Neutral nucleotide diversity does not scale with population size as expected, and this ''paradox of variation'' is especially severe for animal mitochondria. Adaptive selective sweeps are often proposed as a major cause, but a plausible alternative is selection against large numbers of weakly deleterious mutations subject to Hill-Robertson interference. The mitochondrial genealogies of several species of whale lice (Amphipoda: Cyamus) are consistently too short relative to neutral-theory expectations, and they are also distorted in shape (branch-length proportions) and topology (relative sister-clade sizes). This pattern is not easily explained by adaptive sweeps or demographic history, but it can be reproduced in models of interference among forward and back mutations at large numbers of sites on a nonrecombining chromosome. A coalescent simulation algorithm was used to study this model over a wide range of parameter values. The genealogical distortions are all maximized when the selection coefficients are of critical intermediate sizes, such that Muller's ratchet begins to turn. In this regime, linked neutral nucleotide diversity becomes nearly insensitive to N. Mutations of this size dominate the dynamics even if there are also large numbers of more strongly and more weakly selected sites in the genome. A genealogical perspective on Hill-Robertson interference leads directly to a generalized background-selection model in which the effective population size is progressively reduced going back in time from the present.
Avian Influenza (AI) viruses have been sporadically isolated in South America. The most recent reports are from an outbreak in commercial poultry in Chile in 2002 and its putative ancestor from a wild bird in Bolivia in 2001. Extensive surveillance in wild birds was carried out in Argentina during 2006-2007. Using RRT-PCR, 12 AI positive detections were made from cloacal swabs. One of those positive samples yielded an AI virus isolated from a wild kelp gull (Larus dominicanus) captured in the South Atlantic coastline of Argentina. Further characterization by nucleotide sequencing reveals that it belongs to the H13N9 subtype. Phylogenetic analysis of the 8 viral genes suggests that the 6 internal genes are related to the isolates from Chile and Bolivia. The analysis also indicates that a cluster of phylogenetically related AI viruses from South America may have evolved independently, with minimal gene exchange, from influenza viruses in other latitudes. The data produced from our investigations are valuable contributions to the study of AI viruses in South America.
). Postmortem examination and pathogen testing were performed on 212 whales; 208 (98.1%) were calvesof-the-year and 48.0% of these were newborns or neonates. A known or probable cause of death was established in only a small number (6.6%) of cases. These included ship strike in a juvenile and blunt trauma or lacerations (n = 5), pneumonia (n = 4), myocarditis (n = 2), meningitis (n = 1), or myocarditis and meningitis (n = 1) in calves. Ante-mortem gull parasitism was the most common gross finding. It was associated with systemic disease in a single 1−2 mo old calf. Immunohistochemical labeling for canine distemper virus, Toxoplasma gondii and Brucella spp., and PCR for cetacean morbillivirus (CeMV), influenza A, and apicomplexan protozoa were negative on formalin-fixed, paraffinembedded lung and brain samples from a subset of whales; PCR for Brucella spp. was positive in a newborn/neonate with pneumonia. Skin samples from whales with gull parasitism were PCR negative for CeMV, poxvirus, and papillomavirus. This is the first long-term study to investigate and summarize notable post-mortem findings in the PV SRW population. Consistent, significant findings within or between years to explain the majority of deaths and those in high-mortality years remain to be identified.
