How a new population establishes in a novel habitat has been an important question of ecology. Understanding the temporal change of population genetic structure should contribute to answer this question, although its direct observation is difficult. Here, we try to reveal the population dynamics and the temporal change of genetic structure of a Daphnia pulex population from its early establishment using their dormant eggs enclosed in ephippia preserved in the varved sediment.
In lake Fukami-ike, Nagano, we collected sediment core samples, and counted ephippia of D. pulex to reveal the population dynamics. We also explored the population genetic structure based on the SNPs obtained from 177 eggs by the MIG-seq. Previous studies have shown two lineages, JPN1 and JPN2, of the obligated parthenogenetic D. pulex coexist in the lake.
D. pulex first appeared in the lake around 1950, established a stable population in 2000 and continued until 2014. Our population genetic analysis showed the clear genetic difference between JPN1 and JPN2. JPN2 was the only lineage occurred in the lake until JPN1 appeared in 2012, after which they coexisted. No clear temporal trend in the genetic structure within JPN2 was observed. Further analysis of the population genetic structure will follow.