Control of dormancy by lipid metabolism in Calanus finmarchicus: a population model test

Abstract

The life cycle of Calanus finmarchicus includes a prolonged dormancy phase that allows it to avoid the unfavourable environmental conditions typical of the upper ocean from late summer to early spring in the subarctic North Atlantic. Recent demographic, physiological and genetic evidence supports the hypothesis of a crucial role for lipid accumulation and metabolism in the control of dormancy. We present a stage-resolving biomass model of C. finmarchicus, implementing a mechanistic approach of the control of dormancy based on this lipid hypothesis. The dormancy process obeys 2 rules: (1) active copepodite stage Vs (C5s) enter dormancy when the ratio of lipid to total body carbon exceeds some threshold, and (2) diapausing C5s exit dormancy when their lipid storage approaches a lower threshold. We implemented the model into a 1-dimensional water column framework and compared our results to 2 consecutive years of observations of stage-specific copepodite abundances and lipid content of C5 from the Northwest Gulf of St. Lawrence, Canada. The model produced realistic phenology and temporal patterns in lipid content of C. finmarchicus in response to the observed environmental forcing. Interannual variations in the timing of entry and contributions of different generations to the overwintering stock were shown. Our results are consistent with the hypothesis of a lipid-mediated control of entrance and exit from dormancy in C. finmarchicus.

Effects of a future warmer ocean on the coexisting copepods Calanus finmarchicus and C. glacialis in Disko Bay, western Greenland

“…Changes in the environment will change the selective pressures on the Calanus populations and probably induce adaptations that will affect their life cycle, such as the timing of diapause as suggested for North Atlantic C. finmarchicus populations (Johnson et al 2008, Maps et al 2010. Such selectionmediated changes may co-occur with the responses predicted in the present study; however, they are not considered further here.…”

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

“…That being said, there is no doubt that lipids play an important role throughout the entire diapause process, due to the energy requirement during diapause and the subsequent arousal and reproduction period (Jónasdóttir 1999 Maps et al 2010). More importantly, at the C4 or C5 stage, an assumption has to be made on when and at what proportion the energy allocation needs to switch from development and molting to lipid storage.…”

“…This would require the model to keep track of the bioenergetics of Calanus finmarchicus, starting from eggs to the C4 stage. The model can become complex very quickly, with a dramatic increase in model parameters and associated uncertainty (see a recent example by Maps et al 2010). More importantly, at the C4 or C5 stage, an assumption has to be made on when and at what proportion the energy allocation needs to switch from development and molting to lipid storage.…”

“…It has been suggested that this 'decision' Ji: Calanus finmarchicus diapause initiation process could start in the C4 stage , maybe triggered by lipid content at that stage, but no evidence is yet available to support this argument. A recent genetics study by Tarrant et al (2010) showed that genes associated with lipid synthesis, transport, and storage were upregulated (more highly expressed) in active copepods when compared to diapausing ones, but this still does not address the question of what triggered the gene upregulation in the first place.That being said, there is no doubt that lipids play an important role throughout the entire diapause process, due to the energy requirement during diapause and the subsequent arousal and reproduction period (Jónasdóttir 1999 Maps et al 2010). More importantly, at the C4 or C5 stage, an assumption has to be made on when and at what proportion the energy allocation needs to switch from development and molting to lipid storage.…”

Functional genomics resources for the North Atlantic copepod, Calanus finmarchicus: EST database and physiological microarray

“…Decreased food availability has been hypothesized to be one causal agent in increased mortality and decreased population growth and reproduction in C. finmarchicus (Plourde and Runge, 1993; Irigoien et al, 1998; Campbell et al, 2001a; Niehoff, 2004; Madsen et al, 2008; Plourde et al, 2009). In addition, it has been well documented that C. finmarchicus copepodites require lipid stores to successfully enter and complete diapause, and to initiate reproduction in the spring (Irigoien, 2004; Saumweber and Durbin, 2006; Johnson et al, 2008; Jónasdóttir et al, 2008; Madsen et al, 2008; Maps et al, 2010; 2011). However, pre-adult stages within any population vary in both size and lipid stores raising questions about timing and likelihood of diapause for some individuals (Pepin and Head, 2009; Pepin et al, 2011).…”