Biospeleology of the Piemonte
(North-western Italy)

Systematic Photographic
Atlas

   
Web page created and updated by Enrico LANA
   
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An outline of Biospeleology

History

Ecology and environmental factors

Trophic and biospeleological categories

Hypogean evolution

Biogeography


Hypogean evolution

What's the evolution?


The thematic on the evolution is much wide; in the last century has engaged the naturalists giving to biological sciences a strong transformation of thought and a extraordinary development.

It's necessary to dwell first on the meaning of evolution, defined as historical changes, that is in the time, of the whole of the instructions necessary for the formation of an organism; this change is due to the genetic variability and to the environmental selection, for which the descendants of a population are different from their ancestors.

The adaptation is the point of departure of all the evoluzionistic theories and is the main aspect that every theory must explain. In the adaptation is comprised the improvement of the suitability of an organism to its environment and therefore the evolution must be the answer to an environmental change.

As an example, if we consider two species of Coleopters derived from a same ancestor, but today living in different habitats, can be thought that they have had changes and adaptations: differences in the morphology of the exoskeleton, of the length of the legs and antennas, differences in the pigmentation, etc.


The evoluzionistic theories. Two main points of view exist through which it was attempted to explain the mechanisms of adaptation to the environment.

1. The theory of Lamarck presupposes the existence of a natural tendency in the living beings to their improvement, for which the "need" of one determined function would be sufficient to induce the appearance of the organs and the apparatus necessary to execute it: "the necessity creates the organ, the use of an organ leans to perfect it, the disuse leans to regress it". But this theory turned out indefensible. It would be approximately like supposing that an athlete, after to have perfected, by means of suited training, some of his muscular apparatus, suitable to the execution of some kinds of exercises, he have the expectation to generate sons already supplied of those same advantages acquired by him with his activity.

2. According to the theory of Darwin the evolution must be conceived as one consequence of the adaptation of the organisms to the environment. Such evolution is expressed by means of the fight for the existence with the destruction of the individuals less adapted to the environmental conditions and with the survival of the individuals that casually possessed some characteristics that makes them fittest to that determining environment of life.

This concept of evolution that grants a preference to the survival of the individuals more adapted, constitutes one of the more original mechanisms that rewards, through the natural selection in the course of the reproduction, from a part the individuals of a population that possess combinations and characteristics adapted to develop and to multiply in an certain environment in the time, while from the other part, it eliminates the less adaptable ones to the survival in those environmental conditions. Therefore, the exemplary less adapted will be destined to succumb before to reach the reproductive age.

In short the theory of Darwin is founded on these three main factors: individual variability completely fortuitous, natural selection of the fittest characteristics, hereditariness of the advantages achieved through the natural selection.


Mechanisms of hereditariness.
Every living being, to the inside of its cells, has its own genetic code that determines all its characteristics and that contains all the genetic information in the molecule of the DNA (Desoxyribonucleic Acid). The DNA is a macromolecule formed by two long filaments wrapped one on the other to form a double helix and it is normally compacted in the nucleus of every cell to form the chromosomes by means of a most dense and multiple spiralisation of the main filament. One of the fundamental property of the cells is their capability to reproduce themselves. In principle line, all the cells are able of give new generations of cells by means of a duplication process. The cells must have a mechanism for the duplication of the DNA in order to supply to the daughters cells complete copies of their genetic patrimony. In fact, before every cellular division, the two filaments of DNA divide themselves and everyone of they will reconstruct an other complementary filament, reforming the double helix: so we will obtain two daughters cells with a complete genetic patrimony. The genes are parts of DNA that contain all the information that are necessary for to reproduce very precise characters. The changes in the genes are called mutations and are modifications of the sequence of the informations in the DNA, that often provoke the appearance of new property in the organisms. Such changes can be transmitted to the descendants. The genic mutations happen by chance to the inside of a same species (microevolution) and can also be bad for the survival (regressive mutations). Altogether the genetic material of an organism constitute its genome. More exactly the particular whole of genes that codifies a particular individual represents the genotype of that individual. The whole of the physical characteristics with which the genes are manifested in an individual is called phenotype. The phenotype of an organism is not influenced only from the genotype (the whole of genes in the chromosomes), but also by the environment, because the environmental conditions provokes in a certain measure the appearance of particular genes. The variability of the different genotypes, and therefore of the phenotypes of the different members of a species and between different species, mahes possible the evolution. Good part of the evolution is due to the natural selection, the phenomenon for which the living conditions of organisms, with different genotypes and phenotypes, carry some of these to have greater success in the reproduction in comparison with the others ones.

