Costs and benefits of brooding among decapod crustaceans: The challenges of incubating in aquatic systems

This chapter discusses general patterns of brooding in decapod crustaceans from aquatic to terrestrial environments, addressing behavioral adaptations as well as costs and benefits. Brooding embryos is a common feature among decapods. However, brooding exhibits a wide range of modes that are highly dependent on the environment. Brooding is less common in marine systems, whereas there is a general pattern of extended brooding with terrestrialization. Exceptions are crabs that have invaded land directly via the seashore, i.e. land crabs that have indirect development like their marine ancestors. During terrestrialization, adaption to environmental stressors like desiccation, UV radiation, temperature variability, mechanical support, and osmolality seemed to generally favor decreasing larval development and increasing duration of brood care. Thus, crustaceans developed more complex brooding mechanisms as adaptive responses to the colonization of land (e.g., osmoregulation of the maternal fluids, marsupial fluid, sealed and specialized marsupium, provision of nutritious material, grooming and cleaning, ventilation of the embryo masses). However, clear brooding behaviors are also observed among several marine species (e.g. grooming and cleaning, oxygen provision). The major efforts to characterize general brooding patterns among decapod crustaceans and describe brooding behaviors were not accompanied by comprehensive studies to understand the costs and the benefits of brooding. Several studies have addressed the positive influence of the mother on embryo development, but the efforts to quantify the impact on embryo survival are still limited. This chapter identifies problems that need further consideration to reach a deeper understanding of the evolution of brooding in decapod crustaceans.