Finding a balance: Reproductive trade-offs in parasitic isopods of the family Cymothoidae

In this study conducted along the coast of Odisha, India, reproductive trade-offs in isopods of the family Cymothoidae were investigated, focusing on the relationship between the number vs. volume of eggs and the percentage of brood to body volume. Ovigerous females from species with substantial sample sizes (n > 30) were analyzed to understand their survival strategies. The findings highlight distinct strategies among different parasite types within Cymothoidae. Buccal parasites such as Cymothoa frontalis and Cymothoa indica, along with branchial parasites like Joryma sawayah and Agarna malayi, generally produced a higher number of smaller eggs, except for A. malayi, which produced fewer but larger eggs. In contrast, the external body surface-attaching parasite, Nerocila orbignyi, was observed to produce fewer eggs of larger size. Across all parasite types (intraspecific), there was a statistically significant negative correlation between egg number and egg volume (p < 0.05). Buccal parasites were observed to have the highest percentage of marsupium volume relative to body volume, indicating a strategy to maximize egg storage. Conversely, external body surface-attaching parasites had the lowest percentage, possibly reflecting adaptation to a different reproductive environment. Additional observations revealed anatomical adaptations in all the studied isopod species which include the shift of the alimentary canal to the dorsal side to accommodate the development of the marsupial sac for egg incubation. In summary, these findings illustrate how parasitic isopods of the family Cymothoidae manage trade-offs between reproductive potential and success, crucial for their species' continuity and survival strategies in coastal ecosystems.