Environmental challenges presented by changing seasons have shaped seasonal patterns of migration and reproduction into two of the most consistent adaptations across the animal world. Broadly, I am interested in the physiological and molecular mechanisms linking significant life-history traits (i.e., animal migration and reproduction) and the evolutionary consequences of variation in these traits. Divergent seasonal behaviors can result in prezygotic isolating mechanisms (i.e., differences in timing and mating preferences) or postzygotic isolating mechanisms (i.e., selection against hybrids), and therefore, could drive speciation.
Additionally, my research program has emphasized sex differences in these mechanisms, by primarily focusing on female birds. Male and female animals differ vastly in their reproductive timing and the physiological basis of their reproduction. Females act as the gatekeepers to reproduction, as they enter reproductive condition after males. However, there is a persistent sex bias favoring males in the literature on reproductive physiology in birds. I discuss one way we can combat this sex bias in the field to learn more about the mechanisms of female reproduction in the paper here.
Additionally, my research program has emphasized sex differences in these mechanisms, by primarily focusing on female birds. Male and female animals differ vastly in their reproductive timing and the physiological basis of their reproduction. Females act as the gatekeepers to reproduction, as they enter reproductive condition after males. However, there is a persistent sex bias favoring males in the literature on reproductive physiology in birds. I discuss one way we can combat this sex bias in the field to learn more about the mechanisms of female reproduction in the paper here.
Reproductive Timing as a Temporal Barrier
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Seasonal sympatry presents an ideal opportunity for studying how divergent migratory behavior might shape isolating barriers. Seasonal sympatry is when populations that differ in their propensity to migrate (i.e., migrant vs. non-migrant) are living in the same geographic space for part of the year, but are otherwise geographically isolated.
In early spring, closely related populations experience the same environmental cues, but physiologically are quite different as one population prepares for migration while the other prepares for reproduction. Differences in reproductive timing could serve as a temporal barrier and prevent interbreeding between seasonally sympatric populations. Our results suggest that females that differ in migratory behavior also differ in timing of reproductive development. Differential transcript abundance of receptors may also explain the mechanisms for how females differ in timing of reproductive development. Therefore, differences in migratory behavior, and consequent differences in reproductive timing, could prevent interbreeding between closely-related populations. |
The hypothalamic-pituitary-gonadal (HPG) axis: the reproductive cascade of hormones
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Be sure to check out the related papers:
1. Kimmitt, A.A., Hardman, J.W., Stricker, C.A. and Ketterson, E.D., 2019. Migratory
strategy explains differences in timing of female reproductive development in seasonally sympatric songbirds. Functional Ecology, 33(9), pp.1651-1662.
2. Kimmitt, A.A., Sinkiewicz, D.M. and Ketterson, E.D., 2020. Seasonally sympatric songbirds that differ in migratory strategy also differ in neuroendocrine measures. General and comparative endocrinology, 285, p.113250.
3. Kimmitt, A.A., Webb, A.L., Greives, T.J. and Ketterson, E.D., 2020. Migrant and resident female songbirds differ in gonadal response to upstream stimulation during seasonal sympatry. General and Comparative Endocrinology, 293, p.113469.
1. Kimmitt, A.A., Hardman, J.W., Stricker, C.A. and Ketterson, E.D., 2019. Migratory
strategy explains differences in timing of female reproductive development in seasonally sympatric songbirds. Functional Ecology, 33(9), pp.1651-1662.
2. Kimmitt, A.A., Sinkiewicz, D.M. and Ketterson, E.D., 2020. Seasonally sympatric songbirds that differ in migratory strategy also differ in neuroendocrine measures. General and comparative endocrinology, 285, p.113250.
3. Kimmitt, A.A., Webb, A.L., Greives, T.J. and Ketterson, E.D., 2020. Migrant and resident female songbirds differ in gonadal response to upstream stimulation during seasonal sympatry. General and Comparative Endocrinology, 293, p.113469.
Mate Preferences in Seasonal Sympatry
Residents that initiate breeding prior to the departure of migrants may avoid interbreeding with migrants by exhibiting mate preferences for local individuals. Choosing a mate with similar reproductive timing in seasonal sympatry may be critical for both males and females.
We found male mate preferences during seasonal sympatry in early spring. We can conclude that males distinguish between females that differ in migratory behavior during seasonal sympatry because risk of interacting with a non-reproductive female is high.
Check out the paper:
Kimmitt, A.A., Dietz, S.L., Reichard, D.G., and Ketterson, E.D., 2018. Male courtship preference during seasonal sympatry may reinforce population divergence. Ecology and Evolution 8(23), pp.11833-11841.
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Molecular Basis of Divergent Migratory Behavior
Complex behaviors in free-living animals, such as migration, are challenging to study because these traits are often driven by large networks of genes that can affect more than one trait. Identifying the genetic basis of migration, however, could explain natural variation in the trait as well as how divergent migratory behavior might act as a reproductive isolating barrier between populations.
I have contributed to work investigating the molecular basis of migratory orientation across a hybrid zone to (1) identify the underlying genetic regions of variation in this migratory trait variation and (2) investigate selection against hybrids with intermediate migratory traits. I am also beginning work to identify a potential hybrid site between populations that differ in the propensity to migrate (migrants vs. non-migrants). I hope to expand this work to map genetic and behavioral variation in the migratory phenotype across the hybrid zone. My past work has shown that prezygotic isolating barriers are likely contributing to population divergence between migratory and non-migratory populations, but I am also interested in how selection against hybrids might further contribute to population divergence. Come back later for more updates on this project! |
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