Ultrastructure of Enteromyxum leei (Diamant, Lom, & Dyková, 1994) (Myxozoa), an Enteric Parasite Infecting Gilthead Sea Bream (Sparus aurata) and Sharpsnout Sea Bream (Diplodus puntazzo)

ABSTRACT. The ultrastructure of the developmental stages of the myxozoan Enteromyxum leei parasitizing gilthead seabream ( Sparus aurata ) intestine and sharpsnout sea bream ( Diplodus puntazzo ) intestine and gallbladder are described. The earliest stage observed was a small dense trophozoite located among enterocytes. Proliferative stages, observed intercellularly in the epithelium of the intestine and gallbladder as well as in the lumen, possessed the typical cell-in-cell configuration throughout their development. Secondary cells were seen undergoing division within a common vacuolar membrane that also encompassed pairs of tertiary cells. Cytochemical studies showed that primary cells stored mainly lipids whereas secondary cells stored abundant β-glycogen granules. Sporogonic development resembled that described for other disporous myxozoans. Within sporogonic stages, nonsporogonic secondary cells were observed accompanying two developing spores. Mature spores had a binucleated sporoplasm in which glycogen stores were abundant and no sporoplasmosomes were found. Our observations are discussed in relation to our knowledge on other myxozoans of the genus Enteromyxum .     

Camouflage and escape decisions in the common chameleon Chamaeleo chamaeleon

In species with reduced locomotory abilities, camouflage seems to be far more important than other behavioural tactics (e.g. running) to elude predatory attacks. In this study, we examined the effects of camouflage on escape decisions in the common chameleon Chamaeleo chamaeleon. The effectiveness of camouflage was assessed by the ability of humans to detect different sized chameleons placed on different backgrounds (vegetation of high and low density, defined here as open and dense bushes), both in the field and in photographs. Escape behaviour was analysed by simulating a predator attack (in our case, approach by a human). As expected, the probability of detection by a potential predator was size- and background dependent. In the field, detection time (but not distance) was significantly higher for chameleons of a given size perched on dense (Myoporum) than open (Retama) bushes. When using photographs, the probability of detection was higher for large (adult) chameleons perched on open (Retama or Nerium) bushes and lower for hatchlings perched on dense (Myoporum or Cupressus) bushes. Con-spicuousness greatly influenced the escape tactics of individuals. Chameleons perched on more protected Myoporum allowed closest approach distances than those perched on less protected Retama. In general, antipredatory responses (defined here as 'first movement', 'fléeing', 'mouth opening' or 'free falling') occurred significantly earlier in the trial sequence in chameleons perched on clear Retama than those perched in Myoporum. Two antipredatory responses were size-dependent: juveniles and adults exhibited 'mouth opening' more frequently than hatchlings whereas 'free falling' was more frequently recorded for hatchlings. Our results suggest that size and vegetation greatly influence the risk of detection by predators and this variation influences an individual's decision about when and how to escape     

Do all Blackcaps Sylvia atricapilla show winter site fidelity?

Fidelity to previous wintering areas (i.e. site fidelity) has important ecological and evolutionary implications. However, since the percentage of recaptures of ringed birds at the same wintering area in subsequent years does not allow the estimation of the proportion of birds alive that exhibit site fidelity, previous studies on different passerine species have failed to show the true extent of this site fidelity. Here we use a recent approach, based on the comparison of survival rate estimates from capture-recapture data at single field stations with recovery data from a much larger area. The idea is to determine the proportion of birds still alive that return to the area. The study was carried out on the Blackcap Sylvia atricapilla , comparing the capture-recapture data of two field stations (Pilas [SW] and Tiana [NE]) situated 1000 km apart in Spain with the complete winter recovery data of the Spanish Ringing Office. Totals of 1936 and 3976 Blackcaps were ringed at Pilas (1981–1986) and Tiana (1975–1986), respectively, and the numbers of recaptures in subsequent winters were 94 and 34. The pooled annual survival rate estimation based on the two sites is 0.40 (s.e. = 0.05). The annual survival rate estimated from the Spanish ringing recovery data was 0.48 (s.e. = 0.08), which is not significantly different. We can conclude, therefore, that migrant Blackcaps in Spain, if alive, tend to return year after year to the previous wintering site.     

Climate increases regional tree-growth variability in Iberian pine forests

Tree populations located at the geographical distribution limit of the species may provide valuable information about tree‐growth response to changes on climatic conditions. We established nine Pinus nigra, 12 P. sylvestris and 17 P. uncinata tree‐ring width chronologies along the eastern and northern Iberian Peninsula, where these species are found at the edge of their natural range. Tree‐growth variability was analyzed using principal component analysis (PCA) for the period 1885–1992. Despite the diversity of species, habitats and climatic regimes, a common macroclimatic signal expressed by the first principal component (PC1) was found. Moreover, considering the PC1 scores as a regional chronology, significant relations were established with Spanish meteorological data. The shared variance held by the tree chronologies, the frequency of narrow rings and the interannual growth variability (sensitivity) increased markedly during the studied period. This shows an enhancement of growth synchrony among forests indicating that climate might have become more limiting to growth. Noticeably, an upward abrupt shift in common variability at the end of the first half of the 20th century was detected. On the other hand, moving‐interval response functions showed a change in the growth–climate relationships during the same period. The relationship between growth and late summer/autumn temperatures of the year before growth (August–September, negative correlation, and November, positive correlation) became stronger. Hence, water stress increase during late summer previous to tree growth could be linked to the larger growth synchrony among sites, suggesting that climate was driving the growth pattern changes. This agrees with the upward trend in temperature observed in these months. Moreover, the higher occurrence of extreme years and the sensitivity increase in the second half of the 20th century were in agreement with an increment in precipitation variability during the growing period. Precipitation variability was positively related to tree‐growth variability, but negatively to radial growth. In conclusion, a change in tree‐growth pattern and in the climatic response of the studied forests was detected since the mid‐20th century and linked to an increase in water stress. These temporal trends were in agreement with the observed increase in warmer conditions and in precipitation variability.