Autosomal differences between males and females in hybrid zones: a first report from Barbus barbus and Barbus meridionalis (Cyprinidae).
(65/1318)
Narrow hybrid zones are generally subjected to the action of two forces: dispersal, which tends to homogenise the hybridising taxa, and selection against hybrids, which, in contrast, produces steep clines of introgression for diagnostic markers. Although differences between sexes in dispersal abilities or in susceptibility to hybrid counterselection are common in hybrid zones, autosomal genetic differences between males and females have never been reported to our knowledge. Barbus barbus and Barbus meridionalis (Cyprinidae) form a hybrid zone along the Lergue river. By carrying out a genetic analysis of males and females in six samples from two central stations of the hybrid zone using codominant markers (six allozymes and four microsatellite loci), we revealed significant multilocus and monolocus differences between the sexes. This could reflect a genetic difference among sexes within a same cohort, caused either by a survival (or fertility) differential among sexes or by a sex-specific pattern of dispersal. Alternatively, this may be due to genetic differentiation between cohorts, since male and female barbel exhibit different maturation, growth and survival patterns leading to different age distributions among sexes, and particularly among reproducers. (+info)
Multiple mating and reproductive skew in Trinidadian guppies.
(66/1318)
Male offspring production in promiscuously mating species is typically more skewed than female offspring production. It is therefore advantageous for males to seek as many mating partners as possible. However, given the documented benefits of polyandry we expect females, as well as males, to mate multiply. We tested these ideas using Trinidadian guppies, Poecilia reticulata. Fishes were collected from the wild, housed in groups of 10 males and 10 females and allowed to reproduce freely over a period of three months. We used hypervariable microsatellite loci to identify the parents of 840 offspring and to quantify the variance in mating success. As anticipated, and in line with the Bateman gradient, there was greater skew in the number of progeny produced by males. By contrast, we found no sex difference in mating partner number over the duration of the experiment. A median of two males fathered each brood and there was marked turnover in the identities of the sires of successive broods. Female partner turnover was, however, less than expected under random mating. We suggest that partner switching over time, as well as polyandry within broods, could contribute to the maintenance of genetic diversity in guppy populations. (+info)
Mitochondrial diversity analysis of Glossina palpalis gambiensis from Mali and Senegal.
(67/1318)
West African riverine tsetse populations of Glossina palpalis gambiensis Vanderplank (Diptera: Glossinidae) were investigated for gene flow, inferred from mitochondrial diversity in samples of 69 flies from Senegal and 303 flies from three river drainages in Mali. Four polymorphic mitochondrial loci were scored. Mean haplotype diversities were 0.30 in Mali, 0 in Senegal and 0.18 over both Mali and Senegal. These diversities estimate the probabilities that two randomly chosen tsetse have different haplotypes. Substantial rates of gene flow were detected among flies sampled along tributaries belonging to the river basins of the Senegal, Niger, and Bani in Mali. There was virtually no gene flow between tsetse in Senegal and Mali. No seasonal effects on gene flow were detected. The implications of these preliminary findings for the implementation of area-wide integrated pest management (AW-IPM) programmes against riverine tsetse in West Africa are discussed. (+info)
Paragonimus ohirai metacercariae in crabs collected along the Arakawa River in Tokyo, Japan.
(68/1318)
Brackish water crabs infected with Paragonimus ohirai metacercariae have been reported in various regions in Japan. However, infected crabs have not been identified in Tokyo. We therefore collected the crab, Chiromantes dehaani, between August 2002 and July 2003 from 12 locations along the Arakawa River that flows through Tokyo. Of the 922 captured crabs, 177 (19%) from 6 locations were infected with Paragonimus metacercariae. The prevalence of metacercariae at these 6 locations ranged from 5 to 89%. The number of metacercariae per infected crab ranged from 1 to 190, with an average of 13.1. The morphological features of the metacercariae and of adult worms recovered from test rats infected with metacercariae showed that the metacercariae in the infected crabs were P. ohirai Miyazaki, 1939. The ITS2 sequence data support this conclusion. This paper is the first description of P. ohirai infection of crabs in Tokyo. (+info)
Amazonian ecology: tributaries enhance the diversity of electric fishes.
(69/1318)
Neotropical rivers support a diverse array of endemic taxa, including electric fishes of the order Gymnotiformes. A comprehensive survey of the main channels of the Amazon River and its major tributaries (>2000-kilometer transect) yielded 43 electric fish species. Biogeographical analyses suggest that local mainstem electric fish diversity is enhanced by tributaries. Mainstem species richness tends to increase downstream of tributary confluences, and species composition is most similar between tributaries and adjacent downstream mainstem locations. These findings support a "nodal" or heterogeneous model of riverine community organization across a particularly extensive and diverse geographical region. (+info)
Selection on insect immunity in the wild.
(70/1318)
The strength of selection on immune function in wild populations has only been examined in a few vertebrate species. We report the results from a study measuring selection on a key insect immune enzyme, phenoloxidase (PO), in a wild population of the damselfly Calopteryx xanthostoma. We followed individually marked males from the pre-reproductive adult phase and recorded their lifetime mating success. We found positive selection on PO activity in response to an immune insult, but no selection on wing-spot quality, a trait actively displayed to females during courtship. We suggest that positive selection on PO activity in the year of study may be explained by annual fluctuations in parasite loads. (+info)
Population control of the malaria vector Anopheles pseudopunctipennis by habitat manipulation.
(71/1318)
Insect vector-borne diseases continue to present a major challenge to human health. Understanding the factors that regulate the size of mosquito populations is considered fundamental to the ability to predict disease transmission rates and for vector population control. The mosquito, Anopheles pseudopunctipennis, a vector of Plasmodium spp., breeds in riverside pools containing filamentous algae in Mesoamerica. Breeding pools along 3 km sections of the River Coatan, Chiapas, Mexico were subjected to algal extraction or left as controls in a cross-over trial extending over 2 years. Initial densities of An. pseudopunctipennis larvae were directly proportional to the prevalence of filamentous algae in each breeding site. The extraction of algae brought about a striking decline in the density of An. pseudopunctipennis larvae sustained for about six weeks, and a concurrent reduction in the adult population in both years of the study. Mark-release experiments indicated that dispersal from adjacent untreated areas was unlikely to exert an important influence on the magnitude of mosquito control that we observed. Habitat manipulation by extraction of filamentous algae offers a unique opportunity for sustainable control of this malaria vector. This technique may represent a valuable intervention, complimenting insecticide spraying of households, to minimize Plasmodium transmission rates in Mesoamerica. (+info)
The initial epidemiological studies in the low endemicity schistosomiasis area in Esteio, Rio Grande do Sul, the southernmost Brazilian state, 1997 to 2000.
(72/1318)
Nor Biomphalaria glabrata neither Schistosoma mansoni were reported from Rio Grande do Sul, the southernmost Brazilian state before 1997. Their detection next to the Sinos River, Esteio, confirmed predictions of schistosomiasis expansion to the south. Parasitological examinations both in snails and fecal samples from the human population were performed from 1997 to 2000. The last 3 out of 5 surveys were performed after a preliminar serological screening procedure in a risk group identified at a population census. A total of 11 infected individuals were found infected and snails from 2 different sites were positive for S. mansoni. Samples from these 2 and other sites were identified as B. glabrata. Egg counts in feces were below 1 per gram in 6 out of 11 patients. Some socio-cultural perceptions of water contact activities next to the Sinos River may cause difficulties to control efforts, but they also may be partially acting against a very rapid increase in transmission intensity. The southernmost schistomiasis mansoni foci in Americas rise the alert for its ongoing expansion. (+info)