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In 2002 phocine distemper virus (PDV) reappeared in the European harbour seal (Phoca vitulina) population. This outbreak seems to have followed a similar pattern to the 1988 one which killed almost 60% of individuals in most localities. Harding et al. (2002) suggested that there is a relatively high (18%) risk that recurrent outbreaks of PDV could reduce the European harbour seal population by 90%. We show that incorporating the effects of observation error during population surveys and of the long‐term immunity of survivors of morbillivirus outbreaks indicate a much lower level of risk (<1%). This suggests that, while the immediate effects of the disease are dramatic, it is unlikely that recurrent epidemics will pose serious conservation problems for this species under current conditions.  相似文献   

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The morphogenesis of the stichotrichous ciliate, Neokeronopsis spectabilis, collected from a freshwater pond near Harbin, north China, was observed following protargol impregnation. The overall morphogenetic events are characterized by: (1) the new oral primordium originates in association with the transverse cirri; (2) the proter's undulating membrane anlage is formed following the dedifferentiation of the parental endoral and paroral membranes, while the old adoral zone of membranelles is retained; (3) the fronto-ventral-transverse cirral anlagen originate independently on the right of the proter's undulating membrane anlage; (4) the left and right marginal cirri are derived from new anlagen that originate within the old marginal rows; (5) the generation of the dorsal kineties is of the "two-group-mode" with fragmentation and hence an oxytrichid pattern; and (6) similar to that in oxytrichids, the caudal cirri are formed at the posterior ends of the rightmost and two leftmost kineties of the group 1. Some new morphological data for N. spectabilis are also presented and the systematic position of the genus Neokeronopsis is briefly discussed. We conclude that its position among the urostylids is peripheral and that it very likely represents an intermediate form between the oxytrichids and urostylids.  相似文献   

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This paper comments on an article ''Pigeon homing: evidence against reliance on magnetic information picked up en route at release sites'' by P. Luschi, C. del Seppia, E. Crosio and F. Papi, which appeared in this journal. It is pointed out that the particular effects which these authors show to be stress-induced artefacts are restricted to their specific strain of homing pigeons. The same effects could not be observed in pigeons from two other lofts: a difference in response that was shown to have a genetic base. In view of this, conclusions drawn from the results of Luschi et al. must be restricted to their own findings; they cannot be generalized to the other findings which indicate the use of magnetic outward journey information in young homing pigeons.  相似文献   

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We agree entirely with Arlettaz et al. that we face an environmental crisis of extraordinary proportions. However, their analysis of how to respond perfectly illustrates our point. In particular, we would transpose their statement 'Although we agree that communication strategies must accommodate human psychology to succeed, we believe that neglecting or euphemizing the dramatic impact that humans have on the biosphere, just through fear of the Cassandra syndrome when addressing an inconvenient truth, is not an acceptable alternative discourse.' to 'Although acknowledging the dramatic impact humans exert on the biosphere, there is no acceptable alternative discourse; to adopting communication strategies that accommodate human psychology.'  相似文献   

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