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Small bugs, big appetites: experimental quantification of duckweed-herbivore interactions

Subramanian, Swapna Krithika (2020) Small bugs, big appetites: experimental quantification of duckweed-herbivore interactions. Undergraduate Thesis, University of Pittsburgh. (Unpublished)

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The role of herbivores in driving the structure of freshwater macrophyte communities remains poorly understood in comparison with terrestrial ecosystems. For instance, although duckweed (subfamily Lemnoideae) are globally distributed, can be ecologically dominant, and are of growing economic importance, their interactions with herbivores remain understudied. It remains unknown if herbivores could strongly impact duckweed’s rapid population growth and how they could influence species composition of macrophyte communities. We here test whether the water-lily aphid (Rhopalosiphum nymphaeae) exhibits a preference between species of duckweed and how duckweed and aphids reciprocally affect each other’s performance. Our two-way choice experiments reveal that aphids display preference for Spirodela polyrhiza > Landoltia punctata = Lemna minor >> Wolffia brasiliensis. By evaluating the growth of aphid populations on each duckweed species we found that preference may be adaptive in certain ecological conditions when high growth rate is advantageous. Quantifying the population growth rate of duckweed in the presence and absence of aphids revealed differential tolerance of herbivory across duckweed species. These results suggest that a single herbivore could have a significant impact on duckweed populations and species composition in nature. We pursued this possibility with a manipulative field experiment. Using exclosures in natural ponds, we manipulated the presence of herbivores. We found that herbivory impacts species composition of duckweed communities in a complex manner. Species are differently affected in ambient herbivory and herbivore addition
treatments, and there is considerable variation in herbivore effect between sites due to difference in local herbivore communities. After finding interspecific variation in duckweed response to herbivory, we tested the possibility of intraspecific variation in plant defenses against herbivores. We found that resistance and tolerance vary between duckweed genotypes, and herbivory could be a potential driver of duckweed evolution. We here highlight the importance of quantifying the plant-herbivore interactions in aquatic ecosystems in the lab and the field.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Subramanian, Swapna Krithikasw.subramanian@gmail.comsks890000-0002-6809-1717
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairTurcotte,
Committee MemberWood,
Committee MemberStephenson,
Committee MemberAli,
Date: 4 May 2020
Date Type: Publication
Defense Date: 7 April 2020
Approval Date: 4 May 2020
Submission Date: 15 April 2020
Access Restriction: 2 year -- Restrict access to University of Pittsburgh for a period of 2 years.
Number of Pages: 87
Institution: University of Pittsburgh
Schools and Programs: David C. Frederick Honors College
Dietrich School of Arts and Sciences > Ecology and Evolution
Degree: BPhil - Bachelor of Philosophy
Thesis Type: Undergraduate Thesis
Refereed: Yes
Uncontrolled Keywords: duckweed herbivory, Lemnaecae, aphid herbivory, plant-defense, plant community
Date Deposited: 04 May 2020 20:27
Last Modified: 04 May 2022 05:15


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