GENETIC ANALYSIS OF SKULL SHAPE VARIATION AND MORPHOLOGICAL INTEGRATION IN THE MOUSE USING INTERSPECIFIC RECOMBINANT CONGENIC STRAINS BETWEEN C57BL/6 AND MICE OF THEMUS SPRETUSSPECIES

Abstract Background Hybridization has been widely practiced in plant and animal breeding as a means to enhance the quality and fitness of the organisms. In domestic equids, this hybrid vigor takes the form of improved physical and physiological characteristics, notably for strength or endurance. Because the offspring of horse and donkey is generally sterile, this widely recognized vigor is expressed in the first generation (F1). However, in the absence of recombination between the two parental genomes, F1 hybrids can be expected to be phenotypically intermediate between their parents which could potentially restrict the possibilities of an increase in overall fitness. In this study, we examine the morphology of the main limb bones of domestic horses, donkeys and their hybrids to investigate the phenotypic impact of hybridization on the locomotor system. We explore bone shape variation and covariation to gain insights into the morphological and functional expressions of the hybrid vigor commonly described in domestic equids. Results Our data reveal the occurrence of transgressive effects on several bones in the F1 generation. The patterns of morphological integration further demonstrate that the developmental processes producing covariation are not disrupted by hybridization, contrary to functional ones. Conclusions These results suggest that an increase in overall fitness could be related to more flexibility in shape change in hybrids, except for the main forelimb long bones of which the morphology is strongly driven by muscle interactions. More broadly, this study illustrates the interest of investigating not only bone shape variation but also underlying processes, in order to contribute to better understanding how developmental and functional mechanisms are affected by hybridization.

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Individual variation of the masticatory system dominates 3D skull shape in the herbivory-adapted marsupial wombats

10.1101/692632 ◽

2019 ◽

Author(s):

Vera Weisbecker ◽

Thomas Guillerme ◽

Cruise Speck ◽

Emma Sherratt ◽

Hyab Mehari Abraha ◽

...

Keyword(s):

Individual Variation ◽

Principal Component ◽

Individual Variability ◽

Shape Variation ◽

Mandibular Ramus ◽

Geometric Morphometric ◽

Skull Shape ◽

Marsupial Species ◽

Masticatory System ◽

The Individual

AbstractBackgroundWithin-species skull shape variation of marsupial mammals is widely considered low and strongly size-dependent (allometric), possibly due to developmental constraints arising from the altricial birth of marsupials. However, species whose skulls are impacted by strong muscular stresses – particularly those produced through mastication of tough food items – may not display such intrinsic patterns very clearly because of the known plastic response of bone to muscle activity of the individual. In such cases, shape variation should not be dominated by allometry; ordination of shape in a geometric morphometric context through principal component analysis (PCA) should reveal main variation in areas under masticatory stress (incisor region/zygomatic arches/mandibular ramus); but this main variation should emerge from high individual variability and thus have low eigenvalues.ResultsWe assessed the evidence for high individual variation through 3D geometric morphometric shape analysis of crania and mandibles of thre species of grazing-specialized wombats, whose diet of tough grasses puts considerable strain on their masticatory system. As expected, we found little allometry and low Principal Component 1 (PC1) eigenvalues within crania and mandibles of all three species. Also as expected, the main variation was in the muzzle, zygomatic arches, and masticatory muscle attachments of the mandibular ramus. We then implemented a new test to ask if the landmark variation reflected on PC1 was reflected in individuals with opposite PC1 scores and with opposite shapes in Procrustes space. This showed that correspondence between individual and ordinated shape variation was limited, indicating high levels of individual variability in the masticatory apparatus.DiscussionOur results are inconsistent with hypotheses that skull shape variation within marsupial species reflects a constraint pattern. Rather, they support suggestions that individual plasticity can be an important determinant of within-species shape variation in marsupials (and possibly other mammals) with high masticatory stresses, making it difficult to understand the degree to which intrinsic constraint act on shape variation at the within-species level. We conclude that studies that link micro- and macroevolutionary patterns of shape variation might benefit from a focus on species with low-impact mastication, such as carnivorous or frugivorous species.

