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Dynamic Cohort Analysis Reveals Fluctuating Patterns of Selection Within a Hybrid Zone Between the Killifish Fundulus heteroclitus and F. grandis

Abstract

Hybrid zones provide excellent opportunities to study speciation processes and ecological interactions between recently diverged taxa. Historically, hybrid zones have been divided into those in which fitness of hybrids is independent of the environment, and those in which environmental factors influence the fitness of different genotypes. The present study investigated the temporal genetic patterns at a location within a hybrid zone between the killifish Fundulus heteroclitus and F. grandis, in an effort to determine the extent and directionality of hybridization and the fitness of different genotypes. Fishes collected over the course of three years were placed into two age classes and genotyped at three nuclear loci and one mitochondrial locus that are highly differentiated between the species, allowing for comparison of genetic patterns between different age classes of the same cohorts. Individuals of hybrid descent were prevalent at the study site, the majority of which were likely advanced generation hybrids or backcrosses to one of the parental taxa. The cohort analyses revealed decreased abundance of both single and dilocus hybrid genotypes, and directional changes in allele frequency with increased age in some, but not all cohorts. These fluctuating patterns of selection across the course of the study suggest that fitness is likely strongly influenced by environmental factors.

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Data Availability

The datasets generated during and/or analyzed during the current study are available upon contacting the corresponding author.

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Acknowledgements

Thanks to Dr. Matt Kimball at the Baruch Marine Laboratory for providing samples of F. heteroclitus for development of marker loci and to Dr. Eric Johnson for providing the model to analyze the size structure of the samples collected and help with estimating FHI. Thanks to all former students that helped with collection of samples over the years. Funding for the project was provided by the George Maier Fund (2017) and funding through UNF Coastal Biology and Academic Affairs. Stipends for C. Kooyomjian and N. Hinojosa were provided by National Science Foundation Grants No. OCE-1156659 and OCE-1560213 respectively. Thanks to Florida Park Service and Division of Recreation and Parks for providing permits and access to Gamble Rogers State Park for the collection of fishes utilized in this study (Permit No: 09061613).

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Correspondence to Matthew R. Gilg.

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Gilg, M.R., Kerns, E.V., Gutierrez-Bayona, N.E. et al. Dynamic Cohort Analysis Reveals Fluctuating Patterns of Selection Within a Hybrid Zone Between the Killifish Fundulus heteroclitus and F. grandis. Evol Biol (2021). https://doi.org/10.1007/s11692-021-09553-x

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Keywords

  • Hybridization
  • Fundulus
  • Exogenous selection
  • Hybrid fitness
  • Hybrid zones