Competitive abilities and distribution ranges of four asexual Daphnia pulex lineages and Daphnia mitsukuri in Eurasian continental islands

Abstract

Daphnia pulex and D. mitsukuri are morphologically similar and distributed in small lowland Japanese lakes. Daphnia pulex in Japan reproduces by obligate parthenogenesis and is composed of four different lineages (JPN1-JPN4) with North American origins. Although this species is found throughout Japan, JPN1 has the largest distribution range, followed by JPN2. Daphnia mitsukuri is a putatively endemic species that is now rarely found in Japan. Since Daphnia share the same algal food, the difference in distribution ranges among the four asexual D. pulex lineages and D. mitsukuri may be caused by exploitative competition for algal food. To examine this possibility, we measured the threshold food concentration (TFC) at zero-net growth rate and the food concentration required for 50% of the individuals to survive (FC50). In addition, we examined the effects of temperature on the somatic growth rate (SGR) and the mortality rates of four asexual D. pulex lineages and D. mitsukuri. The experiments showed that TFC was lowest in D. pulex JPN1 and highest in D. mitsukuri, supporting the idea that the largest distribution range of JPN1 is due to its superiority in inter-lineage competition, and that the distribution area of D. mitsukuri is reduced through exploitative competition with D. pulex.However, although JPN2 was found in relatively large areas, it had higher TFC than JPN3 and JPN4, which appear in very limited areas. These results clearly showed that the difference in distribution ranges among D. pulex lineages are not necessarily determined by their competitive superiority alone.Competitive interaction between congeneric species for food is one potential factor determining their distribution ranges (Connell, 1961;Peterson et al., 2011;Sexton, McIntyre, Angert, & Rice, 2009). In general, competitively superior species occur frequently and occupy large distribution ranges while the presence of inferior species are limited to areas where environmental conditions such as temperature and competitors favor the latter against the former (Reitz & Trumble, 2002;Taniguchi & Nakano, 2000;Urabe, 1990). Thus, to understand the differences in distribution range and the frequency of appearance between congeneric species, it is essential to examine the competitive abilities of these species. Since planktonic animals share algal food, a number of studies

To lose is to win: Long‐term co‐occurrence of two asexual populations realized by a dormant strategy of the inferior competitor

“…When these genotypes were abundant in the lake, the water temperature was ~20°C. Maruoka and Urabe (2020) showed that the somatic growth rate of JPN2 was slower than that of JPN1 at 20°C. More importantly, the laboratory experiment conducted at 20°C in the present study showed that the JPN1 population actually excluded the JPN2 population when cultured together.…”