Nuptial Gifts: Is the Life Cycle Worth Your Life?

Nuptial Gifts: Is the Life Cycle Worth Your Life?

In the case of many insects, a nuptial gift is essential to initiate reproduction among the male and female and to also sustain the offspring after the fact. Among some types of insects, the larger, cannibalistic female often will consume the male after the reproductive process in order to use his body as the nuptial gift in an effort to nourish the offspring. In regards to the nuptial gift, the question remains whether or not it is used to prevent the female from cannibalizing the male, if it is used to entice the female as a method of courtship, or if it is solely for the purpose of increasing the fitness of the male’s offspring. There is empirical evidence to support the fitness hypothesis and courtship hypothesis but very little empirical evidence has been generated for the prevention of cannibalism hypothesis. However, the sexual cannibalism tendency is prominent among several species of spiders including Pisaura mirabilis. It has been observed that over time many features of both the courtship and post-intercourse behavior of P. mirabilis has evolved over time to reduce the risk of sexual cannibalism, thus providing some support of the prevention of cannibalism hypothesis. A study conducted in 2008 by Bilde, Gonzales, Hansen, and Toft studied these modifications to reproductive behavior of Pisaura mirabilis which includes the practice of thanatosis, or death feigning. It is during this practice that when a female Pisaura mirabilis becomes aggressive during the mating process, the male will fake death to avoid being cannibalized. After the female loses interest in killing the male, the two resume the mating process. In addition, thanatosis may continue multiple times throughout the mating process (Bilde, Gonzales, Hansen, Toft, 2008).

www.commanster.eu/commanster/Invertebrates/Spiders/WSpiders/Pisaura.mirabilis.html

In a study conducted in 2001 by Pia Stålhandske, researchers were curious to know if males Pisaura mirabilis without a nuptial gift were more likely to be cannibalized than males with a nuptial gift and if the presence and size of the nuptial gift actually increased the females’ reproductive success. In order to answer these questions, a total of 40 male spiders were observed in their mating process in which 10 had no gift, 10 were given a small gift to present to the female, 10 were given a medium sized gift to present, and 10 were given a large gift. It was observed that the size of the gift related to the time spent during the mating process but not necessarily with the fecundity of the female or the number of offspring. Interestingly, only 5 out of 40 trials resulted in cannibalism. These results were not exclusively collected from trials where no nuptial gift was given. To explain both unexpected observations, the researchers concluded that the lab conditions were not actually able to simulate a natural mating experience thus inhibiting normal mating behavior of the spiders. For instance, the fact that a distinct size dimorphism was not controlled for in this experiment affected whether or not the female could capture the male and ingest him. Also, the experiment did not control for the fact that larger females are much more likely to produce offspring in abundance than smaller females (Stålhandske, 2001).

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In conclusion, the reasons behind certain mating practices are unclear and difficult to simulate under observable lab conditions. However, whether or not nuptial gifts are an effort to increase the fitness of the offspring, an act of courtship, or to prevent predation of the male, all hypotheses seem to be viable in some instances and the hypotheses do not have to be mutually exclusive. Thus, each hypothesis could be considered one tier of this of this multi-faceted tri-hypothesis seeing that each is true to some degree and the motives and logic behind an insect’s behavior is practically immeasurable.

Stålhandske Pia, 2001, Nuptial gift in the spider Pisaura mirabilis maintained by sexual selection

Hansen, L. Gonzales, S. Toft, S. Bilde, T. 2008. Thanatosis as an adaptive male mating strategy in the nuptial gift–giving spider Pisaura mirabilis