Bruno Cicolani

Global diversity of water mites (Acari, Hydrachnidia; Arachnida) in freshwater

The Hydrachnidia (water mites) represent the most important group of the Arachnida in fresh water. Over 6,000 species have been described worldwide, representing 57 families, 81 subfamilies and more than 400 genera. The article analyzes extant water mite diversity and biogeography. Data on distribution and species richness of water mites are substantial but still far from complete. Many parts of the world are poorly investigated, Oriental and Afrotropical regions in particular. Moreover, information among different freshwater habitats is unbalanced with springs and interstitial waters disproportionately unrepresented. Therefore, more than 10,000 species could be reasonably expected to occur in inland waters worldwide. Based on available information, the Palaearctic region represents one of the better investigated areas with the highest number of species recorded (1,642 species). More than 1,000 species have been recorded in each of the Neotropical (1,305 species) and Nearctic regions (1,025 species). Known species richness is lower in Afrotropical (787 species) and Australasian (694 species) regions, and lowest in the Oriental region (554 species). The total number of genera is not correlated with species richness and is distinctly higher in the Neotropical (164 genera); genus richness is similar in the Palaearctic, Nearctic and Australasian regions (128–131 genera) and is lower in the Afrotropical and Oriental regions with 110 and 94 genera, respectively. A mean number of about three genera per family occur in the Palaeartic, Nearctic and Oriental while an average of more than four genera characterizes the families of Australasian and Afrotropical regions and more than five genera those of the Neotropical. Australasian fauna is also characterized by the highest percentage of endemic genera (62%), followed by Neotropical (50.6%) and Afrotropical (47.2%) regions. Lower values are recorded for the Palaearctic (26.9%), Oriental (24.4%) and Nearctic (21.4%). The Palaearctic and Nearctic have the highest faunistic similarity, some minor affinities are also evident for the generic diversification of Holarctic and Oriental families. The faunas of Southern Hemisphere bioregions are more distinct and characterized by the presence of ancient Gondwanan clades with a regional diversification particularly evident in the Neotropics and Australasia. This scenario of water mite diversity and distribution reflect the basic vicariance pattern, isolation, phylogenetic diversification, recent climatic vicissitudes and episodes of dispersal between adjacent land masses together with extant ecological factors can be evoked to explain distribution patterns at a global scale.

The intrinsic rate of natural increase in dung macrochelid mites, predators of Musca domestica eggs

Abstract Capacity for increase in 7 species of macrochelid mites is compared with that of Musca domestica, whose eggs are natural food for these mites. We used the parameter Γm, defined as the infinitesimal rate of increase in a population with a stable age distribution, to determine all the characteristics of a Malthusian population, since it represents all functions affecting natality and mortality rates. The experiments were conducted within an optimum range based on parameters, such as the rate of oviposition and the duration of preimaginal development. Given the particular features of macrochelid biology, such as facultative larviparity and arrhenotoky, special expedients were introduced to estimate Γm rather than the usual methods used in demographic research. The results obtained over a period of 10 years indicate most macrochelids are predators and reduce the numbers of their prey. They play an important part in the natural control of Musca domestica.

Macrochelid mites (Acari: Mesostigmata) occurring in animal droppings in the pasture ecosystem in central Italy

Abstract Coprophilous predatory mites of the family Macrochelidae are often associated with the manure of domestic animals and other sites where there are accumulations of dung and organic matter. Interest has recently been renewed in macrochelid mites because of the following results: (1) their synanthropic habits; (2) the potential use of synanthropic flies as biological control agents; (3) the introduction of exotic species for the biological control of pest flies. The results obtained in Italy from some species of fimicolous Macrocheles tested in laboratory conditions and pastoral settings indicate: the eggs and larval stages of Musca domestica are natural food for macrochelid mites and therefore there is a significant control of fly populations; different strategies of macrochelid mites (species r and K selected) inhabiting the manure of domestic animals and pastoral droppings; a number of instances of phoresy and hyperphoresy; and a succession of macrochelid mites and other invertebrates in pastoral settings and their importance in recycling nutrients. The use of natural ‘natagonists’ which live in manure together with further study of the ecology of these species in the Mediterranean area is recommended.

Diversity, distribution and ecology of water mites (Acari: Hydrachnidia and Halacaridae) in high Alpine lakes (Central Alps, Italy)

Information on water mite assemblages from high elevation lentic biotopes is scant. A survey of 14 small Alpine lakes located between1900 and 2400 m a.s.l. in Italy resulted in the discovery of 17 species of Hydrachnidia and a single species of freshwater Halacaridae. Arrenurus conicus and Lebertia tuberosa were the most widespread and abundant species; Lebertia sefvei, Lebertia rufipes, Oxus setosus, Panisus torrenticolus and Sperchon glandulosus were also widely distributed but relatively less abundant. Atractides fissus and Arrenurus conicus are recorded for the first time from Italy. In contrast to mid/low elevation lakes and ponds, water mite assemblages of alpine lakes are less diverse and are composed mainly of rheo- and crenobiontic taxa, most of which are cold-stenothermic. Typical standing water dwellers represented only a small fraction (23%) of the species sampled. A principal component analysis conducted on lake environmental variables resulted in a clear separation of the lakes mainly based on ionic contents, pH and temperature. Water mites seem to be less influenced by these factors than by temperature fluctuations and habitat stability and heterogeneity. We conclude with some considerations of the influence of abiotic and biotic factors on the altitudinal and latitudinal distribution pattern of water mites.

