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Do differences in fitness traits and their genetic variation explain differences in colonization rate between two alien grass species?

Liu, Chang (2020) BIOM02 20201
Degree Projects in Biology
Abstract
Biological invasions and their underlying mechanisms have become major issues in ecology, conservation and evolutionary biology. In order to better understand the factors determining colonization and invasion success, I obtained common-garden data from more than 1000 greenhouse-grown plants of two alien grass species, Eragrostis minor and E. multicaulis, derived from about 30 sites per species in the city of Malmö. Particularly attention was given to the following questions: (i) Is the more rapid colonizer E. multicaulis characterized by more rapid growth, larger size and higher reproductive output? (ii) Can the contrasting colonization rates of the two species be linked to patterns and amounts of genetic variation within species? (iii) Is... (More)
Biological invasions and their underlying mechanisms have become major issues in ecology, conservation and evolutionary biology. In order to better understand the factors determining colonization and invasion success, I obtained common-garden data from more than 1000 greenhouse-grown plants of two alien grass species, Eragrostis minor and E. multicaulis, derived from about 30 sites per species in the city of Malmö. Particularly attention was given to the following questions: (i) Is the more rapid colonizer E. multicaulis characterized by more rapid growth, larger size and higher reproductive output? (ii) Can the contrasting colonization rates of the two species be linked to patterns and amounts of genetic variation within species? (iii) Is there any evidence for local adaptation across populations? Plants of E. minor reached reproductive maturation earlier and had higher reproductive output, in direct conflict with my expectation of more rapid development and higher reproductive effort in the rapid colonizer. Measures of evolutionary potential (heritability, evolvability) were also lower for E. multicaulis populations; thus, no association between high genetic variation and rapid colonization could be detected. The strongest evidence for local adaptation was found in the slower colonizer (E. minor), manifested as positive relationships between mean culm height and the distance from the putative starting point of the colonization. (Less)
Popular Abstract
What makes two alien grasses have different colonization rates?

Biological invasions and their underlying mechanisms have become major issues in ecology, conservation and evolutionary biology. In order to better understand the factors determining colonization and invasion success, I measured five fitness-related traits on more than 1000 greenhouse-grown plants of two alien grass species, Eragrostis minor and E. multicaulis, derived from about 30 sites per species in an area that has been colonized by both species (city of Malmö). Both species are warm-adapted C4 plants with a recent colonization history in Northern Europe.

Comparison of species means
Plants of E. minor had earlier maturation dates than those of the more recent... (More)
What makes two alien grasses have different colonization rates?

Biological invasions and their underlying mechanisms have become major issues in ecology, conservation and evolutionary biology. In order to better understand the factors determining colonization and invasion success, I measured five fitness-related traits on more than 1000 greenhouse-grown plants of two alien grass species, Eragrostis minor and E. multicaulis, derived from about 30 sites per species in an area that has been colonized by both species (city of Malmö). Both species are warm-adapted C4 plants with a recent colonization history in Northern Europe.

Comparison of species means
Plants of E. minor had earlier maturation dates than those of the more recent “newcomer” E. multicaulis. The E. minor plants also had taller culms with shorter panicles and fewer spikelets per panicle; however, the total floret number was higher, presumably because the spikelets of E. minor contain more florets. Thus, although differences exist for all traits investigated, they cannot explain why E. multicaulis seems to have the most recent and most rapid colonization in the study area.

Genetic variation within species
The variation explained by population differences was higher for E. multicaulis than for E. minor, while the between-family variation showed the opposite pattern. Thus, the estimates of heritability and evolvability (calculated from the between-family variation) were highest for the minor populations, especially when considered on a traits-by-trait basis. In light of this observation, one would not expect a greater potential for selection response in the more recent "newcomer".

Local adaptation across populations
My results provide little evidence that E. multicaulis owes its recent rapid expansion in Malmö to local adaptation: the chosen site variables had no detectable effects on the five traits considered and together only explained a minor portion of the variation in the mean phenotype. In E. minor, there was a significant positive relationship between culm height and the geographical distance to the putative starting point for the initial colonization; consequently, site differences accounted for more of the trait variation in this species. This and other observations - the relatively high genetic variation of populations and the relatively long time available for selection to influence E. minor in the Malmö area - agree with the local adaptation scenario.

Conclusion
My results show no consistent difference in trait means and patterns of genetic variation that explains why the two grasses differ in their colonization rates. It is possible that E. multicaulis populations possess some unmeasured trait (e.g. greater selfing ability or higher temperature optimum) that make them particularly competitive under current environmental conditions.

Master’s Degree Project in Biology 30 credits 2020
Department of Biology, Lund University

Advisor: Stefan Andersson
Department of biology (Less)
Please use this url to cite or link to this publication:
author
Liu, Chang
supervisor
organization
course
BIOM02 20201
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
9023448
date added to LUP
2020-06-30 12:16:32
date last changed
2020-06-30 12:16:32
@misc{9023448,
  abstract     = {Biological invasions and their underlying mechanisms have become major issues in ecology, conservation and evolutionary biology. In order to better understand the factors determining colonization and invasion success, I obtained common-garden data from more than 1000 greenhouse-grown plants of two alien grass species, Eragrostis minor and E. multicaulis, derived from about 30 sites per species in the city of Malmö. Particularly attention was given to the following questions: (i) Is the more rapid colonizer E. multicaulis characterized by more rapid growth, larger size and higher reproductive output? (ii) Can the contrasting colonization rates of the two species be linked to patterns and amounts of genetic variation within species? (iii) Is there any evidence for local adaptation across populations? Plants of E. minor reached reproductive maturation earlier and had higher reproductive output, in direct conflict with my expectation of more rapid development and higher reproductive effort in the rapid colonizer. Measures of evolutionary potential (heritability, evolvability) were also lower for E. multicaulis populations; thus, no association between high genetic variation and rapid colonization could be detected. The strongest evidence for local adaptation was found in the slower colonizer (E. minor), manifested as positive relationships between mean culm height and the distance from the putative starting point of the colonization.},
  author       = {Liu, Chang},
  language     = {eng},
  note         = {Student Paper},
  title        = {Do differences in fitness traits and their genetic variation explain differences in colonization rate between two alien grass species?},
  year         = {2020},
}