We will spoke of favorable mutations, if to the inside of a species it will increase the number of individuals and these will spread in new environments, and of disadvantageous mutations, if their number will be reduced also until the disappearance.


Factors of selection. The selection factors are multiple, the main ones are:

- temporary environmental modifications (minimal temperatures in the winter or summery maximum temperatures, floodings, drought, chemical composition of waters, glaciations, etc.);

- action of enemies , predators, parasites and pathogenic agents;

- competition in the feeding, in the choice of the territory of life (competition);

- competition in the choice of the partner for the copulation (sexual selection);

All these factors can act in measure much various and several combinations; the "pressure of mutation" or the "pressure of selection" can moreover prevail depending if the genic accidental mutations that make adapted the individuals to the environment are preponderant, or the environmental factors have preponderant selective action on genetically stable individuals.

In conclusion, in the evolutionary history of a species, series of adaptations and selections have been, until reaching the current evolutionary phase, with passing of the millenia. Therefore, the hypogean fauna hasn't entered in cave suddenly, but through a gradual adaptation during million of years. Moreover in much species not yet specialized to the hypogean life, periods of transition or of regression can be observe.


Characteristics of the hypogean living beings

The main characteristics of a hypogean environment are:

1. absence or reduction of the light ;

2. elevated and constant relative humidity ;

3. constant temperature.

These are extreme conditions that cannot not have consequences on the population of a cavity. In fact the extreme conditions of such environment determine different and unusual adaptations.



Absence of light. A consequence is the anophthalmy (the absence of eyes or blindness). According to the more or less marked adaptation to the light absence, various morphologies can be observed in some Coleopters: in the Trechus the functional eyes have a semispherical configuration, in the Duvalius the reduction of the visual organ become much more evident and in the Agostinia genus the eyes are totally disappeared.

Similar examples in arthropodology are a lot, but they are much less in the superior animals: as an example in some bony fish the same cavernicole family comprises both cavernicole species and abysmal ones.

The visual organ occupies in the chromosomes a good part of genetic potential; the elimination of this organ, that don't serves in the caves, represents therefore an earn not indifferent of space on the chromosomes.

The reduction of the visual organs, until to the total anophthalmy, generate the development of other sensory organs in the true cavernicoles. This animals in fact perfect usually the tactile sensibility, as it is demonstrated by the particular development of the specific receptors, like the trichobotres (bristle) of the Pseudoscorpiones or the sensory hairs of the Coleopters and other Insects. The lengthening of the antennas and of special bristles can be observed in this organisms and renders these animals also most sensitive to the minimum airflows.

The legs sometimes are lengthened, while the membraneous wings of the troglobite insects are very reduced or lack at all. The bats, in the absolute dark, orient themselves with the ultrasounds generated by their larinx that rebound on the obstacles and are tapped by their specialized auditory apparatus (a system similar to the sonar called echolocation). In some specialized cavernicole insects appear new organs of sense like the organ of Hamann that is situated on the antennas of some Coleopters Cholevidae and that seems deputy to the perception of the atmospheric humidity variations (hygroreceptor).

