Life-cycle associations involving pairs of holococcolithophorid species: intraspecific variation or cryptic speciation?

New holococcolith-heterococcolith life-cycle associations are documented based on observations of combination coccospheres. Daktylethra pirus is shown to be a life-cycle phase of Syracosphaera pulchra and Syracolithus quadriperforatus a life-cycle phase of Calcidiscus leptoporus. In addition, new observations from cultures confirm the life-cycle associations of Crystallolithus braarudii with Coccolithus pelagicus and of Zygosphaera hellenica with Coronosphaera mediterranea. In all four cases previous work has shown that the heterococcolithophorid species is associated with another holococcolithophorid. Two other examples of a heterococcolithophorid being associated with two holococcolithophorids have previously been identified, so this seems to be a common phenomenon. The six examples are reviewed to determine whether a single underlying mechanism is likely to be responsible for all cases. It is concluded that there is no single mechanism but rather that the six examples fall into three categories: (a) in two cases the holococcolith types are probably simply ecophenotypic morphotypes; (b) in two other cases the holococcolith types are discrete and are paralleled by morphometric differences in the heterococcolith types; (c) in the final two cases the holococcolith types are discrete but are not paralleled by any obvious morphological variation in the heterococcolith morphology. We infer that cryptic speciation may be widespread in heterococcolithophorid phases and that study of holococcolithophorid phases can provide key data to elucidate this phenomenon.     

Enzyme electrophoresis as an aid to distinguishing species of Fellodistomum,Steringotrema and Steringophorus (Digenea: Fellodistomidae)

Using isoelectric focusing the enzymes glucose phosphate isomerase, phosphoglucomutase, malate dehydrogenase and acid phosphatase were studied in four fellodistomine species Fellodistomum fellis, Steringotrema ovacutum, Steringophorus agnotus and Steringophorus furciger. Clear genetic separation has been demonstrated for these four species and, in the light of this result, some implications on the taxonomy of these species are discussed.     

New examples of holococcolith–heterococcolith combination coccospheres and their implications for coccolithophorid biology

Recently discovered coccospheres with combinations of coccoliths normally considered to belong to different taxa are presented here. By analogy with other coccolithophorids especially Coccolithus pelagicus we can hypothesize that these associations probably represent moments of phase change in a complex, possibly haplo-diplontic, life-cycle. Seven of these associations are composed of heterococcoliths with holococcoliths; five of them are presented here for the first time: Helicosphaera carteri with Syracolithus catilliferus, Syracosphaera pulchra with Calyptrosphaera oblonga, Syracosphaera anthos with Periphyllophora mirabilis, Acanthoica quattrospina with holococcolithophorid sp. and Syracosphaera sp. with Corisphaera sp. type A (see Kleijne, A., 1991. Holococcolithophorids from the Indian Ocean, Red Sea, Mediterranean Sea and North Atlantic Ocean. Mar. Micropaleontol. 17, 1–76); the other two are Coronosphaera mediterranea with Calyptrolithina wettsteinii, found previously by Kamptner (Kamptner, E., 1941. Die Coccolithineen der Südwestküste von Istrien. Naturhistorischen Museum in Wien. Annalen 51, 54–149), and Syracosphaera nana with undescribed holococcoliths, figured previously by Kleijne (1991) as Syracosphaera sp. type A. In addition the association of Neosphaera coccolithomorpha and Ceratolithus cristatus, recently presented by Alcober and Jordan (Alcober, J., Jordan, R.W., 1997. An interesting association between Neosphaera coccolithomorpha and Ceratolithus cristatus (Haptophyta). Eur. J. Phycol. 32, 91–93) is verified by discovery of a further example. A further five combinations of heterococcoliths and holococcoliths are shown, these probably mostly represent life-cycle combinations but the evidence in each case is insufficient to consider these as definite associations although in these collapsed coccospheres the association of different species is less certain. Two examples of holococcolith–holococcolith associations are presented: S. catilliferus with Syracolithus confusus, and Zygosphaera bannockii with Corisphaera sp. type A. These are probably examples of intra-specific variation.A new species, Syracosphaera delicata sp. nov., is described.     