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Relative skull size as one of the factors limiting skull shape variation in passerines

Canadian Journal of Zoology ◽

10.1139/cjz-2021-0106 ◽

2021 ◽

Author(s):

Oksana Shatkovska ◽

Maria Ghazali

Keyword(s):

Body Mass ◽

Shape Variation ◽

Absolute Size ◽

Terrestrial Locomotion ◽

Skull Shape ◽

Skull Size ◽

Dietary Preferences ◽

Wide Range ◽

Body Sizes ◽

Biomechanical Constraints

Despite a considerable interest of researchers to the issue of variation in skull shapes of birds and factors influencing it, some drivers associated with the design features of an entire bird body, which are important for both successful terrestrial locomotion and flight, are overlooked. One of such factors, in our opinion, is relative skull size (skull length in relation to body mass), which can affect the position of the body's center of gravity. We tested effects of relative skull size, allometry (i.e. absolute skull size), and diet on variation in skull shape. The study was conducted on 50 songbird species with a wide range of body mass (8.3g to 570g) and dietary preferences (granivores, insectivores/granivores, insectivores, omnivores). Skull shape was analyzed using 2D geometric morphometrics. We revealed that similar patterns of skull shape occur among passerines with different body sizes and diets. The relative skull size predicted skull shape to a similar extent and with a similar pattern as the absolute size. In our opinion, the effect of the relative skull size on skull shape variation is likely due to biomechanical constraints related to flight.

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Recombinant Congenic Strains

Brenner's Encyclopedia of Genetics ◽

10.1016/b978-0-12-374984-0.01273-0 ◽

2013 ◽

pp. 76-78

Author(s):

P. Demant

Keyword(s):

Congenic Strains ◽

Recombinant Congenic Strains

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Mapping cis-acting regulatory variation in recombinant congenic strains

Physiological Genomics ◽

10.1152/physiolgenomics.00168.2005 ◽

2006 ◽

Vol 25 (2) ◽

pp. 294-302 ◽

Cited By ~ 17

Author(s):

Peter D. Lee ◽

Bing Ge ◽

Celia M. T. Greenwood ◽

Donna Sinnett ◽

Yannick Fortin ◽

...

Keyword(s):

Gene Expression ◽

Expression Profiles ◽

Fisher Exact Test ◽

Donor Strain ◽

Exact Test ◽

Expression Levels ◽

Cis Acting ◽

Congenic Strains ◽

Recombinant Congenic Strains ◽

Genetic Context

We present an integrated approach for the enriched detection of genes subject to cis-acting variation in the mouse genome. Gene expression profiling was performed with lung tissue from a panel of recombinant congenic strains (RCS) derived from A/J and C57BL/6J inbred mouse strains. A multiple-regression model measuring the association between gene expression level, donor strain of origin (DSO), and predominant strain background identified over 1,500 genes ( P < 0.05) whose expression profiles differed according to the DSO. This model also identified over 1,200 genes whose expression showed dependence on background ( P < 0.05), indicating the influence of background genetic context on transcription levels. Sequences obtained from 1-kb segments of 3′-untranslated regions identified single nucleotide polymorphisms in 64% of genes whose expression levels correlated with DSO status, compared with 29% of genes that displayed no association ( P < 0.01, Fisher exact test). Allelic imbalance was identified in 50% of genes positive for expression-DSO association, compared with 22% of negative genes ( P < 0.05, Fisher exact test). Together, these results demonstrate the utility of RCS mice for identifying the roles of proximal genetic determinants and background genetic context in determining gene expression levels. We propose the use of this integrated experimental approach in multiple tissues from this and other RCS panels as a means for genome-wide cataloging of genetic regulatory mechanisms in laboratory strains of mice.

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