'Many animal species,' he explains, 'must simultaneously choose between foraging and opportunities to reproduce,' and a sensible animal needs a proper strategy. 'For an animal to maximise its fitness, it can neither exclusively feed nor exclusively pursue opportunities to reproduce. Some compromise between these activities must exist.' This may explain why humans tend to go to dinner on dates.
For the guppy, the decision can be crucial: 'An energetically stressed male guppy may substantially increase its risk of starvation if it attempts to court a female.'
So the researcher put groups of male guppies into a tank with a female at one end and some food (onion fly eggs) at the other to see which way they swam. The females had been isolated from male company for four weeks and were presented to the males in glass jars covered by fine wire mesh, 'providing both visual and chemical contact between the males and the female'.
The result of the experiments was unequivocal: 'Male guppies always fed prior to courting the female.' And it wasn't just a question of waiting for their mating urges to assert themselves, because dropping food into the tank more slowly caused the guppies to spend longer feeding.
They did not even reduce their feeding time when offered larger females, though as usual the bigger female guppies were courted by more males post-prandially. Only the biggest females of all did not conform to this pattern, but received the same courtship as wild women guppies one- eighth of their size.
Females, incidentally, are generally bigger than males, and the largest females produce the most offspring. Anyone interested in this aspect of guppydom should consult F J Hester's 1964 paper 'Effects of food supply on fecundity in the female guppy, Lobistes reticulatus (Peters)' J Fish Res Bd Can vol 21, pp 757-764.
The more recent paper concludes that 'male guppies make state-dependent decisions, choosing first to ensure they have sufficient energy reserves before investing time and energy in courtship'. It also points out that guppies are highly promiscuous, that males do not provide parental care and that 'very large females within a population may be senile'.Reuse content