Endozoochory by ducks: Influence of developmental stage of Bythotrephes diapause eggs on dispersal probability

This paper evaluates whether the recent expansion of Bythotrephes longimanus Leydig (Crustacea: Onychopoda) may be a result of endozoochorous avian dispersal. In three experiments, we investigated the survival of diapause eggs in newly produced and end-of-winter developmental stages after their passage through the digestive tract of four species of ducks. Resistance of eggs to digestion was low for both developmental stages (< 12%). Most eggs (67-95%) were recovered by four hours after ingestion, with a longer maximum retention time for newly produced (22 h) than end-of-winter eggs (4-6 h). Ingestion had a detrimental effect on viability: only eggs retrieved one hour after ingestion hatched and the proportion of those ingested that produced viable neonates was low (0.5% for newly produced and 0.3-3% for end-of-winter eggs). We conclude that the probability of endozoochorous dispersal by individual ducks is low but becomes significant when considering the thousands of ducks moving among wetlands. Endozoochorous dispersal of B. longimanus would most likely involve the transport of newly produced diapause eggs from north to south, during the autumn migration of ducks. Based on flight speed estimates of ducks we estimate dispersal probability to drop sharply at distances over 60-80 km.