Energy balance of lettuce fed Arion ater/rufus (Biscay, Northern Spain)throughout development

Abstract: In temperate areas, the big terrestrial slug Arion ater reaches a considerable size withina limited growing season (7 to 14 months) exhibiting remarkable growing rates. In this work,energy balance of different size specimens of Arion ater sampled at distinct moments chosen toportray the various developmental stages along its life cycle has been determined in thelaboratory through short-term experiments using lyophilized lettuce (Lactuca sativa) as foodstuff.In addition allometric relationships of the various components of energy balance (ingestion,absorption and, metabolic rates) have been established. Whereas mass exponent for oxygenconsumption is 1 within each developmental stage (metabolic expenditure scales proportionallyto body size provided animals belong to a similar growth phase) physiological descriptors relatedto energy intake (ingestion and absorption rates) share a common correlation coefficient of 0,610(± 0,130) the combination of both results explaining increased reduction of growth rates fromimmature young phases to active growing males (IGR = 0.035 to 0.020mg/mg/d on dry weightbasis). Assimilation Efficiency has remained constant along the study being 60% of organicuptake. Lettuce appears as a suitable food for Arion and SFG determined in the laboratory hasresulted in positive values for every developmental stage, including egg-lying females: 313 J/dfor young slugs, 934 J/d for males and 1646 J/d to 1452 J/d for October and November femalesrespectively. Integrated Mean Gross Conversion Efficiency (SFG/Ingestion) is 44.6% (±3.8). Asa conclusion, cumulative ingestion of a given slug from an initial size of ~3.5g live weight to afull-grown female of ~23g would require about 600g of fresh lettuce.