Christophe Destombe | Sorbonnes Universités, UPMC (P6) (original) (raw)

Papers by Christophe Destombe

Proceedings of The Royal Society B: Biological Sciences, 1999

In haploid^diploid red seaweeds, the dispersal of male gametes is presumed limited due to their l... more In haploid^diploid red seaweeds, the dispersal of male gametes is presumed limited due to their lack of £agella. It has been suggested that this group su¡ers from sperm limitation and, consequently, that fertilization is relatively ine¤cient. Fertilization in most £oridean rhodophytes results in the formation a cystocarp, a swelling on the haploid female thallus housing the diploid zygote and its thousands of diploid daughter spores. To study the performance of non-motile male gametes in the sea, we evaluated both female and male fertilization success in a natural population of the red marine alga Gracilaria gracilis. Female fertilization success, estimated by cystocarp yield per unit female thallus, was evaluated with respect to the availability of male gametes. Male fertilization success, estimated by the individual contribution of di¡erent males to zygotes, was assessed by paternity analyses on 350 cystocarps produced in one reproductive season using two microsatellite loci. The results show that cystocarp yield is not sperm limited and that the large variation in male fertilization success cannot be solely explained by the distance travelled by the male gamete to ¢nd a mate. Taken together, the results suggest that, not only is fertilization e¤cient, but that male^male competition and/or female choice may play a role in shaping population mating patterns.

European Journal of Phycology, 2005

In the genus Fucus, the character dioecy/hermaphroditism has undergone multiple state changes and... more In the genus Fucus, the character dioecy/hermaphroditism has undergone multiple state changes and hybridization is possible between taxa with contrasting mating systems, e.g. between the dioecious Fucus vesiculosus and the hermaphrodite F. spiralis. In the context of mating system evolution, we evaluated the potential consequences of hybridization by studying the variation in sexual phenotype and prezygotic fertility. Firstly, as a result of hybridization between the two sexual systems, gender variation may arise depending on the relative importance of genes with large versus small phenotypic effects. We thus qualitatively examined the extent of gender variation within and among individual hybrids in comparison with both parental species. Secondly, if hybridization breaks up co-adapted gene complexes, hybrid fertility may be reduced in comparison with both parental species. Therefore, we also quantified male and female prezygotic fertility in parental species and their hybrids in order to test for reduction in hybrid fitness. A total of 89 sexually mature individuals (20 F. spiralis, 40 F. vesiculosus, 10 hermaphrodite hybrids and 19 dioecious hybrids) were sampled in two geographically distant regions (France and Portugal) and six conceptacles per individual were observed. Within-individual variation was very restricted qualitatively -only one hybrid carried a conceptacle with a different sexual phenotype from the five others -as well as quantitatively. This suggests a simple genetic system for sex determination involving a few genes with major effects. In addition, analyses showed no significant decrease in hybrid fertility compared with parental species. Moreover, hybrids exhibited all sexual phenotypes, suggesting several generations of hybridization and backcrossing and, therefore, that hybrids are reproductively successful. Finally, the occurrence of sterile paraphyses in female and hermaphrodite individuals was interpreted as a relic of male function and suggests that, as in higher plants, evolution from hermaphroditism to dioecy may be the most parsimonious pathway.