Another effect reulting from the total absence of light is the depigmentation (loss of color). Many animals appear white or with light colors (to have the exoskeleton of red or blue color in the hypogean environment it serves very little). For some aquatic Crustaceans as the Niphargus the light can be even lethal. Also with the depigmentation an energetic earn is realized.

Humidity (or dampness). The exoskeleton of many Arthropods is constituted of chitine, an ammino-polysaccaridic substance, that renders it leathery and to whose formation concurs the solar light. For the Arthropods living in the epigean environment an exoskeleton containing a lot of chitine is often an advantage because it defends them from the parasites, the predators and many external physical agents that are absent inside the caves. In the cavernicole Arthropods the exoskeleton often appears reduced; this is an ulterior example of energetic saving, but it involves advantages and disadvantages; the reduction of chitine in the exoskeleton causes a weakening of the spiracles (the openings of the tracheas), which cannot more keep the inner humidity of the organism. The insects, in fact, do not have lungs and their respiration is made by means of the tracheas, small aerial channels that lead oxygen to all the organs through fine ramifications. An epigean insect, placed in an environment with reduced relative humidity, would be exposed to a lethal dehydration without its particular adaptations of the spiracles of the tracheas that are fortified by curious tufts of hairs and without the microscopical structures able to keep the inner humidity. Nevertheless in several cavernicole insects these structures are not more functional and for this in the fossil branches of a hypogean system (with water lack and therefore with scarce humidity) very rarely we can meet living organisms: the fossil cave environment can be azoic (lacking in life).

The humidity, in fact, represents an environmental factor of critical importance for most of the terrestrial cavernicoles, that are in uneasiness conditions as soon as they are removed from an environment almost saturate of aqueous vapor; this is due to the marked stenohygry (minimal endurance of small humidity variations) of these organisms. Just in connection with this fact it would be evolued the pseudophysogastry of some Coleopters, mainly Cholevidae. As an example, in Leptodirus hohenwarti, (the first described blind Cholevidae, discovered in 1831 by Franz von Hohenwart, an Austrian naturalist), the elytras, very developed and knitted between themselves don't serve to cover an big abdomen, but in order to keep an bubble of very humid air useful for short periods in which it is forced to cross zones with low relative humidity.

In the hypogean environment all is turned to an energetic saving. An epigean grasshopper has antennas and legs very different from a hypogean grasshopper. In fact the hypogean fauna has indirectly renounces to several "facilitations" typical of the epigean one (eyes, wings, colors, etc). This genetic saving has been used for the mutations with "facilitations" suitable to lead hypogean life: the lengthening of the antennas and legs is a classic example.

When our home fall in the dark because of a black-out we spontaneously stretch out one's arms in order to sound the ambient around us; the length of the legs and the appendages is without doubt an advantage, and often the antennas and palps of many hypogen arthropods are provided with sensitive apparatus, that is specific structures, as an example, act to locate biochemically the proximity of food or of other individuals of the same or different species. Others sensitive structures can be the silked hairs posizioned in very precise points on the exoskeleton of many Coleopters like in Doderotrechus (troglobite Coleopter Carabidae).

Some insects are sensitive also to more the minimal airflows and are equipped with bristles encircled from cells that inform them in case of dehydration danger. The sense of smell too is very developed. The velocity with which the Leptodirinae, and some aquatic organisms, reach the smelling decoys, also from considerable distances, is a clear indication of their sense of smell.

In a cave we can distinguish predators, detritivores, saprophages and limivores. The feeding is obviously the main problem of a living being and every species, beacuse of the ecological niche that occupies, has an suitable mouth apparatus: we can think to the jaws of the Carabidae or to the mouth apparatus suitable to suck of the Diptera (flies and mosquitos) and of the Lepidoptera (butterflies).

Another morphologic modification in several insects, is the apterism (absence of wings); in the case of the Coleopters it isn't possible to observe it directly because the membraneous wings are covered from elytras of chitine. In the Diptera, instead, with external membraneous wings, the apterism of the cavernicoles is evident, like in Chionea alpina.



