Male offering a nuptial gift (right) to the female (left) in Paratrechalea ornata

M.C. Trillo

Females from nuptial gift-giving species usually obtain direct benefits in the form of food gifts by mating multiple times. This adaptive foraging strategy allows them to gather important resources to improve their survival and the number and/or success of their offspring. In such mating systems, females prefer males offering nutritious gifts and, therefore, males invest in such gifts as these confer access to more partners during the reproductive period.

However, sometimes males are not able to provide the gifts that females prefer, for instance if they have limited food available or low body condition. In such situations, males may decide to maximize their success by reducing the nuptial gifts cost, even if this is against females’ interest. Such is the case in spider species in which males´ gift-giving behaviour evolved into offering non-nutritious items, also known as worthless gifts.

在紫红色蜘蛛中描述了毫无价值的礼物来欺骗Pisaura mirabilis,in which there is an occurrence of 38% in nature. As most of the gifts are nutritious, females follow the theoretical prediction and they mate with multiple males to increase their fecundity, especially when they are hungry. Indeed, females penalize males offering worthless gifts by reducing mating duration and the amount of sperm transferred, reducing the number of offspring produced with such males.

But, what happens in mating systems where male deception via worthless gifts is the rule? That is the unique case of the Neotropical gift-giving spiderParatrechalea ornata(Trechaleidae). This species is exceptional for studying sexual selection in relation to gift content, because 70% of nuptial gifts are worthless. In this species, females do not discriminate gift content before or during mating, and males offering worthless gifts are able to mate as successfully as males with nutritious gifts (similar frequencies of acceptances and similar mating durations).

We predicted that in this scenario of high frequency of worthless gifts there should be little or no influence of hunger state on female receptivity. Following this prediction, we set up a laboratory experiment where we exposed well and poorly fed females to multiple matings with males offering nutritious or worthless gifts. This resulted in three experimental groups: well-fed females exposed to males offering nutritious gifts, well-fed females exposed to males offering worthless gifts and poorly fed females which could feed only from nutritious gifts offered by males.

We found that all female groups had similar mating rates irrespective of feeding condition, and even poorly fed females did not significantly increase the number of matings with males offering nutritious gifts. Thus, as predicted, polyandry (i.e. a female mating with multiple males) doesn’t seem to be an adaptive foraging strategy in the Neotropical spider.

在该物种的进化时间内，交配行为如何改变，但一种可能性是，由于男性欺骗的发展，女性的接受性可能已经改变。因为十分之七的男性提供了毫无价值的礼物，所以女性避免交配作为觅食策略。我们建议女性的接受能力取决于在具有营养丰富的礼物的交配系统中的饥饿感，而不是大多数毫无价值的礼物的交配系统中。

送礼蜘蛛交配系统是研究与性选择相互作用的生态条件如何塑造个人生殖成功的好模型。我们知道，男性欺骗与猎物的可用性和男性身体状况有关，因此与环境变化有关。因此，我们目前正在开发比较研究，考虑到种类和人群之间的男性欺骗和生态变化不同。这将使我们可以推断出关于男性欺骗是否会影响女性接受和送礼物种交配率的更多一般观念。