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Carnival of Biodiversity - 2 - Biodiversity and adaptation: the constant struggle for food and space

male Chalcosoma atlas. Photo by Andrea Mangoni.

If we could imagine a male Chalcosoma (...), with its shiny armor burnished, and its large and complex horns, enlarged fino alla taglia di un cavallo, o anche di un cane, esso sarebbe uno dei più imponenti animali del mondo.

Charles Darwin

202 anni fa nasceva Charles Darwin. Ed è in suo onore che - ancora una volta - apro il secondo appuntamento del Carnevale della Biodiversità proprio con una sua citazione.

Già, l'aspetto di un Chalcosoma atlas maschio è davvero impressionante, con quelle sue straordinarie escrescenze toraciche e cefaliche a forma horns. But what selective pressures led to these giant beetles dinastini to evolve a similar ingombrantissimo paraphernalia? One of the first things to be said in this regard is that the horns and the appendices of dinastini have long been studied. In several animals in which the male secondary sexual characteristics include hypertrophic similar bodies, the latter may be the result of selection sexual females that is they may be more attracted to males from the ornamentations larger, so that would be favored at the time of mating. In reality, this can hardly apply to the case of these beetles, as many females have no way of choosing their partner, and sometimes may even be forced to compulsorily copula. More likely is the actual advantage gained by males during the fighting for possession of food resources, territory and the right to mate: males with horns longer can control the opponent from a distance, avoiding confrontation at close range that could be harbingers of major damage. Moreover, studies on another dinastino, Podischnus Agenor (whose males have a slightly forked horn chest directed forward and a rearward-facing thin cephalic horn) have noted that the adult sex male fight each other using stereotyped movements similar to those used by the beetles themselves to drill cane sugar they eat and where they hide during the day. Perhaps these ornaments then, at least for certain species of Dinastini, have evolved just as an aid to excavation activities and search for food, and then have provided an additional benefit to their owners at the time of the disputes related to reproduction or conquest of territory and food resources. But of course the streets are covered by one thousand animals and plants in the race to grab food from the teeth and put in a place to live, a wonderful article on the rich community of organisms that live and decided to draw sustenance from ... nostro corpo lo potete leggere nel post che Continuo proceso de cambio ha scritto per la precedente edizione del Carnevale. In ogni caso, gli Insetti sono da sempre maestri incontrastati a tal riguardo.

Se gli straordinari adattamenti morfologici di questi artropodi hanno permesso loro di conquistare virtualmente tutti gli ambienti disponibili, eccezion fatta per il mare aperto e i ghiacci più impenetrabili, non meno eccezionali sono state anche le strade percorse nell'adattare il loro plasticissimo piano strutturale utilizzandolo per sopravvivere nell'ambiente e procacciarsi il cibo nei modi più vari. Alcuni esempi molto gustosi, come il nuoto, il volo e le spiritrombe sono stati ben disquisiti tempo fa da Biosproject: Earth ; ma tra tutte le soluzioni sperimentate dall'evoluzione su questi organismi, impossibili da citare esaustivamente senza scrivere un'opera pari per dimensioni all'Enciclopedia Britannica, vorrei guardare con un po' d'attenzione in più con voi quelle riscontrabili in un ordine molto particolare: quello dei Mantodea, che comprende gli insetti noti comunemente come mantidi religiose .

In passato ho già avuto modo di parlare di Mantis religiosa , una specie quasi cosmpolita che è molto comune anche in Italia. Nelle regioni calde del globo, però, le mantidi hanno trasformato le proprie fattezze fino a renderle quali irriconoscibili. Nelle continua lotta per conquistarsi uno spazio vitale, sfuggire i predatori e cacciare le proprie prede, infatti, questi insetti hanno abbracciato con entusiasmo le strade del mimetismo criptico, divenendo tutt'uno con l'ambiente che le circonda. Così ecco mantidi che hanno l'esatta forma di un roseo fiore di orchidea (come la celeberrima Hymenopus coronatus ), altre che invece sembrano foglie secche mezze arrotolate, altre ancora che somigliano ad ammassi di sterpi o a legnetti spezzati. Le somiglianze a volte sono così incredibili che anche a distanza ravvicinata può essere difficile a glimpse of these animals if they are completely immobile. We said that this form of mimicry can be extremely useful both to escape predators, which hunt their prey: for insects and small animals that eat the mantis is not normally aware that these predators until it is too late. And if the prey are scarce? If the environment is so poor that they ensure the existence of a mantis going to adopt the technique of hunting waiting? Evolution has solved, in some genera, even at this problem: Eremiaphila Africa, for example, although strikingly similar to the stones of the desert where they live, have two pairs of legs cursor that make them highly effective in active hunting of the great sprinter to their prey.

Mantids shaped Orhidea, dry leaves, twigs or clusters of flowers: so many exceptional examples of cryptic camouflage adopted by these insects to escape predators and hunt their prey. Photo by Andrea Mangoni.

