The adaptive value of energy storage and capital breeding in seasonal environments

Abstract

Timing of reproduction in a seasonal cycle is a life history trait with important fitness consequences. Capital breeders produce offspring from stored resources and, by decoupling feeding and reproduction, may bend the constraints caused by seasonality in food or predation. Income breeders, on the other hand, produce offspring from concurrent food intake, with the disadvantage of less flexibility, but with high efficiency and no inventory costs of carrying stores. Here, we assess relative profitability of capital and income breeding in herbivorous zooplankton inhabiting seasonal, high-latitude environments. We apply a state-dependent life history model where reproductive values are used to optimise energy allocation and diapause strategies over the year. Three environmental scenarios were modelled: an early, an intermediate, and a late feeding season. We found that capital breeding was most important in the early season. Capital breeding ranged from 7Á9% of the eggs produced but, because of the high reproductive value of early eggs, capital breeding ranged from 9Á30% when measured in terms of reproductive value. The main benefit of capital breeding was reproduction prior to the feeding season Á when the reproductive value of an egg peaked. In addition, capital breeding was also used to increase egg production rates at times of income breeding. For individuals born late in the season the model predicted a two-year cycle instead of the typical annual life cycle. These individuals could then reap the benefits of early reproduction and capital breeding in their second year instead of income breeding late in the first year. We emphasize the importance of evaluating reproductive strategies such as capital and income breeding from a complete life cycle perspective. In particular, knowing the seasonality in offspring fitness is essential to appreciate evolutionary and population-level consequences of capital breeding.

Grazing, egg production, and biochemical evidence of differences in the life strategies of Calanus finmarchicus, C. glacialis and C. hyperboreus in Disko Bay, western Greenland

“…Available life-history models show eggs produced from lipid stores prior to the phytoplankton bloom to have the highest reproductive value and importance to population recruitment in high-latitude systems (Varpe et al 2007), thus favoring species capable of spawning independent of food before the phytoplankton bloom (C. hyperboreus, and to a lesser extent C. glacialis). However, if the bloom occurs at a later time, the importance of lipid-fueled early-spawned eggs in recruitment decreases relative to later-spawned eggs fueled by feeding (Varpe et al 2009), which may also be true if the bloom is prolonged (C. finmarchicus). However, simultaneous high-resolution measurements of distribution, grazing, body composition, and reproduction before, during, and after the phytoplankton bloom are needed to positively identify differences in strategies and life-cycle traits between these species.…”

“…Considering overlapping spawning and molting periods (Smith 1990, Niehoff et al 2002, late molters may also choose to prioritize refueling and postpone spawning until the next season. This strategy would also ensure higher reproductive success considering the greater reproductive value of early spawned eggs (Varpe et al 2009). The present study indicates that female C. glacialis and C. hyperboreus can reproduce in more than 1 yr. …”

Spatial and temporal structure of the meroplankton community in a sub-Arctic shelf system

“…Seasonal variation in hydrodynamics also interacts with the timing of larval release because encounter with a suitable benthic habitat ultimately influences larval success (Metaxas 2001, Ayata et al 2011. Although a substantial literature discusses reproductive strategies and larval nutrition in holoplankton (taxa spending their entire lives in the water column) (Varpe et al 2009, Daase et al 2013, the transferability of all of these conceptual models directly to studies of the pelagic developmental stage of benthic organisms (meroplankton) remains unclear.…”

Seasonality of occurrence and recruitment of Arctic marine benthic invertebrate larvae in relation to environmental variables

“…In contrast, the income breeder relies on energy obtained during the reproductive period rather than stored energy. This concept is based on vertebrate life history, but it has a broad application across all phyla including marine invertebrates (see Varpe et al 2009;Nygård et al 2010). Theoretically, for Arctic benthic organisms with planktotrophic larvae feeding in the water column, the most beneficial timing for reproduction would be just prior to the period of highest food abundance, assuming that the phytoplankton bloom is the primary food source.…”