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Phylogeography of lethal male fighting in a social spider mite
Yukie Sato1,2, Yoshiaki Tsuda1, Hironori Sakamoto3,4
1Sugadaira Research Station, Mountain Science Center University of Tsukuba Ueda Nagano Japan.
Abstract:
When males fight for access to females, such conflict rarely escalates into lethal fight because the risks and costs involved, that is, severe injury or death, are too high. The social spider mite, Stigmaeopsis miscanthi, does exhibit lethal male fights, and this male-male aggressiveness varies among populations. To understand the evolution of lethal fighting, we investigated aggressiveness in 42 populations and phylogenetic relationships in 47 populations along the Japanese archipelago. By analysis of the male weapon morph, a proxy for aggressiveness, we confirmed the existence of a mildly aggressive (ML) form, besides the low aggression (LW) and high aggression (HG) forms reported earlier. To evaluate demographic history of these three forms, we employed the approximate Bayesian computation approach using mtCOI sequences and taking into consideration the postlast glacial expansion history of the host plant, Miscanthus sinensis. As results, hierarchical split models are more likely to explain the observed genetic pattern than admixture models, and the ML form in the subtropical region was considered the ancestral group. The inferred demographic history was consistent with the one reconstructed for the host plant in a previous study. The LW form was split from the ML form during the last glacial period (20,000-40,000 years BP), and subsequently, the HG form was split from the ML form at the end of or after the last glacial period (5,494-10,988 years BP). The results also suggest that the mite invaded Japan more than once, resulting in the present parapatric distribution of LW and HG forms in eastern Japan.
Insights
Lethal male fighting in spider mites evolves through distinct aggression forms. Their demographic history, linked to host plant expansion, reveals an ancestral mildly aggressive form, with low and high aggression forms diverging over millennia.
Area of Science:
- Evolutionary Biology
- Animal Behavior
- Population Genetics
Background:
- Lethal male-male aggression is rare due to high costs, but occurs in the social spider mite, *Stigmaeopsis miscanthi*.
- Male aggressiveness in *S. miscanthi* varies across populations, suggesting evolutionary divergence.
- Previous studies identified low aggression (LW) and high aggression (HG) forms.
Purpose of the Study:
- Investigate the evolution of lethal fighting in *Stigmaeopsis miscanthi*.
- Analyze the phylogenetic relationships and aggressiveness of different mite populations.
- Determine the demographic history and evolutionary pathways of aggression forms.
Main Methods:
- Field surveys of aggressiveness in 42 populations and phylogenetic analysis in 47 populations.
- Analysis of male weapon morphology as a proxy for aggressiveness.
- Approximate Bayesian computation using mtCOI sequences, incorporating host plant (*Miscanthus sinensis*) demographic history.
Main Results:
- Identified a third, mildly aggressive (ML) form, considered ancestral.
- Hierarchical split models better explained genetic patterns than admixture models.
- Demographic history inferred for mites aligns with their host plant's post-glacial expansion.
- LW and HG forms diverged from the ML form during and after the last glacial period.
- Evidence suggests multiple invasions of Japan by the mite.
Conclusions:
- The evolution of male aggression in *S. miscanthi* is shaped by demographic history and host plant dynamics.
- Divergence of aggression forms occurred over tens of thousands of years, linked to glacial cycles.
- Multiple colonization events contributed to the current distribution of aggression forms in Japan.
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