell and Blackburn are not doing their colleagues a favour. By drawing an unjustified parallel with climate change denialism, their paper constitutes a pre-disapproval of ecologists who are trying to explore the concept of novel ecosystems, or take a long-term view of micro-evolutionary reconstitution of invaded ecosystems. I would take issue with labelling such ecological viewpoints as denialism. Rather, they are a legitimate way of dealing with the long-term effects of invasive species. Perhaps even more responsible than uncritically walking the conventional line of viewing IAS as one of the major challenges to biodiversity conservation of our time.

Russell and Blackburn end their paper by writing: “There should be a vibrant and robust dialogue on the negative, and potentially any positive, impacts of IAS and on the allocation of resources to remediate their diverse threats.” However, “such a discussion should be evidence based and not disrupted by appeals to values or denial of the magnitude of the threat. We believe it is imperative that invasion biologists engage constructively and lead on such discussions”. I could not agree more. But with this paper, the authors achieve the opposite. By drawing parallels with climate change denialism, they aid in creating an atmosphere in which any scientist exploring an unconventional long-term view on the issue of species invasions, may be labelled as politically incorrect.

Paperback is out!

On April 28th, the paperback edition of Nature’s Nether Regions appears in the US (on May 14th in the UK). With a quirky, young-adultish cover, and a delightful quote from Isabella Rossellini, I hope it will open up a new segment of the readership. To promote the paperback version, some excerpts have been published, and I’ll be on a book tour in the UK 20-30 May.nether-regions

Burying Beetles Play for Both Teams

Since Bruce Bagemihl‘s wonderful book Biological Exuberance (and Ricky Gervais’s stage adaptation of it), there’s no denying the fact that homosexuality is everywhere in the animal kingdom. Not as the occasional embarassing mistake, but often as a standard part of the sexual repertoire. Clearly, homosexuality has evolved in many species, but the question is, how and why? Since evolution works via success in spreading one’s genes, how could a behaviour that is not primarily geared towards leaving offspring, be advantageous?

The crucial word here is “directly”. Perhaps in most cases homosexuality itself is not *directly* advantageous, but it may be indirectly so. One example of this has just been published in the journal Biology Letters. Katharina Engel and colleagues of the University of Ulm, Germany, studied the burying beetle Nicrophorus vespilloides. This is a common beetle in Europe and Asia, known for its habit of interring dead animals (small birds or rodents, usually) and then tending the buried cadaver as food for their young. (In fact, they are one of the few kinds on insect where the parents care for the young larvae till they are grown up.)

In the scramble around a newly-discovered corpse, where many beetles will vie for the right to take possession of the corpse, male beetles face great risks but also great opportunities: if a male manages to outcompete rivals *and* fertilize the female that eventually is going to lay its eggs on the dead mouse, it will have reached its reproductive goal. And, as Engel and colleagues discovered, whether these males will engage in any gayness, will depend on how frantic the scramble around the mouse is.

They conducted two experiments.

In the first one, they placed males in cages with zero, one, or three females. After several weeks, they introduced such males to other males to see whether they would fancy them. The beetles that had been housed with females would never mount another male, but the males that had been housed in celibacy, would be more so inclined. So, the researchers say, males that “think” females are few and far between, won’t let a potential female get away, even if the female is actually a male. In other words, they can no longer afford to check first.

In the second experiment, they kept males in isolation for 60 days and then gave some a dead mouse and some not. Then, they introduced a male “lover”. As it turned out, the males-with-a-mouse were less likely to try to mate with the new male than the males-without-a-mouse. The explanation in this case is that the other male will be more inclined to fight the starry-eyed male if there’s food around that’s worth fighting for. So in this case, mounting a potential female and running the risk that it turns out to be a male, is a wise choice only if there’s little risk that the male (if in fact it turns out to be one) will bite back.

A heterosexual copulation in the burying beetle Nicrophorus vespilloides (male on top). Photo by Heiko Bellmann (from the Biology Letters paper--supplementary information)

A (heterosexual) copulation in the burying beetle Nicrophorus vespilloides (male on top). Photo by Heiko Bellmann (from the Biology Letters paper–supplementary information)

In conclusion, in male burying beetles, homosexuality seems to be an option born out of the risk of missing out on a heterosexual encounter with a real female.

