Aquatic animals commonly use chemical cues to gain sensory information. These cues mediate many of the animals’ behavior and interactions such as reproduction, foraging strategies and predator detection. Many studies have been done to investigate the role of olfaction in fish and these research studies have demonstrated the important role of chemosensory cues in fishes’ recognition of conspecifics (a member of the same species) and heterospecifics (an individual belonging to a different species) in freshwater habitats. For instance, not only can the Trinidadian guppy (Poecilia reticulata) have the ability to recognize both familiar and unfamiliar individuals, females are also able to differentiate between the odors of individual males. However, only recently have researchers began to investigate the role of olfaction in influencing the life choices of coral reef fishes.
In a recent study, researchers examined the role that chemosensory cues play in the recognition of conspecifics and heterospecifics in a guild of coral reef dwelling damselfish species: Dascyllus melanurus, D. reticulatus, Chrysiptera arnazae and Pomacentrus moluccensis. They wanted to investigate if the damselfish’s response to chemical cues during their settlement phase as juveniles can explain the degree of co-habitation or avoidance. The researchers came up with four hypotheses:
- Species that are commonly found in conspecific groups will be attracted to the smell of a conspecific
- Species that commonly occur in heterospecific groups will respond positively to the smell of any heterospecific species that they frequently live with
- Species that are not found in conspecific groups will react neutrally or negatively to the smell of a conspecific
- Species that do not occur in heterospecific groups will show a neutral or negative response to the smell of heterospecifics
This study was carried out by using a two-channel-choice-flume whereby the individual fish can move freely between water flowing from two alternate sources: one was treated with a specific chemical cue (conspecific or heterospecific) and one was not treated with any chemical cues.
Response to conspecific odor cues
- D. melanurus, D. reticulatus and C. arnazae are the three most naturally gregarious species and had significant preferences towards conspecific odors.
- On the other hand, P. moluccensis showed a neutral response toward conspecific, spending just over half the time in the conspecific treated water.
Response to heterospecific odor cues
- D.melanurus showed a range of responses to heterospecifics: neutral toward D. reticulatus and strong avoidance from water seeded with P. moluccensis and C. arnazae chemical cues.
- D.reticulatus demonstrated a significant aversion to all three heterospecific test species
- C. arnazae exhibited a neutral response toward D. melanurus but demonstrated significant avoidances toward the other two test species
- D. moluccensis showed very strong aversions toward all three heterospecific test species.
Attraction towards the small of a heterospecific did not occur. Only in two instances did they find neutral responses exhibited toward heterospecifics. As it turns out, one of these instances occurred between two sister species (D. melanurus and D. reticulatus) that are commonly found sharing the same coral refugia. With respect to C. arnazae, it is unclear why it would respond neutrally toward chemical cues from D. melanurus as D. melanurus is known to be competitively dominant species. However, these two species rarely appear to share the same reef space. Thus, it is possible that they do not present a high threat to one another in terms of competition for resources.
All in all, the results from this study showed that individuals are capable of species-specific responses. The results from this study is a significant contribution to studying the role of olfactory stimuli as it is the first to demonstrate the potential role of olfactory cues in conspecific attraction and heterospecific spacing in coral reefs. This study demonstrates that damselfish are capable of distinguishing heterospecifics beyond merely detecting the presence of predators but also extends to the identification of other species within the same guild and thus having the ability to identify potential competitors.
Coppock, A. G., Gardiner, N.M., Jones, G. P. (2016) Sniffing out the competition? Juvenile coral reef damselfishes use chemical cues to distinguish the presence of conspecific and heterospecific aggregations. Journal of Behavioral Processes 125, 43-50
Watt, P.J., Shohet, A.J. (2003) Female preferences based on olfactory cues in the guppy Poecilia reticulata. J. Fish Biol 63, 258