Spiders with bizarre gift-giving male head structures: morphology, biochemistry and sexual selection

在许多物种中，雄性拥有与交配有关但与精子转移无关的特征，即似乎具有夹紧装置或刺激装置功能的特征。有三种主要的假说可以解释这种第二性征：1.它们可能是物种之间的隔离机制；2.由于雌性选择而进化的性选择；3.由于性别冲突。眼蛛亚科的蜘蛛是检验这些假说的理想生物，因为许多物种的雄性蜘蛛都有奇怪的头部结构，这些结构在交配过程中发挥作用，并与分泌腺相关。到目前为止所能获得的少数观察结果表明，雌性金龟子将爪子伸入雄性头部结构，并摄取相关腺体产生的分泌物。如果这些奇怪的头部结构起到隔离机制的作用，种间配对应该是不可能的，与头部结构的接触应该是成功交配的先决条件。如果这些结构及其相关的腺体是由于雌性的选择而在性选择下进化的，那么头部结构更明显的雄性或能够产生更多分泌物的雄性可能对雌性更具吸引力，如果它们为自己或后代获得物质或遗传利益。头部结构也可能是在两性对交配和受精的控制发生冲突的情况下进化的。雄性分泌物可以用来操纵雌性，因为它阻止了与更多的雄性发生关系，尽管雌性一生的繁殖力或寿命都要付出代价。我对可能的功能进行了研究，涉及到三种可能的矮小蜘蛛：Dplocephatus perMixtus，Oedothorax retusus和Oedothorax gibBosus。我们目前正在通过操纵分泌物转移到雌性体内来研究分泌物的功能，并计划操纵分泌物的数量。这项研究结合了行为、形态、组织化学和生化方法，将有助于理解这些奇怪的男性次要特征的功能。

In many species males possess traits that are involved in mating but not in sperm transfer, i.e. traits that seem to function as clasper devices or stimulatory devices. There are three main hypotheses to explain such secondary sexual traits: 1. they may function as isolating mechanisms between species or 2. have evolved under sexual selection due to female choice or 3. due to sexual conflict. Spiders of the linyphiid subfamily Erigoninae are ideal organisms to test these hypotheses as males of many species possess bizarre head structures that play a role in the mating process and are associated with secretory glands. The few observations available todate suggest that the females sink their claws (chelcicerae) into the male head structures and ingest secretion produced by the associated glands. If these bizarre head structures function as isolating mechanisms, interspecific matings should be impossible and contact with the head structures should be a prerequisite for successful copulation. If the structures and their associated glands have evolved under sexual selection due to female choice, males with more pronounced head structures or males that are able to produce more secretion may be more attractive for females if they gain material or genetic benefits for themselves or for their offspring. The head structures may also have evolved under conflict between the sexes over control of mating and fertilization. Male secretion may serve to manipulate females in that it prevents remating with additional males despite costs for female lifetime fecundity or longevity. My investigations of the possible functions involve three focal species of dwarf spiders, Diplocephatus permixtus, Oedothorax retusus and Oedothorax gibbosus. We are currently investigating the function of the secretion by manipulating its transfer to the female and plan also to manipulate its amount. The study entails a combination of behavioural, morphological, histochemical and biochemical approaches and will help to understand the function of these bizarre male secondary traits.