Mosquitoes pose significant threats to human health because they act as vectors for disease causing viruses and protozoans. Indeed, Aedes aegypti is known as the Yellow Fever Mosquito because of its role as a vector for viral infections that kill thousands of people each year. A more thorough understanding of mosquito physiology will aid development of novel control strategies. Previous work on ion transport across the midgut has been focused primarily on larval A. aegypti, while research on the midgut of the adult stage is less complete. The posterior midgut of the adult female is of particular interest because it is used for the storage and digestion of the blood meal which is required for the production of eggs. This study used an array of electrophysiological methodologies such as the Scanning Ion Electrode Technique (SIET) in order to elucidate the patterns and mechanisms of Na + , H + and K + transport across the posterior midgut at intervals during postprandial diuresis and digestion of the blood meal. Measurements of transepithelial potential indicated that the lumen was at its most negative (-13.2 mV) three hours after the blood meal and then gradually became less negative during the time course of digestion. Na + was absorbed (from lumen to bath) at all intervals after the blood meal (6 min, 30 min, 2h, 24 h); calculations of the electrochemical potential indicated that absorption required active transport. H + absorption at all times (6 min -48 h) after the blood meal was also active (i.e. against the electrochemical gradient for H + ) and was greatly reduced by inhibition of carbonic anhydrase. K + transport across the midgut exhibited two distinct phases. During diuresis, luminal concentrations of K + were in the range 24 -28 mM and secretion into the midgut was opposed by the electrochemical iv gradient, indicating active transport. After diuresis, during blood meal digestion, concentrations of K + in the midgut contents were high (95 -134 mM) and absorption of K + was favoured by the electrochemical gradient. K + absorption was sensitive to the channel blocker Ba 2+ during this period.v Acknowledgements

Whole genome duplication, leading to polyploidy and endopolyploidy, occurs in all domains and kingdoms and is especially prevalent in vascular plants. Both polyploidy and endopolyploidy increase cell size, but it is unclear whether both processes have similar effects on plant morphology and function, or whether polyploidy influences the magnitude of endopolyploidy. To address these gaps in knowledge, fifty-five geographically separated diploid accessions of Arabidopsis thaliana that span a gradient of endopolyploidy were experimentally manipulated to induce polyploidy. Both the diploids and artificially induced tetraploids were grown in a common greenhouse environment and evaluated with respect to nine reproductive and vegetative characteristics. Induced polyploidy decreased leaf endopolyploidy and stem endopolyploidy along with specific leaf area and stem height, but increased days to bolting, leaf size, leaf dry mass, and leaf water content. Phenotypic responses to induced polyploidy varied significantly among accessions but this did not affect the relationship between phenotypic traits and endopolyploidy. Our results provide experimental support for a trade-off between induced polyploidy and endopolyploidy, which caused induced polyploids to have lower endopolyploidy than diploids. Though polyploidy did not influence the relationship between endopolyploidy and plant traits, phenotypic responses to experimental genome duplication could not be easily predicted because of strong cytotype by accession interactions. K E Y W O R D SArabidopsis thaliana, colchicine, endopolyploidy, induced polyploidy, phenotype, polyploidy, trade-off, whole genome duplication | 199 PACEY Et Al.

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PremiseEndopolyploidy is widespread throughout the tree of life and is especially prevalent in herbaceous angiosperms. Its prevalence in this clade suggests that endopolyploidy may be adaptive, but its functional roles are poorly understood. To address this gap in knowledge, we explored whether endopolyploidy was associated with climatic factors and correlated with phenotypic traits related to growth.MethodsWe sampled stem and leaf endopolyploidy in 56 geographically separated accessions of Arabidopsis thaliana grown in a common garden to explore species variation and to determine whether this variation was correlated with climatic variables and other plant traits.ResultsStem endopolyploidy was not associated with climate or other traits. However, leaf endopolyploidy was significantly higher in accessions from drier and colder environments. Moreover, leaf endopolyploidy was positively correlated with apparent chlorophyll content and leaf dry mass.ConclusionsEndopolyploidy may have a functional role in the storage of chloroplasts and starch, and it may offer an adaptive avenue of tissue growth in cold and dry environments.