Invasion and molecular evolution of Daphnia pulex in Japan

Abstract

We examined Daphnia pulex in Japan to clarify if they were representative of indigenous populations or colonized recently. Phylogenetic analysis of mtDNA suggests that Japanese lineages of D. pulex are immigrants from North America, and are hybrids formed with Daphnia pulicaria prior to this immigration. Based on the mtDNA sequences, the D. pulex individuals aggregated into four distinct genetic groups (JPN 1‐4) comprising a total of 21 haplotypes. Surprisingly, microsatellite analysis with 12 loci revealed only a single multilocus genotype per genetic group, suggesting that D. pulex populations in Japan are comprised of asexual individuals, derived from only four clones. According to the reported mutation rate of mtDNA, JPN 1 and 2, now widely distributed across Japan, were estimated to have invaded between 680 yr and 3400 yr ago, while JPN 3 and 4 colonized much more recently. Results also indicated that the invasion of some clones could not be attributed to recent human activities and most likely occurred by rare natural events. Since the evolutional longevity of asexual clones is thought to be limited, genetic diversity of D. pulex in Japan has the possibility of decreasing in the near future without addition of novel gene flow.

Clonal diversity and substantial genetic divergence of the Daphnia similis species complex in Chinese lakes: Possible adaptations to the uplift of the Qinghai‐Tibetan Plateau

“…Possibly the two D. similis populations found in Northern China may have originated from Europe, either directly or indirectly through Russia. Similar phenomena have been observed in Japan (So et al ), Africa (Mergeay et al ), and New Zealand (Duggan et al ), where Daphnia clones of North American origin were detected. Such long distance migration could be facilitated by migratory birds transporting Daphnia resting eggs via their digestive tract (Havel and Shurin ), or attributed to human activities (So et al ).…”

“…Microsatellites are powerful molecular markers for tracing clonal lineages and exploring population structure, especially for Daphnia (e.g., Thielsch et al ; Yin et al ; Walser and Haag ; So et al ; Ma et al ). Thielsch et al () used microsatellites to explore the genetic structure of European D. longispina species complex populations.…”

“…Thielsch et al () used microsatellites to explore the genetic structure of European D. longispina species complex populations. So et al () found only a single multilocus genotype (MLG) in Japanese D. pulex based on 12 microsatellite loci, suggesting asexual reproduction. Walser and Haag () used microsatellites to demonstrate strong intraspecific variation in genetic diversity and genetic differentiation of Daphnia magna populations, likely due to the effects of population turnover and population size.…”

High mutational rates of large-scale duplication and deletion in Daphnia pulex

“…Because such genotypes accumulate mutations in nature in a perpetually clonal manner, a direct comparison between MA experiments and patterns of variation in natural asexual lineages has the potential to yield insight into the role of selection in either eliminating or promoting various classes of mutation (Tucker et al 2013;So et al 2015).…”

Invasive invertebrates associated with highly duplicated gene content

“…We defined species registered in the invasive species databases as invasive species (Supporting Information Table ). We also defined A. pisum and D. pulex as invasive species, because A. pisum is a global agricultural pest (International Aphid Genomics Consortium, ) and D. pulex , which originated in America, is a global invasive species that has expanded to Asia and Africa (Crease, Omilian, Costanzo, & Taylor, ; Mergeay, Verschuren, & De Meester, ; So et al, ). Note that Nasonia vitripennis parasitises its host, but it is a parasitoid (predator); therefore, we did not define N. vitripennis as a parasitic species.…”