Sex, food and conflicts: nutrition dependent nuptial feeding and pre-mating struggles in scorpionflies

A general framework for modelling trade-offs in adaptive behaviour

An animal's behaviour can influence many variables, such as its energy reserves, its risk of injury or mortality, and its rate of reproduction. To identify the optimal action in a given situation, these various effects can be compared in the common currency of reproductive value. While this idea has been widely used to study trade-offs between pairs of variables, e.g. between energy gain versus survival, here we present a unified framework that makes explicit how these various trade-offs fit together. This unification covers a wide range of biological phenomena, highlighting similarities in their logical structure and helping to identify knowledge gaps. To fill one such gap, we present a new model of foraging under the risk of predation and damage accumulation. We conclude by discussing the use and limitations of state-dependent optimisation theory in predicting biological observations.

Does seed size mediate sex-specific reproduction costs in the Callosobruchus maculatus bean beetle?

There is a trade-off between reproductive effort and adult longevity, and when resource allocation is taken into account, it is especially pronounced in species that have aphagous adult forms. This trade-off may be further complicated by environmental factors such as nutrient availability during larval development and by the other sex, which influences the costs of reproduction due to the presentation of nuptial gifts. Here, we examined the influence of larval nutrient quantity on the sex-specific longevity costs of reproduction in the gift-giving seed beetle Callosobruchus maculatus. We found no indication that differences in the nutrient quality of larger and smaller host seeds influence survival in virgin and reproducing individuals or nuptial gift size in reproducing individuals. However, in the case of reproducing individuals, the effect of seed size on survival was statistically marginal. Therefore, we advise taking this into account when investigating reproductive efforts in this species. We have also observed interesting interactions between male and female reproductive costs. While females had generally higher mortality than males, nuptial gifts resulted in lowered female mortality and increased male mortality. Additionally, we found a possibly non-linear relationship between nuptial gift size and the offspring production rate of female recipients.

Copulatory mechanism and functional morphology of genitalia and anal horn of the scorpionfly Cerapanorpa dubia (Mecoptera: Panorpidae)

The scorpionfly genus Cerapanorpa is characterized by the male possessing a single finger-like anal horn on the posterior portion of tergite VI. However, the functional morphology of this anal horn and the genitalia have not been studied to date. Herein, we investigated the functional morphology of the genitalia and the nongenital structures of the scorpionfly Cerapanorpa dubia by observing the mating process and dissecting the freeze-fixated pairs in copula to reveal the copulatory mechanism. The male C. dubia provides a solid salivary mass to the female as a nuptial gift prior to copulation. When the female starts to feed on the gift, the male uses his notal organ and complex genital structures to control the closest wing and genitalia of the female to establish a V-shaped mating position. In the maintenance phase of copulation, the male uses his anal horn in cooperation with the basally-constricted abdominal segment VII to clamp female abdominal segment VIII. The male hypovalves grasp female cerci, and move up and down rhythmically. The paired parameres clasp both sides of female tergite IX. The basal processes on male gonostyli grip the pleural membranes of the female genital chamber. In the sperm transfer phase, the male aedeagus directly couples with the female medigynium to transmit sperm by connecting his phallotreme to the female's copulatory pore. The evolution of the male complex grasping structures in Panorpidae is also briefly discussed.

Mating behaviour and copulatory mechanism in the scorpionfly Neopanorpa longiprocessa (Mecoptera: Panorpidae)

Sexual conflict during copulation may drive morphological and behavioral evolution in insects. Although nuptial feeding behaviour is well studied in Panorpa, whether this behaviour is universal in Panorpidae remains unknown. The scorpionfly Neopanorpa longiprocessa Hua & Chou, 1997 was investigated for its mating behaviour, functional morphology of the notal organ, and external genitalia using light microscopy and scanning electron microscopy. The results show that the mating behaviour is not associated with nuptial feeding in N. longiprocessa. The morphological basis of this non-nuptial copulation is likely related to the developed notal organ of the male. The notal organ serves a function to seize wings of the female during copulation. Only males that succeed in seizing the female with the notal organ are able to establish genital contact and copulate. The male genitalia exhibit distinct species-specific modification. The epandrium (tergum IX) has evolved a pair of ventral bulbs to grasp the subgenital plate of the female. The hypandrium (sternum IX) has a pair of dorsal processes to control the abdominal end of the female. These results indicate that nuptial feeding is not a universal behaviour in Panorpidae. Presumably, these grasping apparatuses compensate the scorpionflies that fail to provide nuptial gifts, as exemplified by N. longiprocessa.