First direct documentation of associations of Ceratolithus cristatus ceratoliths, hoop-coccoliths and Neosphaera coccolithomorpha planoliths

Study of plankton sample from the northeast Atlantic has revealed an exceptional specimen of Ceratolithus cristatus. This consists of a rostratus-type ceratolith surrounded by a collapsed coccosphere of delicate hoop-coccoliths and a partial outer collapsed coccosphere of nishidae-type planoliths. This provides the final direct evidence needed to support the earlier hypothesis that these three calcareous structures are all provided by the single species Ceratolithus cristatus. It appears likely that this species has a complex life-cycle.     

The phenology of Ophrys sphegodes (the early spider orchid): what annual censuses can miss

Ophrys sphegodes is a rare species in the United Kingdom. The largest extant population of the species, at Castle Hill National Nature Reserve in Sussex, has been monitored each year since 1975. At each annual census, which is conducted during the peak period of flowering (May), the co-ordinates of each plant are recorded, allowing the fate of individuals to be followed from one census to the next. In the present study the population was monitored throughout one complete year. The data collected allow the phenology of the species to be described and the effectiveness of the annual census to be assessed. The study shows that a substantial number of Ophrys sphegodes plants emerge above ground and re-enter the below ground phase before the census date. These results suggest that reliance on annual census records alone may result in the size of the population being underestimated and incorrect life-histories being ascribed to individual plants. True counts of the population may be obtained only if 'dormant' plants are retrospectively added to the population.     

Population biology of the rare military orchid (Orchis militaris L.) at an established site in Suffolk, England

In Britain, where it reaches the north-westerly limit of its European distribution, Orchis militaris L. is extremely rare. Well-established and persistent populations of O. militaris are known to exist at only two sites. The largest extant population of O. militaris occurs in a disused chalk pit in Suffolk. A preliminary demographic analysis of this population, covering the period 1975 to 1991, along with estimates of key life stage transition probabilities are presented here. From 1975 to 1986 the number of separate identifiable plants in the population declined substantially. Until 1986 recruitment of rosettes was poor. The largest cohort of new plants, recorded in 1976, was 35. Approximately 48% of new individuals recruited between 1976 and 1985 failed to flower. Of those flowering, approximately 55% flowered during their first year above ground. Of the original population recorded in 1975, 67.8% flowered at least once during the study. The reproductive performance, i.e. the frequency of flowering and the period between episodes of flowering, varied considerably between individuals. Some plants flowered every year while others only flowered once during the study. Few plants remained below ground for more than one year, while several apparently persisted below ground for more than 6 successive years. Although the number of plants that can be identified as separate individuals has declined, the total number of rosettes in the population has, from 1986, increased dramatically. Because of the dense clumping of these recruits it is not possible to determine whether they are derived from seed or vegetative propagation. When post 1986 recruitment is combined with the number of plants that established before 1986 and survive, the apparent number of plants present at the site has more than doubled between 1975 and1991.     

Further evidence for the heterococcolith–holococcolith combination Calcidiscus leptoporus–Crystallolithus rigidus

New findings of combination coccospheres bearing heterococcoliths of Calcidiscus leptoporus and holococcoliths of Crystallolithus rigidus are documented. These findings confirm previous suggestions that these two “species” are separate phases of the life-cycle of a single species.     

Sexual reproduction: nuclear cycles and life-histories with particular reference to lower eukaryotes

Sexual reproduction is defined as the union of two haploid nuclei each derived from one of two different meioses. The implications of this definition for the interpretation of sexuality in coenocytes and homothallic haploids is discussed. The separation of the concept of the nuclear cycle from that of the life-history is advocated, and a new terminology for the nuclear cycle is proposed. The distinction between the terms life-cycle and life-history is reiterated.