Evidence of Heritability in Prebiotically Realistic Membrane-Bound Systems

Abstract

The vesicles of short chain amphiphiles have been demonstrated to grow and divide. Here, we explored whether vesicle populations show evidence of heritability. We prepared 1:1 decanoic acid:decylamine vesicles with or without a detergent and in either water or prebiotic soup, a mixture of compounds that might have been present on early Earth. The mixtures were subjected to transfer with dilution, where, after 24 h of incubation (one generation), we transferred 10% of the mix into a 90% volume of a fresh vesicle-containing solution. This was continued for 30 generations. Samples with a history of transfers were compared to no-transfer controls (NTCs), initiated each generation using the same solutions but without 10% of the prior generation. We compared the vesicle size distribution and chemical composition of the transfer samples and NTCs and compared their fluorescence signals in the presence of Nile Red dye. We observe changes in the vesicle size but did not detect differences in the chemical composition. In the samples with detergent and soup, we observed irregular changes in the Nile Red fluorescence, with a tendency for parent and offspring samples to have correlated values, suggestive of heritability. This last result, combined with evidence of temporal autocorrelation across generations, suggests the possibility that vesicles could respond to selection.

Keywords: evolution; heritability; membranes; origins of life; vesicles.

Figure 1

Scheme of the recursive seeding experimental design.

Figure 2

Change in NR fluorescence over generations for samples containing Triton: (A) fluorescence intensity with 640 nm emission (I₆₄₀); (B) ratio of intensity at 610 nm to 660 nm (I₆₁₀/I₆₆₀). The TR/NTC ratio for each measured generation is shown. Stars mark significant (p < 0.05) differences between TRs and NTCs as determined using heteroscedastic t-tests on raw TR and NTC values. Error bars are standard errors (12 replicates per measurement).

Figure 3

Particle size distributions for samples containing Triton. DLS intensity/hydrodynamic radius distributions are shown for selected generations of EPS ((A) generation 1, (D) generation 20, (F) generation 30) and water ((B) generation 9, (C) generation 11, (E) generation 30). Error bars are standard errors across the 10 replicate samples. Data for other generations are shown in Figure S7.

Figure 4

DLS results for samples without Triton. DLS intensity/hydrodynamic radius distributions are shown for selected generations: generation 25, EPS (A) and water (C) and generation 30, EPS (B) and water (D). Error bars are standard errors across 10 replicate samples.

Figure 5

Principal component analysis of the relative abundance of spectral features identified using Compound Discoverer for generation 25 EPS (A,B) and generation 30 EPS (C,D). (A,C) are plots of principal component (PC) 1 vs. PC2; (B,D) are PC3 vs. PC4 (12 replicates per category).