Reproductive Strategies of Erpobdella punctata (Hirudinoidea) in Two Temporary Ponds

Abstract

The reproductive strategies of Erpobdella punctata (Leidy) were studied in two limnologically similar temporary ponds in Alberta. In Cairn Pond, E. punctata was the dominant erpobdellid, but in Jail Pond Nephelopsis obscura Verrill was dominant. In Jail Pond, E. punctata demonstrated a simple annual cycle, while in Cairn Pond a more complex cycle is shown with reproduction after one or two years. In Jail Pond, E. punctata reproduces at a smaller size, after a shorter period of time, earlier in the season and over a longer season than in Cairn Pond. Thus in Jail Pond E. punctata shows many of the characteristics of r-selection but in Cairn Pond it shows the characteristics of K-selection. On the basis of the close proximity and limnological similarity of the two ponds and the great overlap in prey organisms eaten by E. punctata and N. obscura, it is hypothesized that the differences in reproductive strategies shown by E. punctata are brought about by inter-specific competition. While phenotypic plasticity in reproductive strategy is shown by many species it is a reverse of the normal pattern for resource limitation in E. punctata to bring about reproduction at a smaller size and earlier in the season. It is suggested that the r-strategy characteristics shown by E. punctata are adaptations to utilize the spring secondary production as early as possible. Seasonal movements from the shore to deeper waters and back coincided with ice formation and break up. These movements were first observed in the larger animals.