Despite its inhospitable appearance and lack of any ... - Udine Cultura

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94 ■ Ecology of springs 95 The perennial underground stream of the Pod Lanisce cave (Julian Pre-Alps, Friuli Venezia Giulia) Springs are like windows opening on the underground environment - Botosaneanu, a Romenian researcher, defined them as “the gates to the river Styx”. They are often the only means of analysing aquifers, because they are composed of surfacing groundwater which filters into recharge zones at different times, and reach spring points due to gravity. Springs may therefore be studied from the “outside” to analyse surface organisms colonising the crenal zone (thus, crenobiology), or from the “inside”, to examine the fauna of the aquifers supplying them - the stygian zone (thus, stygobiology). Springs are particular physical environments which have constant temperature over time and sometimes undergo changes in the chemical composition of their waters, due to the nature of the aquifers supplying them. These parameters define extreme natural situations. For instance, according to their thermic regime, there are thermal springs (like those in the Euganean Hills (Veneto), which host an endemic species of gastropods of the genus Heleobia) and glacial ones (such as those in the Adamello-Brenta, between Lombardy and Trentino, which are colonised by endemic stygophilic harpacticoid copepods). Brackish springs are saline (like the Poiano springs in Emilia Romagna, whose exclusive guest is the stygobiotic amphipod crustacean Niphargus poianoi), and those with particular values of pH and hydrogen sulphide, i.e., sulphuric springs, which are found throughout Italy and its islands. ■ Groundwater inhabitants Sulphuric spring: the saline waters of Nirano (Emilia Romagna) The “darkness syndrome”. Contrary to ideas in the past, the underground environment can host great biodiversity. As described in the previous section, groundwater species may be divided into stygoxenes, stygophiles and stygobionts, according to their degree of dependency on this habitat for their survival. Stygobionts are species which are exclusive to groundwater and have developed special adaptations to life in this habitat. All their adaptations
96 Modified sensory setae on the antennule of a male harpacticoid (top: ca. 2000x; bottom: ca. 4000x, photo by SEM, scanning electron microscopy) define the so-called “darkness syndrome”, a condition made up of a series of morphological, physiological and behavioural changes that these species underwent during their evolution in the geological past, which brought their ancestors from surface waters to the underground ecokingdom. According to how species react to the underground environment, adaptations are distinguished from Aesthetasc on antennule of a harpacticoid (ca. 8000x, SEM photo) specialisations. Adaptations are strategies developed by species as responses to what are called the macrodescriptors of the underground environment, like constant darkness and scarce organic matter. Specialisation is the reaction to microdescriptors of the various types of habitats found in the hypogean environment in general. Groundwater organisms are depigmented (white, transparent or translucent), or sometimes pinkish (haematic pigments are visible through their semitransparent bodies), and their visual organs are generally small (microphthalmy) or totally absent (anophthalmy). Clearly, in totally dark environments, there is no advantage in having functioning visual organs or similarly, exhibiting gaudy colours. But it is more complex to understand what the disadvantages could be in maintaining these characteristics, since these same disadvantages often caused them to become extinct over time. Generally speaking, if an organism has a particular feature that is neither an advantage nor a disadvantage, a random neutral mutation may occur, causing that feature to disappear. In addition, if there is also an energy advantage, because during the ontogeny of these structures available energy can be used to develop compensatory sensory structures, then the loss of useless organs also has an adaptive logic. Presumably due to lack of resources, no stygobiont has developed the complex structures typical of animals living in sea abysses (like bio-luminescence). Moreover, pre-adaptive dynamics cannot be ruled out: in surface populations made up of both blind and sighted individuals, spatial segregation of blind phenotypes in groundwater and survival of sighted individuals in surface water may have given rise, over time, to two different, ecologically isolated genotypes. However, the evolutionary dynamics that led stygobionts to lose their eyes are still being discussed, as even within the same species eyes may show different evolutionary stages - for example, in some isopod, amphipod and decapod crustaceans. 97
Page 1 and 2: Fauna FABIO STOCH Despite its inhos
Page 3 and 4: 44 45 Methods for sampling and anal
Page 5 and 6: 48 Shells of gastropods Iglica voba
Page 7 and 8: 52 collected in phreatic waters in
Page 9 and 10: 56 ● Cyclopoid copepods. So far,
Page 11 and 12: 60 those associated with percolatin
Page 13 and 14: 64 Species of genus Niphargus; top:
Page 15 and 16: 68 ■ Decapods Italian fauna has o
Page 17 and 18: 72 Stygofaunal provinces in Italy T
Page 19 and 20: 76 aquifers in the Sabini mountains
Page 21 and 22: 80 ■ The ecology of aquifers Acco
Page 23 and 24: 84 85 The discovery of a new submer
Page 25 and 26: 88 anastomoses, often adjacent to t
Page 27: 92 93 The saline springs of Poiano:
Page 31 and 32: 100 Theoretical evolutionary sequen
Page 33 and 34: 104 Sketch showing degrading phases
Page 35 and 36: 108 109 Stygodiversity in the Presc
Page 37: 112 animal groups still living on t

Despite its inhospitable appearance and lack of any ... - Udine Cultura

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