Snake fangs from the Lower Miocene of Germany: evolutionary stability of perfect weapons

There is a general consensus that most of today’s nonvenomous snakes are descendants of venomous snakes that lost their venomous capabilities secondarily. This implies that the evolutionary history of venomous snakes and their venom apparatus should be older than the current evidence from the fossil record. We compared some of the oldest-known fossil snake fangs from the Lower Miocene of Germany with those of modern viperids and elapids and found their morphology to be indistinguishable from the modern forms. The primary function of recent elapid and viperid snake fangs is to facilitate the extremely rapid, stab-like application of highly toxic venoms. Our findings therefore indicate that the other components of the venom-delivery system of Early Miocene vipers and elapids were also highly developed, and that these snakes used their venom in the same way as their modern relatives. Thus, the fossil record supports the view that snakes used their venoms to rapidly subdue prey long before the mid-Tertiary onset of the global environmental changes that seem to have supported the successful radiation of venomous snakes.     

Monitoring of iodinated X-ray contrast media in surface water

A monitoring programme was carried out in order to determine iodinated X-ray contrast media (ICM) in the River Danube and to investigate the raw water quality for drinking water production at Langenau waterworks. The study revealed that the maximum concentrations of ICM (over 500 ng l(-1) for diatrizoic acid and iopamidol) were found in 2h-composite samples taken from the downstream of the Ulm/Neu-Ulm metropolitan area. By means of a concentration profile over one month the highest ICM concentrations were observed on weekdays. The extended data evaluation with principal component analysis shows that the upstream and downstream samples had different pattern of variations in ICM concentration and also demonstrates a clear change in ICM composition by the discharge of municipal wastewater. In addition to load profiles of ICM, time-dependent plots of principal component 1 exhibited peaks, indicating a short-term discharge of ICM between the two sampling sites. In conclusion, a point source for ICM contamination between the sampling sites in Ulm upstream and Leipheim downstream seems to be the reasonable explanation for peak ICM concentrations. Due to the observed high variations of ICM concentrations in river, the evaluation of natural waters by means of a single analysis is not representative.     

Aristolochic acid content of South-East Asian troidine swallowtails (Lepidoptera: Papilionidae) and of Aristolochia plant species (Aristolochiaceae)

Summary. Analysis of South-East Asian troidine swallowtails revealed high variability in the content of aristolochic acids among individuals. The presence or absence of these compounds depends on the Aristolochia species available as food plant for the larvae. Only one plant species (Aristolochia philippinensis) contained a high concentration of aristolochic acids, while other species from various localities contained none or only marginal amounts. Whether aristolochic acids have a distinct function in chemical defense of these swallowtails is still an open question. Received 11 December 2000; accepted 4 August 2001.     

Spermatozoan ultrastructure and spermatogenesis in aplousobranch ascidians,with some phylogenetic considerations

Spermatozoa and some stages of spermatogenesis were studied for four species of aplousobranch ascidians. Spermatozoa of Clavelina lepadiformis (Müller) (family Clavelinidae) are plesiomorphous in that they have apical acrosomal vesicles and a moderately elongated, cylindrical nucleus. The elongated mitochondrion is twisted ea. 11/2 times around the nucleus. In their ultrastructural morphology, C. lepadiformis sperm conform in some respects to the least-derived ascidian sperm, those of the phlebobranch ascidian Ciona intestinalis L.; however, the sperm of Clavelina lepadiformis have two apomorphies not shared with those of Ciona sp.: (1) the mitochondrion of Clavelina lepadiformis is long and spiralled along the entire nucleus rather than being comparatively compact and not at all helical; (2) the mitochondrial cristae are elongated parallel to the long axis of the nucleus, whereas in Ciona sp. sperm the cristae are unmodified. In Distaplia sp., Aplidium sp. and Synoicum pulmonaria (Ellis and Solander) the spermatozoa are more derived and consist of a proximal cylindrical and a distal corkscrew-like part. The mitochondrion in Distaplia sp. and Aplidium sp. contains electron-dense material and extends in a long thread around the nucleus. In S. pulmonaria the mitochondrion surrounds the anterior part of the nucleus in mature spermatozoa, and an elongated, dense structure displaying fine striation is enclosed in the mitochondrion in late spermatids. The sperm ultrastructural morphology observed in this study is consistent with the majority view that clavelinids are closest to the ancestral ascidian but is also consistent with other conclusions, particularly that the Cionidae are closest to the stem ascidian.     

Zoogeography of Northwest Atlantic opisthobranch molluscs

Currently available information on the distribution of species of the opisthobranch orders Cephalaspidea, Nudibranchia and Sacoglossa (Mollusca: Gastropoda) in the northwest Atlantic Ocean is presented. Except for Sacoglossa, the fauna is markedly amphiatlantic, but the temperate West Atlantic component increases southward and dominates south of New Jersey. Species' diversity of nudibranchs and cephalaspids on the continental shelf decreases between northern New England and Cape Hatteras in association with a southward decline in the proportion of amphiatlantic species. This is not evident for the cephalaspids of the continental slope, a higher percentage of which are amphiatlantic. The entire fauna is subdivided into 5 groups: arctic, boreo-subarctic, boreal, West Atlantic temperate, and West Atlantic tropical. The latter does not extend north of Cape Hatteras, but the remaining groups broadly overlap in the northwest Atlantic. The southward limits of amphiatlantic species are presented and related to sea surface temperatures. The thermal characteristics of a critical zone between Cape Cod and Connecticut are discussed, and a maximum temperature of 15 °C is suggested for successful reproduction of the boreo-subarctic component, and 25 °C for the boreal component. The distribution of boreal species on both sides of the North Atlantic is discussed, and a suggestion is made that the southward speread of these species in North America is limited by extreme summer warming south of New Jersey, despite favorable winter temperatures, which extend much farther south.Contribution No. 66 of the Marine Research Laboratory, University of Connecticut, USA.     

Adaptive behaviour of chironomid larvae (Chironomus riparius) in response to chemical stimuli from predators and resource density

Chemical-mediated effects of predatory fish on chironomid larvae behaviour have been ignored so far. Sediment-dwelling chironomid larvae inhabit protective burrows from which they extend their bodies only to feed on deposited detritus and microalgae from the surrounding sediment. Here, we performed factorial laboratory experiments to study whether fish-borne chemical cues (kairomones) are responsible for behavioural trait changes of chironomid larvae, and whether chironomid larvae are able to assess the densities of fish predators and food resources and the trade-off between them. We exposed naïve Chironomus riparius larvae to the chemical presence of zero, one, and ten predator fish (Rutilus rutilus) and offered two resource levels (low food, high food) for each treatment. Kairomones induced significant inherent behavioural trait changes in chironomid larvae. During the first 120 min after exposing chironomids to fish-conditioned water, we found a significant increase in digging activity with increasing predator density. After 3 days of exposure, the deepest chironomid burrows were found in treatments with the highest predator density. Chironomid larvae were significantly able to adjust their foraging behaviour to different predator densities and food concentrations and trade off between them; that is, when fish predators were more abundant or when more food resources were available, the foraging activities of larvae were significantly reduced. Our data suggest that chemically mediated trait changes (burrowing and foraging behaviour) may cascade through the littoral food web.