The 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 genomic 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 phenology 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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Differences in reproductive timing could serve as a temporal barrier and prevent interbreeding between seasonally sympatric populations. Seasonal sympatry is a population distribution, in which populations that differ in migratory behavior are living in the same geographic space for part of the year, but are otherwise geographically isolated. Females act as the gatekeepers to reproduction because (1) they become reproductive later in the calendar year than males and (2) females likely make the final mating decisions. To determine whether interbreeding was possible between seasonally sympatric populations, I focused on differences between migrant and resident female reproductive timing.
In order to determine how females differ in reproductive timing, despite exposure to the same environmental cues, I have analyzed differences in transcript abundance of genes associated with reproduction using quantitative PCR (qPCR). Our results suggest that resident and migrant females 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. |
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., 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.
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., 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.
1. 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.
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., 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.
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. Although most mate choice research focuses on female preferences, choosing a mate with similar reproductive timing in seasonal sympatry may be critical for both males and females.
In order to study male mating preferences, I conducted Simulated Courtship Interaction (SCI) trials, by presenting free-living resident males with either a caged migrant or resident female stimulus. I quantified courtship behavior early in the breeding season, when residents have initiated breeding prior to the departure of migrants.
Resident males preferentially court resident females. We can conclude that males distinguish between migrants and residents during seasonal sympatry when risk of interacting with a non-reproductive migrant 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.
In order to study male mating preferences, I conducted Simulated Courtship Interaction (SCI) trials, by presenting free-living resident males with either a caged migrant or resident female stimulus. I quantified courtship behavior early in the breeding season, when residents have initiated breeding prior to the departure of migrants.
Resident males preferentially court resident females. We can conclude that males distinguish between migrants and residents during seasonal sympatry when risk of interacting with a non-reproductive migrant 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 in a Hybrid Zone
I started my postdoctoral position at Texas A&M in August 2019. I will be studying migratory gene expression across a hybrid zone. Return later to learn more once the project is underway!
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