Across-population variation in phosphorus limitation in triploid asexual freshwater snails (Potamopyrgus antipodarum)

Background/Question/Methods

Local adaptation, defined as higher fitness of local vs. non-local individuals in the local population, is pervasive because natural selection varies in space. Although local adaptation has been primarily studied with respect to biotic interactions, widespread variation in abiotic characteristics of environments suggests that local adaptation in response to abiotic factors should also be common. The New Zealand freshwater snail Potamopyrgus antipodarum possesses local adaptation to parasites and flow rate. As an initial step to determining whether P. antipodarum are also locally adapted to phosphorus availability, we examined whether snails collected from different New Zealand lake populations also differ in their responses to phosphorus (P) limitation.  We focused on phosphorus because we have previously shown that growth of juvenile P. antipodarum is severely reduced by limited P and substantial genetic variation exists in P. antipodarum for response to P limitation. 

Results/Conclusions

Growth of P. antipodarum was substantially lower on a diet that was limited in phosphorus relative to a diet with high phosphorus content. We also found that growth of snails varied among populations. Although we lacked the power to detect a population by phosphorus diet interaction, growth was suppressed by low phosphorus twice as much in some populations than others. We conclude that populations of P. antipodarum differ in their response to phosphorus limitation and hence, that local adaptation may explain this variation. Local adaptation to P availability should result in snails from lakes with relatively low P availability being less severely affected by low P than snails from lakes with higher P. We will assess whether this pattern occurs with future experiments.