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Combined Use of Morphological and Molecular Tools to Resolve Species Mis-Identifications in the Bivalvia The Case of Glycymeris glycymeris and G . pilosa

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ABSTRACT

Morphological and molecular tools were combined to resolve the misidentification between Glycymeris glycymeris and Glycymeris pilosa from Atlantic and Mediterranean populations. The ambiguous literature on the taxonomic status of these species requires this confirmation as a baseline to studies on their ecology and sclerochronology. We used classical and landmark-based morphometric approaches and performed bivariate and multivariate analyses to test for shell character interactions at the individual and population level. Both approaches generated complementary information. The former showed the shell width to length ratio and the valve asymmetry to be the main discriminant characters between Atlantic and Mediterranean populations. Additionally, the external microsculpture of additional and finer secondary ribs in G. glycymeris discriminates it from G. pilosa. Likewise, landmark-based geometric morphometrics revealed a stronger opisthogyrate beak and prosodetic ligament in G. pilosa than G. glycymeris. Our Bayesian and maximum likelihood phylogenetic analyses based on COI and ITS2 genes identified that G. glycymeris and G. pilosa form two separate monophyletic clades with mean interspecific divergence of 11% and 0.9% for COI and ITS2, respectively. The congruent patterns of morphometric analysis together with mitochondrial and nuclear phylogenetic reconstructions indicated the separation of the two coexisting species. The intraspecific divergence occurred during the Eocene and accelerated during the late Pliocene and Pleistocene. Glycymeris pilosa showed a high level of genetic diversity, appearing as a more robust species whose tolerance of environmental conditions allowed its expansion throughout the Mediterranean.

No MeSH data available.


Geometric morphometrics landmarks.This image represents a right valve of Glycymeris glycymeris with the position of 12 landmarks (open dots) and 3 semi-landmarks (fill dots).
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pone.0162059.g003: Geometric morphometrics landmarks.This image represents a right valve of Glycymeris glycymeris with the position of 12 landmarks (open dots) and 3 semi-landmarks (fill dots).

Mentions: The GM analyses implemented in software MorphoJ [36] were used to quantify shape variation from 60 images of Glycymeris sp. from different localities (15 samples from each group). For all specimens, the inner side of the right valve was photographed and digitized with the software TPS dig2 [37]. From these images 12 landmarks and 2 semi-landmarks were defined (Fig 3). Landmarks were subjected to a standard generalized Procrustes alignment to remove differences between specimens based on scale, rotation, and location. A PCA was also applied to the Procrustes coordinates to explore variation in the shape components. Multivariate regression of shape with centroid size as the independent variable was computed to assess intrapopulation allometry. Permutation test with 10,000 rounds was used to evaluate the independence between the shape and size variables. Finally, a canonical variate analysis (CVA) was performed to find out which shell shape features best discriminated between species.


Combined Use of Morphological and Molecular Tools to Resolve Species Mis-Identifications in the Bivalvia The Case of Glycymeris glycymeris and G . pilosa
Geometric morphometrics landmarks.This image represents a right valve of Glycymeris glycymeris with the position of 12 landmarks (open dots) and 3 semi-landmarks (fill dots).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5036790&req=5

pone.0162059.g003: Geometric morphometrics landmarks.This image represents a right valve of Glycymeris glycymeris with the position of 12 landmarks (open dots) and 3 semi-landmarks (fill dots).
Mentions: The GM analyses implemented in software MorphoJ [36] were used to quantify shape variation from 60 images of Glycymeris sp. from different localities (15 samples from each group). For all specimens, the inner side of the right valve was photographed and digitized with the software TPS dig2 [37]. From these images 12 landmarks and 2 semi-landmarks were defined (Fig 3). Landmarks were subjected to a standard generalized Procrustes alignment to remove differences between specimens based on scale, rotation, and location. A PCA was also applied to the Procrustes coordinates to explore variation in the shape components. Multivariate regression of shape with centroid size as the independent variable was computed to assess intrapopulation allometry. Permutation test with 10,000 rounds was used to evaluate the independence between the shape and size variables. Finally, a canonical variate analysis (CVA) was performed to find out which shell shape features best discriminated between species.

View Article: PubMed Central - PubMed

ABSTRACT

Morphological and molecular tools were combined to resolve the misidentification between Glycymeris glycymeris and Glycymeris pilosa from Atlantic and Mediterranean populations. The ambiguous literature on the taxonomic status of these species requires this confirmation as a baseline to studies on their ecology and sclerochronology. We used classical and landmark-based morphometric approaches and performed bivariate and multivariate analyses to test for shell character interactions at the individual and population level. Both approaches generated complementary information. The former showed the shell width to length ratio and the valve asymmetry to be the main discriminant characters between Atlantic and Mediterranean populations. Additionally, the external microsculpture of additional and finer secondary ribs in G. glycymeris discriminates it from G. pilosa. Likewise, landmark-based geometric morphometrics revealed a stronger opisthogyrate beak and prosodetic ligament in G. pilosa than G. glycymeris. Our Bayesian and maximum likelihood phylogenetic analyses based on COI and ITS2 genes identified that G. glycymeris and G. pilosa form two separate monophyletic clades with mean interspecific divergence of 11% and 0.9% for COI and ITS2, respectively. The congruent patterns of morphometric analysis together with mitochondrial and nuclear phylogenetic reconstructions indicated the separation of the two coexisting species. The intraspecific divergence occurred during the Eocene and accelerated during the late Pliocene and Pleistocene. Glycymeris pilosa showed a high level of genetic diversity, appearing as a more robust species whose tolerance of environmental conditions allowed its expansion throughout the Mediterranean.

No MeSH data available.