Stay tuned for more discoveries from the realm of biological exuberance.

Get that phallus out of my face!

The “widow periwinkle” Littoraria melanostoma is a handsome little periwinkle living in mangroves along the coasts of East and Southeast Asia. Unlike many landsnails (which are usually hermaphrodite, that is, male and female at the same time), these estuarine snails come in separate males and females. Unhindered by any detailed knownledge of mollusks, one might assume that in sexual and other matters alike, snails are generally sluggish and docile. This is not generally the case, and also not in the widow periwinkle, as shown by Terence Ng and Gray Williams of the University of Hong-Kong in a paper just published in the Journal of Molluscan Studies.

Ng and Williams discovered that females, when they are mounted by a male, often use their snout to push the probing phallus away, time and time again, until the male gets so exhausted that he gives up:

In the video, the female is above, the male below; the female’s snout is seen pushing away the male’s phallus, which repeatedly appears out of the male shell beneath her.

The researchers tried to understand why a female would reject males so often (in about 90% of all mating attempts). They confronted large and small females with large and small males, but in all combinations the females were equally likely to push away a male’s penis, so it was not that the male’s weight and size was a reason to reject him. Also, they deprived females of sex for several months and yet found that after this long celibacy, the females still only accepted one out of ten suitors.

Long story short: the researchers still don’t understand why females give so many males the cold…ehm…snout. But one thing is clear: widow periwinkles are no pushovers.

It’s official: genitals *do* evolve faster!

Want to tell one species from another (identical-looking) one? Check their genitals! That’s the rule of thumb applied by taxonomists worldwide. In fact, many an identification manual, be it for cicadas, spiders, or snakes, often supplies little more than detailed images of the genitalia to assist in the identification of species that look very similar on the outside. My book Nature’s Nether Regions is all about why this would be so–which evolutionary processes are responsible for the breakneck speed by which genitals evolve and change their shape and function all the time. But surprisingly, nobody had ever actually measured the evolutionary rates of genitals and compared these with those of other organs. Nobody, that is, until Julia Klaczko and colleagues of Harvard University did so and reported on it in a new paper in Journal of Zoology last week.

What Klaczko and colleagues did was take a closer look at Anolis lizards. Almost 400 species of these colorful lizards are known, and especially the Caribbean species are famous among evolutionary biologists for adapting rapidly in body shape to their local environment. The researchers picked 25 Anolis species. For each species they selected 30 specimens and took measurements from their legs, dewlaps (a colourful skin fold under the chin) and one of their penises (like all lizards, a male anole is doubly endowed with two “hemipenes”). They then calculated how fast each of these organs evolved, by plotting the traits on the lizards’ evolutionary tree. And they found that, as expected, the genital shapes evolved faster than the other organs. About six times as fast, in fact.

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Each of these pictures shows one of the two hemipenes of five different Anolis species. The picture on the right shows the measurements that the researchers took.

The graph below shows how fast the lizards’ penis shape evolves compared with their legs and dewflap. The horizontal axis shows the evolutionary time separating two species, and the vertical axis shows the difference in organ shape. The line that climbs the fastest shows the genital evolution; the other lines (which climb slower) are for dewlap and limbs.

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A video (in Portuguese) on Julia Klaczko research:

The dangers of display

Sex is a risky business. Courtship, display, combat in rivalry, and copulation are all behaviors that expose the protagonists to predators. For example, bats home in on the ripples produced by calling túngara frogs, as research by Wouter Halfwerk and colleagues showed earlier this year. And it is no surprise that acts of copulation often take place in hidden sites, where the animals’ natural enemies cannot make use of the fact that they can catch them with their trousers down, as it were. The same also applies to males that are engaged in rivalry. In capercaillie grouse, for example, the males often engage in one-to-one territorial defenses. The fact that they are completely absorbed by this reproductively essential behavior, is often abused by the birds’ enemies, which include hunters, but also eagles, as this striking video shows: