Polyploidy in Daphnia : methodology and effects on life history traits

Abstract

Four arctic, obligate parthenogenetic populations assumed to be polyploid and one temperate, cyclic parthenogenetic, diploid population were used to compare life history traits, growth rates and content of nucleic acids for polyploidy versus diploidy. Cytogenetic studies were done to evaluate the level of ploidy optically or with the aid of optical instruments. A life history experiment was run to identify variations in fitness parameters, fertility, maturation, growth and survival, identifying the adaptive effects and costs of polyploidy. Variations in nucleic acids in polyploids and diploids were accessed by quantifying DNA, RNA and protein. A microsatellite analysis was run to verify the assumed ploidy levels, and species identification was done by sequencing mtDNA and comparing with previously published sequences. The study has a strong focus on assessment of different methods and is in structure affected by this. Microsatellite analysis positively identified the arctic populations as polyploids, and the temperate as diploid. No assessment of the chromosome numbers was reached using cytogenetic analyses. Statistical difference was noted between the nuclei size in the intestine and connective tissue between the diploid and polyploid populations. Polyploid populations were found to have lower population growth, lower fertility, smaller size and delayed maturation, lower growth rate and lower survival than the diploid population. Ploidy level and quantity of nucleic levels and ratios were not found to be correlated, but RNA and DNA per dry weight and RNA/DNA ratio was found to be weakly correlated with specific growth rate when controlled for the ploidy levels.