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.     

OSTRACODS AS MARKERS OF THE PERMIAN/TRIASSIC BOUNDARY IN THE KHUFF FORMATION OF SAUDI ARABIA

Abstract:  Ostracods are described for the first time from Permian–Triassic shallow marine sediments of the Khuff Formation of central Saudi Arabia. They were collected using a modified acetolysis technique for releasing calcareous shells from limestones that is described herein. Thirty-four species belonging to 17 genera are recognized. Two new species are described: Arqoviella arabica sp. nov. and A. khartamensis sp. nov. The ostracod fauna supports a Late Permian age for the lower Khartam Member and a probable Early Triassic age for the upper Khartam Member of the Khuff Formation of central Saudi Arabia. This suggests that the Permian/Triassic boundary is located within the Khartam Member, rather than at the major lithological break between the Midhnab and Khartam members. Palaeoecological analysis suggests that the palaeoenvironment of the Khuff Formation was shallow marine (between 1 and 50 m deep) on an internal shelf.     

Somatic and Oral Cortical Ultrastructure of the Plagiopylid Ciliates Lechriopyla mystax Lynch, 1930 and Plagiopyla minuta Powers, 19331

The somatic and oral cortical ultrastructure of the plagiopylid ciliates Lechriopyla mystax Lynch, 1930 and Plagiopyla minuta Powers, 1933 are described. The somatic kinetids are monokinetids with an anteriorly directed kinetodesmal fibril originating near triplets 5, 6, 7, a divergent postciliary ribbon originating at triplet 9, and an unusual transverse ribbon originating in dense material adjacent to triplets 1, 2, 3. The transverse ribbon extends beneath the right surface of the cortical ridge adjacent to the kinety from which it originated. The oral kinetids are also monokinetids from whose base rootlet fibrils extend inwards beneath the oral kineties and converge on the furcula. The striated band on these ciliates is composed of a series of short ridges orthogonal to the longitudinal axis of the band. The sides of the striated band groove are apparently supported by macrotubules. The cortical ultrastructure of the plagiopylids is discussed with reference both to the optical microscopy of the organisms and to the ultrastructure of other ciliate taxa. The plagiopylids are not clearly related to any other higher taxon and are placed incertae sedis in the Subphylum Cyrtophora Small, 1976.     

All-female broods and mimetic polymorphism in Acraea encedon (L.) (Lepidoptera: Acraeidae) in Tanzania

In some populations of the African butterfly, Acraea encedon, there are two kinds of females, one producing offspring in a normal 1:1 sex ratio, the other producing females only; in other populations the sex ratio is apparently normal. All-female broods had hitherto been mainly associated with populations in which field sampling revealed an excess of females. The all-female brood trait is described from a population at Dar es Salaam which field sampling suggested was normal, and this indicates that the trait may be much more widespread and common than had previously been supposed. This discovery also extends the known distribution of the trait across Africa from Sierra Leone to eastern Tanzania. The butterfly is also a polymorphic Müllerian mimic of Danaus chrysippus, which is a highly unusual phenomenon as Müllerian mimicry is almost invariably monomorphic. The relative frequencies of two corresponding colour forms of the two species of butterflies at Dar es Salaam adds support to the hypothesis that they are indeed Mullerian mimics. The results of breeding experiments suggest that the polymorphic forms in Acraea encedon are allelic with dominance.     

Reproductive allocation in multinest colonies of the ponerine ant Pachycondyla goeldii

Abstract.  1.  Pachycondyla goeldii constitutes the only recorded case of a monogynous (i.e. one queen per colony) polydomous (i.e. several nests per colony) species in the Ponerinae subfamily. This study examines the impact of polydomy on reproductive allocation between nests (also called 'calies' in polydomous society) in Pachycondyla goeldii Forel, by: (i) recording the number of workers and sexuals in 67 nests belonging to 21 colonies; (ii) dissection of workers in nine nests containing a queen (QR nests), nine nests without a queen but associated to a QR nest (QL nests) and five nests belonging to colonies that permanently lost the queen (OR nests); and (iii) measuring the length of all eggs present in the nests (our laboratory study shows that queen-laid eggs were significantly longer than worker-laid eggs).
2. The number of workers was significantly higher in QR nests than in QL nests, while the number of virgin queens was significantly higher in QL nests compared with QR nests.
3. Worker ovarian activity is inversely related to queen proximity: highest in OR nests, intermediate in QL nests, and lowest in QR nests.
4. Egg length was highest in QR nests, where the queen was most likely the primary egg-layer, intermediate in QL nests, where eggs could have originated from both the queen and workers, and lowest in OR nests, where workers were the sole egg-layers.
5. We postulate that the proximal mechanism explaining differences between QR and QL nests is the pheromonal absence of the queen from QL nests and that the evolutionary reasons of these divergences between nest types are likely to originate from the different conflicts occurring in ant colonies.     

Impact of intraguild predation on parasitoid foraging behaviour

1. Trophic interactions between predators and parasitoids can be described as intraguild predation (IGP) and are often asymmetric. Parasitoids (typically the IG prey) may respond to the threat of IGP by mitigating the predation risk for their offspring. 2. We used a system with a facultative predator Macrolophus caliginosus, the parasitoid Aphidius colemani, and their shared prey, the aphid Myzus persicae. We examined the functional responses of the parasitoid in the presence/absence of the predator on two host plants (aubergine and sweet pepper) with differing IGP risk. 3. Estimated model parameters such as parasitoid handling time increased on both plants where the predator was present, but impact of the predator varied with plant species. The predator, which could feed herbivorously on aubergine, had a reduced impact on parasitoid foraging on that plant. IG predator presence could reduce the searching effort of the IG prey depending on the plant, and on likely predation risk. 4. The results are discussed with regard to individual parasitoid's foraging behaviour and population stability; it is suggested that the presence of the predator can contribute to the stabilisation of host–parasitoid dynamics     

Reconsidering the taxomony of several Ostrinia species in the light of reproductive isolation: a tale for Ernst Mayr

We reconsider the taxonomy of a group of closely related Ostrinia spp., illustrating how useful Mayr's biological species concept remains for studying speciation patterns and processes. We review and re-analyse recent data on Ostrinia scapulalis , Ostrinia nubilalis , Ostrinia narynensis and Ostrinia orientalis , along with those obtained over > 45 years in the former Soviet Union. The ten species of the 'trilobed uncus' group in the Ostrinia genus are classified into subgroups according to male mid-tibia morphology. However, none of the characters that further discriminate between them (female sex pheromones, male genitalia and calling time) varies together with male mid-tibia morphology, and neither do molecular markers. Moreover, male mid-tibia morphology appears to depend on only two diallelic loci and seems to be unrelated to reproductive isolation between Ostrinia taxa. By contrast, reproductive isolation is strongly related to host-plant type. In accordance with Mayr's species concept, we thus propose a revision of the trilobed uncus Ostrinia spp. based primarily on host-plant type. We propose that O. narynensis Mutuura & Munroe, 1970 ( syn. nov. ) and O. orientalis Mutuura & Munroe, 1970 ( syn. nov. ) be synonymized with O. scapulalis (Walker, 1859). We further demonstrate that O. nubilalis auctt. pro parte feeding on mugwort, hop, and several other dicotyledons (previously called the ' O. nubilalis mugwort-race' in France) also belongs to O. scapulalis . Consequently, we propose that only O. nubilalis specimens feeding on maize (the former French ' O. nubilalis maize-race') belong to O. nubilalis (Hübner, 1796). The implications of this revision are discussed.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 49–72.