7.2 The real deal?: behavioral mimicry in hymenoptera  (Page 5/7)

Box

Female mimicry as post-copulatory mate-guarding behavior

In the polygynous parasitic wasp species, Cotesia rubecula , several males compete for a single female. One of the three competitive mating tactics employed by these males is to distract the rival male using female mimicry, lure the rival into a false mating situation, and then to court the actual female (Field&Keller 1993). Although most females mate only once, there is a brief post-copulatory period during which females have been shown to respond to courting advances by males. In 64 out of 84 laboratory observations of mating behavior, the first-mating male employed a post-copulatory female-mimicking behavior to distract 55 of 64 rival males. Panel (a) shows a female (left) accepting the male’s (right) courtship, with the characteristic lowering of the antennae. Panel (b) shows the male and female copulating. As shown below in the bottom left panel (c), most rival males approach a mating pair in copula , and the copulating male immediately lowers his antennae and begins to mimic a female in an attempt to confuse the rival male (right). Following copulation and separation, as shown in panel (d), the female (left) moves away and the rival male (right) attempts to mate with the female mimic (center). This attempt at mating continues unsuccessfully for a short period of time, after which the female mimic leaves, having successfully warded off the rival male from copulating with his female. This suggests that female mimicry is a mate-guarding mechanism (Field&Keller 1993).

Interspecific mimicry

All of the examples discussed in the previous section dealt with intraspecific female mimicry and how it affected the organisms’ reproductive success. This section will discuss a unique case of interspecific mimicry that requires cross-gender interactions to achieve social parasitism.

In the cleptoparasitic cuckoo bee genus, Nomada , females gain entry into the host nests of Andrena bees, where they lay their eggs so that their larvae can eat and survive based off of the pollen stores in Andrena nests (Dettner&Liepert 1994, Ayasse et al. 2001). This is necessary because Nomada cuckoo bees lack pollen baskets, or scopa , on their hind legs, and therefore are unable to gather their own pollen. This cleptoparasitic behavior is accomplished in Nomada bees through chemical mimicry of Andrena nest odors secreted from female Dufour’s glands. The Nomada females do not produce these Andrena odors on their own. However, Nomada males produce the compounds in their mandibular glands, and during mating, spray them onto the Nomada females. This is a very unique circumstance, in that the chemical mimicry occurs in one sex of the parasitic species, but the actual cleptoparasitic behavior is performed by the other sex, and is entirely dependent on a behavioral interaction between the two sexes. The compounds that allow for Nomada females to enter Andrena nests undetected are specific to pairs of hosts and parasites. For example, the compound trans -farnesyl hexanoate is released from the Dufour’s gland of the hosts Andrena haemorrhoa and Andrea caratonica , and is also chemically mimicked by Nomada males specific to these hosts. Likewise, geranyl octanoate is released by Andrena helvola and Andrena clarkell a and is specifically mimicked by other Nomada males (Dettner&Liepert 1994, Ayasse et al. 2001).