RT Journal Article
SR Electronic
T1 The effect of ethanol concentration on the preservation of insects for biodiversity studies
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 2020.03.05.978288
DO 10.1101/2020.03.05.978288
A1 Daniel Marquina
A1 Fredrik Ronquist
A1 Piotr Łukasik
YR 2020
UL http://biorxiv.org/content/early/2020/03/06/2020.03.05.978288.abstract
AB Traditionally, insects collected for scientific purposes have been dried and pinned, or preserved in 70% ethanol. Both methods preserve taxonomically informative exoskeletal structures well. Highly concentrated ethanol (95-100 %), preferred as a DNA preservative for molecular biology, has generally been assumed to make specimens brittle and prone to breaking. However, systematic studies of the correlation between ethanol concentration and specimen preservation are lacking.Here, we tested how preservative ethanol concentration in combination with different sample handling regimes affect the integrity of seven insect species representing four orders, and differing substantially in the level of sclerotization. After the treatments, we counted the number of appendages (legs, wings, antennae or heads) that each specimen had lost.We found that high ethanol concentrations indeed induce brittleness in insects. However, the magnitude and nature of the effect varied strikingly among species. In general, ethanol concentrations at or above 90 % made the insects more brittle and resulted in more shriveling, but insects with more robust or sclerotized exoskeletons actually retained more of their appendages at high concentrations. Surprisingly, neither freezing the samples nor drying the insects after immersion in ethanol had a negative effect on the loss of appendages. However, the morphology of the insects was severely damaged if they were allowed to dry.While higher ethanol concentrations might positively affect long-term DNA preservation, there is a clear trade-off between collecting and preserving insects for morphological examination and genetic analysis, since the optimal ethanol concentration for the latter is detrimental for the former and vice versa. The trade-off needs to be considered in large insect biodiversity surveys and other projects aiming to combine molecular work with traditional morphology-based characterization of the samples.