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Investigating the evolutionary consequences of sexual conflict through pollen and pistil traits in several Collinsia heterophylla (Plantaginaceae) populations

Hersh, Evan (2012) BIOP31 20111
Degree Projects in Biology
Abstract
Abstract

Sexual selection is considered to be one of the most important processes influencing the evolution and diversification of species. Sexual conflict, a subset of sexual selection theory, describes how opposing interests in the male and female reproductive systems can lead to one sex increasing its fitness at a cost to the other sex. Traits involved in this conflict may come under selection and evolve, leading to antagonistic coevolution that can increase diversification in separate populations. These forces, traditionally pertaining to animals, have only recently been considered in plants. This study investigates the potential for sexual conflict in Collinsia heterophylla, a mixed mating species (utilizing both selfing and... (More)
Abstract

Sexual selection is considered to be one of the most important processes influencing the evolution and diversification of species. Sexual conflict, a subset of sexual selection theory, describes how opposing interests in the male and female reproductive systems can lead to one sex increasing its fitness at a cost to the other sex. Traits involved in this conflict may come under selection and evolve, leading to antagonistic coevolution that can increase diversification in separate populations. These forces, traditionally pertaining to animals, have only recently been considered in plants. This study investigates the potential for sexual conflict in Collinsia heterophylla, a mixed mating species (utilizing both selfing and outcrossing strategies) with two main pollen and pistil traits thought to be engaged in antagonistic coevolution during pollen competition: 1) the ability of stigmas to delay stigma receptivity in the presence of pollen, and 2) the ability of pollen to force early fertilization in immature stigmas. To explore possible evolutionary outcomes of this conflict, I performed crossing experiments in the greenhouse (within eight natural populations from four regions of California that presumably differ in mating system), as well as measured various floral traits relating to mating system and pollen competition. In the field, the potential for early pollinator visitation was investigated in order to evaluate if the conflict is likely to occur under natural conditions. In the greenhouse, I found that there was a maternal cost of early fertilization in all eight populations, indicating that the cost to the recipient individual is widespread. Across all populations, the timing of stigma receptivity was only influenced by the identity of the recipient, denoting that the female function may generally have more control over onset. Within populations, however, the male and female influence on this trait varied. There were no regional effects on either the cost or the male vs. female influence on onset, but timing of self--‐pollination appeared positively correlated to timing of stigma receptivity. Interestingly, a positive relationship was found between measures of the magnitude of the cost and the level of female control over onset, potentially suggesting selection on female control when the cost is high. Novel to this study system, I found a negative correlation between donor and recipient influence on onset within individuals; this result hints at trade--‐offs in sex--‐allocation and/or a direct genetic link between the male and female traits. In the field, I confirmed that nectar was also produced in early floral developmental stages and that seeds could be produced after pollinators visit flowers in early stages. I conclude that the result of this study is consistent with an influence of antagonistic selection on patterns of timing of stigma receptivity across populations of C. heterophylla. Further research in this area is clearly needed to illuminate the intricate forces driving plant evolution, particularly in relation to the impact of pollinators and mating system.

Popular science summary:

Sexual Conflict in the annual plant Collinsia heterophylla

Sexual selection describes the evolutionary process in which individuals compete with each other in an effort to obtain mates. Sexual conflict is a form of sexual selection that is realized when one sex negatively impacts the opposite sex while gaining a benefit for its own. These processes are thought to be important influences on plant and animal evolution, and can be held partially responsible for shaping the multitude of diverse life forms we see today. This study evaluates the potential evolutionary consequences of sexual selection and conflict in the annual flowering plant Collinsia heterophylla, the results of which may help illuminate the significance that these forces have on plant species diversification.

C. heterophylla is a flowering plant native to California. Previous studies have shown that C. heterophylla may be involved in a sexual conflict over the timing of stigma receptivity, or the time when flowers are able to be successfully fertilized. Two traits are thought to be involved in this conflict: 1) a female trait that delays stigma receptivity, which ensures that flowers are fully mature and enables fertilization by the highest quality mates, and 2) a male trait that forces early stigma receptivity, which ensures successful fertilization but incurs a cost on the receiving plant. In this study I have investigated the potential effects of these conflicting traits by performing cross-pollination experiments in the greenhouse and in the field.

I conducted a large cross-pollination experiment in the greenhouse at Lund University utilizing seeds originating from eight natural C. heterophylla populations in four different regions of California. The results of this experiment allowed me to assess the intensity and prevalence of the costs of early fertilization, and whether there was a relationship between the conflicting traits within individual plants. I also conducted field experiment, the results of which assessed the relevance of the sexual conflict in natural populations.

My results suggest that the cost of early fertilization occurs in all populations, indicating that the sexual conflict is widespread. I found a negative relationship between the functionality of the male and female trait within individuals, which hints at a genetic link between the traits involved in the conflict. Furthermore, I showed that flowers are successfully fertilized in early floral stages in the field, which confirms that the cost of the sexual conflict can be realized in natural populations of C. heterophylla. These observations provide further evidence that sexual conflict can be an important process influencing the evolution and diversification of plant species.

