MEDI: Macronutrient Extraction and Determination from invertebrates, a rapid, cheap and streamlined protocol

Area of Science:

• Ecological biochemistry
• Invertebrate physiology
• Analytical chemistry

Background:

• Macronutrients (carbohydrates, proteins, lipids) are crucial for ecological processes.
• Current methods for macronutrient quantification are time-consuming, costly, and require bulk samples, hindering individual-level analysis.
• There is a need for efficient methods to determine macronutrient content in individual invertebrates.

Purpose of the Study:

• To present a novel protocol, Macronutrient Extraction and Determination from Invertebrates (MEDI), for rapid, direct, and cost-effective macronutrient analysis from single macroinvertebrates.
• To validate the MEDI protocol's accuracy and efficiency for determining protein, carbohydrate, and lipid content.
• To demonstrate the protocol's applicability across a range of invertebrate sizes and for identifying taxonomic differences.

Main Methods:

• Developed a sequential extraction process involving chloroform:methanol solution for lipids and 0.1 M NaOH for tissue solubilization.
• Employed colorimetric assays for the quantification of proteins, carbohydrates, and lipids from the same individual specimens.
• Determined the limits of detection for each macronutrient using standard laboratory equipment.

Main Results:

• The MEDI protocol allows for direct determination of macronutrient content from single macroinvertebrates, including very small specimens (dry mass ~3 mg).
• Established limits of detection: 0.067 mg/ml for proteins, 0.065 mg/ml for carbohydrates, and 0.006 mg/ml for lipids.
• Successfully identified significant taxonomic differences in macronutrient composition among five insect species.
• The protocol enables analysis of over 50 macroinvertebrates within approximately 3 days at a cost of ~$1.35 per sample.

Conclusions:

• MEDI provides a rapid, direct, and cost-effective method for quantifying macronutrients in individual invertebrates.
• This protocol overcomes previous limitations, enabling individual-level ecological and physiological studies.
• MEDI has broad applicability for ecological research requiring precise macronutrient data from small sample sizes.