Host kairomone learning and foraging success in an egg parasitoid: a simulation model

Abstract 1. Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae) is an egg parasitoid that recognises chemical residues left by its host the green stink bug Nezara viridula (L.) (Heteroptera: Pentatomidae) as kairomone signals, enabling it to find egg masses in which to lay eggs. 2. Kairomones are usually present as patches deposited by N. viridula females, and recent results (Peri et al., Journal of Experimental Biology, 209 , 3629–3635, 2006) indicated that females of T. basalis are able to learn the features of their foraging environment and to adjust accordingly the amount of time spent on the patches of kairomones they are visiting, depending on whether or not host eggs are found. 3. In order to assess the impact of this learning ability, a Monte Carlo, spatially explicit and individual‐based simulation model was built to quantify the foraging efficiency of T. basalis females in environments with different levels of host abundance and distribution. In all cases, the present study compared the foraging efficiency of simulated T. basalis females having the ability to learn with those lacking this ability. 4. Learning females always visited a higher number of kairomone patches and attacked a higher number of hosts than non‐learning females, especially when there was a high density of kairomone patches in the environment. 5. Learning ability globally appears to allow the maintenance of efficient foraging success, especially when there is a low probability for the kairomone patches to contain discoverable hosts. 6. The increase in foraging efficiency for learning females appears to depend on the characteristics of the habitat in which they are foraging. Results thus suggest that significant variation in learning ability is likely to occur in natural wasp populations facing different environments with different host spatial distributions.     

Dancing to the rhythms of geological time: the biorhythm capabilities of Polychaeta in a geological context

Summary

Errant polychaete worms in the Orders Eunicida (family Eunicidae) and Phyllodocida (families Nereidae and Polynoidae) exhibit a highly developed biorhythmic capability. The Pacific palolo worms are well known for a precisely timed annual breeding event in which mass spawning occurs at a particular time of day, on one day per year, that day having a fixed relationship to the lunar period. Nereidae and Polynoidae exhibit photoperiodic responses that determine the breeding season by regulation of oocyte growth. Nereis virens shows short-term cycles of foraging activity; automated recording of these patterns has revealed four distinct behaviour rhythm phenotypes: circadian, tidal, lunidian and arrhythmic, the last phenotype being expressed during the photoperiod induced growth diapause. The Eunicids and Phyllodocids are represented in the fossil record by scolecodonts, their fossilised jaws. There was a major radiation of these polychaetes during the Ordovician and the earliest suggested polychaete fossils are from the Cambrian. The simultaneous expression of tidal and circadian rhythmicity is characteristic of intertidal animals and it is likely that this complex behavioural repertoire was found in the ancestors of modern terrestrial forms, such as tetrapods and arthropods, prior to their emergence onto land during the Carboniferous and Silurian periods at least 400 Ma. The period of the earth's rotation, and hence day length and tidal period, has long been known to be increasing, and additionally the moon to be retreating from the earth, due to the phenomenon of tidal friction caused by the gravitational interactions between the moon and the earth. These changes are significant over a geological time scale. Consequently, the length of day was substantially less (and the number of days in a year more) than at present in the Cambrian and Ordovician periods. Recent theoretical analysis of the period of the earth's rotation suggests that the day length prior to a critical period (t _crit ) around 1800 Ma may have been stable, with a length of only 4 h. At that time a period of more rapid change in the dynamics of the rotation was initiated. The implications of this theory for the evolution of the biological clock are discussed.