Genetics and the Fitness of Hybrids

Abstract

Over the years, the evolutionary importance of natural hybridization has been a contentious issue. At one extreme is the relatively common view of hybridization as an evolutionarily unimportant process. A less common perspective, but one that has gained support over the past decade, is that of hybridization as a relatively widespread and potentially creative evolutionary process. Indeed, studies documenting the production of hybrid genotypes exhibiting a wide range of fitnesses have become increasingly common. In this review, we examine the genetic basis of such variation in hybrid fitness. In particular, we assess the genetic architecture of hybrid inferiority (both sterility and inviability). We then extend our discussion to the genetic basis of increased fitness in certain hybrid genotypes. The available evidence argues that hybrid inferiority is the result of widespread negative epistasis in a hybrid genetic background. In contrast, increased hybrid fitness can be most readily explained through the segregation of additive genetic factors, with epistasis playing a more limited role.

Growth-related quantitative trait loci in domestic and wild rainbow trout (Oncorhynchus mykiss)

“…For commercial rainbow trout strains that have previously been selected for more uniform and rapid growth (i.e., the parents of family 96-7-C) this would be the expectation. These findings are also consistent with the observation that hybrid breakdown, through epistatic interactions, appear to be more pronounced the more distant genetically/geographically the hybridizing populations are that give rise to F 1 individuals (summarized in [51]).…”

“…Additional data is required from both intra- and inter-strain sources to assess the repeatability of the epistatic marker associations. The postulated and empirical basis for the origins of epistasis can relate to deleterious/detrimental gene combinations that can arise when the two strains are interbred following a prolonged temporal period of divergence [51,52]. The fact that multiple epistatic interactions were observed on RT-8 with two of the three siblings from family 96-7-C also suggests that familial and heritable differences may exist in the expression of epistasis.…”

Pharmacogenomic Evaluation of the Antidepressant Citalopram in the Mouse Tail Suspension Test

“…It resulted from an over-representation of both BALB/cJ and A/J homozygotes in the most responsive F 2 mice and over-representation of heterozygotes in the least responsive F 2 mice. This may be a case of inbreeding depression (Burke and Arnold, 2001), in which there is an increased strength of certain characteristics of genes in hybrids. In this study, the response to citalopram seemed to be diminished in the heterozygous F 2 mice.…”

Mating with the wrong species can be right

“…The division arose from the, on average, higher number of successful hybrids in plants than in animals [1,2]. With the application of molecular tools, scientists increasingly came to realize that, in both kingdoms, interspecific hybridization (see Glossary) is very unequally distributed among and within taxa; and in some animals the rate of hybridization even exceeds that in plants [2][3][4].…”

“…late in the season) and in areas where population density of conspecifics is low (e.g. at the fringe of the geographic distribution area) [1,[10][11]. In such areas, hybrid matings are usually between the females of a rare species and the males of a common species, but not vice versa.…”