Antipredator tactics: a kin-selection benefit for defensive spines in coral catfish?

Morphological features that impair a predator’s ability to consume a prey item may benefit individual prey; but what of features that prolong prey-handling but do not enhance prey survival? For example, a Striped Eel Catfish (Plotosus lineatus) will be fatally envenomated if struck by its specialist predator, the Greater Sea Snake (Hydrophis major). Nonetheless, the catfish typically erects long, toxic pectoral and dorsal spines that increase prey-handling times for the snake by around eightfold. Because the catfish travel in swarms of closely-related individuals, the delay enforced by spines may enable the victim’s swarm-mates to disperse before the snake is able to search for another meal. In keeping with that hypothesis, defensive spines tend to be longer in catfish from regions where the Greater Sea Snake occurs, than from areas where the snake does not occur. Our data thus suggest that defensive weaponry in catfish, as in some eusocial insects, can evolve via kin selection as well as natural selection.

Methods

Coral catfish (Plotosus lineatus) were measured either from live specimens or preserved museum specimens, to quantify lengths of the pectoral and dorsal defensive spines relative to catfish body length and maximum body diameter.   Times taken for Greater Seasnakes (Hydrophis major) to handle and ingest coral catfish were measured in captivity.