COS 80-2
Testing predictions of ecological stoichiometry in Daphnia using ionomic tools

Wednesday, August 13, 2014: 1:50 PM
Regency Blrm E, Hyatt Regency Hotel
Punidan D. Jeyasingh, Department of Integrative Biology, Oklahoma State University, Stillwater, OK
Priyanka Roy Chowdhury, Zoology, Oklahoma State University, Stillwater, OK

Ecological stoichiometry (ES) is an ideal framework for integrating ecology and evolution. At the heart of ES lies the assumption that each species has a distinct and relatively fixed somatic stoichiometry, which manifest in ecological functions of species such as nutrient recycling. Little attention has been paid to intraspecific is stoichiometric traits. Furthermore, we know little about the stoichiometric composition of even well studied organisms such as Daphnia beyond three elements (carbon, nitrogen, phosphorus). Advances in mass spectrometry (specifically, inductively coupled plasma) enable high throughput quantification of all the elements represented in biology (~25). Here, we utilized this approach to quantify the entire elemental profile (i.e. the ionome) of six distinct Daphnia genotypes. We further tested whether changes in the supply of key ecologically important elements (e.g., P) alter ionomic profiles of individuals, and whether such ionomic shifts were genotype-specific.


We found 19 elements in Daphnia – C, H, N, O, S, P, Na, Mg, K, Ca, Mn, Fe, Co, Ni, Cu, Zn, Mo, Se, I. Overall, ionomic profiles were not significantly different among the six genotypes studied. However, when supply stoichiometry was altered (high and low phosphorus diet), the content of 9 elements varied significantly. Such responses were genotype-specific (e.g., some genotypes varied in C, while others varied in Fe, while P exhibited the greatest homeostasis). Finally, a PCA revealed strong correlated shifts among elements, with major elements C, N, S, P, and trace metals (e.g., Mn, Fe, Co) clustering separately. Our study clearly indicates that: (i) the content of some elements is more variable than others potentially indicating different evolutionary rates, (ii) content of some elements are more sensitive to changes in supply stoichiometry, and (iii) the ionomic response to changes in supply stoichiometry is genotype-specific. The ecological consequences (e.g., consumer-driven nutrient recycling) of such variation remains to be explored, although our previous work focusing on P indicated shifts in both algal quality and quantity depending on the genotype of Daphnia they coexist with. This new view of ES, one that embraces intraspecific variation in stoichiometric traits has the potential to illuminate the ecological consequences of evolutionary change – a central challenge in both ecology and evolution in a rapidly changing globe.