The genomic and ecological context of hybridization affect the probability that symmetrical incompatibilities drive hybrid speciation

Despite examples of homoploid hybrid species, theoretical work describing when, where, and how we expect homoploid hybrid speciation to occur remains relatively rare. Here I explore the probability of homoploid hybrid speciation due to “symmetrical incompatibilities” under different selective and genetic scenarios. Through simulation, I test how genetic architecture and selection acting on traits that do not themselves generate incompatibilities interact to affect the probability that hybrids evolve symmetrical incompatibilities with their parent species. Unsurprisingly, selection against admixture at ‘adaptive’ loci that are linked to loci that generate incompatibilities tends to reduce the probability of evolving symmetrical incompatibilities. By contrast, selection that favors admixed genotypes at adaptive loci can promote the evolution of symmetrical incompatibilities. The magnitude of these outcomes is affected by the strength of selection, aspects of genetic architecture such as linkage relationships and the linear arrangement of loci along a chromosome, and the amount of hybridization following the formation of a hybrid zone. These results highlight how understanding the nature of selection, aspects of the genetics of traits affecting fitness, and the strength of reproductive isolation between hybridizing taxa can all be used to inform when we expect to observe homoploid hybrid speciation due to symmetrical incompatibilities.

A Targeted Capture Linkage Map Anchors the Genome of the Schistosomiasis Vector Snail, Biomphalaria glabrata

The aquatic planorbid snail Biomphalaria glabrata is one of the most intensively-studied mollusks due to its role in the transmission of schistosomiasis. Its 916 Mb genome has recently been sequenced and annotated, but it remains poorly assembled. Here, we used targeted capture markers to map over 10,000 B. glabrata scaffolds in a linkage cross of 94 F1 offspring, generating 24 linkage groups (LGs). We added additional scaffolds to these LGs based on linkage disequilibrium (LD) analysis of targeted capture and whole-genome sequences of 96 unrelated snails. Our final linkage map consists of 18,613 scaffolds comprising 515 Mb, representing 56% of the genome and 75% of genic and nonrepetitive regions. There are 18 large (> 10 Mb) LGs, likely representing the expected 18 haploid chromosomes, and > 50% of the genome has been assigned to LGs of at least 17 Mb. Comparisons with other gastropod genomes reveal patterns of synteny and chromosomal rearrangements. Linkage relationships of key immune-relevant genes may help clarify snail–schistosome interactions. By focusing on linkage among genic and nonrepetitive regions, we have generated a useful resource for associating snail phenotypes with causal genes, even in the absence of a complete genome assembly. A similar approach could potentially improve numerous poorly-assembled genomes in other taxa. This map will facilitate future work on this host of a serious human parasite.

Genetic and Linkage Studies of New Autosomal Sex-Limited Mutant Hairless Antenna in Anopheles stephensi Liston

A new morphological mutant hairless antenna (hla) was induced in the mosquito Anopheles stephensi by γ-irradiation. The expression of the mutant in the male adult revealed the antennae without the hairs. The inheritance pattern from our data demonstrates that hairless antenna is essentially sex-limited to males and is autosomal and recessive. The linkage relationships studies between the hairless antenna and greyish brown larva (grb) mutant indicated independent assortment and are present on different chromosomes, while the linkage relationship studies between the hairless antenna and ruby eye (ru) mutant revealed the suppression of hla by the ru gene in heterozygous condition. These mutants can be useful in conducting basic and applied research such as construction of linkage maps and understanding biochemical pathways and in genetic control programmes.

Features of Inheritance to Individual Traits of Millet (Panicum mileaceum L.)

Aim. To determine the inheritance of the millet morphological traits: seed color, size, anthocyan coloring of its parts, raсе specifi ed resistance to smut and genetic linkage relationships between these features, which are a reliable basis for the breeding of a new generation of varieties. Methods. Genetic analysis of the F1, F2 and F3 hybrids. Results. The interrelations between the seed size, its color and shape, and especially raсе specifi ed resistance to smut have been determined. Conclusions. The degree of linkage between the loci of genes that control the expression of the relevant characteristics in experimental combinations interbreeding has been stated.

Inheritance and linkage of allozymes in Juniperus phoenicea L. (Cupressaceae)

Eight enzyme systems coding for 14 loci were assayed in <em>Juniperus phoenicea</em>. Mendelian inheritance was confirmed for allozymes at 10 loci (Fle 2, Gdh, Got 1, Idh, Mdh 1, Mdh 2, Men 1, Pgi, Pgm I, Pgm 2) by testing the fit of band-pattern segregation in macrogametophytes from heterozygous trees to the expected I: I ratio. Linkage relationships were examined for 21 pairs of allozyme loci and these pairs do not appear to be linked in our material.