The effects of heterospecific mating frequency on the strength of cryptic reproductive barriers

Heterospecific mating frequency is critical to hybrid zone dynamics and can directly impact the strength of reproductive barriers and patterns of introgression. The effectiveness of post‐mating prezygotic (PMPZ) reproductive barriers, which include reduced fecundity via heterospecific matings and co...

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Published in:	Journal of evolutionary biology Vol. 32; no. 9; pp. 900 - 912
Main Authors:	Larson, Erica L., Brassil, Margaret M., Maslan, Jonathan, Juárez, Danielle, Lilagan, Flordeliza, Tipton, Hallie, Schweitzer, Andrew, Skillman, Joe, Monsen‐Collar, Kirsten J., Peterson, Merrill A.
Format:	Journal Article
Language:	English
Published:	Switzerland Blackwell Publishing Ltd 01-09-2019
Subjects:	Animal reproduction Beetles Chrysochus cobaltinus conspecific sperm precedence cryptic reproductive barriers Dynamic structural analysis Fecundity Females hybrid zone hybridization frequency Mating Natural populations post‐mating prezygotic barriers Relative abundance Reproductive isolation speciation System effectiveness hybridization frequency conspecific sperm precedence hybrid zone cryptic reproductive barriers relative abundance post-mating prezygotic barriers speciation
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Summary:	Heterospecific mating frequency is critical to hybrid zone dynamics and can directly impact the strength of reproductive barriers and patterns of introgression. The effectiveness of post‐mating prezygotic (PMPZ) reproductive barriers, which include reduced fecundity via heterospecific matings and conspecific sperm precedence, may depend on the number, identity and order of mates. Studies of PMPZ barriers suggest that they may be important in many systems, but whether these barriers are effective at realistic heterospecific mating frequencies has not been tested. Here, we evaluate the strength of cryptic reproductive isolation in two leaf beetles (Chrysochus auratus and C. cobaltinus) in the context of a range of heterospecific mating frequencies observed in natural populations. We found both species benefited from multiple matings, but the benefits were greater in C. cobaltinus and extended to heterospecific matings. We found that PMPZ barriers greatly limited hybrid production by C. auratus females with moderate heterospecific mating frequencies, but that their effectiveness diminished at higher heterospecific mating frequencies. In contrast, there was no evidence for PMPZ barriers in C. cobaltinus females at any heterospecific mating frequency. We show that integrating realistic estimates of cryptic isolation with information on relative abundance and heterospecific mating frequency in the field substantially improves our understanding of the strong directional bias in F1 production previously documented in the Chrysochus hybrid zone. Our results demonstrate that heterospecific mating frequency is critical to understanding the impact of cryptic post‐copulatory barriers on hybrid zone structure and dynamics, and that future studies of such barriers should incorporate field‐relevant heterospecific mating frequencies. Cryptic barriers between species, such as conspecific sperm precedence, have been typically studied under simple conditions, by crossing species at equal heterospecific mating frequencies in the lab. But these studies do not account for the complexity of hybrid zone dynamics—where species are rarely equally abundant. We show that the costs of heterospecific matings are greater for one species over a range of heterospecific mating frequencies, and that incorporating estimates of cryptic barriers better accounts for patterns of hybridization in natural populations.
Bibliography:	https://doi.org/10.5061/dryad.g708nd7 . Data deposited at Dryad ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	1010-061X 1420-9101
DOI:	10.1111/jeb.13495