Cooperative Breeding in the Lake Tanganyika Cichlid Julidochromis ornatus

Cooperative breeding has been described for several cichlids from the genus Julidochromis (Perciformes: Cichlidae) under laboratory conditions, but field evidence is scarce. Here we describe the breeding system of the cichlid Julidochromis ornatus (Boulenger) in Lake Tanganyika (Zambia). Groups defended a breeding shelter under a large flat stone. Smaller group members stayed and fed under or close to the stone, actively guarded by the larger group members. Six out of 28 groups were newly established by breeders, joined by subordinates from a large pool of independent fish (comprising 50-70% of the total population), and four groups were seen to dissolve during a total of 77 observation days. Breeding groups consisted of a large breeding male and female with zero to five smaller subordinates (average 2). Larger breeders and subordinates were found in larger groups. All group members participated in territory defence and -maintenance, but the breeders were only present at the shelter 48% of the time, in contrast to the subordinates which guarded the breeding shelter 94% of the time. Smaller group members showed submissive behaviours to larger group members. We conclude subordinates in J. ornatus are helpers, but we did not find evidence that helpers increased the group's current reproductive success. Personal observations combined with a literature review revealed at least 19 species of Lake Tanganyika cichlids show evidence of cooperative breeding, entirely confined to the substrate breeding tribe of the Lamprologini (24% of 80 species in total): 2 Chalinochromis spp., 5 Julidochromis spp., 12 Neolamprologus spp. More effort should be put into detecting cooperative breeding in American and Asian substrate breeding cichlid species.