No species barrier by call in an avian hybrid zone between California and Gambel's quail (Callipepla californica and C. gambelii)

The house mouse hybrid zone (HMHZ) is a species barrier thought to be maintained by a balance between dispersal and natural selection against hybrids. While the HMHZ is characterized by frequency discontinuities for some sex chromosome markers, there is an unexpected large-scale regional introgression of a Y chromosome across the barrier, in defiance of Haldane's rule. Recent work suggests that a major force maintaining the species barrier acts through sperm traits. Here, we test whether the Y chromosome penetration of the species barrier acts through sperm traits by assessing sperm characteristics of wild-caught males directly in a field laboratory set up in a Y introgression region of the HMHZ, later calculating the hybrid index of each male using 1401 diagnostic single nucleotide polymorphisms (SNPs). We found that both sperm count (SC) and sperm velocity were significantly reduced across the natural spectrum of hybrids. However, SC was more than rescued in the presence of the invading Y. Our results imply an asymmetric advantage for Y chromosome introgression consistent with the observed large-scale introgression. We suggest that selection on sperm-related traits probably explains a large component of patterns observed in the natural hybrid zone, including the Y chromosome penetration.

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Prevalence and intensity of avian malaria in a quail hybrid zone

10.22541/au.160795716.69387589/v1 ◽

2020 ◽

Author(s):

Allison Roth ◽

Nick Kaiser ◽

Judson Williams ◽

Jennifer Gee

Keyword(s):

Avian Malaria ◽

Sympatric Species ◽

Blood Parasite ◽

Infection Status ◽

Intensity Of Infection ◽

Species Barrier ◽

Species Identity ◽

The Status ◽

Evolutionary Consequences ◽

Gambel's Quail

Hybridization is a common and important stage in species formation in plants and animals. The evolutionary consequences of hybridization depend not only on reproductive compatibility between sympatric species, but also on factors like vulnerability to each other’s predators and parasites. We examine infection patterns of the blood parasite Haemoproteus lophortyx, a causative agent of avian malaria, at a site in the contact zone between California quail (Callipepla californica) and Gambel’s quail (C. gambelii). We tested whether species identity, sex, and year predicted infection status and intensity. While we found no effect of sex on the status or intensity of infection, we found differences in infection status and intensity across species and between years. The prevalence of infection in California and hybrid quail was lower than in Gambel’s quail. Once infected, however, California and hybrid quail had higher infection intensities than Gambel’s quail. California and hybrid quail exhibited no significant differences in prevalence or intensity of infection. These findings suggest that infection by H. lophortyx has the potential to influence species barrier dynamics in this system, however, more work is necessary to determine the exact evolutionary consequences of this blood parasite.

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