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Ecological and Evolutionary Consequences of Herbivory in the Perennial Herb Lythrum salicaria
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Plant Ecology and Evolution.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, I combined field, common-garden and greenhouse experiments to examine the ecological and evolutionary consequences of plant-herbivore interactions in the perennial herb Lythrum salicaria. More specifically I examined (1) whether resistance and tolerance to damage from herbivores vary with latitude and are positively related to the intensity of herbivory in natural populations, (2) whether effects of herbivory on plant fitness vary with latitude, (3) whether populations are locally adapted and whether herbivory influences the relative fitness of populations, and (4) whether the intensity and effects of insect herbivory on reproductive output vary locally along a disturbance gradient and are associated with differences in plant resistance.

A common-garden and a greenhouse experiment demonstrated that plant resistance decreased whereas plant tolerance increased with latitude of origin among populations sampled along a latitudinal gradient in Sweden. Oviposition and feeding preference in the greenhouse and leaf damage in the common-garden experiment were negatively related to natural damage in the source populations.

Experimental removal of insect herbivores in three populations sampled along the latitudinal gradient demonstrated that intensity of herbivory and its effects on plant fitness decreased towards the north. A reciprocal transplant experiment among the same three populations showed that herbivory affected the relative fitness of the three populations, but did not detect any evidence of local adaptation. Instead the southernmost population had the highest relative fitness at all three sites.

A herbivore-removal experiment conducted in nine populations in an archipelago in northern Sweden demonstrated that insect herbivory strongly influenced among-population variation in reproductive output. However, variation in resistance was not related to differences in intensity of herbivory at this spatial scale.

Taken together, the results demonstrate that resistance and tolerance to herbivory vary with latitude but in opposite directions, that intensity of herbivory is a major determinant of flowering and seed output, and that the strength of herbivore-mediated selection varies among populations in Lythrum salicaria. They further indicate that both physical disturbance regime and latitudinal variation in abiotic conditions may strongly influence the performance and abundance of perennial herbs because of their effects on interactions with specialized herbivores.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. , 37 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1238
Keyword [en]
Disturbance gradient, Female reproductive success, Galerucella calmariensis, Galerucella pusilla, Herbivore removal, Latitudinal gradient, Local adaptation, Nanophyes marmoratus, Plant-herbivore interactions, Plant size, Resistance to herbivory, Tolerance to damage
National Category
Natural Sciences
Research subject
Biology with specialization in Ecological Botany
Identifiers
URN: urn:nbn:se:uu:diva-247088ISBN: 978-91-554-9196-3 (print)OAI: oai:DiVA.org:uu-247088DiVA: diva2:795447
Public defence
2015-05-08, Zootissalen, Villavägen 9, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2015-04-17 Created: 2015-03-13 Last updated: 2015-07-07
List of papers
1. Latitudinal variation in resistance and tolerance to herbivory in the perennial herb Lythrum salicaria is related to intensity of herbivory and plant phenology
Open this publication in new window or tab >>Latitudinal variation in resistance and tolerance to herbivory in the perennial herb Lythrum salicaria is related to intensity of herbivory and plant phenology
2015 (English)In: Journal of Evolutionary Biology, ISSN 1010-061X, E-ISSN 1420-9101, Vol. 28, no 3, 576-589 p.Article in journal (Refereed) Published
Abstract [en]

Both the length of the growing season and the intensity of herbivory often vary along climatic gradients, which may result in divergent selection on plant phenology, and on resistance and tolerance to herbivory. In Sweden, the length of the growing season and the number of insect herbivore species feeding on the perennial herb Lythrum salicaria decrease from south to north. Previous common-garden experiments have shown that northern L. salicaria populations develop aboveground shoots earlier in the summer, and finish growth before southern populations do. We tested the hypotheses that resistance and tolerance to damage vary with latitude in L. salicaria, and are positively related to the intensity of herbivory in natural populations. We quantified resistance and tolerance of populations sampled along a latitudinal gradient by scoring damage from natural herbivores and fitness in a common-garden experiment in the field, and by documenting oviposition and feeding preference by specialist leaf beetles in a greenhouse experiment. Plant resistance decreased with latitude of origin, whereas plant tolerance increased. Oviposition and feeding preference in the greenhouse, and leaf damage in the common-garden experiment were negatively related to damage in the source populations. The latitudinal variation in resistance was thus consistent with reduced selection from herbivores towards the northern range margin of L. salicaria. Variation in tolerance may be related to differences in the timing of damage in relation to the seasonal pattern of plant growth, as northern genotypes have developed further than southern have when herbivores emerge in early summer.

