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.

Larval density in the invasive Drosophila suzukii: Immediate and delayed effects on life-history traits.

The effects of density are key in determining population dynamics, since they can positively or negatively affect the fitness of individuals. These effects have great relevance for polyphagous insects for which immature stages develop within a single site of finite feeding resources. Drosophila suzukii is a crop pest that induces severe economic losses for agricultural production; however, little is known about the effects of density on its life-history traits. In the present study, we (i) investigated the egg distribution resulting from females' egg-laying strategy and (ii) tested the immediate (on immatures) and delayed (on adults) effects of larval density on emergence rate, development time, potential fecundity, and adult size. The density used varied in a range between 1 and 50 larvae. We showed that 44.27% of the blueberries used for the oviposition assay contained between 1 and 11 eggs in aggregates. The high experimental density (50 larvae) has no immediate effect in the emergence rate but has effect on larval developmental time. This trait was involved in a trade-off with adult life-history traits: The time of larval development was reduced as larval density increased, but smaller and less fertile females were produced. Our results clearly highlight the consequences of larval crowding on the juveniles and adults of this fly.

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.

Dietary macronutrient balance and fungal infection as drivers of spermatophore quality in the mealworm beetle.

Males of many insects deliver ejaculates with nutritious substances to females in the form of a spermatophore. Different factors can affect spermatophore quality. We manipulated males' diet and health to determine the balance of macronutrients deposited in the spermatophores of Tenebrio molitor beetles. For diet, we varied the concentration of proteins and carbohydrates, while for health status we used a fungal infection. Males with different condition copulated with unmanipulated females, and spermatophores were extracted to measure the amount of proteins, lipids and carbohydrates. Diet and infection had an effect on the quality of the spermatophore. Diets with high protein and low carbohydrate contents produced spermatophores with higher protein, carbohydrate, and lipid contents. In contrast, diets with little protein and high in carbohydrates led to low quality spermatophores. Infected males produced spermatophores with the highest amount of all three macronutrients. In general, spermatophore content was carbohydrates>proteins>=lipids. The fact that sick males produced richer spermatophores can be explained as a terminal investment strategy. The large investment of carbohydrates may be related to the preparation of spermatozoa in males, and eggs in females.

Mutual mate choice and its benefits for both sexes.

In mating interactions, it is common in nature for both sexes to choose simultaneously. However, this mutual mate choice and its consequences for progeny has received relatively little study; an approach where both male and female condition is manipulated is thus desirable. We compared both sexes' preferences in Tenebrio molitor beetles when individual condition varied (healthy vs infected with a fungus), and observed the direct benefits of those preferences. We predicted that: (a) females and males in good condition would prefer high quality mates; (b) preferences would be weaker when the choosing individual is in poor condition (and thus less selective given, for example, time and energetic constrains); and, (c) high quality mates would lay a larger number of total eggs and/or viable eggs than low quality mates. We found that both males and females in good condition were not more likely to choose mates that were also in good condition. However, poor-condition animals were more likely to prefer similar quality animals, while high-condition animals did not necessarily prefer mates of similar condition. Choosing sick males or females had a negative impact on egg number and viability. Our results suggest a non-adaptive mate choice in this species. Possibly, a deteriorated condition may drive individuals to invest more in attracting mates, because their chances of surviving the infection are very low. However, we do not discount the possibility that the fungus is manipulating individuals to increase its transmission during mating.