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Does divergence from normal patterns of integration increase as chromosomal fusions increase in number? A test on a house mouse hybrid zone.

ABSTRACT: Chromosomal evolution is widely considered an important driver of speciation because it can promote the establishment of reproductive barriers. Karyotypic reorganization is also expected to affect the mean phenotype, as well as its development and patterns of phenotypic integration, through processes such as variation in genetic linkage between quantitative trait loci or between regulatory regions and their targets. Here we explore the relationship between chromosomal evolution and phenotypic integration by analyzing a well-known house mouse parapatric contact zone between a highly derived Robertsonian (Rb) race (2n?=?22) and populations with standard karyotype (2n?=?40). Populations with hybrid karyotypes are scattered throughout the hybrid zone connecting the two parental races. Using mandible shape data and geometric morphometrics, we test the hypothesis that patterns of integration progressively diverge from the "normal" integration pattern observed in the standard race as they accumulate Rb fusions. We find that the main pattern of integration observed between the posterior and anterior part of the mandible can be largely attributed to allometry. We find no support for a gradual increase in divergence from normal patterns of integration as fusions accumulate. Surprisingly, however, we find that the derived Rb race (2n?=?22) has a distinct allometric trajectory compared with the standard race. Our results suggest that either individual fusions disproportionately affect patterns of integration or that there are mechanisms which "purge" extreme variants in hybrids (e.g. reduced fitness of hybrid shape).

SUBMITTER: Fruciano C

PROVIDER: S-EPMC7705516 | biostudies-literature | 2020 Oct

REPOSITORIES: biostudies-literature

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Does divergence from normal patterns of integration increase as chromosomal fusions increase in number? A test on a house mouse hybrid zone.

Fruciano Carmelo C Colangelo Paolo P Castiglia Riccardo R Franchini Paolo P

Current zoology 20200911 5

Chromosomal evolution is widely considered an important driver of speciation because it can promote the establishment of reproductive barriers. Karyotypic reorganization is also expected to affect the mean phenotype, as well as its development and patterns of phenotypic integration, through processes such as variation in genetic linkage between quantitative trait loci or between regulatory regions and their targets. Here we explore the relationship between chromosomal evolution and phenotypic in ...[more]

PMID: 33293931

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Project description:BACKGROUND:Western house mice Mus musculus domesticus are among the most important mammalian model species for chromosomal speciation. Hybrids between chromosomal races of M. m. domesticus suffer various degrees of fertility reduction between full fertility and complete sterility, depending on the complexity of the chromosomal differences between the races. This complexity presents itself in hybrids as meiotic configurations of chromosome chains and rings, with longer configurations having a stronger impact on fertility. While hybrids with short configurations have been intensively studied, less work has been done on hybrids with very long configurations. In this study, we investigated laboratory-reared wild mice from two chromosomally very different races in Switzerland found in close proximity. Hybrids between these races form a meiotic chain of fifteen chromosomes. We performed a detailed analysis of male and female hybrid fertility, including three generations of female backcrosses to one of the parental races. We also tested for possible divergence of mate preference in females. RESULTS:While all male F1 hybrids were sterile with sperm counts of zero, 48% of female F1 hybrids produced offspring. Their litter sizes ranged from one to three which is significantly lower than the litter size of parental race females. When hybrid females were backcrossed to a parental race, half of the offspring resembled the parental race in karyotype and fertility, while the other half resembled the F1 hybrids. In the preference test, females of both races indicated a lack of a preference for males of their own karyotype. CONCLUSIONS:Although the fertility of the F1 hybrids was extremely low because of the complexity of the chromosomal differences between the races, reproductive isolation was not complete. As we did not find assortative female preferences, we expect that contact between these races would lead to the production of hybrids and that gene flow would occur eventually, as fertility can be restored fully after one backcross generation.

Dataset Information

Does divergence from normal patterns of integration increase as chromosomal fusions increase in number? A test on a house mouse hybrid zone.

Publications

Does divergence from normal patterns of integration increase as chromosomal fusions increase in number? A test on a house mouse hybrid zone.

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