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Evolutionary and mechanistic aspects of insect host plant preference
Stockholm University, Faculty of Science, Department of Zoology. (Niklas Janz)ORCID iD: 0000-0002-3187-3555
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Plant feeding insects comprise about 25% of all animal species on earth and play an important role in all ecosystems. Although we understand that their association with plants is a key-factor driving the diversification in this group, we still have large gaps in our knowledge of the underlying processes of this relationship. Female choice of host plant is an important event in the insect life-cycle, as it is a major determinant of the larval food plant. In this Thesis I studied different aspects of insect host plant choice and used butterflies from the family Nymphalidae as my study system. I found that butterflies have a well developed olfactory system and that they use odors when searching for food or host plants. However, the information obtained from the odor of host plants does not seem to be sufficient for the studied species to make a distinction between plants of different qualities. Interestingly, even when in full contact with the leaf they do not make optimal decisions. I show for example that a sub-optimal female choice may be mitigated by larval ability to cope with unfavorable situations. Moreover, species that utilize a broader set of host plants may not be very well adapted to all the hosts they use, but at the same time they may survive in areas where there is only a subset of the plants available. Lastly, differences in the evolution of life-history traits between species can account for differences in how each species realizes its lifestyle. Thus, by incorporating findings on mechanisms of host plant choice with the ecological and evolutionary context of a species, our ability to explain the dynamics of host plant choice and insect-plant interactions can be improved.

Place, publisher, year, edition, pages
Stockholm: Department of Zoology, Stockholm University , 2016. , 25 p.
Keyword [en]
host plant choice, host range, diet breadth, butterfly, oviposition, specialist, generalist, insect-plant interaction, search behavior, olfaction, decision making, evolution, parasite-host interaction
National Category
Evolutionary Biology Ecology Behavioral Sciences Biology
Research subject
Animal Ecology
Identifiers
URN: urn:nbn:se:su:diva-128488ISBN: 978-91-7649-381-6 (print)OAI: oai:DiVA.org:su-128488DiVA: diva2:915461
Public defence
2016-05-20, Vivi Täckholmsalen (Q-salen), NPQ-huset, Svante Arrhenius väg 20, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

Available from: 2016-04-27 Created: 2016-03-30 Last updated: 2017-02-24Bibliographically approved
List of papers
1. Odour Maps in the Brain of Butterflies with Divergent Host-Plant Preferences
Open this publication in new window or tab >>Odour Maps in the Brain of Butterflies with Divergent Host-Plant Preferences
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2011 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 6, no 8, e24025Article in journal (Refereed) Published
Abstract [en]

Butterflies are believed to use mainly visual cues when searching for food and oviposition sites despite that their olfactory system is morphologically similar to their nocturnal relatives, the moths. The olfactory ability in butterflies has, however, not been thoroughly investigated. Therefore, we performed the first study of odour representation in the primary olfactory centre, the antennal lobes, of butterflies. Host plant range is highly variable within the butterfly family Nymphalidae, with extreme specialists and wide generalists found even among closely related species. Here we measured odour evoked Ca2+ activity in the antennal lobes of two nymphalid species with diverging host plant preferences, the specialist Aglais urticae and the generalist Polygonia c-album. The butterflies responded with stimulus-specific combinations of activated glomeruli to single plant-related compounds and to extracts of host and non-host plants. In general, responses were similar between the species. However, the specialist A. urticae responded more specifically to its preferred host plant, stinging nettle, than P. c-album. In addition, we found a species-specific difference both in correlation between responses to two common green leaf volatiles and the sensitivity to these compounds. Our results indicate that these butterflies have the ability to detect and to discriminate between different plant-related odorants.

National Category
Biological Sciences
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-62479 (URN)10.1371/journal.pone.0024025 (DOI)000294298000039 ()
Available from: 2011-09-20 Created: 2011-09-20 Last updated: 2017-12-08Bibliographically approved
2. The Role of Olfactory Cues for the Search Behavior of a Specialist and Generalist Butterfly
Open this publication in new window or tab >>The Role of Olfactory Cues for the Search Behavior of a Specialist and Generalist Butterfly
2015 (English)In: Journal of insect behavior, ISSN 0892-7553, E-ISSN 1572-8889, Vol. 28, no 1, 77-87 p.Article in journal (Refereed) Published
Abstract [en]

