Ligula intestinalis (Cestoda: Pseudophyllidea) infection of Engraulicypris sardella (Pisces: Cyprinidae) in Lake Malawi

Fish parasites have diverse ecological impacts on fish populations and are presently becoming useful as bio-indicators of fish migration and feeding. Studies of fish parasite in Lake Malawi severely lag behind the strides made in eco-evolutionary studies of its ichthyofauna. Over a period of eleven months from April 2003, we examined more than 1300 Engraulicypris sardella from Lake Malawi for cestode parasites. About 54 % of the fish had infections of between one and eight Ligula intestinalis plerocercoids. The infection occurred throughout the study period (mean prevalence 59 ±13%) but was most prevalent in December and June and was least prevalent in April. The majority of the hosts (78%) had a light parasite burden (one or two). Parasite prevalence increased with age of the fish. Prevalence and infection intensity oscillated closely with periods of peak abundance of zooplankton, the main food of E. sardella and intermediate hosts (copepods) of L. intestinalis. Increased exposure to the parasite with age aggravated by an ontogenetic diet shift from phytoplanktivory to zooplanktivory may be interacting with fluctuations in zooplankton production in driving the trophic transmission patterns of L. intestinalis in this ecosystem.Keywords: Engraulicypris sardella; Ligula intestinalis; trophic transmission; Lake Malaw

Genetic diversity within the genus Cynotilapia and its phylogenetic position among Lake Malawi’s mbuna cichlids

Cynotilapia’s unicuspid teeth, a unique character used to delineate it from all other mbuna genera, leaves evolutionary biologists wondering which is the closest relative to this genus among mbuna cichlids. This genus has only two described species out of the 10-13 species/taxa, whereby theundescribed taxa are either known by their colouration or place where they occur. AFLP genetic marker was used to determine the phylogenetic position of Cynotilapia among the mbuna and also the genetic diversity within this genus. Nei’s genetic distance, frequency of polymorphic loci and averageheterozygosity were used to unravel the genetic diversity. The neighbour-joining (NJ) dendrogram revealed that the genus Maylandia is the closest relative to Cynotilapia. Genetic distances were higher among all pairs of undescribed taxa than between the two species (Cynotilapia afra vs. C. axelrodi). Frequency of polymorphic loci and average heterozygosity were also higher within undescribed taxa than in two species. These results, coupled with already known phenotypic differences among thesetaxa (including colour, a crucial factor in speciation through sexual selection), do provide a strong base to taxonomists who can formally describe these taxa as species. The uncovered genetic differentiationis very important for conservation of this endemic fish fauna

Taxonomic investigation of the zooplanktivorous Lake Malawi cichlids Copadichromis mloto (Iles) and C. virginalis (Iles)

The taxonomic status of the zooplanktivorous cichlids Copadichromis mloto and C. virginalis has been confused since their original descriptions by lles in 1960. Whilst two forms of C. virginalis, ‘Kaduna’ and ‘Kajose’, were distinguished in the type material, C. mloto has not been positively identified since its original description. Here we re-examined the types as well as 54 recently collected specimens from multiple sampling locations. Genome sequencing of 51 recent specimens revealed two closely related but reciprocally monophyletic clades. Geometric morphological analysis indicated that one clade morphologically encompasses the type specimens of C. virginalis identified by Iles as the Kaduna form, including the holotype, whilst the other clade encompasses not only the paratypes identified as the Kajose form, but also the type series of C. mloto. Given that all three forms in Iles’s type series are from the same locality, that there are no meristic or character states to differentiate them and that there are no records of adult male C. mloto in breeding colours, we conclude that the Kajose form previously identified as C. virginalis represents relatively deeper bodied sexually active or maturing individuals of C. mloto

Natural variation at a single gene generates sexual antagonism across fitness components in Drosophila

Mutations with conflicting fitness effects in males and females accumulate in sexual populations, reducing their adaptive capacity.1,2 Although quantitative genetic studies indicate that sexually antagonistic polymorphisms are common,3-5 their molecular basis and population genetic properties remain poorly understood.6,7 Here, we show in fruit flies how natural variation at a single gene generates sexual antagonism through phenotypic effects on cuticular hydrocarbon (CHC) traits that function as both mate signals and protectors against abiotic stress8 across a latitudinal gradient. Tropical populations of Drosophila serrata have polymorphic CHCs producing sexual antagonism through opposing but sex-limited effects on these two fitness-related functions. We dissected this polymorphism to a single fatty-acyl CoA reductase gene, DsFAR2-B, that is expressed in oenocyte cells where CHCs are synthesized. RNAi-mediated disruption of the DsFAR2-B ortholog in D. melanogaster oenocytes affected CHCs in a similar way to that seen in D. serrata. Population genomic analysis revealed that balancing selection likely operates at the DsFAR2-B locus in the wild. Our study provides insights into the genetic basis of sexual antagonism in nature and connects sexually varying antagonistic selection on phenotypes with balancing selection on genotypes that maintains molecular variation