Correspondence analysis of shell morphology in the African freshwater snail Biomphalaria pfeifferi (Kraus 1848) (Pulmonata: Gastropoda)

A correspondence analysis of shell measurements taken from 521 widely dispersed specimens of the African aquatic pulmonate snail Biomphalaria pfeifferi suggests the existence of eight morphological groups. These groups appear to relate to either ecophysiological factors or to factors associated with the stability of the freshwater system rather than to aspects of geographic distribution and genetic isolation.     

Studies of coccidian parasites of fish from the coast of Senegal (West Africa): new species of the genus Goussia (Apicomplexa, Eucoccidiida, Calyptosporidae)

Six new species of coccidian parasites of fish are described from the coast of Senegal: Goussia dakarensis sp.n. from Brachydeuterus auritus, Pomadasys peroteti and Galeoides decadactylus; Goussia decapteri sp.n. from Decapterus rhonchus; Goussia exoceti sp.n. from Hirundichthys affinis; Goussia emissolei sp.n. and Goussia soumbediounensis sp.n. from Leptocharias smithii; and Goussia trachinoti sp.n. from Trachinotus ovatus. Goussia clupearum (Thélohan, 1894) was found in eight new host species and G. senegalensis Faye, 1988 in one new host species.     

Early Seedling Growth in Normal and Opaque-2 Zea mays L. cv. Maya: I. COMPOSITION AND MOBILIZATION OF THE ENDOSPERM PROTEIN RESERVE

Grain of op-2 Maya have a higher total protein content in bothendosperm and germ than normal maize. In large grain, differencesin total grain protein are due mainly to the endosperm whilein small grain, differences are due to the germ, particularlythe scutellum which is larger in op-2 kernels. Reserve proteincomposition was distinct: op-2 endosperms showed an increasein the proportions of albumins, globulins, and the glutelinG₃ fraction which was accompanied by a marked decrease in zeincontent in comparison with normal endosperms. During endosperm depletion there was a net increase in the salt-solublefraction prior to day 3 from imbibition; glutelins and zeinhowever decreased throughout, the former being degraded at initiallyfaster rates. In general, regardless of protein composition,the most abundant fraction was utilized most rapidly. Water uptake during imbibition was greater in op-2 grain, thoughno differences in axis growth in terms of dry weight or laminaarea were apparent at the end of reserve degradation. In bothnormal and op-2 seedlings, protein was mobilized both earlierand faster than endosperm dry matter and the shoot, principallythe first leaf lamina, received more reserve nitrogen than theroot.     

Etude Comparée de Quelques Grégarines Acanthosporinae

SYNOPSIS. Numerous species of gregarines of subfamily Acanthosporinae are parasites of Trichoptera and Coleoptera. Eight species belonging to genus Ancyrophora are compared. One of them, A. rostrata , is new. This study makes it possible to recognize also a new genus, named Rhizionella and erected to contain another new species, R. tenuis.     

Female mating preferences and male coloration covary with water transparency in a Lake Victoria cichlid fish

Rapid speciation in Lake Victoria cichlid fish of the genus Pundamilia may be facilitated by sexual selection: female mate choice exerts sexual selection on male nuptial coloration within species and maintains reproductive isolation between species. However, declining water transparency coincides with increasingly dull coloration and increasing hybridization. In the present study, we investigated the mechanism underlying this pattern in Pundamilia nyererei, a species that interbreeds with a sister species in turbid but not in clear water. We compared measures of intraspecific sexual selection between two populations from locations that differ in water transparency. First, in laboratory mate‐choice experiments, conducted in clear water and under broad‐spectrum illumination, we found that females originating from turbid water have significantly weaker preferences for male coloration than females originating from clear water. Second, both the hue and body coverage of male coloration differ between populations, which is consistent with adaptation to different photic habitats. These findings suggest that the observed relationship between male coloration and water transparency is not mediated by environmental variation alone. Rather, female mating preferences are indicated to have changed in response to this variation, constituting the first evidence for intraspecific preference‐trait co‐evolution in cichlid fish. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 398–406.     

Pliocene and Pleistocene events shaping the genetic diversity within the central corridor of the Brazilian Atlantic Forest

Dinoponera lucida (Formicidae; Ponerinae) is an extinction‐threatened species of ant which is endemic in the central corridor of the Atlantic Forest. We used mitochondrial sequences of the Cox1, Cox2 and Cytb genes in order to infer some aspects of the evolutionary history and phylogeography of this ant. High genetic divergence and population structure were observed for the whole species. The current pattern of D. lucida diversity seems to be shaped during different geological times: middle Pliocene, early Pleistocene and mainly late Pleistocene, when the reduction of populations generated a structure pattern of the genetic variation of this species. Our data show that this structure results from the maintenance of populations of D. lucida within very small putative refuges to the south of the central Bahia refugium. We thus argue that, for some Atlantic forest endemic species, especially those resistant to very small fragments of forest, such as D. lucida, the small putative refuges were as important as, or even more important than, larger and stable refuges for the creation and maintenance of diversity, adding another piece to the puzzle of the mechanisms underlying local endemism. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 949–960.     

Do past experience and competitive ability influence foraging strategies of parasitoids under interspecific competition?

