Hybrid inviability
Hybrid inviability is a
The barrier of hybrid inviability occurs after mating species overcome pre-zygotic barriers (behavioral, mechanical, etc.) to produce a
Evolution of Hybrid Inviability in Tetrapods
In the 1970s,
Recognizing that hybrid viability decreases with time, the researchers used
Wilson et al. (1974) proposes two hypotheses to explain the relatively faster evolution of hybrid inviability in mammals: the Regulatory and the Immunological Hypotheses. Subsequent research finds support for these hypotheses.
The Regulatory Hypothesis accounts for two characteristics of mammals, and explains the general formation of hybrid inviability in mammals, birds, and frogs.
First, mammals display relatively lower protein diversity than frogs. As Wilson et al. (1974) suggests, “mammals that can hybridize with each other differ only slightly at the protein level, whereas frogs that differ substantially in
Second, the evolution of anatomical diversity occurred far faster in mammals than in either birds or frogs. As Fitzpatrick (2004) indicates, “the morphological disparities among bats, mole-rats, and whales are more dramatic than any disparities in birds and frogs.” This anatomical diversity is evidence for the diversification of regulatory systems. This mammalian characteristic suggests that, although mammals are genetically similar, dramatic changes in regulatory genes caused distinct developmental differences.[6]
The Regulatory Hypotheses specifically attributes hybrid inviability in mammals, birds, and frogs to differences in
Wilson et al. (1974) recognizes that the development of embryos in the mammalian
The Immunological Hypothesis proposes that the divergence of certain protein structures associated with mother and child causes hybrid inviability. The hypothesis applies only to mammals, where
This hypothesis stems from the immunological characteristics of the placenta, where the growing fetus is in constant contact with the fluids and tissues of the mother. Variation within species and variation between species may contribute to fetal-maternal incompatibility, and according to the hypothesis, if the proteins of the fetus varies significantly from the proteins of the placenta, the mother may produce anti-bodies that will attack and abort the fetus. Therefore, if the fetal proteins of the father species are incompatible the mother's placental proteins, the mother's immune system may abort the embryo.
Evidence for the Immunological Hypothesis varies considerably. Wilson et al. (1974) recognizes studies that provide no support to the Immunological Hypotheses. In these experiments, the use of
Notes
- ^ Hybrid inviability. (2009). In Encyclopædia Britannica. Retrieved November 03, 2009, from Encyclopædia Britannica Online: http://www.britannica.com/EBchecked/topic/278018/hybrid-inviability
- ^ Campbell, N. A., J. B. Reece, L. A. Urry, M. L. Cain, S. A. Wasserman, P. V. Minorsky, and R. B. Jackson. 2008. Biology: Eighth Ed. San Francisco, CA:491.
- ^ Freeman, S., and J. C. Herron. 2007. Evolutionary Analysis:Fourth Ed. Upper Saddle River, NJ:627.
- ^ Prager, E. M., and A. C. Wilson. 1975. Slow evolutionary loss of the potential for interspecific hybridization in birds: a manifestation of slow regulatory evolution. Proc. Natl. Acad. Sci. USA 72:200-204.
- ^ Wilson, A. C., L. R. Maxson, and V. M. Sarich. 1974. Two types of molecular evolution: evidence from studies of interspecific hybridization. Proc. Natl. Acad. Sci. USA 71:2843-2847.
- ^ Fitzpatrick, B. M. 2004. Rates of evolution of hybrid viability in birds and mammals. Evolution 58:1865-1870.
- ^ Elliot, M. G., and B. J. Crespi. 2006. Placental invasiveness mediates the evolution of hybrid inviability in mammals. Am. Nat. 168:114-120.