Influence of Parasitism on Shoal Choice in the Banded Killifish (Fundulus diaphanus,Teleostei, Cyprinodontidae)

Banded killifish, Fundulus diaphanus, were presented individually with a choice of ‘shoaling’ with either of two conspecific stimulus shoals, one consisting of fish with externally visible black spots (indicating the presence of a parasitic trematode worm, Crassiphiala bulboglossa), the other consisting of fish without such spots. Both parasitized and unparasitized test fish significantly preferred to shoal with unparasitized stimulus shoals over parasitized ones. The relative preference of unparasitized killifish for unparasitized shoals increased with increasing degree of parasite load in parasitized stimulus fish. However, no significant preference by unparasitized fish for unparasitized shoals was observed if unparasitized shoals were presented versus mixed shoals consisting of parasitized and unparasitized fish. We conclude that killifish preferred unparasitized shoals over parasitized shoals only if all fish in the respective stimulus shoals were phenotypically uniform (either with or without black spots). A final experiment showed that killifish used black spots as an indicator of parasite presence to make their shoal choice. The significance of these results for the formation of parasite-assorted shoals is discussed.     

Behaviourally mediated crypsis in two nocturnal moths with contrasting appearance

The natural resting orientations of several species of nocturnal moth on tree trunks were recorded over a three-month period in eastern Ontario, Canada. Moths from certain genera exhibited resting orientation distributions that differed significantly from random, whereas others did not. In particular, Catocala spp. collectively tended to orient vertically, whereas subfamily Larentiinae representatives showed a variety of orientations that did not differ significantly from random. To understand why different moth species adopted different orientations, we presented human subjects with a computer-based detection task of finding and ‘attacking’ Catocala cerogama and Euphyia intermediata target images at different orientations when superimposed on images of sugar maple (Acer saccharum) trees. For both C. cerogama and E. intermediata, orientation had a significant effect on survivorship, although the effect was more pronounced in C. cerogama. When the tree background images were flipped horizontally the optimal orientation changed accordingly, indicating that the detection rates were dependent on the interaction between certain directional appearance features of the moth and its background. Collectively, our results suggest that the contrasting wing patterns of the moths are involved in background matching, and that the moths are able to improve their crypsis through appropriate behavioural orientation.     

Anatomy of the heart of the beluga whale (Delphinapterus leucas)

The heart of the beluga whale (Delphinapterus leucas) is described from the dissection of seven specimens. As in most whales the heart is characterized by a transverse broadness and a flatness of the ventricles from one surface to the other and by an apex formed by both ventricles. Heart size parameters are used for comparison with parameters of other marine and land mammals. The heart width index (heart height/heart circumference) averages 31.3 in comparison to 28.7 for the Weddell seal and 39.0 for the felids. The right ventricle is relatively long and narrow with a mean length index (TS/heart height) of 64.7 and a mean breadth index (TP/heart height) of 38.7. These heart parameters are discussed in functional terms.     

Arterial and venous vasculature of the heart of the beluga whale (Delphinapterus leucas)

The arteries and veins of the heart of the beluga whale (Delphinapterus leucas) are described from the dissection of nine specimens. The arterial distribution is composed of the basic mammalian pattern of two major vessels, the left and right coronary arteries, which supply the cardiac tissue. The venous drainage is provided by three major systems which are the great, middle, and small cardiac veins. The vascular characteristics of the heart of the beluga whale are the marked sinuosity of both coronary arteries and their main branches, the numerous large interarterial anastomoses between major vessels, and the duplication of vessels in parallel branches. These characteristics are discussed in functional terms and correlated with the diving ability of the species.     

The social organization of free-ranging fish shoals

The phenotypic composition of social groups can affect the foraging efficiency and predation risk of their individual members. In shoaling fishes, active choice of shoal companions on the basis of phenotypic characters such as body length has been reported. In this study, we investigated the phenotypic composition of free-ranging, multi-species fish shoals in a temperate freshwater lake. We collected 21 entire shoals, each consisting of up to four species and comprising 3622 fish in total. Shoals were strongly assorted by species, body length, parasite prevalence and parasite load. Using a mark-recapture procedure involving 785 banded killifish ( Fundulus diaphanus ), we found no evidence for shoal fidelity or site fidelity, as individuals from different shoals mixed extensively after just 24 h and ranged all over the study site irrespective of initial capture locations. Killifish showed strong changes in shoal-size choice over 24 h, and no evidence was found that shoals might break up into sub-units of individuals that are more phenotypically assorted than their original shoals. The mechanisms by which assortative groups may arise and the consequences of low group fidelity for the evolution of cooperative behaviour are discussed.     

Mapping studies of the Peach latent mosaic viroid reveal novel structural features

Knowledge of the structure of a viroid is critically important to elucidate the roles played by the various RNA motifs in the steps of the viroid's life cycle. A new technique, RNA-selective 2'-hydroxyl acylation analysed by primer extension (SHAPE), has recently been shown to be fast, reliable and applicable to the study of various RNA molecules. Consequently, this method was used to probe sequence variants of Peach latent mosaic viroid (PLMVd). Initially, probing data from RNA strands of both polarities of the Siberian C variant confirmed the secondary structures previously determined using both conventional and fastidious approaches. Subsequently, analysis of an Alberta variant showed an identical structure for the strand of (-) polarity, but the (+) polarity strand exhibited two differences from the Siberian C variant: the P11-L11 stem-loop domain formed a cruciform structure, and nucleotides from loops L1 and L11 were involved in the formation of a pseudoknot. The existence of both of these motifs was confirmed by site-directed mutagenesis. The subsequent probing of 12 natural sequence variants led to the elucidation of the criteria governing the formation of this novel pseudoknot. Importantly, this study revealed that the heterogeneity of a viroid is not limited to its nucleotide sequence, but may also occur at the structural level.