European Journal of Phycology, 2014

Phycologia, 1993

2Division 0/ Environmental and Evolutionary Biology, School 0/ Biology and Biochemistry, The Quee... more 2Division 0/ Environmental and Evolutionary Biology, School 0/ Biology and Biochemistry, The Queen's University 0/ Bel/ast, Bel/ast BT7 INN, UK J. GODIN, C. DESTOMBE AND CA. MAGGS. 1993. Unusual chromosome number of Graci/aria verrucosa (Gracilariales, Rhodophyta) in the Cape Gris-Nez area, Northern France. Phyc% gia 32: 291-294. The chromosome number of Graci/aria verrucosa (Hudson) Papenfuss was estimated in numerous individuals from different populations of the Cape Gris-Nez area of Northern France. To optimize estimates and to minimize counting errors, several counts were made on the same nucleus and in dif f erent nuclei of the same individual. The haploid chromosome number was estimated in vegetative gametophytic cells and tetrasporocytic cells; the diploid number was estimated from tetrasporo phytic vegetative cells. The basic haploid number was n = 17 ± I, whereas all other Graci/aria species for which chromosome numbers are available are reported to have n = 24. These include populations of G. verrucosa from Norway and Wales that have previously been shown to be conspecific with the Cape Gris-Nez populations by comparison of plastid DNA data. G. verrucosa is therefore one of the few red algae for which populations with different chromosome numbers are known.

Botanica Marina, 2000

ABSTRACT In some red algae, the establishment of new fixed individuals is due to two kinds of spo... more ABSTRACT In some red algae, the establishment of new fixed individuals is due to two kinds of spores: haploid spores producing gametophytes and diploid spores producing sporophytes. Spore dispersal abilities were studied in order to understand settlement patterns in algal populations. Spore dispersal depends principally on their survival and how long they remain viable whilst suspended in the water column. It has been suggested that there is a positive correlation between spore size and their sedimentation rate. In Gracilaria verrucosa haploid spores are smaller than diploid ones. Nevertheless when submitted to a slow controlled water current, spore size had no effect on their dispersal. Conversely, under different light conditions, haploid spores have a better survival and remain free-floating longer than diploid ones, thus haploid spores could have better dispersal abilities than diploid ones.

In this paper, we first reviewed the trophic ecology studies carried out on Laminaria digitata be... more In this paper, we first reviewed the trophic ecology studies carried out on Laminaria digitata beds, at two rocky areas of Northern Brittany (France), Batz Island and Ar Pourven, displaying contrasted ecological conditions. The general trophic structure did not vary between the two sites, with a wide diversity of filter-feeders and predators, and only 14% of grazers. The results of stable isotope analyses allow drawing a simplified model for the food web associated to L. digitata beds. Kelp-derived organic matter is channeled into two distinct trophic pathways, the particle feeding-based and the grazing-based, which are coupled with higher trophic levels. The L. digitata detritic pathway contributes most to the diet of filter-feeders inhabiting sheltered sites. Although detritus feeding seems to be the main pathway transferring matter from kelps to the upper trophic levels, we showed that the direct grazing of kelps by herbivores can be locally important. Indeed, the gastropod Helcion pellucidum based exclusively his diet on the consumption of L. digitata and therefore its grazing pressure was studied on L. digitata sampled in two sites of Bay of Morlaix. In both sites, the herbivory pressure was significantly higher on reproductive adult plants than juvenile algae and the distribution of grazing damages showed strong variations along L. digitata thalli. To study the specific algal responses against herbivory, a laboratory-controlled system was established using L. digitata / H. pellucidum model. Defense-related gene transcripts were monitored in grazed tissues of L. digitata, showing the induction of molecular responses upon grazing. Altogether, the functioning of kelp-associated food web and the contribution of L. digitata are likely to be affected by two important factors, hydrodynamism and nutritive values of the food source. However, our results suggest that specific induced defense responses upon grazing and chemical interactions in natural environment could also interfere with trophic links in kelp beds.

Related to commercial seaweeds (eg. Laminaria spp.)

Cahiers De Biologie Marine, 2011

Kelp forests are threatened by human activities that result in habitat loss or deplete natural st... more Kelp forests are threatened by human activities that result in habitat loss or deplete natural stocks, but little is known about genetic diversity, importance of gene flow and effect of population fragmentation on genetic structure. We reviewed the literature to characterize the patterns of connectivity and scales of population structure in kelps. In all, 44 papers have been published on the patterns of genetic differentiation in 17 kelp species, using various kinds of molecular markers. Our literature review showed that population connectivity depends mainly on species' dispersal abilities and habitat characteristics (intertidal vs. subtidal), but little on their life-span characteristics. Data on within-population gene diversity were found for only seven species and reflect differences in effective population sizes. In addition, we focused on the Brittany populations of Laminaria digitata, one of the most commonly harvested species in Europe, and re-sampled populations studied seven years prior. Our analyses of spatio-temporal variation clearly demonstrate the effect of small population sizes on the genetic instability of isolated L. digitata populations and have implications for managing this genetic resource.

