Mate choice enhances post-zygotic barriers to gene flow via ancestry bundling

Hybridization and subsequent genetic introgression are now known to be common features of the histories of many species, including our own. Following hybridization, post-zygotic selection tends to purge introgressed DNA genome-wide. While mate choice can prevent hybridization in the first place, it is also known to play an important role in post-zygotic selection against hybrids, and thus the purging of introgressed DNA. However, this role is usually thought of as a direct one: a mating preference for conspecifics reduces the sexual fitness of hybrids, reducing the transmission of introgressed ancestry. Here, we explore a second, indirect role of mate choice as a barrier to gene flow. Under assortative mating, parents covary in their ancestry, causing ancestry to be "bundled" in their offspring and later generations. This bundling effect increases ancestry variance in the population, enhancing the efficiency with which post-zygotic selection purges introgressed DNA. Using whole-genome simulations, we show that the bundling effect can comprise a substantial portion of mate choice's overall effect as a postzygotic barrier to gene flow, and that it is driven by ancestry covariances both between and within maternally and paternally inherited genomes. Using estimates of the strength of assortative mating in avian hybrid zones, we calculate that the bundling effect of mate choice may increase the amount of purging of introgressed DNA by 40-80%, contributing substantially to the genetic isolation of species.

First evidence of multiple paternity in the bull shark (Carcharhinus leucas)

The present study assessed the occurrence of multiple paternity in four litters of bull shark Carcharhinus leucas (n=5, 8, 9 and 11 embryos) sampled at Reunion Island in the Western Indian Ocean. Using 21 microsatellite loci, we revealed that two litters were generated from two sires each, demonstrating for the first time multiple paternity for this species. We also reported a high paternal skew (10:1 in Litter 1 and 7:1 in Litter 3), which may be because of post-copulatory or post-zygotic selection processes. These results contribute to a better understanding of the reproductive behaviour of the bull shark, which remains poorly documented. The present study must be expanded to assess the frequency of multiple paternity in this species, and to test for genetic or cryptic benefits (convenience polyandry), which is important for long-term conservation and management plans.

Segregation Analysis of SSR, SNP, and AFLP Markers in F2 Population of Solanum lycopersicum × S. arcanum (Analisis Segregasi Marka SSR, SNP, dan AFLP pada Populasi F2 Persilangan Solanum lycopersicum × S. arcanum)

<p>Distorted marker segregation is a common phenomenon in interspecific cross of various crops. Previous mapping study of early<br />blight fungus (Alternaria solani) resistance loci showed 52% marker distortion in the genetic linkage map of 176 F2 progenies<br />derived from Solanum lycopersicum cv. Solentos × S. arcanum LA2157. The objectives of this study were to analyze in detail the<br />marker segregation in the map and to determine the cause of segregation distortion by calculating the allele and genotype<br />frequencies of each marker. Out of 371 mapped markers, 192 markers deviated from the expected Mendelian ratio of 1 : 2 : 1.<br />Distorted markers occurred in all chromosomes, ranging from 1% to 92%. Surplus of S. arcanum homozygotes contributed most<br />to the skewness (40%), followed by heterozygotes (18%), and S. lycopersicum homozygotes (5%). The allele frequencies of 152<br />markers deviated from the expected allele homogeneity frequency, indicating that their segregation might be affected by<br />gamethophytic selection. Sixty-one markers deviated from the expected F2 genotype frequency distribution, indicating that their<br />segregation might be influenced by zygotic selection. Thirty-seven of the distorted markers showed deviation from expected<br />frequencies of allele homogeneity and F2 genotype frequency distribution. Distorted markers can be retained in linkage analysis<br />since chromosomal regions containing distorted markers showed linkage with early blight fungus resistance loci. Further<br />identification of the mechanism contributing segregation distortion requires detailed and extensive mapping studies.</p>

Mapping of quantitative trait loci for thermosensitive genic male sterility in indica rice

The objective of this work was to select and use microsatellite markers, to map genomic regions associated with the genetic control of thermosensitive genic male sterility (TGMS) in rice. An F2 population, derived from the cross between fertile and TGMS indica lines, was used to construct a microsatellite-based genetic map of rice. The TGMS phenotype showed a continuous variation in the segregant population. A low level of segregation distortion was detected in the F2 (14.65%), whose cause was found to be zygotic selection. There was no evidence suggesting a cause-effect relationship between zygotic selection and the control of TGMS in this cross. A linkage map comprising 1,213.3 cM was constructed based on the segregation data of the F2 population. Ninety-five out of 116 microsatellite polymorphic markers were assembled into 11 linkage groups, with an average of 12.77 cM between two adjacent marker loci. The phenotypic and genotypic data allowed for the identification of three new quantitative trait loci (QTL) for thermosensitive genic male sterility in indica rice. Two of the QTL were mapped on chromosomes that, so far, have not been associated with the genetic control of the TGMS trait (chromosomes 1 and 12). The third QTL was mapped on chromosome 7, where a TGMS locus (tms2) has recently been mapped. Allelic tests will have to be developed, in order to clarify if the two regions are the same or not.