Changes in reproductive life-history strategies in response to nest density in a shell-brooding cichlid, Telmatochromis vittatus
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To determine whether the appearance of a reproductively parasitic tactic varies, and how this variation affects territorial males of the Lake Tanganyika cichlid fish Telmatochromis vittatus, we examined the reproductive ecology of territorial males in Mtondwe and compared it with that of a neighboring Wonzye population, where nest density differs from that at Mtondwe. In Wonzye, with high nest density, male tactics change with their body size from a territorial to a non-territorial parasitic tactic called piracy in which they conquer several nests defended by territorial males and take over the nests while females are spawning. These “pirate” males could decrease the costs incurred by travelling among nests by exclusively targeting aggregations of nests in close proximity while avoiding separate nests. Territorial males in Wonzye sacrifice the potential higher attractiveness offered by large nests and instead compete for nests farther from neighbors on which pirates less frequently intrude. In contrast, the Mtondwe population had lower nest density and piracy was absent. Given that the success of piracy depends on the close proximity of nests, nest density is likely responsible for the observed variation in the occurrence of piracy between the two populations. Furthermore, in Mtondwe, territorial males competed for larger nests and were smaller than the territorial males in Wonzye. Thus, this lower nest density may free territorial males from the selection pressures for increased size caused by both defense against nest piracy and the need to develop into pirates as they grow.
KeywordsAlternative reproductive tactics Interpopulation comparison Nest choice Nest piracy Sperm competition Body size
We thank the staff of the Lake Tanganyika Research Unit at the Fisheries Research Institute of Zambia for their support during field work. We are very grateful to Kaya Matsuoka and Anny Mogollon for English correction and anonymous reviewers for their helpful comments on an earlier version of this manuscript. This work was supported partly by Overseas Scientific Research grant (Ministry of Education, Culture, Sports, Science and Technology; MEXT) to M.K. and Global COE project A06 (MEXT). The present study was conducted with permission from the Zambian Ministry of Agriculture, Food and Fisheries for fish research in Lake Tanganyika.
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