Fluctuating and Directional Asymmetry of the Blue Mussel (Mytilus edulis): Improving Methods of Morphological Analysis to Explore Species Performance at the Northern Border of Its Range

Abstract

Abstract:In this work we examined morphological variation at different levels to study performance and population structuring of the blue mussel Mytilus edulis. Our objectives were: (i) to develop an integrated technique for analyzing morphological variation in blue mussels and, based on this technique; (ii) to perform a morphometric description of mussels from the northern part of their range; and (iii) to verify the hypothesis that populations at the outer range of their distribution have reduced performance due to harsh climatic conditions. Means, directional asymmetry (i.e., systematic differences between left and right structures), fluctuating asymmetry (random deviations from perfect symmetry, a measure of developmental instability), factorial variation (difference between total variance and variance of fluctuating asymmetry, an indirect index of genotypic variation), and measurement error were examined for 14 bilateral characters of muscle scars on mussel shells. Also, we analyzed one non-bilateral character. For the first time directional asymmetry-approaching 13% of the right:left ratio-was described in blue mussels. Measurement error, often ignored in morphometric studies, contributed 26% of total variance. Accurately addressing these methodical challenges is key to further and improved ecological interpretations. Morphological differences were found between (i) samples from estuarine areas in the White and Pechora Seas and (ii) samples from Barents Sea areas with oceanic salinity. Samples from the first group exhibited lower OPEN ACCESSSymmetry 2015, 7 489 fluctuating asymmetry, indicating higher developmental stability likely due to better feeding conditions and lower factorial variation, which may result from lower genotypic variation. Absence of correlation between fluctuating asymmetry and temperature suggests that low temperatures in the northern border of their range do not degrade the performance of adult blue mussels in this region.

Radiation exposure causes developmental alterations in size and shape of wings and structures associated with song production in male crickets (Acheta domesticus)

“…This is significant as increased fluctuating asymmetry has been identified as a reliable biomarker of environmental stress in insects (Beasley et al, 2013). Fluctuating asymmetry has also been indicated as a general indicator of individual quality (Lajus et al, 2015). However, these results are contrary to recent literature on radiation impacts on fluctuating asymmetry in grasshoppers in areas surrounding Chernobyl (Beasley et al, 2012).…”

Divergent scute asymmetry among pure and crossed individuals of Testudo hermanni (Gmelin, 1789)

“…Las sumas de cuadrados (SS) y las medias de cuadrados (MS) son en unidades de distancias Procrustes (sin dimensiones). Vishalakshi and Singh, 2009;Demontis et al, 2010;Ducos and Tabugo, 2014;Lajus et al, 2015). This has usually been interpreted as a direct consequence of the fact that the genome of such hybrids is a combination of two different parental genomes and, hence, the mechanisms that stabilize the interferences due to development noise are disrupted (Rego et al, 2006).…”

Heritabilities and genetic correlation of shell thickness and shell length growth in a mussel,Mytilus chilensis(Bivalvia:Mytilidae)

“…The heritability values estimated in this study are larger than those described in the literature for the same species; among some of the causes (change in heritability values along the life animal span or environmental causes), the measure of right and left valves, and using the average of both in the analysis could be an explanation. This procedure reduces significantly the residual error variance error (V R ) in the analysis (Briones & Guiñez ; Lajus, Katolikova, Strelkov & Hummel ), and therefore decreasing the phenotypic variation (denominator) thus increasing the additive variance.…”