Epibionts and parasites were recovered from the grapsid crabs Cyrtograpsus angulatus and Neohelice granulata in the Bahía Blanca estuary, Argentina. Among epibionts, we identified a filamentous bacterium, the protozoan Epistylis sp., and the copepod Neocancrincola platensis on the gills; and the barnacles Balanus amphitrite and Balanus glandula as well as the bryozoan Conopeum reticulum on the caparace. Among endoparasites, we identified the acanthocephalan Profilicollis chasmagnathi in the hindgut, nematodes of the subfamily Acuariinae and Ascarophis sp. in the haemocoel, and an encysted cyclophyllidean cestode in the gut wall. Among microphallid digeneans, we found four metacercariae: Maritrema bonaerensis in the gills, muscle, haemocoel, and gonads, Maritrema orensensis in the gills, Levinseniella cruzi in the gonads, and Odhneria sp. in the muscle. Except for P. chasmagnathi, N. platensis, and M. bonaerensis, all other epibionts and digeneans represent new host records. This paper also presents novel information regarding the possible sites of infection for M. bonaerensis. Our results add relevant data about possible life cycles of helminths in the study area. RESUMENSe recuperaron epibiontes y parásitos de los cangrejos grápsidos Cyrtograpsus angulatus y Neohelice granulata en el estuario de Bahía Blanca, Argentina. Entre los epibiontes, se identificaron una bacteria filamentosa, el protozoo Epistylis sp. y el copépodo Neocancrincola platensis en las branquias, y los cirripedios Balanus amphitrite y Balanus glandula y el briozoo Conopeum reticulum en el caparazón. Entre los endoparásitos, se identificaron el acantocéfalo Profilicollis chasmagnathi en el intestino posterior, los nematodes Acuariinae y Ascarophis sp. en el hemocele y un cestode cyclophyllideo en la pared intestinal. Entre los digeneos microphallidos, se encontraron cuatro metacercarias: Maritrema bonaerensis en las branquias, el músculo, el hemocele y las gónadas, Maritrema orensensis en las branquias, Levinseniella cruzi en las gónadas y Odhneria sp. en el músculo. Excepto por P. chasmagnathi, N. platensis y M. bonaerensis, todos los otros epibiontes y digeneos representan nuevos registros para los hospedadores. Además, este trabajo presenta nuevos 1 )
This paper presents new records that considerably expand the geographical range of the invasive shrimp Palaemon macrodactylus in Argentina to include new estuarine areas on the Argentine south Atlantic coast: Bahía Samborombón, and the Bahía Blanca and Río Negro estuaries. The latter 2 locations are the southernmost reports for this species. The epibiotic barnacle Balanus amphitrite and a microphallid metacercaria Odhneria sp. are reported for the first time in P. macrodactylus. The prevalence of white spot syndrome virus (WSSV) was 10% in the Bahía Blanca estuary. Our results strongly suggest that WSSV is spreading in crustacean populations in the Argentine Sea and that P. macrodactylus plays a role in the ecology of parasite infections in this environment. MATERIALS AND METHODS Shrimp were sampled between March 2007 andMarch 2011 at 4 sites in Argentina: the Río Salado flood re lief channel (Site 1: 35°50' S, 57°25' W; n = 49) and Tapera de López (Site 2: 36°19' S, 56°46' W; n = 46) in Bahía Samborombón, the Bahía Blanca estuary (Site 3: 38°44' S, 62°22' W; n = 110), and the Río Negro estuary (Site 4: 41°1' S, 62°47' W; n = 1). The first 3 sites are located in the Buenos Aires province, and the fourth site is in the Río Negro province (Fig. 1). Specimens were collected using cast nets and minnow traps baited with fish meat. The specimens were transported alive to the laboratory and kept in small aquaria with seawater. Some ovigerous females were kept alive until their eggs hatched, and the resulting larvae were fixed in 10% formalin for morphological studies.The shrimp were studied alive, killed by freezing, and fixed in 10% formalin until examination for parasites using a stereomicroscope. A total of 20 specimens from Bahía Blanca estuary were examined fresh for the presence of white spots suggestive of WSSV. These specimens were then preserved in 96% ethanol and tested for WSSV using nested PCR. DNA was extracted from the gills using DNeasy kits (Quiagen). PCR amplification was conducted using illustra PuReTaq Ready-To-Go™ PCR Beads (GE Healthcare). Details of the primers and PCR procedures used are de scribed by Martorelli et al. (2010). Unless otherwise stated, throughout the present study, we refer to parasites and pathogens as simply 'parasites'.We deposited voucher specimens from each sampling area in the invertebrate collection of the La Plata Museum (voucher number): Río Salado (26753) and Tapera de López in Bahía Samborombón (26754), Bahía Blanca estuary (26755), and Río Negro estuary (26756). We also deposited one specimen with an epibiont from Tapera de López (26757) and zoea larvae from Bahía Blanca estuary (26758). RESULTSThe present paper presents the southernmost report of Palaemon macrodactylus off the southwestern Atlantic coast. We also report for the first time a helminth parasite and an epibiotic exotic crustacean in P. macrodactylus and provide new data on the prevalence of WSSV in P. macrodactylus from the Argentine Sea. P. macrodactylus individuals, including females bearing ...
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