Pick your battles: competitive strategies of green chromides (Etroplus suratensis) during inter- and intraspecific contests

Abstract

Competitive ability is a key determinant of organismal fitness, yet high costs of interference competition necessitate strategic behavioural responses. This study investigated how green chromide (GC), a cichlid native to the Indian subcontinent, competes with the globally invasive tilapia species (T, Oreochromis spp.) that has encroached upon its habitats. We staged dyadic feeding competitions between GC and T, and analysed aggression, feeding, and hiding behaviours of both the species and further contrasted them with intraspecific contests in GC. We varied developmental stages, residency status of opponents, and used different combinations of body sizes of competitors to test their effects on the outcome of dyadic contests. We hypothesized that competitors would adjust their strategies based on the context of the competition, and thus, we aimed to identify the factors that contributed to such decision-making. Our findings showed residency as the primary driver of competitive strategy, wherein residents had higher aggression and feeding when compared to intruders. The developmental stage had a significant effect on feeding, increasing from young to older stages, but body size contrasts did not contribute significantly towards the outcome of the contests. For the species effect, T emerged as a winner in most of the interspecific contests, exhibiting a significant amount of total aggression. However, GC showed distinct behavioural strategies when competing against T versus conspecifics, and exhibited higher levels of aggression and reduced hiding during intra- when compared to interspecific trials. Surprisingly, the feeding behaviour of GC was not significantly impacted in the presence of T, possibly because GC used hiding as a defence strategy, emphasizing the context-dependent, strategic thinking of the species. Overall, the variety of behavioural tactics exhibited by GC in staged competitive interactions showcases robust survival skills of the species, a key trait that may help maintain its fitness in challenging ecological habitats.