Speciation driven by internal genetic conflicts: a test in Drosophila by an introgression study Open Access

Sun, Tianai (2014)

Permanent URL: https://etd.library.emory.edu/concern/etds/2n49t194n?locale=en
Published

Abstract

Speciation, the evolution of reproductive isolations (RI) between two incipient species, has long been a focus of evolutionary genetics. Hybrid male sterility (HMS) is typically the fastest evolved one among all RI mechanisms. The evolution of HMS has been thought to be the consequence of adaptive evolution, but the nature of the adaptation remains elusive until recently a major role is attributed to intragenomic conflicts, as illustrated in meiotic drive systems. Typically, a meiotic drive system consists of distorter, responder and suppressor. Chromosome harboring the distorter gains fitness advantage by favoring the transmission of its own on the cost of its homolog. This must be assisted by the tightly linked responder to distinguish itself from its homolog. Meanwhile, suppressor(s) is required to evolve as a counterbalancing force of the distorter because meiotic drive causes fitness loss to the genes not closely linked to it. Due to the lack of recombination between the X and Y, meiotic drive is most likely to evolve on sex chromosomes. The "drive theory" posits that the perpetual conflicts between the three elements disturb the balance of meiosis genes, thus leading to fast evolution of HMS. One prediction of the "drive theory" is that the same set of genes are capable of controlling both sex ratio and fertility in the male hybrids between two very incipient species such as Drosophila albomicans and D. nasuta. Quantitative trait loci (QTL) mappings have implicated 5 regions that underlie either sex ratio or HMS, or both. To increase the accuracy of mapping, I used molecular markers to assist the introgression from D. albomicans with various combinations of the five QTL into the D. nasuta background. As expected, every individual region expresses dual function of sex ratio and male fertility. For one QTL region (suppressor) spanning the centromere of the 2nd chromosome, I generated shorter introgressions for fine mapping. The result suggests that this suppressor region can be further partitioned to three factors, allworking to decrease sex ratio while increase fertility. We therefore conclude that genes affecting sex ratio also contribute to male fertility, as predicted by the "drive theory".

Table of Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

Figure 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

Figure 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Figure 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

Material and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Table 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

Figure 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

Figure 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Figure 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Figure 7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

Appendix I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28

Appendix II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29

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