This paper presents 75 new radiocarbon dates based on late Quaternary mammal remains recovered from eastern Taimyr Peninsula and adjacent parts of the northern Siberian lowlands, Russian Federation, including specimens of woolly mammoth (Mammuthus primigenius), steppe bison (Bison priscus), muskox (Ovibos moschatus), moose (Alces alces), reindeer (Rangifer tarandus), horse (Equus caballus) and wolf (Canis lupus). New evidence permits reanalysis of megafaunal extinction dynamics in the Asian high Arctic periphery. Increasingly, radiometric records of individual species show evidence of a gap at or near the Pleistocene/Holocene boundary (PHB). In the past, the PHB gap was regarded as significant only when actually terminal, i.e., when it marked the apparent ''last'' occurrence of a species (e.g., current ''last'' occurrence date for woolly mammoth in mainland Eurasia is 9600 yr ). However, for high Arctic populations of horses and muskoxen the gap marks an interruption rather than extinction, because their radiocarbon records resume, nearly simultaneously, much later in the Holocene. Taphonomic effects, C 14 flux, and biased sampling are unlikely explanations for these hiatuses. A possible explanation is that the gap is the signature of an event, of unknown nature, that prompted the nearly simultaneous crash of many megafaunal populations in the high Arctic and possibly elsewhere in Eurasia.

f Circoviruses are among the smallest and simplest of all viruses, but they are relatively poorly characterized. Here, we intensively sampled two sympatric parrot populations from Mauritius over a period of 11 years and screened for the circovirus Beak and feather disease virus (BFDV). During the sampling period, a severe outbreak of psittacine beak and feather disease, which is caused by BFDV, occurred in Echo parakeets. Consequently, this data set presents an ideal system for studying the evolution of a pathogen in a natural population and to understand the adaptive changes that cause outbreaks. Unexpectedly, we discovered that the outbreak was most likely caused by changes in functionally important regions of the normally conserved replicationassociated protein gene and not the immunogenic capsid. Moreover, these mutations were completely fixed in the Echo parakeet host population very shortly after the outbreak. Several capsid alleles were linked to the replication-associated protein outbreak allele, suggesting that whereas the key changes occurred in the latter, the scope of the outbreak and the selective sweep may have been influenced by positive selection in the capsid. We found evidence for viral transmission between the two host populations though evidence for the invasive species as the source of the outbreak was equivocal. Finally, the high evolutionary rate that we estimated shows how rapidly new variation can arise in BFDV and is consistent with recent results from other small singlestranded DNA viruses.

Although well known as a widespread parasitic disease of columbids and birds of prey, there have been few studies of trichomonosis in populations of wild birds. In Mauritius, trichomonosis has been highlighted as a major threat to an endangered endemic, the Pink Pigeon (Neosoenas [Columba] mayeri). In this study, we examined the role that populations of other columbids in Mauritius might be playing as infectious reservoirs of the causal flagellate protozoan, Trichomonas gallinae. We screened 296 wild individuals of three columbid species (Madagascan Turtle Dove [Streptopelia picturata], Spotted Dove [Streptopelia chinensis], and Zebra Dove [Geopelia striata]) between September 2002 and April 2004. Prevalence varied significantly among species (ranging from 19% in S. chinensis to 59% in G. striata) and between S. picturata sampled from upland and coastal sites; S. picturata from upland sites (>500 m) were significantly less likely to be infected with T. gallinae than those from lowland sites (<50 m; 62% and 27% prevalence, respectively). There was no significant difference in the prevalence of T. gallinae at sites where Pink Pigeons were also present compared to those sampled at sites without Pink Pigeons. We show that T. gallinae infection prevalence is higher at sites and times of warmer temperatures and lower rainfall.

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