Tangled Bank Seminar
Tangled Bank Seminar by Daniel Hooper at Cornell University on "Chromosome inversions and reproductive isolation in an avian hybrid zone".
Chromosome inversions and reproductive isolation in an avian hybrid zone
The Cornell Lab of Ornithology, Cornell University
Chromosome inversions are common in birds and appear to be more frequent in sympatric species pairs than allopatric ones - suggesting a potential role for gene flow in the evolution of inversions. Across hybrid zones, the sex chromosomes are often more strongly differentiated than the autosomes and this is regularly attributed to the greater rate of reproductive incompatibilities accumulating on sex chromosomes and their exposure in the heterogametic sex. I explore the possibility that chromosome inversions differentially accumulate on the Z chromosome compared to the autosomes as well and thereby also contribute to Z chromosome differentiation. I will discuss our work on the northern Australian hybrid zone between two subspecies of the long-tailed finch (Poephila acuticauda), where autosomal differentiation between subspecies is minimal but 75% of the Z chromosome is highly differentiated and appears to be associated with two or more putative chromosomal inversions, each predominating in one subspecies. If inversions reduce recombination between hybrid incompatibilities, they are selectively favored and should therefore accumulate in hybrid zones. I will argue that this predisposes inversions to differentially accumulate on the Z chromosome in a process of feedback.
My research interests are focused on better understanding the origin of species: the process of speciation. Speciation is associated with not just the accumulation of molecular changes but also with regulatory changes in gene expression and structural changes, such as chromosomal inversions‚ structural rearrangements to the order and recombination landscape of genes on a chromosome. Because the speciation process can take millions of years to complete, gene flow among incipient species is common and can often influence the development of reproductive isolation. Gene flow generally acts to remove differences between diverging populations but it can also play a creative role in speciation by promoting the evolution of pre-mating barriers and for chromosome inversions that encompass and keep together sets of locally adapted genes.