Summary 1.Adopting alternative reproductive tactics may require divergent solutions to reproductive competition among individuals of a population. Often investment in reproduction differs substantially between individuals pursuing bourgeois and parasitic tactics, which may result in different trade-offs and limitations. 2. Here we identify divergent behavioural, morphological and physiological traits of bourgeois and parasitic male morphs in Lamprologus callipterus, a Lake Tanganyika cichlid with an extreme size dimorphism among males. We focus on limiting factors and compare these between large, nest-building males and dwarf males parasitizing their reproductive effort. 3. Only nest males invest in courtship, and they exhibit much more aggression than dwarf males. In contrast, dwarf males spend 20% of their time feeding, whereas nest males hardly ever feed. 4. Nest males accumulate reserves before breeding and use these up before taking a reproductive break, thereby performing a 'capital breeder' strategy. In contrast, dwarf males use assimilated energy immediately for reproduction, thus acting as 'income breeders'. This is a requirement of their spawning tactic, which only works out with a small and slim body. 5. A field experiment showed that nest males lose weight by their restricted feeding opportunities while holding a nest, which would allow them to hold a territory for 103 days on average. Due to their reproductive investment, however, they held territories only for a mean period of 33 days, which reveals the relative importance of opportunity costs and reproductive expenditure. 6. Nest males are also limited by the requirement to fertilize each egg of a clutch with a separate ejaculate. Their ejaculation rate and the number of sperm released both decline sharply after 5 h, whereas undisturbed spawning lasts 2-4 h longer than that. 7. There is a strong allometric relationship between body mass and gonad weight, with smaller males of both tactics investing disproportionately more in testes than large males. The major limitation of dwarf males is apparently access to spawning females, which is prevented by the monopolization of nest owners and becomes more difficult with increasing size of dwarf males. 8. Our results show that different males in a population may act as capital or income breeders depending on tactic and may face very different limitations, which is a direct result of highly divergent spawning tactics and resulting body sizes. 9. We argue that capital and income breeding are useful concepts to understand divergent life history decisions associated with alternative reproductive tactics, i.e. behavioural polymorphisms within a species and within one sex. It might turn out that in general, bourgeois tactics rather adopt a capital breeding strategy whereas parasitic tactics are inclined to perform as income breeders, due to the diverging constraints faced by these types of reproduction, although we discuss possible exceptions.

In species with indeterminate growth, age-related size variation of reproductive competitors within each sex is often high. This selects for divergence in reproductive tactics of same-sex competitors, particularly in males. Where alternative tactics are fixed for life, the causality of tactic choice is often unclear. In the African cichlid Lamprologus callipterus, large nest males collect and present empty snail shells to females that use these shells for egg deposition and brood care. Small dwarf males attempt to fertilize eggs by entering shells in which females are spawning. The bourgeois nest males exceed parasitic dwarf males in size by nearly two orders of magnitude, which is likely to result from greatly diverging growth patterns. Here, we ask whether growth patterns are heritable in this species, or whether and to which extent they are determined by environmental factors. Standardized breeding experiments using unrelated offspring and maternal half-sibs revealed highly divergent growth patterns of male young sired by nest or dwarf males, whereas the growth of female offspring of both male types did not differ. As expected, food had a significant modifying effect on growth, but neither the quantity of breeding substrate in the environment nor ambient temperature affected growth. None of the environmental factors tested influenced the choice of male life histories. We conclude that in L. callipterus growth rates of bourgeois and parasitic males are paternally inherited, and that male and female growth is phenotypically plastic to only a small degree.

Ejaculate adjustments to sperm competition can lead to sperm limitation. Particularly in polygynous species, males may face a trade-off between investing sperm in current or future mating opportunities. The optimal sperm allocation decision should depend on the relative intensity of sperm competition experienced in a mating sequence. Here we ask how males respond to this tradeoff in polygynous fish with alternative male mating tactics, intense sperm competition and sperm limitation. Large bourgeois males of the shell brooding cichlid Lamprologus callipterus build nests consisting of empty snail shells, in which females spawn and raise offspring. During spawning, nest males release ejaculates into the shell opening. Genetically distinct, parasitic dwarf males enter shells during spawning to fertilize the eggs from inside the shell. These dwarf males were previously shown to be superior sperm competitors to nest males. Here we show that when spawning with several females simultaneously, nest males reduce the spawning duration for each clutch and the number of ejaculations per female tends to decrease, reflecting sperm limitation. Experimental exposure of nest males to sperm competition with dwarf males caused a reduction of the number and duration of ejaculations roughly by half. Hence, when exposed to competition with a superior rival, nest males do not increase their sperm expenditure as predicted by sperm competition risk models, but in fact save sperm for future mating opportunities as predicted by sperm competition intensity theory. This seems to be adaptive because of the considerable sperm demands in this species, which is partly due to their high degree of polygyny.