Keyword
Galerucella calmariensis, Galerucella pusilla, herbivore removal, latitude, Lythrum salicaria, Nanophyes marmoratus, plant resistance, plant tolerance, plant–herbivore interactions
National Category
Botany Evolutionary Biology
Research subject
Biology with specialization in Ecological Botany
Identifiers
urn:nbn:se:uu:diva-247082 (URN)10.1111/jeb.12589 (DOI)000352628400006 ()
Funder
Swedish Research Council
Available from: 2015-03-13 Created: 2015-03-13 Last updated: 2017-12-04Bibliographically approved
2. Herbivory Differentially Affects Plant Fitness in Three Populations of the Perennial Herb Lythrum salicaria along a Latitudinal Gradient
Open this publication in new window or tab >>Herbivory Differentially Affects Plant Fitness in Three Populations of the Perennial Herb Lythrum salicaria along a Latitudinal Gradient
2015 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 10, no 9, e0135939Article in journal (Refereed) Published
Abstract [en]

Herbivory can negatively and selectively affect plant fitness by reducing growth, survival and reproductive output, thereby influencing plant population dynamics and evolution. We documented intensity of herbivory and experimentally examined its effect on survival, growth and reproductive output in three natural populations of the perennial herb Lythrum salicaria along a latitudinal gradient from southern to northernmost Sweden over two years. The intensity of herbivory and the effects of herbivory on plant fitness were strongest in the southern population and intermediate in the central population. The mean proportion of the leaf area removed ranged from 11% in the southern to 3% in the northern population. Herbivore removal increased plant height 1.5-fold in the southern and 1.2-fold in the central population, the proportion plants flowering 4-fold in the southern and 2-fold in the central population, and seed production per flower 1.6-fold in the southern and 1.2-fold in the central population, but did not affect plant fitness in the northern population. Herbivore removal thus affected the relative fecundity of plants in the three populations: In the control, seed output per plant was 8.6 times higher in the northern population compared to the southern population, whereas after herbivore removal it was 2.5 times higher in the southern population compared to the northern. Proportion of leaf area removed increased with plant size, but tolerance to damage did not vary with size. The results demonstrate that native herbivores may strongly affect the demographic structure of L. salicaria populations, and thereby shape geographic patterns of seed production. They further suggest that the strength of herbivore-mediated selection varies among populations and decreases towards the north.

