Calanus finmarchicus diapause initiation: new view from traditional life history-based model

Abstract

Organisms have evolved to optimally align the timing of diapause with the seasonality of environmental conditions in order to maximize their fitness. Observations from the Northwest Atlantic suggest that Calanus finmarchicus diapause initiation date varies significantly by geographic location, inconsistent with patterns of seasonal changes of any single environmental factor such as photoperiod, sea surface temperature, or food availability. In the present study, a life history-based model was used to reconcile the apparent inconsistency. The model results suggest that (1) the induction of diapause involves multiple environmental factors as a result of fitness maximization, and (2) in addition to temperature and food condition, predation pressure is another key factor that could affect diapause initiation process. It is further suggested that phenotypic plasticity is likely to be the major source of variation in the timing of diapause initiation for C. finmarchicus. KEY WORDS: Calanus finmarchicus · Diapause · Life history · Fitness Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 440: [105][106][107][108][109][110][111][112][113][114] 2011 be achieved if individuals start diapause whenever they are physiologically ready. For instance, the Calanus finmarchicus population in the Gulf of Maine is known to have 2 or more generations (Meise & O'Reilly 1996, Durbin et al. 1997, Miller et al. 2000. Based on the LAW hypothesis, the reason for some of the first-generation individuals not entering diapause remains not very clear. Those first-generation individuals may be capable, and have an option, of shifting energy from active development and reproduction to lipid storage in preparation for diapause. This suggests that factors other than physiological constraint may play a role in the diapause initiation process.In the present study, it is hypothesized that (1) the induction of diapause indeed involves the interaction of multiple environmental factors, but this is due to fitness maximization rather than physiological constraints; and (2) in addition to temperature and food condition, predation pressure is another key environmental factor that could affect the diapause initiation process. The focus of the present study is on the ultimate cause of selection rather than a direct mechanistic modeling on behavioral responses to environmental cues. The approach used to test the hy potheses is based on the theoretic framework developed for explaining dormancy strategy from a life history theory point of view (e.g. Levins 1968, 1969, Cohen 1970. Although this framework was developed many years ago, new insights can still be gained by using recently observed species-specific vital rates and diapause pattern. The objective here is to reconcile the apparent inconsistency between the observed patterns of diapause onset with induction of diapause by any single observed environmental cue. This would then provide a valuable understanding of the relationship between environm...

Copepod diapause and the biogeography of the marine lipidscape

“…(a) Model I: The biogeography of the copepodid diapause trait under the Ji (Ji, ) model. Colour indicates the proportion of the population, averaged over the year, entering diapause under a long‐term fitness maximization assumption.…”

“…These data are resolved to 1‐degree in space and interpolated to 1 day in time. Stochastic variability was added to the seasonal cycle, and ensembles of output computed, to capture the inherent variability in conditions (following Fiksen, ; Ji, ). The models were computed essentially as they appeared in their original publications, with only minor modifications (see Supporting Information Appendix S1).…”

“…For a higher resolution and dynamic picture, we can use approach (3). There is a large body of work modelling diapausing copepods (Fiksen, ; Hairston & Munns, ; Huntley, Zhou, & Lopez, ; Maps, Plourde, & Zakardjian, ; Maps, Record, & Pershing, ; Miller, Lynch, Carlotti, Gentleman, & Lewis, ; Pierson, Batchelder, Saumweber, Leising, & Runge, ; Speirs et al., ; Tittensor, DeYoung, & Tang, ; Varpe, Jørgensen, Tarling, & Fiksen, ; Wang, Wei, & Batchelder, ; Wilson, Banas, Heath, & Speirs, ; Zakardjian et al., ), incorporating some aspects of the trait‐based perspective (Ji, ; Maps, Pershing, & Record, ; Maps, Runge, et al., ; Record, Pershing, & Maps, 2013a). Most modelling studies focus on a single region and just one species.…”

“…There is a wide range of copepod models, including empirical statistical models (Chust et al., ; Reygondeau & Beaugrand, ), population dynamical and life history models (Fiksen & Carlotti, ; Ji, ; Ji, Davis, Chen, & Beardsley, ; McGillicuddy et al., ; Record et al., ; Speirs et al., ; Varpe, ; Varpe et al., ; Zakardjian et al., ), detailed individual‐based models (Leising, ; Leising & Franks, ; Maps, Pershing, et al., ; Maps, Runge, et al., ), and community‐based models (Record, Pershing, & Maps, 2012; Record et al., 2013a). In some models, life history strategies emerge, and in others, life history is prescribed.…”

On the surprising lack of differences between two congeneric calanoid copepod species, Calanus finmarchicus and C. helgolandicus

“…To survive this period C. finmarchicus undergoes a long period of overwintering, commonly referred to as diapause, spent in deep waters with reduced respiration rates (reviewed in Hirche, 1996). The reasons for this period of overwintering are thought to be multiple, including the need to survive long periods of low food supply and avoiding high predation rates (Ji, 2011). Individuals normally enter diapause during the fifth copepodite stage (Heath and Jónasdóttír, 1999), however significant numbers of CIV copepodites have been observed in some overwintering populations (Head and Pepin, 2007).…”