We must remember that it's possible to meet epigean Diptera in caves at depths of 800-900 m; this is an demonstration that these bugs have the particular organs that allow them to find one's way in the dark for great distances.

Also the metabolism of the cavernicole fauna has suffered some modifications. As an example the oxygen consumption decrease respect to the surface fauna: the life in the caves is much less animated, there are less predators, less environmental risks, etc.

Lacking the light also the nictemeral and seasonal rhythms vanish; all the biological rhythm suffer a slowing down, in the opinion of some authors, due also to an insufficient and sporadic food regimen.

The more studied physiological adaptations concern the reproduction:

- decrease of the fecundity;

- correlated increase of the volume of eggs and the vitelline reserves;

- decrase of the egg number;

- lengthening of the duration of embryonic and postembryonic development and of the adult life and the entire biological cycle with modifications of the larval cycle (like in the contracted cycle of the Leptodirinae);

- fall of the reproductive regularity or, more frequently, a change of the seasonality determined by the characteristics of the cave.

In the hypogean environment every action is based on the energetic saving; to have too many sons would mean to give life of too many individuals destined to die of hunger: there aren't so many predators like in the epigean environment, isn't necessary the selection in an environment already selective and moreover not would be sufficient maintenance for numerically abundant descendants.

The less prolific animals, are generally those that reserve to the descendants the greater parental cares, and this happens also for some among the more specialized cavernicole insects.

As an example the Cholevidae with globular elytras matures a single egg to the time, two or three in the course of their entire existence, but in compensation they avoid every existential problem to their larvas: the greater part of the juvenile increase is effected inside to the maternal body and the larva, contrarily to what happens in the overwhelming majority of the insect, does not lead active life, but very soon it is transformed in pupa and then in adult.

The cavernicole organisms adopt like survival strategy the K-selection that foresee a delay of the maturation, small litters, abundant parental cares and birth in advanced stages of developement.

A curious case is the reproduction of the bats: the copulation happens at the end of the summer or more frequently in autumn, then follows the dormancy; it would be improper for a female that don't eat to carry forward a gestation; in fact the spermatozoa are kept in the uterus during all the winter and are fed by a nourishing secretion of the uterine epithelium and the fecundation happens only in spring after the beginning of the normal activity.

In the epigean environment the choice of the partner is "made in the sun light": there are courtships, colorful wedding liveries, very remarkable sexual dimorphism.

In the hypogean environment "all is made in the dark", therefore there are biochemical sexual callbacks, that is hormones secreted by specialized glands. As an example, some females of Diplopoda leave as callback a thinnest thread, a slime that the male perceives and follows in the dark for to catch up the female, hoping to find her not yet occupied.

All these mechanisms have made possible the evolution in the underground environments in much different way than in the solar light and we must remember that, in a certain sense, the mammals are the product of a selection happened in the dark for hundred of million years, by night or in natural holes and cavities, in the time when the Earth surface was kept of by the voracious dinosaurs; this fact has allowed them to develop senses and characteristics, as the intelligence, that has made the mammals the organisms with greater evolutionary success during the Tertiary, after the decline of the great reptiles.

 



An outline of Biospeleology

History

Ecology and environmental factors

Trophic and biospeleological categories

Hypogean evolution

Biogeography


    Glossary
bgsound:_J._Pachelbel_-_Three_voices_canon
SPECIFIC
BIBLIOGRAPHY
      
BIOSPELEOLOGICAL
BIBLIOGRAPHY
      
GENERAL
BIBLIOGRAPHY


Biospeleo SUMMARY

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BABEL ALTA VISTA - ON LINE TRANSLATOR

Currently are in course studies that would revalue partially the theory of Lamarck, to molecular level, for which the environment would influence the formation of determined molecules that would favour the organism in the fight for the survival and the genes - that allow the synthesis of such compound - would be genetically transmissible (olistic theory).