Seasonal pattern and induction cues of diel vertical migration of Chaoborus flavicans in Lake Fukami‐ike, Nagano, Japan

Abstract

Diel vertical migration (DVM), which is a wellknown behavior of planktonic organisms, is influenced by several factors, including predation, ultraviolet radiation, temperature, and food. The larvae of Chaoborus (Diptera) exhibit DVM in lakes and ponds. However, it is unclear whether the DVM of Chaoborus larvae changes seasonally and whether induction cues influence the seasonal pattern of DVM. In this study, we report that Chaoborus larvae showed DVM throughout the year in a eutrophic lake (Lake Fukami-ike, Japan). Our laboratory experiment demonstrated that the larvae showed DVM in response to light change even when they were not exposed to fish kairomone at water temperatures typical of winter and summer in the studied lake. These results differed from those of previous studies on other Chaoborus populations showing that both fish kairomone and light change were necessary to induce DVM, which suggests variation in the induction cues among local populations. We suggest that for Chaoborus larvae in Lake Fukami-ike, a seasonally continuous DVM induced solely by light change is adaptive to their particular habitat where the population is exposed to fish predation throughout the year.

Degree of high phenotypic plasticity in wild populations of Daphnia in early spring

“…In this study, we found that inducible defense tends to increase during the season as o n l y predatory larvae emerge from sediment. Chaoborus population in our study lake emerged into water column and gradually gained height, and probably migrated vertically, but limited in this observation periods (Nagano et al, 2015). When the lower population of larvae changed their habitat to the water column from February to March, their degree of inducible defense showed highly.…”

“…The morphology ordinate from individuals collected in February could be assumed to be the non-defensive morphology (degree of inducible defense is zero, Fig. 3), because Chaoborus larvae were absent from the water column at daytime and migrate at night time (Nagano et al, 2015). We calculated the degree of inducible defense of the species on each sampling date (Fig.…”

“…In fact, Daphnia in the study lake might also show this defensive behavior with diel vertical migration (DVM), since an anoxic layer was observed in this lake (Nakagawa et al, 2012;Suda et al, 2016). Chaoborus larvae also showed DVM in the lake against fish predation (Nagano et al, 2015). In future studies, it is important to integrate these multiple defensive traits into the analysis, as well as consider how Daphnia adapts to their multiple traits against predation pressures.…”

“…The circulation and stagnation periods were from November to March and April to October, respectively. Two Daphnia species (D. ambigua and D. pulex), C. flavicans (Nagano et al, 2015), and planktivorous fish (bluegill sunfish Lepomis macrochirus and largemouth bass Micropterus salmoides; Kawanobe and Hosoe, 2010) inhabited the lake. Chaoborus larvae and daphnids were captured on the same observation date by vertically towing three times with a plankton net (NXX7, φ30 cm) above 7.5-m depth, with sampling carried out at approximately 10:00 hrs.…”

“…The larvae that coexist with fish reside deeper in the water column or sediments during the daytime and migrate to upper layer at night, i.e., diel vertical migration (DVM, Teraguchi and Northcote, 1966;Dawidowicz et al, 1990;Tjossem, 1990). The migration amplitudes of the larvae vary by season; large migration amplitude is observed in summer while short or no migration occurs in winter and at low temperatures (Goldspink and Scott, 1971;Nagano et al, 2015). Given the impact of Chaoborus larvae on Daphnia, the larvae change distribution areas from sediment to water column in the daytime with simple age structure before summer.…”