Giovanni Costa

Patterns of Movement

Motility is one of the most characteristic features of animals. Modification of the body for movement in different media represents the main course pursued by biological evolution throughout the animal kingdom. Locomotion allows animals to solve many environmental problems, from self-protection and nutrition to reproduction and social interactions. Movement may be continuous or discontinuous, periodic or aperiodic, individual or collective, small- or large-range, slow or fast. It may involve several mechanisms of orientation, and represents the basis of dispersal and the colonization of new territories.

A ‘mathematical’ spider living on gravel plains of the Namib Desert

Abstract In certain areas of the Namib gravel plains a new Ariadna sp. was discovered. It rims its vertical burrow with a stone circle, made on average of seven quartz stones. Some mathematical relationships between hole diameter, stone sizes and weight, and animal size were studied. A correlation was found, and stone selection by this spider postulated. Different hypotheses on the adaptive value of stone circle are suggested.

Bioaccumulation of trace elements in the sandhopper Talitrus saltator (Montagu) from the Ionian sandy coasts of Sicily.

The Ionian beaches of Sicily are of particular ecological interest because they include the basin of the largest active volcano in Europe and hosts both sites subject to natural protection constraints, as well as important industrial settlements. Consequently, the possibilities for these areas to become polluted are numerous. The sandhopper Talitrus saltator has proven to be a good bioindicator of contamination by numerous trace metals on some European coasts. Nevertheless, no data are available for the populations inhabiting the shores of the southern Mediterranean. Now, as metal accumulation has been shown to vary intraspecifically, the aim of this study was to evaluate trace metal accumulation in adults of T. saltator inhabiting Ionian coastal areas of Sicily and make an assessment of natural and anthropogenic metal pollution of this strip of coast. We also extended our survey to As, Co, Mo, Se, Sn and V never investigated before in this species. Significant differences in metal concentration among sites were found in both sand samples and amphipod tissues. The highest metal content was observed near the mouth of Simeto, the longest river of Sicily which collects waters coming from the volcanic territory of Mount Etna. The bioaccumulation of Cd, Cu, Hg and Zn in T. saltator is fully confirmed; it is also proven for As and Mo and assumed for Cr, Fe, Mn and V. Our outcomes let us to evaluate the prevailing influence of telluric contamination of the Ionian sandy shores of Sicily by trace metals. We also come to the conclusion that in the northern sites, pollution originates from volcanic emission while anthropogenic influence prevails in the southern ones.

Opening and closing of burrows by the Namibian spider Ariadna sp. (Araneae: Segestriidae) in a year of heavy rainfall

Abstract The Ariadna spiders (Araneae: Segestriidae) inhabiting the gravel plains of the Central Namib Desert construct individual burrows with a circular entrance surrounded by a ring of small pebbles; sometimes they close their burrows by a small stone. In the lichen fields, about 20 km east of Walvis Bay (Namibia), there is a consistent population of Ariadna spiders that can also use pieces of lichen both in the ring composition and as the plug when the burrow is closed. We sampled and monitored 175 burrows repeatedly between December 1999 and August 2000. In March 2000, an exceptionally high rainfall occurred in the Namib, leading to flooding even in our fieldwork station. We tested whether and to what extent an event of this magnitude could affect burrow closing. We found the rain event increased burrow closure by large, but not small or medium-sized, Ariadna sp. We suggest that the flooding event acted as an ecological resource pulse for these spiders.

Exploitation of Food Resources

The exploitation of adequate food resources by animals is fundamental to life in every environment. From the trophic point of view, animals can be regarded as specialists or generalists. Specialists are monophagous or oligophagous species, i.e. they feed on one or only a few types of nourishment. Such animals may survive thanks to a marked ability to locate and utilize particular food. They are endowed with precise, genetically controlled systems to recognize nourishment. Moreover, they possess endogenous mechanisms which define the timing and duration of feeding. Their trophic patterns are usually invariable and, therefore, not susceptible to potential improvement by learning. In contrast, generalists are polyphagous, often omnivorous species (Fig. 45). They have a varied diet, based upon high nutritional versatility. Thus, they do not suffer from occasional or periodic shortage of food. Moreover, they are prone to investigate new trophic opportunities and, therefore, discover and learn to use new kinds of nourishment; they also explore and colonize new habitats.

The ground beetle Parallelomorphus laevigatus is a potential indicator of trace metal contamination on the eastern coast of Sicily

Carabids are generally considered to be non-specialized predators, and they have been considered useful ecological indicators. They can play a key role in clarifying the route of contaminants in food webs because they are predators of small invertebrates and, in turn, part of the diet of several vertebrates. The Mediterranean species Parallelomorphus laevigatus, which so far has not been studied from an ecotoxicological point of view, is an excellent ecological indicator in sandy coastal environments. We investigated the accumulation of trace elements in Ionian populations of P. laevigatus and evaluated the transfer of metal through the food chain of the coastal ecosystem. We analyzed 15 metals, including 11 essential metals (Co, Cr, Cu, Fe, Mn, Mo, Ni, Se, Sn, V and Zn) and four toxic metals (As, Cd, Hg and Pb). Significant differences were found in metal concentration in animal tissues among sites. Our results support the existence of defense mechanisms for the studied species. High values of As, Cd, Cr, Pb, Ni, and Hg detected in the beetles from the control site can be explained by both the emission sources from the nearby industrial plants and the intense agricultural activity. The present paper shows increasing Hg concentrations in the simplified trophic web of sandy beaches and confirms the capability of this pollutant to biomagnify. Moreover, the high value of biomagnification factor (BMF) points to the severe pollution level in this protected area.

The chorion of eggs in a Namibian Ariadna species (Araneae: Segestriidae): morphological and SEM analyses

Abstract Morphological and SEM analyses were carried out on the chorion of freshly laid eggs, eggs at different time intervals after oviposition and after hatching of a Namibian segestriid spider Ariadna sp. The eggs laid in the laboratory are held together by a milky-white mucous secretion that gradually decreases until it almost entirely disappears. The eggs are spherical/ellipsoid in shape and, only after the reduction of the secretion, are granular structures of the exochorion evident. Granules are arranged in a single layer and lie on a compact endochorion covering the thin vitelline membrane. No significant difference was found in the chorion of hatched eggs compared to eggs a few hours after oviposition.

Biotope and Vegetation Features

From a study of the surface of our planet, about one third of all the land consists of territories with distinctively arid features (Fig. 1). Deserts form a very heterogeneous whole due to the differing climatological and geological histories of each of them. Scientists agree that aridity is the common denominator. Nevertheless, there is some disagreement about the way in which temperature, scarcity of rainfall, evaporation, etc. interact in causing desert conditions. Moreover, the criteria used to grade various arid regions of the Earth and to determine their limits are very subjective.

Self-Protective Mechanisms

All the behavioural patterns that preserve animals from environmental challenges should be included in this chapter. Many of these, however, have already been described in the preceding chapter. Therefore, only the ethological mechanisms which maximize protection from predators will be treated. This can be achieved by several strategies, in which morphological and behavioural features concur. Various expressions have been employed by students of animal behaviour to describe them. Not surprisingly, therefore, a certain confusion of terms exists. Expressions such mimicry, protective resemblance, camouflage, masking, homochromy, concealment, crypsis, adaptive colouration, protective colouration, etc. are not always used correctly (Cloudsley-Thompson 1986). Therefore, I will give my own opinion on this matter.