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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.

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Maps of Mount Tomaros with sampling locations of courtship song phenotypes (A) and with interpolated song trait values at unsampled sites (B). Hybrid indices from 1 (S. clavatus) to 12 (S. rubicundus) indicated by different colors are shown at the right. The center of contact zone I is shown by the black line.
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ece32265-fig-0010: Maps of Mount Tomaros with sampling locations of courtship song phenotypes (A) and with interpolated song trait values at unsampled sites (B). Hybrid indices from 1 (S. clavatus) to 12 (S. rubicundus) indicated by different colors are shown at the right. The center of contact zone I is shown by the black line.

Mentions: The spatial distribution of the courtship song phenotypes in the hybrid zone showed only one contact zone, in the southern part of Mount Tomaros (CZI). This may be explained by the lower number of sites for which songs were recorded (Fig. 10A), compared to the sites for which the wings and the antennae were studied. In the northern part of Mount Tomaros, all song phenotypes were found to be clavatus‐like, whereas in the northeastern part of Mount Tomaros, they were of the rubicundus type. The distribution of the song phenotypes in CZI was somewhat similar to that obtained for the antenna morphology, with pure clavatus phenotypes found at the southern end of the contact zone (Fig. 10B). Meanwhile, clavatus‐like song phenotypes were also found in the most eastern sites of the contact zone, which was similar to the wing pattern distribution. The song cline across CZI has a sigmoid shape (Fig. 11) similar to those found for the wings and the male antennae.


Variation in complex mating signals in an “ island ” hybrid zone between Stenobothrus grasshopper species
Maps of Mount Tomaros with sampling locations of courtship song phenotypes (A) and with interpolated song trait values at unsampled sites (B). Hybrid indices from 1 (S. clavatus) to 12 (S. rubicundus) indicated by different colors are shown at the right. The center of contact zone I is shown by the black line.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4979727&req=5

ece32265-fig-0010: Maps of Mount Tomaros with sampling locations of courtship song phenotypes (A) and with interpolated song trait values at unsampled sites (B). Hybrid indices from 1 (S. clavatus) to 12 (S. rubicundus) indicated by different colors are shown at the right. The center of contact zone I is shown by the black line.
Mentions: The spatial distribution of the courtship song phenotypes in the hybrid zone showed only one contact zone, in the southern part of Mount Tomaros (CZI). This may be explained by the lower number of sites for which songs were recorded (Fig. 10A), compared to the sites for which the wings and the antennae were studied. In the northern part of Mount Tomaros, all song phenotypes were found to be clavatus‐like, whereas in the northeastern part of Mount Tomaros, they were of the rubicundus type. The distribution of the song phenotypes in CZI was somewhat similar to that obtained for the antenna morphology, with pure clavatus phenotypes found at the southern end of the contact zone (Fig. 10B). Meanwhile, clavatus‐like song phenotypes were also found in the most eastern sites of the contact zone, which was similar to the wing pattern distribution. The song cline across CZI has a sigmoid shape (Fig. 11) similar to those found for the wings and the male antennae.

View Article: PubMed Central - PubMed

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.


Related in: MedlinePlus