Searching for resources is often a challenging task, especially for small organisms such as insects. Complex stimuli have to be extracted from the environment and translated into a relevant behavioral output. A first step in this process is to investigate the relative roles of the different senses during search for various resources. While the role of olfaction is well documented in nocturnal moths, the olfactory abilities of the closely related diurnal butterflies are poorly explored. Here we investigated how olfactory information is used in the search for host plants and asked if these abilities varied with levels of stimulus complexity. Thus, we tested two nymphalid butterfly species with divergent host plant range in a two-choice olfactometer testing different combinations of host and non-host plants. The experiments show both the monophagous Aglais urticae and the polyphagous Polygonia c-album could navigate towards an odor source, but this ability varied with context. While mated females exhibited a preference for their host plant, unmated females of both species did not show a preference for host plant cues. Furthermore, both species showed inabilities to make fine-tuned decisions between hosts. We conclude that olfactory cues are important for butterflies to navigate towards targets. We argue that there are limitations on how much information can be extracted from host volatiles. These results are discussed in the light of neural processing limitations and degree of host plant specialization, suggesting the necessity of other sensory modalities to sharpen the decision process and facilitate the final oviposition event.

Keyword
Olfaction, Lepidoptera, search behavior, information processing hypothesis, host plant specialization
National Category
Biological Sciences
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-112330 (URN)10.1007/s10905-014-9482-0 (DOI)000347688400008 ()
Available from: 2015-01-12 Created: 2015-01-12 Last updated: 2017-12-05Bibliographically approved
3. Specialist and generalist oviposition strategies in butterflies: maternal care or precocious young?
Open this publication in new window or tab >>Specialist and generalist oviposition strategies in butterflies: maternal care or precocious young?
2016 (English)In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 180, no 2, 335-343 p.Article in journal (Refereed) Published
Abstract [en]

Herbivorous insects specialized on a narrow set of plants are believed to be better adapted to their specific hosts. This hypothesis is supported by observations of herbivorous insect species with a broader diet breadth which seemingly pay a cost through decreased oviposition accuracy. Despite many studies investigating female oviposition behavior, there is a lack of knowledge on how larvae cope behaviorally with their mothers' egg-laying strategies. We have examined a unique system of five nymphalid butterfly species with different host plant ranges that all feed on the same host plant. The study of this system allowed us to compare at the species level how oviposition preference is related to neonate larval responses in several disadvantageous situations. We found a general co-adaptation between female and larval abilities, where species with more discriminating females had larvae that were less able to deal with a suboptimal initial feeding site. Conversely, relatively indiscriminate females had more precocious larvae with better abilities to cope with suboptimal sites. Despite similarities between the tested species with similar host ranges, there were also striking differences. Generalist and specialist species can be found side by side in many clades, with each clade having a specific evolutionary history. Such clade-specific, phylogenetically determined preconditions apparently have affected how precisely a broad or narrow diet breadth can be realized.

Keyword
Host plant specialization, insect-plant interaction, preference-performance, co-adaptation, Nymphalidae
National Category
Biological Sciences
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-118877 (URN)10.1007/s00442-015-3376-5 (DOI)000368829300004 ()
Available from: 2015-07-16 Created: 2015-07-16 Last updated: 2017-12-04Bibliographically approved
4. Clutch size and host use in butterflies - and how to measure diet breadth
Open this publication in new window or tab >>Clutch size and host use in butterflies - and how to measure diet breadth
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The utilization of host plants is a central aspect of herbivorous insect life-history and known to promote processes of diversification in this group. In species that aggregate their eggs, female selection of a suitable egg-laying site is especially important, since a large proportion of the realized fitness will depend on few oviposition events. A cluster of larvae also requires a large resource to complete development and thus resource size may further limit the range of suitable hosts. We investigated whether there is a relationship between clutch size and diet breadth for 206 nymphalid butterfly species, using phylogenetic comparative methods. Results were consistent across several taxonomic and phylogenetic diet breadth measures, suggesting that some taxonomic measures may be as good approximations as the more cumbersome estimates based on phylogenetic distance. Treating diet breadth and clutch size as continuous data indicated no relationship between the traits, while categorizing them into binary form showed that they evolve in a correlated fashion. The discordance between analyses indicated that clutch size may be constrained among extreme generalists, as polyphagous clutch layers were rare. We found clutch-laying to be a relatively conserved trait in the phylogeny and less flexible than variation in degree of host plant specialization. Host plant growth form did not influence the clutch size diet breath relationship, but was weakly correlated with both factors. We discuss the general role of conservative life-history traits, such as clutch size, for the evolutionary dynamics of more labile traits such as diet breadth among phytophagous insects.

Keyword
egg aggregation, Nymphalidae, host range, phylogenetic diversity, PD, comparative methods, herbivorous insects, host-parasite interaction
National Category
Biological Sciences
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-128486 (URN)
Funder
Swedish Research Council, 2011-5636Swedish Research Council, 2015-04218Swedish Research Council, 2013-4834
Available from: 2016-03-30 Created: 2016-03-30 Last updated: 2016-04-06Bibliographically approved

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