Copulatory courtship, body temperature and infection in Tenebrio molitor.

Ectothermic animals can raise their body temperature under varying circumstances. Two such situations occur during sexual activity (as metabolic rate rises during copulatory movements) and during infection (to control pathogens more effectively). We have investigated these two situations using Tenebrio molitor males. We recorded the copulatory courtship behavior of sick (= infected with Metharizium robertsii fungus) vs healthy males and its link with body temperature. We predicted a positive relation between copulatory courtship (measured as antennal and leg contact behavior) and body temperature, especially in sick males. We found that the intensity of contacts correlated with increased body temperature in sick males. Previous studies in this species indicated that partner females laid fewer eggs after mating with sick males above a certain male body temperature threshold. Thus, our present findings suggest that females may detect male infection via intensity of antennal-mediated courtship, body temperature or their combination. If this is the case, females may assess male cues directly related to health status such as body temperature.

When is a male too hot? Fitness outcomes when mating with high temperature, sick males.

Infection may cause some insects to increase their body temperature to deal against pathogens successfully. However, one unclear aspect is whether females may use male temperature to discriminate sick from healthy partners. We tested this by using Tenebrio molitor beetles whose females use the intensity of male antennal and leg stroking that take place during mating, to discriminate among partners. We predicted that females will not choose males that are too hot and/or will penalize these male partners in terms of a reduced egg number and hatching success. We manipulated males by infecting them with an entomopathogenic fungus, and exposed these males versus control males to females. Infected and non-infected males increased their temperature during copulation but females did not choose on the basis of male's temperature or infection status. However, females laid fewer eggs and/or had a reduced hatching success after mating with infected males that had a body temperature higher than ca. 24 °C. We postulate that male temperature is another source of information involved in postcopulatory mate choice that, along with courtship traits, compose a multimodal signaling system.

Condition-dependent male copulatory courtship and its benefits for females.

Postcopulatory sexual selection has shaped the ornaments used during copulatory courtship. However, we know relatively little about whether these courtship ornaments are costly to produce or whether they provide indirect benefits to females. We used the mealworm beetle, Tenebrio molitor, to explore this. We challenged males using an entomopathogenic fungus and compared their courtship (frequency of leg and antennal contacts to the female), copulation duration, number of eggs laid, and hatching rate against control males. Infected males copulated for longer yet they reduced their leg and antennal contacts compared to control males. However, there was no obvious relation between infection, copulation duration, and courtship with egg production and hatching success. In general, our results indicate that the ornaments used during postcopulatory courtship are condition-dependent. Moreover, such condition dependence cannot be linked to male fitness.

Sex and burrowing behavior and their implications with lytic activity in the sand-dwelling spider Allocosa senex.

The immune response can be costly. Studies in several arthropod species have indicated a trade-off between immunity and other life-history traits, including reproduction. In sexually dimorphic species in which females and males largely differ in their life history strategies and related energetic demands, we can expect to find sex differences in immune functions. Sex differences in immunity are well documented in vertebrates; however, we largely lack data from invertebrate systems. Lytic activity, the immune system's ability to lysate bacteria and viruses, has been widely used as a proxy for the strength of the immune response in several invertebrates. With this in mind, we used the burrowing wolf spider Allocosa senex to test differences in lytic activity between females and males. We also studied whether digging behavior affects the immune responses in this species. While females of A. senex construct simple refuges where they stay during the day, males construct deep burrows, which they donate to females after copulation. In accordance with our hypothesis, females showed higher lytic activity compared with males, and those males who dug showed higher levels of lytic activity than those that did not dig. Furthermore, male body condition and lytic activity did not correlate with burrow length, a trait under female choice in this species. Our results show sexual dimorphism in lytic activity responses, which are likely related to differences in life-history strategies and energetic requirements of each sex in A. senex spiders.

Female secondary sexual traits in spiders: Adaptive interpretations of the sternum projection in the pholcid Holocnemus pluchei.

Sexually dimorphic traits are the outcome of a network of selective pressures acting upon each sex. While male secondary sexual traits are frequently restricted to intrasexual competition, female ornaments or weapons are mostly associated to social interactions for the access to limited resources. Here we investigate a sexually dimorphic trait expressed within the female's sternum of the spider species Holocnemus pluchei (Pholcidae), and its adaptive maintenance under the three leading hypotheses: sexual receptivity signaling, mate choice and sexual conflict hypothesis. We provide fine-scaled behavioral descriptions of the copulatory behavior of Holocnemus pluchei, corroborating that mating interactions are mediated by the female's sternum projection. The single moment of contact between the female projection and male body occurs during sperm transfer, always followed by a reduction on the intensity of the male genital movement. Additionally, biometrical properties of the female sternum projection corroborate our functional interpretation for the trait as restricting the intensity of males' copulatory movements. We claim that female sternum projection is a sexually selected trait mediating sexual conflict, with several adaptive consequences upon the sexes.