Raw Data Pavón-Peláez et al Beh Eco Soc 2021

In the spider Paratrechalea ornata, males offer either a nutritive (prey) or a worthless (prey leftovers) wrapped gift to females. Both gift types confer similar mating success and duration, and afford males a higher success rate than when they offer no gift. The nature of the gift is potentially dependent on prey availability, but it may also arise through intrinsic individual differences (male’s hunting ability). We allocated males (n = 36) to one of two groups. In the “Worthless” group, no prey items were available, while in the “Nutritive-Worthless” group, males had access to a live housefly and could produce a nutritive prey gift. In both groups, males could also produce either no gift or a worthless gift from a mealworm exuviae. We let males’ court individual females over five consecutive trials and examined the differences by using an analysis of repeatability. We found that males were plastic in their decision making, presenting the female either a nutritive or a worthless gift in the Nutritive-Worthless group. But, they were more likely to present a worthless gift in the Worthless group and when they were large. However, rather than worthless gift-giving being a cheap tactic, males highly invest in silk when producing such gifts. Our data suggest males can adjust their behaviour differentially investing in the gift content or in the silk wrapping according to prey availability and their own size. This content quality – silk-wrapping trade-off is probably determining the final fitness success of these mating tactics in P. ornata.

在饰饰长颈蛛（Paratrechalea ornata）中，雄性会向雌性赠送两种包裹好的礼物：一种为营养性礼物（即完整猎物），另一种为无价值礼物（即猎物残渣）。两类礼物均可使雄性获得相近的交配成功率与交配时长，且均比不赠送礼物的雄性拥有更高的交配成功率。礼物的性质可能取决于猎物可获得性，也可能源于雄性个体的内在差异（如狩猎能力）。
我们将36只雄性个体随机分为两组。“无价值礼物组”无任何猎物可用；而“营养-无价值礼物组”的雄性可获取活家蝇，从而制作营养性猎物礼物。两组雄性均可选择不赠送礼物，或利用黄粉虫蜕制作无价值礼物。
我们让雄性在连续5次试验中向单独的雌性求偶，并通过重复性分析检验各组间的行为差异。
研究发现，雄性的决策具有可塑性：在营养-无价值礼物组中，雄性可向雌性赠送营养性或无价值礼物；但在无价值礼物组中，以及体型较大的雄性，更倾向于赠送无价值礼物。
然而，赠送无价值礼物并非低成本策略：雄性在制作此类礼物时，会投入大量蛛丝。我们的数据表明，雄性可根据猎物可获得性与自身体型，差异化调整礼物内容或蛛丝包裹的投入。
这种礼物质量与蛛丝包裹的权衡，或许决定了饰饰长颈蛛这些交配策略的最终适合度收益。