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United States Department of Agriculture

Agricultural Research Service

Research Project: OBJECTIVE GRADING AND END-USE PROPERTY ASSESSMENT OF SINGLE KERNELS AND BULK GRAIN SAMPLES Title: Divergent Host Plant Adaptation Drives the Evolution of Sexual Isolation in the Grasshopper Hesperotettix viridis (Orthoptera: Acrididae) in the Absence of Reinforcement

Authors
item Grace, Tony -
item Wisely, Samantha -
item Brown, Susan -
item Dowell, Floyd
item Joern, Anthony -

Submitted to: Biological Journal of the Linnean Society, London
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 3, 2010
Publication Date: July 15, 2010
Repository URL: http://naldc.nal.usda.gov/download/43941/PDF
Citation: Grace, T., Wisely, S.M., Brown, S.J., Dowell, F.E., Joern, A. 2010. Divergent Host Plant Adaptation Drives the Evolution of Sexual Isolation in the Grasshopper Hesperotettix viridis (Orthoptera: Acrididae) in the Absence of Reinforcement. Biological Journal of the Linnean Society, London. 100:866-878.

Interpretive Summary: The beginning stages of lineage divergence can be difficult to detect, as correlations between altered genotypic and phenotypic attributes are often weak early in the process. Shifts in host plant use and divergence in mating signals can lead to sexual isolation and ultimately speciation. To understand the process, it is important to recognize the initial barriers that reduced contact between populations, the evolutionary factors leading to adaptation if it occurs, and the contributions of such factors and traits to better understand lineage divergence. Genetic studies of the grasshopper Hesperotettix viridis suggest that selection contributes to genetic differentiation in response to host use. Here we used near infrared spectroscopy to examine the host preferences, degree of differentiation in mate choice, and divergence in cuticular morphology. Significant host-based preference of individuals from two host plant groups was detected. No-choice mate selection experiments reveal preference for individuals collected from the same host species independent of location, and little mating observed between individuals from different host species. Significant differentiation in color and cuticular composition of individuals from different host plants was also observed. Results of our study indicate that divergent selection for host plant use promotes sexual isolation in this species.

Technical Abstract: The beginning stages of lineage divergence can be difficult to detect, as correlations between altered genotypic and phenotypic attributes are often weak early in the process. Shifts in host plant use and divergence in mating signals can lead to sexual isolation and ultimately speciation. To understand the process, it is important to recognize the initial barriers that reduced contact between populations, the evolutionary factors leading to adaptation if it occurs, and the contributions of such factors and traits to better understand lineage divergence. The grasshopper Hesperotettix viridis is an oligophagous species feeding on host plants primarily in the genus Gutierrezia and Solidago in Kansas. Genetic studies conducted in our lab suggest that selection contributes to genetic differentiation in response to host use. Here I present results examining the host preferences, degree of differentiation in mate choice, and divergence in cuticular morphology using near infrared spectroscopy. I compared the divergence in these traits on different host plants in H. viridis populations in Kansas in zones of contact and in populations with access to only one host species to identify the nature and origins of putative initial barriers that isolate populations in the formative stages of divergence. Significant host-based preference of individuals from the two host plant groups was detected in host paired-feeding preference studies. No-choice mate selection experiments reveal preference for individuals collected from the same host species independent of location, and little mating observed between individuals from different host species; female mate choice tests between males from the two host species resulted in 100% fidelity with respect to host use. Significant differentiation in color and cuticular composition of individuals from different host plants was also observed. A correlation between host choice and mate choice and phenotypic divergence resulted. No evidence for reinforcement or character displacement in the zone of contact was detected. Results of our study indicate that divergent selection for host plant use promotes sexual isolation in this species.

Last Modified: 11/27/2014
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