Obviously, however, is not only a camouflage to establish the success of these predators: their basic weapon is another fact, an evolutionary ploy that allowed insects are structurally similar to large and placid cockroaches to become very efficient killer. We are talking about the transformation that brought the first pair of limbs of these animals to become raptatorie legs. Coxae long and relatively thin, in fact, bring massive femora with two sets of sharp thorns on the underside, and these in turn are the counterpoint tibiae also equipped with short strong spines, somewhat reminiscent of a set closely the structure of a knife. At rest the legs raptatorie were held in front of or below the chest, folded as in the act of a person who prays, but when the prey is approached within range, they are turned outward at great speed (about one twenty-fifth of a second! ) and trapped in a deadly grip the hapless animal. All of this complex natural weaponry is so efficient to allow the larger species to capture not only insects but also small vertebrates: the American picture of a mantis, a Tenodera aridifolia that captured a small hummingbird did, years ago , around the web.
In fact, the appendices raptatorie turn out to be so efficient that thanks to the pressure of natural selection to be found in very different taxa, a clear sign of convergent evolution. Even among the crustaceans are similar appendages, just think of the shrimp (Squilla mantis ) which are processed chelipedi in appendici raptatorie. Restando invece tra gli insetti, negli emitteri (cimici & Co.) gli arti raptatori sono presenti in diverse  famiglie che comprendono generi predatori, come ad esempio il reduvide Ploiaria domestica o gli esponenti della famiglia dei nepidi, i cosiddetti scorpioni d'acqua, emitteri specializzati nella caccia all'agguato nelle acque interne dalla corrente blanda o nulla.



Sopra, Nepa cinerea , un emittero dulciacquicolo, mentre preda una larva; sotto, Mantis religiosa . La convergenza evolutiva ha portato both of these predatory insects to develop raptatori forelimbs. Photo by Andrea Mangoni.

The environment that organisms elect as their domicile so often direct influence the availability of food resources for organisms, leading to surprising new solutions, even in those animals and plants that we would not have thought capable of such. It 's the case of a small terrestrial gastropods, the pretty Oxychilus draparnaudi , a mollusk that has chosen as a habitat of choice caves. Seeing no one would say the course is different from many other snails, except perhaps for the color of the body, a soft turquoise blue. But habits are Food that makes it special: the snails that are used to seeing because they eat mostly vegetables, but definitely not abound in these caves. So what? Cha road could choose the poor Oxychilus ? The only apparently possible to become an efficient predator. Its radula, that sort of language that characterizes the toothed mouthparts gastropods, is not operated for munching vegetables, but is used instead to break chitinous integument of insects, such as those of a moth that has decided to spend the winter in a cave. So placid dome-cap is covered with the red skin of the wolf and devour the poor insettuccio asleep. A strategy in a certain winner, as the underground, which is certainly not known for its abundance of food!

carvernicola Oxychilus The snail prey to a moth asleep. Photo courtesy of Francis Tomasinelli of Isopoda.net .

And from the caves we pass to another very special environment: peat bogs. Here the food problems do not have animals, as ... plants. Already, in these remarkable places, plants struggle hard to find sufficient nutrients in the soil, especially those from the nitrogen metabolism. What to do? Nothing better, in this case, which actively get their "fertilizer" from the origins, namely capturing small animals that can decompose to provide the plant nutrients it needs. The plant world in this case it is indulged: leaves exuding a kind of glue that traps small insects, leaves, covered with forests, ending with a droplet of sticky hairs that fold with easy to digest the unfortunate animal finished too close, trapping, vegetable shot like that of Dionea, where the simultaneous pressing of at least two of the three hairs in the central part of the leaves causing them to close, or funnel traps of Sarracenia in cui si riesce ad entrare ma non ad uscire, condannati ad affogare e decomporsi nel pozzo costituito da quella foglia modificata che è l'ascidio. E le prede, in questo caso, non sono solo insetti o invertebrati: anche piccoli mammiferi e rettili possono in certi casi fare una fine assai poco piacevole! Se poi volete scoprire in che modo un'apparentemente innocua pianta di patate possa trasformarsi anch'essa in killer, non perdetevi questo bel post di Evolve or Die . Insomma, un vero campionario di efficientissimi predatori vegetali che per una volta sovverte l'ordine con cui siamo abituati a pensare alla catena alimentare.

Ma anche in questo caso l'armata degli invertebrati ha in qualche caso trovato a counter: Malaysia in fact some species of insects and arachnids have evolved the ability to live as good diners at the expense of some plants of the genus Nepenthes . Spiders that weave the fabric nell'ascidio, flies whose larvae develop by filtering the liquid in the plant, invertebrate predators and scavengers insects: a small army of species that did just the old but always apparenentemente winning philosophy of "if you can not beat them, join them ".

Different types of carnivorous plants: Drosera , Dionaea, Sarracenia , Pinguicola . Tanti modi differenti per catturare piccoli animali. Foto di Andrea Mangoni.

BIBLIOGRAFIA

Arrow, G.J. (1951). Horned beetles . Dr. W, Junk, The Hague.

Beaver, R.A. (1979). "Fauna and food webs of pitcher plants" in west Malaysia, in Malayan Nature Journal , 33:1-10.

Eberhard, W.G. (1979). "The function of horns in Podischnus agenor ", in Blum, m & Blum, N. (eds.)  Sexual selection and Reproductive Competition in Insects . Academic Press, New York (231-258).

Mangoni, A. (2006). Beetles. Help and rearing scarabeidi Lucanidi . WILD Edizioni, Milan.
Mogi, M. & Yong, HS (1992). "Aquatic arthropod communities in Nepenthes pitchers: the role of niche differentiation, aggregation, predation and competition in community organization" in Oecologia 90 (2): 172-184.
Pietropaolo, J. & Pietropaolo, P. (1993). Carnivorous Plants of the World . Timber Press inc., Portland.