Impact of rising temperature on reproductive investment in a capital breeder: The lesser sandeel

Capital breeding, whereby adult's build-up energy reserves at times when food is abundant in order to invest in reproduction during a time of low prey availability, is common in seasonal environments. A dependence on stored energy for reproductive investment may make capital breeders sensitive to rising temperatures during winter when activity and energy demands are typically low. The lesser sandeel, Ammodytes marinus (Raitt, 1934), is an extreme capital breeder, as gonad development is entirely dependent on stored energy whilst the fish remains buried in sand overwinter. In this laboratory study, the energetic consequences of high and low overwintering temperatures on energy allocation to reproduction in A. marinus were examined. The laboratory conditions led to growth and mass changes that were consistent with previously published field observations. Loss in wet mass was greater in the high temperature treatment, consistent with the higher metabolic cost predicted. Despite this, somatic energy loss did not differ between the two temperatures, the difference in mass being related to the lower relative gonad size in the high temperature treatment. The negative effect of temperature on reproductive investment in A. marinus highlights that although temperature can have a permissive effect on reproductive development it is limited by available energy reserves. Based on these findings it seems likely that warming will lead to a change in reproductive investment in A. marinus that mature but will not impact their overwinter survival.