The nature of interactions that contribute to postzygotic reproductive isolation in hybrid copepods

Abstract

Deleterious interactions within the genome of hybrids can lower fitness and result in postzygotic reproductive isolation. Understanding the genetic basis of these deleterious interactions, known as Dobzhansky-Muller incompatibilities, is the subject of intense current study that seeks to elucidate the nature of these deleterious interactions. Hybrids from crosses of individuals from genetically divergent populations of the intertidal copepod Tigriopus californicus provide a useful model in which to study Dobzhansky-Muller incompatibilities. Studies of the basis of postzygotic reproductive isolation in this species have revealed a number of patterns. First, there is evidence for a breakdown in genomic coadaptation between mtDNA-encoded and nuclear-encoded proteins that can result in a reduction in hybrid fitness in some crosses. It appears from studies of the individual genes involved in these interactions that although this coadaptation could lead to asymmetries between crosses, patterns of genotypic viabilities are not often consistent with simple models of genomic coadaptation. Second, there is a large impact of environmental factors on these deleterious interactions suggesting that they are not strictly intrinsic in nature. Temperature in particular appears to play an important role in determining the nature of these interactions. Finally, deleterious interactions in these hybrid copepods appear to be complex in terms of the number of genetic factors that interact to lead to reductions in hybrid fitness. This complexity may stem from three or more factors that all interact to cause a single incompatibility or the same factor interacting with multiple other factors independently leading to multiple incompatibilities.

Cytonuclear interactions affect adaptive traits of the annual plantArabidopsis thalianain the field

“…In addition to being a characteristic feature of CMS, asymmetrical responses to reciprocal cytonuclear exchange have been previously reported in plants, including at the interspecific level (7). Symmetrical responses have also been observed in the reciprocal exchange of genetic compartments, with nonparental combinations showing impaired phenotypes compared with the parental lines, e.g., longevity in intraspecific seed beetle (Acanthoscelides obtectus) cytolines (40) and fitness breakdown in reciprocal F2s of a copepod (Tigriopus californicus) (41,42). In this latter case, nuclear-encoded cytochrome c and mitochondria-encoded subunits of cytochrome c oxidase have diverged between the two parental populations such that the interaction between the mismatched partners impairs complex IV activity (43).…”

Temperature stress increases hybrid incompatibilities in the parasitic wasp genus Nasonia

“…This is in contrast with most diploid species in which nuclear–nuclear interactions appear to dominate among genes leading to hybrid incompatibilities (reviewed by Presgraves, 2010). Cytonuclear incompatibilities may be a specific feature of male hybrids of haplodiploid species, as they appear rarely in F 1 diploid hybrids (but see Willett, 2011). This could be due to higher detection ability in haploids, assuming that such incompatibilities are largely recessive (supported by the lack of such incompatibilities in F 1 diploid hybrid females of haplodiploids).…”

“…Although it remains unresolved whether changes in gene expression, G · E interactions or the effect of temperature on cytonuclear incompatibilities is the cause of the results found in the current study, it is evident that homoeostasis in hybrid individuals is disrupted and that small perturbations lead to more incompatibilities between genes. G · E interactions in disrupting epistasis in hybrids have not received much attention apart from the marine copepod T. californicus (reviewed by Willett, 2011). Here, we provide the first genome-wide screen of the effect of temperature on the regions associated with inducing hybrid mortality.…”

Behavioral Isolation and Incipient Speciation in Birds

“…For example, in Drosophila and several flowering plants, prezygotic barriers evolve before hybrid sterility and inviability (Baack et al 2015, Coyne & Orr 1997, though more subtle postzygotic barriers are less often studied. Conversely, intrinsic postzygotic barriers can evolve with little to no prezygotic isolation, as in Tigriopus copepods (Willett 2011). With respect to rates of evolution, prezygotic isolation in the form of pollen and ovule incompatibility evolves faster in annual than in perennial plants (Baack et al 2015), whereas hybrid inviability evolves faster in mammals than in birds and frogs (Wilson et al 1974).…”