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Variation in complex mating signals in an “ island ” hybrid zone between Stenobothrus grasshopper species

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ABSTRACT

Two grasshopper species Stenobothrus rubicundus and S. clavatus were previously shown to meet in a narrow hybrid zone on Mount Tomaros in northern Greece. The species are remarkable for their complex courtship songs accompanied by conspicuous movements of antennae and wings. We analyzed variations in forewing morphology, antenna shape, and courtship song across the hybrid zone using a geographic information system, and we documented three contact zones on Mount Tomaros. All male traits and female wings show abrupt transitions across the contact zones, suggesting that these traits are driven by selection rather than by drift. Male clines in antennae are displaced toward S. clavatus, whereas all clines in wings are displaced toward S. rubicundus. We explain cline discordance as depending on sexual selection via female choice. The high covariance between wings and antennae found in the centers of all contact zones results from high levels of linkage disequilibria among the underlying loci, which in turn more likely results from assortative mating than from selection against hybrids. The covariance is found to be higher in clavatus‐like than rubicundus‐like populations, which implies asymmetric assortative mating in parental‐like sites of the hybrid zone and a movement of the hybrid zone in favor of S. clavatus.

No MeSH data available.


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Plot of the first two canonical variables (CV1 and CV2) illustrating the differences in the forewing morphology between allopatric Stenobothrus clavatus (open marks) and allopatric S. rubicundus (black marks); the differences are similar in males (circles) and females (triangles). Specimens from Mount Tomaros (crosses in males and squares in females) are split into two groups: rubicundus‐like and clavatus‐like specimens.
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ece32265-fig-0003: Plot of the first two canonical variables (CV1 and CV2) illustrating the differences in the forewing morphology between allopatric Stenobothrus clavatus (open marks) and allopatric S. rubicundus (black marks); the differences are similar in males (circles) and females (triangles). Specimens from Mount Tomaros (crosses in males and squares in females) are split into two groups: rubicundus‐like and clavatus‐like specimens.

Mentions: We did not find significant differences in the wing morphology among five allopatric populations of S. rubicundus (CVA/MANOVA test, P > 0.5). At the same time, the difference between allopatric S. rubicundus and S. clavatus was highly significant both in males and in females (CVA/MANOVA test, P < 0.001). The results of CVA applied to allopatric populations and specimens from Mount Tomaros also show the difference between allopatric specimens (Fig. 3). Comparison of CV1 scores shows that specimens from Mount Tomaros could be split into two groups: rubicundus‐like and clavatus‐like specimens. To some degree, the specimens from Mount Tomaros overlapped with allopatric specimens. Most of them, however, were different from allopatric specimens. Intermediate phenotypes were in the minority. Notably, a bimodal distribution of CV1 scores was found in both sexes.


Variation in complex mating signals in an “ island ” hybrid zone between Stenobothrus grasshopper species
Plot of the first two canonical variables (CV1 and CV2) illustrating the differences in the forewing morphology between allopatric Stenobothrus clavatus (open marks) and allopatric S. rubicundus (black marks); the differences are similar in males (circles) and females (triangles). Specimens from Mount Tomaros (crosses in males and squares in females) are split into two groups: rubicundus‐like and clavatus‐like specimens.
© Copyright Policy - creativeCommonsBy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4979727&req=5

ece32265-fig-0003: Plot of the first two canonical variables (CV1 and CV2) illustrating the differences in the forewing morphology between allopatric Stenobothrus clavatus (open marks) and allopatric S. rubicundus (black marks); the differences are similar in males (circles) and females (triangles). Specimens from Mount Tomaros (crosses in males and squares in females) are split into two groups: rubicundus‐like and clavatus‐like specimens.
Mentions: We did not find significant differences in the wing morphology among five allopatric populations of S. rubicundus (CVA/MANOVA test, P > 0.5). At the same time, the difference between allopatric S. rubicundus and S. clavatus was highly significant both in males and in females (CVA/MANOVA test, P < 0.001). The results of CVA applied to allopatric populations and specimens from Mount Tomaros also show the difference between allopatric specimens (Fig. 3). Comparison of CV1 scores shows that specimens from Mount Tomaros could be split into two groups: rubicundus‐like and clavatus‐like specimens. To some degree, the specimens from Mount Tomaros overlapped with allopatric specimens. Most of them, however, were different from allopatric specimens. Intermediate phenotypes were in the minority. Notably, a bimodal distribution of CV1 scores was found in both sexes.

View Article: PubMed Central - PubMed

ABSTRACT

Two grasshopper species Stenobothrus rubicundus and S.&nbsp;clavatus were previously shown to meet in a narrow hybrid zone on Mount Tomaros in northern Greece. The species are remarkable for their complex courtship songs accompanied by conspicuous movements of antennae and wings. We analyzed variations in forewing morphology, antenna shape, and courtship song across the hybrid zone using a geographic information system, and we documented three contact zones on Mount Tomaros. All male traits and female wings show abrupt transitions across the contact zones, suggesting that these traits are driven by selection rather than by drift. Male clines in antennae are displaced toward S.&nbsp;clavatus, whereas all clines in wings are displaced toward S.&nbsp;rubicundus. We explain cline discordance as depending on sexual selection via female choice. The high covariance between wings and antennae found in the centers of all contact zones results from high levels of linkage disequilibria among the underlying loci, which in turn more likely results from assortative mating than from selection against hybrids. The covariance is found to be higher in clavatus&#8208;like than rubicundus&#8208;like populations, which implies asymmetric assortative mating in parental&#8208;like sites of the hybrid zone and a movement of the hybrid zone in favor of S.&nbsp;clavatus.

No MeSH data available.


Related in: MedlinePlus