Response to fish kairomone in Daphnia galeata life history traits relies on shift to earlier instar at maturation

Abstract

The aim of the present study was to clarify the mechanisms underlying the expression of phenotypic plasticity in Daphnia life history traits in response to fish kairomone and to explore how these mechanisms interact with genetic variation for life history traits. I studied the effect of fish kairomone on life history traits in 16 Daphnia galeata clones. Maturation occurred more often at the earlier instars in response to the fish treatment, resulting in earlier age and smaller size at maturity. The changes in age and size at maturity which occurred in the response to the fish treatment could be attributed to a large extent to this shift. In addition, fish kairomone resulted in smaller instar increments after the maturation process was initiated, but not during the juvenile period. Within groups of animals maturing at the same instar, larger size at birth resulted in larger size at maturity, but had no effect on age at maturity. However, larger size at birth brought about earlier maturity because animals which were larger at birth matured more often at the earlier instar. Fish treatment resulted in more, but smaller, offspring in the first clutch relative to the size of the mother. Genetic variation was found in all measured life history traits. Genetic variation in plasticities of life history traits was not detectable by standard methods, and was only shown when the above mechanisms of expression of life history traits were taken into account. This study illustrates the importance of a thorough understanding of the mechanisms underlying the expression of life history traits, in this case, sources and consequences of maturation in the multiple instars. Not only is this necessary to predict the long-term effect of the environment, but also to understand the response of life history traits and their plasticities to natural selection. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s00442-002-0901-0.

Persistent maternal identity effects on life history traits in Daphnia

“…Similarly, no interactions between size at birth and the fish kairomone treatment were significant. However, because an earlier study (Sakwińska 2002) suggested that size at birth can have nonlinear effects on plasticity of size at maturity, the additional analysis of plasticity was carried out. Plasticity values for each mother were calculated by subtracting the average trait values for three offspring in the fish treatment from the average values in the control treatment.…”

“…In the presence of a waterborne cue released by a predator, individuals shift their life history towards earlier maturation at smaller size, an adaptive response to the mortality risk for larger-sized individuals (Stibor 1992;Weider and Pijanowska 1993). A previous study (Sakwińska 2002) suggested that such a response to the fish cue might depend on size at birth. It has been hypothesized that, for a Daphnia female, her own age could be an indicator of predation pressure: the fact that an individual survived to an older age signals that predation pressure is low (Lampert 1993).…”

“…Maternal effects are often large for traits expressed early in life, but later in life they appear to diminish. Although the consequences of variation in size at birth for the rest of the Daphnia life history is well established (Tessier and Consolatti 1989;Ebert 1991Ebert , 1994Barata and Baird 1998;Sakwińska 2002), the persistence of maternal effects and their influence on life history traits expressed later in life have only rarely been studied (Tessier and Consolatti 1989;Boersma 1997). It has been shown that mothers grown at low food levels produce neonates which resist starvation better , and that maternal food supply affected some life history traits of the offspring expressed later in life (Reede 1997).…”

A parasite-mediated life-history shift in Daphnia magna

“…Daphnia, for example, produce larger clutches of smaller offspring earlier when exposed to predatory fishes (Sakwinska 1998;Sakwinska 2002). For parasitism, fecundity compensation has been documented for a number of taxa, and may be most common where parasites sterilize their hosts (Minchella & Loverde 1981;Krist 2001).…”

Threat or treat: the role of fish exudates in the growth and life history of Daphnia

“…The presence of kairomones resulted in reductions in growth rate, size at first and second reproduction, egg volume (Machácek 1991, Stibor 1992, Weider and Pijanowska 1993, and caused a decline in the egg and body integrated lipid volumes in first-clutch females. Furthermore, kairomones produced (1) accelerated maturation, (2) an increased number of eggs per clutch vs. body length (e.g., Machacek 1991, Stibor 1992, and (3) a reduced number of pre-adult instars (Sakwinska 2002). Although the results we have obtained are in accordance with those of the previous studies indicated above, the strength of the significance between different algal food conditions, species, and within parameters is more realistic because of the semi-controlled abundance of fish-related bacterial food.…”