Food Threshold for Diapause in Daphnia under the Threat of Fish Predation

Abstract

The chances of prey to survive and leave viable offspring may be determined by many environmental constraints, of which food conditions may be of key importance. When food is not limited, the high reproductive effort of a well-fed prey individual displaying various defensive responses may assure successful reproduction, whereas low food supplies may prevent it by limiting energy gains and expenditures on defense and procreation. Under low chances for survival of active forms in a local environment, production of diapausing forms of enhanced resistance to unfavorable conditions or dispersion to more favorable places may assure persistence.The laboratory batch-cultured experiments detailed here sought to test whether food concentration may influence probability of producing resting eggs by Daphnia when under chemically simulated fish predation pressure. In ''fish-free'' conditions, no production of resting eggs was observed with either the tested low (0.4 mg C/L) or high (1.6 mg C/L) food concentrations, whereas in ''fish'' treatments, resting eggs were produced by various proportions of females according to food concentration. With the limited food (0.4 mg C/ L) there was production of ephippial (dormant) eggs in the early broods of almost all females in the ''fish'' treatment. Where food concentrations were higher, proportions of ephippial females were progressively lower, with females postponing the formation of resting eggs until later broods. At the highest food concentration (1.6 mg C/L), only about 17% of females produced ephippia when exposed to fish cues. These results are considered to indicate an adaptive response of prey individuals to a simulated danger of predation in various food conditions, determining relative gains of producing active vs. dormant offspring. It seems that D. magna may ''assess'' their chances of survival and successful reproduction in accordance with the anticipated danger of predation and food conditions, and enter diapause when the expected gains from diapause exceed those of active life. A graphical model explaining observed production of active vs. dormant offspring by D. magna under predation pressure at various food concentration is proposed.

To sink or swim: Variable diapause strategies among Daphnia species

“…The exact nature of the late-spring risks for D. pulicaria cannot be determined from the field data. Evidence from other species of zooplankton from permanent lakes suggests that diapause is used to avoid both competition (Santer and Lampert 1995;Hansen and Hairston 1998) and predation (Hairston 1987;Ś lusarczyk 2001), and both types of interspecific interactions become more intense for D. pulicaria as the summer progresses. Field competition experiments for D. pulicaria and D. dentifera indicate that the rank order of competitive ability changes during the season (Hu and Tessier 1995;Cáceres 1998b), and in the Michigan lakes, D. pulicaria is a superior competitor in the spring but D. dentifera is the better competitor in late summer.…”

Evaluation of Daphnia Magna Neonate Viability under Low Temperature Exposure Conditions

“…Most of the literature, however, shows that ephippia formation occurs and may be attributable to a number of factors, including overcrowding, reduction in food supply, reduction in temperature, change in photoperiod, increased predation risk, kairomone release by fish, and in some cases, a combination of the known factors (Carvalho and Hughes, 1983;Pijanowska and Stolpe, 1996;Slusarczyk, 1995Slusarczyk, , 1999Slusarczyk, , 2001; and others). When "conditions" become unfavorable, normally parthenogenetic females go into sexual reproduction and start producing haploid eggs and males.…”

Morphological examination of the resting egg structure of 3 cladoceran species [Ceriodaphnia quadrangula (O. F. Müller, 1785), Daphnia longispina (O. F. Müller, 1776), and D. magna Straus, 1820]

“…In unfavorable environmental conditions (e.g., low water temperature, predation pressure, dry periods), males appear, and thick-shelled, resistant, fertilized eggs (called 'resting eggs') are produced (Slusarczyk, 2001;Panarelli et al, 2008;Slusarczyk and Pietrzak, 2008). When conditions return to normal, these resting eggs hatch and create new offspring; thus, these organisms ensure the continuity of generations by means of these eggs (Panarelli et al, 2008;Vanickova et al, 2010).…”

“…Until now, studies about resting eggs have generally focused on subjects such as the genetic characterization of resting eggs (Reid et al, 2000), maternal effects on the size of resting eggs (Boersma et al, 2000), resistance to predation (Slusarczyk, 2001), ecological and evolutionary significance of the resting egg (Brendonck and De Meester, 2003), the importance of the resting egg in terms of continuity of zooplankton populations (Jankowski and Straile, 2003;Panarelli et al, 2008;Conde-Porcuna et al, 2011), the buoyancy of the ephippium (Slusarczyk and Pietrzak, 2008), and the hatching of resting eggs (Rother et al, 2010;Haghparast et al, 2012).…”