Journal of Applied Phycology, 2015

Cahiers De Biologie Marine, 2001

ABSTRACT The aim of this paper is to highlight the questions raised by a population genetics appr... more ABSTRACT The aim of this paper is to highlight the questions raised by a population genetics approach in order to discuss them in the context of seaweed populations studies. First, basic concepts of population genetics and their application in conservation biology are briefly reviewed. Second, we rapidly survey the methods for analysing the genetic structure of populations : these methods estimate parameters that characterise mating systems, quantify gene flow and evaluate genetic drift. To illustrate these points, examples taken from studies on algal populations are presented and discussed.

Evolution, 2015

The evolutionary stability of haploid-diploid life cycles is still controversial. Mathematical mo... more The evolutionary stability of haploid-diploid life cycles is still controversial. Mathematical models indicate that niche differences between ploidy phases may be a necessary condition for the evolution and maintenance of these life cycles. Nevertheless, experimental support for this prediction remains elusive. In the present work, we explored this hypothesis in natural populations of the brown alga Ectocarpus. Consistent with the life cycle described in culture, E. crouaniorum in NW France and E. siliculosus in SW Italy exhibited an alternation between haploid gametophytes and diploid sporophytes. Our field data invalidated, however, the long-standing view of an isomorphic alternation of generations. Gametophytes and sporophytes displayed marked differences in size and, conforming to theoretical predictions, occupied different spatio-temporal niches. Gametophytes were found almost exclusively on the alga Scytosiphon lomentaria during spring while sporophytes were present year-round on abiotic substrata. Paradoxically, E. siliculosus in NW France exhibited similar habitat usage despite the absence of alternation of ploidy phases. Diploid sporophytes grew both epilithically and epiphytically, and this mainly-asexual population gained the same ecological advantage postulated for haploid-diploid populations. Consequently, an ecological interpretation of the niche differences between haploid and diploid individuals does not seem to satisfactorily explain the evolution of the Ectocarpus life cycle. This article is protected by copyright. All rights reserved.

Kelp forests are one of the most diverse and productive ecosystems worldwide. Global climate chan... more Kelp forests are one of the most diverse and productive ecosystems worldwide. Global climate change and human exploitation threaten the stability of many of these ecosystems. In this study we compare differences in temperature responses during the microscopic haploid stage development between two kelp species in order to test if the annual Saccorhiza polyschides outperforms the perennial Laminaria ochroleuca at the northern limit of range distribution of L. ochroleuca, in Northern Brittany. Germination and mortality, sex ratio, fecundity and reproduction were measured in culture for the two species and under three different temperatures (10, 15 and 25°C). An effect of temperature was found for all traits except the sex ratio. Both species showed no ability to develop gametophytes at the highest temperature of 25ºC and were more tolerant to lower temperatures. S. polyschides showed higher germination rate, higher fecundity and lower mortality than L. ochroleuca during the period of the experiment. In addition, its gametophytes developed earlier than those of L. ochroleuca, a competitive advantage found in all temperature conditions. Germination rate, mortality and fecundity were significantly different between the two species. In addition, the two species showed a structural difference in the development of microscopic stages, with S. polyschides gametophytes occupying a larger area, which is suggested to result in a greater adhesion capacity. In conclusion, the microscopic stage of the annual species S. polyschides had a significant advantage in fitness compared to the perennial L. ochroleuca. This annual opportunistic species may out compete L. ochroleuca, at least in Brittany, the study region, corresponding to its northern limit, in areas where they share habitat.