Abstract
Desert locusts (Schistocerca gregaria) show a dramatic form of socially induced phenotypic plasticity known as phase polyphenism. In the absence of conspecifics, locusts occur in a shy and cryptic solitarious phase. Crowding with conspecifics drives a behavioural transformation towards gregariousness that occurs within hours and is followed by changes in physiology, colouration and morphology, resulting in the full gregarious phase syndrome. We analysed methylation-sensitive amplified fragment length polymorphisms (MS-AFLP) to compare the effect of acute and chronic crowding on DNA methylation in the central nervous system. We find that crowd-reared and solitary-reared locusts show markedly different neural MS-AFLP fingerprints. However, crowding for a day resulted in neural MS-AFLP fingerprints that were clearly distinct from both crowd-reared and uncrowded solitary-reared locusts. Our results indicate that changes in DNA methylation associated with behavioural gregarisation proceed through intermediate states that are not simply partial realisations of the endpoint states.
Highlights
Modification of neural DNA by cytosine methylation is emerging as an important mechanism in tailoring behavioural phenotypes to environmental conditions, including the social environment[1,2,3,4]
The DNA in locust central nervous systems is heavily methylated by insect standards: in S. gregaria, methylation occurs on 1.6–1.9% of all genomic cytosines and on over 3% of the cytosines in exons[10,11]
These values are over tenfold higher than in honeybees, where methylation is implicated in caste polyphenism[12,13,14], suggesting that DNA methylation has important functions in locust behaviour
Summary
Long-term gregarious (LTG) locusts were removed from the colony as final larval instars, sexed, and set up as one all-male and one all-female cohort of 40 each in separate tanks (40 × 30 × 25 cm3) in the controlled-environment room that housed the solitarious locusts. There were three treatment groups of four males and four females each: (i) n = 8 1GS locusts that never experienced crowding; (ii) n = 8 LTG locusts; and (iii) n = 8 behaviourally gregarised 1GS locusts. These were produced by placing four male and four female 1GS locusts in the tanks that housed the 40 LTG virgins of the respective sex for 24 h before sacrifice. DNA was extracted with the QIAamp DNA Micro Kit (QIAGEN) following the manufacturer’s instructions
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