The infrapopulation dynamics of trypanosomes in red-spotted newts

Abstract

SUMMARYThe parasitic protozoan Trypanosoma diemyctyli has a life-cycle that involves a vertebrate host, the red-spotted newt Notophthalmus viridescens, and an invertebrate host, the amphibian leech Batrachobdella picta. A study of the distribution and dynamics of this parasite in newts of known adult age and history of breeding in montane ponds in Virginia revealed a pattern of: (1) moderate prevalences of infection in post-metamorphic juvenile and adult stages, (2) rapid increases in numbers of trypanosomes in newts during their first year of maturity, (3) significant differences in the numbers of trypanosomes in male and female newts in mid-summer, (4) sustained high levels of infection in the first two years of newt adulthood, (5) significantly lower levels of infection in newts by the fourth and subsequent years of adulthood and (6) annual oscillations in the intensity of infection in older adult newts from spring and autumn lows to mid-summer peak levels. Newts with a history of skipping breeding seasons had higher levels of infection than those newts which returned to the pond for every breeding season. Newts brought to the laboratory and maintained under leech-free conditions failed to develop infection levels comparable to those in the field. The dynamics of infrapopulation sizes of trypanosomes in newts depend on multi plication rates of the trypanosomes, variable transmission rates from the invertebrate host and the development of resistance in older adult newts.