Impacts of water hyacinth detritus on the growth, reproduction, and survival of the snail hosts of human schistosomes Pubblico

Abstract

Machines that shred the invasive macrophyte water hyacinth may inadvertently produce resources for the intermediate host of human schistosomes, Biomphalaria glabrata. Yet, prior work has shown that shredding water hyacinth in experimental mesocosm tanks resulted in substantial B. glabrata egg laying but juvenile recruitment failure. One potential explanation of this phenomenon is that the consumption of water hyacinth detritus may differentially impact juvenile and adult B. glabrata individuals. In this 12-week study, we evaluated this hypothesis by characterizing the life history traits of snails of different initial sizes fed either water hyacinth detritus or detritus from another invasive plant, water lettuce, which is a known high-quality resource. Overall, water hyacinth increased mortality for large, adult snails, decreased growth and reproduction for all snails, and resulted in altered growth patterns for snails across size classes. This study contextualizes prior work on the potential effects of shredding machines on human schistosome host ecology by demonstrating that water hyacinth is a low-quality food source for B. glabrata of all sizes with significant negative effects on snail life history traits. Thus, population-level effects may have arisen from other factors, such as complementary food sources or changes in egg-hatching rates, that were possible in prior experiments but excluded from this study. More broadly, this work contributes to ecological understanding of the effects of diet on life history traits as well as the role of size in mediating these effects.

Table of Contents

Introduction................................................................................................................................................................ 1

Methods...................................................................................................................................................................... 5

a.     Study system........................................................................................................................................................ 5

b.    Life table experiment............................................................................................................................................. 5

c.     Growth data analysis ............................................................................................................................................ 7

d.    Reproduction data analysis.................................................................................................................................... 8

e.     Mortality data analysis.......................................................................................................................................... 8

Results........................................................................................................................................................................ 9

a.     Snail growth......................................................................................................................................................... 9

b.    Snail reproduction................................................................................................................................................ 12

c.     Snail mortality..................................................................................................................................................... 14

Figures......................................................................................................................................................................... 9

Figure 1. Effect of detritus type on snail growth within each initial size class over 12 weeks............................................... 9

Figure 2. Effect of initial size class and detritus type on snail growth over 12 weeks......................................................... 10

Figure 3. Effect of initial size class and detritus type on log-transformed snail cumulative egg production over 12 weeks... 12

Figure 4. Snail mortality after 12 weeks by initial size class and detritus type.................................................................. 14

Discussion.................................................................................................................................................................. 16

References.................................................................................................................................................................. 23

Appendix A................................................................................................................................................................. 27

Table 1. Size contrasts by detritus type within each starting size class............................................................................ 27

Table 2. Size contrasts by starting size class within water lettuce detritus treatment....................................................... 27

Table 3. Log-transformed cumulative egg count contrasts by detritus type within each starting size class ........................ 28

Appendix B................................................................................................................................................................ 29

Table 4. Weekly detritus amounts by starting size class and detritus type....................................................................... 29

About this Honors Thesis

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School	Emory College
Department	Biology
Degree	B.S.
Submission	Honors Thesis
Language	English
Research Field	Biology, Parasitology Biology, Ecology
Parola chiave	life history schistosomiasis disease ecology juvenile bottleneck diet ecology
Committee Chair / Thesis Advisor	Dr. David Civitello, Emory University
Committee Members	Dr. Carolyn Keogh, Emory University Dr. Christopher Beck, Emory University

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