Is horizontal gene transfer common in multicellular organisms?

How common is horizontal gene transfer in multicellular organisms?

Horizontal gene transfer (HGT) is a well-established and frequent driver of evolution in bacteria, but in multicellular eukaryotes (plants, animals, fungi) it is much less common and often debated. The strongest evidence comes from specific, well-documented cases. For instance, a 2022 study discovered at least 54 instances of a mobile DNA element called BovB being transferred from snakes to frogs, with a striking geographic hotspot in Madagascar [2]. Another study found that parasitic nematomorph worms have acquired numerous host-derived genes, which are likely used to manipulate the behavior of their insect hosts [3]. These examples show that HGT can and does happen, but they are exceptions rather than the rule.

In contrast, a 2024 review argues that the overall frequency of HGT in eukaryotic nuclear genomes is low because the selective pressures that favor it in bacteria (like rapid adaptation to antibiotics) are weaker in most multicellular organisms [4]. Furthermore, a 2026 perspective paper warns that many reported cases of HGT in plants may be artifacts of flawed methods, and that alternative evolutionary explanations (like gene loss or convergent evolution) can often explain the same data [1]. So while HGT is real in multicellular life, it is not a dominant force like it is in the microbial world.

What are the best-documented cases of HGT in multicellular organisms?

The most convincing examples of HGT in multicellular organisms often involve parasites, close physical contact, or mobile genetic elements. The snake-to-frog BovB transfer is a standout: researchers found that the element jumped from snakes to frogs at least 54 times over the past 85 million years, and the transfer was especially common in Madagascar, likely because of parasite vectors [2]. Another compelling case is in nematomorph worms (horsehair worms), which acquire genes from their insect hosts. A 2023 study found that these host-derived genes are often turned on during the parasite's manipulation of the host's behavior, suggesting HGT provides the molecular toolkit for this bizarre 'mind control' [3].

In plants, a 2021 review notes that HGT is 'very common in nature and concerns all living organisms including plants,' but the evidence is often based on sequence similarity that can be misleading [6]. A concrete functional example comes from the soil-dwelling springtail Folsomia candida, which acquired a bacterial gene for digesting plant material. When the gene was expressed in the lab, it produced a working enzyme, proving the transfer was functional [8]. Similarly, a 2021 study found that fungi have acquired methionine sulfoxide reductase genes from bacteria on several occasions, helping them manage oxidative stress [7]. These cases show that HGT can provide new, useful abilities, but they are scattered across the tree of life rather than being a universal phenomenon.

Why is HGT so much rarer in multicellular organisms than in bacteria?

The main reason is that multicellular eukaryotes have a separated germline (reproductive cells) and a more complex cellular architecture, making it harder for foreign DNA to enter and become inherited. Bacteria, by contrast, readily swap genes via conjugation, transformation, and transduction, and they lack a separated germline. A 2024 review explains that while eukaryotes do have unique features like phagocytosis (engulfing other cells) that could increase HGT, the selective advantage of acquiring new genes is often lower because multicellular organisms rely more on mutation and sexual reproduction for variation [4].

Additionally, the methods used to detect HGT in eukaryotes are prone to error. A 2026 perspective on plant HGT points out that many candidate genes may actually be the result of gene duplication, loss, or contamination, and that rigorous controls are often missing [1]. This means the true rate of HGT in multicellular organisms is likely lower than many early studies claimed. In contrast, in bacteria, HGT is so common that it can be measured directly in real time, such as in biofilms where antibiotic resistance genes spread rapidly [9] or in the human gut microbiome where industrialization has increased HGT rates [5]. This stark difference in frequency underscores that HGT is a core feature of prokaryotic life but only a rare, occasional event in multicellular eukaryotes.

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