Keyword
Galerucella calmariensis, Galerucella pusilla, Herbivore removal, Nanophyes marmoratus, Plant-herbivore interactions, Plant resistance, Plant size, Plant tolerance, Seed production
National Category
Botany Ecology
Research subject
Biology with specialization in Ecological Botany
Identifiers
urn:nbn:se:uu:diva-247084 (URN)10.1371/journal.pone.0135939 (DOI)000360437700025 ()
Funder
Swedish Research Council
Available from: 2015-03-13 Created: 2015-03-13 Last updated: 2017-12-04Bibliographically approved
3. Herbivory influences the relative fitness of three native Lythrum salicaria populations, but no evidence of local adaptation along a latitudinal gradient
Open this publication in new window or tab >>Herbivory influences the relative fitness of three native Lythrum salicaria populations, but no evidence of local adaptation along a latitudinal gradient
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Local adaptation along environmental gradients has been documented in many plant species, but the extent to which biotic interactions influence the relative fitness of local and non-local genotypes has rarely been examined experimentally. Previous common-garden experiments detected clinal variation in life history, phenology and resistance to herbivory in the perennial herb Lythrum salicaria along a latitudinal gradient in Sweden, which coincides with a decrease in the length of the growing season and intensity of herbivory from south to north. Here, we included a herbivore-removal treatment in a reciprocal transplant experiment to test whether three populations sampled along the latitudinal gradient are locally adapted, whether differences in resistance and tolerance are consistent across sites and whether herbivory influences the relative performance of the study populations. The results did not reveal any evidence of local adaptation. Instead the southernmost population had the highest relative fitness at all three sites and was consistently less damaged by herbivores than were the other populations. The intensity of herbivory was greatest at the southern site and very low at the northernmost site. The removal of insect herbivores positively affected plant growth and fecundity at the southern and central sites. Herbivore removal also affected the relative fitness of the study populations at the southern site, and tended to do so at the central site. However, the relative ranking of the three populations did not change, indicating that herbivores influenced the strength but not the direction of selection. Genetic drift, recent climatic warming and intermittent strong selection against southern genotypes at northern latitudes may all contribute to the documented patterns of among-population variation in fitness, while similarity in the behaviour and preferences of herbivore populations along the studied gradient may explain the consistent differences in resistance.

Keyword
Female reproductive success, Galerucella calmariensis, Galerucella pusilla, Nanophyes marmoratus, Plant-herbivore interactions, Reciprocal transplant, Plant resistance, Tolerance to herbivory
National Category
Natural Sciences
Research subject
Biology with specialization in Ecological Botany
Identifiers
urn:nbn:se:uu:diva-247252 (URN)
Funder
Swedish Research Council
Available from: 2015-03-16 Created: 2015-03-16 Last updated: 2015-07-07
4. Herbivory strongly influences among-population variation in reproductive output of Lythrum salicaria in its native range
Open this publication in new window or tab >>Herbivory strongly influences among-population variation in reproductive output of Lythrum salicaria in its native range
2016 (English)In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 180, no 4, 1159-1171 p.Article in journal (Refereed) Published
Abstract [en]

Herbivory can negatively affect several components of plant reproduction. Yet, because of a lack of experimental studies involving multiple populations, the extent to which differences in herbivory contribute to among-population variation in plant reproductive success is poorly known. We determined experimentally the effects of insect herbivory on reproductive output in nine natural populations of the perennial herb Lythrum salicaria along a disturbance gradient in an archipelago in northern Sweden, and we quantified among-population differentiation in resistance to herbivory in a common-garden experiment in the same area. The intensity of leaf herbivory varied >500-fold and mean female reproductive success >400-fold among the study populations. The intensity of herbivory was lowest in populations subject to strong disturbance from ice and wave action. Experimental removal of insect herbivores showed that the effect of herbivory on female reproductive success was correlated with the intensity of herbivory and that differences in insect herbivory could explain much of among-population variation in the proportion of plants flowering and seed production. Population differentiation in resistance to herbivory was limited. The results demonstrate that the intensity of herbivory is a major determinant of flowering and seed output in L. salicaria, but that differences in herbivory are not associated with differences in plant resistance at the spatial scale examined. They further suggest that the physical disturbance regime may strongly influence the performance and abundance of perennial herbs not only because of its effect on interspecific competition, but also because of effects on interactions with specialized herbivores.

Keyword
Disturbance gradient, Flowering, Plant-herbivore interactions, Plant resistance, Seed production
National Category
Natural Sciences
Research subject
Biology with specialization in Ecological Botany
Identifiers
urn:nbn:se:uu:diva-247086 (URN)10.1007/s00442-015-3520-2 (DOI)000373186100022 ()26678991 (PubMedID)
Funder
Swedish Research Council
Note

Erratum in: OECOLOGIA 180(4), pg. 1173-1174. DOI: 10.1007/s00442-016-3570-0

Available from: 2015-03-13 Created: 2015-03-13 Last updated: 2017-12-04Bibliographically approved

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