Behavioural and physiological mechanisms behind extreme longevity in Daphnia

Barbara Pietrzak,Magdalena Markowska,Ewa Szymanska,Maciej Rojek,Miroslaw Slusarczyk,Anna Bednarska

doi:10.1007/s10750-012-1420-6

Abstract

The combined effect of external environment and energy allocation strategy of the organism on longevity can be exceptional. In a cold oligotrophic fishless habitat, individual Daphnia can live for over a year, several times the usual Daphnia lifespan. This extreme lifespan is in part a consequence of the overwintering strategy which includes storing resources and delaying reproduction until another spring. Yet, contrasting strategies may be applied by Daphnia, resulting in over twofold differences in lifespan within a single habitat. We identify physiological mechanisms mediating such differences in longevity in closely related Daphnia of two lineages coexisting within a high altitude lake, testing the predictions that long-lived animals stay in colder waters and have lower metabolic rates, irrespective of temperature. Vertical distribution of the animals was assessed during three summer stratification seasons, and metabolic activity was measured as oxygen consumption and RNA:DNA ratio. The results not only support our predictions but also reveal that habitat choice is dependent on reproductive status rather than genotype. The young individuals of the overwintering lineage may delay reproduction in part by staying in colder waters than the reproducing adults, which together with low intrinsic metabolic rates may underlie the longevity of Daphnia of this lineage.

Highlights

In lakes and ponds of the temperate zone, life cycle of most planktonic cladoceran species is short and in the order of weeks (Threlkeld, 1987)
We identify physiological mechanisms mediating such differences in longevity in closely related Daphnia of two lineages coexisting within a high altitude lake, testing the predictions that long-lived animals stay in colder waters and have lower metabolic rates, irrespective of temperature
Temperature governs metabolism through its effect on the rate of biochemical reactions, and the rate of metabolism observed at the level of the organism increases exponentially with temperature (Gillooly et al, 2001)

Summary

Introduction

In lakes and ponds of the temperate zone, life cycle of most planktonic cladoceran species is short and in the order of weeks (Threlkeld, 1987) This may be a result of selection by temporarily changing abiotic conditions: drying or overfreezing in shallow habitats, or oxygen deficits in deep lakes of high trophic level. In deep oligotrophic habitats with no oxygen deficits, where fish predation pressure is reduced or absent, released from the selective pressure on early reproduction, Daphnia can maximize fitness by applying different strategies, including those involving the delay of the onset of reproduction and lengthening the lifespan (Dawidowicz et al, 2012). The quality of the fat stores appears meaningful, as these two differ in the way they manage and expend the very limited resources, and as such—in their overwintering strategy and in longevity (Gliwicz et al, 2001; Slusarczyk, 2009)

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