Influence of aperiodic summer droughts on leaf litter breakdown and macroinvertebrate assemblages: testing the drying memory in a Central Apennines River (Aterno River, Italy)

Climate changes, geomorphologic modifications and the rise in water demand for human uses contribute to “aperiodic summer drought” (ASD) events in Mediterranean-type rivers. ASD results in a reach that flows in one summer, dries in next or more summers, and then flowing again. The ecological structure and function of streams affected by ASD are understudied, especially with respect to permanent and regular intermittent streams. We tested the drying memory in a reach of Aterno River (Italy) disturbed by ASD. Leaf litter breakdown of Phragmites australis and macroinvertebrate assemblages were studied. Discharge was monitored since 2006. The experiment was performed during summer 2010 using the litterbag technique, and was replicated four times. The disturbed site was affected by drought in the three previous summers while the control was always flowing. Taxonomic diversity indices, abundance and structure of macroinvertebrate assemblages varied significantly between sites. Instead, leaf litter breakdown wasn’t influenced by ASD. Therefore ASD events seem to affect the structure of macroinvertebrate assemblages, confirming the role of drying memory of the systems. The resilience of leaf litter breakdown in reach affected by ASD seems to be high, probably depending on the activity of selected microbial communities and macroinvertebrate features like metabolism and biomass.

Fine-scale differences in diel activity among nocturnal freshwater planarias (Platyhelminthes: Tricladida)

Background Although most freshwater planarias are well known photonegative organisms, their diel rhythms have never been quantified. Differences in daily activity rhythms may be particularly important for temperate-climate, freshwater planarias, which tend to overlap considerably in spatial distribution and trophic requirements. Methods Activity of stress-free, individually tested young adults of three common planarian species was recorded at 3-h intervals in a 10-d experiment under natural sunlight and photoperiod during autumnal equinox (D:L ~12:12). Individual activity status was averaged over the 10-d experiment, each tested individual thus serving as a true replicate. Twelve individuals per species were tested. Food was provided every 36 h, resulting in alternating day- and nighttime feeding events. Activity during the first post-feeding h was recorded and analyzed separately. Statistical procedures included ANOVAs, correlations, and second-order analyses of angles. Results Dugesia (= Girardia) tigrina Girard 1850 exhibited clear nocturnal behavior, Dugesia (= Schmidtea) polychroa Schmidt 1861 was predominantly but not exclusively nocturnal, and Polycelis tenuis Ijima 1884 was relatively more active from midnight through noon. Species-specific activity peaks were statistically similar, with peaks at dawn for P. tenuis and just before midnight for the two dugesiids; however, D. tigrina was comparatively more active in the early night hours, while D. polychroa was more active than D. tigrina during daytime. D. tigrina also responded less readily to daytime food addition. P. tenuis remained poorly active and unresponsive throughout the experiment. Individual variability in diel behavior was highest for D. polychroa and lowest for D. tigrina. P. tenuiss general low degree of activity and late activity peak in the experiment may be related to a strong reliance on external stimuli. Conclusions The tested species are mainly nocturnal, consistent with their photonegative characteristics. The fine-scale differences in diel behavior among these three triclad species may not be sufficient to allow coexistence in the wild, with the nonnative D. tigrina eventually displacing D. polychroa and P. tenuis in many European waters. The link between planarian diel rhythms and ecological characteristics are worth of further, detailed investigation.

Planarian ( Dugesia polychroa ) predation on freshwater gastropod eggs depends on prey species, clutch morphology, and egg size

Though triclad planarias could limit littoral snail recruitment by preying on eggs with their muscular ventral pharynx, planarian predation on eggs has never been quantified. Intact egg clutches encompassing eight snail species x three developmental stages were offered to Dugesia (= Schmidtea) polychroa (Paludicola: Dugesiidae) individuals (body length = 6-12 mm) in one-on-one, no-choice 24-h feeding trials to gain a first insight on snail egg palatability to dugesiid planarias. Predatory losses were quantified as differences in planaria-present trials v.s. parallel planaria-absent controls. D. polychroa predation on snail eggs was generally low. Eggs in monolayered, flat clutches of bithyniids (Bithynia leachii) and planorbids (Planorhis planorbis, Helisoma trivolvis, and Planorbarius corneus) were more susceptible to planarian predation than multilayered eggs in sausage-shaped clutches of physids (Physa acuta) and lymnaeids (Lymnaea stagnalis, Radix auricularia, and Stagnicola fuscus). Planarian predation also was higher on smaller eggs, and was not related to planarian body size. Vulnerability was also markedly species-specific, with appreciable losses recorded only for pre-hatching eggs of P. planorbis and, to a lesser extent, H. trivolvis. The results suggest that, with the possible exception for the soft-clutch, small eggs of P. planorbis, predation by D. polychroa on eggs does not impact gastropod recruitment appreciably.

Water mites (Acari: Hydrachnidia, Halacaridae) from the hyporheic habitat of the Mugnone stream (Tuscany, Italy)

The interstitial fauna of a small Apennine stream was investigated over a one year period. Special attention was given to the water-mite taxocoenosis in relation to abundance, diversity and ecological specialization. Seventeen water mite species (Hydrachnidia and Halacaridae) were collected. Eight species are reported for the first time from Italy and one was new to science. Presence and abundance of the species along the stream were analyzed and discussed. Anthropogenic perturbations of the aquatic ecosystem, natural variation of flow regime and the type of groundwater circulation seem to affect presence and distribution of species. The same factors could also be responsible for the numerical predominance of Halacaridae in the first layers of interstices. As reported from similar habitats, water mites show unique features amongst aquatic invertebrates, being amongst the most diverse and specialized meiofaunal groups. This, combined with the complexity of their life cycle, may make water mites a model taxocoenosis for the description and understanding of aquatic communities.