Brother From a Different Mother
Written by Naomi Hammerschlag
Edited by Aseel Albokhari
There are few facts of life that you can always count on: the human body is 60% water, you are one centimeter taller in the morning than at night, and animals give birth to offspring of the same species. Well, maybe almost always count on. Recently, researchers studying a species of Mediterranean harvester ants known as Messor ibericus discovered that these ants can produce males belonging to a different species [1]. Rarely, two distinct species can produce hybrid offspring, such as a wholphin or a liger, but producing males that are genetically identical to another existing species is unprecedented.
This phenomenon, in which a species produces offspring of another, has been described by researchers as ‘xenoparity,’ meaning ‘foreign birth’ [1]. The term was newly proposed in this study to capture the novelty of the finding. While other organisms have not yet been observed to possess this ability, ants have unique reproductive systems [2]. “The M. ibericus queens utilize a strategy known as sperm parasitism, mating with males of another ant species, Messor structor, to produce males that carry the M. structor nuclear genome while maintaining their own mitochondrial DNA [2]. Scientists hypothesize that over evolutionary time, M. ibericus queens developed the ability to produce male ants carrying the M. structor genome, while retaining their own mitochondrial DNA [2]. This evolutionary adaptation allows M. ibericus queens to produce males with the M. structor genome even without the presence of M. structor females [2].
Photos from Pixabay. Curated by Kayla Vance (kmv53@cornell.edu)
Researchers propose that this process may involve the removal of the M. ibericus nuclear genome from eggs fertilized by M. structor sperm, resulting in males that contain only the M. structor nuclear DNA [2]. By contrast, a research team, led by Hugo Darras and colleagues observed that M. structor males residing in M. ibericus colonies had DNA in their mitochondrial organelles that align with the same sequences as M. ibericus [2]. Thus, M. structor males in M. ibericus colonies contain “mismatched” nuclear and mitochondrial genomes, with a nuclear genome from M. structor and a mitochondrial genome from M. ibericus [3]. This finding led to the conclusion that in M. ibericus colonies in which M. structor workers also exist, both the M. structor and M. ibericus worker ants originated from a common mother [3]. The researchers observed that this mismatch between nuclear and mitochondrial genomes occurred only in males produced by M. ibericus queens, and it has not been detected in males from pure M. structor colonies. In this case, none of the maternal nuclear genome is transmitted to the male offspring, thus mating between an M. ibericus queen and an M. structor male results in the production of male offspring with the M. structor genome [2].
Photo from Stocksnap. Curated by Kayla Vance (kmv53@cornell.edu)
The difference between males produced by M. ibericus and typical M. structor males is evident in several physical traits, including differences in hair coverage (pilosity) and other morphological features [3]. Male M. ibericus ants exhibit a denser pilosity in comparison to M. structor males, who are generally perceived as hairless [3]. These differences are thought to stem from a divergence of the species more than five million years ago [3].
Ultimately, this discovery challenges traditional boundaries of how species are defined, revealing a rare reproductive strategy that blurs, but does not erase, the lines between distinct species [1][2]. With this revelation, scientists will be able to further explore the role of hybridization in evolution and the opportunity for genetic transformation.
Naomi Hammerschlag ‘29 is in the College of Arts & Sciences. She can be reached at nh442@cornell.edu.
