Creationism in Crisis - How Watermelons Evolved, With Gene Loss AND Gene Duplication

Cultivated watermelon, Citrullus lanatus

Photo: James E. Scarborough
via Wikipedia Public Domain

Behind the Rind: New Genomic Insights into Watermelon Evolution, Quality, and Resilience - Boyce Thompson Institute

Fig. 6 Fruits types in C. lanatus, C. mucosospermus, C. amarus, and C. colocynthis: a, b C. colocynthis, c C. lanatus subsp. lanatus, d-f C. lanatus subsp. vulgaris, g, h C. mucosospermus, i: Citrullus sp.

Fig. 8 Fruit flesh colour in C. lanatus, C. mucosospermus, C. amarus, and C. colocynthis: a, b C. lanatus subsp. vulgaris, c, d C. mucosospermus, e C. amarus, f C. lanatus

Achigan-Dako, E.G., et al., (2015)

The embarrassment for creationism continues unabated with news that scientists from the Boyce Tompson Institute, Itheca, New York, USA, have worked out how the cultivated watermelon evolved.

This might seem trivial to normal people, but to creationists, it shatters several cherished pieces of dogma and exposes them as bogus.

1. Firstly, the scientists have shown that the process of domestication from wild ancestors included an incident of gene doubling, so creating new genetic information (and increasing the sweetness of the watermelon). Creationists claim there is no mechanism for increasing the information in the genome without the intervention of a magic man doing magic.
2. Secondly, the scientists have also discovered that the process of domestication involved the loss of several genes from the cultivated watermelon genome, yet creationist dogma says all genetic loss is fatal and all mutations are deleterious, and yet here we have an improved cultivar, resulting in millions more watermelons than had the mutations not happened.
3. Thirdly, the Bible claims all life on earth was created by God for its special creation, mankind, and yet here we have evidence that the cultivated watermelon is the result of selective breeding, meaning that, even if we allow for the sake of argument that watermelons were created for mankind, whoever created them didn't do a very good job, or failed to anticipate what humans would require from a watermelon, so we needed to improve on what was provided. Imagine buying an intelligently designed motor car, then finding it needs considerable modification and improvement to make it fit for purpose! Would you buy from that designer again?

That latter point can be made for all domesticated animals, by the way, since very few of them have remained unchanged compared to their wild ancestors.

So, what is the evolutionary history of watermelons?

According to the press release by Aaron Callahan, from the Boyce Thompson Institute :

Watermelon is a globally significant agricultural product, both in terms of the total amount produced and the total economic value generated.

Divergence and genome evolution of watermelon species. Synteny among the genomes of melon, C. colocynthis, C. amarus, C. mucosospermus and C. lanatus.

We aimed to delve deeper into the genetic variations that make watermelons so diverse and unique. Our findings not only provide insights into the evolutionary journey of watermelons but also present significant implications for breeding and disease resistance.

These beneficial genes [lost during evolution] could be reintroduced into modern cultivars to breed more resilient watermelon varieties.

The super-pangenome provides a valuable genetic toolkit for breeders and researchers to improve cultivated watermelon. By understanding the genetic makeup and evolutionary patterns of watermelons, we can develop varieties with enhanced yield, increased disease resistance, and improved adaptability.

Professor Zhangjun Fei, lead author.
Boyce Thompson Institute
Ithaca, New York, USA

Scientists at the Boyce Thompson Institute have constructed a comprehensive “super-pangenome” for watermelon and its wild relatives, uncovering beneficial genes lost during domestication that could improve disease resistance and fruit quality of this vital fruit crop.

The watermelon super-pangenome was built using reference genome sequences and genome resequencing data from 547 watermelon accessions spanning four species – cultivated watermelon (Citrullus lanatus) and its wild relatives C. mucosospermus, C. amarus, and C. colocynthis.

Analyses of the super-pangenome revealed that many disease-resistance genes present in wild species were lost during domestication, as early farmers selected for fruit quality traits like sweetness, flesh color, and rind thickness.

A key discovery of the research, recently published in the Plant Biotechnology Journal, was the identification of a tandem duplication of the sugar transporter gene ClTST2 that enhances sugar accumulation and fruit sweetness in cultivated watermelon. This genetic variant was rare in wild watermelons but was selected during domestication.

Abstract

Cultivated watermelon (Citrullus lanatus subsp. vulgaris) has a narrow genetic base due to domestication and breeding focusing primarily on fruit quality traits. Bitter or bland-tasting wild watermelons, such as C. mucosospermus, C. amarus and C. colocynthis, have been used in watermelon breeding to introduce disease resistance to modern cultivars (Levi et al., 2017). These wild relatives are valuable sources for broadening the improvement potential of cultivated watermelon, providing additional functionally important genes and alleles that are absent in cultivated watermelon. However, the lack of genome sequences of these wild watermelon species has limited their utilization in watermelon breeding.

Wu, S., Sun, H., Gao, L., Branham, S., McGregor, C., Renner, S.S., Xu, Y., Kousik, C., Wechter, W.P., Levi, A. and Fei, Z. (2023),
A Citrullus genus super-pangenome reveals extensive variations in wild and cultivated watermelons and sheds light on watermelon evolution and domestication.
Plant Biotechnol. J.; https://doi.org/10.1111/pbi.14120

Copyright: © 2023 The authors.
Published by John Wiley & Sons, Inc. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)

So, selecting for sweeter watermelons inadvertently gave us watermelons with duplicated genes, but in the process, missing some genes that protected against diseases. Now science has provided the tools to do what any intelligent, omnibenevolent, homophilic designer would have done in the first place, and given us sweet, disease resistant watermelons.

Instead, we have the results of unplanned evolution.

And, as though to add insult to injury, the scientists are in no doubt that the current watermelon genome is the result of an evolutionary process in which no supernatural deities were involved.

Just another of the daily examples of the facts being completely at odds with creationism's counter-factual superstitions.

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