HYBRIDIZATION STUDIES ON THE HOST RACES OF EUROSTA SOLIDAGINIS: IMPLICATIONS FOR SYMPATRIC SPECIATION

Area of Science:

• Evolutionary Biology
• Speciation Research
• Insect-Plant Interactions

Background:

• Host-associated populations of Eurosta solidaginis flies on Solidago altissima and S. gigantea goldenrods are hypothesized to be sympatric host races.
• Sympatric speciation models require disruptive selection for host use, a critical assumption tested in this study.

Purpose of the Study:

• To investigate the inheritance of survival ability in Eurosta solidaginis host-associated populations.
• To test predictions of sympatric speciation models regarding host use and hybrid fitness.

Main Methods:

• Studied survival rates of pure host races and their hybrids (F1, F2, backcross) on different goldenrod hosts.
• Analyzed inheritance patterns of survival ability, assessing maternal and sex-linked influences.

Main Results:

• Evidence of disruptive selection for host use was found, with each host race exhibiting higher survival on its primary host.
• Hybrid flies (F1, F2, backcross) showed reduced survival compared to pure host races on their respective hosts, supporting host adaptation.
• High hybrid survival on certain plant genotypes/years indicated host adaptation rather than strong genetic incompatibilities.
• Gene flow is possible between host races, as evidenced by viable hybrid offspring and emergence on alternative hosts.

Conclusions:

• The findings support the host adaptation hypothesis and provide evidence for disruptive selection, a key component of sympatric speciation.
• Survival ability inheritance appears to be an autosomal trait, with no significant maternal or sex-linked influence.
• The potential for gene flow and the existence of genes for alternative host utilization suggest mechanisms for host shifts and speciation.