Advisors: Åsa Lankinen and Josefin Madjidian
Master´s Degree Project 60 credits, Plant Ecology and Systematics 2012.
Department of Biology, Lund University. (Less)
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author
Hersh, Evan
supervisor
organization
course
BIOP31 20111
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
3633886
date added to LUP
2013-04-17 15:58:57
date last changed
2013-04-17 15:58:57
@misc{3633886,
  abstract     = {Abstract

Sexual selection is considered to be one of the most important processes influencing the evolution and diversification of species. Sexual conflict, a subset of sexual selection theory, describes how opposing interests in the male and female reproductive systems can lead to one sex increasing its fitness at a cost to the other sex. Traits involved in this conflict may come under selection and evolve, leading to antagonistic coevolution that can increase diversification in separate populations. These forces, traditionally pertaining to animals, have only recently been considered in plants. This study investigates the potential for sexual conflict in Collinsia heterophylla, a mixed mating species (utilizing both selfing and outcrossing strategies) with two main pollen and pistil traits thought to be engaged in antagonistic coevolution during pollen competition: 1) the ability of stigmas to delay stigma receptivity in the presence of pollen, and 2) the ability of pollen to force early fertilization in immature stigmas. To explore possible evolutionary outcomes of this conflict, I performed crossing experiments in the greenhouse (within eight natural populations from four regions of California that presumably differ in mating system), as well as measured various floral traits relating to mating system and pollen competition. In the field, the potential for early pollinator visitation was investigated in order to evaluate if the conflict is likely to occur under natural conditions. In the greenhouse, I found that there was a maternal cost of early fertilization in all eight populations, indicating that the cost to the recipient individual is widespread. Across all populations, the timing of stigma receptivity was only influenced by the identity of the recipient, denoting that the female function may generally have more control over onset. Within populations, however, the male and female influence on this trait varied. There were no regional effects on either the cost or the male vs. female influence on onset, but timing of self--‐pollination appeared positively correlated to timing of stigma receptivity. Interestingly, a positive relationship was found between measures of the magnitude of the cost and the level of female control over onset, potentially suggesting selection on female control when the cost is high. Novel to this study system, I found a negative correlation between donor and recipient influence on onset within individuals; this result hints at trade--‐offs in sex--‐allocation and/or a direct genetic link between the male and female traits. In the field, I confirmed that nectar was also produced in early floral developmental stages and that seeds could be produced after pollinators visit flowers in early stages. I conclude that the result of this study is consistent with an influence of antagonistic selection on patterns of timing of stigma receptivity across populations of C. heterophylla. Further research in this area is clearly needed to illuminate the intricate forces driving plant evolution, particularly in relation to the impact of pollinators and mating system.

Popular science summary:

Sexual Conflict in the annual plant Collinsia heterophylla

Sexual selection describes the evolutionary process in which individuals compete with each other in an effort to obtain mates. Sexual conflict is a form of sexual selection that is realized when one sex negatively impacts the opposite sex while gaining a benefit for its own. These processes are thought to be important influences on plant and animal evolution, and can be held partially responsible for shaping the multitude of diverse life forms we see today. This study evaluates the potential evolutionary consequences of sexual selection and conflict in the annual flowering plant Collinsia heterophylla, the results of which may help illuminate the significance that these forces have on plant species diversification.

C. heterophylla is a flowering plant native to California. Previous studies have shown that C. heterophylla may be involved in a sexual conflict over the timing of stigma receptivity, or the time when flowers are able to be successfully fertilized. Two traits are thought to be involved in this conflict: 1) a female trait that delays stigma receptivity, which ensures that flowers are fully mature and enables fertilization by the highest quality mates, and 2) a male trait that forces early stigma receptivity, which ensures successful fertilization but incurs a cost on the receiving plant. In this study I have investigated the potential effects of these conflicting traits by performing cross-pollination experiments in the greenhouse and in the field.

I conducted a large cross-pollination experiment in the greenhouse at Lund University utilizing seeds originating from eight natural C. heterophylla populations in four different regions of California. The results of this experiment allowed me to assess the intensity and prevalence of the costs of early fertilization, and whether there was a relationship between the conflicting traits within individual plants. I also conducted field experiment, the results of which assessed the relevance of the sexual conflict in natural populations. 

My results suggest that the cost of early fertilization occurs in all populations, indicating that the sexual conflict is widespread. I found a negative relationship between the functionality of the male and female trait within individuals, which hints at a genetic link between the traits involved in the conflict. Furthermore, I showed that flowers are successfully fertilized in early floral stages in the field, which confirms that the cost of the sexual conflict can be realized in natural populations of C. heterophylla. These observations provide further evidence that sexual conflict can be an important process influencing the evolution and diversification of plant species.

Advisors: Åsa Lankinen and Josefin Madjidian
Master´s Degree Project 60 credits, Plant Ecology and Systematics 2012.
Department of Biology, Lund University.},
  author       = {Hersh, Evan},
  language     = {eng},
  note         = {Student Paper},
  title        = {Investigating the evolutionary consequences of sexual conflict through pollen and pistil traits in several Collinsia heterophylla (Plantaginaceae) populations},
  year         = {2012},
}