Freshwater Snails' Phenotype Alterations Response To Food Limitation And Food Type Change: A Study Of Feeding Control And Isotope Analysis

Food limitation caused by intraspecific competition is an inducement for species phenotype change,body sizes for some decreased and food type altered,especially in the high density of one population.Food type change affects some element assimilation and flux into different organs.Quantifying the element alteration and organs'turnover rates in species are key points in the research.Moreover,main methods of the study are control-feeding and stable isotope analysis.Our study species was Elimia in the slack water,which is a species of gill-breathing snail in the family of Pleuriceridae and normally distributed in southeastern the USA.In the field study,we designed enclosures to manipulate gradient density of the freshwater snails.Four weeks in-situ culture for Elimia showed that length and benthic organic matter Ash Free Dry Mass?AFDM??P-value:0.0071,0.035?were significant different among controls,gradient ambient density treatments.However,some influencing factors cannot be diminished since freshwater snails'immigration from external,but field freshwater snails were test samples for guts food content analysis.In order to avoid the influencing factors and study food quality impact on freshwater snails'phenotype change,lab control feeding was applied by using romaine lettuce and Spirulina Flakes as low and high-quality food treatment.We estimated the specific food treated freshwater snails and compared the result with the control group,length and weight variation among the groups were significant different with P-value less than 0.001.Furthermore,length and weight of each group was strongly correlated compared with field control group.Food content was identified by microscope and found that benthic diatoms,Macrophytes,and terrestrial plant particles were reduced with increasing density.Meanwhile,stable isotope carbon and nitrogen were used to trace element flux and content in muscle and gonads of the freshwater snails under the two food treatments.Exponential model was used to estimate the half-life and 99.99%turnover days of the lab culture freshwater snails under the Spirulina Flakes treatment.We found that gonads generally had faster turnover rate?carbon0.244,nitrogen 0.250?and short turnover days?carbon 37.7days,nitrogen 36.91days?than muscle parts with 50 sampling days.Nevertheless,the stable isotope carbon and nitrogen fluctuated above the romaine lettuce standards.Finally,the transmitting rate of food treatment and lab freshwater snails were deviated from the standards,0.04‰and 0.34‰of?¹³C and?¹⁵N between trophic levels.The detailed and specific mechanism and process of nutrient and element flux process can be explored for further research.Freshwater snails as primary consumer and keystone species in many aquatic systems are worth studying for ecosystem resistance and food web structures.