A narrow hybrid zone between two crayfish species from a Mexican cave

In Northern Chiapas (Mexico), two newly discovered species of Procambarus crayfish inhabit a subterranean stream. These species can be morphologically distinguished only by comparing extreme phenotypes (dark, thick-eyed, surface dwelling-like individuals vs light, elongated, microphtalmic, cave dwelling-like individuals). Individuals with intermediate phenotypes co-occur with those exhibiting extreme phenotypes. Crayfish were assayed electrophoretically and individual patterns at 23 gene loci were obtained. Unusually high levels of heterozygosity in both species and a clear discrimination between the two gene pools were revealed. The relationships between individuals were investigated by means of multivariate analysis on individual multilocus genotype profiles. Results showed the occurrence of individuals genetically intermediate between the two major clusters, which shared allozymic variants with both species. Due to the occurrence of alternative alleles in the two gene pools, we could quantify patterns of introgression, which revealed asymmetric gene flow between the two species. Moreover, differential levels of introgression in subsamples within the surface-like species were found: most introgressed individuals came from the inner section of the cave, where the two species were greatly mixed. These results are also discussed in reference to the morphometric results from a companion paper. A possible evolutionary pathway, leading to the situation in this cave, and possibly in neighbouring cave systems, is outlined. The hypothesis of a past history of allopatric divergence from a common ancestor and a subsequent secondary contact between these two Procambarus species is supported by geological studies. Crayfish sympatry and competitive exclusion are also discussed.     

Protein variation in wild Atlantic salmon, with particular reference to southern Ireland

The extent of genetic variation in wild Atlantic salmon parr, Sulmo salur L., from river systems in Ireland, Iceland and eastern Canada, was investigated using starch gel electrophoresis. Within Ireland, seven polymorphic enzyme loci ( sAAT-4 *, GPI-1 *, IDDH-1 *, IDDH-2 *, IDHP-3 *, MDH-3 * and mMEP-2 *) were screened in nine different rivers and nine tributaries from the River Blackwater. Significant heterogeneity in gene frequencies occurred between riverine samples and between samples from tributaries of the River Blackwater. Variation between tributaries was as great as between rivers elsewhere in the country. Levels of population differentiation were comparable to those found in other regions throughout the range of the species, and temporal stability in gene frequencies was apparent when the results were compared with previously published data. Screening of riverine samples from Iceland and eastern Canada (Newfoundland and New Brunswick) allowed the Irish results to be considered in a broader context. Irish salmon cluster in the western European group, to which may be added Icelandic populations. Salmon from eastern Canada show a high level of genetic distinctiveness from the European group.     

Characterizing bisexual Artemia populations by isoelectric focusing

Isoelectric focusing (IEF) of protein extracts, -Esterase and Phosphoglucose isomerase, from groups of Artemia adults from different bisexual populations were studied. Both gave clear separation between the Old and New World species. The second was more polymorphic, allowing a discrimination among Mediterranean populations.     

The effects of re-use of polyethylene glycol priming osmotica upon the development of microbial populations and germination of leeks and carrots

Three batches of leek seeds were osmotically primed successively in the same polyethylene glycol solution in a bubble column at a seed concentration of 100 g/litre for seven days at 15°C. Three batches of carrot seeds were similarly primed in a separate solution for six days at 15°C. The concentration of microorganisms in the solutions increased rapidly during priming of the first seed batch for both seed types, but increases during priming of the second and third batches were small. The seeds were the main source of the microorganisms; priming reduced the numbers of colonies of filamentous fungi and increased those of bacteria and yeasts. The priming treatments improved the percentage germination of the three seed batches of primed carrots and reduced the mean time to germination in both species and the mean time to emergence in compost. Percentage emergence was not affected by priming except in the third batch of primed carrot seed. The presence of large numbers of microorganisms in the priming solutions did not greatly affect seed performance when the same osmoticum was used three times with leeks and twice with carrots. Priming did not affect the number of abnormal seedlings.     

The extinction of slowly evolving dynamical systems

The time evolution of slowly evolving discrete dynamical systems x _{i + 1} = T(r _i ,x _i ), defined on an interval [0, L], where a parameter r _ichanges slowly with respect to i is considered. For certain transformations T, once r _i reaches a critical value the system faces a non-zero probability of extinction because some x _j [0, L]. Recent ergodic theory results of Ruelle, Pianigiani, and Lasota and Yorke are used to derive a simple expression for the probability of survival of these systems. The extinction process is illustrated with two examples. One is the quadratic map, T(r, x) = rx(1 – x), and the second is a simple model for the growth of a cellular population. The survival statistics for chronic myelogenous leukemia patients are discussed in light of these extinction processes. Two other dynamical processes of biological importance, to which our results are applicable, are mentioned.     

The reproductive cycle in the population of Saccostrea cuccullatta (Born) from the coast of Karachi,Pakistan

Periphytic diatom communities on clay tile and sterilized rock substrates were compared with those on natural substrates. Clay tiles yielded diatom communities with the least variability between replicate samples, and the greatest similarity to the natural substrate assemblage. The advantages of utilizing introduced substrate communities and problems encountered with their simulation of the natural substrate community are discussed.     

Etude de la dynamique des populations de cilies d'un torrent experimental pendant deux annees

The sampling of Ciliates performed in a little experimental torrent through two years, showed a great similarity of the two annual cycles. This similarity concerns both the species composition as well as the dynamics of the Ciliates populations. The basic species which affect the community structure are as follows: Ctedoctema acanthocrypta, Mesodinium acarus, Cyclidium glaucoma, Cinetochilum margaritaceum, Pleuronema coronatum, Lacrymaria pupula, Aspidisca costata and Holosticha vernalis. The dynamics of the ciliated Protozoa living in this environment seem to be influenced by the speed of the current, the temperature and the amount of dissolved organic matter in the water.

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Etude de la dynamique des populations de cilies d'un torrent experimental pendant deux annees

     

Trophic ecology of an introduced top predator (Felis catus) on a small African oceanic islet (Santa Luzia,Cabo Verde Islands)

Studies on feral cat diet offer important ecological information and are the first step towards determining their impact upon endangered species. However, in comparing seasonal changes in diet with seasonal prey availability, the scarce amount of research into oceanic islands worldwide must be considered when deciding if a specific population is actually affected by cat predation. Cat diet was analysed on Santa Luzia (Cabo Verde Islands) since this invasive predator is considered one of the main threats to native endangered species that require conservation measures. These previous studies were carried out in different seasons, providing contrasting results, skinks being more preyed upon in the rainy season and mice in the driest periods. To check these different results, we focussed on how cat diet varied seasonally in response to changes in prey abundance. Saurians were the most important prey group, followed by mice, invertebrates and birds. No seasonal differences were, however, observed in the different prey groups consumed, saurians being the main prey in both seasons. All cases reflected their respective abundances. Results corroborate the generalist and opportunistic trophic ecology of feral cats, providing important information to assess their impact on prey populations and design future eradication programmes.