Local adaptation occurs when individuals have higher fitness in their local environment compared to non-native individuals (i.e. those from different populations/environmental conditions). This process is driven by natural selection favoring different suites of traits that maximize fitness in different environments. Lakes and streams vary greatly in an array of environmental characteristics (both biotic and abiotic) and, thus, local adaptation may result because of strong selective pressures. In fish, body size and shape are often targets of selection because of their impact on many aspects of daily life and, therefore, may reflect local adaptation. Utilizing a reciprocal transplant experiment in 3 lake-stream field sites, differences in survival rates of a small freshwater fish, the blackstripe topminnow (Fundulus notatus), were examined every third day for one month. Geometric morphometrics was incorporated to determine if body size and shape impact survival. The computer program MARK was used to construct models that best fit the data.
Results/Conclusions
The models with the lowest AICc scores find a difference in recapture probability between lakes and streams, with fish in lakes having a higher probabilty of being recaptured than those in the stream. Surprisingly models that incorporated varied survival rate were not strongly supported, regardless of whether it was between the original habitats or the habitats fish were transplanted into. Further models incorporating morphometric data are currently being explored. These preliminary results suggest that blackstripe topminnows do not demonstrate local adaptation to lakes and streams. This may result from the behavior and habitat utilization pattern of this species. A lack of evidence for local adaptation is intriguing in that, as other researchers have suggested, it implies that populations/species are prevented from reaching an adaptive optimum.