Interaction between the X chromosome and an autosome regulates size sexual dimorphism in Portuguese Water Dogs.

Size sexual dimorphism occurs in almost all mammals. In Portuguese Water Dogs, much of the difference in skeletal size between females and males is due to the interaction between a Quantitative Trait Locus (QTL) on the X-chromosome and a QTL linked to Insulin-like Growth Factor 1 (IGF-1) on the CFA 15 autosome. In females, the haplotype of CFA 15 resulting in small size is dominant. In males, the haplotype for large size is dominant. Females, homozygous at the CHM marker on the X chromosome and homozygous for the large size CFA 15 haplotype are, on average, as large as large males. However, all females that are heterozygous at the CHM marker are small, regardless of their CFA 15 genotype. This interaction suggests a genetic mechanism that in turn leads to a scenario for the evolution of size sexual dimorphism consistent with a proposal of Lande that sexual dimorphism can evolve because females secondarily become smaller than males as a consequence of natural selection for optimal size. Our results also can explain Rensch's Rule, which states that size is often positively correlated with the level of size sexual dimorphism.

[1]  J. E. Rice,et al.  Multiple and ancient origins of the domestic dog. , 1997, Science.

[2]  R. Preziosi,et al.  Sexual Selection and the Evolution of Allometry for Sexual Size Dimorphism in the Water Strider, Aquarius remigis , 1994, The American Naturalist.

[3]  Luquan Wang,et al.  Analysis of a human brain transcriptome map , 2002, BMC Genomics.

[4]  M. Lynch,et al.  Genetics and Analysis of Quantitative Traits , 1996 .

[5]  R. Peters.  The Ecological Implications of Body Size , 1983 .

[6]  R. Matthews,et al.  Ants. , 1898, Science.

[7]  S. Mohan,et al.  Insulin-like growth factor-binding protein-5 induces a gender-related decrease in bone mineral density in transgenic mice. , 2005, Endocrinology.

[8]  G. Mahairas,et al.  A 1-Mb resolution radiation hybrid map of the canine genome , 2003, Proceedings of the National Academy of Sciences of the United States of America.

[9]  C. Darwin.  The Descent of Man and Selection in Relation to Sex: INDEX , 1871 .

[10]  B. Rensch.  Die Abhängigkeit der relativen Sexualdifferenz von der Körpergröße , 1950 .

[11]  Daphne J. Fairbairn,et al.  A Comparative Analysis of Allometry for Sexual Size Dimorphism: Assessing Rensch's Rule , 1997, The American Naturalist.

[12]  P. Jarman.  MATING SYSTEM AND SEXCUL DIMORPHISM IN LARGE TERRESTRIAL, MAMMALIAN HERBIVORES , 1983 .

[13]  G. Lanfranchi,et al.  A comprehensive, high-resolution genomic transcript map of human skeletal muscle. , 1998, Genome research.

[14]  M. Reiss.  Sexual dimorphism in body size: are larger species more dimorphic? , 1986 .

[15]  J. Oldham,et al.  Sexual dimorphism is associated with decreased expression of processed myostatin in males. , 2003, American journal of physiology. Endocrinology and metabolism.

[16]  Fang Yang,et al.  An abundance of X-linked genes expressed in spermatogonia , 2001, Nature Genetics.

[17]  P. Hedrick,et al.  PERSPECTIVE: DETECTING ADAPTIVE MOLECULAR POLYMORPHISM: LESSONS FROM THE MHC , 2003, Evolution; international journal of organic evolution.

[18]  R. Lande,et al.  SEXUAL DIMORPHISM, SEXUAL SELECTION, AND ADAPTATION IN POLYGENIC CHARACTERS , 1980, Evolution; international journal of organic evolution.

[19]  K. Lark,et al.  Evidence for dominant mutations reducing HGPRT activity , 1978, Nature.

[20]  H. Chandra,et al.  An apparent excess of sex– and reproduction–related genes on the human X chromosome , 1999, Proceedings of the Royal Society of London. Series B: Biological Sciences.

[21]  D. Carrier,et al.  Genetics of canid skeletal variation: size and shape of the pelvis. , 2005, Genome research.

[22]  M. Webster.  SEXUAL DIMORPHISM, MATING SYSTEM AND BODY SIZE IN NEW WORLD BLACKBIRDS (ICTERINAE) , 1992, Evolution; international journal of organic evolution.

[23]  Elizabeth J. Robertson,et al.  Role of insulin-like growth factors in embryonic and postnatal growth , 1993, Cell.

[24]  J. Cheverud,et al.  Mapping quantitative trait loci for murine growth: a closer look at genetic architecture. , 1999, Genetical research.

[25]  Frederick R Adler,et al.  Genetic basis for systems of skeletal quantitative traits: Principal component analysis of the canid skeleton , 2002, Proceedings of the National Academy of Sciences of the United States of America.

[26]  E. Vallender,et al.  How mammalian sex chromosomes acquired their peculiar gene content. , 2004, BioEssays : news and reviews in molecular, cellular and developmental biology.

[27]  K. Chase,et al.  Teaching a new dog old tricks: identifying quantitative trait loci using lessons from plants. , 1999, The Journal of heredity.

[28]  E. Ostrander,et al.  Bilaterally asymmetric effects of quantitative trait loci (QTLs): QTLs that affect laxity in the right versus left coxofemoral (hip) joints of the dog (Canis familiaris) , 2004, American journal of medical genetics. Part A.

[29]  W. Vogel,et al.  A high density of X-linked genes for general cognitive ability: a run-away process shaping human evolution? , 2001, Trends in genetics : TIG.

[30]  W. Leutenegger.  Scaling of sexual dimorphism in body size and breeding system in primates , 1978, Nature.

[31]  R. Snell,et al.  Requirement of STAT5b for sexual dimorphism of body growth rates and liver gene expression. , 1997, Proceedings of the National Academy of Sciences of the United States of America.

[32]  Carolyn J. Brown,et al.  A stain upon the silence: genes escaping X inactivation. , 2003, Trends in genetics : TIG.

[33]  H. Willard,et al.  X-inactivation profile reveals extensive variability in X-linked gene expression in females , 2005, Nature.

[34]  A. Mclaren,et al.  What makes a man a man? , 1990, Nature.

[35]  B. Rensch,et al.  Evolution above the species level , 1959 .

[36]  R. Freckleton,et al.  Sexual selection explains Rensch's rule of size dimorphism in shorebirds. , 2004, Proceedings of the National Academy of Sciences of the United States of America.

[37]  S. Leal.  Genetics and Analysis of Quantitative Traits , 2001 .