Fitness consequences of the timing of metamorphosis in a freshwater crustacean

Abstract

Metamorphosis is a common life-cycle transition in organisms as diverse as amphibians, insects, fishes and crustaceans, and the timing of this transition often affects an individual's fitness. Here, we manipulated the timing of the metamorphosis in the freshwater copepod, Diaptomus leptopus, and then followed individuals over their entire life cycle to assess the fitness consequences of variation in age and size at metamorphosis. In 3 separate experiments, individuals were raised in different food conditions: low food (0.2 J..Lg C/ml) switched to high food (0. 7J..Lg C/ml), or high food switched to low food, at several different larval and juvenile stages. Control individuals were reared on high or low food concentrations over their entire life cycles. For each individual, we measured age and size at metamorphosis and age and size at maturity; for females we also measured total lifetime egg production and calculated a composite fitness measure, A.. Statistical analyses showed few effects of treatment on age or size at metamorphosis; of these two traits, only age at metamorphosis correlated significantly with age at maturation, suggesting fitness effects. Changes in food conditions during juvenile stages also had no effect on size at maturity, but caused significant differences in age at maturity. Only age at maturity and egg production covaried significantly with A.. Because egg production was significantly correlated to age at maturity, the fitness differences we observed may be primarily due to variation in developmental rates and age at maturity. These results suggest that natural selection should favor rapid development in field populations, and that larvae should metamorphose (and perhaps mature) at minimum possible sizes. They also suggest that body size plays a different life-history role in these organisms than is recognized in most poikilotherms... AbstractMetamorphosis is a common life-cycle transition in organisms as diverse as amphibians, insects, fishes and crustaceans, and the timing of this transition often affects an individual's fitness. Here, we manipulated the timing of metamorphosis in the freshwater copepod, Diaptomus /eptopus, and then followed individuals over their entire life cycle to assess the fitness consequences of variation in age and size at metamorphosis. In 3 separate experiments, individuals were raised in different food conditions: low food (0.2 ).lg C/ml) switched to high food (0. 7 ).lg C/ml), or high food switched to low food, at several different larval and juvenile stages. Control individuals were reared on high or low food concentrations over their entire life cycles. For each individual, we measured age and size at metamorphosis and age and size at maturity; for females, we also measured total lifetime egg production and calculated a composite fitness measure, A.. Statistical analyses showed few effects of treatment on age or size at metamorphosis; of these two traits, only age at metamorphosis correlated significantly with age at maturation, suggesting fitnes...

Plasticity of the duration of metamorphosis in the African clawed toad

“…Variation in the duration of the larval period, for example, has been demonstrated in several studies covering a wide range of taxa (e.g. marine invertebrates: Twombly, 1996; insects: Blakley, 1981; fish: Policansky, 1983; amphibians: Werner, 1986; Harris, 1999). The duration of the transition between stages, often involving a metamorphosis, has received considerable attention in terms of developmental mechanisms, but much less in terms of the effects of environmental circumstances.…”

Effect of temperature, food and individual variability on the embryonic development time and fecundity of Arctodiaptomus salinus (Copepoda: Calanoida) from a shallow saline pond

“…Knowledge of these life traits is not only necessary for this kind of studies but, when it is analyzed at the individual level, it can also provide very useful information about the environment and the strategies of populations for surviving in their habitats. Individual variability in development can increase when the environment is non-optimal or unpredictable and can determine the coexistence between species (Caramujo & Boavida, 1999;Jiménez-Melero et al, 2005), population fitness (Twombly & Tisch, 2002), or even population persistence (López, 1991). Moreover, during the last decade, interest in individual variability has increased owing to the increased use of the individual-based model (IBM) approach in ecological studies (Grimm & Railsback, 2005).…”

Effects of a patchy food environment across life history stages

“…This loss of a larval legacy through time has been found in non-molluscs as well. In a freshwater copepod, the larval legacy from a variable diet was erased through juvenile growth by the time organisms reached maturity (Twombly and Tisch, 2002).…”

“…In most studies on the legacy effects of variable food, larvae are starved for a period of time, and then returned to a high food availability environment (e.g., Pechenik et al, 1996aPechenik et al, ,b, 2002Qian and Pechnik, 1998) or experience a temporary change in food concentration (e.g., moved once from a high food concentration to a low food concentration and back, Pechenik et al, 1996aPechenik et al, , 2002. Other studies (e.g., Howard and Hentschel, 2005;Phillips, 2004;Twombly and Tisch, 2002) make a single switch in feeding rations (e.g., low to high) at various stages in larval development. In nature, many organisms experience repeated fluctuations between favorable and unfavorable conditions.…”