Nonlethal injury is a common and ubiquitous feature of ecological systems and can result in altered growth and survival rates. Ecological theory predicts that injured animals should face an energetic tradeoff between investing in recovery vs. investing in reproduction. Possible impacts on reproduction may range in magnitude from very strong (elimination of reproduction), to intermediate (reduced number of offspring), to weak (reduced investment in each offspring). While this tradeoff is well established in terrestrial systems, it has received little attention in the marine environment, particularly in a way that quantitatively relates the degree of injury to the degree of reproductive impact. We examined injury via limb loss across four sites in the mangrove tree crab Aratus pisonii. Using dissections, we correlate the loss of limbs and limb regeneration with energy storage in the hepatopancreas and energy allocated to current (egg clutch) and future (gonads) reproduction. We also used gut size as a proxy for diet quality to determine how diet quality varied across sites with different levels of human impact, and how this was influenced by limb loss.
Results/Conclusions
We found that limb loss was highest at the site that was closest to roads and had the highest level of human presence, and conversely injury was lowest at the site furthest from the road and with the lowest level of human presence. We found evidence that the quality of consumed food likely decreases with the number of limbs lost, but found no influence of limb loss on amount of food consumed or on energy storage. We show that limb loss reduced the number of eggs produced and that the mass of the ovary declined with the number of regenerating limbs, providing direct evidence for a tradeoff between reproduction and injury recovery. Our study provides evidence from a marine system that supports ecological theory, showing that injured animals face an energetic tradeoff between investing in injury recovery and investing in reproduction. Further, our study suggests that energetic intake and the resulting energetic tradeoff associated with limb loss may be influenced by the level of human disturbance.