Abstract 1. In solitary parasitoids, several species can exploit the same host patch and competition could potentially be a strong selective agent as only one individual can emerge from a host. In cereal crops, Aphidius rhopalosiphi and A. ervi share the grain aphid Sitobion avenae as host. 2. The present work studied foraging strategies of both species on patches already exploited by the other species. The study analysed larval competition in multi‐parasitised hosts and compared the foraging behaviour of females with and without previous experience. 3. It was found that A. ervi wins larval competition three times more often than A. rhopalosiphi. Both species spent less time on patches exploited by a heterospecific than on unexploited ones. When they foraged on heterospecifically exploited patches, experienced females induced less mortality in aphids than inexperienced ones. 4. Although A. rhopalosiphi is a specialist on cereal aphids and is the most abundant species due to its early appearance in the season, S. avenae is still a profitable host for A. ervi, because: (i) A. rhopalosiphi leaves patches partially exploited, (ii) A. ervi wins larval competition in three out of four multi‐parasitised hosts, and (iii) A. ervi is only slightly deterred by the cornicular secretions of the host and can thus easily parasitise hosts.     

Chlamydomonas reinhardtii as a model system for pro-active herbicide resistance evolution research

Modern herbicides greatly contribute to world agricultural production but their sustainability is threatened by the widespread evolution of herbicide resistant weedy plant populations. Despite the commercial and scientific importance of resistance, there has not been an experimental model system for pro-actively evaluating the potential for herbicide resistance evolution. Here, utilizing the rapidly growing, unicellular photosynthetic microalgae Chlamydomona s reinhardtii (Dangeard), a ratchet protocol has been developed that solves the problem of maintaining both large populations and strong herbicide selection. The ratchet protocol is a progressive set of cycles, each cycle commencing with a population of approximately one million individuals apportioned amongst three herbicide doses for 14 days. Whenever the evolving population demonstrates growth across the three herbicide selection intensities, then the population ratchets to the next cycle of higher herbicide dose. Therefore, by always maintaining large populations under selection pressure, this system offers the opportunity for beneficial mutations to arise and be enriched. Using the well-characterized atrazine herbicide, the ratchet protocol resulted in rapid evolution of populations with different levels of resistance. This robust laboratory based Chlamydomonas system is proposed for application in establishing the respective propensity for resistance evolution to herbicides or other selecting agents.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 257–266.     

GEOGRAPHICAL PATTERNS OF GENETIC DIFFERENTIATION IN THE LANDSNAIL HELIX ASPERSA MuLLER (GASTROPODA: PULMONATA)

In order to investigate the initial processes responsible forthe geographical distribution of the Mediterranean landsnailHelix aspersa, populations from 64 locations in Maghreb andin Europe were studied at 17 enzyme loci by both starch andpolyacrylamide gel electrophoresis. Allele frequencies and genotypedistributions were analysed to provide information on populationstructure and genetic differentiation among populations. Valuesof Nei's unbiased (D) and Rogers (R) genetic distances led tothe formation of two main groups, namely Europe-west Algeriaand east Maghreb (average D = 0.182). Such splitting supportedthe pattern of anatomical variation recently described. Twosamples from Morocco were excluded from these groups becauseof an average D = 0.224. Within this Moroccan entity, geneticdivergences did not distinguish the ‘giant’ snailsH. a.maxima from the brownsnails H. a. aspersa. Such biochemicalsimilarities among morphological heterogeneity throws the subspecificstatus of H. a. maxima into question. Values of fixation indicesindicated that the greatest differentiation between samplesoccurred on the Maghreb territory ( = 0.393). The patterns of population differentiation are discussed inrelation to past geological and historical events. Thus, threescenarios, not mutually exclusive, are considered: the disjunctionof populations by plate tectonics during the Tertiary, the formationof geographically isolated populations during the Pleistoceneglacial/interglacial cycle and the possibility of human introductionas early as the Neolithic period. (Received 9 December 1992; accepted 11 November 1993)     

Ecology,Wolbachia infection frequency and mode of reproduction in the parasitoid wasp Tetrastichus coeruleus (Hymenoptera: Eulophidae)

Whereas sexual reproduction may facilitate adaptation to complex environments with many biotic interactions, simplified environments are expected to favour asexual reproduction. In agreement with this, recent studies on invertebrates have shown a prevalence of asexual species in agricultural (simplified) but not in natural (complex) environments. We investigated whether the same correlation between reproductive mode and habitat can be found in different populations within one species. The parasitoid wasp Tetrastichus coeruleus forms an ideal model to test this question, since it occurs both in natural and agricultural environments. Further, we investigated whether Wolbachia infection caused parthenogenesis in female‐biased populations. In contrast to the general pattern, in Dutch and French natural areas, we found Wolbachia‐infected, highly female‐biased populations that reproduce parthenogenetically. In contrast, populations on Dutch agricultural fields were not infected with Wolbachia, showed higher frequencies of males and reproduced sexually. However, we also found a female‐only, Wolbachia‐infected population on agricultural fields in north‐eastern United States. All Wolbachia‐infected populations were infected with the same Wolbachia strain. At this moment, we do not have a convincing explanation for this deviation from the general pattern of ecology and reproductive mode. It may be that asparagus agricultural fields differ from other crop fields in ways that favour sexual reproduction. Alternatively, Wolbachia may manipulate life history traits in its host, resulting in different fitness pay‐offs in different habitats. The fixation of Wolbachia in the United States populations (where the species was introduced) may be due to founder effect and lack of uninfected, sexual source populations.