Developmental Changes in Biophysical Properties of Photoreceptors in the Common Water Strider (gerris Lacustris): Better Performance at Higher Cost 2

9 Although dependence of invertebrate photoreceptor biophysical properties on visual ecology has 10 already been investigated in some cases, developmental aspects have largely been ignored due to 11 the general research emphasis on holometabolous insects. Here, using the patch-clamp method, we 12 examined changes in biophysical properties and performance of photoreceptors in the common 13 water strider Gerris lacustris during postembryonic development. We identified two types of 14 peripheral photoreceptors, greenand blue-sensitive. Whole-cell capacitance (a measure of cell 15 size) of blue photoreceptors was significantly higher than the capacitance of green photoreceptors 16 (69 ± 20 vs. 43 ± 12 pF, respectively). Most of the measured morphological and biophysical 17 parameters changed with development. Photoreceptor capacitance increased progressively, and was 18 positively correlated with: sensitivity to light, magnitudes and densities of light-induced (LIC) and 19 delayed rectifier K (IDR) currents, membrane corner frequency and maximal information rate 20 (Spearman rank correlation coefficients: 0.70 (sensitivity), 0.79 (LIC magnitude), 0.79 (IDR 21 magnitude), 0.48 (corner frequency), and 0.57 (information rate). Transient K current increased to 22 a smaller extent, while its density decreased. We found no significant changes in the properties of 23 single photon responses or levels of light-induced depolarization, the latter indicating a balanced 24 Articles in PresS. J Neurophysiol (May 28, 2014). doi:10.1152/jn.00239.2014 Copyright © 2014 by the American Physiological Society. 2 channelome expansion associated with IDR expression. However, the dramatic, ~7.6-fold increase in 25 IDR from first instars to adults indicated a development-related rise in the metabolic cost of 26 information. In conclusion, this study provides novel insights into functional photoreceptor 27 adaptations with development and illustrates remarkable variability in patterns of postembryonic 28 retinal development in hemimetabolous insects with dissimilar visual ecologies and behaviours. 29