论文标题：Phylogenomics of palearctic Formica species suggests a single origin of temporary parasitism and gives insights to the evolutionary pathway toward slave-making behaviour
By Jonathan Romiguier et al
Digital identification code: 10.1186/s12862-018-1159-4
In a recent article published in BMC Evolutionary Biology, researchers used phylogenetic genomics analysis to decipher the relationships between ants in the genus Ant, providing recommendations for the evolutionary origins of enslavement behavior. They offer an explanation for this behavior that has plagued generations of biologists and even Darwin humans.
The Blood Red Forest Ant (Formica sanguinea) is a slave species that can invade its nests of enslaved ants and catch the ants that live in them.
Admittedly, the complex social structures of life in anthills are fascinating, and the enslavement of certain species of the genus can serve as a classic example of social parasitism.
The evolution of slavery has captivated generations of natural scientists and sparked a discussion rooted in Darwin's theory of the "origin of species."
According to the father of evolution, slavery in the genus ants evolved gradually through the intermediate step of so-called "temporary parasitism". This hypothesis is supported by some modern researchers, but other scientists have proposed another explanation, arguing that parasitic ant colonies have formed through several independent evolutions.
To answer this 150-year-long disagreement, Jonathan Romiguier and a team of researchers from the University of Lausanne, Montpellier, British Columbia and Helsinki used modern phylogenetic genomics methods to finally uncover complex relationships in the subgenera Ant in the Palearctic region.
Using a combination of experimental and bioinformatics methods, Romiguier and colleagues built phylogenetic trees to reconstruct the evolutionary processes of four ant subgenera. Based on the branches of the phylogenetic tree, we can trace the history of the genus Ant in the Paleopic Region, highlighting key points in the process from freedom to slavery.
Molecular phylogeny of ant genus
Image from the paper
The free-living Sermiformica is located at the base of the evolutionary tree, which is the only colony that can form colonies independently, indicating that the genus has a free-living ancestor who independently formed colonies.
Along the evolutionary tree, ant species evolved, and a separate branch can be found covering other subgenera, including Coptoformica, Formica s. str., and Raptiformica, which exhibits enslavement behavior.
They share certain common features, such as the loss of the ability to independently establish new and temporary parasitic colonies, suggesting that they are closely related and that their common ancestors began to parasitize in the Serbiformica nest and passed on this ability to the three subgenera.
The subgenus Coptoformica and Formica s. str., also known as "wood ants," rely on mechanisms other than enslavement to create new colonies. They usually perform "budding," the process by which a new queen and worker ants leave and establish a new colony nearby. This behavior has led to many interconnected nests and the formation of super colonies, and is considered an adaptation to cold habitats, although successful establishment of independent colonies is limited by high mortality rates. In this case, the movement of ant colonies between nests is often observed.
Wood ants can perform so-called "temporary parasitism", in which case the new queen enters the nest of the Serbiformica ant, expels and replaces the original queen, and uses the worker ants in the original nest to work. Over time, the original worker ants were gradually replaced by the offspring of the temporary parasitic queen.
Subsequently, raptiformica developed a unique feature of active slavery, in addition to temporary parasitism. This can be done seasonally interspecifically from the Serifica nest, increasing the worker ant workforce. After enslavement, Serviformica worker ants still behave like they are in their own colonies.
In this case, the typical colony swap of wood ants may have evolved into selfish plunder in territorial warfare, eventually becoming the interspecies enslavement observed in Raptiformica.
A deep analysis of the evolutionary relationships of ant species has led to a theory that confirms Darwin's earliest hypothesis.
The phylogenetic clade sequence suggests that the evolutionary pathway of slavery had a single origin and then evolved in several steps, with temporary parasitism being seen as an intermediate step between free-living ants and slave-owning parasitic ants.
At the end of this evolutionary discussion, we can see Romeguier's phylogenetic tree as a strong support for the classical model described in "The Origin of Species", which adds new evidence to the worldwide puzzle of ant enslavement evolution.
summary:
Background
The ants of the Formica genus are classical model species in evolutionary biology. In particular, Darwin used Formica as model species to better understand the evolution of slave-making, a parasitic behaviour where workers of another species are stolen to exploit their workforce. In his book “On the Origin of Species” (1859), Darwin first hypothesized that slave-making behaviour in Formica evolved in incremental steps from a free-living ancestor.
Methods
The absence of a well-resolved phylogenetic tree of the genus prevent an assessment of whether relationships among Formica subgenera are compatible with this scenario. In this study, we resolve the relationships among the 4 palearctic Formica subgenera (Formica str. s., Coptoformica, Raptiformica and Serviformica) using a phylogenomic dataset of 945 genes for 16 species.
Results
We provide a reference tree resolving the relationships among the main Formica subgenera with high bootstrap supports.
Discussion
The branching order of our tree suggests that the free-living lifestyle is ancestral in the Formica genus and that parasitic colony founding could have evolved a single time, probably acting as a pre-adaptation to slave-making behaviour.
Conclusion
This phylogenetic tree provides a solid backbone for future evolutionary studies in the Formica genus and slave-making behaviour.
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期刊介绍：BMC Evolutionary Biologyis an open access, peer-reviewed journal that considers articles on all aspects of molecular and non-molecular evolution of all organisms, as well as phylogenetics and palaeontology.
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