Desiccation resistance: effect of cuticular hydrocarbons and water content in Drosophila melanogaster adults
- Published
- Accepted
- Subject Areas
- Ecology, Entomology, Genetics
- Keywords
- insect, drosophila, selection, dehydration, cuticle, fat body, desaturase
- Copyright
- © 2018 Ferveur et al.
- Licence
- This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ Preprints) and either DOI or URL of the article must be cited.
- Cite this article
- 2018. Desiccation resistance: effect of cuticular hydrocarbons and water content in Drosophila melanogaster adults. PeerJ Preprints 6:e3501v1 https://doi.org/10.7287/peerj.preprints.3501v1
Abstract
Background.The insect cuticle covers the whole body and all appendages and has bi-directionnal selective permeability: it protects against environmental stress and pathogen infection and also helps to reduce water loss. The adult cuticle is often associated with a superficial layer of fatty acid-derived molecules such as waxes and long chain hydrocarbons that prevent rapid dehydration. The waterproofing properties of cuticular hydrocarbons (CHs) depend on their chain length and desaturation number. Drosophila CH biosynthesis involves an enzymatic pathway including several elongase and desaturase enzymes.
Methods.The link between desiccation resistance and CH profile remains unclear, so we tested (1) experimentally selected desiccation-resistant lines, (2) transgenic flies with altered desaturase expression and (3) natural and laboratory-induced CH variants. We also explored the possible relationship between desiccation resistance, relative water content and fecundity in females.
Results.We found that increased desiccation resistance is linked with the increased proportion of desaturated CHs, but not with their total amount. Experimentally-induced desiccation resistance and CH variation both remained stable after many generations without selection. Conversely, flies with a higher water content and a lower proportion of desaturated CHs showed reduced desiccation resistance. This was also the case in flies with defective desaturase expression in the fat body.
Discussion. We conclude that rapidly acquired desiccation resistance, depending on both CH profile and water content, can remain stable without selection in a humid environment. These three phenotypes, which might be expected to show a simple relationship, turn out to have complex physiological and genetic links.
Author Comment
This is a submission to PeerJ for review.
Supplemental Information
Survival in flies of different ages and mating statuses
We determined the survival curve of virgin (dashed lines) and mated (plain lines) females (A) and males (B) of different ages (measured at the beginning of the desiccation experiment): 1 day old (cyan), 3-4 day-old (green) and 7-8 day-old (magenta). The LT50 (C) and slope (D) corresponding to the different conditions is shown below the survival curves. N = 5-8. For parameters and statistics, see legend to Fig. 2.
Survival in F1-F6 males of selected lines
Male flies were selected using the experimental procedure described in Figs. 1 and 2. (A) For each generation (F1 to F6), the curves represent the cumulative lethality measured in various genotypes (dashed = Di2, cyan = 77S selected lines pooled, magenta = backcross between 77S females and unselected sibling males). At F1, three selected lines are shown. (B) At each generation, the two box-plots represent LT50 and lethality slope using colors similar to those of the corresponding genotypes. After excluding extreme outliers using Tukey's method, LT50 and slopes were tested using Kruskall-Wallis test completed by a Conover-Iman multiple pairwise comparison (p=0.05, with a Bonferroni correction) or with a Mann-Whitney test. Stars or different letters indicate significant differences for either parameter. (***: p<0.001; **: p<0.01; *: p<0.05). N = 6-13 (except for 5S line at F1: N = 3).
Principal cuticular hydrocarbon levels in flies of selected lines after relaxation of selection
CH levels were measured in F7, F8 and F9 females and in F8 males separately in the six 77S lines (77S0-77S5) produced by selection for desiccation resistance (Fig. 4). Absolute (Q in µg; A) and relative (%; B) amounts of desaturated CHs (alkenes; top of each panel) and of linear saturated CHs (alkanes; bottom). N = 5-20. For statistics, CHs and lines, see legends to Figs. 2, 4 & 5. The flies tested here correspond to those shown in Fig. 4.
Principal cuticular hydrocarbon levels in females of selected lines between F18 and F57
In F18, F19, F55 and F57 females of various selected lines, the absolute (Q in µg; A) and relative (%; B) amounts of desaturated CHs (alkenes; top of each panel) and of linear saturated CHs (alkanes; bottom) were measured. N = 7-38. For statistics, CHs and lines, see legends to Figs. 2, 4 & 5. The flies tested here correspond to those shown in Fig. 5.
Fecundity and sex-ratio in the progeny of selected lines at F57
The progeny of individual mated females from the control Di2 line and from selected (77S1-5) and reselected (77S-Sel1-3) lines for increased desiccation resistance was counted to determine their respective fecundity (number of adults left) and the sex ratio (Female : Male). Data were tested using a Kruskall-Wallis test completed by a Conover-Iman multiple pairwise comparison (p=0.05, with a Bonferroni correction). N = 5-20. No significant difference was detected except for 77S3 females, which showed increased fecundity and for 77S-Sel 3 which showed a decreased sex-ratio.
Principal cuticular hydrocarbon levels in various desat1 transgenic females
CHs were measured in transgenic female progeny of mothers carrying a UAS-desat1-IR transgene (IR) and fathers either carrying each desat1 putative regulatory region fused with Gal4 (PRR-Gal4) corresponding to each desat1 transcript (RA, RC, RE, RB, RD, RDiO), or the complete desat1 regulatory region (6908bp = 6908; a, b). Di2, Di2W and Di2-IR control females were also tested (left box plots) either at F55 (a) or at F57 (b). Control genotypes carrying one copy of each PRR-Gal4 or the 6908 transgene were also tested (c). The absolute (Q in µg; A) and relative (%; B) amounts of desaturated CHs (alkenes; top of each panel) and of linear saturated CHs (alkanes; bottom) are shown. N = 8-12. For more information on statistics, CHs and lines, see legends to Figs. 2, 4 & 7. The flies tested here correspond to those shown in Fig. 8.
Fecundity and sex ratio in the progeny of various desat1 transgenic females
Total adult progeny (A, C) and progeny sex ratio (B, D) of individual mated females of experimental (A, B) and control (C, D) genotypes (see Fig.S5 legend). N = 7-12 For more information on statistics and lines, see legends to Figs. 2, 7 & Fig. S5.