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The composition of fish communities of nine Ethiopian lakes along a north-south gradient: threats and possible solutions
No full textFish populations of nine Ethiopian freshwater lakes were quantitatively sampled with a standardized protocol, using multi-mesh gill nets. In total, 27 species were identified, but only 14 species were common. Based on the common species, the fish communities showed large differences in their species composition, except for Lake Abaya and Lake Chamo which were similar. Most fish species were observed in only one or two lakes. Compared with the information reported in literature the present study generally underestimated the species richness. The empirical model of Amarasinghe and Welcomme (2002) for African lakes was used to estimate fish species richness, which was compared with species presence reported in literature. Biodiversity in the two northern highland lakes is low, but not lower than the model estimate. Lake Tana has a high biodiversity which is close to what is estimated by the model, but three Rift Valley lakes have low biodiversity, lower than estimated by the model. There are also strong indications for the Rift Valley lakes that species richness was higher in the past because the species richness reported in the older literature was generally much higher than those observed by us in the present study and those reported in the more recent literature. Threats like overfishing, high sediment load and degradation of habitats were identified. It is recommended that Ethiopia should develop guidelines for fishery legislation and implement it through an enforcement agency. Moreover, catchments management should be practiced to save the water bodies and their fish communities.
Host behaviour and physiology underpin individual variation in avian influenza virus infection in migratory Bewick's swans
No full textIndividual variation in infection modulates both the dynamics of pathogens and their impact on host populations. It is therefore crucial to identify differential patterns of infection and understand the mechanisms responsible. Yet our understanding of infection heterogeneity in wildlife is limited, even for important zoonotic host–pathogen systems, owing to the intractability of host status prior to infection. Using novel applications of stable isotope ecology and eco-immunology, we distinguish antecedent behavioural and physiological traits associated with avian influenza virus (AIV) infection in free-living Bewick's swans (Cygnus columbianus bewickii). Swans infected with AIV exhibited higher serum δ13C (−25.3 ± 0.4) than their non-infected counterparts (−26.3 ± 0.2). Thus, individuals preferentially foraging in aquatic rather than terrestrial habitats experienced a higher risk of infection, suggesting that the abiotic requirements of AIV give rise to heterogeneity in pathogen exposure. Juveniles were more likely to be infected (30.8% compared with 11.3% for adults), shed approximately 15-fold higher quantity of virus and exhibited a lower specific immune response than adults. Together, these results demonstrate the potential for heterogeneity in infection to have a profound influence on the dynamics of pathogens, with concomitant impacts on host habitat selection and fitness.
Las proyecciones de población como método estadístico
No full textLa estructura del trabajo es la siguiente. En la sección 2 se introduce el proceso de evento. Se trata de un solo proceso con un resultado. Se describen las principales
características del proceso y se utiliza la microsimulación para determinar la distribución de los tiempos de espera de los acontecimientos. En la sección 3, se considera un proceso recurrente con múltiples eventos. La ocurrencia de un evento no implica el final del proceso, sino la entrada a un nuevo estado. En un proceso recurrente, un estado se puede visitar más de una vez (repetidamente). En el estudio de estos procesos, la tasa
de evento se llama, generalmente, tasa de transición ya que un evento es una transición de un estado a otro. La sección 4 es la conclusión.
Cladoceran community composition in tropical semi-arid highland reservoirs in Tigray (Northern Ethiopia): a metacommunity perspective applied to young reservoirs
No full textA field survey of zooplankton communities was carried out in 32 recently established tropical semi-arid reservoirs in the highlands of Northern Ethiopia with the aim to identify to what extent environmental factors determine species composition of the cladoceran community in such isolated and young reservoirs. To address seasonal variation, the survey was carried out both at the beginning and the end of the dry season. A total of 15 species of cladocerans were identified. Daphnia was the most abundant cladoceran genus, and was present in all reservoirs. Using presence–absence data, no association between cladoceran community composition and geographic distance was found. RDA results indicate that the set of environmental variables that explained cladoceran community composition differed among seasons. Depth, altitude and fish biomass showed a significant association with cladoceran community composition during the wet season, whereas variation in cladoceran community structure was associated with phytoplankton biomass in the dry season. The relative abundance of Daphnia was much higher in the pelagic than in the littoral zone of our study systems. Two key groups of pelagic filter-feeding cladocerans, Diaphanosoma and Daphnia, showed a clear pattern, in which one or the other tended to strongly dominate the community. In addition, we observed a negative association between dominance of Daphnia in the zooplankton community and dominance of cyanobacteria in the phytoplankton community.
Consequences of constitutive and induced variation in the host’s food plant quality for parasitoid larval development
No full textConstitutive and induced changes in plant quality impact higher trophic levels, such as the development 27
of parasitoids, in different ways. An efficient way to study how plant quality affects parasitoids is to 28
examine how the parasitoid larva is integrated within the host during the growth process. In two exper- 29
iments, we investigated the effects of varying nutritional quality of Brassica oleracea on parasitoid larval 30
development inside the host, the diamondback moth (Plutella xylostella). First, we compared larval 31
growth of the specialist Diadegma semiclausum and the generalist Diadegma fenestrale, when the host 32
was feeding on Brussels sprout plants that were either undamaged or were previously induced by cater- 33
pillar damage. Larvae of the generalist D. fenestrale showed lower growth rates than larvae of the special- 34
ist D. semiclausum, and this difference was more pronounced on herbivore-induced plants, suggesting 35
differences in host-use efficiency between parasitoid species. The growth of D. semiclausum larvae was 36
also analyzed in relation to herbivore induction on Brussels sprouts and on a wild B. oleracea strain. Par- 37
asitoid growth wasmore depressed on induced than on undamaged control plants, andmore on wild cab- 38
bage than on Brussels sprouts, which was largely explained by differences in host mass. The effects of 39
induction of wild Brassica on parasitoid development were pronounced early on, but as P. xylostella feed- 40
ing began inducing the previously undamaged control plants, the effect of induction disappeared, reveal- 41
ing a temporal component of plant–parasitoid interactions. This study demonstrates how insights into 42
the physiological aspects of host–parasitoid interactions can improve our understanding of the effects 43
of plant-related traits on parasitoid wasps.
The Development of a Genome Wide SNP Set for the Barnacle Goose Branta leucopsis
No full textMigratory birds are of particular interest for population genetics because of the high connectivity between habitats and populations. A high degree of connectivity requires using many genetic markers to achieve the required statistical power, and a genome wide SNP set can fit this purpose. Here we present the development of a genome wide SNP set for the Barnacle Goose Branta leucopsis, a model species for the study of bird migration. We used the genome of a different waterfowl species, Mallard Anas platyrhynchos, as a reference to align Barnacle Goose second generation sequence reads from an RRL library and detected 2188 SNPs genome wide. Furthermore, we used chimeric flanking sequences, merged from both Mallard and Barnacle Goose DNA sequence information, to create primers for validation by genotyping. Validation with a 384 SNP genotyping set resulted in 374 (97%) successfully typed SNPs in the assay, of which 358 (96%) were polymorphic. Additionally, we validated our SNPs on relatively old (30 years) museum samples, which resulted in a success rate of at least 80%. This shows that museum samples could be used in standard SNP genotyping assays. Our study also shows that the genome of a related species can be used as reference to detect genome wide SNPs in birds, because genomes of birds are highly conserved. This is illustrated by the use of chimeric flanking sequences, which showed that the incorporation of flanking nucleotides from Mallard into Barnacle Goose sequences lead to equal genotyping performance when compared to flanking sequences solely composed of Barnacle Goose sequence.