Reproductive Biology and Adaptability of the Invasive Alien Freshwater Amphipod Crangonyx floridanus (Crustacea: Amphipoda, Crangonyctidae)

We studied the reproductive biology and adaptability of the alien freshwater crangonyctid amphipod Crangonyx floridanus, currently inhabiting a large portion of Japan, both in the field and under controlled laboratory conditions. In the Chikuma River population of this alien amphipod, egg-bearing individuals were found throughout the year. In terms of egg maturation cycle, egg development (during embryogenesis), and egg count per ovipositional cycle, these amphipods display a very efficient reproductive system. This study also established their adaptability to a wide range of water temperatures (primarily 4-20 degrees C, however in some cases, these individuals are able to survive at up to 30 degrees C). C. floridanus's strong capacity to adapt to broad and variable environmental conditions is certainly contributing to its high rate of population increase, and rapid dispersion throughout Japan.ArticleZOOLOGICAL SCIENCE. 27(6):522-527 (2010)journal articl

Rapid expansion of the distributional range and the population genetic structure of the freshwater amphipod Crangonyx floridanus in Japan

The freshwater amphipod Crangonyx floridanus (Amphipoda: Crangonyctidae) is considered to have been recently introduced from North America to Japan, and the recorded sites at which it has been collected now cover nearly all of Japan except for the northern part. In this study, we surveyed further areas outside of its known distribution range, and examined the population genetic structure and the phylogenetic relationships between Japanese and North American populations of this species based on nuclear (18S rRNA) and mitochondrial (COI) DNA sequences. We found that this amphipod has already reached Hokkaido, northernmost Japan, which suggests that it has undergone rapid expansion in a pattern of concentric circles from the central part of Japan. Genetic analysis showed that the Japanese population is genetically homogeneous, in contrast to the genetic diversification of this species seen in North American Crangonyx populations. The process of introducing, establishing, and expanding this amphipod in Japan may be explained as follows. A limited number of individuals from a North American native population were probably inadvertently introduced and established somewhere within the Kanto region. The local population size then increased and its distribution range expanded rapidly across Japan.ArticleLIMNOLOGY. 12(1):75-82 (2011)journal articl